The design of the Internet of Things (IoT) system over space–air–ground-integrated network (SAGIN) is still in its infancy. It is critical to get 6G technology involved, in order to address the current problems in the combined SAGIN and IoT ecosystem. This work utilizes a reconfigurable intelligent surface (RIS) to enhance the existing SAGIN infrastructure. We highlight channel modeling and estimate as a major component of RIS beam control and present a sparse Bayesian super-resolution estimation approach to achieve a good balance of accuracy and computing complexity. Our numerical results justify that, with our proposed models and algorithms, RIS will become a cost-effective and spectral-efficient solution for SAGIN-based 6G networks.

In this paper, the buffer-constrained throughput performance of a multi-user wireless-powered communication (WPC) system is investigated, where energy harvesting follows a non-linear model. The investigation focuses on the buffer overflow performance of sending data in the downlink (DL) from the access point (AP) node to each user equipment (UE) node and that in the uplink from each UE node to the AP node, based on which the throughput performance on both directions when a buffer constraint is enforced is studied. Specifically, the buffer overflow probability at each node is analyzed, based on which the buffer-constrained throughput is studied. In addition, to ensure the throughput performance under the buffer constraint, the DL transmission power allocation policy and the required energy storage capacity at each UE are investigated. Also, the optimal channel time allocation policy is studied with the objective of maximizing the minimum buffer-constrained throughput guaranteed to each UE at the same time. To this aim, an optimization problem is first formulated and then a dichotomy-based time allocation algorithm combined with a one-dimensional search is proposed to solve this problem. The analysis and results, explicitly relating the throughput to the buffer constraint in addition to WPC characteristics, shed new light on the design and performance analysis of WPC systems.

It is a promising way to successfully operate the fifth generation (5G) system with Internet of Things (IoT) in potential mmWave spectrum bands. This paper investigates the intelligent co-channel coexistence between the 5G IoT system and the fixed-satellite service (FSS) system at 40 GHz. The key issue, as identified, is the accurate estimation of interference based on mmWave propagation characteristics. Our simulation results reveal that interference from the 5G IoT system into the FSS ground stations can be kept below the protection threshold by considering different deployment parameters, such as antenna patterns, height of Earth station (ES), and separation distance.

Vehicular ac-hoc network (VANET) is a promising technology for intelligent transportation systems (ITS) to improve the safety and efficiency of transportation. Vehicles broadcast status messages periodically containing status information such as velocity, position, etc. The information can be used for road safety and collected by Internet of Things (IoT) elements for traffic management. The mobility of the vehicles will impact the reliability of vehicular communications, which leads to performance degradation especially in high density and highly dynamic scenarios. This paper presents a rate control algorithm based on the widely recognized car following model proposed by Wiedemann, which considers the movement interaction effect of vehicles and the driver's behavior. The car following process is common in high density situations and autonomous vehicles. We analyze the oscillation of vehicle's speed in car following process and derive the theoretical lower bound of message broadcast interval. The proposed algorithm can reduce redundant messages and meet the requirements of vehicle location accuracy. The rate control algorithm is evaluated using the network simulator ns-3 and the microscopic vehicle traffic simulator VISSIM.

In this paper, we investigate the delay and delay-constrained throughput performance of a point-to-point wireless-powered communication system, where one node, e.g. a user equipment (UE), is powered by the wireless energy transferred from the other node, e.g. an access point (AP), and uses the harvested wireless energy to send data to the other node. Our focus is on the delay performance of sending data over the uplink from the UE node to the AP node, and on its throughput performance when a delay constraint is enforced. Two representative time allocation schemes in using the link for the AP node to transfer energy (maybe together with data) and for the UE node to send data are considered. In particular, a lower bound on the cumulative capacity of the uplink is derived. In addition, an upper bound on the delay distribution is obtained for stochastic traffic arrivals, based on which, the delay-constrained throughput performance is further analyzed. Moreover, the accuracy of the analysis is validated by comparison with extensive simulation results. The analysis and results shed new light on the performance of such a wireless-powered communication system.

As a transport layer protocol, TCP is widely used in the various applications especially for video transmission in the mobile network. The TCP protocol not only provides an end-to-end connection to guarantee the reliability and in-order delivery of packets, but also shapes the transmission rate from the server to client through the mobile network. In wireless link, the available bandwidth varies significantly due to the changes in the underlying radio channel conditions. Traditional TCP congestion control has difficulties in adapting to these rapidly varying conditions which leads to low throughput and long delay. This paper analyzes the TCP issues in the mobile wireless network, and proposes two radio-aware TCP optimization solutions. The loose coupled radio-aware TCP optimization solution controls the parameters of TCP layer according to the cross-layer information which includes the client predicted rate and low layer's assisted information, while the close coupled radio- aware TCP solution modifies the traditional TCP congestion control mechanism to a novel TCP request- grant mechanism. The simulation proves the solutions can acquire significant TCP performance gain with extreme low latency.

In this, study, a new channel tracking algorithm for time‐varying millimetre wave (mmWave) system is proposed. The transmitter employs hybrid beamforming architecture which is generally adopted in mmWave system and the receiver is assumed to have perfect channel knowledge. Due to the short feedback interval in mmWave system, the authors propose a low overhead channel tracking algorithm in which the receivers feedback the channel state information every several channel indices. Obviously, the proposed channel tracking algorithm can reduce feedback times and improve feedback efficiency. Based on the mutual information analysis and 3 dB criterion on signal‐to‐noise ratio, the upper bound of the loss on system capacity and the maximum gap of discrete channel tracking, together with the desired number of data steam are given. Simulation results are presented to verify the analysis above and demonstrate the performance in discrete channel tracking.

In this paper, a spectrum sharing scheme adapted for the operation of Long Term Evolution (LTE) in unlicensed band (LTE-U) and WiFi system is proposed. This scheme optimizes the resource in unlicensed band based on decision tree learning and repeated game. We consider a flexible architecture decoupling control plane from data plane in the coexistence system. In control plane, strong ability of data processing is provided. Controllers learn the latest data set in the pool to build decision trees. According to the decision tree, controllers deduce the network status of the opponent. Repeated game is played to share spectrum resources for maximizing the resource utilization in the coexistence system. At the beginning of each game stage, controllers use decision tree to make informed decisions quickly. In repeated game, an encouragement mechanism is proposed to stimulate operators to share spectrum resources. Simulation results show that dynamic spectrum sharing is able to improve throughput and spectrum efficiency in unlicensed band. At the same time, this scheme also balances the traffic load and guarantees fairness among multiple systems.

Studies of multi-server networks are usually conducted on the assumptions of independent servers and specific arrivals, which may not capture the characteristics of realistic networks. In this paper, we propose a novel stochastic network calculus approach to perform delay analysis for a general multi-server network. The stochastic network service curves are derived in two ways with different assumptions. After that, we use these service curves to derive queueing delay bounds including delay bound distribution and mean delay bound for a specific scenario of which the classical M/M/N model is a subset. Compared with previous studies, it is worth highlighting that our analysis contains the cases where the arrival and service processes as well as the servers can either be independent or correlated. In addition, the accuracy of the analytical delay bounds are verified by comparing with the queueing theory results in an M/M/N model.

Energy evaluation of wireless transmission for data service under different QoS (quality of service) constraints is a hot topic in green communications. In this paper, we employ the theory of the stochastic network calculus to investigate the relationship between the traffic arrival rate and energy harvesting rate under the delay and energy storage constraints. We first construct a wireless system model which works only by consuming the harvested renewable energy. Also, stochastic traffic arrivals, packet size as well as a two-state Markov chain interference on energy harvesting are jointly considered to ensure the accuracy of the analysis. We derive the minimum energy harvesting rate needed to satisfy the delay and energy storage constraints under a given average arrival rate. The efficiency of the harvested energy is also studied and shown to be convex in the numerical simulation. Numerical results illustrate that while the minimum energy harvesting rate is positively correlated with the packet size, it is negatively related to the delay requirement, under a given arrival rate. Additionally, the probabilistic bound of energy insufficiency is shown to be positively correlated with the transition cycle of the interference.

In this article, we investigate the capacity of large-scale multiple-input multiple-output (MIMO) multiple access channels (MACs) with linear receivers in ultra dense networks (UDNs) where the number of antennas at the base station and the number of total interfering terminals approach to infinity while maintaining a fixed ratio. To study the multicell uplink capacity of a large-scale MIMO system, we first find the probability distribution of the post-processed signal to interference and noise ratio (SINR) using large dimensional random matrix theory without the limiting condition that the channel vectors between users orthogonalize in the large-scale MIMO system in contrast to previous work. Then modeling the practical 2-D UDN topology, we analyze which factors affect the capacity of large-scale MIMO MACs in UDNs. Finally, simulation results verify our analytical results and demonstrate a comparison on the capacity between three user equipment (UE) distribution models.

The latest video coding standard, High Efficiency Video Coding (HEVC), has a large amount of complexity in its inter coding. To reduce the complexity of the inter coding for HEVC, an adaptive searching range algorithm is proposed in this paper. The proposed method separates inter coding into a learning stage and predicting stage. In the learning stage, the relationship between the prediction units (PU) difference, the length of the motion vector prediction (MVP), and the best searching range is learned. In the predicting stage, the k-nearest neighbor algorithm is adopted to find the best searching range based on the learned data. Experiments showed that 91% of the complexity of the motion estimation is reduced compared with the full search method.

Ultra-dense Small Cell deployment is a sensible design of heterogeneous network, which provides a good performance of hot spots coverage enhancement and traffic load balancing. The growing energy consumption pressure becomes one of the main challenges of the Small Cell application. Cloud Radio Access Network (C-RAN) can promise significant energy consumption savings for Small Cells via the separation between RRH and BBU. In this paper, we propose a novel software defined C-RAN (SDC-RAN) architecture in Small Cell network. Moreover, a self-adaptive power adjustment scheme (SA-PAS) is introduced, considering the influence of users' current and history traffic demands during downlink power allocation. The goals are to strike a good balance between energy efficiency and user experience. Simulation results show that the expected system throughput can be achieved with limited resource consumption in SDC-RAN based on Small Cell deployment.

A sensible design of ultra-dense Small Cell network involves striking a good balance between energy efficiency and user experience especially in hot spots. In this paper, we propose a self-organized resource allocation scheme (SO-RAS) as an enhanced solution for the system performance, which can coordinate resource allocation within Small Cell clusters based on the self-organized mechanism. We take the users' access distribution as a constraint weight when conducting downlink cooperative power adjustment, aiming to adapt system resource consumption corresponding with the current traffic load. Simulation results show that the proposed strategy improves system performance in hot-spot users' throughput and can contribute to the system energy efficiency ratio in ultra-dense networks.

LTE on unlicensed bands is a promising strategy in the future communication system. In order to improve the efficiency of resource utilization for LTE operating on both licensed and unlicensed bands, a flexible resource allocation scheme based on utility function is proposed. This scheme optimizes the resource allocation by integrating and dynamically adjusting the resource on licensed bands and unlicensed bands. At the same time, the utility function in this scheme can guarantee the tradeoff between system efficiency and user fairness. Finally, numeric simulation results are given to demonstrate that by comparing with the present cooperation mechanism the performance of the integrated wireless system is improved through the scheme we propose.

The dynamic uplink-downlink reconfiguration of TD- LTE is regarded as an effective method to increase the resource efficiency and optimize the system performance. With different transmission directions and the dense deployment of small cells in the heterogeneous network, the interference situation becomes complex and critical in both uplink and downlink, especially for the cell-edge UE. In this paper, we discuss the interference coordination and mitigation problem in the dynamic TDD network. With cell-clustering interference mitigation, the synchronous operation can be provided in a cluster and well isolation can be obtained between cells in the different clusters. Furthermore, we propose that the simplified downlink CoMP DCS mode can be used in the clusters to optimize the downlink performance. At last of the paper, we analyze the performance gain of the proposed scheme by system level simulation. The results show that both uplink and downlink performance for the cell-edge UE are improved.

Heterogeneous network (HetNet) which contains different transmission power NodeBs, has been discussed earlier in LTE system. But recently, HetNet is currently being standardized for HSPA system by 3GPP working group. In co-channel HSPA HetNet (CHH), Uplink-Downlink (UL-DL) imbalance caused by the hugely different power from different types of transmission nodes is a key problem leading to many undesirable conditions such as unbalanced load and severe interference. The main contribution of this paper is to propose an adaptive range expansion (ARE) mechanism to mitigate the UL-DL imbalance in uplink CHH (UCHH). Our scheme tries to adaptively calibrate the parameter of range expansion (RE) by means of introducing a "Equivalent User Equipment (UE)" and using it as a reference to reflect the uplink reception quality of other UEs. Simulation results will show the advantage of our proposed scheme.

Small cell deployment and device-to-device (D2D) communications can significantly enhance the system performance by offloading core network traffic and reducing the overall energy consumption, especially in the dense network. However, the interference emerging in it is severe and complicate. In this paper, we develop a model aiming to achieve the maximal system throughput and simultaneously ensuring the quality of service (QoS) of each user accessed into the heterogeneous network (HetNet). Further, we solve the optimization formulation in three steps. First, we find a feasible radio resource allocation profile of small cell networks without D2D communications. Then we optimize the D2D resources based on convex optimization theory. Finally, we get the maximal HetNet capacity according to the theoretical analysis by comparing different resource allocation profiles of small cell networks. Simulation results demonstrate that our approach is feasible and effective to achieve the maximal HetNet throughput simultaneously ensuring each user's QoS.

Relay-assisted Device-to-Device (D2D) communication is an enhanced technology for D2D communication. With relay nodes' assistances, the communication distance of the D2D pair is extended and the quality of communication can be improved. This paper focuses on the achievable transmission capacity of relay-assisted D2D network while keeping a low outage probability of the cellular users. based on stochastic geometry, the mathematical model of relay-assisted D2D network, with relay selection criterion, is formed and analyzed. Subsequently, the optimal transmission power ratio of the cellular system to the D2D system and the optimal relay selection range are derived. Furthermore, the achievable transmission capacity with derived optimal parameters is presented as a close-form expression. Then the numerical results show that the performance of the D2D network can be improved by relay-assisted transmission in case of poor wireless environment. In addition, the influences of the densities of both cellular, D2D and relay users and the communication distances between D2D pairs are evaluated in this paper.

Recently, hybrid analog/digital beamforming (BF) system is attracting increasing attention in the study on multiuser millimeter wave systems. In these systems, a relatively large number of antennas are connected to a less number of analog front-end chains so as to reduce both of the hardware complexity and power consumption. This paper investigates on optimizing phase-only analog BF and digital BF weights, with the objective of minimizing the total transmit power subject to signal-to-interference-plus-noise ratio (SINR) constraints. An floating-point genetic algorithm, in which the fitness function is defined as the linear scale of the objective function, is proposed to solve the optimization problem. Chaos crossover probability, chaos mutation probability and elitist strategy are introduced into the genetic algorithm in purpose of improving the operating efficiency as well as increasing the convergent rate. Simulations results under Gaussian channel environment reveal the advantages of the proposed genetic algorithm over the existed iterative algorithm. Besides, under 60GHz channel model, it is shown that the correlation on different subcarriers has profound impact on the performance of hybrid phase-only analog/digital BF.

This paper investigates a typical optimization problem for 60 GHz multiuser hybrid beamforming, which is to maximize the minimal SINR over all of the considered subcarriers under a total power constraint. In order to reduce the complexity, two methods of using the fixed analog beamforming (ABF) weights are presented rather than traditional iterative methods, which are codebook-based method and singular value decomposition (SVD) based method. The performance of hybrid beamforming with the fixed ABF weights are evaluated by computer simulations and compared with that of using the existing iterative method. Channel model defined in IEEE 802.11ad is utilized in the simulation. Simulation results show that the average max-min SINR achieved by the presented methods of using the fixed ABF weights are close to or even higher than that of the iterative method.

The standardization of HSPA+ heterogeneous network (HetNet) is underway recently. Interference coordination is a noticeable topic to cope with the severe interference issues. In this paper, we propose a distributed uplink interference coordination via pricing (DUIC-P) scheme in which pricing stands for UE's harm to the uplink co-channel HSPA+ HetNet. To mitigate the harm which is brought by interference and to achieve a more reasonable power allocation, we formulate the scheme as efficient non-cooperative power control games with linear pricing (ENPCG-LP) and with exponential pricing (ENPCG-EP), both of which are based on an efficient non-cooperative game theoretic approach. A new utility function that includes pricing, UE transmission rate and frame success rate (FSR) is defined. For the two games, firstly we justify the existence and the uniqueness of their Nash equilibriums. Then we consider a feasible implementation for ENPCG-LP through closed-form best response (CBR) and for ENPCG-EP through table look-up scheme (TLS). Simulation results show the advantages of our proposed schemes.

Small cell networks as an important evolution path for the next generation cellular networks, have drawn much attention. Different from traditional base stations (BSs) always-on model, we proposed a BSs on-off model where a new simple expression of the BS active probability of HetNet is derived. This model is more suitable for the practical network where BSs are not always-on. Based on this, we develop an analytical framework for downlink performance evaluation of small cell networks, adopting stochastic geometry theory. The system coverage probability (CP) is derived, which is analytical tractable and is useful for small cell networks. This new result is then applied to evaluate the 2-tier HetNet average rate (AR) and average energy efficiency (AEE). It is analytically shown that increasing the small cells density is beneficial to the system overall throughput, but not affect the system overall AEE obviously. While the range expansion is helpful to the overall AEE, but it will cause some loss in system throughput.

Small cell technology significantly improves the coverage and boosts the capacity in Heterogeneous Cellular Network. And Cell Range Expansion technology makes average rate nearly optimal in downlink. However, because of large transmit power disparities of different kinds of base stations, uplink and downlink need to be considered as two different networks. In uplink, the problem is that many user equipments have to be associated with suboptimal base stations due to old Uplink-Downlink relationship. So we propose a new Uplink-Downlink relationship under which user equipments can be associated with optimal (may not the same) base stations in both directions. Numerical results demonstrate that performance under new Uplink-Downlink relationship has impressive gain in uplink coverage probability and average rate. Besides, when user equipments are all associated with their optimal base stations, network interference will be effectively mitigated through controlling uplink transmit power.

The green communication draws a lot of attention in recent years. Meanwhile, as a promising technology, cognitive radio will constitute an important part of the future communication networks. Energy consumption of cognitive radio network is worthy studying, which is analyzed in this paper applying stochastic network calculus. A multi-channel cognitive radio network model is introduced. Stochastic network calculus is then used in the analysis, which is a newly developed theory dealing with queuing system found in computer networks. Guaranteed service for secondary users is firstly derived, followed by stochastic service curve derivation. Then, minimum transmission rate is conducted which is an important variable in energy analysis. After that, relationship between energy consumption and transmission rate is presented. As part of the derivation, delay bound and transmission power are discussed. Finally, numerical results of transmission rate, transmission power and energy consumption are shown for different constraint, where the influence of channel quantity is further discussed.

The latest standard of High Efficiency Video Coding (HEVC) has a better coding efficiency compared to H.264/AVC. It is reported that the bitrate of the video applied HEVC is the half of video applied H.264/AVC at the same encoding quality. However, the cost of improvement is the increasing computational complexity which is mainly brought by the quadtree based coding tree unit (CTU). In this paper, a fast coding units (CU) splitting and pruning method is proposed to speed up the process of searching the best partition for CTU. Experiment has shown that our method can save 46% computational complexity on average at the cost of increasing Bjontegaard delta rate (BD-rate) by 0.82% when the method is applied to sequences in Class A.

Heterogeneous network (HetNet) which contains different transmission power NodeBs has been researched extensively earlier in LTE system. Owing to the great improvement achieved by HetNet, HSPA HetNet is currently being standardized by 3GPP working group. In co-channel HSPA HetNet (CHH), Uplink-Downlink (UL-DL) imbalance caused by the hugely different power from different types of transmission nodes is a key problem leading to many undesirable conditions such as unbalanced load and severe interference. The main contribution of this paper is to propose an adaptive range expansion (ARE) mechanism to mitigate the UL-DL imbalance in CHH. Our scheme tries to adaptively calibrate the parameter of range expansion (RE) by means of introducing an Imb value and using it as a reference to reflect the imbalance condition in the system. Simulation results will show the advantages of our proposed scheme.

In seeking to address the problem of prolonged surge of traffic demand, heterogeneous network is now being seen as an attractive method. Heterogeneous network consists of different types and quantities of small cells which can provide a huge amount of data. Simultaneously, those high density deployed small cells consume a large amount of energy that raise another knotty issue. In this paper, we investigate the control strategy of small cell sleep mode and provide a novel one which establish a macroscopically controlling mechanism. Specifically, we consider both the performance gain small cells may bring to the system and the energy small cells may consume. And the strategy combines this two most important consideration into a priority level that can help to achieve a balance in macro-scale. Besides, we introduce three types of small cells with different parameters and performances that fit actual situation. Our strategy is evaluated by comparison with existing strategies, and results from extensive simulations demonstrate our strategy's superiority in energy saving.

Heterogeneous network (HetNet) where the macro cells are underlaid with low power node (LPN) has been introduced to HSPA+ to enhance the system performance in a cost-efficient way. But the Uplink and Downlink (UL-DL) mismatch issue caused by applying the heterogeneous deployment will inevitably limit the performance in both uplink and downlink HSPA+ system. To mitigate the UL-DL mismatch effect, E-DCH decoupling was proposed in HSPA+ HetNet recently, which has been discussed in 3GPP standardization process. However, some new problems driven from E-DCH decoupling have emerged, and one of the hugely important issues in this area comes to be known as the negative impact along with the reception delay of control channels for UL. In this paper, we will focus on this control channel delay issue in co-channel HSPA+ HetNet. The main contribution of this paper is to propose a novel adaptive grey prediction (AGP) using the recently historical data to make delay compensation. Furthermore, we develop a feasible implementation in practical HSPA+ HetNet to achieve our AGP method in practice. System-level simulation results will show the notable advantages of our proposed method.

Power consumption and costs of analogue front‐end (AFE) chains are often not negligible for large‐scale antenna array systems. A low‐complexity hardware architecture is to use a number of AFE chains that are less than the number of antennas. Beamforming for this low‐complexity hardware architecture involves both digital and analogue beamforming, which is termed hybrid analogue/digital beamforming. In this study, minimising the transmit power subject to signal‐to‐interference‐plus‐noise ratio (SINR) constraints and maximising the minimal SINR under the constraint of the transmit power, are investigated, respectively, for hybrid analogue/digital beamforming. Properties on the feasibility and optimality of the two problems are derived. Numerical algorithms based on semi‐definite positive relaxation are proposed in an attempt to solve the two optimisation problems. The performance of the proposed algorithms is evaluated under the Gaussian and 60 GHz channel models. It is shown that the performance of hybrid analogue/digital beamforming is highly related to the correlation of the channel coefficients of subcarriers. Additionally, for different extents of the users’ spatial separability, some heuristics ways of designing analogue beamforming are shown to be able to approach to at least the local optimums under the 60 GHz channel model.

Heterogeneous network (HetNet) has been discussed earlier in LTE system. But recently, there also exist some studies concerning the standardization of HSPA HetNet. Interference coordination is still a critical topic in HSPA HetNet. Considering the network architecture of HSPA HetNet, in this paper, we develop a distributed interference coordination (DIC) scheme which involves power allocation and scheduling to reduce the negative effect of interference in the downlink co-channel HSPA HetNet. Our DIC scheme is modeled as an energy-efficient non-cooperative game with QoS constraint (EENGQ). We first reveal the existence and uniqueness of the equilibrium for this game. Then, a closed-form best response of this game is derived. Finally, a feasible implementation is proposed to achieve our DIC scheme in practice. Simulation results show the notable advantages of our proposed scheme which can remarkably mitigate the interference and enhance the energy efficiency.

Antenna calibration to enhance the channel reciprocity between the uplink and downlink channels is necessary for the practical wireless system operating in the time division duplexing (TDD) mode. This paper investigates on the computation of the antenna calibration coefficients of the cooperative base stations' antennas in the network multiple-input and multiple-output (MIMO) system. An efficient scheme for computing the calibration coefficients for an arbitrary number of distributed antennas is proposed. In addition, we also propose two methods of refining the calibration coefficients for the proposed scheme. The evaluations of the proposed scheme and methods are performed through computer simulations.

Multi-point transmission has been paid attention in the evolution of multi-carrier HSPA+networks because of its capability to deal with the negative channel conditions. Multipoint coordination is a key issue to be investigated in this area. In the existing deployment, the multi-point transmission is only applied in a non-coordinated way in the current multi-carrier Multi-flow HSDPA (MF-HSDPA) network. Besides, the metric measuring the quality of multi-point transmission is limited. In this paper, we propose a cross-cell coordination scheme which considers both the maximization of sum-rate and the minimization of packet sum-delay in multi-carrier MF-HSDPA network. The proposed scheme involves the cooperation of the cross-cell scheduling and power optimization. The cross-cell scheduling can be further divided into the intra-cell and inter-cell processes. Then, we propose a heuristic method based on the theory of flow network to solve the whole scheduling issue with a reasonable tradeoff between the performance and complexity. Simulation results will show the advantages of our proposed scheme.

Co-channel heterogeneous network (HetNet) where the conventional macro cells are underlaid with some co-channel low power node (LPN) cells has been recently introduced into HSPA+ to satisfy the rapidly growing demands for improving system coverage and capacity. However, the severe cross-tier uplink interference caused by applying the heterogeneous deployment will inevitably limit the uplink performance in HSPA+. Thus, the uplink interference issues have become a critical topic in this area. In this paper, we propose a quasi-distributed uplink interference coordination (QDUIC) scheme based on non-cooperative game with local restriction to reduce the uplink interference in HSPA+ HetNet. The existence and uniqueness of Nash equilibrium for our proposed game are justified in detail. Furthermore, to achieve our scheme in practice, we develop a feasible implementation for practical HSPA+ HetNet system. System-level simulation results show that our scheme can not only mitigate the uplink interference level, but also save the uplink power consumption and enhance the throughput performance of HSPA+ HetNet.

Device-to-Device (D2D) communication is considered to be a promising resource reuse technology for local users. Unlike the previous studies on centralized scheduling methods, we develop several distributed resource management schemes for D2D communication underlay cellular networks. In the distributed resource management framework, each D2D user independently decides the transmit resources and power. In this paper, we propose two efficient algorithms and demonstrate the distributed implementation. The first algorithm is based on the Lagrangian dual decomposition method, and aims at maximizing the sum-rate of D2D system. We design the second algorithm by game theory with the utility function to maximize the transmission rate with interference price. The convergence to the Nash equilibrium is proved and simulated. By numerical simulation, we evaluate the network throughput and power consumption of the proposed algorithms. It is proved that the proposed resource management schemes can satisfy the interference constraints and achieve high system capacity.

Under the consideration of the cost and power consumption, analog or radio frequency (RF) beamforming is usually adopted in the 60 GHz wireless systems. Hence, obtaining the multiple- input and multiple-output (MIMO) channel information is costly and of high overhead for the concerned system. In this work, an efficient multi-user scheme is proposed for the single carrier block transmission (SCBT) based 60 GHz system. It schedules users that are unlikely to cause strong multi-user interference (MUI) without knowing the MIMO channel information. Additionally, the proposed scheme enables to further mitigate the residual MUI after scheduling on the effective channels while the system can still employ low cost arrays that have very limited capability of nulling the interference. Evaluation of the proposed scheme is performed by computer simulation based on the channel model defined in 802.11ad.

In this paper, we propose an effective resource allocation scheme in macrocell/femtocell OFDMA uplink networks. A cross-layer mitigation algorithm is designed firstly to avoid the severe cross-layer interference which will decouple the resource allocation between two networks. Then utilizing the result of cross-layer mitigation, a resource allocation strategy including power allocation and frequency assignment is proposed to meet the UE's target data rate and obtain better throughput performance. Simulation results show that the proposed algorithm can achieve significant performance gains over the traditional methods, especially in view of the guarantee of UE's quality of service (QoS) and throughput performance.

The performance of Perceptual Evaluation of Speech Quality (PESQ), a most prevailing voice service Quality of Experience (QoE) assessment method, is evaluated in Chinese environment. A normative Chinese speech database has been developed, especially considered the distortions from the real transmission situation. Through the huge subjective result, a distinct conclusion can be drawn that it is not convinced to use PESQ assess Chinese voice service directly. A non-linear compensation factor is proposed in this paper to make the universal PESQ be suitable for the Chinese voice service accurately. After compensation, the score of PESQ matches the Mean Opinion Score (MOS) much more, and the residual error distribution has also been improved greatly compared with the result given in ITU P.862.1.

In this letter, we investigate the outage performance of a dual-hop fixed-gain amplify-and-forward relaying systems in presence of interference at the relay.We assume the desired signal has Nakagami-m fading and the interfering signals experience independent and identically distributed (i.i.d) κ - μ and η - μ fading. We present exact and closed-form expressions for the outage probability. Then we derive closed-form expression for the outage probability when the interfering signals experience i.i.d Nakagami-m fading as the special case of κ-μ and η-μ fading,respectively. Furthermore, the asymptotic outage performance is investigated in high signal-to-interference-noise ratio (SINR). Finally, Monte-Carlo simulation results are given to verify the analytical results.

Multi-point transmission has not received adequate attention in the evolution of UMTS networks until multi-flow transmission is proposed in the HSPA+network recently. In the multi-flow transmission, the cross-point coordination is regarded as an important technique to enhance the system performance. In the existing research, most studies have only involved the multi-flow transmission in a non-coordinated pattern and considered it in the single-carrier HSPA+system. The major contribution of this paper is to propose a cross-point coordination scheme in the multi-carrier Multi-flow HSDPA (MF-HSDPA) network. Our scheme is able to achieve the coordination of both the aggregated scheduling and power allocation to improve the system performance in the multi-point and multi-carrier layout. Simulation results will show the advantages of the proposed scheme.

This paper investigates the performance of multi- antenna spatial diversity in the overlaid wireless ad hoc network. We apply the more practical stochastic geometry tools to model the network. Then we derive closed-form expressions for the outage probability of two coexisting networks employing two basic diversity techniques, the maximum ratio combining (MRC) and the transmit antenna selection (TAS). Monte Carlo simulations verify the accuracy of our expressions, based on which, we further evaluate these two basic diversity schemes from the newly developed perspectives of transmission capacity and overlaid network. We explore the gain source for the transmission capacity of the overlaid network over that of a single network. Our work shows that employing low complexity diversity schemes at either transmit or receive side can significantly improve the overall transmission capacity requiring little or no feedback.

Device-to-Device (D2D) communication is considered to be a promising resource reuse technology for local users, which can support high-speed and power- saving services. However, when D2D users are far away from each other or the quality of D2D channel is not good enough for direct communication, transmission via a direct link is not a good choice. In this paper, we focus on the performance of relay assisted D2D network. Unlike the previous works that mainly study practical relay selection algorithm, we analyze the achievable transmission capacity of multi-hop D2D system over Rayleigh fading channels. First, by using stochastic geometry, the probability distribution of end-to-end signal-to-interference- plus-noise ratio (SINR) in the spectrum sharing network is formulated. Then the achievable transmission capacity is modeled as an optimization problem with constraints that guarantee the outage probability of both cellular and D2D systems. Finally the optimal design of D2D spatial density and transmit power is analyzed and the achievable transmission capacity of multi-hop D2D system is given in closed-form expression. Numerical results show the performance of the D2D network can be effectively enhanced by relay-assisted transmission. We also verify the optimal design of D2D parameters and evaluate the influence of the number of relay hops on the system capacity and power efficiency.

In modern communication systems, service rate and energy consumption have achieved increasing attention. To support high-speed local services, Device-to-Device (D2D) communication is introduced to cellular networks. However, the co-channel interference and power consumption brought by D2D bring new challenges. In this paper, we focus on energy-efficient power allocation in D2D-cluster scenario. Based on the dual method in convex optimization, we propose a practical Joint Resource Allocation and Power Control (JRAPC) scheme in D2D- cluster scenario, which is to allocate proper power for each D2D user on each channel and guarantee the Quality of Service (QoS) requirements. Numerical results show that the proposed JRAPC scheme can optimize the energy efficiency, lower the scheduling complexity and lead to higher QoS satisfactory.

The performance of Transmission Control Protocol (TCP) degrades over wireless links which are characterized by varying channel condition and high error rate. TCP misinterprets these as network congestion. In this paper, we analyze the TCP send rate of parallel multi-radio transmission diversity (MRTD) schemes with and without redundancy in heterogeneous wireless networks (HWNs). Through developing a cross-layer model, MAC layer packet error rate and link rate are taken into consideration. By comparing the performance of these schemes, we propose a hybrid MRTD scheme which aims at obtaining good tradeoff between robustness and efficiency to improve TCP performance. The feasibility of the proposed scheme is validated by user-level simulation. Moreover, system-level simulation results show that hybrid MRTD scheme improves the wireless TCP performance comparing with parallel MRTD schemes.

Picocell is an emerging and key item in LTE-Advanced system, for providing improved service coverage and high spectral efficiency with low power. However, in heterogeneous networks (Het-Nets) with macrocells and picocells, more complicated interference scenario can severely degrade the system performance, especially for system capacity and data rate of cell-edge users. Consequently, effective interference coordination schemes are in great demand to mitigate these interference problems. In this paper, we propose a new effective dynamic interference coordination scheme based on an innovative combination of soft frequency reuse (SFR) and improved Graph-based resource allocation in orthogonal frequency-division multiplexing access (OFDMA) macrocell-picocell network. The system-level simulation results show that the proposed scheme can achieve superior system performance improvements, higher cell-edge user data rate and more efficient frequency reuse, comparing with the time domain interference coordination Almost Blank Subframes (ABS) scheme and the conventional co-channel resource allocation scheme.

Heterogeneous network (HetNet) which can provide the remarkable cell-splitting gain has already received adequate attention in the LTE-A system. Since the standardization of HetNet in HSPA+ is currently in progress, it is necessary to focus on the application of HetNet in the HSPA+ system. Cross- tier interference coordination is one of the crucial issues to be discussed in this area. Considering the HetNet deployment in the multi-flow HSDPA (MF- HSDPA), the main contribution of this paper is to propose a novel cross-tier interference coordination scheme in the MF-HSDPA HetNet. Our method combines the cross-tier multi-flow transmission with the adaptive time domain muting and cross-tier scheduling to deal with the interference problem. System-level simulation results will show the advantages of our proposed scheme.

Performance metrics such as outage probability, average error rate and capacity have been studied in cooperative diversity systems by a large number of papers. However, the second-order statistics properties in cooperative diversity systems have not been completely investigated. In this letter, we investigate the second-order statistics properties of an adaptive selection decode-and-forward relaying (SR) cooperative diversity system. We focus on two performance metrics: average outage rate (AOR) and average outage duration (AOD). The accurate closed-form approximations for the AOR and AOD performances are derived using Gauss-Legendre quadrature. The accuracy of our approximations is validated by the Monte-Carlo simulations. Furthermore, we compare conventional SR protocol and adaptive SR protocol in AOR and AOD. It is shown that adaptive SR protocol has a better performance in AOR but two protocols have similar performance in AOD.

This paper investigates the transmission capacity of the secondary network in overlaid ad hoc networks with multi-antenna spatial multiplexing. Based on stochastic geometry tools, we study the effects of the node density and the transmission power of the secondary network on the transmission capacity performance. We derive the optimal node density for the secondary network, and subsequently the optimal transmit power ratio between the primary network and the secondary network. Our findings show that increasing the node density of the secondary network will result in an increase in the transmission capacity of the secondary network under a reasonable target outage probability assumption. The optimal node density and transmit power ratio are mainly influenced by the target outage probability and the permitted outage probability increment. On the other hand, numerical results show that the transmission capacity increases over the antenna number. Moreover, the antenna number has little effect on the optimal transmission power ratio.

Coordinated multi-point transmission with limited rate feedback has been paid much attention recently due to its ability to overcome the detrimental propagation conditions. In the limited feedback multi-point transmission, how to allocate the appropriate feedback bits among the users has become a critical issue to be investigated. The existing schemes have not considered the impact of the flexible power allocation on the feedback bit allocation among the users. The main contribution of this paper is to propose a user-specific coordination scheme to dynamically coordinate the feedback bit number for each user according to the overall result of power allocation in the limited feedback multi-point transmission. We also develop an iteration algorithm to efficiently achieve the satisfactory solution of our proposed issue. Simulation results will show the advantages of our proposed scheme.

Conventional channel estimation algorithms devised for OFDM systems suffer from significant performance degradation in the presence of interference. This paper develops a robust least square (LS) channel estimation scheme with low complexity. The received pilot symbols are first separated into several groups, then each group is divided into two parts. After that, we apply the conventional LS algorithm to estimate the channel of the first part, then combine the result of each group to get the final estimation result. Meanwhile, the second part is utilized to determine the weight matrix of this combining operation. We mainly analyze the performance under 2 typical interferences, the worst interference (WI) and the narrow-band interference (NBI). Both theoretical analysis and simulations indicate that the proposed algorithm can achieves better performance than the conventional LS algorithm under both the WI and the NBI.

This paper proposed an efficient iterative frequency domain equalization (FDE) for cooperative multi-relay-assisted automatic repeat request (ARQ) single carrier systems operating over multiple-input-multiple-output (MIMO) channel. The receiver employs each retransmission as an additional set of virtual receive antennas to exploit the space diversity. At each iteration, soft inter-symbol interference (ISI) cancellation and inter-antenna interference (IAI) cancellation followed by minimum-mean-square-error (MMSE) based frequency domain filtering are carried out. The estimated symbols are demapped into bit extrinsic log likelihood ratio (LLR) using an equivalent Gaussian channel assumption as the input of the soft-in-soft-out (SISO) decoder. Both implementation for decode-and-forward (DF) and amplify-and-forward (AF) are investigated. Simulation results demonstrate the effectiveness of the proposed algorithm compared to conventional LLR-based combining scheme.

In this paper, we investigate the performance of open-loop spatial multiplexing in overlaid ad hoc networks. Based on a stochastic geometry model, we derive exact closed-form expressions for the transmission capacity of two coexisting networks (a primary network vs. a secondary network) employing spatial multiplexing with zero-forcing (ZF) receivers. Simulation results confirm the accuracy of our expressions. In addition, we discuss the impact of multi-antenna scheme on the transmission capacity of the overlaid networks. Our findings show that the sum transmission capacity of the overlaid networks will improve significantly over that of a single network if a slight outage probability increase is allowable for the primary network. This improvement can be further boosted if spatial multiplexing is employed with more antennas. But when the antenna number exceeds a certain limit, spatial multiplexing may produce negative effect for the overlaid network.

Device-to-Device (D2D) communication underlaying cellular networks can enhance the network capacity and spectrum efficiency when sharing cellular resources. However, the severe interference between D2D and cellular networks may lead to performance decrease of D2D and cellular communication. In this paper, we concentrate on suppressing the interference between D2D users and cellular networks when D2D communication reuses the cellular resources in downlink. An efficient resource allocation scheme is proposed to manage the interference between D2D and cellular networks. First, the mutual interference is restricted under the constraints by adopting the interference limited area control method. After that, the resources are assigned to D2D users to improve the sum rate of cellular communication and D2D communication. Besides, the simulation results are presented and analyzed. Finally, we conclude that the proposed scheme can significantly improve the total capacity of cellular and D2D communication, while at the same time suppressing the mutual interference.

The next generation wireless network (NGWN) is envisioned as convergence of heterogeneous wireless networks. The vertical handoff plays an important role in supporting the service continuity and guaranteeing the quality of service (QoS). How to select the target network becomes the vital issue of designing the vertical handoff algorithm. In this paper, we propose a novel service-adaptive multi-criteria vertical handoff (SMVHO) algorithm. The algorithm formulates the network selection process as a multiple attributes decision making (MADM) problem. The candidate networks are evaluated by a set of decision metrics including SINR, bandwidth utilization, transmission delay, packet loss rate and monetary cost. The QoS requirements and network conditions determine the comprehensive performance ranking of alternative networks. Under different network conditions, the SMVHO algorithm can keep the mobile terminal connected to the optimal network by changing the weight of each metric. System-level simulations reveal that the SMVHO algorithm is effective in lowering the dropping probability and improving overall system throughput comparing with the RSS based vertical handoff (RVHO) algorithm.

Cognitive radio technology is considered to be an effective solution to improve the spectrum utilization efficiency. The dynamic spectrum allocation algorithm assigns the available spectrum to the secondary users. In this paper, we propose a spectrum allocation algorithm based on the graph-coloring theory. Unlike some already existed allocation algorithm, our algorithm considers the bandwidth matching between secondary users' bandwidth requirements and the available channels. The interference avoidance to the primary users is also taken into account. Our objective is to optimize the total spectrum reward under the premise of fully protecting the primary users. Simulation results prove that this algorithm can improve the total spectrum reward, the satisfaction rate of secondary users, the protection rate of primary users, and the spectrum allocation efficiency.

Cooperative diversity is an effective transmission technique allowing multiple users to create a virtual antenna array although each of them is equipped with single antenna. In this paper, an iterative channel estimation and equalization (ICEE) scheme for single-carrier transmissions is proposed, realizing space-time block code (STBC) with amplify-and-forward (AF) relaying in a distributed fashion. Most existing researchers assume perfect channel information available at the receiver, however, the effect of imperfect channel estimation should be considered for practical applications. In the proposed algorithm, pilot-aided channel estimation (CE) and soft inter-symbol interference (ISI) cancelation with minimum mean squared error (MMSE) filtering are performed iteratively to suppress interferences. An implementation that accounts for imperfect channel estimation is also investigated. The bit error rate (BER) performances and extrinsic information transfer (EXIT) charts are presented for Rayleigh fading channels. Simulation results demonstrate the effectiveness of the proposed algorithm.

In traditional cellular networks, the capacity of downlink channels is limited by inter-cell interference (ICI). Basestation cooperation is a promising technique which yields large performance improvements by mitigating or eliminating ICI. However, many existing cooperation methods are far from practical due to intensive computational complexity. In this paper, we propose a practical method of base-station cooperation for multi-cell multi-user multi-input multi-output (MIMO) systems. This method is mainly composed of two parts - cooperative scheduling and cooperative precoding. For cooperative scheduling, we design a channel-dependent scheduling algorithm based on proportional fair scheduling (PFS). For cooperative precoding, we use multiuser eigenmode transmission (MET). The computational complexity of this method is acceptable. And it shows considerable potential in terms of spectrum efficiency.

Resource allocation is one of the key issues to improve the efficiency of spectrum utilization in cognitive radio networks. It has been widely investigated with the assumption that the secondary users have a good knowledge of the channel state information of primary system. However, it is not reasonable in practice owing to the imperfect sensing. In this paper, a high-efficiency resource allocation scheme is proposed by considering the imperfect spectrum sensing. Particularly, in order to solve the problem of interference and lower efficiency of spectrum utilization, interference constraints and quality of service requirement are considered to reduce the impact from imperfect spectrum sensing. The goal of the presented scheme is to maximizing the capacity under the interference constraints of primary users. Simulation results indicate that the proposed resource allocation scheme can represent the better performance successfully.

With the deployment and development of high-speed railway in the world, the corresponding research on high-speed railway communication technology has made great progress. Generally, the dedicated high-speed railway communication network is believed to be required to meet the demand of high data rate with QoS guarantee on this high-speed scenario. The long term evolution (LTE), supporting the speed of 500 km/h as well as throughput of 50M to 100M bps, has a great advantage in high-speed railway communication scenario. However, little or none of the previous research involves the aspects of coexistence between the dedicated high-speed railway communication system and the adjacent cellular network systems along the railway. Thus, in this paper, we first introduce the high-speed railway communication system as well as propose a model of it, and then evaluate its coexistence performance with macro cellular communication system based on this model. Our research results show that, when these two network systems are deployed on the same frequency band, or when macro cellular system is densely deployed in urban areas, the high-speed railway communication system will be severely affected by the inter- system interference, and additional isolation will then be needed in these cases.

In this paper, we propose a distributed resource allocation mechanism with inter-cell interference (ICI) coordination for practical orthogonal frequency division multiple access (OFDMA) uplink. The designed scheme combines soft frequency reuse (SFR) and interference limited power control of neighboring cells. It avoids severe interference to neighboring cells through adjusting the interference limited power constraints according to the load variations across cells. The computational complexity is greatly lowered by decomposing a multi-cell optimization problem into distributed single-cell sub-problems. The simulation results demonstrate that the proposed scheme not only guarantees the cell-edge UEs' quality of service (QoS) but also improves the overall system performance significantly. Moreover, this scheme can adapt to the load variations in a certain cell or across cells.

This paper investigates the outage probability of joint relay selection and power allocation for two- way relay networks over Rayleigh Fading channels. Firstly, a tight lower bound of outage probability with equal power allocation is derived. Furthermore, a joint relay selection and optimum power allocation scheme is proposed, which minimizes the outage probability, then, a lower bound of outage probability is also obtained. Based-on the closed-form outage probabilities, we obtain a relay selection strategy, which requires only a single integer parameter to be broadcasted to all relays. The analysis is verified by using Monte-Carlo simulations.

An efficient frequency domain soft interference cancellation (FD-SIC) scheme is proposed for turbo frequency domain equalization (FDE) in multiple-input multiple-output (MIMO) system. It is designed that at the receiver the inter-antenna interference (IAI) is cancelled by prior information in terms of data expectation. It can improve the input signal to interference and noise ratio (SINR) for the equalizer. Then block (data of one transmit antenna) wise frequency domain minimum mean square error (MMSE) equalization is implemented. Later a low complexity algorithm on the basis of single frequency tone (SFT) is deduced. Symbol Log-likelihood ratio (LLR) is calculated from the output of equalizer. Simulation results show that the proposed scheme has better link performance than traditional algorithms.

As a mainstream technology in the 4G TDD (Time Division Duplex) systems, TD-LTE (Long Term Evolution) introduces heterogeneous network topology, utilizing a diverse set of base stations, to improve spectral efficiency per unit area. In heterogeneous network deployment comprised of macrocell and picocell, inter-cell interference coordination (ICIC) is very important to significantly improve the system and cell-edge throughput. Moreover, variety of complex situation of inter-cell interference (ICI) occurs in heterogeneous TDD LTE cellular networks due to different downlink/uplink (DL/UL) sub-frame configurations of macrocell and picocell. Therefore, this paper proposes an efficient ICIC scheme consisting of four sub-schemes according to relevant interference scenarios based on different sub-frame configurations. The scheme first analyzes interference level and finds out strong interference for each scenario. The basic idea of ICIC is that only primary interfering sources of each scenario avoid using the same frequency resource occupied by interfered victim, and other interfering sources can reuse frequency resource. Numerical results show that our proposed ICIC scheme can not only improve performance of whole region including macrocell area and picocell area, but also significantly achieve higher throughput for cell edge users.

In this paper, we investigate the performance of multiuser scheduling with open-loop spatial multiplexing in ad hoc networks. Closed-form expressions for outage probability and spatial throughput are derived for spatial multiplexing transmission with zero forcing (ZF) receiver and multiuser scheduling. Monte Carlo simulation results reveal that these expressions accurately demonstrate the performance of multiuser scheduling with open-loop spatial multiplexing. Based on these expressions, transmission capacity performance is analyzed and the effects of system parameters over network performance metrics are studied. Our finding indicates that spatial multiplexing with opportunistic multiuser scheduling can provide boosted network performance for ad hoc network by exploiting multiuser diversity gain, whilst requiring very low feedback requirements.

Field test in high speed environments is very difficult. To make the field test more feasible, this paper presents a scheme to extend the low speed field test system to estimate the measured data in high speed condition through an additional baseband processor, without changing the major parts of the base stations. The additional baseband processor changes the characteristics of the low speed signal through adding proper Doppler shift into the signal. In this paper, the system is introduced and the baseband model is discussed in detail. Simulation results are presented and discussed. And the hardware simulation plan is also presented.

The future wireless communication networks will integrate different radio access technologies (RATs), which are referred to as heterogeneous wireless networks (HWNs). In this paper, we deal with two data oriented access networks, the Long Term Evolution (LTE) and the high speed downlink packet access (HSDPA). Assuming that the networks can support multi-homing access and the user can be served by both networks simultaneously, we propose a traffic split scheme with the aim of maximizing the throughput based on common radio resource management (CRRM). The split ratio in the scheme is dynamically adjusted under the consideration of the user's channel quality and the network load. The simulation results show that the proposed scheme can improve the throughput, also reduce the delay of the networks compared with the scheme using the fixed split ratio.

Cooperative diversity is an effective transmission technique allowing multiple users to create a virtual antenna array although each of them is equipped with single antenna. In this paper, an iterative channel estimation and equalization (ICEE) scheme for single-carrier systems is proposed, realizing space-frequency block code (SFBC) with amplify-and-forward (AF) relaying in a distributed fashion. Most existing researchers assume perfect channel information available at the receiver, however, the effect of imperfect channel estimation should be considered for practical applications. In the proposed algorithm, pilot-aided channel estimation (CE) and soft inter-symbol interference (ISI) cancelation with minimum mean squared error (MMSE) filtering are performed iteratively to suppress interferences. An implementation that accounts for imperfect channel estimation is also investigated. The bit error rate (BER) performances and extrinsic information transfer (EXIT) charts are presented for Rayleigh fading channels. Simulation results demonstrate the effectiveness of the proposed algorithm.

In this paper, we present a distributed algorithm combining power control and scheduling for densely deployed femtocells networks. The strong interference in the downlink from the femtocells should be well mitigated to satisfy the quality of service (QoS) requirement of femtocell users. The considered optimization problem is formulated as minimizing the total power consumption, while the QoS requirements of femtocell users are guaranteed. An optimal scheme requires global information of channel qualities, which is very difficult to put into practice. This paper proposed a suboptimal algorithm joining power control with scheduling policy, which is operated in distributed manner. The distributed algorithm provides a suboptimal solution using local information including the channel quality of users and the iterative power values. Simulation results prove that our proposed algorithm can effectively allocate power and frequency resource to the femtocell users, while achieve superior system performance in terms of outage ratio and scheduling fairness.

The fixed-complexity sphere decoder (FSD) has been proposed to attain the near-optimal performance achieving the same diversity order as the maximum-likelihood decoder (MLD) recently. However, it suffers great redundant computations resulting in high power consumption. In this paper, we conduct an improved algorithm for the original FSD by using early termination (ET). This algorithm (abbreviated as ET-FSD) preserves the advantages of sphere decoder (SD) such as branch pruning and an adaptively updated pruning threshold. We compare the ET-FSD with the original FSD and a lately developed statistical threshold-based FSD (ST-FSD). Simulation results demonstrate that the ET-FSD attains the same performance with a much lower cost than the FSD, and is much more efficient than the ST-FSD in practice. In addition, the statistical threshold-based method can also be used for the ET-FSD (i.e., ST-ET-FSD) to further reduce the complexity.

Since the standardization of Long Term Evolution - Advanced (LTE-A) is currently carried through in 3rd Generation Partnership Project (3GPP), it is of great importance to ensure the coexistence between LTE-A system and other mobile systems. This paper is aiming at presenting the performance loss of 3G/B3G TDD systems (TD-SCDMA, TD-HSDPA and TD-LTE) interfered by LTE-A system. The detailed interference models are analyzed theoretically. Afterwards, three representative interference scenarios are simulated by adopting Monte Carlo method and discussed from the following respects: inter-site distances (ISD), offsets between two systems, carrier frequency, frequency reuse schemes, uplink power control mechanism and system bandwidth of TD-LTE. In the end, a few suggestions concluded through simulation results are proposed to better realize the co-deployment of LTE-A and 3G/B3G TDD systems.

The problem of distributed coordination in multi-cell wireless network has been concerned in the research community recently due to its ability to enhance intended signal and mitigate interference in the system. In the previous research, the design of beamforming weights at transmitter has been addressed from the perspective of egoism and altruism concepts considering the tradeoff between egoistic and altruistic solutions. The main contribution of this paper is to extend the existing strategy and exploit a much simpler hybrid coordination scheme with semi-distributed mode in multi-cell wireless network using the analytic hierarchy process. The significant advantage of our approach is to provide transmitter with a method which is easier to achieve compared with the existing pattern in a semi-distributed way. The performance of proposed scheme is finally illustrated through the numerical simulation results.

Cooperated multi-point technique in HSPA+system has not been paid attention until the Single Frequency Dual Cell (SF-DC) mode, where one user equipment (UE) may be served by dual NodeBs simultaneously in the single carrier frequency network, is proposed recently. In the previous research, the system-level performance with SF-DC operation had not been studied comprehensively. The main contribution of this paper is to exploit SF-DC transmit mode in the perspective of the system level and evaluate the system-level performance of SF-DC in HSPA+system with different simulation scenes. The impact of SF-DC on legacy UEs and the load balancing capability of SF-DC in asymmetric loading case are investigated properly in different channel conditions. System-level simulation results show that SF-DC transmit mode performs better compared with single point transmission and the influence of SF-DC mode on legacy UEs is negligible. It also reflects that SF-DC has the ability to balance load in asymmetric loading case.

Recently, Coordinated Multi-Point (CoMP) transmission/Reception technology is introduced into the fourth-generation cellular mobile communication system. Time-division duplex (TDD) system is more suitable to apply CoMP when joint processing is needed because it can easily get the channel information through channel reciprocity. Actually, a crucial point to realise channel reciprocity is the antenna calibration, especially in the inter-base station (BS) case. Self-antenna calibration within the BS in the conventional system has been studied in previous works. In this paper, the authors investigate the impact of un-calibrated antennas of BSs and mobile stations (MSs) on the precoding matrix of two precoding techniques [block diagonal (BD) and zero forcing (ZF)] in the CoMP system. A theoretical model is set and analysed. The discussion of some properties gives a complete overview of the calibration problem in the CoMP system. In addition, the authors propose a practical scheme to solve inter-BS antenna calibration problem. System simulation results, which validate their analysis, are presented to show the necessity of antenna calibration.

This paper addresses an adaptive multi-user resource allocation for a distributed multi-carrier direct sequence-code division multiple access (MC DS-CDMA) network. The packet throughput, which turns out to be nonconvex and nondifferentiable, is considered to measure the system performance. A sub-optimal non-cooperative power control game is proposed to adaptively allocate the transmit power, available subchannels and alphabet size by minimizing the transmit power with a transmit power constraint and a packet throughput requirement. Also, the paper investigates the effect of channel estimation error on the adaptive resource allocation in a distributed MC DS-CDMA network, and shows that using the Gaussian approximation for the signal-dependent noise can lead to a nontrivial discrepancy in system performance.

Multi-user multi-input and multi-output based on block diagonalization algorithm can eliminate the multi-user interference, but in fact the existence of the non-ideal factors lead to the interference can not be cancelled completely. In this paper we study the performance of the 3GPP long term evolution system based on BD algorithm and propose a low complexity multi-user scheduling scheme to reduce the mismatch between the CQI and the PostSINR. To get the tradeoff between the cell average capacity and the cell edge user capacity, proportional fairness scheduling is applied. Finally, simulation results with 3GPP LTE are presented using system level simulator.

In this paper, we study the joint resource allocation for the multi-destination amplify-and-forward relay network with direct source-to-destination links based on orthogonal frequency division multiplexing (OFDM) transmission. We aim to maximize the sum rate by jointly optimizing power allocation, subcarrier pairing, user assignment and transmission mode classification subject to the individual power constraints for the source and relay nodes. The optimization problem is solved based on dual method and a near-optimal joint resource allocation scheme is proposed. Besides, two sub-optimal schemes with reduced complexity are presented. Finally, simulation results show that the proposed near-optimal scheme outperforms other sub-optimal resource allocation schemes.

Diversity is an effective technique to enhance link quality and increasing network capacity. In this paper, we propose a generalized distributed turbo codes (DTC)-based coded cooperation protocol for two-hop relay networks with an arbitrary number of relays. This scheme aims at achieving improved diversity over the classical coded cooperation method in Rayleigh fading channels. We develop a closed-form expression for the pairwise error probability (PEP) and a tight upper bound for the bit error rate (BER) using DTC. The results demonstrate the merits of DTC-based coded cooperation with multiple relays, under various relay and uplink channel conditions. Moreover, the analytical upper bounds are validated with simulation results.

In real environments, channel reciprocity cannot be directly exploited between uplink and downlink in time-division duplex (TDD) due to antenna gain mismatch. Previous work about antenna calibration mainly focused on single cell. This work proposes an adaptive scheme for antenna calibration between two cooperative BSs. The proposed scheme aims at achieving an equal ratio between antenna transmitter and receiver analog gains among cooperative BSs in flat fading channels. The essential idea is to relay calibration parameter through a calibration path. This procedure can be controlled by a certain BS dubbed primary BS. Evaluation of the proposed scheme is carried out by computer simulation.

Block diagonalization (BD) algorithm is an efficient precoding technique for multiuser multiple-input multiple-output (MU-MIMO) system. In previous researches, BD precoding was mostly realized based on the singular value decomposition (SVD). However, in the cooperative transmission scenario where the dimension of channel matrix is significantly enlarged compared with the single base station (BS) transmission scenario, implementing SVD decomposition requires heavy computational amount, which is impractical in some real systems. The main contribution of this work is a low complexity solution scheme for BD. When the number of antennas of the receiver is two, instead of using SVD, the proposed scheme computes the null space and eigenvectors by solving linear equations and projection method, respectively. It has a lower complexity when the number of transmit antennas is not large. For example, when the number of transmit antennas is 20, the total computational amounts of the proposed scheme is about 53000 flops while it is around 78000 flops in the SVD based scheme.

Cooperative communications enable single antenna mobiles in a multi-user environment to share their antennas and form a virtual multiple antenna array that allows them to achieve transmit diversity. In order to achieve improved diversity over the classical coded cooperation method in fading channels, we consider a coded cooperation diversity strategy that is suitable for multiple relays channels. We derive a finite range single integral solution for the outage probability, which characterize the coded performance with multiple relays at various rates. Numerical results demonstrate the merits of coded cooperation and other repetition-based methods, under various relay and uplink channel conditions, and show that it achieves the full diversity order.

In this paper, we propose a cooperative load balancing scheme focusing on improving effective resource utilization and mitigate the co-channel interference across domains through fair resource allocation in heterogeneous network (Het-Net). We models the load balancing issue as an optimization problem for minimizing the effective resource utilization. Simulation results have demonstrated that the system effective resource utilization is significantly reduced through our proposed inter-domain load balancing scheme. It is also demonstrated that by incorporating the co-channel interference in the optimization process, the proposed scheme has great advantages in interference management of Het-Net.

In this paper, we consider practical multiuser multiple-input multiple-output (MU-MIMO) systems where each user has multiple receive antennas and limited channel feedback is available at the base station (BS). The joint combiner and precoding scheme for downlink transmission is proposed, in which we consider the joint use of the receive antenna combiner at each user and precoding at the BS. In the proposed scheme, each user independently chooses the codeword as its preferred-beam vector from the predefined codebook, which maximizes the effective channel gain after the receive antenna combiner. Utilizing the received feedback from users, the BS can easily construct the precoding matrix by zero-forcing beamforming (ZFBF) criterion. In addition, a user selection algorithm is provided to select served users, when the number of users exceeds the number of transmit antennas. Numerical results show that the proposed scheme improves the sum-rate performance of MU-MIMO downlink systems.

In this paper, we propose a new efficient distributed dynamic resource allocation (DDRA) scheme to coordinate the inter-cell interference and verify the existence of the Nash equilibrium. This new scheme can be utilized in the long term evolution (LTE) uplink and downlink scenarios to mitigate the inter-cell interference effectively. The system level simulations show that the system performance is improved compared with the conventional random resource allocation scheme.

This paper considers the multiuser relay network, which applies Laneman's seminal protocol of selective decode and-forward relaying. We mainly consider the opportunistic scheduling scheme which selects the user who has the largest received signal-to-noise ratio at the destination for transmission. We derive the exact and asymptotic expressions for the outage probability under Rayleigh fading, and the diversity analysis reveals that a total diversity order of K + 1 can be achieved, where K is the number of users. Besides, we propose a new multiuser scheduling scheme which achieves the same outage performance and improves the fairness among users. Finally, numerical simulations are presented to validate the analytical results.

Deployment of heterogeneous networks is one of the key technologies in LTE-Advanced. After low-power nodes were introduced to cellular system, great changes have taken place in the structure of traditional networks. Thus, range expansion (RE) scheme is proposed to adapt to these changes in the standardization process of heterogeneous networks. This paper studies the performance of heterogeneous networks with RE scheme introduced. First, we describe heterogeneous deployment scenario and analyze the benefits and disadvantages of introducing RE scheme. Next, physical downlink control channel (PDCCH) and physical downlink shared channel (PDSCH) are both modeled with a novel PDCCH distribution strategy design. Finally, numerical simulation results, involving pico UE ratio, PDCCH SINR and outage rate, PDSCH throughput, are provided to comprehensively evaluate the performance of heterogeneous networks.

Considering the latest development after introducing Relay Nodes (RNs) into the cellular networks and the effect of inter-cell interference coordination in the cellular networks, we propose a novel method of inter-cell interference coordination for relay enhanced cellular networks. Firstly, for each cell, all available frequency resource is divided into two parts. The first part is for the users connected to the BS directly, and the other part is allocated to the users connected indirectly to the BS through Relay Nodes. Furthermore, the second part of frequency resource is divided into three parts which are utilized by cell-edge users. System-level simulation results show that the proposed scheme performs better on system capacity and spectrum efficiency than the Soft Frequency Reuse (SFR) scheme.

Device-to-Device (D2D) communication will become an important technology in future networks with the increase of the requirements of local communication services. The interference between cellular communication and D2D communication can be coordinated by proper power control and resource allocation. In this paper, we analyze the resource allocation methods for D2D communication underlaying cellular networks. A novel resource allocation method that D2D can reuse the resources of more than one cellular user is proposed. After that, we discuss the selection of the optimal resource allocation method from the proposed method and the conventional methods. Finally, the performance of different methods is evaluated through numerical simulation. The simulation results show that the proposed method is the optimal resource allocation method when the D2D pair locates at the most part of the cell area in both uplink and downlink. The proposed method can improve the sum throughput of cellular communication and D2D communication significantly.

Single and Multi-layer adaptive eigen based beamforming (EBB) has been proved to be a promising method to achieve the tradeoff between diversity and spatial multiplexing. But the CQI in multi-layer mode is calculated according to the CQI in single-layer mode. Lack of accurate multi-layer CQI will induce performance loss when implementing layer adaptation at eNodeB. In this paper, aiming to reduce the complexity of the UEs, we deduce a low complexity eigen value calculation algorithm. In order to considering the effects of interference among different layers, virtual equalization (VE) algorithm is proposed. On the basis of these, a novel single- / multi-layer adaptive scheme for EBB is presented. Finally, the performance of the proposed scheme is studied using semi-dynamic system level simulator.

To meet the increasing demand for mobile broadband, multiple carrier features were subsequently introduced into UMTS Release-8 to Release-10. As a consequence, the UE capabilities of rejecting inter-stream interference have increased considerably. To fully utilize the UE capabilities and wireless resources, multi-point transmissions raised concerns in 3GPP High Speed Downlink Packet Access (HSDPA) standardizing process. Multi-point transmission is a promising technique to increase both the average cell throughput and cell edge user throughput. A novel cooperative sector selection algorithm, which takes both channel condition and sector loading into consideration, and an adaptive precoding transmission scheme are proposed for HSPA multi-point transmission. Through the system level simulation, the proposed transmission scheme effectively outperforms the non-cooperative system and non-adaptive cooperative scheme on both the average sector throughput and sector-edge UEs' rates significantly.

A cognitive radio (CR) network should have the ability to detect the presence of incumbent users and adjust its transmission in order to utilize unused licensed spectrum without causing interference to incumbent users. To effectively protect incumbent users, properly modeling expected interference from the CR system is therefore important.We model the accumulative interference generated from a cellular CR network and formulate interference constraints of digital television (DTV) system, e.g. coverage area loss, as a function of feasible network planning parameters, e.g. minimum isolation distance and maximum transmitted power. Then interference constraints of the DTV system can be translated to feasible network planning parameters. Furthermore, we investigate how network parameters affect sensing requirements of the CR system to meet DTV interference constraints.

Transmit diversity can be regarded as a technology in wireless communication in order to enhance the system performance. Some relevant methods of transmit diversity have been presented on the basis of link-level research but do not consider multiple access interference (MAI) existing among users in the uplink of multi-user system. In this paper, we proposed one uplink transmit diversity scheme, which considers the effect of MAI in HSUPA. System-level simulation shows our strategy can degrade the interference level at receiver, save transmit power of user, and make an improvement to system throughput compared with the traditional method which does not consider MAI to some extent.

This paper investigates the performance of selection combining (SC) amplify-and-forward (AF) relaying with adaptive modulation to maximize the spectral efficiency. We derive the closed-form expressions of the average spectral efficiency and the outage probability of the proposed scheme over independent and non-identical Nakagami-m fading channels. The analysis results are verified by using Monte Carlo simulations. Our results indicate that the proposed scheme not only has simplified receiver architecture, but also can offer similarly high spectral efficiency as the MSE-AM scheme proposed in [1], when the relay link is stronger enough than the direct link.

Femtocells are designed to cover a short range of area and improve the cellular system capacity in an economically viable way. In this paper, we propose an adaptive sub-band allocation (ASA) scheme for the downlink transmission of the LTE system, which consists of orthogonal sub-band assignment (OSA) algorithm and adaptive sub-band reuse (ASR) algorithm based on the interference graph. The interference graph is used to model the interference relationships between femtocells and femtocell users, while it could be simplified as the interference relationships of adjacent femtocells in this paper. The OSA algorithm is performed to eliminate the inter-cell interference, while the ASR algorithm is operated to increase with spectral reuse and suppress the interference level of the network. An instance of our ASA scheme is described in detail, which considers the mobility of the serving users and the operation complexity. By extensive simulations, it has been proved that our proposed scheme effectively mitigates the interference level in the femtocell networks and obtains superior performance in terms of cell-edge and femtocell throughput compared with the reference schemes available in the paper.

In this paper, we consider a joint power control and resource allocation scheme for co-channel deployed femtocells in macrocell networks. The strong interference in the downlink from the femtocells should be well controlled to satisfy the quality of service (QoS) requirement of both macrocell users and femtocell users. We provide both centralized and distributed schemes to solve the formulated optimization problem, which is aimed at minimizing the total power consumption as well as guaranteeing the QoS of both macrocell and femtocell users. The centralized scheme is based on the Hungarian algorithm, which is proved to achieve the near optimal performance. The distributed scheme is easily operated by individual femtocell with some coordination information delivered by nearby macrocells indicating the downlink interference power level. Simulation results demonstrate our proposed schemes can effectively allocate power and frequency resource to the femtocells, while obtaining superior performance of the outage ratio and power consumption.

Antenna gain mismatch between transmitter and receiver circuits has been regarded as an obstacle for exploiting channel reciprocity between uplink and downlink channels in time-division duplex (TDD) multiple-input multiple-output (MIMO) systems. To the best knowledge of the authors, little work to date has been on about the impact of antenna mismatches on the precoding vector. Motivated by this fact, this paper investigates some characteristics of downlink precoding in the presence of non-ideal antenna gains. Specifically, properties about inter-MS interference when mismatches exist at the base station (BS) side are presented as well as the perturbation of non-normalized precoding vector caused by mismatches at the mobile station (MS) side under two kinds of linear precoding algorithms. These properties are mostly irrelevant to specific distributions of antenna mismatch parameters and can help to provide a deeper insight into the antenna gain mismatch problem and the corresponding calibration.

This paper investigates a novel relaying strategy for cooperative networks over Nakagami-m fading channel, namely selection incremental relaying (SIR), which combines selection relaying (SR) with incremental relaying (IR) based on decode-and-forward (DF). The closed-form expression for the outage probabilities of both single relay and opportunistic relay strategies are derived. Simulation results confirm the presented mathematical analysis and show that the proposed SIR strategy outperforms DF, SR and IR strategy over all signal-to-noise ratio (SNR) values.

The virtual MIMO (V-MIMO) and coordinated multipoint transmission (CoMP) are adopted by the LTE system to extend the uplink spectral efficiency. V-MIMO makes use of spatial multiplexing to increase system throughput while CoMP by means of mitigating inter cell interference (ICI) significantly achieve the same effect. In this paper, we present an orthogonality based proportional fair scheduling (OPF) scheme for virtual MIMO and CoMP in TD-LTE uplink. To evaluate the effectiveness of the OPF algorithm, three schemes are analyzed and compared: conventional single input multiple output (SIMO), V-MIMO and CoMP. Finally, we evaluate and compare the potential gain in spectral efficiency for the SIMO, V-MIMO and CoMP using LTE semi-dynamic system level simulator.

A cognitive radio (CR) system should have the ability to detect the presence of incumbent users and adjust its transmission so that it can utilize unused licensed spectrum without causing interference to incumbent users. To effectively protect incumbent users, properly modeling the expected interference from CR system is therefore very important. We model the accumulative interference generated from CR system to translate interference constraints of digital television (DTV) system, e.g. coverage area loss, to feasible network planning parameters such as minimum isolation distance or maximum transmitted power. Using the model coverage area loss can be formulated as a function of inter-system isolation distance as well as secondary BS or UE transmitted power. Furthermore, we investigate how the network parameters affect the sensing requirements of the CR system to meet DTV interference constraints.

This paper investigates the symbol error rate (SER) performance of the multiple-input multiple-output (MIMO) multi-channel beamforming (MB) in the general double-scattering channel. We derive an asymptotic expansion on the marginal eigenvalue distribution of the MIMO channel matrix, and apply the result to get an approximate expression on the average SER at high signal-to-noise ratio (SNR). Two parameters pertaining to the SER, i.e., the diversity gain and the array gain, are analyzed. Our results show that it suffices for the double-scattering channel to have only limited scatterers, if the same diversity gain as the Rayleigh channel is desired; however, once the number of scatterers is below a certain level, the array gain in the double-scattering channel will vary with the SNR logarithmically.

The asymptotic performance of transmit antenna selection (TAS) in a two-hop amplify-and-forward (AF) MIMO relay network over Rayleigh-fading channels is analyzed. Assuming that the source and destination are equipped with NSand NDantennas, respectively, and communicate with each other with the help of an NR-antenna relay, we derive closed-form statistics of received signal-to-noise ratio (SNR) around original, and present the asymptotic average symbol error rate (SER). By analyzing the high SNR performance, we show that the diversity order, min {NSNR, NRND} can be achieved for the transmission. The optimal relay selection problem, selecting the relay that minimizes the average SER, is also analyzed which shows that the position of the selected optimal relay depends on the number of antenna of source, relay, and destination. Numerical results that confirm our analysis are also presented in the paper.

A novel spatial-multiplexing orthogonal frequency- division multiplexing (OFDM) transmission system with transmit diversity provided by space-frequency block code (SFBC) is proposed in this paper. The proposed scheme combines Alamouti scheme and Bell Labs layered space-time (BLAST) together, thus can achieve transmit diversity and spatial multiplexing gains altogether. Two-step iterative detection algorithm is also proposed for this system, in which MMSE detection is performed firstly and then SFBC decoding coupled with successive interference cancellation (SIC) is performed separately and iteratively for each layer. Simulation results show that the proposed system with iterative detection algorithm can achieve better tradeoff between transmission rate and bit error rate (BER) performance than existing multiple-input multiple-output (MIMO) OFDM systems.

A novel transmission and retransmission scheme is proposed in this paper, which integrates Superposition Coding (SC) with Network Channel HARQ (NC-HARQ). First of all, the scheme is proposed through the design of the transmission and retransmission flows. Then the channel capacity and the transmission efficiency of the proposed scheme and conventional schemes are formulated and analyzed. The scheme is fit for the traffic with messages of different priorities. Both the gain on spectrum efficiency of SC in the transmission and that of NC-HARQ in the retransmission, which are represented by the data rate and the transmission efficiency, can be combined in the proposed scheme. Finally, the performance of different schemes is evaluated through numerical simulation. The results show that the proposed scheme can obtain higher transmission efficiency than conventional NC-HARQ and HARQ scheme through SC in both correlated and uncorrelated packet loss models.

The paper establishes connections between orthogonal space-time block codes (OSTBC) and multiple-input multiple-output beamforming (MIMO BF). Different from previous work, where the two schemes were studied independently and under specific fading conditions, we consider a framework which unifies the analysis of both schemes in arbitrary fading. In particular, we demonstrate that the diversity gains of OSTBC and MIMO BF are equivalent, regardless of the underlying channel fading distribution. We also derive bounds on the difference in transmit power required for the two schemes to achieve the same outage probability. This result, which again applies for arbitrary fading, quantifies the gain of MIMO BF over OSTBC due to the presence of transmitter channel knowledge.

The performance of transmit antenna selection (TAS) in a two-hop amplify-and-forward (AF) MIMO relaying network over Rayleigh-fading channels is analyzed. Assuming that the source, destination are equipped with NSand NDantennas, respectively, and communicate with each other with the help of an NR-antenna relay, we derive closed-form cumulative distribution function (CDF) of received signal-to-noise ratio (SNR), and based on the CDF, we then present outage probability and exact symbol error rate (SER) for the AF MIMO relay channel with TAS. Numerical results that confirm our analysis are also presented in the paper.

Interference cancellation (IC) is an effective and easy implemented technology in the multi-user system. Previous studies demonstrate the principles of IC and IC process which show a great improvement in the system capacity with IC. However, no research has focused on the IC system's capacity domain by giving an accurate formula. This article carries on the theoretical analysis of CDMA reverse link capacity with IC, presents the expressions as well as its optimal answer for synchronous frame and brings forward the formula as well as its suboptimal solution for asynchronous frame. Numerical result reveals that the commercial EV-DO reverse link capacity with IC will increase by at least 135% compared with the one without IC. Finally, the stability of the IC system is explored.

In this paper, the performance of beamforming in two-hop relay networks with Rayleigh-Rician asymmetric fading channels is investigated. This network consists of a relay node equipped with a single antenna, a source and a destination node both equipped with multiple antennas. The first and the second hop are respectively subjected to Rayleigh and Rician fading. Transmit beamforming and receive beamforming (or named MRC) are implemented at source and destination nodes, respectively. Analytical expressions for outage probability and average symbol error rate (SER) are derived in both infiniteseries form and simple asymptotic results. The infinite-series representation expressions are shown to converge rapidly of a few terms for high accuracy and the simple asymptotic results the system can achieve a diversity order of min(Nt,Nr), where Nt, Nr denote the number of antenna at source and destination node, respectively. Monte Carlo simulation is performed to verify the proposed analytical results.

In this paper, we investigate the outage performance of dual-hop relay networks with co-channel interference which is a major problem in the cellular radio system. A more realistic channel fading model for micro-cellular radio network is adopted as follows, and the desired signal is assumed to have Rician fading due to the presence of line-of-sight (LOS) propagation and the interfering signals from neighboring cells are assumed to experience Rayleigh fading because of the absence of a LOS propagation. An upper bound of outage probability and the asymptotic expression for amplify-and-forward (AF) protocol are derived. Meanwhile, we also propose the optimal power allocation for dual-hop relay networks in high signal-to-interference ratio (SIR) regime. Computer simulations have been performed to verify the validity and the accuracy of theoretical results.

Cooperative Communication enables wireless devices with relatively less antennas to share their antennas and create virtual multiple-antenna transmitter, thereby achieving transmit diversity to combat fading caused by multi-path propagation in wireless environment. At the receiver in a multi- input multi-output (MIMO) relay system, we can still utilize the traditional detection algorithm, such as zero-forcing successive interference cancellation (ZF-SIC), which have been widely employed in the Vertical Bell Laboratories Layered Space-Time (V- BLAST) system model. However, the inevitable error- propagation in the procedure of such algorithms may cause great performance degradation, which cannot meet the demand for high data rate while maintaining high quality wireless communications. In this paper, we develop a reliability-based detection algorithm that includes a new log likelihood ratio (LLR) calculation for MIMO Relay system to alleviate error propagation. In addition, to further improve the system performance, we utilize a pair-wise LLR combining scheme suits for cooperative communication system with incremental relaying protocol. Simulation results show that our proposed algorithm outperforms the traditional ones in a MIMO Relay system.

In this paper, a novel interference coordination scheme based on Dynamic Resource Allocation (DRA) for mitigating inter-cell interference in Long Term Evolution (LTE) cellular systems is presented. In both OFDMA and SC-FDMA systems, inter-cell interference is the most important interference source. Inter-cell interference coordination is considered to improve coverage and increase date rate at cell edge. Some interference coordination schemes such as Soft Frequency Reuse (SFR) are proposed in 3GPP Long Term Evolution (LTE). However, the existed schemes always have not researched the interference issues on both the downlink and uplink interference at the same time. And some algorithms like SFR have low spectrum efficiency because the cell edge users can only use a fraction of the entire frequency band. The simulation results show that, the scheme we proposed, can not only improve performance of the cell section, but also get higher throughput for cell-edge users.

Coordinated Multi-Point (CoMP) Transmission/Rec-eption technology has shown to improve the system performance. In Time-division duplex system, it can easily obtain channel information by the channel reciprocity. However, a crucial point to realize the channel reciprocity is the antenna calibration problem. This paper aims at analyzing the impact of un-calibrated channel on the precoding matrix under zero forcing precoding in CoMP system. A theoretical model is set and some properties presented in this work give an overview of the calibration problem. Additionally, we propose a new scheme for inter BS calibration. System simulation results show the necessity of antenna calibration.

Multi-cell cooperation has been regarded as a promising technique of the future cellular wireless network to achieve higher transmission rate and better QoS (quality of service) performance. Cooperation among base stations can be classified into two categories: centralized and distributed cooperation. In this work, we mainly consider efficient and practical cooperation clustering approaches in the downlink Coordinated Multi-Point (CoMP) system. A novel Multi-Layered clustering method is proposed for distributed cooperation, which is able to make a significant enhancement with limited overhead increment compared with traditional static clustering. We also develop a new concept for centralized cooperation. Simulation results are presented under the block diagonal precoding algorithm.

Coordinated scheduling is a hot topic recently. Inter-cell interference is crucial to the improvement of system throughput, especially in OFDMA system. In this work, the optimization of beamforming in multiple-input single-output (MISO) downlink system is considered. The uplink-downlink duality has been widely used in this sort of research. By the conclusion of a previous work, we provide some practical iterative algorithms which help to obtain the beamformers satisfying the necessary optimality conditions of the dual uplink problem. Simulation results show the convergence and the efficiency of proposed algorithms.

The fixed-complexity sphere decoder (FSD) has been proposed to attain the near-optimal performance and achieves the same diversity order as the maximum-likelihood decoder (MLD) recently. However, its equally handling all the branches obtained via the full expansion (FE) stages till reaching the final minimum Euclidean distance (MED) decision is unnecessary. In this paper, we conduct an adaptive control of the number of surviving branches for each of the single expansion (SE) stages in the original FSD (AC-FSD). In this controlling method, for each stage, the surviving branches are selected by a threshold value which is calculated from the minimum partial accumulated branch metric and the noise level. We compare the AC-FSD with the original FSD and a recently proposed simplified FSD (SFSD), and simulation results demonstrate that the AC-FSD with proper threshold can attain near-optimal performance with a much lower cost than that of the FSD and the SFSD when the system works in mid and high signal-to-noise ratio (SNR) regimes in practice.

In the downlink cellular network, the coordinated multi-point transmission for single-user multi-input multi-output (CoMP-SU-MIMO) is employed in Long Term Evolution Advanced (LTE-A) system, which can effectively reduce inter-cell interference for cell-edge user equipments (UEs). A novel transmission scheme with the joint proportional fairness (PF) scheduling algorithm, which does not need to allocate the dedicated frequency band to cell-edge UEs for transmission and can make best of frequency diversity gain, is proposed for CoMP-SU-MIMO system. By using Non-CoMP SU-MIMO system as a baseline, the average sector throughput and cell-edge UEs' rates of the proposed scheme are evaluated through our system level simulation compared to the traditional flexible frequency allocation plan (FFAP) scheme. The results present that the proposed transmission scheme which can be applied to multiple scenarios effectively outperforms the FFAP scheme on both the average sector throughput and cell-edge UEs' rates significantly.

It is widely accepted that the emergence of cognitive radio (CR) will lead to a wireless communication revolution. Spectrum sensing is one key process of CR, which makes effective use of scarce spectrum. Two novel schemes, clustering and locating schemes, are presented for spectrum sensing based on energy detection on the condition that there are multiple primary users in the cognitive radio network. Clustering scheme is used for estimating the number of primary users and dividing the secondary users into several groups based on their geographical position as well as received energy by my proposed iterative max-min theory, and then locates the position of primary user by locating scheme based on the center of gravity algorithm. These schemes work well when only geographic information and the amount of energy can be obtained. Finally, numerical analysis and simulation results of these schemes are provided. It is proved that the proposed criteria are practical and efficient in the absence of the type of primary signal and the amount of noise which are necessary for previous methods.

Incremental selection amplify-and-forward relaying (ISAF) has the best performance of outage probability among relaying strategies and has been identified as the best protocol. This paper proposes to jointly optimize power allocation (PA) and best-relay position based on cooperative diversity for ISAF in order to minimize outage probability. The closed-form solution to the adaptive allocation algorithm based on high signal-to-noise ratio (SNR) approximation of outage probability is presented, assuming maximum ratio combining (MRC) at the destination. Simulation results have shown that the system performance of outage probability with the proposal outperforms the fixed PA algorithms, and much less power is needed to achieve the same outage probability at the same effective rate. The power saving can be as much as 9 dB compared to the equal power allocation scheme.

In LTE downlink multiple-input multiple-output (MIMO), eigen based beamforming (EBB) is a promising approach for single-user scenario, while block diagonalization based beamforming (BDBF) eliminates intra-cell interferences significantly for multi-user scenario. However, both of them neglect inter-cell interferences which may lead system performance degradation. This paper presents an interference suppression based beamforming (ISBF) scheme to suppress inter-cell interferences. We first introduce interference suppression matrix (ISM) into EBB and BDBF to propose a novel beamforming matrix construction method. Then the ISM reporting scheme is discussed to support ISBF, and a precoded uplink pilot based (PUPB) reporting scheme is presented exploiting the channel reciprocity in TDD system. Finally, the simulation results are provided using dynamic system level simulator. Our results show that ISBF improves cell average and cell edge spectral efficiency significantly compared with traditional EBB and BDBF.

To ensure Evolved-Universal Terrestrial Radio Access Network (E-UTRA) or Long Term Evolution (LTE) can coexist with other mobile systems operating in the same geographical area, coexistence studies involving E-UTRA are ongoing in the 3rd Generation Partnership Project (3GPP). Related work is also on the way in China Communications Standards Association (CCSA) which may influence the allocation of frequency bands. In this paper, coexistence issues between E-UTRA and Universal Terrestrial Radio Access Network (UTRA) deployed in adjacent frequency bands are investigated. Two classical approaches are used to evaluate the performance degradation of both systems caused by inter-system interference. One is theoretical analysis and the other is system level simulation. The deterministic calculation is carried out in detail for base station (BS) to BS interference scenario, while the static Monte-Carlo simulation is adopted to analyze almost all the interference scenarios. System level evaluation methodology and assumptions are provided, and simulation results for a number of typical scenarios are discussed. The results show that E-UTRA has the ability to resist interference to some extent, but it brings severe interference to UTRA, and the interference between base stations is more severe than other scenarios. It is also found that the offset of E-UTRA system sites, different frequency bandwidths and power control schemes have various impacts on UTRA performance, so they should be carefully considered during E-UTRA deployment to ensure the coexistence with UTRA.

Adaptive beam-forming antenna (ABA) has been adopted as one of the key techniques of the TDD system. Because of the spatial variation of UE and imprecise digital signal processing (DSP) in the practical system, the system performance is deteriorated by the estimation errors of the direction of arrival (DOA). We evaluate the LTE TDD downlink performance of ABA without DOA estimation errors. Meanwhile, the impact of imperfect ABA on the system performance for the FTP-specific service as well as mixed services including FTP and video is investigated. Also a simple mixed services scheduler with adaptive emergency threshold (AET) is proposed over LTE TDD system to improve the system throughput while guaranteeing the quality of service (QoS) of video service.

A novel joint blind channel estimation and turbo equalization algorithm is proposed for orthogonal frequency-division multiplexing (OFDM) system in this paper. It has been proved that, blind channel estimation based on linear precoding can obtain channel information exactly. However, the precoding will cause inter-symbol interference (ISI). With the existence of ISI, the bit error rate (BER) performance of OFDM will be degraded seriously. In our proposed algorithm, we plan to combine this blind channel estimation algorithm with turbo equalization. On the one hand, turbo equalization can eliminate the ISI and improve system's performance; On the other hand, the a priori information provided by channel decoder conversely can be employed to boost the accuracy of blind channel estimation. Simulation results show that, compared with existing methods, our proposed algorithm can achieve better channel estimation accuracy and BER performance.

In order to avoid the resource inefficiency of all-participated cooperation in wireless amplify-and-forward relay networks, a novel relay selection scheme based on the channel gain of the source-relay and relay-destination links is proposed. A condition is introduced to maximize the upper bound of the overall received signal-to-noise ratio (SNR). The relay nodes which have bad channel conditions are excluded in turn from the cooperation so that their released resources can be reallocated to other nodes. This paper adopts a simplified power allocation scheme that assumes each selected relay has equal power. The total power is optimally assigned between the source and the relay set. Simulation results show that the proposed scheme can achieve similar BER performance with the scheme which employs all relays and optimal power allocation, but only applies a subset of available relays.

Maximum-likelihood detection (MLD) is the optimal scheme for multiple-input multiple-output (MIMO) channels. However, due to its exponentially high complexity, many alternative algorithms, including some parallel detection (PD) ones with low complexity and high stability, have been proposed for practical applications. Nevertheless, the existing PD algorithms are unable to exploit sufficiently the diversity order increment for low-complexity algorithms via MLD for partial layers, consequently, the complexity of the sub-detectors is still undesirably high. In this paper, a novel PD algorithm with relative low-complexity sub-detectors, i.e., the partial decision feedback sub-detectors, has been developed. Numerical analysis indicates that the proposed parallel algorithm can achieve the near-optimal performance with much lower complexity in comparison with the existing PD algorithms. Thus, this algorithm makes the parallel detection more feasible in real-life systems with limited parallel processing elements.

In this paper, we investigate the performance of multiple-input multiple-output (MIMO) multi-channel beamforming (MB) systems in double-scattering channels. In particular, we first derive new expressions for the marginal ordered eigen-value distributions of the double-scattering channel matrices. Based on these results, we present analytical expressions for the symbol error rate of MIMO MB. It is demonstrated that MB sub-channels can achieve full spatial diversity even in the presence of double scattering, if the number of effective scatterers is greater than or equal to the maximum number of transmit and receive antennas.

This paper analyzes the performance measures of amplify-and-forward (AF) relaying over non-identical Nakagami-m fading channel. The exact probability density functions (PDFs) of total signal-to-noise ratio (SNR) for variable gain relaying and fixed gain relaying are deduced, and the theoretical formulas of moment generating function (MGF) and moments for fixed gain relaying are presented. Since the exact PDF of total SNR for variable gain relaying is not tractable, its approximation is used to derive the formulas of MGF and moments. Using these statistic characteristics, the average symbol error rate (ASER) and amount of fading (AoF) for fixed gain relaying are derived, and the tight approximate ASER for variable gain relaying are given. These proposed mathematics results are verified by simulation.

After relaying technology is introduced into the cellular system, many research fields emerge. Among them, resource allocation strategy for distributed and centralized scheduling is an important topic. This paper analyzes and compares the differences between these two scheduling modes in relaying systems under interference limited conditions, especially the advantages and disadvantages of centralized scheduling. We point out that interferer indetermination problem is a challenge to employ centralized scheduling. Several efficient scheduling schemes are proposed to reveal their characteristics. System simulation results and our analysis show that these two scheduling modes each have their strong points.

In this paper, we focus on the frequency reuse algorithms for the downlink of fixed two-hop Orthogonal Frequency Division Multiple Access (OFDMA) cellular relaying networks which operate in decode-and-forward and half-duplex mode. An Orthogonal Resource Allocation Algorithm (ORAA) has been proposed in [1]. After analyzing the co-channel interference and SINR of the ORAA, we propose a modified ORAA to improve the spectrum efficiency. Based on this scheme, co-channel interference and SINR are analyzed compared to the ORAA. In the theory analysis, a key design parameter is found and its optimal value is selected through the simulations. Intensive system-level simulation demonstrated the performance of the modified ORAA is superior to the ORAA remarkably.

Orthogonal frequency division multiple access (OFDMA), which is known as one of the most promising physical techniques for advanced wireless communications system, generally has a guard interval (GI) to mitigate the inter-symbol interference (ISI) and inter-carrier interference (ICI) caused by delay paths. However, the intra-cell interference (ISI and ICI) may be severe, when GI becomes insufficient in an execrable radio environment. Under fractional load (FL), resource allocator doesn't have to occupy entire system bandwidth due to the lack of traffic in the network, that is, the flexibility of allocator is increased for resource management. Instead of the complicated interference reduction algorithms at the receiver, in this paper we proposed a novel adaptive resource allocation (ARA) scheme, which utilizes the flexibility of radio resource management under FL, to efficiently avoid intra-cell interference in insufficient GI scenario. System-level simulations show that, the proposed ARA improves system performance than the conventional resource allocation (CRA) under FL, whereas the performance of proposed ARA approaches the CRA under the full load.

As a mainstream technology in the B3G TDD systems, TD-HSDPA (LCR TDD HSDPA, High-Speed Downlink Packet Access of Low Chip Rate TDD) adopts some key techniques to achieve high system throughput and high peak data rate, such as AMC (Adaptive Modulation and Coding) and HARQ (Hybrid Automatic Repeat reQuest). However, feedback delay is inevitable in practical TD-HSDPA systems due to the conventional scheduling mechanism, and its impact on wireless scheduling is critical. In this paper, the joint system performances of the key techniques are studied; furthermore, a new efficient scheduling algorithm is proposed. Compared to the conventional scheduling, the delay-restricted scheduling can reduce the feedback delay to improve the system capacity remarkably. Detailed network-performance results are shown from a comprehensive dynamic system-level simulator, and these presented results are obtained for a macrocellular scenario with best effort packet data services to reflect the expected improvement from introducing delay-restricted scheduling in a multi-carrier TD-HSDPA system.

It is well-known that, the cyclic prefix (CP) protects orthogonal frequency-division multiplexing (OFDM) system from inter-block interference (IBI), but it also reduces the spectral efficiency. In this paper, a low-complexity turbo equalization algorithm is proposed for multiple input multiple output (MIMO) OFDM system without CP. In our algorithm, tail cancellation is performed firstly by using the previously detected signal. Then soft cyclic restoration, soft co-antenna interference (CAI) cancellation and subcarrier-wise combining based on signal to interference plus noise ratio (SINR) maximization are performed iteratively to minimize the performance degradation. Simulation results show that our algorithm achieves better tradeoff between bit error rate (BER) performance and computational complexity compared to other existing algorithms.

This paper proposes a novel sub-optimal transmit antenna selection (TAS) strategy for non-regenerative half-duplex MIMO relay channel. While antenna selection is a sub-optimal form of beamforming, it still enjoys the advantage of tractable optimization and low feedback overhead. The diversity order of this proposed strategy is derived to prove that it can achieve the full diversity order as the optimal strategy with only a small performance loss. Furthermore, it is shown that our scheme lead to a reduction of complexity in terms of time slots for SNR estimation when the number of the transmit antennas are more than two. Monte Carlo simulation results of outage probability are presented to demonstrate its advantage over the other two conventional TAS schemes.

We consider the resource allocation of centralized and distributed scheduling in the two-hop relaying cellular system. The limited spectrum resource is one of the obstacles which conflicts with the evolution of being wider coverage and larger capacity in the wireless system. In this paper, system performance and signaling overhead are analyzed and compared. Then we propose a novel routing strategy for choosing the access link and three practical scheduling strategies. Simulation results are provided and analyzed in several scenarios, which show the benefit of adopting the relay technique.

This paper proposes a novel structure of multi-antenna spectrum sensing to solve the problem of the SNR Wall under harsh channel condition like deep fading. Our objective is to exploit the spatial diversity largely with resort to singular value decomposition (SVD) of the auto-correlation of the parallel signal flows. To evaluate its performance, the ROC of the proposed scheme is deduced in close form. Furthermore, normalized constellation distance is utilized as a criterion for measuring signal space under the same noise variance in comparing our proposed scheme with conventional energy detection. Simulation results reveal the significant performance enhancement especially in low SNR. This method can be applied widely, because it can be in the acylic primary user signal.

In this paper, a novel effective low-complexity single carrier frequency-domain equalization SC-FDE scheme in multiple-input multiple-output (MIMO) system is introduced under frequency selective channel. It contains the advantages of SC-FDE and the complexity decreasing in MMSE algorithm by frequency-domain QR (FD-QR) decomposition. Also a rearrangement is implemented according to signal to noise (SNR). So performance gain can be obtained from rearrangement, demodulation after detection and equalization on specific antenna. Simulation result shows that the proposed scheme can obtain a significant performance gain to the conventional MMSE algorithm.

The maximum likelihood detection with QR decomposition and M-algorithm (QRM-MLD) has been proposed as a near-optimal multiple-input multiple-output (MIMO) detection scheme which can achieve near maximum likelihood (ML) performance with complexity greatly reduced. However, the performance of the QRM-MLD algorithm will deteriorate with the increasing of the number of transmit antennas, as well as the decreasing of the number of the selected nodes in each stage due to the abandoning of some hypotheses in each step of the tree search. To solve this problem, we modify the QR decomposition method through rearranging the channel columns based on the post-detection signal-to-noise ratio (SNR), which makes the process of the abandoning more reliable. Simulation results show that the new proposed algorithms achieve better performance compared with the conventional QRM-MLD algorithm, especially when the number of transmit antennas is large. Additionally, the increase of the complexity is negligible compared with that of the conventional QRM-MLD algorithm.

An efficient frequency domain soft interference cancellation (FD-SIC) scheme is proposed for turbo frequency domain equalization (FDE) in multiple-input multiple-output (MIMO) system. At the transmitter, vertical-bell laboratory layered space-time (VBLAST) is suitable for multiple modulation and coding scheme (MCS) on different antennas, which can also enhance channel capacity. At the receiver, inter-antenna interference (IAI) is cancelled by prior information of data on other antennas from Soft-In Soft-Out (SISO) decoder at each iteration, which can improve the input signal to interference and noise ratio (SINR) of equalizer. Also conventional frequency domain Turbo equalization in MIMO system is derived. Then block (data of one transmit antenna) wise frequency domain minimum mean square error (MMSE) equalization is implemented, which utilizes prior information of all blocks. Symbol Log-likelihood ratio (LLR) is calculated from the output of equalizer. Simulation results show that the proposed scheme has better link performance than traditional algorithms.

A novel Frequency Domain Turbo Equalization (FD-TE) is proposed in multiple input multiple output (MIMO) systems, in which equalization is executed on Single Frequency Tone (SFT). It is proposed that received data from all receive antennas on one frequency tone are considered jointly, and then minimum mean square error (MMSE) equalization is implemented. This algorithm can reduce the calculation complexity greatly, and has the same performance as the conventional algorithms. After equalization, data from one transmit antenna on all frequency tones are processed together and transformed into time domain. Later, extrinsic Log-likelihood ratio (LLR) is calculated and sent to Soft-In Soft-Out (SISO) decoder. Theoretical deduction and simulation prove that it can obtain the same performance with a low complexity.

To further improve and satisfy the spectral efficiency requirements addressed in LTE-Advanced system, in this paper, a Coordinated Multi-Cell MU-MIMO scheme is proposed to achieve this goal, especially to enhance the cell-edge user(the 5% of user throughput) throughput substantially. In our proposed cooperative scheme, we adopt multi-cell block diagonalization (BD) algorithm to perform joint procession across the evolved coordinated eNodeBs to mitigate the inter-cell interference (ICI) so as to enhance the whole system performance. Proportional fair (PF) scheduling algorithm is also applied to guarantee the fairness between the users. Furthermore, different numbers of antennas employed at the eNodeB are considered and their affects on our proposed cooperative scheme are analyzed as well. Of course, a system simulation platform is established for the downlink LTE-Advanced system to evaluate the performance of this scheme from the system level perspective. Ultimately, from the simulation results, we can draw that the coordinated multi-cell MU-MIMO scheme we proposed is an effective approach to improve the spectral efficiency prominently and much more spectral efficient comparing to conventional non-cooperative MIMO scheme for the downlink LTE-Advanced system.

For orthogonal frequency-division multiplexing (OFDM) systems, the length of cyclic prefix (CP) is selected on the basis of the maximum delay spread of channel. However, the use of a CP reduces both the spectral efficiency and the power efficiency. In this paper, we proposed an iterative receiver for the space frequency block code (SFBC) OFDM system without CP. After tail cancellation, our proposed algorithm performs soft cyclic reconstruction, SFBC decoding and one-tap minimum mean-square error (MMSE) frequency domain equalization (FDE) iteratively to suppress interferences. Simulation results show that our proposed algorithm can achieve good performance in multi-path environments.

For orthogonal frequency-division multiplexing (OFDM) system, the length of cyclic prefix (CP) is selected on the basis of the expected maximum delay spread. When the CP length is shorter than the maximum delay spread, inter-symbol interference (ISI) and inter-carrier interference (ICI) will occur. By means of conventional one-tap frequency domain equalization (FDE), the desired symbols can not be recovered. In this paper, a soft-decision-directed one-tap turbo FDE technique is proposed for OFDM system without CP. After tail cancellation, the proposed algorithm performs soft cyclic reconstruction and one tap minimum mean-square error (MMSE) FDE iteratively to minimize the performance degradation. Simulation results show that, compared with existing methods, our proposed algorithm can achieve better performance.

Spectrum aggregation (SA) is one of the potential LTE advanced technologies. The analysis and simulation for SA in LTE-Advanced system are addressed in this paper. We first analyze the system model of SA, and propose some evaluation methodologies for SA. Then the schedulers for SA with joint queue and disjoint queue are proposed. Finally, different traffic models are considered in the system level simulation to evaluate the performance gain of spectrum aggregation over deploying independent carriers on the eNode-B. The simulation results show that the SA technology can enhance the throughput, fairness and latency performance in LTE-Advanced system comparing with independent carrier scenario for different traffic models.

Proportional fair (PF) scheduling is a widely used technique in recent wireless communication systems. However, scheduling will also bring about a lot of signaling overhead especially in OFDMA based systems which have many subchannels, assigning these subchannels to users and feeding back channel quality information to Base Station produce much overhead. In many situations, neglecting the overhead leads to wrong performance conclusions. In this paper, we first theoretically optimize the amount of channel quality indication signaling fed back by users in WiMAX system so that the net system throughput can be maximized. Then system level simulation is used to validate the theoretical conclusion.

We address the problem of frequency reuse schemes in the downlink of the fixed two-hop orthogonal frequency division multiple access (OFDMA) cellular relaying networks. There has been little work on specific frequency reuse schemes for this system in the literatures, although this is the key element for realizing the potential capacity and coverage increase offered by the relay. Therefore, we propose a novel frequency reuse scheme for spectrum efficiency enhancement. Based on this scheme, inter-cell interference (ICI) and SINR received by one- hop and two-hop users are analyzed. System-level simulation results show that our presented frequency reuse scheme can achieve significant improvement on spectrum efficiency compared to modified soft frequency reuse (MSFR) scheme.

Compared to conventional network coding, which must combine bit streams after they are decoded, the physical layer network coding (PNC) could make full use of electromagnetic (EM) waves arrived and combine bit stream at the physical layer. Because of this the system throughput could be improved. In this scheme we integrate PNC technique into wireless video transmission based on H.264 for relay channel. At the relay node the bit streams for exchanging are received and combined with different coefficients for the prioritized importance at each source node. Based on this process unequal error protection (UEP) could be realized. The proposed scheme could be outspreaded into the multi-user access model. Also a scheme of adaptively allocating the coefficient is proposed and as the simulation results depict the adaptive method could improve the quality of received image compared to conventional equal error protection (EEP) scheme. And compared to traditional video transmission the system throughput could be improved because of the use of PNC technique.

We propose a novel iterative physical layer network and channel decoding scheme based on XOR network coding and turbo code for the multiple-access relay channel. Firstly, the system model of two access nodes and one terminal with a relay between them is presented. At the relay node physical-layer network coding (PNC) is employed to combine the data information transmitted from resource, then at the terminal with the help of a check node an iterative scheme of soft information exchanging between PNC decoding and channel decoding is implemented. Meanwhile the complexity of the relay node also could be significantly reduced. And as the simulation results depict this scheme outperforms other joint decoding schemes and the complexity at the relay node is also reduced, especially in the case the channel condition between one transmitter and receiver is poor. Then multiple access nodes model is presented, also the scheme could propose good performance by contrast with other schemes only perform better in two sources case.

Fixed relay as a candidate solution in the cellular system attracts more and more attention due to its improvements of coverage and capacity. In this paper, we make our study on the optimal configurations of two-hop relay downlink system. Based on former works, two typical resource allocation schemes of the two hops are considered on the assumption of TDD system-one is in time domain and the other is in frequency domain. Based on the improved evaluation model, we demonstrate that it is critical to improve the capacity of the BS to RS link to achieve higher system throughput. Then, different RS positions are discussed in terms of the system throughput and the optimal deployment of Relay Station (RS) is concluded. In addition, we find that the ratio between the transmit power of base station (BS) and that of RS influences the throughput greatly.

In the conventional zero-forcing ordered successive interference cancellation (ZF-OSIC) or minimum mean square error ordered successive interference cancellation (MMSE-OSIC) detection algorithm of vertical Bell-Labs layered space-time (V-BLAST) architecture, there exists an undesirable processing delay due to the calculation of the matrix pseudo-inverse and power reordering in detecting the symbol in each layer. The parallel interference cancellation (PIC) algorithm has a lower processing delay but poorer performance. Based on the features of SIC and PIC algorithms, an integrated PIC and OSIC detection (IPOD) algorithm is proposed which can lower the complexity as well as the processing delay of the whole algorithm with little performance loss. Moreover, there is an alterable parameter in IPOD algorithm which can be changed to obtain different trade off between complexity and performance. Thus, the proposed algorithm is more feasible for practical applications.

We investigate and evaluate the application of the soft information in the detection of cooperative spatial multiplexing (CSM) systems. The destination detects the signals transmitted from the relays with successive interference cancellation (SIC) whose performance suffers from the error propagation. The traditional detection methods assuming that the prior-detected symbols are correct, none of them considers the still existing error propagation. In this paper, we propose a novel soft-information-aided detection algorithm which takes advantage of the log-likelihood ratio (LLR) information of the prior-detected signals. In the proposed algorithm, the interference cancellation and detection ordering both take the error propagation effect into consideration, thus making the detection more reliable. The new algorithm will be performed in the ZF-SIC CSM systems, and the simulation results will show that the new proposed algorithm can achieve better BER performance compared with traditional ones.

Femtocell is an emerging technology aiming for a better indoor coverage. Due to its low costs, high grade of service, promotion of fixed-mobile convergence (FMC) and no change of core network, it has drawn close attention from the standardization organizations and the industrial field. In the two-hierarchy networks composed of traditional macro cellular networks and the embedded femtocell hotspots, moving mobiles will face up to the continual handovers when they pass along buildings. In this paper, handover algorithms considering signal strength and velocity are proposed using the mathematics concept of "set". Different handover methods are discussed and simulated. The results show that the proposed algorithms can obviously cut down unnecessary handovers compared with conventional soft handover on the same handover signal level limit. What's more, throughput of high speed mobiles and the total throughput of macro base station are increased.

The standardization of the long term evolution (LTE) of 3G networks is currently carried through in 3GPP. With the deployment of frequency planning, the coexistence issue between TDD and FDD LTE systems is becoming urgent in certain frequency bands. In this paper, the detailed LTE system interference environment is investigated, including single system scenario and inter-system interference, network deployment, propagation models, power control scheme, adjacent channel leakage power ratio (ACLR) model and link level model. Typical coexistence scenarios with two LTE systems deployed in macro cellular networks are simulated and analyzed. The discussion includes the influence of several system parameters on network performance, such as power control sets, system bandwidths and occupied frequency bands. Meanwhile, the possible approach of adopting beam-forming technology or intercell interference coordination mechanism is also investigated in TDD-LTE systems of coexisting cases. The simulation results show that two LTE systems could coexist with proposed advanced techniques under current LTE radio frequency (RF) system parameters.

We compare the outage performance by applying transmit antenna selection strategies to amplify-and-forward protocol in the MIMO relaying scenario. Although antenna selection is a suboptimal form of beamforming, it enjoys the advantages of tractable optimization and low feedback overhead. Specifically, by combining transmit antenna selection strategies with amplify-and-forward protocol, we propose two suboptimal strategies, TAS-SD&RD and TAS-SR&RD, and compare their performance with the optimal strategy, TAS-Optimal. By observation of simulation, the suboptimal strategy TAS-SD&RD can achieve the full diversity order with only a small performance loss compared with the optimal strategy TAS-Optimal in some antenna configuration scenarios.

OFDM has become one of the most important Beyond-3G transmission technologies. Mobile WiMAX is a typical representative of OFDM systems. The cross-layer optimization problem of inter-cell coordinated resource allocation for OFDM systems is addressed in this paper. We first analyze the problem by utility-based method, and formulate this optimization problem. Then the globally optimal and a sub-optimal inter-cell resource allocation strategy are proposed respectively in multi-cell scenario. Finally, Mobile WiMAX system is taken as an example for evaluation by system level simulation. The results show that the inter-cell resource allocation strategy can achieve better fairness among users in the entire network. Besides, inter-cell adaptive power allocation can enhance the throughput performance while considering the interference of neighbor cells. And the cell-edge throughput gain decreases with the increase of the number of users in one sector.

Recently, cooperative sensing which can enhance the sensing performance becomes popular in the design of cognitive radio (CR) networks. CR networks need reliable information exchange to conduct cooperative sensing, but it is difficult to transmit information for CR networks without licensed band over the air interface. In this paper, we propose to use spread spectrum technology to transmit low rate exchange information through wide bandwidth. Simulation results show that the capacity loss of primary user is minor, while the exchange information can be demodulated and decoded at a high SNR level based on our proposed scheme. The tradeoff between detection performance and interference to primary user is also discussed.

Maximum-likelihood detection (MLD) can achieve optimum performance for the vertical Bell laboratories layered space-time (V-BLAST) architecture. However, due to its exponentially high computational complexity, several near-optimal detection algorithms, including some parallel detection (PD) ones with low complexity and high stability, have been proposed instead for practical systems. Nevertheless, the existing PD algorithms have a common drawback in equally handling all the branches obtained via exhaustive interference cancellation (EIC) till reaching the final minimum Euclidean distance (MED) decision. In this paper, a simplified PD algorithm, i.e., a generalized parallel interference cancellation (GPIC) algorithm has been developed by means of early termination of the inferior parallel branches. The algorithm is abbreviated as simplified GPIC (SGPIC) algorithm. Numerical analysis indicates that SGPIC algorithm can achieve the near-optimal performance with much lower complexity in comparison with the existing PD algorithms, especially for the cases of high order constellations. Thus, the SGPIC algorithm makes the parallel detection more feasible in practical systems with limited parallel processing elements.

In this paper, we propose a novel receiver consists of the Inter Symbol Interference (ISI) canceller and the turbo equalizer for orthogonal frequency division multiplexing (OFDM) systems over frequency selective fading channels where the multipath delay exceeds the guard interval duration. The proposed turbo equalization algorithm performs soft Inter Carrier Interference (ICI) cancellation and frequency domain minimum mean-square error (MMSE) filtering to minimize the performance degradation caused by ICI distortion and frequency-selective channels. Simulation results of the system performance show that the proposed receiver effectively recovers the contaminated OFDM signals.

In wireless networks, node cooperation has been proposed as a strategy to improve communication reliability and system capacity. This paper investigates employing linear dispersion codes (LDC) over non-regenerative MIMO relay system with gain matrix. Gain matrix at the relay is found that increases the capacity between the source and the destination. The relay stations exploit the knowledge of the first hop and second hop channel to adaptively assign power among the relays. We deduce the capacity of the proposed system and compare the capacity with that of employing LDC over conventional amplify and forward (AF) system through simulation. Improvement of capacity can be achieved.

In this paper, we propose a linear minimum mean square error (MMSE)-based turbo frequency domain equalization (FDE) scheme for single carrier space-time block coded (STBC) transmissions. In the proposed iterative receiver, FDE is performed for each individual tone after space-time (ST) decoding and exchanges extrinsic information with the soft in soft out (SISO) decoder according to the turbo principle. Due to the tone-wise equalization, no matrix inversion is required in the computation of the FDE weight coefficients compared to the conventional turbo FDE and resulting in a lower complexity. We also consider an approximate implementation of the proposed scheme suffering from little performance loss in exchange for further complexity reduction. The simulation results demonstrate that high performance improvement can be obtained using the proposed iterative scheme compared with the non-iterative one.

An iterative receiver algorithm is derived for single carrier cyclic prefix (CP) assisted block transmission systems. The proposed algorithm is based on iterative frequency domain detection and decoding. At each iteration, soft inter-symbol interference cancellation (ISIC) and minimum mean-square-error (MMSE) equalization both in the frequency domain are used symbol by symbol to minimize the performance degradation caused by frequency-selective channels. We also consider an approximate implementation of the proposed algorithm suffering from little performance loss in exchange for complexity reduction. The bit-error rate (BER) as a function of the signal-to-noise ratio (SNR) is used as a performance measure. In addition, the convergence characteristic of the iterative loop is studied with the extrinsic information transfer (EXIT) chart.

The Rao-Blackwellized particle filter (RBPF) is proposed to estimate the carrier frequency offset (CFO) and channel state information (CSI) for uplink multiple-input multiple-output orthogonal frequency division multiple access (MIMO-OFDMA) systems. In the proposed scheme, the channel response and the frequency offset are described as auto- regressive (AR) model and generalized AR model, respectively. The carrier frequency offset can be estimated using the particle filter, and the distribution of the fading channel is updated analytically using the Kalman filter, which is associated with each particle. Furthermore, the expectation-maximization (EM) algorithm is evolved to learn model parameters recursively. Simulation results show that the proposed RBPF algorithm has lower block error rate (BLER) than the conventional particle filter and the Rao-Blackwellized Gauss-Hermite filter (RB-GHF), while the processing complexity is rather reasonable.

This paper proposes an efficient turbo frequency domain equalizer (FDE) for single carrier systems with cyclic-prefix (CP). At each iteration, the proposed algorithm performs soft inter-symbol interference (ISI) cancellation and symbol-wise minimum mean-square error (MMSE) filtering both in the frequency domain to minimize the performance degradation caused by frequency-selective channels. After the one-tap frequency domain filtering, the assumption of an equivalent additive white Gaussian noise (AWGN) channel is used to compute the extrinsic log likelihood ratios (LLRs) of coded bits as the inputs of soft-in soft-out (SISO) decoder. Simulation results show that our proposed algorithm achieves the best trade-off between BER performance and computational complexity compared to other existing methods.

In this paper, taking the channel estimation error (CEE) and noise into consideration, an analytical expression for envelope correlation coefficient (ECC) of the maximal ratio combining (MRC) output has been obtained in correlated Rician fading environments in the high signal-to-noise ratio (SNR) region, which provides a deep insight into the impacts of CEE, noise, frequency separation, Rician factor and channel attenuation, etc. Besides, we found that the ECC can be used to predict system performance such as average channel capacity and outage probability quantitatively in the identical statistical characteristic environment.

The complex central semi-correlatedWishart matrix is the product of a zero-mean row-wise correlated (or column-wise correlated) complex Gaussian matrix and its Hermitian transposition. In this paper, we investigate the distribution of the smallest eigenvalue of the Wishart matrix, which is generated from the square Gaussian matrix. A closed-form expression for distribution of the smallest eigenvalue is derived. Compared with previous results, our expression is very concise, since the distribution has been known in terms of matrix determinants. Numerical results that confirm the expression are also presented. And a complicated equality is proved due to the fact that our distribution is mathematically equivalent to those reported.

Adaptive beamforming antenna (ABA) is widely recognized as a primary technique which can remarkably enhance the performances of wireless networks in terms of capacity and throughput by spatial filtering. However, in practical networks, beamforming weights of ABA can be deteriorated due to direction of arrival (DOA) estimation errors. In this paper, the performances of ABA in existing DOA estimation errors scenarios are investigated from system capacity and throughput aspects. Noticeable performance degradations are observed due to the DOA estimation errors and the extent of effect on performance is presented.

Since the permission of WiMAX (802.16e) as a member in IMT-2000 enables it to use 3G systemspsila bandwidth by WRC-07, more researchers have paid attention on the analysis of coexistence issue between WiMAX and WCDMA systems in 2500 to 2690 MHz band. In this paper, the detailed interference environment analysis, including several interference scenarios, network deployment, propagation models and interference models, is described. Based on appropriate assumptions, some representative interference scenarios in which WiMAX and WCDMA systems are operated on the adjacent frequency bands are simulated and discussed from four different respects: separation distances for these two systems, base station antenna coupling loss, uplink power control mechanisms of WiMAX system and frequency reuse schemes. It is shown that the interference from MSs of one system to BSs of another system is not quite severe after using appropriate techniques. Meanwhile, a few suggestions are introduced to better deploy these two systems.

In this paper, we investigate the potential benefit of successive interference cancellation (SIC) in high speed uplink packet access (HSUPA). We explore the possibility of improving the performance of HSUPA by introducing the SIC and we also bring forward a novel scheduling method named effective power-based load control (EPBLC) to extend its advantage. Finally we give the conclusion that with SIC and EPBLC, we can get 43%-56% throughput gain under different interference cancellation efficiency.

The uplink power control is essentially important to the link performance and the system stability. By analyzing the SC-FDMA system's interference character, we view the SC-FDMA system as a modified OFDMA system with multichannel model, and accordingly propose a power control scheme composed of intra-cell and inter-cell power control based on the multi-channel model. Especially the Inter-cell power control based on the interference overload with the form of frequency dependent and event triggered, along with the intra-cell power control, can achieve the target IoT in NodeBs and ensure its stability. This conclusion is achieved by our multi-cell simulation implemented with this power control scheme.

In this paper, a multi-user multiple input multiple output (MIMO) system using semi-orthogonal space division multiplexing (semi-OSDM) and single-user QR-triangular detection with Alamouti code is studied. In this proposed semi-OSDM with STBC system, the transmit signals for each user are grouped into pairs and separately coded by using the standard Alamouti space-time code, while QR decomposition is used to make the signaling streams triangular so that the serial interference cancellation (SIC) can be utilized to maintain an accurate signal detection at the receiver. The bit error rate (BER) performance of the proposed semi-OSDM with STBC system outperforms the orthogonal space division multiplexing (OSDM) system as well as the semi-OSDM system, while exploiting a reduced complexity and stability when the correlation of the channel changes. Moreover, it largely reduces the complexity of the receivers.

Adaptive beam forming antenna, which is adopted in TDD HSDPA system, has been proved to be an effective way to improve the system performance. In the realistic system, however, the high correlation of the multi-path signal will cause the estimation of direction of arrival (DOA) angles arriving at the antenna arrays to be imprecise, so the beam forming will be imperfect. And the system performance will be deteriorated owing to the imperfection. In this paper, the evaluation of round robin (RR), proportional fairness (PF), and maximum carrier to interference ratio (Max C/I) algorithms in three channel conditions will be studied with the imperfect adaptive beam forming antenna in the TDD HSDPA system. Finally, the authors give an analysis of the results, and the error DOA estimation threshold angles of different algorithms were presented.

In this paper, Smart Antennas and HSDPA technology in TD-SCDMA will be discussed. It is demonstrated to be inefficient when they are combined together due to the shortage of channelization code resources. To use Smart Antennas more efficiently in TD-SCDMA HSDPA, one SDMA algorithm with combination of generic schedule algorithms is proposed. With SDMA, the system can allocate same channelization codes to different users who are spatially separable well enough. To reduce the complexity, the algorithm is simplified based on some reasonable scenario. The performances of the simplified algorithm with 3 different common schedule algorithms are evaluated through a system simulator, and the parameters affecting the algorithm are studied. In the end, the simulation results show that the system throughputs can be increased with optimized parameters.

A novel likelihood particle filter is proposed to estimate the carrier frequency offset for uplink MIMO-OFDMA systems. In the proposed scheme, the likelihood is employed to approximate to the posterior rather than the prior, because the likelihood is more similar to the posterior than the prior. The importance density is an approximation to the posterior. Therefore, using a better approximation based on the likelihood, rather than the prior, can be expected to achieve better performance. In addition, the multiuser interference (MUI) cancellation strategy is combined in every recursion. Simulation results show that the proposed algorithm has lower mean square error (MSE) than the regular particle filter and the extended Kalman filter, while approaching the Cramer-Rao Bound (CRB) closely with quite reduced complexity.

In this paper, a resource allocation algorithm and a connection access control scheme (CAC) for LTE systems with heterogeneous services are proposed. The proposed allocation algorithm introduces a transmission guard interval which gives high priority to real-time (RT) service packets approaching the delay deadline. The proposed CAC can adaptively adjust the threshold according to the network condition. Simulation results show that the proposed CAC scheme can not only balance the ongoing connections of different classes of traffics but also be easy to reserve resource and support handover users potentially.

This paper proposes a new approach to apply singular value decomposition (SVD) in fractionally spaced frequency domain equalizer (FSFDE) for the single carrier MIMO-CDMA systems. Multiple data streams can be reliably transmitted through the parallel subchannels by using SVD, which can improve the capacity effectively without increasing frequency bandwidth or the average transmit power. Fractional sampling at the receiver is equivalent to having multiple virtual receive antennas with correlated channel gains and colored noise, which may be seen as a virtual receive diversity. Therefore, each polyphase component is denoted as a virtual antenna, and it is also called fractionally spaced system as virtual antennas system. Simulations show that high performance can be achieved by using SVD with virtual antennas.

In this paper, we present a new error robust method for H.264 video transmission. This scheme uses unequal error protection (UEP) and automatic repeat request (ARQ) protocol to provide better error-resilience performance and efficiently bandwidth utilization. In order to realize the layered video coding with transport prioritization, the proposed scheme adopts different HARQ (hybrid ARQ) schemes for the different priority-data. Simulations are conducted over the AWGN and Rayleigh channels, respectively. Simulation results demonstrate that the UEP scheme improves transmission performance and achieves better video quality than equal error protection (EEP) scheme over wireless channels under the same bandwidth.

In this paper, we investigate the outage probability and bit error rate performance of the amplify-and forward relay network. The system model we consider has three nodes, with one antenna at the transmit end, one antenna at relay node, and multiple antennas at the receive end where maximal ratio combining is employed. In the Rayleigh fading channel, we derive closed-form upper and lower bounds of the outage probability and bit error rate of the system instead of the expressions of exact values due to considerable complexity. Then we proceed to validate our analytical results through link-level simulations. The simulation results reveal that our theoretical analysis agree well with link-level simulation results, thus our results greatly contributes to the simplification of calculating outage probability and bit error rate of our system.

In this paper, a progressive hybrid automatic repeat request (HARQ) scheme on degree distribution for irregular low-density parity-check (LDPC) codes is proposed. In this scheme, lower degree nodes are retransmitted. During the process of choosing nodes for retransmission, not only degree distribution but also unequal error protection (UEP) property and iterative decoding process of irregular LDPC codes are considered. Compared with initial Degree Distribution Based HARQ (DDB-HARQ), the proposed scheme has better performance.

A Code Division Multiple Access (CDMA) downlink receiver based on Adaptive Overlap-Cut (AOC) Method Frequency Domain Equalization (FDE) and non-linear feedback Parallel Interference Cancellation (PIC) is proposed. Firstly, the analysis for the generation and the distribution of the inherent error of Overlap-Cut (OC) Method FDE carries out the improved version of it called AOC Method FDE. Secondly, one PIC scheme with non-linear feedback is designed. After the nonlinear processing, the users' feedback information during the PIC iteration will be adjusted according to its reliability. As a result of both theoretical analysis and simulation, AOC Method FDE outperforms the original OC Method with lower complexity, and the non-linear feedback PIC improves the performance of the receiver further.

This paper presents a new clustering based strategy for path loss prediction. We demonstrate how data mining technology can be utilized to explore the knowledge existing in massive geographical data thus improving path loss prediction accuracy and reducing field measurement cost. Comparative path loss prediction experiments between new strategy and traditional ones confirm that the new strategy guarantees the high predicting accuracy by making full use of Geographical Information System (GIS), and significantly reduces the cost/time requirements.

Wishart matrix and its eigenvalues are very important to the analysis of multiple-antenna systems. In this paper, we derive a polynomial expression for the distribution of the smallest eigenvalue of Wishart matrices. Compared with earlier results in matrix determinant forms, our expression is much easier to handle. The expression obtained applies for Wishart matrices of arbitrary orders and is an extension to Edelman's and Park's results. Moreover, our work here can also be viewed as an interesting proof of one complicated equality, since the distribution is unique and our result must be equivalent to earlier researchers'. In a word, with the result of this paper, further mathematical analysis on the statistics of the smallest eigenvalue becomes possible.

Channel quality indication (CQI) is directly related to the accuracy of AMC (adaptive modulation and coding) and the performance of HSDPA (high speed downlink packet access). There will be feedback-delay if we consider the CQI in current specification. In this paper, we propose a novel CQI adjustment scheme, which makes use of the power control information of DPCH (dedicated physical channel) updated from UE (user equipment), to improve the veracity of the feedback information, so as to improve the throughput of the system. Simulation shows that our proposed scheme performs more precisely than the conventional one.

In this paper, we propose a novel load control strategy for TD-SCDMA Enhanced Uplink, called as system-based load control strategy. We compare its performance with the cell-based load control strategy, which was widely accepted in TD-SCDMA release 4/5. It is concluded that system-based load control outperforms cell-based load control in the rise over thermal (RoT) control and the system throughput.

Need arises to increase the network throughput by broadening the bandwidth. One effectively approaches are multichannel technique in which multiple separate frequency channels are used for communications. In this paper we describe a channel-aware multichannel random access based on non-persistent CSMA scheme, where each user only has knowledge of its own channel gain. Through the theoretical model and simulation results, we confirm that the proposed algorithm can mitigate traffic congestion and has the advantage of giving high network throughput and delay performance.

In this paper, we study the intercell interference influence on the performance of cell search in TD-SCDMA and propose a new cell search scheme which aims at improving the success probability of the cell search in severe inter-cell interference environment. In our scheme, the multi-cell joint detection (JD) is adopted to reduce the inter-cell interference. The number of cells considered in the multi-cell JD, can be dynamically adjusted in order to reduce the computation complexity. The simulation results reveal that the performance of cell search is considerably improved by this new scheme.

WiMAX (802.16e) has been recognized as an official member of IMT-2000 by WRC-07, which permits its use of 3G systems bandwidth, including 2500 to 2690 MHz. The work of coexistence interference analysis between WiMAX and WCDMA systems in 2.5 GHz band is a potential research field. This paper presents several interference paths, investigates the methods of evaluating two coexisting systems in details, and analyzes necessary assumptions as well as simulation parameters. Some typical interference scenarios in which WiMAX and WCDMA systems are operated on the adjacent frequency bands are simulated and discussed from three different respects: separation distances for these two systems, uplink power control mechanisms of WiMAX system and frequency reuse schemes. It is shown that when uplink power control methods or frequency reuse scheme is implemented, the interference from WiMAX mobile stations to WCDMA system is not quite severe. At last, a few suggestions and mitigation technologies are introduced to better implement these two systems.

Superposition coding can be used to improve capacity of communications in a variety of scenarios. In this paper, we propose a novel location-based data transmission strategy using superposition coding for forward link (FL) of TDMA system with adaptive modulation and coding (AMC). By taking advantage of the total received signal to interference and noise ratio (SINR) disparities on the forward link, the system can transmit to multiple users at the same time and frequency by using superposition coding. The proposed scheme divides the users in a cell into two sets based on their locations. In each time slot, the base station transmits to the selected pair of users belonging to these two sets, respectively, with superposition coding. The average sector throughput of TDMA system with our scheme is mathematically analyzed for a multi-cell scenario. From numerical examples, it is shown that our proposed scheme significantly increases the average throughput of the system.

The Vertical Bell Laboratories Layered Space-Time (V-BLAST) scheme achieves very high spectral efficiency while maintaining low implementation complexity. There have been great efforts focusing on the V-BLAST detection algorithms. However, all these algorithms concentrate on the symbol-wise detection. In this paper, a bit-wise V-BLAST detection algorithm is proposed based on the fact that the bits in one modulation symbol may have different reliabilities depending on their mapping methods. This new algorithm regards bit, rather than symbol in traditional algorithms, as the minimum process unit to do the interference nulling, canceling and ordering. Considerable performance gains are achieved over the symbol-wise detection algorithms, which are demonstrated by simulations. Also, two simplified algorithms are proposed to reduce the computation complexity.

In the conventional zero-forcing successive interference cancellation (ZF-SIC) detection algorithm of vertical Bell-Labs layered space-time (V-BLAST) architecture, the detection algorithm does not attempt to eliminate the effect of the error propagation, which is significantly deleterious to hybrid automatic repeat request (H-ARQ) scheme using bit-level Chase combining. Based on two ordering approaches respectively, we propose two novel H-ARQ bit-level Chase combining algorithms in this paper, which employ a new log-likelihood ratio (LLR) calculation algorithm to minimize the effect of the error propagation. Additionally, we bring forward a new pairwise LLR combining technique to enhance the reliability of ordering stage considerably. Through simulation results, it is shown that the new proposed algorithms outperform the conventional ones in system performance.

In this paper, we propose a hybrid receiver scheme called FDE-PPIC, which combines minimum-mean-square-error frequency domain equalization (MMSE-FDE) with multistage partial parallel interference cancellation (P-PIC), for the downlink of single-carrier cyclic-prefix code division multiple access (CP-CDMA) system over frequency-selective channels. MMSE-FDE instead of conventional RAKE receiver is utilized to alleviate the effect of frequency- selective channel and obtain the initial data estimation. Multistage P-PIC in frequency domain is then employed to mitigate the residual multiuser interference (MUI) for further improving the system performance. Simulation results show that the proposed receiver scheme can achieve better bit error rate (BER) performance than MMSE-FDE and FDE-PIC which is a combination of MMSE-FDE and multistage PIC.

On the reverse link of CDMA systems, two options are possible for resource allocation: rate control (RC) and centralized scheduling (CS). The rate control algorithm can be further divided into Common Rate Control (CRC) and Dedicated Rate Control (DRC). In CRC, each mobile station (MS) independently determines its reverse link rate using the system interference level information broadcasted by a base station (BSs) and rate control mechanism at the MS side. While in DRC, the BS sends each MS a rate movement command. On the other hand, centralized scheduling directly assigns reverse link rates to a subset of MSs. In this paper, the Token Bucket based Common Rate Control (TB- CRC) mechanism is discussed and compared with the centralize scheduling. Performances have been evaluated through system level simulation. It is shown that the token bucket based rate control philosophy outperforms the centralized scheduling from the aspect of throughput, fairness, system stability, signaling overhead and transmission delay.

In this paper, we propose a novel frequency reuse scheme for multi-cell orthogonal frequency division multiplexing access (OFDMA) systems for co-channel interference reduction. Each cell is partitioned into three sectors. All the available subcarriers are divided into two groups. One is reused in the central region of the sectors, and another is divided into three parts used orthogonally for the edge of the three sectors (no overlap). Which subcarrier group a user can use is dependent on the location or the received signal to interference plus noise ratio (SINR) of the user. Thus, intra-cell orthogonality is guaranteed, and inter-cell interference can be greatly reduced. All the subcarriers may use the same transmit power in this scheme. Simulation results show that this scheme can bring higher system throughput and lower CCI, and it also can increase the data rate at the cell edge.

In this paper, two popular radio access network architectures, centralized architecture and distributed architecture, are analyzed. Then we propose a novel architecture on the basis of the comparisons and system level simulation results. In this new architecture, control plane and user plane are terminated in different nodes and can be processed simultaneously. Analysis and simulation results show that this proposed network architecture can provide better performance in lower signaling overhead and robustness.

In this paper, we present some evaluation methodologies for 3G long term evolution (LTE) employing orthogonal frequency division multiplexing (OFDM) from the view of system level. A system simulation platform is established to evaluate the system performance of LTE. Many important research topics, such as packet scheduling algorithms and fractional frequency reuse (FFR) scheme, can be studied through this platform. Some popular scheduling algorithms are evaluated in OFDMA systems for the mixed services, such as real-time (RT) and non-real-time (NRT) services. FFR scheme is proposed in this paper to avoid the co-channel interference. Finally, the system performance of LTE is evaluated under various scheduling algorithms for mixed services with the use of FFR.

Localized transmission with frequency hopping in E-UTRA uplink can avoid some drawbacks of distributed transmission and offer improved possibilities for the frequency diversity. However, it is difficult to find out a general hopping pattern applicable to various transmission bandwidths while keeping single carrier transmission at the same time. In this paper, a new RB (Resource Block) adaptive hopping method based on predefined pattern of intra/inter-TTI frequency hopping is proposed for E-UTRA uplink. The method that can keep single carrier transmission and avoid collisions is suitable for various transmission bandwidths. Simulation results show that the proposed hopping mode is effective.

The Vertical Bell Laboratories Layered Space-Time (V- BLAST) scheme achieves very high spectral efficiency while maintaining low implementation complexity. However, the error propagation resulting from a wrong cancellation limits the overall system performance greatly. The traditional detection methods proceed assuming that the prior-detected sub-streams are correct at each stage. None of them considers the still existed error propagation. In this paper, we propose a novel soft-information-aided detection algorithm which makes use of the log-likelihood ratio (LLR) information of the prior-detected signals. In this new algorithm, the interference canceling and ordering all take the error propagation effect into consideration, thus making the detection more reliable. We derive the new algorithms for ZF-SIC and MMSE-SIC V-BLAST respectively. Simulation results show that the new proposed algorithms achieve good BER performance compared with the traditional ones.

There have been great efforts to study the adaptive MIMO systems, while all of them concentrate on the systems without channel coding. This paper presents a new adaptive V-BLAST scheme adopting turbo-codes as the channel coding. Through a two-step method, we derive two algorithms for fixed rate and variable rate applications respectively. We derive a close- form bit and power allocation algorithm which reduces the computation complexity greatly by avoiding exhaustive search. For adaptive coding, we propose the Average SNR mapping method to select the proper coding scheme. Simulation results show that the algorithms for fixed rate and variable rate both provide very good throughput performance with low complexity and less feedback information.

In this paper, we provide some exact expressions in a close form for central moment envelope correlation coefficient (ECC) and joint moment ECC of the maximal ratio combining (MRC) output in correlated Rayleigh and Rician fading environments. Besides, we deduce an analytical formula for average capacity with minor approximation. With these expressions, a simple relationship between joint moment ECC and the average capacity is presented, which means that only joint moment ECC can be used to predict system performance such as average channel capacity quantitatively. Furthermore, it has been demonstrated by Monte Carlo simulation that our analysis are matched with the numerical results excellently.

The performance of frequency hopped OFDM cellular system depends on the designing of frequency hopping sequences. This paper explores fast frequency hopped OFDM in the link level of a cellular communication system. Each user is assigned several sub-carriers by the base station in each cell in every time slot according to the predetermined hopping sequences. The frequency hopped OFDM technique based on orthogonal hopping sequences can improve communication performance in a cellular system since it could minimize intra-cell interference and average inter-cell interference. In this paper, Welch-Costas array pattern is derived under independent and cluster hopping schemes, which enable us to evaluate the system performance with the Turbo code modulation scheme. Examples of the frequency sequences and how they are assigned to users are also given. We also simulate and analyze the impacts of the channel environment and parameters, frequency diversity, and inter-cell interference diversity on the performance of the coded frequency hopped OFDM cellular system.

This work investigates a design of minimizing the system outage probability adaptive modulation algorithm in the downlink of the multi-user multiple-input multiple-output (MIMO) system. Based on a beamforming scheme that maximizes the signal-to-leakage ratio (SLR), this new algorithm is proposed for constant bit rate services to maximize the number of satisfied users and minimize the transmission power. Furthermore, this proposed algorithm has advantage in the system spectral efficiency.

In this paper, we propose a modification of overlap-cut method (OC method) frequency domain equalization (FDE) to reduce complexity in code division multiple access (CDMA) downlink systems. FDE based on fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) carries out single-tap equalization on received signal, moreover, its complexity is much lower than its time-domain counterpart. The analysis for the generation and the distribution of the inherent error of OC method FDE indicates some improvement to the equalizer. As a result of both theoretical analysis and simulation, we obtain a better performance with lower computation burden than conventional algorithms.

Golden code is one of the algebraic space-time codes, which has the full rate, full diversity with the better performance than other codes. Sphere decoding (SD) algorithm can achieve near ML performance with moderate complexity. We proposed the modified complex sphere decoding algorithm based on Schnorr-Euchner strategy (SE-CSD) including sorting the order of the system that can reduce the computational effort than general sphere decoding algorithm over the range of SNRs. Combining Golden code with low complexity SE-CSD can obtain perfect performance than other solutions.

Golden code is one of linear dispersion space-time block codes (LD-STBC), which has full rate, full diversity with better performance than other codes. sphere decoding (SD) algorithm can achieve near ML performance with moderate complexity. We propose the complex sphere decoding algorithm based on Schnorr-Euchner strategy (SE-CSD) needing no initial radius and it is implemented without a nodelist enjoying more complexity savings than general complex sphere decoding (CSD) algorithm over the range of SNRs. Combining golden code with low complexity SE-CSD can obtain perfect performance than other solutions.

This paper introduces a full rate, full diversity orthogonal space-time block code for 4 transmit antennas. The codeword blocks can be viewed as quaternions which are drawn from the icosahedral group and no constellation expansion. We prove the full diversity of the proposed STBC and analysis the performance under the correlated MIMO channel. By utilizing the quaternionic form, we can find the decoding algorithm to reduce the complexity of maximum likelihood (ML) coherent decoding and introduce a non-coherent differential decoding rule.

In this paper, a proportional fair scheduling algorithm for the mixed delay sensitive and delay insensitive services in a high speed data transmission system is proposed. The proposed forward link scheduling algorithm not only maximizes total throughput under certain fairness constraints, but also takes the specific delay requirements and the data arrival rates of delay sensitive data services into account. It can ensure the successful delivery of delay sensitive data packets without losing the channel diversity gains that is achieved by conventional proportional fairness.

This paper focuses on the research of distributed rate control algorithms for the reverse link of 1times EV-DO systems. First, following the basic idea proposed by Kelly (1997), a utility maximization system model is formulated. The objective of the rate control algorithms is to make the system converge to the optimal state of the system model. We investigate the performance of two distributed rate control algorithms: the conventional distributed rate control (CDRC) algorithm and the modified distributed rate control (MDRC) algorithm. The CDRC is based on the MAC algorithm in CDMA2000 1times EV-DO Standard (2005). With the CDRC, we give our conclusions as how to design the specific functions of the algorithm according to the utility functions to ensure the objective mentioned above. The MDRC is a new proposed algorithm based on the optimal solution of the system problem which can also ensure the objective. Our numerical simulation results give the performance comparisons between them and validate our deduction.

In this paper, an LDPC based MIMO scheme is proposed in which matrix modulation scheme of MIMO and unequal protection ability of irregular LDPC codes are employed. The new scheme named degree distribution based-MIMO (DDB-MIMO for short) combines the two schemes, in which the important bits with large degrees are transmitted in transmission diversity (TD) symbols and bits with small degrees are mapped to the spatial multiplexing (SM) mode symbols. Since the TD mode could offer more protection to the data streams by offering more transmission power, the important bits with large degrees which could contribute more to the decoding process would have more protection from TD mode and hence the system performance would be improved namely. The performance of the new scheme has also been evaluated by the Gaussian approximation (GA) scheme which is used to analyze the asymptotic performance of LDPC coded system. The analysis results provide us the optimal mapping fractions between the bits with different degrees and transmitted symbols in different modes which is almost the same as the DDB-MIMO scheme offering. The simulation results also proved the new scheme.

Initial transmission power and spatial user information (ITP&SUI)-based channel assignment algorithm in CAC procedure is proposed and studied in a TDD-CDMA cellular system. Time slot priority is introduced as the criteria of channel assignment. New user will be assigned in the time slot which has the highest priority. The time slot priority is updated dynamically according to our proposed algorithm at the node B. The performance of the algorithm is compared together with other traditional algorithms under both homogeneous and hot spot traffic loading via computer simulation. The results show that the ITP&SUI-based channel assignment algorithm always outcomes the traditional algorithm in both downlink and uplink. The primary benefit of ITP&SUI-based channel assignment algorithm in the TDD-CDMA cellular system, however, lies in improving the system performance and saving the power consumption of UE, especially under hot spot traffic.

Both adaptive beam-forming antenna (ABA) and joint detection (JD) are key techniques in the LCR (low code rate) TD-CDMA system. ABA is adopted to suppress multi-path fading with antenna diversity and to increase system capacity by using digital signal processing (DSP) algorithms and dynamically generating the beam patterns, while JD can be used to reduce multiple-access interference (MAI) and inter-symbol interference (ISI) with advanced equalization techniques. As spatial variation of UE has existed in practical system, the system performance will be deteriorated by the DOA (direction-of- arrival) estimation error. In this paper, simulation results on the both downlink and uplink of LCR TD-CDMA in different environments are included, which can provide both the system performance with joint detection or imperfect ABA and the maximum system tolerance of DOA estimation error. Two kinds of packet services, full-buffer FTP and scheduling HTTP, will be adopted in simulation process to simulate DCH (dedicated channel) and DSCH (downlink share channel) features, respectively.

CDMA system capacity is interference limited. The multiuser transmission (MUT) with adaptive antenna arrays for the downlink direction is considered to increase system capacity and to eliminate the multiple-access interference (MAI) and the inter-symbol interference (ISI) of the CDMA system. In this paper, the angular gain of the spatial filter is modeled by a piece-line function to analysis the interference difference between the in-beam users and the out-beam users. Based on this analysis, a lower complexity MUT scheme using spatial classes is proposed for avoiding MUT computation complexity, which can achieve the nearly same performance with the conventional MUT scheme. The bit-error probability approximation of this MUT scheme is also analyzed as well. The simulation result is used to confirm the availability of this lower complexity MUT scheme.

In this paper, a downlink packet scheduling algorithm for OFDMA systems is proposed, which is based on the utility function to guarantee both the packet drop ratio and the play-out outage ratio of video streaming service. The existing algorithms, both modified-largest weighted delay first (M-LWDF) and exponent proportional fair (EXP/PF) rule can achieve good results in terms of head-of-line (HOL) packet delay, which affects the packet drop ratio. However, they can not consider the play-out outage ratio. Simulation results show that our proposed algorithm outperforms the existing scheduling algorithms in term of packet drop ratio and play-out outage ratio.

In this paper, we propose a novel frequency reuse scheme for multi-cell orthogonal frequency division multiplexing access (OFDMA) systems for co-channel interference (CCI) reduction. We divide all the available subcarriers into two groups with one used for the central region of the cell and another for the cell boundary. The frequency reuse factor (FRF) is 1 in the central region and 3 in the boundary. The edge of the cell is partitioned into three sectors. Intra-cell orthogonality is guaranteed in this scheme, so all the subcarriers may use the same transmit power. The subcarriers of the super and regular group can be allocated adaptively and flexibly according to the users' distribution and service requirements. Which frequency group a user can use is determined according to the distance between the user and the serving BS or the signal to interference plus noise ratio (SINR) of the user. Simulation results show that this scheme can bring higher channel capacity and lower CCI, and can also increase the data rate at the cell edge.

In this paper, we propose a downlink packet scheduling algorithm in OFDMA systems for the mixed services, such as real-time (RT) and non-real-time (NRT) services. The proposed scheduling algorithm is based on the channel state information and utility function of queuing delay. Simulation results show that this algorithm can not only guarantee the fairness and delay requirements of users with different types of services but also obtain good system throughput.

Superposition coding can be used to improve capacity of communications in a variety of scenarios. This paper is concerned with the application of superposition coding in TDMA system forward link packet data transmission with adaptive modulation and coding (AMC). By taking advantage of the total received SINR disparities on the forward link, the system can transmit to multiple users at the same time and frequency by using superposition coding. The average sector throughput of TDMA system forward link packet data transmission with the proposed superposition coding technique is mathematically analyzed for a multi-cell scenario. From numerical examples, it is shown that superposition coding can significantly increase the average throughput of the system.

In this paper, we propose a novel fractionally spaced frequency domain equalization scheme for the downlink of single carrier cyclic prefix assisted MIMO-CDMA system over frequency selective channels. This scheme combines the fractionally spaced frequency domain equalizer with parallel interference cancellation (PIC) in the frequency domain to cancel the inter chip interference (ICI), inter antenna interference (IAI) and multiple access interference (MAI). It is shown that our proposed scheme significantly outperforms the conventional frequency domain equalization algorithms with low complexity.

The use of oversampling at the receiver results in colored noise when the bandwidth of the noise-limiting filter is not sufficiently large. This paper proposes a fractionally-spaced single-carrier linear MMSE frequency domain equalizer (LMMSE-FDE) over frequency-selective multiple input multiple output (MIMO) channels. The performance of the fractionally-spaced LMMSE-FDE with colored noise samples is analyzed and the relation between the time domain correlation and the frequency domain correlation of noise samples is presented. Simulation results show that the proposed technique significantly outperforms the conventional frequency domain equalization by exploiting the frequency domain correlation of noise samples.

The wireless link with fixed parameters is subject to time-varying channel, and the battery energy is limited in mobile terminals. Thus we consider the co-existence of 20 msTTI and 5 ms TTI in E-DCH of TD-SCDMA HSUPA. In this paper, based on the comparative study on the link performances with different TTI and the analysis on the link simulation results, we discuss the different TTI's influence on the terminal power consumption. Furthermore, the system level performances of semi-static TTI and traditional single TTI configurations are compared. Finally the conclusions are drawn: 20 ms and 5 msTTI should co-exist in TD-SCDMA HSUPA, and be adopted respectively in different channel condition to save the terminal power. The data throughput of semi-static TTI configuration is greater than those of both single TTI configurations, and the semi-static TTI selection between 20 ms and 5 ms is implemented according to the moving speed of a specific UE.

In this paper, single-carrier asynchronous uplink multi-user MIMO-CDMA system with an unconventional spreading approach is proposed. With the spreading and despreading approach the multi-user interferences (MUI) caused by the asynchronous signals in the uplink can be completely eliminated. The interferences between different antennas can be further suppressed by a layered space-frequency equalization (LSFE) algorithm. In order to reduce the influence of error propagation brought by the SIC in the procedure of detection, we proposed an improved iterative LSFE.

Universal Mobile Telecommunications Systems (UMTS) consist of two modes: UTRA-TDD and UTRA-FDD. The spectrum allocation is in such a way that both modes have an adjacent carrier at 1920 MHz. Due to the imperfection of transmitter and receiver hardware, adjacent channel interference (ACI) can not be completely avoided when both modes operate in 1920 MHz. In this paper, co-existence of UTRA-TDD low chip rate (TD-SCDMA) and UTRA-FDD (WCDMA) system is investigated. We use theoretical and simulation methods respectively to investigate the impact of TD-SCDMA and WCDMA when both operate in 1920 MHz. In the simulation method, we also research the influence of smart antenna which is deployed in TD-SCDMA system. Capacity loss is used to access the adjacent channel interference from TD-SCDMA base station (BS) to WCMA BS, then detailed theoretical and simulation results are presented, we give some useful suggestions for the deployment of the system based on our results.

There have been great efforts to study the adaptive MIMO systems, while all of them concentrate on the systems without channel coding. This paper presents a new adaptive V-BLAST scheme adopting turbo-codes as the channel coding. This new scheme divides the optimization problem into two steps which simplifies the design greatly. Also, through this two-step method, we derive two algorithms for fixed rate and variable rate applications respectively. We combine the bit and power allocation with antenna selection effectively with very low complexity through a new ordering scheme and derive a simplified power allocation algorithm. For adaptive coding, we propose a new metric - Equivalent Capacity SNR, which can indicate the overall channel condition, to select the proper coding scheme. Simulation results show that the algorithms for fixed rate and variable rate both provide very good throughput performance with low complexity and less feedback information.

The Vertical Bell Laboratories Layered Space-Time (V-BLAST) scheme achieves very high spectral efficiency while maintaining low implementation complexity. However, the error propagation resulting from a wrong cancellation limits the overall system performance greatly. There have been great efforts focusing on alleviating the error propagation. In detection procedure, however, none of them considers the still existed error propagation in itself, i.e., all these detection methods proceed assuming that the prior-detected sub-streams are correct at each stage. In this paper, we propose a new detection algorithm which makes use of the log-likelihood ratio (LLR) information of the prior-detected signals. In this new algorithm, the interference nulling and canceling all take the error propagation effect into consideration, thus making the detection more reliable. We derive the reliability-based algorithms for ZF-SIC and MMSE-SIC V-BLAST respectively. Simulation results show that the new proposed algorithms achieve more than 2dB gains over the traditional ones both with and without channel coding. The increase of computation complexity is limited.

In the TD-SCDMA system, joint detection (JD) is used to detect the data symbols of the whole timeslot on the receiver, which is based on the channel estimates from the midamble part of the timeslot. However, for a rapidly time-varying environment, the channel states may vary a lot within one timeslot, leading to worse performance on the receiver. Considering the multiple timeslots per subframe for one user in 144 kbps and 384 kbps services, a novel design using interpolation of channel estimates for JD of different data blocks is introduced to solve this problem. Simulation results show that there is significant performance improvement with this novel method, which is verified perfectly by MSE of channel estimates.

In this paper, a frequency-domain equalization architecture for the downlink over a space-time block coded MIMO-CDMA system is proposed. This architecture exploits transmit diversity by equally dividing theNT(NT=2Q,Qis a positive integer) transmit antennas intoQgroups and implementing an Alamouti-like space-time block coding scheme for each group. At the receiver, the single-carrier minimum- mean-square-error frequency-domain equalization is combined with the successive interference cancellation to combat various interferences resulting from frequency-selective fading channels under multi-antenna and multi-user conditions. It is shown that our proposed architecture significantly outperforms the conventional MIMO-CDMA structures.

In this paper, with minor approximation, we provide analytical expressions in a close form for the envelope correlation coefficient (ECC) and outage probability of the maximal ratio combining (MRC) output in correlated Rayleigh and Rician fading environments. Moreover, we find a simple relationship between ECC and the outage probability, which indicates that ECC can be used to predict system performance such as outage probability quantitatively. Besides, it has been demonstrated by Monte Carlo simulation that our analysis are matched with the numerical results excellently.

This paper proposes a new approach to apply fractionally spaced frequency-domain equalizer (FSFDE) for the single carrier MIMO-CDMA systems. The complexity of this equalizer can be significantly reduced with the help of performing the equalization in the frequency domain. Analogous to the previously developed layered space-time architectures, we proposed layered space-frequency detection (LSFD) which is performed layer by layer in a successive way. In this work, the concept of virtual antennas is also introduced. Oversampling at the receiver is equivalent to having multiple virtual receive antennas with the correlated channel gains and the colored noise. This may be viewed as a virtual receive diversity, and therefore, each polyphase component is denoted as a virtual antenna. Simulations demonstrate that high performance can be achieved by using the proposed detection with virtual antennas.

Cooperative transmission is considered as an efficient way to combat multipath fading and to increase the system capacity. Combining with effective coding scheme, the diversity and coding gain can be obtained. The concept of coded cooperation which employs distributed linear dispersion codes (LDC) for two-hop non-regenerative (NR) relay scenario is introduced and analyzed in terms of capacity gains over the system with the traditional coding scheme. Taking the maximum end-to-end data rate as the optimal criterion, an adaptive resource allocation (RA) scheme under the transmit power constraint is proposed to distribute appropriate resource to each hop based on the channel state information (CSI) and certain conditions for optimizing the performance of the distributed LDC. Theoretic analysis and numeric results indicate that with the adaptive scheme, the proposed coded cooperation system will obtain higher capacity benefits than the system with direct transmission and traditional uniform RA.

In the sub-channel reliability based HARQ (sRB-HARQ) scheme the channel qualities are exploited in retransmission to enhance the system throughput. The sub-channels with poor channel qualities measured by signal to noise ratio (SNR) are considered to be more unreliable, and the data on such sub-carriers are prior to be retransmitted when necessary. In this paper, an improved sRB-HARQ scheme for OFDM system is proposed, and the retransmission amount of sub-channels is determined adaptively by the target reliability of the received information which is related with the error ratio of received data (e. g. BLER in this paper). The target reliability for each (re)transmission could be same or different which are categorized as single target and multi target respectively. The sub-channels with least reliabilities are retransmitted on better sub-channels in order to achieve higher diversity gain. Thus the system throughput could be improved significantly and high power efficiency is achieved which are also proved by simulation results.

Based on the m-sequence, a time-domain channel estimation algorithm for orthogonal frequency division multiplexing (OFDM) is designed. The m-sequence with cyclic prefix (CP) is inserted between OFDM symbols in time domain as training sequence. The cross-correlation is calculated between the received sequence with CP removed and the appointed circular shifted m-sequence, which takes reliability of the estimation of channel impulse response on account of the two-valued auto-correlation property of the m-sequence, thereby the channel frequency response can be advisably decided. As a result of both theoretical analysis and simulation, we obtain an impressive performance with less system overhead and lower computation burden than conventional algorithms.

This paper proposes a novel power control algorithm on the reverse link (RL) of the CDMA system, which takes the interference interaction among mobile stations (MSs) into consideration. The proposed algorithm is based on power control commands with the assumption that each MS can collect power control information for other MSs in the same cell as references to determine its own transmit power. The action of keeping current transmit power is introduced to MS. So the power variation is smaller and the system is more stable compared with the traditional power control algorithm. It is shown, by dynamic system level simulation, that the proposed algorithm can reduce interference and improve system capacity. In addition, the proposed algorithm is flexible to implement, since it can be located at MS or base station.

This paper introduces a full rate, full diversity orthogonal space-time block code for 4 transmit antennas. The4times4 codeword matrix consists of four 2times2 Alamouti blocks, and these blocks can be viewed as quaternions which in turn represent rotations in R3. The Alamouti blocks that appear in a codeword are drawn from the icosahedral group. The code is no constellation expansion unlike some full-rate full-diversity codes in the literature. By utilizing the quaternionic form, we can find the decoding algorithm to reduce the complexity of maximum likelihood (ML) coherent decoding.

In this paper, we analyze the capacity of delay- sensitive services in forward link of TDMA system when multiuser packet (MUP) is used. A new transmission strategy based on two buffers is proposed to meet the stringent quality of service (QoS) requirement. Besides, we employ a throughput optimal scheduler in a constrained delay boundary to achieve a good balance between throughput and latency. The delay boundary in our analysis is defined as the longest time a packet may experience, including waiting time in a buffer and transmission time over the air interface. Our scheduler purely relies on subscribers' channel condition which has an analogy to maximum C/I. According to the buffer-based transmission and channel condition-oriented scheduler, we develop an analytical model and give the numerical results in the end.

CDMA2000 Nx EV-DO, also known as DO-REV. B, is a third generation (3G) wireless solution providing high-speed mobile Internet access. In this paper we describe the design of the access channel MAC protocol considering the QoS of traffic. A QoS-aware multichannel random access based on slotted ALOHA scheme was proposed. Through the theoretical model and simulation results, we confirm that the proposed algorithm has the advantage of giving high throughput to high priority service.

A new adaptive irregular modulation technique is proposed for Turbo iterative detected multi-antenna system with different bit mapping schemes or (and) modulation schemes used in different transmit antennas. The modulation scheme and the bit mapping scheme can be adaptively chosen according to the time varying channel quality to improve the channel throughput. When combining the proposed approach and the irregular modulation scheme, it can provide more flexible adaptation to the current channel quality. Simulation results show that using this adaptive technique, the system can converge earlier without changing the system throughput; meanwhile, system using this adaptive method can have higher system throughput compared with conventional adaptive method.

The idea of distributed space-time codes which is being applied to wireless relay network, seems to be a promising approach to reduce the total radiated power and to insure the delivery of the information with desired quality of service. In this paper, we propose a feasible coding scheme based on distributed linear dispersion codes (LDC) for two-hop regenerative multi-relay scenario, and further analyze the advantage of the proposed case in terms of capacity gains over the system with orthogonal transmission. Moreover, we show how to effectively allocate the limited resource among the source and relay terminals in order to maximize the performance of the proposed system. Numerical results indicate that with the adaptive scheme, the proposed system not only achieves higher capacity gains than the system with direct transmission and traditional uniform PA, but also performs very close to the optimum relay system.

As existing wireless network, system, and standards evolve to beyond 3G capability, the ability to roam between heterogeneous wireless networks becomes increasingly desirable. However, when attempt is made to achieve the vision of seamless handover between heterogeneous wireless networks, a number of formidable barriers appear due to unreasonable roaming strategy. In this paper, we propose a novel roaming solution which takes into account the call activity rates and moving speed of users, and analyze the impact of the different parameters on the rate of inter-networking handover and the fraction of calls undergoing call setup delay. Theoretic analysis and numeric results demonstrate that the proposed scheme can obtain better performance than traditional roaming strategy, in terms of improving the capability of inter-networking roaming and reducing the signaling cost of handover.

An improved channel estimation scheme based on estimation of parameters is presented for frequency-selective MIMO channels. In the algorithm, the propagation delays and the angles of multipath are firstly estimated by a extended TST-MUSIC algorithm. With the information of multipath delays and angles, an estimator based on parametric channel model is derived and the estimator's performance is analyzed. Simulation results show that the method can effectively decrease the dimension of estimated parameters, consequently has much better performance than the nonparametric least square (LS) estimator.

Oversampling at each receive antenna is equivalent to having multiple polyphase components with correlated channel gains and colored noise, provided that the signal bandwidth is higher than Nyquist bandwidth. To exploit the potential of these polyphase components in the MIMO systems, this letter advocates the approach of using deliberately designed asynchronous transmission instead of the synchronous transmission usually employed. Simulations show that the asynchronous transmission can easily outperform its synchronous counterparts. Moreover, it opens up the possibility of using fewer antennas at the receiver, particularly in a subscriber unit where there are severe constraints on size, weight, and power consumption.

In this paper, a new MIMO system named turbo-BLAST which utilizes the turbo principle is investigated. Meanwhile, we propose the idea of using advanced channel codes in the system , such as turbo code and TCM (trellis code modulation) code. New algorithm of detector is deducted in order to fit for non-constant envelope modulation. There new structures are proposed: a modified structure named selective feedback are proposed to reduce the time-delay of turbo-BLAST for high-order modulation, the decoding algorithm of trellis code modulation is modified to provide the detector with extrinsic information, and the new decoder structure of turbo code is also given. The simulation results show that selective feedback can achieve better performance, and the structure using turbo code can achieve better performance and faster convergence rate in high-order modulation

Adaptive modulation and coding (AMC) has gained a lot of attention in the research of high speed downlink packet access (HSDPA). The idea is to adapt the transmission to the fast changing channel conditions by the use of different modulation and coding schemes (MCS). In this paper, an adaptive algorithm (ITA) is presented for the AMC technique in HSDPA and a theoretical analysis model is introduced to investigate the throughput and FER of ITA. Subject to the given FER target, the numerical and link level simulation results both show that ITA outperforms the adaptive algorithms

A prediction-based smoothing scheme for real-time video transmission in 3G CDMA systems is proposed in this paper. It is carried out within group of pictures (GOP), using data prediction method to reduce delay, setting the minimum rate based on delay requirement, and choosing transmission rate among CDMA physical layer rate sets. This scheme can considerably reduce the peak rate and variance of the transmitted signal. Furthermore, we proposed a scheduling algorithm combining smoothing scheme and channel quality. Simulation results show that with the proposed smoothing scheme, higher system stability and better QoS have been achieved. Moreover, the system performance gain is more considerable when the channel condition is relatively poor. The scheduling algorithm can well adapt to channel quality to utilize system resource efficiently with the QoS requirement

This paper focuses on the rate allocation schemes on the reverse link (RL) of cdma2000 IxEV-DV system. Two schemes, the time-scheduled (TS) scheme and the rate-controlled (RC) scheme are described and compared. Based on their pros and cons, we propose a modified version to bring together the merits of the two schemes. The proposed scheme, which is called multi-step-up RC scheme, can enable a mobile to increase its rate by multiple steps when needed. The TS scheme, RC scheme and the proposed scheme are respectively simulated on our cdma2000 IxEV-DV Release D reverse link system level simulation platform. Our simulation results show that the proposed scheme can efficiently utilize the radio resource and improve the user's QoS performance of delay. In addition, the performance gain is achieved using the same amount of signaling overhead as that of RC scheme, which is much less than that of TS scheme. The idea of the proposed scheme can be applied to other similar communication systems

With the increasing requirement on QoS of data service, the long term evolution (LTE) of 3G is being researched and standardized to provide higher bit rates with lower latency, lower cost and improved coverage. In this paper, a novel network topology optimization of UMTS access networks combining mobility management and improved authentication schemes is proposed to support these requirements. The architecture presents a concept of URA (UMTS terrestrial radio access network registration area) self-control system in control plane (C-plane) of access network, so that the handover process of C-plane can be independent of that of user plane (U-plane), which significantly reduces the handover latency. Moreover, a novel layered tunnels topology method is proposed in U-plane to achieve load equilibrium in access gateway (AGW). Based on the proposed network architecture, we give examples of signaling sequence combining fast handover process and proposed authentication scheme, and shows that their performance is generally superior to current 3G network architecture, in terms of reducing handover latency and increasing data security and integrity

Wireless network optimization is an important factor in the wireless communication constructions and operations. Drive test is a necessary method to evaluate the wireless network performance, but it produces a great many drive test data, and the performance of processing drive test data restricts the capability of wireless network optimization toolkits. Because of the special structure of drive test data, it is necessary to find an available method to process a great number of these data effectively. This paper presents a novel model which can process a huge amount of DTD files and improve the performance of the toolkits

Flexible channel allocation is one of the key advantages in TD-SCDMA system. In this paper, a novel channel allocation scheme based on pathloss partitioning is proposed to resist near-far effect and improve the system robust. The proposed scheme is evaluated by means of simulation and the results are compared to that of a system configured with other allocation schemes. It can be seen that the proposed scheme provides better system performance in terms of outage probability.

Turbo decoding has large iteration delay. Based on tail bits of turbo codes, a low-complexity adaptive iterative decoder is proposed for turbo codes in this paper. In the proposed algorithm, tail bits work as CRC bits to detect whether the decoding succeeds or not. From simulation results, the new algorithm reduces average iteration times, compared with turbo decoding with fixed iterations. At the same time, it achieves better performances of BER, FER and average iteration times for short frame size and similar performance for medium frame size without additional overhead bits or computation complexity, compared with CRC based adaptive iterative turbo decoder

This paper presents a new equivalent SNR calculation method of received frame in AMC algorithm to decide for the appropriate MCS to be used in the next frame. The equivalent SNR calculation is based on channel capacity equivalence and combined with a factor Q which penalizes channel variations. Simulation results show that this method provides a good throughput performance, and it can be generalized for other application cases easily

This paper proposes a new approach to apply fractionally spaced frequency-domain equalizer for the single carrier broadband wireless systems in the presence of colored noise. The complexity of this equalizer can be significantly reduced with the help of performing the equalization in the frequency domain, when the channel is highly dispersive. In addition, the overlap-cut method, which can be applied to the existing single carrier air interfaces directly, takes the place of the well-known cyclic-prefix method. It is shown that the fractionally spaced frequency- domain equalizer is superior to the conventional baud spaced ones.

A MIMO system named Turbo-BLAST was introduced recently. We investigate the structure of Turbo- BLAST, and study its three kinds structures using different channel codes. Some necessary deductions and new structures are proposed: the decoding algorithm of trellis coded modulation (TCM) is modified to provide the detector with extrinsic information, and a new decoder structure for Turbo code is also given. Simulation results show that the structure using Turbo code can achieve better performance and faster convergence rate for high-order modulation. And the performance improvement of the structure using TCM is also obvious. Since TCM can bring high spectral efficiency, it would be useful to apply TCM in Turbo-BLAST.

Dedicated pilot is used in CDMA uplink to facilitate coherent reception. Traffic-to-Pilot power ratio (T/P) is an important system parameter that determines system performance and QoS. Previous work has obtained the optimal T/P for CDMA uplink through simulations. In this paper, we propose a theoretical method to achieve the optimal T/P that minimizes the average total uplink transmission power (i.e., pilot plus traffic channel power) of a mobile station with the given link quality. Through the analyses, this paper obtains that the optimal T/P is independent of channel profile in the case of low velocity. At the same time, the optimal T/P has a small variation over different environments

The main objective of this work is to investigate service quality of VoIP in wireless communication networks through a simulation study. This paper outlines a simulation framework for VoIP quality, which incorporates wireless links, system performance, and speech quality. There has been a focus on packet voice quality simulation. In the proposed framework, the Gilbert model is used to simulate packet dropping in transportation and perceptual evaluation of speech quality (PESQ) algorithm is for calculating mean opinion score (MOS) of voice. The results show that packet loss rate, continuous packet loss and active user number have obvious impact on the voice quality

A real-time smoothing scheme of MEPG-4 video for CDMA systems is proposed in this paper. It is carried out within group of pictures (GOP), using data prediction method to reduce delay, setting the minimum rate based on delay requirement, and choosing transmission rate among CDMA physical layer rate sets. This scheme can considerably reduce the peak rate and variance of the transmitted signal. Simulation results show that with the proposed smoothing scheme, higher system stability and better QoS have been achieved. Moreover, the system performance gain is more considerable when the channel condition is relatively bad.

Adaptive modulation for Vertical Bell Laboratories Layered Space-Time (V-BLAST) systems is considered in this paper with peak power constraints on each antenna besides the average total power limit on the entire system. The bit loading and power allocation of margin maximization problem and rate maximization problem is given by modifying the incremental allocation algorithm. The loading algorithm of combination of both fixed and variable rate services is presented as well. The results show that the power limit which is very practical for a real V-BLAST system saves the total energy of the whole system at a target bit error rate (BER), but decreases bit rate for rate maximization or deteriorates BER performance for margin maximization

In this paper, the effect of the height of the base station antenna and the ratio of indoor to outdoor mobile stations on the reverse link capacity for a CDMA Manhattan like microcellular system is evaluated. The analytical expressions for the relative other-cell interference factor as a function of the height of base station and the ratio of indoor to outdoor mobile stations is also obtained. It is shown that the capacity decreases when the height of the base station's antenna increases. Furthermore, the capacity is the increasing function of the ratio of indoor to outdoor mobile stations when the antenna of the base station is low and the decreasing function of the ratio when the antenna is high. The paper will contribute to the design of CDMA systems.

A new timing control scheme, named as pair-synchronisation, is proposed for synchronous reverse link in CDMA systems. This scheme employs the received signal(s) to generate the timing reference instead of using a common reference from system timing of the receiver side. Analysis and numerical results show that this scheme can further improve the reverse link capacity by achieving better orthogonality while reducing the forward link overhead for closed loop timing control.

In mobile communications, power efficiency is an important factor in the design of the handset. HPSK modulation is used to transmit multiple channels in the reverse link of cdma2000. In this paper, we propose an improved scheme that includes zero phase transition and zero crossing reduction can reduce the peak-to-average power ratio (PAR) of the HPSK signals. The improved scheme is analysed. The scheme can reduce the PAR obviously. The zero crossing rate reduction can reduce the out-of-band power effectively. The simulation results are given and prove the validity of the schemes.

This paper focuses on short-term performance analysis of turbo decoding in power-controlled fading channel, as is the case in cdma2000 reverse link. Before employing the log-normal distribution approximation on the SNRs in the power control groups (PCGs), we study the short-term distribution in the closed-loop power control system and verify the approximation in the short-term sense. Then we study the short-term frame error rate (FER) performance under this approximation and give some comments on the effect of the parameters of fading.

Generic propagation model always have accuracy problems. Without model calibration, it can hardly be used in practice. This article develops a recursive algorithm on radio propagation model calibration for CDMA systems. An evaluation method is introduced and actual drive test results are used to verify the refined model's goodness of fit. From the results it can be seen that the calibration method in this paper is feasible in practice.

MIMO communication systems can offer much more advantages in terms of rate and reliability than SISO communication systems. In cellular wireless communication system, however, gains may be limited due to fading and interference. For downlink case, one potential solution is known as multiuser diversity, in which a packet scheduler improves throughput by exploiting the independence of the fading and interference statistics of different users. In this paper, the performance of downlink multiuser diversity with a large number of users for SISO and MIMO systems is considered. Through approximate analysis, it is found that in SISO systems, the multiuser diversity gain in terms of information capacity is A log(log K)/sup 1/ asymptotically, where K is the number of users, A is a constant. However in MIMO systems, if the same schedule strategy is used as in SISO systems, the multiuser diversity gain is upper bounded by Blog(log K/M)/sup 2/, where M is the number of antennas, B is a constant independent of M . When the number of transmit and receive antennas approaches infinity, multiuser diversity gain vanishes, which means that the total downlink information capacity doesn't increase with the increase of the number of users. It is also pointed out that the goal of optimizing a cellular system with multiple antennas is to maximize the total gain consisting of the multiuser diversity gain and the spatial multiplexing gain.

Near Shannon limit error-correcting coding and decoding - turbo codes were proposed in 1993 and lots of work was done on this aspect. Several adaptive iterative decoding algorithms for turbo codes were proposed to reduce the decoding delay. We investigate and improve these adaptive algorithms. The simulation results, comparison and analysis are presented.

The use of multiple antenna elements both at the transmitter and receiver results in enormous capacity increase. But for the use of this technique, the multipath scattering must be sufficiently rich; otherwise the performance of communications system will get worse compared with not using this technique. In order to make full use of the advantage of this technique under appropriate radio propagation environment, we present a standard for evaluating the correlation characteristics of the MIMO channel. With this standard, we can judge if the multipath scattering of the radio propagation environment is sufficiently rich, and then decide if this propagation mode is used.

Data transmission control schemes have significant influence on QoS and system capacity. In this paper, three types of data transmission control scheme are presented and their influences on the system performance are simulated. According to the simulation results, some conclusions are obtained.

Trellis codes (including convolutional codes and turbo codes) have been widely used in DS-CDMA systems for their good performance. In this paper we study the performance of convolutional codes and turbo codes in an environment where E/sub b//N/sub 0/ changes sinusoidally. We study four cases of both scenarios. For each case we obtain some conclusions and give their analysis. In this paper a very important characteristic, named additivity, is acquired.

The algorithm of the multiuser detector (MUD) based on decision-feedback is analyzed in this paper. The performance of the proposed detector is evaluated and simulated. Numerical and simulation results show that, under ideal power control, this detector is better than the conventional and decorrelating multiuser detectors in terms of BER performance, while in terms of "near-far" resistance, after ranking the signals in descending order of received powers, this detector is still better than conventional and decorrelating ones and finally approaches to the single-user bound.

The authors develop a hyperstable adaptive algorithm that can be used in the multichannel IIR (infinite impulse response) configuration and permits the high-order IIR or zero-pole configuration to be realized in the parallel form for joint process estimation. The multichannel IIR configuration cannot be implemented by using the conventional hyperstable algorithm. The high-order configuration implemented by the proposed algorithm has much better rounding-error performance than that implemented by the direct-form configuration. Simulations results are presented for both the parallel zero-pole and multichannel configurations.>