An unmanned aerial vehicle (UAV) can be utilized as a flying data collector and wireless power source in wireless charging sensor networks (WCSNs). Different from conventional studies that focused on maximizing the efficiency of wireless power transfer (WPT) for UAV route design, in this article, we maximize the lifetime of WCSNs by considering sensor energy consumption and energy harvesting simultaneously. We consider simultaneous wireless information and power transfer (SWIFT), where data collection capability guarantees power leftover for UAV to complete its round-trip flight. Our objective is to jointly optimize the UAV hovering location and duration to maximize the minimum energy of sensors after data transmission and energy harvesting under data collection and UAV energy consumption constraints. To tackle this nonconvex optimization problem, we first assume that the UAV hovering location for each sensor is fixed and optimize UAV hovering duration by the Lagrange multiplier method. Next, for each UAV hovering location, we propose a geometry-based update algorithm, which can be used to find initial feasible UAV routes to the problem. Last, a near-optimal UAV route is determined by adjusting the initial feasible UAV route iteratively, where UAV hovering locations and duration are updated at each iteration. The numerical results are provided to validate the performance of our proposed algorithm.

In this paper, we introduce the 5G K-Simulator, which is standard-compliant open-source simulator and has flexible, open and modular (FOM) structure. The 5G K-Simulator is developed to follow the Third Generation Partnership Project (3GPP) roadmap for fifth generation (5G) communication systems, and its current version is based on Release 15. The 5G K-Simulator consists of a link level simulator (5G K-SimLink), a system level simulator (5G K-SimSys) and a network level simulator (5G K-SimNet), where individual simulator is designed to test physical (PHY) layer, medium access control (MAC) layer and transport layer technologies for 5G communication systems. At the same time, simulators at different levels are connected by mapping modules, which enable one simulator to transfer its simulated data to the other, thereby achieving more accurate simulation results. To allow users to access and execute the 5G K-Simulator, a highly accessible web-based platform, named 5G K-SimPlatform, is also developed. The 5G K-SimPlatform provides a graphic user interface (GUI) for simulation configurations and simulation results, while supporting stable computing environments to run simulators. To guarantee the simulation accuracy and satisfy the strict requirements of 5G systems, the 5G K-Simulator and the 5G K-SimPlatform are verified through beta test by expert groups, hence they are valuable and power simulation tools for researchers in the research institute as well as in the company.

The fifth-generation (5G) communication systems are expected to be an important connecting infrastructure for information and knowledge exchanges among people, machines, sensors, devices, and even environments. The technical specifications for 5G communication systems are being made to satisfy performance requirements that are defined in ITU-R documents. In addition, the key performance indicators in 5G communication systems include peak and average data rate, mobility, energy efficiency, spectral efficiency, latency, connection density, and so on. These performance metrics need to be evaluated by simulators at different levels. Therefore, simulators play an important role in evaluating the performance of 5G communication systems as well as an individual technique. Most research institutes, universities, and industries have their own simulators, but with different levels of assumption and implementation depth according to technical needs of individual organization, which makes a fair comparison impossible.

In this paper, two dimensional (2D) target location is estimated in the passive coherent location (PCL) system in noisy and cluttered environment. Compared to the conventional filter based target estimation schemes that require a prior information of target dynamics, the proposed target estimation scheme does not require that information and can track a target with various movements, such as maneuvering or non-maneuvering target, using a grid point (GP)-based estimation method. Bistatic range sum (BRS) measurements from all receivers are combined and processed for target estimation, but some of them are reflected by clutters rather than a target, degrading estimation accuracy. To tackle this problem, the proposed scheme first eliminates â€false†clutter-reflected BRS measurements by taking multiple time measurements into account. Then, a successive GP update scheme is applied for the remaining sets of BRS measurement, and candidate target locations are determined as a result. In the last step, a soft decision method is applied to determine the target location from the candidates. Simulation results show that our proposed target estimation scheme can track a target with various movements, especially highly-maneuvering target, despite the lack of prior knowledge of target dynamics.

Passive Coherent Location (PCL) system is a field of radar systems that exploits non-cooperative illuminator of opportunity to detect and track a target. Due to bistatic configuration of PCL system, the locations of transmitter and receiver with respect to a target are important to target estimation accuracy. In this paper, we propose a receiver selection algorithm that utilizes the Position Dilution of Precision (PDOP) to estimate a single target location. Previous works utilize the PDOP to select the optimal receiver, but require comparison of all possible combinations of transmitter and receiver, limiting real-time target estimation. On the other hands, our proposed receiver selection algorithm lowers the computational complexity based on the optimal receiver configuration derived from the PDOP. Once receivers are selected, Extended Kalman Filter (EKF) is used to correct the estimation errors. Simulation results demonstrate that performance of the proposed algorithm is comparable with that of the exhaustive search that provides optimal receiver selection.

Simultaneous wireless information and power transfer (SWIPT) has been considered one of the emerging techniques to overcome power limitation of wireless devices using batteries as well as to send information at the same time. Although the SWIPT techniques have been intensively investigated, the fairness among wireless-powered devices in the SWIPT-enabled multicell networks has not been studied yet. In this paper, we propose an adaptive proportional fairness ( α-PF) scheduling algorithm in SWIPT-enabled multi-cell downlink networks. We define an adjustable weighted sum of achievable rate and harvested energy as the utility function of each user and investigate fairness among utilities of users. Through extensive simulations, we evaluate the proposed scheduling algorithm in terms of rate-energy (RE) tradeoff, the fairness of achievable rate and harvested energy. Compared to various existing scheduling algorithms such as random scheduling, maximum signal-to-interference-plus-noise (SINR) scheduling, and α-adaptive scheduling algorithms, the proposed scheduling algorithm achieves better fairness measure (e.g., Jain's fairness index). In addition, we can adaptively control parameters of the proposed scheduling algorithm to satisfy certain requirements of the system.

In-band full-duplex (FD) systems have been widely studied because they can double the spectral efficiency (SE) compared with conventional half-duplex (HD) systems, theoretically. However, inherent interference caused by both self-interference (SI) and co-channel interference (CCI) makes FD systems to achieve theoretical SE hard. In this paper, we propose a CCI estimation and cancellation (CCI-EC) protocol for the FD systems to overcome performance degradation due to CCI. We suggest to use a coherence channel block for two phases: CCI channel is estimated at a downlink (DL) user through uplink (UL) pilot signals in the first phase, then a base station (BS) and a UL user transmit their data simultaneously in the second phase, in which a DL user cancels interfering signals from a UL user by utilizing the estimated CCI channel information. We analyze the achievable SE of FD systems with CCI-EC and formulate a resource allocation problem to maximize it, where resource includes pilot and data transmission time, and transmit power of a BS and a UL user. A closed-form optimal power allocation for UL pilot and data transmissions and a suboptimal power allocation for DL data transmission are provided. The simulation results show that FD systems with the proposed CCI-EC achieve near-optimal achievable SE and outperform the conventional HD systems and FD systems without CCI-EC in terms of the achievable SE. Especially, the SE gain achieved by the proposed CCI-EC protocol in FD systems is remarkable under severe interference environment.

New duplexing methods are emerging to improve spectral efficiency (SE) and reduce delay as wireless network evolves. Dynamic time division duplexing (D-TDD) and in-band full duplex (IFD) systems are strong candidate technologies for next-generation wireless communication. Recently, many studies about above two duplexing methods have been conducted through stochastic geometry models. For uplink direction, however, existing studies do not adequately reflect the geographical characteristics of the newly introduced interference. In this paper, to increase the accuracy of analysis, we re-derive two types of uplink interference considering the geometrical relationship and dependency between typical base station (BS) and other cell nodes (e.g., BS and(or) user equipment (UE)). Also, we analyze the outage probabilities on the D-TDD and IFD systems under the homogeneous network focusing on the uplink direction. The results show that our derived outage probability matches very well with the Poisson Point Process (PPP) simulation among the existing uplink analysis.

Due to proliferation of portable smart devices (e.g., laptops, tablets, smart phones), mobile data traffic even in high-mobility environments has been explosively increasing. Hence, recently, high-speed train (HST) communications have particularly attracted a lot of attention. In order to provide emerging services (e.g., virtual reality (VR) / augmented reality (AR), video- conferencing, online gaming) in HSTs, the HST communications system is required to support not only higher data rate but also lower latency. However, recent studies are mostly focusing on increasing data rate while reducing latency is also indispensable, especially when the HST communications system is a time-division duplex (TDD) system. Therefore, this paper proposes a latency reducing method for TDD-based HST communications that involves a new TDD configuration and interference cancellation (IC) method. Simulation shows that the proposed scheme with IC is capable of efficiently reducing the latency without performance loss in data rate.

In IoT network, one of the most challenging issues is to minimize the energy consumption and to prolong the network lifetime as well as to accommodate random access (RA) requests of massive number of machine-type communication (MTC) devices. As the number of MTC devices increases, the collision happens more frequently, which results in the waste of energy. Especially, for MTC devices located in the cell-edge experience severe energy deficiency which should be taken into account. This paper proposes a novel energy efficient random access response (EE-RAR) scheme, which provides higher access priority to farther devices than near devices by utilizing the timing advance (TA) information at the middle of RA procedure. We mathematically derive the expected number of MTC devices that succeed in random access and the corresponding energy consumption of the proposed EE-RAR scheme. The performance evaluation shows that the proposed EE-RAR scheme enables the IoT networks to consume less energy as well as achieves 15% better connectivity over the conventional RAR scheme when 500 MTC devices try to access eNodeB simultaneously.

An unmanned aerial vehicle (UAV) has been considered as a base station (BS) or a relay node in wireless communication systems due to its cost-effective and fast deployment. UAV BSs (UBSs) can provide a wireless connectivity to user equipments (UEs) within a given coverage, while UAV relay systems (URSs) can extend a service coverage of BS to provide a reliable communication link to an isolated UE (IU). The deployment of UAV(s) impacts greatly on the performance of UBS and URS. In this paper, a novel UAV deployment algorithm for multi-layer URS is proposed to maximize an average data rate of UEs while guaranteeing a seamless communication service to IU. The proposed algorithm utilizes the minimum number of UAVs and derives the minimum number of transmission time slots to improve an average data rate. In addition, a single-layer URS is considered as a special case of multi-layer URS, and its deployment algorithm is introduced. The performance comparison between multi-layer and single-layer URSs is presented in numerical results based on the position of IU.

This paper investigates the energy-efficiency of licensed-assisted access (LAA) which enable long-term evolution systems to operate in unlicensed spectrum. Since Wi-Fi with 802.11 n/ac is a typical radio access technology in the unlicensed spectrum, we consider a scenario that the LAA small-cell base stations (SCBSs) are deployed together with Wi-Fi access points. We propose three different listen-before-talk (LBT) schemes according to the channel sensing mechanisms for LAA SCBC, and establish Markov chain models for each scheme under non-saturated traffic condition. Using these analytical models, the energy-efficiencies of LAA SCBSs that perform the different LBT schemes are investigated. We also propose the algorithm to obtain the optimal contention window size of LAA SCBSs by which total energy-efficiency of networks is maximized while satisfying the required energy-efficiency of both LAA and Wi-Fi networks. Numerical results show that the LBT scheme which has an efficient channel sensing mechanism outperforms the other LBT schemes for the energy-efficiency perspective.

An unmanned aerial vehicle (UAV) can be used as a relay node to provide a communication service to an isolated user equipment (iUE), which does not have a direct communication link from/to a near base station (BS). UAV-aided relay network (UARN) has been considered to provide a reliable communication service to iUE, and a non-orthogonal transmission scheme is utilized at BS to avoid performance degradation of user equipments inside a cell (cUEs). UE scheduling schemes, which are used for conventional relay networks, cannot maximize the longterm average throughput of cUEs in UARN, where UAV moves from BS to iUE or stays close to iUE. In this paper, a novel UE scheduling scheme is proposed to achieve higher long-term average throughput and fairness simultaneously in UARN, while providing a seamless relay transmission to iUE. Simulation results demonstrate that the proposed UE scheduling scheme outperforms the conventional UE scheduling schemes in UARNs.

Recent development of wireless communications has resulted to the augmentation of small cell to traditional macrocell networks. This constitutes an improved coverage and system capacity of the networks. However, it consequently results to interference and high blockage rate, which are the problems we are treating in this paper. This work proposes two cell selection schemes that adopt the enhanced inter-cell interference coordination technique developed by 3GPP in Rel-10 for LTE- Advanced networks. Initial results are provided as a proof-of-concept,where the two proposed algorithm's results are provided.

In-band full-duplex (IBFD) radio system can potentially double the spectral efamp;#64257;ciency of wireless networks. For IBFD radio system, the residual self-interference (RSI) is a critical issue. In addition, in-band full-duplex cellular (FDC) networks, particularly when the cell size is small, inter-user interference (IUI) would be another key factor for the performance degradation. To overcome these issues, we propose the scheduling scheme which adaptively utilizes bidirectional FD (BFD) mode and unidirectional FD (UFD) mode in the halfduplex (HD) networks. This scheme is based on the RSI channels after interference cancellation and IUI channels for each carrier, in order to maximize the proportional fairness. Simulation results revealed that the use of BFD mode is extremely dominant for a small cell with few mobile stations (MSs) if self- interference is sufamp;#64257;ciently canceled since IUI could be large.

This paper proposes optimal beam adaptation (BA) and initial access (IA) algorithms for millimeter wave (mmWave) uplink systems, which make use of the estimated location of user equipment (UE) by access points (APs) rather than using exhausting full beam sweep for the beam direction toward UEs. Based on the location estimation, the optimal beamwidth guaranteeing the highest connection probability is derived for the optimal BA method. The proposed IA procedure selects the best AP not only based on the channel gain but also based on the location estimation, which leads to reduce the outage probability of cell-edge users. Numerical evaluation shows that both BA and IA outperform the conventional procedure in terms of of average achievable rate for the cell edge users, when separately applied. Numerical results are also provided with better performance than conventional systems without BA and IA suggested, for the case when both BA and IA are applied.

Heterogeneous Network (HetNet) has been a major feature for next generation wireless networks, where femtocell has attracted much attention as a most promising radio access technology (RAT) for providing improvements on network capacity, service coverage and power efficiency. And for the efficient utilization of scarce spectral resource, coexistence/sharing of unlicensed band between wireless fidelity (Wi-Fi) and Long Term Evolution (LTE) systems has recently been proposed and investigated. It is shown that analysis by Voronoi diagram achieves superior performance under homogeneous environment. In this paper, we extend the Voronoi diagram approach to HetNet environment with Wi-Fi and LTE femtocells, which is shown to achieve superior performance under homogeneous network. For the HetNet, we formulate an optimization problem, which is derived from a weighted Voronoi tessellation and the corresponding characteristic functions, to maximize network capacity over an optimal femtocell operation scheme in LTE-U. For the optimal femtocell operation, we provide an optimal AP density ratio under the objective of HetNet capacity maximization with convex analysis, where partial femto APs are turned to open access mode in the HetNet coverage. Simulation results are provided to demonstrate effectiveness of the proposed algorithm, and validate importance of the AP density ratio and the transmit power ratio to network capacity. This analysis can be easily extended to HetNets with multiple RATs.

Efficient utilization of limited spectrum resource has been a major issue in wireless communication systems, which has triggered the design and development of advanced cellular networks. Recently, heterogeneous network (HetNet) with small cells to satisfy the demand for higher data rate transmission and throughput has attracted a lot of attention in the unlicensed spectrum bands environment to overcome the scarcity of licensed spectrum. In this paper, we consider network capacity optimization problem for HetNet comprised of Long-Term Evolution (LTE) small cell and wireless fidelity (Wi-Fi) in LTE unlicensed spectrum (LTE-U) with optimal spectrum splitting ratio. We derive coverage probabilities and average achievable rates for each radio access technologies (RATs) based on the conditions of user equipment (UE) association in multi-RAT wireless network system. Then the optimal unlicensed spectrum splitting ratio can be obtained by maximizing HetNet capacity under the derived constraints on respective coverage probabilities. Simulation results reveal effectiveness of the proposed scheme, where both the spectrum splitting ratio and transmit power ratio are key parameters. This analysis can be easily extended to HetNets with multiple RATs.

In-band full-duplex (IFD) system has been considered as an attractive solution for increasing the spectral efficiency of wireless networks. Compared to the conventional half-duplex (HD) node, an IFD node suffers not only selfinterference (SI) from its own transmitted signal, but also more severe co-channel interference (CCI), which affect the system performance significantly. To investigate the performance gain of IFD system with both interferences over the conventional HD system, this paper considers two different IFD systems, pairwise IFD (P-IFD) and 3 node form IFD (3n-IFD) under IEEE 802.11ax outdoor large BSS scenario. Also, this paper adopts an intuitive space scheduling (SSC) algorithm to reduce additional CCI of IFD nodes. Numerical results reveal that the self-interference cancellation (SIC) requirement can be reduced with help of the SSC and the implementation burden of IFD devices can be loosened. In addition, numerical results show that the performance of 3n-IFD is similar to that of P-IFD. 3n-IFD has backward compatibility with conventional HD station as well as sufficient performance gain of IFD mode.

Carrier aggregation (CA) is an essential feature in the Long Term Evolution-Advanced (LTE-A) system, which can aggregate two and more component carriers (CCs) to form a much wider transmission bandwidth up to 100 MHz. By means of CA, a user equipment (UE) can be scheduled on multiple CCs simultaneously to transmit data traffic. Recently, the studies on the efficient operation of an LTE-A based CA system have received much attention under simultaneous access scenarios for multiple CCs. However, the existing literature lacks efforts on Quality of Experience (QoE)-aware CA, especially in the uplink. In this paper, we propose a joint resource allocation algorithm for an uplink LTE-A based system, focusing on QoE-aware CA. We first present a framework for the evaluation of UE's QoE satisfaction level by designing a link reward, resource cost, and link utility function. Then, a QoE-aware joint resource allocation algorithm is proposed for the efficient sharing of radio resource by UEs, so that uplink system utility is maximized. Numerical results demonstrate the validity of the proposed algorithm.

This paper proposes a joint radio resource allocation algorithm for uplink parallel multi-radio access (MRA)in heterogeneous networks, first introducing an economic link utility function, which quantifies Quality of Experience (QoE) satisfaction level of user, as a combination of link reward and resource cost function. Then, a QoE-based joint resource allocation algorithm is proposed for the efficient sharing of radio resources by multi-mode terminals, so that uplink system utility is maximized. In particular, this work studies two cases of parallel MRA systems that are distinguished by the existence of free wireless access points. We provide a sensitivity analysis on how cost in the joint resource allocation algorithm affects the performances of various parallel MRA systems.

One of major issues in the efficient use of radio resource for multiuser multiple-input/multiple-output (MU-MIMO) systems is the selection of users to achieve the maximum system throughput. The optimal user selection algorithm, which requires exhaustive search, is prohibitive due to its high computational complexity where Block diagonalization (BD) method is applied and known as a suboptimal precoding technique for downlink MU-MIMO systems, which intents to perfectly eliminate inter-user interference. In this paper, we propose efficient, iterative user selection algorithms with low complexity, where the product of eigenvalues of effective channels is utilized as a selection metric by applying the concept of principal angles between subspaces. And, we further examined the applicability of the proposed algorithms to limited feedback systems and proportional fair (PF) scheduling. Through computational complexity analysis, we show that the proposed algorithm has low complexity with a little loss in throughput. Simulation results validate that the proposed algorithm achieves almost the same system throughput by a capacity-based algorithm under high SNR regime with considerable reduction in complexity.

In this paper, we suggest a multiple-input/single-output (MISO) transmission technique for free-space optical links with intensity modulation and direct detection. Specifically, time-domain repetition coding is investigated over slow and weak turbulence fading channels, where we suggest a set of efficient codewords for MISO transmission with time-domain repetition coding. The proposed approach increases signal to noise ratio (SNR) most effectively by allocating total radiated power fully into only one transmit aperture for a single bit period with postprocessing followed by equal gain combining at a receiver. We evaluate instantaneous electrical SNR and conditional bit error rate (BER) numerically. Numerical results show that as the number of transmit apertures increases the BER performance gap increases, which reveals its outperformance over other schemes not only in weak turbulence channels but also in weak turbulence channel with misalignment problem.

In heterogeneous networks (HetNet), interference coordination techniques among cells have been widely investigated to reduce co-channel interference (CCI), which causes severe system performance degradation when a same channel is shared at both femtocells and macrocell. In this paper, we examine a coordinated beamforming technique to reduce downlink (from macrocell to femtocells) CCI and processing complexity. Using uplink sounding reference signal (SRS), we propose an efficient beamforming searching function for a macro-BS reducing feedback burden compared to conventional schemes. Simulation results are provided for performance comparison in terms of the spectrum efficiency of femtocells and system throughput.

In downlink multi-user multiple-input/multiple- output (MU-MIMO) systems with BD where there are a lot of users, selecting a user set supported by a base station (BS) is very critical to maximize the total throughput. The optimal user selection algorithm, which requires exhaustive search, is computationally prohibitive in real systems. In this paper, we propose a user selection algorithm with low complexity, where the product of eigenvalues of effective channels is utilized as a selection metric. We adopt the concept of principal angles between subspaces to obtain the product of eigenvalues of effective channel matrix at each iteration. Contrary to conventional low complex user selection algorithms, the proposed algorithm is straightforward to apply to PF scheduling because the proposed selection metric indicates data rate in high SNR regime. Computational complexity analysis and simulation results show that the proposed algorithm achieves almost the same the system throughput of capacity-based algorithm in high SNR regime with considerable reduction in complexity.

In this paper, a relay selection issue is studied to improve data rate performance in a multi-user environment. Previous opportunistic relay selection protocols only consider channel condition in relay selection. However, the target performance is affected by other system attributes, such as delay and load in relay node (RN). The proposed relay selection scheme, which is based on analytic hierarchy process (AHP), adopts signal-to-noise ratio (SNR), switching, and the number of connections to RN as a selection criteria. Also, a special form of eigenvector is proposed and proved analytically. From the proposed eigenvector, the computational complexity is obviously reduced. Target system performance is examined under different weighting parameter values to the above attributes. This work shows that average data rate can be maximized corresponding to the number of RN. Simulation results reveal the benefits of the proposed scheme over the conventional opportunistic relay selection scheme and the threshold-based relay switching selection scheme. The performance of our scheme is verified in terms of average data rate and distribution of the data rate.

Smart grid has emerged in our fight against global warming by integrating renewable power sources into electrical power transmission network. We use dynamic pricing to control power demand in respond to the fluctuation in renewable power output. In dynamic pricing, the operator needs to collect information about power supply and to broadcast the latest power price. This information exchange is done through the wireless communication network within the smart grid. Wireless transmissions are error-prone and transmission errors will result in a loss of precision in demand control, which will further lead to a loss of profit to the operator. In view of the problem, this paper proposes a cooperative wireless transmission scheme called Cooperative Dissemination of Power Price and Supply (CDPS) for smart grid. The scheme exploits broadcast nature of radio channel to improve efficiency in delivering power prices to all customers, and in collecting power supply information from all renewable power sources. In CDPS, a customer that has overheard transmitted power supply information from its neighbors may help in delivering the information to the operator. Similarly, a customer that has received the latest power price may cooperatively retransmit the information to its neighbors that have not received the information. We have evaluated the performance of CDPS through random event simulations. The simulation results confirm that CDPS can indeed improve the operator's profit through more effective dissemination of information. Also, CDPS can help in reducing the amount of renewable power wasted due to a loss of reported information.

This paper considers a distributed power allocation scheme for sum-rate-maximization under cognitive Gaussian multiple access channels (GMACs), where primary users and secondary users may communicate under mutual interference with the Gaussian noise. Formulating the problem as a standard nonconvex quadratically constrained quadratic problem (QCQP) provides a simple distributed method to find a solution using iterative Jacobian method instead of using centralized schemes. A totally asynchronous distributed power allocation for sum-rate maximization on cognitive GMACs is suggested. Simulation results show that this distributed algorithm for power allocation converges to a fixed point and the solution achieves almost the same performance as the exhaustive search.

In uplink 3GPP LTE, SC-FDMA has been regarded as an attractive alternative to OFDMA due to lower Peak-to-Average Power Ratio (PAPR) characteristic. However, in order to get the benefit of PAPR, it requires a contiguous assignment of resource blocks to a single user. In this paper, we suggest heuristic algorithm for proportional fair (PF) scheduling which is known to be NP-hard problem. Under the contiguity constraint, conventional heuristic algorithms assign resource block to a user who has the highest metric and keep on doing assignment according to greedy selection but without any examination of prior selected choice. Our work differs from the conventional works in considering user selection based on PF metric difference and comparison of marginal scheduling metric for examination of selected choice. In simulation results, we demonstrated that the proposed scheme shows better fairness in terms of CDF of normalized throughput and Jain's fairness index.

Existing positioning systems such as global positioning system (GPS) or WiFi positioning system (WPS) are limited mainly to outdoor applications or are of poor accuracy without associated maps. Indoor work environment where one spend most of the time and wide adoption of smartphones with numerous embedded sensors provide new opportunities for researches on indoor user positioning. In this paper, we present an indoor positioning scheme using recently introduced smartphones equipped with sensors such as accelerometer, magnetometer, and gyroscope. We propose a practical indoor positioning method to handle complicated human movements and noisy inertial sensors in smartphones. We focus on providing indoor locations with accuracy by applying improved heading estimation solution. The key concept is to reduce errors caused by directional change since the critical component of positioning system is a heading orientation. We have simply used iPhone 4S for experiments and validated its practical usage in indoor environments. The extensive experimental results show that our system is needily applicable as a fundamental system for various mobile services on smartphones providing 2.42 times accuracy over than traditional methods on the average.

In this paper, we address the issue of resource management for coordinated multi-point transmission/reception (CoMP) systems. We propose a dynamic transmission mode selection scheme combined with proportional fair (PF) scheduling, where each cell performs scheduling in a consecutive order. Based on the prior user selection information, each cell decides transmission mode, and makes user scheduling according to the selected transmission mode. Furthermore, we extend precoding matrix indicator (PMI) coordination in order to mitigate intra-cluster interference. The proposed scheme provides adequate resource allocation in JT-CoMP systems without central scheduling unit. Simulation results show that the proposed algorithm provides significant edge user throughput gain without any loss in average throughput.

To encourage data offloading in heterogeneous networks, range expansion techniques have been introduced in LTE-Advanced system. By adding a positive bias in cell selection process, more users can select picocells as their serving cells even the picocell is not of the strongest signal. Also, to protect offloaded users from severe macrocell interference, a specific subframe called almost blank subframe (ABS) is introduced. Since macrocell is kept silent during ABSs, the offloaded users can be allocated without strong macrocell interference within ABSs. It is noted that the offloaded user's average data rate highly depends on the amount of ABSs rather than the bias value because the scheduling opportunities of offloaded users are limited within ABSs. And from the user's point of view, the cell which is expected to give high data rate should be selected as a serving cell. In this paper, we propose a cell selection scheme based on expected user data rate which is a function of the ABS ratio. Simulation results show that the performance of our proposed cell selection scheme can improve average user rate and increase the number of offloaded users as the ABS ratio increases.

In this paper, we deal with a relay selection issue to improve throughput performance under signaling overhead and delay constrained system. The proposed relay selection protocol, which is based on analytic hierarchy process (AHP), adopts signal-to- noise ratio (SNR), system delay, and switching weight as selection criteria. We examined target system performance under various weighting to the above attributes. Also, average throughput can be maximized adaptively in various system environments. The proposed protocol entirely realizes the feature of opportunistic relaying (OR) protocol by totally weighting the SNR criterion. The performance of our protocol is verified in terms of average throughput, average delay and average relay switching counts.

Spatial diversity techniques are now widely adapted in most wireless radio-frequency communication systems to increase robustness against signal fading, and also attract a considerable amount of attention in free-space optical (FSO) communications. On downlink, user terminal cost and power consumption considerations indeed favor transmit diversity over receive diversity, and orthogonal space-time block code (OSTBC) appears to be most well-known transmit diversity scheme. However, OSTBC loses 3 dB in terms of total transmit power with respect to ideal hybrid power transmit diversity technique which requires perfect channel state information at the transmitter. In this paper, we present a simple scheme to recover the power loss using partial feedback for FSO links with intensity modulation and direct detection over log-normal atmospheric turbulence-induced fading channel. We also consider the deployment of other conventional transmit diversity techniques including equal power transmit diversity and switching transmit diversity as benchmarks. Simulation results show that most of the power loss is restored, and the proposed scheme performs very close to ideal performance outperforming other techniques.

Dual-carrier High Speed Packet Access (DC-HSPA) system has been developed as an alternative method to double data rate using more bandwidth, without use of MIMO. Since it utilizes two carriers at a time, scheduling is more important feature than a single-carrier HSPA (SC-HSPA) system. From the nature of the DC-HSPA, both carriers can be allocated to one user when the user has the highest priority on both carriers. However, if a single carrier is enough to empty the queue, one of carriers has to be selected to transmit own data, while the other carrier is assigned to the other user. Available resource on each carrier varies accordingly to the selected carrier, therefore, efficient carrier selection schemes for DC-HSPA system are proposed based on relative scheduling metric difference between users on each carrier. Simulation results show that proper carrier selection increases throughput as well as average user rate in DC-HSDPA system.

With the growing need of high rate data services, 3GPP standard has investigated ways to support multimedia services with multi-carrier transmissions. Supporting high data rate guaranteeing the quality of service (QoS) and fairness of users is an important issue and should be addressed in an advanced wireless system. This paper investigates packet scheduling considering QoS of real-time traffic and fairness of non-real-time traffic through fixed delay adjustment based on multi-user PF scheduling in a dual-carrier (DC) HSDPA system. The proposed algorithm results in the QoS improvement of real-time traffic and fairness of non-real-time traffic, and the decrease of average sector throughput due to tradeoff between throughput and fairness.

This paper investigates the effect of non-orthogonal decode-and-forward (NDF) relaying scheme in wireless network coding environments. It is well known that network coding is effective to improve overall network performance, but because of error propagation, it may not be always advantageous under a hostile wireless channel. To mitigate error propagation, we adopt NDF relaying scheme in wireless network coding, which allows the source to keep on transmitting the same signal when the relay cooperates to forward the network-coded signal. By NDF relay scheme, SNR of the link between source and destination nodes can be increased, which results in reduced number of errors through the link. Simulation results show that network coding with NDF relay scheme average packet error rate performance as well as goodput in wireless butterfly network.

This paper considers a distributed power allocation scheme for sum-rate-maximization under cognitive Gaussian multiple access channels (GMACs), where primary users and secondary users may communicate under mutual interference with the Gaussian noise. Formulating the problem as a standard nonconvex quadratically constrained quadratic problem (QCQP) provides a simple distributed method to find a solution using iterative Jacobian method instead of using centralized schemes. Numerical results show that this distributed algorithm for power allocation is converged to a fixed point and the solution achieves almost the same performance of the exhaustive search.

This paper investigates multi-cell coordinated shared relay with joint processing (JP) scheme in interference limited network. In general, multi-cell coordinated shared relay network increases the Signal to Interference-plus-Noise Ratio (SINR) in cell edge users, but resource usage efficiency is decreased by two-phase transmission of relay protocol. We propose JP of cooperating BSs and shared relay station (RS) in the relay transmission phase (second phase) to increase resource usage efficiency, and introduce the SVD precoding with phase correction based on the multi-cell coordinated shared RS network to mitigate other cell JP interference in the cluster. Simulation results show that the proposed scheme leads to network capacity enhancement.

In uplink 3GPP Long-Term Evolution (LTE), single-carrier frequency division multiple access (SC-FDMA) is considered partly because of the fact that Peak-to-Average Power Ratio (PAPR) for Multi-Carrier Orthogonal Frequency Division Multiplexing (MC-OFDM) is still a hindrance. But, an unique characteristic of SC-FDMA is that subcarriers have to be assigned by contiguous manner for a specific user, which induces a complicated scheduling algorithm to SC-FDMA because a user is not able to exploit frequency selectivity gain fully. To increase system throughput, we propose a new frequency scheduling method using each user's channel gain difference and a contiguity assigning method. Focused on maximizing the total system capacity of SC-FDMA uplink, we compare our algorithms with others in uplink 3GPP LTE. Simulation results show that our proposed scheme outperforms over the existing schemes.

Multihop relay network can be adopted to increase cell edge data rate and extend cell coverage. Performance degradation, however, might be caused due to co-channel interference because of common frequency resource sharing among relay stations. In this paper, we propose an adaptive frequency reuse scheme among relay stations for interference reduction and enhancement spectral efficiency in orthogonal frequency division multiple access - time division duplex based location awareness two-hop relay networks. Our scheme is shown to achieve interference reduction and higher spectral efficiency through simulations.

This paper investigates the effect of combined network coding and power control based on network utility under wireless butterfly networks. Although it is well known that network coding improves network performances, it might not be always advantageous for a hostile wireless environment due to error propagation problem through relaying. Therefore, in this paper, the crossover point for profit-and-loss of network coding and non-network coding according to wireless link quality is derived, and then we show that network utility in terms of spectral efficiency per power is improved, and average power consumption is reduced by adaptively applying relay mode control and power control, which is of bang-bang type with a threshold in wireless butterfly networks.

Power control plays significant role in the cognitive network system where secondary users (SUs) co-exist with primary users (PUs), but the interference due to SUs may affect the performance of PUs. The approach of considering the outage probability of PU as quality of service (QoS) constraint, while using the maximization function of secondary user throughput is used in this paper. A generalized regional model is suggested, while using Binary Power Control (BPC) as an example case. The results conclude that under these conditions the cognitive radio relay network (CRRN), where SUs communicate through a cognitive radio base station (CRBS), with three regions (N=3) and three thresholds provides better performance, in terms of more active SUs and outage probability of SUs.

This letter considers a sum-rate-maximizing power allocation problem under the Gaussian cognitive multiple-access channel (MAC), where primary users and secondary users may communicate under mutual interference. Formulating the problem as a standard nonconvex quadratically constrained quadratic problem (QCQP) provides a simple method to find a solution using semidefinite relaxation (SDR). Simulation results show that the solution achieves almost the same performance of the exhaustive search, within polynomial time.

Heterogeneous wireless networks where several systems with different bands coexist for multimedia service are currently in service and will be widely adopted to support various traffic demand. Under heterogeneous networks, a mobile station can transmit over multiple and simultaneous radio access technologies (RATs) such as WLAN, HSPA, and WCDMA LTE. Also, cognitive radio for the efficient use of underutilized/unused frequency band is successfully implemented in some networks. In this letter, we address such operational issues as air interface and band selection for a mobile and power allocation to the chosen links. An optimal solution is sought and analyzed and a distributed joint allocation algorithm is proposed to maximize total system capacity. We investigate the benefit of multiple transmissions by multiple RATs over a single transmission by a single RAT at a time, which can be interpreted as network diversity. Numerical results validate the performance enhancement of our proposed algorithm.

OFDM has been a widely accepted technology in high rate and multimedia data service systems such as long term evolution (LTE) in the 3rd generation partnership project (3GPP). In this paper, we investigate a synchronization signal structure and corresponding cell search algorithm in the LTE system where two, primary and secondary synchronization signals are employed. We focus on the secondary synchronization signal which possesses two layered scrambling sequences in addition to basic sequences. These scrambling sequences minimize performance degradation in cell search, but incur a high complexity to a mobile station receiver. In this paper, we propose a new secondary synchronization signal structure which does not require additional scrambling sequences while maintaining almost the same performance as the current LTE scheme. We evaluate the performance of the proposed scheme under various channel environments by examining the impacts of multipath fading, frequency offset, and vehicular speed. We also compare the complexity of the proposed scheme with the LTE scheme.

Cognitive radio (CR) systems have been proposed for efficient usage of spare spectrum licensed to primary systems. This leads to the issue of providing as much spectrum to CR users as possible while not degrading the quality of service (QoS) of primary users of the spectrum. This paper proposes a novel cooperation scheme between primary and CR users to guarantee QoS of primary users up to the cell edge while making the licensed spectrum available for opportunistic access by the CR users. Thus the proposed method can provide a so called ¿win-win strategy¿ by benefiting both primary and CR users. The proposed scheme solves efficiently the Gaussian multiple access problem for power allocation of primary systems that cooperates with CR systems. We show that the Gaussian multiple access problem can be formulated as a standard semi-definite programming (SDP) problem. Numerical results show that the QoS of primary users at the cell edge is improved by the proposed cooperative access scheme.

In this paper, we propose a spectral efficiency enhancement algorithm through simultaneous accesses to heterogeneous networks, where a mobile station (MS) can simultaneously access different non-interfering networks with different radio access technologies (RATs). This simultaneous access (i.e., RAT diversity) is determined in terms of the distributed optimal solution, which implies that MSs can decide whether they connect with multiple RATs or not. To derive the optimal solution, we first show the advantages of multiaccess (MA) by an example in heterogeneous networks, and analyze the spectral efficiency of MA in multi-RAT system. Through our analysis and simulations, it is shown that the proposed algorithm is able to achieve the increase of spectral efficiency compare with vertical handoff (VHO) method, which selects only one network having the best channel quality. As a result, the proposed MA algorithm can be considered as a viable solution to get more spectral efficiency in heterogeneous environments.

In this paper, we analyze the advantages of multi-access (MA) systems in heterogeneous networks, where a mobile station (MS) can simultaneously access different non-interfering networks with different radio access technologies (RATs). For this analysis, we consider the following problem: How many RATs should the MS connect to? First, the beneficial aspects of MA is demonstrated by a simplified example, and then, MA methods in multi-RAT systems are investigated in terms of the spectral efficiency. Through our analysis and simulations, it is shown that usage of 2-RAT MA is enough to obtain most of the advantages of MA (i.e., network diversity). Also, MA is able to achieve an increase in spectral efficiency, which is compared to the increase obtained by vertical handoff (VHO) method. As a result, 2-RAT MA can be considered as a viable solution to get more spectral efficiency in multi-RAT systems and reduce signaling overhead, as compared to other MA scheme.

For maximizing the benefit of network coding in two-way relay networks, the data rate of links from sources to a relay should be the same, since only the same number of received bits can be network-coded at a given time and the rate for broadcast at the relay is limited by the minimum rate over all links. Therefore, we investigate rate control scheme based on power control to maintain the link to be symmetrical while maximizing sum of data rates. We show the impact of rate asymmetry and formulate such problem as a max-min rate optimization problem. A simple iterative solution based on binary search algorithm is provided. Numerical results show the radio resource utilization in terms of bit/sec/Hz/watt is maximized by the proposed rate control scheme when the network coding is applied.

This paper suggests an efficient power allocation scheme for multiple input and multiple output - orthogonal frequency division multiplexing (MIMO-OFDM) systems achieving near-optimum. We deal with power allocation problem with low complexity. It is well known that the conventional waterfilling algorithm runs repetitive calculations and logarithm operations to find out an optimal water level over whole time and spatial dimensions. To cope with this complexity problem, we investigate the problem structure originated from the characteristic of optimal waterfilling in MIMO-OFDM system through convex analysis, which leads to a unique step structure for optimal power allocation. Taking advantage of this structure, we propose a successive waterfilling algorithm with low complexity. The proposed algorithm calculates the allocated power of each subchannel recursively after setting an initial power by the step structure. Underlying assumption is that the perfect channel state information is available to both transmitter and receiver sides.

In wireless systems, a relay station (RS) is introduced to overcome capacity degradation in a shadowing area or a cell edge. Various relay schemes have been proposed to improve capacity by increasing link quality and diversity gain. However, there is no study about relay scheme in multiple cooperative relay network environments which means that more than one RS are cooperatively operated in same domain : time, frequency and space. In conventional relay scheme, RSs operates individually and independently, so resources are allocated exclusively due to interference. It brings inefficient and nonflexible use of resources problem. Therefore, although it brings the increase of performance for specific RS coverage, total system performance is not improved. In this paper, we propose a novel relay system model and frame structure. Also, cooperation strategy of multiple relays for adaptive transmission modes which maximizes diversity gain is described. Simulation shows our proposed scheme has better performance compared with existing schemes.

Partner selection is a critical process for maximizing the effect of spatial diversity in cooperative communications. Most studies have proposed to select a partner node with best received SNR. These algorithms can achieve maximum system throughput in practical cooperative environment, but incur frequent coupling which leads additional system load, such as power consumption and data transmission delay. Furthermore, mobility of nodes, which causes Doppler shift of received signals, is not generally considered. In this paper, we propose a novel partner selection criterion which takes both SNR and mobility into account. Our simulation results show that the proposed algorithm keeps high system throughput, while minimizing system load.

In this paper, we studied the method that improves the downlink performance of cellular relay system in multiple-cell environment by using cognitive radio. When relay stations in the network have spectrum agility, they can establish downlink channels which are orthogonal to downlink of base station. In this way, interference between base station and relay station can be reduced and spectral resource can be utilized more efficiently as well. To investigate the performance gain with spectrum agility, we quantify channel usage of the incumbent systems by i.i.d ON/OFF model and evaluate the normalized system capacity of spectrum-agile cellular relay network. The result of this paper shows that the spectrum-agile cellular relay network relieves other-cell interference and thus the system capacity is improved.

In cognitive radio networks, the sensing capability of a secondary user is crucial to guarantee the privileged use of a primary user. One of major parameters, the sensing duration (i.e., ldquoquiet periodrdquo) in a frame by a secondary user, during which the secondary user does not access the spectrum, can affect performance of both. In this paper, we examine a sensing scheme involved in a compromise between a secondary user and a primary user. Also, we provide problem formulation from each user perspective with following objectives: throughput maximization from the secondary userpsilas perspective, and interfering duration minimization from the primary userpsilas perspective. Three parameters for the optimization, sensing duration, sensing interval (i.e., time between adjacent sensing durations), and the arrival rate of the primary user, are considered in the analysis. Simulation results validate our analysis.

In multicarrier systems, the feedback information from a mobile station to a base station can be used to efficiently allocate the radio resource such as power and/or subchannels to a user. The quality of subchannel is measured by a signal-to-noise ratio (SNR), whose range, in a real system, must be quantized because channel information should be represented as a finite number of bits due to signaling overhead. Therefore, some subchannels whose data rates are the same can exist even though the measured SNRs are different. In this paper, we propose an efficient and fair algorithm to allow users and subchannels to compete through bidding. The bidding price of each user is determined by the difference between the data rate of the best subchannel and the second best, where the highest bidder wins the use of the best subchannel. Simulation results show that the proposed algorithm has better performance than a random selection method in terms of throughput and fairness.

This paper considers a sum-rate-maximizing power allocation for the Gaussian cognitive multiple-access channel (MAC), where primary users and secondary users may communicate under mutual interference. Formulation of the problem as a standard nonconvex quadratically constrained quadratic problem (QCQP) provides a simple method to find a solution using semidefinite relaxation (SDR). Numerical examples for the comparison illustrate a tradeoff between the maximum sum-rate and computational complexity.

In this paper, we propose a performance analysis model to analyze the joint effects of queueing and adaptive transmission in multiple input multiple output (MIMO) systems. We analyze various performance measures of the queueing model proposed and based on these measures, we provide a new model for adaptive modulation and space time block codes in MIMO Nakagami fading channels. We also provide numerical results under various system parameters.

Beyond third generation (B3G) mobile communication systems may allow users to simultaneously launch multiple multimedia applications with very diverse quality of service (QoS) requirements. In order to achieve resource efficiency, if two applications of the same user have different bit-error-rate (BER) constraints, depending on the multi-user mutiple access technology, the symbols of these two applications need to be transmitted using, either different frequency sub-bands, or different times, or different codes, or different combinations of these. We derive achievable user-throughput regions (AUTRs) for time division (TD), frequency division (FD), and code division (CD) application media access (AMA). These AUTRs are based on a capacity formula, which takes into account the BER of each application. This is a novelty with regard to existing works, where only the average signal-to-noise ratio (SNR) is used, regardless of users' applications. Moreover, the existing works treat multi-user system capacity, while we focus on the capacity achievable by a user with multiple applications. These AMA techniques are also compared in terms of complexity and implementability.

A larger amount of works has been reported for forward link CDMA scheduling compared to its reverse link case. In this paper, we propose generalized proportional fair (GPF) scheduling algorithms for uplink CDMA packet services, which have the ability to control the degree of fairness (DoF). We first establish a framework for GPF scheduling in wireless networks which render a GPF scheduling as a well-established optimization problem. For uplink CDMA, it is known that the rate sum maximization is achieved when the best K users in terms of channel condition transmit simultaneously. Based on this principle and the proposed GPF framework, we propose two GPF packet scheduling algorithms for uplink CDMA. Performance of our algorithms is verified through simulations.

OFDM has been a widely accepted technology in high rate and multimedia data service systems, such as 3G Long Term Evolution (3G LTE) system in the 3rd Generation Partnership Project (3GPP). In this paper, we propose a new cell search scheme based on the frequency domain sequence hopping of synchronization channel symbols. The assigned hopping pattern provides frame boundary information as well as cell identification (cell ID) to a mobile station (MS). The proposed synchronization channel structure allows MS to acquire OFDM symbol/frame timing, cell ID and frequency offset estimates in the initial cell search stage. The cell search in MS is composed of 2 steps; OFDM symbol synchronization step, frequency offset correction and cell ID/frame boundary detection step. We evaluate the performance of proposed scheme under various channel environments. The impacts of multipath fading, vehicular speed and frequency offset on the performance are investigated. We also compare the performance of proposed scheme with 3G LTE cell search scheme.

Recently, Wireless Local Area Network (WLAN) mesh networks are attracting significant attention. Because the Institute of Electrical and Electronics Engineers (IEEE) 802.11 Medium Access Control (MAC) protocol has been designed for single- hop networks, the performance of WLAN mesh networks degrades due to congestion, and buffer overflow in intermediate Mesh Nodes (MNs). In this article, we propose new congestion control scheme which applies Adaptive Modulation and Coding (AMC) scheme and effective buffer usage to enhance the performance. AMC scheme uses multiple fragmentation thresholds, modulation levels and coding rates for various data sizes according to Channel State Information (CSI). Because CSI can be used more effectively to squeeze more bits into the medium, the throughput is enhanced. Simulation results show that the proposed scheme achieves much higher throughput than other congestion control schemes.

OFDMA is suitable for multiple access technique for packet- based wireless communication system. OFDMA-based system can achieve high system throughput by multi-user diversity in limited radio resource. One important technique to increase system performance is a scheduling supporting multi-traffic in the 4G system. The proposed algorithm provides priority regarding delay requirement and then allocates user's packets in a frame according to required data rate of each traffic class. Simulation results show that proposed algorithm satisfies require data rate of real time and non-real time traffic class at large number of users and has low outage ratio.

In mobile WiMAX based on the IEEE 802.16e wireless MAN technologies using an OFDMA, the system throughput is improved by subchannelization schemes such as Diversity and AMC in multipath fading channel environment. Especially, in high mobility environment, mobile WiMAX systems uses FUSC which is one of the diversity subchannelization schemes, and get frequency diversity under multipath fading channel. However, the FUSC scheme is not flexible for channel variations inherent to user's speed. In this paper, we propose dynamic subchannelization scheme under multipath fading channels which is varied with a user's speed. Simulation results show that the proposed subchannelization algorithm leads to better the system throughput as compared to conventional subchannelization scheme such as FUSC in various channel environments.

We develop a novel auction algorithm for subchannel allocation using the difference of throughput among subchannels to allow users to compete through bidding. This bidding price is calculated by the difference between the data rate of the best subchannel giving the maximum transmission rate and the second best one. Regarding this throughput difference as bidding price, the highest bidder wins the use of his best subchannel. All users try to minimize their potential loss by causing not to receive the best subchannel so they can maintain fairness by balancing the received throughput. This bidding price means the valuation or cost the user can pay for his/her subchannel with the maximum transmission rate. This is called willingness to pay in economic theory. It is the competitive fairness that a user reveals his valuation through bidding procedure and he/she is responsible for his action and its resulting data rate [1]. The algorithm we proposed can achieve a competitive fair subchannel allocation through auction mechanism. Numerical result shows that the proposed algorithm has the similar performance with sum rate maximization and guarantees fairness by minimizing user's potential throughput loss.

Vertical handoff is a switching process for seamless communication between heterogeneous wireless networks. By applying pre-handoff concept for the heterogeneous traffic, we propose a two-step vertical handoff algorithm, which can select the best suitable system to a user. From this point of view, we can get a better performance than existing vertical handoff algorithms. Simulation results show that the proposed algorithm increases the throughput and decreases the handoff rate and the connection time ratio with target systems.

In a wireless system, the relay station (RS) is introduced to increase the data rate of a mobile station (MS) in a shadowing area or a cell edge. RS is stationary of non-stationary and takes charge of relaying between a base station (BS) and an MS. However, the adoption of several RSs causes inefficient time-slot. In this paper we propose a novel algorithm for utilizing RSs and provide an appropriate frame structure. We divide the zone into two, inner and outer zone for a sectorized cell structure. RSs are stationary at inner zone edge in each sector and connect an MS at outer zone with a BS. And a special time-slot is shared by all RSs existing in the same sector. The proposed algorithm will increase the opportunity of connection between a BS and an MS out of RS coverage. Simulation result shows that throughout increases about three times in inner and outer zone.

Beyond third generation (3 G) mobile communication systems are expected to support various multimedia services. A mobile user, under the constraint of his/her maximum transmission rate and power may launch multiple services simultaneously. In the uplink, the mobile station (MS) will need to allocate its limited resources (processing and transmit power, rate) among the user's different services, based on the user's preferences and the services' quality of service (QoS) requirements. In this paper, we derive an optimum algorithm to allocate uplink available rate and power to multimedia services. The algorithm maximizes user satisfaction under QoS, rate and power constraints.

As the demand for high data rate increases, load balancing across cell is highly desirable. A handover (HO) among frequency assignment (FA) may be possible for load balancing theoretically, when a serving FA is crowded to accommodate additional bandwidth request in such system as IEEE 802.16e, where the multiple FAs are possible. However, this handover is impossible in the current specification because an indication to target FA is not defined. It also requires unnecessary long scanning and network re-entry procedure. In this paper, we propose novel inter-FA handover, handover among FAs for load balancing by modifying general handover algorithm. It also satisfies HO user's quality of service (QoS) by reducing HO latency, unnecessary scanning, and network re-entry. We compare with previous HO schemes for load balancing by simulation. We show that this HO scheme can achieve significantly better performance in HO user's QoS and HO delay.

In this paper, we propose a packet-by-packet scheduling algorithm which grants priority to each packet instead of a user. The proposed scheduler classifies packets inside of each user into three classes such as emergency, near emergency, and non-emergency packets based on packet delay ratio, and applies different scheduling schemes to grant priority in each region respectively. It can be possible to manage packets more efficiently for guaranteeing various Quality of Services (QoS) in wireless multimedia systems. Simulation results show that the proposed scheme offers higher system throughput and lower packet drop rate than other scheduling algorithms.

Vertical handoff is the switching process to provide seamless service among heterogeneous systems. An accurate estimation for utilities of target systems must precede a handoff for the efficient use of system resources. In this paper, we propose a vertical handoff decision algorithm based on the utility function to satisfy wireless QoS. Shannon's capacity is used to maximize throughput and traffic load is considered to utilize systems evenly. The tradeoff between handoff rate and throughput is investigated based on user's mobility. Simulation results show that the utility function effectively increases throughput

In this paper, we propose a novel framework for proportional fair scheduling in wireless communications. Our framework includes a new definition of generalized proportional fairness, new objective function, and definition of degree of fairness which is widely applicable and has the ability of controlling the degree of fairness. We illustrate application of our framework to the CDMA downlink and provide simulation results

This paper observes the inter-carrier interference (ICI) by Doppler effect in time domain in orthogonal frequency division multiplexing systems. This observation allows us to propose a new time domain two-stage equalization scheme that iteratively cancels the ICI. The proposed scheme consists of the following two stages. First, we apply low-complexity linear minimum mean squared error (MMSE) employing partial rank of time impulse response matrix to shorten the ICI components into diagonal region. Second, we propose new parallel interference cancellation with hard decision feedback to remove the residual ICI. Performance evaluations and complexity analyses show that the bit error rate and the signal-to-interference-plus-noise ratio performances of the proposed scheme are very close to those of the classical frequency domain linear MMSE equalization scheme with much reduced complexity

In order to provide a smooth migration toward 4G, studies on 3G long-term Evolution (3G-LTE) have been announced recently in third generation partnership project (3GPP) [1] and standardization work is under way. This paper investigates multiplexing method combined with transmit antenna diversity for the downlink control channels in 3G- LTE. Four schemes, such as FDM-STBC, CDM-STBC, FDM- SFBC and CDM-SFBC, are investigated for the downlink control channels, in particular, for one bit type control channels. Through computer simulation, the receiver performance of these candidate schemes are analyzed under multi-path fading channel environments. The effects of channel estimation, Doppler shift and the number of users on the performance are investigated. It is shown that the CDM-SFBC outperforms other schemes. We believe that results will provide beneficial information to design the 3G-LTE downlink control channels.

We suggest load sharing algorithm that can be applied between heterogeneous wireless systems. The basic idea of sharing load between different systems is to transfer users in a highly loaded system to a lowly loaded system. In this scenario, we need a common load measure that can be used in different systems. The degree of a load in cellular systems is affected by many factors such as the number of users, channel conditions and the required QoS(quality of service). To accommodate such factors in a load measure, we propose a new measure based on each user's satisfaction level. The validity of the measure and the performance of the load sharing algorithm are tested by simulation

In this paper, we propose a heuristic dynamic channel assignment (DCA) algorithm to achieve the tradeoff between system throughput and fairness in downlink OFDMA systems. The proposed algorithm is divided into two stages: first, a proportional fairness is taken into account with quality-of- service (QoS) guaranteed to users for the system to accommodate as many users as possible; second, the remaining subcarriers are assigned for system throughput to be maximized. Numerical results reveal that a good tradeoff between system throughput and fairness is achieved. Furthermore, as a performance measure, the probability of outage is significantly reduced when compared to the optimal water-filling algorithm.

In this letter, an analysis on CDMA forward link capacity with hard and soft handoffs, when a handoff decision is based on filtered pilot signal strengths, is provided. For the soft handoff, capacity based on three different power allocation schemes is investigated: equal power, equal signal to interference ratio and selection diversity. Contrary to previous results that soft handoff provides a capacity decrease in the CDMA forward link, it is concluded that soft handoff mitigates capacity loss due to filtering through diversity gain, and may in fact provide higher capacity.

This paper presents and evaluates the performance of a temporal dynamic spectrum allocation (DSA) scheme based on the CDMA as an alternative to the fixed spectrum allocation (FSA) methods. The paper considers the spectrum allocation between two code division multiple access (CDMA) systems with different time-varying traffic pattern. The traffic pattern is based on the real CDMA traffic data from Daegu urban area in Korea. A proposed algorithm is investigated by simulation based on CDMA call processing and shows that an algorithm can produce significant gains for the RAN in DSA.

We suggest an iterative power and greedy subcarrier allocation algorithm to improve rate-sum capacity in an uplink OFDMA system. For the downlink, it has been accepted as an optimal solution that each subcarrier is allocated to the user with the best channel condition and power is allocated by water-filling over subcarriers. However, it is not true in an uplink OFDMA system which has distributive power constraints. We formulate the optimization problem having constraints power and subcarriers in uplink, then draw two necessary conditions for optimality. Using the conditions, we propose a greedy subcarrier allocation algorithm based a marginal rate junction and iterative power allocation algorithm based on water-filling. Simulation results show that the enhanced system capacity is achieved by our proposed scheme.

We propose a structure of an array transceiver for W-CDMA base station based on cdma2000-1x RTT. The structure has several advantages, such as a practical SINR (signal-to-interference-plus-noise power ratio) measure, efficient channel estimation, and an array transceiver based on LMS/DA (LMS with decision-aid), in the cdma2000-1x system. Under this structure, BER (bit error rate) improvements by both beamforming and an estimation scheme based on channel state information are analyzed for 614.4 ksps in the vehicular environment model provided by ITU-R.

We propose an efficient methodology to support the maximum possible throughput of NRT (non-real time) users while satisfying the QoS (quality of service) requirements of all ART (almost real time) for a mixed service in HDR (high data rate). Moreover, we present the modified exponential rule that can improve the total throughput and individual average throughput while guaranteeing the minimum throughput and delay requirement for ART service alone. A token-based mechanism to guarantee each minimum throughput of all users is employed. Simulation results are shown in terms of both average packet delay and throughput according to the choice of total or individual user. Our main conclusion is that adaptive scheduling algorithm in conjunction with both the token bucket and the adaptive rule provides an effective foundation for supporting a mixed service in the system.

In this paper, a proportional fairness scheduling for the non-realtime service in high speed data transmission systems is proposed For a forward link scheduler even in CDMA systems, it is shown that the time division through rate control provides better performance than code division through power control. Our proportionally fair scheme is based on the average requested rate, requested rate and average transmission rate. Therefore, long-term channel as well as short-term channel conditions and opportunities of transmissions are taken into account for the scheduler to determine the order of transmission to maximize the average throughput. The effect of the proposed scheduling scheme is investigated to result in the increase of total average throughput while maintaining the proportional fairness ever the existing schemes through simulations.

In this paper, we suggested an algorithm to guarantee QoS (Quality of Service) and provide priority for users in 1xEV-DO systems. On forward link, a selected user is served in a TDM fashion with full base station power. The transmission rate depends on the forward link channel quality of each access terminal, which is reported by DRC channel. 1xEV-DO systems adopted an efficient scheduling algorithm of proportional fairness. This algorithm takes channel condition and fairness into account but leaves QoS and priority unattended. These issues are as important as the throughput and fairness in high-speed data networks. A proportional fairness algorithm which guarantees QoS and considers priority is presented. Several figures of merit are addressed compared to other schemes through simulations.

In this paper, we proposed an efficient packet scheduling scheme, where the tradeoff of channel condition and QoS (quality of service) is factored according to the user traffic. It can be performed by adding the exponent term to the part of DRC (data rate control) which indicates the channel condition, in the proportional fair algorithm. With measuring the current level of supporting the QoS and controlling the DRC exponent, the proposed scheme can enhance the overall throughput without violating the QoS threshold.

A call admission control (CAC) scheme for downlink multimedia services in a WCDMA system is proposed. Admission control based on instantaneous measurements may cause capacity loss and quality of service (QoS) degradation because of abrupt fluctuations of the power level at the base station (BS). Instead, both the average power level of real-time circuit services and the average queue size of non-real-time packet services are considered in our scheme. The performance of the proposed admission control scheme is investigated by simulation results in terms of, e.g., blocking probability, outage probability, average throughput, and average queue size.

An efficient base station (BS) power allocation scheme for the forward link is proposed to to improve the overall throughput in a multicell high data rate (HDR) system, which is designed to support a high data rate. In HDR, if a cell is properly designed, users located close to a BS acquire an excessive signal to interference power ratio (SIR) for a maximum achievable data rate. This excessive power results in lower SIR for users at cell boundary. By allocating lower power for users near a BS than the maximum power, other-cell interference can be alleviated to users near the cell boundary. Even though HDR adopts time division duplexing (TDD) type of scheduling, the capacity can be increased through the control of interference. Simulation results validate the throughput gain, which is about 6/spl sim/9% under ideal condition.

In order to perform coherent demodulation under fading channel conditions, channel phase and amplitude estimation are required at the receiver. In WCDMA/FDD (wideband code division multiple access frequency division duplexing), proposed for the third-generation mobile communication systems, downlink channel estimation can be performed in both CPICH (common pilot channel) and DPCCH (dedicated physical control channel). Considering the different link quality between CPICH and DPCCH according to the location of a mobile station (MS), estimation schemes that use both channels are suggested and their performances are compared.

A packet transmission scheduling scheme is proposed in a multicode WCDMA/TDD network. Multicode allocation based on SIR and traffic load, for packet transmission with variable rate, is investigated. The proposed scheme gives consideration to delay control and takes priority into account for on-going users. Delay control minimizes the buffer size and supplies fairness to users. Priority to on-going users prevents packets being discarded during transmission. The effect of delay control and giving priority to the on-going users is investigated with respect to system performance and throughput.

In this paper, mixed voice and data packet traffic handling schemes are presented in a wireless multimedia communication environment. Three different schemes are provided with analysis and simulation for comparison on the blocking probability and delay characteristics as performance measures. Analytical models such as a bivariate Markov process are provided and extensive simulation experiments are carried out to investigate the impact of major parameters on the system performance. These reveal that mixed priority schemes for delay sensitive data outperform error-sensitive data with queueing. Also, an optimal queue size as well as the optimal number of reserved channels for handoff delay-sensitive data are given for various traffic conditions.