Integrated sensing and communication (ISAC) is emerging as a pivotal technology for next-generation wireless networks. However, existing ISAC systems are based on fixed-position antennas (FPAs), which inevitably incur a loss in performance when balancing the trade-off between sensing and communication. Movable antenna (MA) technology offers promising potential to enhance ISAC performance by enabling flexible antenna movement. Nevertheless, exploiting more spatial channel variations requires larger antenna moving regions, which may invalidate the conventional far-field assumption for channels between transceivers. Therefore, this paper utilizes the MA to enhance sensing and communication capabilities in near-field ISAC systems, where a full-duplex base station (BS) is equipped with multiple transmit and receive MAs movable in large-size regions to simultaneously sense multiple targets and serve multiple uplink (UL) and downlink (DL) users for communication. We aim to maximize the weighted sum of sensing and communication rates (WSR) by jointly designing the transmit beamformers, sensing signal covariance matrices, receive beamformers, and MA positions at the BS, as well as the UL power allocation. The resulting optimization problem is challenging to solve. Thus, we propose an efficient two-layer random position (RP) algorithm to tackle it. In addition, to reduce movement delay and cost, we design an antenna position matching (APM) algorithm based on the greedy strategy to minimize the total MA movement distance. Extensive simulation results demonstrate the substantial performance improvement achieved by deploying MAs in near-field ISAC systems. Moreover, the results show the effectiveness of the proposed APM algorithm in reducing the antenna movement distance, which is helpful for energy saving and time overhead reduction for MA-aided near-field ISAC systems with large moving regions.

This paper investigates energy efficiency maximization for movable antenna (MA)-aided multi-user uplink communication systems by considering the time delay and energy consumption incurred by practical antenna movement. We first examine the special case with a single user and propose an optimization algorithm based on the one-dimensional (1D) exhaustive search to maximize the user’s energy efficiency. Moreover, we derive an upper bound on the energy efficiency and analyze the conditions required to achieve this performance bound under different numbers of channel paths. Then, for the general multi-user scenario, we propose an iterative algorithm to fairly maximize the minimum energy efficiency among all users. Simulation results demonstrate the effectiveness of the proposed scheme in improving energy efficiency compared to existing MA schemes that do not account for movement-related costs, as well as the conventional fixed-position antenna (FPA) scheme. In addition, the results show the robustness of the proposed scheme to imperfect channel state information (CSI) and provide valuable insights for practical system deployment.

In this paper, we investigate physical layer security (PLS) for full-duplex (FD) multi-user systems. We consider a base station (BS) that operates in FD mode and transmits artificial noise (AN) to simultaneously protect uplink (UL) and downlink (DL) transmissions. Conventional fixed-position antennas (FPAs) at the FD BS struggle to fully exploit spatial degrees of freedom (DoFs) to improve signal reception and suppress interference. To overcome this limitation, we propose a novel FD BS architecture equipped with multiple transmit and receive movable antennas (MAs). The MAs introduce the DoFs in antenna position optimization, which can improve the performance of secure communication systems. To serve users and counter the cooperative interception of multiple eavesdroppers (Eves), we formulate a sum of secrecy rates (SSR) maximization problem to jointly optimize the MA positions, the transmit, receive, and AN beamformers at the BS, and the UL powers. We propose an alternating optimization (AO) algorithm, which decomposes the original problem into three sub-problems, to solve the challenging non-convex optimization problem with highly coupled variables. Specifically, we propose the multi-velocity particle swarm optimization (MVPSO), which is an improved version of the standard particle swarm optimization (PSO), to simultaneously optimize all MA positions. The transmit/AN beamformers and the UL powers are solved by successive convex approximation (SCA). The optimal receive beamformer is derived as a closed-form solution. Simulation results demonstrate the effectiveness of the proposed algorithms and the advantages of MAs over conventional FPAs in enhancing the security of FD multi-user systems.

This paper investigates physical layer security (PLS) in a movable antenna (MA)-assisted full-duplex (FD) system. In this system, an FD base station (BS) with multiple MAs for transmission and reception provides services for an uplink (UL) user and a downlink (DL) user. Each user operates in half-duplex (HD) mode and is equipped with a single fixed-position antenna (FPA), in the presence of a single-FPA eavesdropper (Eve). To ensure secure communication, artificial noise (AN) is transmitted to obstruct the interception of Eve. The objective of this paper is to maximize the sum secrecy rate (SSR) of the UL and DL users by jointly optimizing the beamformers of the BS and the positions of MAs. This paper also proposes an alternating optimization (AO) method to address the non-convex problem, which decomposes the optimization problem into three subproblems and solves them iteratively. Simulation results demonstrate a significant performance gain in the SSR achieved by the proposed scheme compared to the benchmark schemes.

Full duplex (FD) radios have attracted extensive attention due to the co-time and co-frequency transceiving capability. However, the potential gain brought by FD radios is closely related to the management of self-interference (SI), which imposes high or even stringent requirements on SI cancellation (SIC) techniques. When the FD deployment evolves into next-generation mobile networking, the SI problem becomes more complicated, significantly limiting its potential gains. In this paper, we conceive a multi-cell FD networking scheme by deploying a reconfigurable intelligent surface (RIS) at the cell boundary to configure the radio environment proactively. To achieve the full potential of the system, we aim to maximize the sum rate (SR) of multiple cells by jointly optimizing the transmit precoding (TPC) matrices at FD base stations (BSs) and users, as well as the phase shift matrix at the RIS. Since the original problem is non-convex, we reformulate and decouple it into a pair of subproblems by utilizing the relationship between the SR and minimum mean square error (MMSE). The optimal solutions of TPC matrices are obtained in closed form, while both complex circle manifold (CCM) and successive convex approximation (SCA) based algorithms are developed to resolve the phase shift matrix suboptimally. Our simulation results show that introducing an RIS into an FD networking system not only improves the overall SR significantly but also enhances the cell edge performance prominently. More importantly, we validate that the RIS deployment with optimized phase shifts can reduce the requirement for SIC and the number of BS antennas, which further reduces the hardware cost and power consumption, especially with a sufficient number of reflecting elements. As a result, the utilization of an RIS enables the originally cumbersome FD networking system to become efficient and practical.

In this paper, we propose a multi-cell full-duplex (FD) networking scheme by deploying a reconfigurable intelligent surface (RIS) at the cell boundary to configure the radio environment proactively. We aim to maximize the sum rate (SR) of multiple cells by jointly optimizing the transmit precoding (TPC) matrices at FD base stations (BSs) and the phase shift matrix at RIS. Since the original problem is non-convex, we reformulate and decouple it into a pair of subproblems by utilizing the relationship between SR and minimum mean square error. The optimal solutions of TPC matrices are obtained in closed form, while a successive convex approximation-based algorithm is developed to resolve the phase shift matrix suboptimally. Simulation results show that introducing an RIS into the FD networking system can improve the overall SR significantly. More importantly, we validate that the RIS deployment with optimized phase shifts can reduce the requirement for self-interference cancellation (SIC) and the number of BS antennas effectively, especially with enough reflecting elements. As a result, the utilization of RIS enables the originally cumbersome FD networking system to become efficient and practical.

High mobility of vehicles causes time-frequency selective fading over physical channels within the Internet of Vehicles (IoV). To improve the resource utilization efficiency, a novel transmission strategy, based on dynamic pilot design, is proposed, in this article, to reduce the pilot consumption in doubly selective channel estimation for the multicast to vehicles running at different speeds. As the channel coherence time is mainly influenced by the receiver mobility in the multicast from a base station to vehicles, we define a multicast block as the channel coherence time of the slowest vehicle in the multicast group, where common pilot symbols are shared. Then, the multicast data destined for different vehicles are loaded into the block according to their own channel coherence times. To evaluate the performance and resource utilization of our dynamic pilot design, the metrics of overhead rate, spectral efficiency, and energy efficiency are formulated for the IoV multicast using multiple-input–multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) transmissions. In terms of these three metrics, illustrative numerical results on the comparisons between our dynamic pilot design and the conventional counterpart are provided, which not only substantiate that the former outperforms the latter but also present useful tools and specifications for the pilot design in the IoV multicast using MIMO–OFDM transmissions over doubly selective channels.

To promote energy and spectrum efficient communications in multiantenna channels, broadcast can provide a substantial gain in system throughput. However, the hardware constraints and strong Line of Sight (LoS) limit the implementation and performance of multiantenna broadcast in the Internet of unmanned aerial vehicles (UAVs). Based on the pseudo-Doppler principle, we propose a joint precoding and antenna array design to reduce the number of radio frequency (RF) chains required by the broadcast and free the LoS path from the interstream interference. The reduction of RF chains is realized by designing the precoding matrix that makes at least one of the transmit antennas have null inputs during any broadcast and, moreover, the LoS path is formed to match the obtained precoding matrix through antenna array design at the broadcasting UAV. The algorithms with low computational complexity for optimizing this design are developed to minimize the transmit power within the UAV broadcast paradigms. Theoretical formulation and numerical results in the metrics of sum data rate and bit error rate substantiate the validity of our proposed design, specifically in the Internet of UAVs with strong LoS.

In this paper, the concept of permutation-based transmissions is developed at the transport layer of short-packet communications, where the application-layer data is divided into two parts: one is conveyed by the permutation of various lengths in a group of packets, and the other is encapsulated into these various-length packets. The former part, referred to as permutation-conveyed data unit (PCDU), improves the goodput and reduces the latency. From a finite blocklength perspective, the maximal payload rate of permutation-based transmissions is formulated, based on which the goodput and latency are derived and obtained in analytical forms. Moreover, the spectral efficiency and energy efficiency are analysed. Illustrative numerical results on the performance and resource utilisation comparisons not only substantiate the advantages of our permutation-based transmissions over conventional transport-layer encapsulation schemes, but also provide useful tools and specifications for the PCDU design in short-packet communications.

In this paper, we consider an uplink Internet of Things (IoT) network consisting of time-sensitive devices and throughput-sensitive devices, focusing on effective coordination between different performance requirements. To improve the spectral efficiency, Non-Orthogonal Multiple Access (NOMA) is introduced to obtain a potential performance gain by assigning the spectrum resources to different types of devices with diverse performance requirements in a coordinative and resource-sharing manner. Considering the performance diversity of heterogeneous devices, we provide two NOMA user grouping strategies: Mixed Block Strategy (MBS) and Uniform Block Strategy (UBS) which configure NOMA user groups as those consisting of different types of devices and those containing only a single type of device, respectively. Then, we propose a hybrid resource allocation protocol by switching between these two strategies. The performance of a special case with two time-sensitive devices and two throughput-sensitive devices is first optimized to evaluate the proposed strategies, and then extended to compare with traditional strategy in the multi-user scenarios. Simulation results illustrate that MBS and UBS outperform the traditional strategy, i.e., lower Age of Information (AoI) and higher throughput, and have their own advantages at different system parameters. On the basis, the hybrid protocol can further improve the system performance.

In this paper, a novel transmission scheme, referred to as difference-based spatial modulation (DBSM), is proposed to improve the performance of spatial modulation (SM) within multi-antenna systems. The DBSM delivers two adjacent symbols in an arbitrary transmission, where one of the two symbols is radiated from a single transmit antenna. Different from conventional SM, the DBSM selects the active transmit antenna based on the difference between the two adjacent symbols. Although the other symbol is not physically radiated, the information carried by it is conveyed not only through the radiated symbol but also through the selection of active transmit antenna. For the purpose of performance evaluation, the proposed DBSM is compared with conventional SM in terms of bit error rate for the same system settings and the same multi-antenna configurations. Illustrative simulation results substantiates that our DBSM outperforms conventional SM while achieving the same data rate, specifically in the systems with low-order modulation.

In this paper, a multi-vehicle multi-task non-orthogonal multiple access (NOMA) assisted mobile edge computing (MEC) system with passive eavesdropping vehicles is investigated. To heighten the performances of edge vehicles, we propose a vehicle grouping pairing method, which utilizes vehicles near the MEC to assist edge vehicles as full-duplex relays. For promoting transmission security, we employ artificial noise to interrupt eavesdropping vehicles. Furthermore, we derive the approximate expression of the secrecy outage probability of the system. The combined optimization of vehicle task division, power allocation, and transmit beamforming is formulated to minimize the total delay of task completion for edge vehicles. Then, we design a power allocation and task scheduling algorithm based on the genetic algorithm to solve the mixed-integer non-linear programming problem. Numerical results demonstrate the superiority of our proposed scheme in terms of system security and transmission delay.

Abstract A full‐duplex (FD) multiuser multiple‐input multiple‐output (MU‐MIMO) system, where a FD base station (BS) with multiple antennas serves multiple half‐duplex (HD) user equipments (UEs) in both uplink (UL) and downlink (DL) via the same time‐frequency resources, is considered. UE scheduling is in demand to manage the UL‐to‐DL interference (UDI) incurred by the FD operation. Existing scheduling algorithms require UDI channel state information between each pair of the candidate UEs, which incurs a significant amount of overhead as the number of UEs grows. To reduce the overhead, a new UE scheduling algorithm that uses channel reciprocity and UL‐DL duality to design a scheduling algorithm based on downlink performance was designed. By selecting UEs only based on their DL channels and received UDI strength, the proposed scheme no longer requires the massive UDI channel state information (CSI). Numerical results demonstrate the proposed algorithm can achieve a near optimal performance without knowing any UDI CSI.

As the digital version of a continuous-time delay, the concept of fractional delay (FD) is exploited to approximate a desired delay that is not a multiple of the sampling interval. However, in FD filters, there is always a severe distortion at the beginning of delayed signals, referred to as head distortion. This letter identifies the cause of head distortion and proposes a solution to this problem for reducing the overall distortion in FD filters. For the purpose of performance evaluation, relative root-mean-square (RMS) error is formulated as a metric to quantify the overall difference between the frequency-domain response of an FD filter and the ideal one. Moreover, illustrative numerical results on the proposed scheme applied in FD filters with classical sinc, Farrow and Lagrange interpolation substantiate the validity and feasibility of our solution.

In this paper, the concept of opportunistic bits (OBs) is developed in short-packet communications and investigated from a finite blocklength perspective. In the OB-based transmission, the data unit of a packet is divided into two parts: OBs and conventional bits (CBs). The OBs are not physically transmitted but used to indicate the index of the time slot (TS) when the packet containing CBs is transmitted. The loading of a bulk of OB-based packets into multiple TSs can be modelled as a Repeated Balls-into-Bins process with a multi-queue storage. If the bulk is not large enough, certain combination(s) of OBs will not appear, which leaves certain TS(s) empty and hence reduces the TS load efficiency. To evaluate the OB-based transmission performance, we formulate its maximal payload rate and TS load efficiency. With the aid of these two formulations, the energy gain, the goodput, and the latency of OB-based short-packet communications are derived and obtained in analytical forms. For achieving further insights, illustrative numerical results on the resource utilisation efficiency and the performance not only substantiate the advantages of the OB-based transmission over the conventional but also provide useful tools and specifications for its design in massive short-packet communications.

To achieve physical layer security (PLS) with a flexible implementation, a novel design named security-oriented trellis coded spatial-modulation (SO-TCSM) is proposed in this article, where the transmitter does not know the channel state information (CSI) of wiretapping channels and relies on the legitimate CSI to vary the mapping patterns for the antenna information and the radiated information, aiming at the optimisation of free Euclidean distances between the resultant SO-TCSM symbols. Eavesdroppers cannot decode the confidential information delivered in the legitimate link, as they do not know the legitimate CSI and, hence, have no basis to acquire the transmitter's mapping pattern of the moment. Moreover, the SO-TCSM symbols are then compensated to maximise their Euclidean distances, which further improves the legitimate receiver's decoding performance while enhancing the PLS. However, the compensation results in high transmit power when the legitimate channels are in deep fades. To boost the energy efficiency, a constraint is set to limit the transmit power. Under this constraint, the SO-TCSM performance is investigated in terms of bit error rate and transmit power consumption. The outcome of these investigations substantiates that, compared to conventional TCSM designs, our SO-TCSM achieves better performance in the legitimate link with lower decoding complexity.

In this paper, a decode-and-forward (DF) short-packet relaying model is developed to achieve timely status updates for intelligent monitoring within the Internet of Things (IoT), where the status updates generated at an IoT device are delivered to a remote server with the aid of a relay in both half-duplex (HD) and full-duplex (FD) modes. To characterise the data freshness of status updates, we exploit the age of information (AoI) as a metric, which is defined as the time elapsed since the generation of the latest successfully decoded status update. The average AoI is formulated and minimised for both HD-DF and FD-DF relaying IoT networks in finite blocklength regime. For the HD-DF relaying, we introduce a perfect approximation of the average AoI to solve the problem of average AoI minimisation with the optimal blocklengths in two phases. For the FD-DF relaying, we propose an iterative algorithm to solve the problem of average AoI minimisation by optimising the relay’s transmit power and the blocklength. Illustrative numerical results not only substantiate the validity of our proposed algorithms, but also provide useful references for the IoT monitoring network design, specifically for the transmit power thresholds at the IoT device and the relay.

In a wideband full‐duplex system, the residual self‐interference (SI) channel exhibits significant frequency selective fading characteristics after radio frequency SI cancellation. Resource allocation using the difference between the signal channel and the residual SI channel is a new method of suppressing residual SI and increasing system capacity. In this work, the residual SI channel and the user uplink channel are modelled as multi‐path frequency selective fading channels that satisfy the Rayleigh distribution. To improve system capacity, the authors propose to allocate the spectrum resource avoiding occupation of subcarriers with high residual SI, while guaranteeing a fair subcarrier assignment (SA) and power allocation (PA). A sum rate of uplink maximisation is formulated, and an algorithmic solution is developed to effectively conduct SA and PA. Numerical results demonstrate the effectiveness of the scheme in increasing system capacity and suppressing residual SI.

Due to the severity of self-interferences, analog interference canceller is an essential part of a full duplex radio system. As the self-interference can potentially be even much stronger than the received signal, it must be meritoriously suppressed before analog-to-digital conversion. This paper is aimed to provide an optimal radio frequency domain multi-tap interference cancellation design. To this end, the following two key problems are addressed: the hardware design problem and the adaptive weight adjusting problem. For optimal hardware design, a trade-off between widening effective delay range and maximizing the minimum cancellation capability is formulated. The principles and guidelines for optimal solution and hardware parameter design are derived. We also formulate adaptive weight adjusting as a multi-dimensional optimization problem, which is proved to be non-convex while adjusting the attenuators and phase shifters independently. By using a coordinate transformation technique, it is then converted into a convex optimization problem, and a convergent iterative algorithm based on the gradient descent method is applied to obtain the global optimum. The hardware implementation and experimental results substantiated the effectiveness of the proposed principles and algorithms.

In this paper, a cooperative power control scheme is proposed for two-user Gaussian interference channel (GIC) to mitigate the interference and improve the sum-rate. In the proposed scheme, codewords are divided into several segments. By jointly adjusting the power of each segment for the two users, the proposed scheme achieves a balance between increasing the entropy of signal and decreasing the entropy of interference, and thus maximizes the sum-rate. To solve the sum-rate maximization problem, an iterative algorithm combining both simulated annealing and gradient descent methods is also proposed. Numerical results show that the proposed scheme not only achieves higher sum-rate, but also provides better user fairness compared with the traditional schemes.

This paper studies the application of non-orthogonal multiple access (NOMA) to a cooperative multicast system (termed CM-NOMA). In particular, the multicast subscribers are served as secondary users underlaying a primary user. To enhance the secondary user fairness and compensate for the primary user, a two-stage cooperative strategy is proposed by selecting a certain secondary user to perform NOMA transmission distributedly. The maximum ratio combining (MRC) is further employed to harvest spatial diversity. We explicitly formulate the primary outage probability and secondary ergodic throughput in closed form. Moreover, we derive the asymptotic expressions and accordingly investigate the power allocation optimization with a primary outage constraint to maximize the secondary throughput. Numerical results validate that the proposed scheme achieves superior secondary user fairness and primary outage performance as well as higher energy efficiency.

At the time of writing, vehicle-to-vehicle (V2V) communication is enjoying substantial research attention as a benefit of its compelling applications. However, the ever-increasing tele-traffic is expected to result in overcrowding of the available band. As a first resort, multiple input multiple output (MIMO) can be utilized to enhance the attainable bandwidth efficiency or link reliability. However, in hostile V2V wireless propagation environments, the achievable multiple-antenna gain is eroded by the channel correlation. As a promising MIMO technique, spatial modulation (SM) only activates a single transmit antenna (TA) in any symbol interval and, hence, completely avoids the inter-antenna interference, hence showing robustness against channel correlation. As a further powerful solution, non-orthogonal multiple access (NOMA) has been proposed for improving the bandwidth efficiency. Inspired by the robustness of SM against channel correlation and the benefits of NOMA, we intrinsically amalgamate them into NOMA-SM in order to deal with the deleterious effects of wireless V2V environments as well as to support improved bandwidth efficiency. Moreover, the bandwidth efficiency of NOMA-SM is further boosted with the aid of a massive TA configuration. Specifically, a spatio-temporally correlated Rician channel is considered for a V2V scenario. We investigate the bit error ratio performance of NOMA-SM via Monte Carlo simulations, where the impact of the Rician K-factor, spatial correlation of the antenna array, time-varying effect of the V2V channel, and the power allocation factor is discussed. Furthermore, we also analyze the capacity of NOMA-SM. By analyzing the capacity and deriving closed-form upper bounds on the capacity, a pair of power allocation optimization schemes are formulated. The optimal solutions are demonstrated to be achievable with the aid of our proposed algorithm. Again, instead of simply invoking a pair of popular techniques, we intrinsically amalgamate SM and NOMA to conceive a new system component exhibiting distinct benefits in the V2V scenarios considered.

In spatial modulation (SM) systems, when channel state information is available at the transmitter, adaptive power allocation can be exploited to enhance the SM performance. In this paper, optimal power allocation in SM systems is considered from an information-theoretical view. First, as there is no closed-form expression of the SM capacity, the instantaneous mutual information is formulated in an analytic form for SM systems with two transmit antennas. Then, two power-allocation algorithms are proposed to maximize the SM mutual information. One is a sub-optimal power-allocation algorithm that is established in closed form to maximize the upper bound of SM mutual information. The other is an iterative algorithm for optimal power allocation that is proposed to achieve the maximum mutual information of SM systems while dramatically reducing the operational complexity compared with global computer searching. To evaluate the performance of the proposed power-allocation algorithms, numerical and simulation results are reported in terms of outage capacity and ergodic capacity, which demonstrates that the proposed power-allocation algorithms significantly improve the SM performance, compared with conventional equal-power allocation.

Ventricular tachyarrhythmia, in particular Ventricular Fibrillation (VF), is the primary arrhythmic event to cause Sudden Cardiac Death (SCD). Thus, the quick and accurate detection of a VF event is crucial for capturing the life-threat cardiac arrhythmias in real time. However, almost all existing VF detection algorithms are challenged by low accuracy or/and high complexity. To address this challenge, a Successive Projections Algorithm (SPA)-weighted Arrhythmias-risk ValuatING (SAVING) algorithm is proposed, in which SPA method is first applied to valuate arrhythmias-risk clinical features with using fisher criterion. Clinical trials show that it can obtain accuracy (Ac) of 96.81%, sensitivity (Se) of 95.41%, and specificity (Sp) of 97.15% in our WE-CARE 2.0 system. Compared to conventional algorithms, clinical tests demonstrate that the SAVING algorithm achieves comparative gains, which is a useful tool that can be embedded into WE-CARE systems and Automatic External Defibrillators.

As defined by WHO and ITU, mobile health (mHealth) is expected to change healthcare service modes and will be at the core of the future healthcare system. As for considering human activities, hotspot and indoor environments are the major scenarios to carry mHealth services (e.g., homecare). To accommodate mHealth services, dense/superdense small-cell layout in Heterogeneous Networks (HetNets) is a typical deployment scenario. On the other hand, mHealth services should be guaranteed with reliability and security in any wireless networks, since health-risk or medical-related information involved. In this study, we focus on how to guarantee control-information delivery in HetNets, so that mHealth users can be allowed to access wireless facilities reliably. To handle this challenge, we extend Interference Self-Coordination theory into HetNets, in order to enable service-sensitive healthcare services in mobile networks if needed. The system-level simulation experiments demonstrate that our proposal can achieve significant performance gain: the SINR of control channel is increased by around +104%; the packet error-loss rate can be reduced by -73%; the packet delay is reduced by -46%. These gains are valuable for quality-sensitive applications in HetNets, such as mHealth.

Full duplex is a promising technique for enhancing spectral efficiency in wireless relay networks. In this paper, we study a three-node relay network consisting of a full duplex base station, a half duplex relay station, and a half duplex mobile station. Four kinds of decode-and-forward strategies are analyzed in terms of achievable rate region and sum-capacity, and a hybrid decode-and-forward scheme, which adaptively selects the best among the four strategies, is proposed to achieve the maximized capacity according to the channel conditions. Simulation results compare the capacities of the four kinds of strategies, and show that the proposed hybrid scheme provides significant capacity gain, especially in the edge of the cell.

In this paper, the authors study a half‐duplex two‐way relay channel with correlated sources exchanging bidirectional information. In the case, when both sources have the knowledge of correlation statistics, a source compression with physical‐layer network coding scheme is proposed to perform the distributed compression at each source node. When only the relay has the knowledge of correlation statistics, the authors propose a relay compression with physical‐layer network coding scheme to compress the bidirectional messages at the relay. The closed‐form block error rate expressions of both schemes are derived and verified through simulations. It is shown that the proposed schemes achieve considerable improvements in both error performance and throughput compared with the conventional non‐compression scheme in correlated two‐way relay networks.

Motivated by the concept of spatial modulation (SM), a differential scheme has been recently proposed. This scheme, termed as differential (D-)SM, dispenses with channel estimation while maintains a similar bit error rate (BER) performance to SM. The conventional optimal DSM detector based on a maximum likelihood (ML) criterion, however, gives rise to prohibitive computational complexity when either the space-domain or signal-domain constellation size is large. In this paper, we propose a low-complexity yet optimal detection algorithm for DSM by utilizing sphere decoding (SD). The complexity analysis concerning Euclidian distance equation for DSM-SD is derived. Simulation results show that the proposed DSM-SD algorithm maintains an identical BER performance and achieves a significant reduction of computational complexity compared with the DSM-ML algorithm. The DSM- SD algorithm is especially efficient when the number of receive antennas is large. Moreover, compared with SD applied to SM, its application to DSM is verified to be more useful and attractive.

In this paper, we focus on the downlink (DL) and uplink (UL) power control issue in a wireless full-duplex system consisting of a full-duplex base station with single antenna and mobile stations working in time-division duplex mode. First, we investigate the signal-to-interference ratios (SIRs) of DL and UL and obtain a formula reflecting their relationship. Then, by employing the Lagrange multiplier method, we derive an optimal joint power control solution to maximize the sum rate of DL and UL channels. Consequently, we propose an efficient switching scheme between the full-duplex mode and the opportunistic half-duplex mode that can be considered as a compensation mode in sum rate maximization. The proposed switching scheme is verified by numerical simulations.

In this paper, a novel artificial-noise strategy is proposed for single-antenna point-to-point systems over multi-path fading channels. Unlike existing artificial-noise schemes that are used in multi-antenna systems for the only purpose of confusing eavesdroppers, the main objectives of the artificial noise generated in the proposed strategy are not only to guarantee secure communications, but also to compensate inter-symbol interference induced by multi-path propagation while achieving full multi-path diversity in the desired link between source and legitimate destination. Based on maximal-ratio combining at the destination, the artificial noise herein is specified by the channel state information (CSI) of the desired link. Specifically for the time-division duplex mode, thanks to channel reciprocity, the CSI is available at the source to generate the artificial noise. However, third-party eavesdroppers that are blind to the CSI are not able to decode the source information injected with the artificial noise. Illustrative discussions on the performance not only substantiate the validity of the proposed strategy both in overcoming multi-path effects and for physical layer security, but also provide a useful tool for the frame design with the proposed strategy.

In this paper, we propose a novel centralized time-division multiple access (TDMA)-based scheduling protocol for practical vehicular networks based on a new weight-factor-based scheduler. A roadside unit (RSU), as a centralized controller, collects the channel state information and the individual information of the communication links within its communication coverage, and it calculates their respective scheduling weight factors, based on which scheduling decisions are made by the RSU. Our proposed scheduling weight factor mainly consists of three parts, i.e., the channel quality factor, the speed factor, and the access category factor. In addition, a resource-reusing mode among multiple vehicle-to-vehicle (V2V) links is permitted if the distances between every two central vehicles of these V2V links are larger than a predefined interference interval. Compared with the existing medium-access-control protocols in vehicular networks, the proposed centralized TDMA-based scheduling protocol can significantly improve the network throughput and can be easily incorporated into practical vehicular networks.

Nowadays, more and more communication systems are deployed under mobile environments with very high velocity. This paper focuses on the channel estimation problem in vehicular scenarios, which is very challenging in view of the extremely time-varying characteristics of mobile channels. Specifically, we propose a novel channel estimator named constructed data pilot (CDP) estimator for the current communication standards by fully exploiting the channel correlation characteristics across two concatenated symbols. On the basis of the CDP estimator, we further resort to two efficient techniques to improve its performance over the entire signal-to-noise-ratio (SNR) region. For the first technique, the time-variant mobile channel is modeled as a first-order Markov process so that the exact autocorrelation value of the two adjacent symbols can be derived. For the second technique, the SNR is estimated and serves as a priori information. Simulation results reveal that our proposed channel estimators outperform existing alternatives with lower computational complexity.

Adverse Drug Reactions (ADRs) has become a worldwide problem that draws the attention of people from all racial and ethnic groups. The number of deaths caused by ADRs has greatly increased and led to many drug withdrawals in the last decades. Recent research findings indicate that most ADRs can be effectively prevented to some extent by using computer-aided information technologies. Though many spontaneous reporting systems (SRSs) have been built to enhance the pharma-covigilance, the ADRs data is still very sparse because the large amount of reports obtained from consumers contains insufficient hints to identify a possible causal relationship between an adverse event and drug. Based on this motivation, we developed Adverse-Tracking, a spontaneous reporting system of ADRs via crowd-sourcing. Our proposed system interacts with consumers through a Q&A interface and collects the ADR reports. The decision tree support vector machine (DTSVM) based on the genetic algorithm is used in our system to automate the Q&A procedure. We carried out experiments to evaluate the performance at Peking University First Hospital. As demonstrated by the results, our system is an efficient tool to track and discover adverse events in the consumers' reports of ADRs, which facilitates the detection of “signal”.

In this paper, we investigate the pilot position selection (PPS) problem in the frequency domain pilot multiplexing technique (FDPMT) for channel estimation of single-carrier block transmission with frequency domain equalization (SC-FDE). Unlike the widely accepted point of view that the conventional PPS technique is the optimal one, this paper for the first time questions this viewpoint and demonstrates the suboptimal property of the conventional PPS technique. To further improve the performance of the FDPMT, an optimal PPS technique is proposed based on the minimization of the average bit error rate (BER). Compared with the conventioanl PPS technique, the proposed PPS technique exhibits better performance with similar complexity.

Recently, localization has become an indispensable technique for wireless applications. In view of the limitation of global position system (GPS) in certain environments, alternative approaches are in demand. In this paper, we consider a cooperative localization approach named sum-product algorithm over a wireless network (SPAWN). Although SPAWN theoretically facilitates cooperative localization, it has several practical limitations. Specifically, SPAWN results in high computational complexity and increased network traffic. The main complexity of SPAWN lies in the selection of agents/anchors involved in the cooperative localization. To this end, we formulate the agent/anchor selection problem into a network formation game. Together with a practical limit on the number of agents/anchors used for cooperative localization, our proposed approach can markedly reduce the computational complexity and the resultant network traffic. Simulations show that these advantages come with a slight degradation in the localization mean squared error (MSE) performance.

In this paper, the specific-band power minimization precoding technique is incorporated with spectrally precoded OFDM to suppress near spectral sidelobes more efficiently and thus improve the spectral compactness. When the total number of redundant symbols introduced by both spectral precoder and specific-band power minimization precoder is fixed, the proposed OFDM system can find a balance between near sidelobe power suppression capability and sidelobe decaying capability to meet the desired spectral performance by properly allocating redundancy to the two precoders.

In this study, we consider the selective combining in hybrid cooperative networks (SCHCNs scheme) with one source node, one destination node and N relay nodes. In the SCHCN scheme, each relay first adaptively chooses between amplify‐and‐forward protocol and decode‐and‐forward protocol on a per frame basis by examining the error‐detecting code result, and N c (1 ≤ N c ≤ N ) relays will be selected to forward their received signals to the destination. We first develop a signal‐to‐noise ratio (SNR) threshold‐based frame error rate (FER) approximation model. Then, the theoretical FER expressions for the SCHCN scheme are derived by utilising the proposed SNR threshold‐based FER approximation model. The analytical FER expressions are validated through simulation results.

In previous studies on the capacity of orthogonal frequency division multiple access (OFDMA) systems, it is usually assumed that co‐channel interference (CCI) from adjacent cells is a Gaussian‐distributed random variable. However, very‐little work shows that the Gaussian assumption does not hold true in OFDMA systems. In this study, the statistical property of CCI in downlink OFDMA systems is studied, and spectral efficiency of downlink OFDMA system is analysed based on the derived statistical model. First, the probability density function (PDF) of CCI in downlink OFDMA cellular systems is studied with the considerations of path loss, multipath fading and Gaussian‐like transmit signals. Moreover, some closed‐form expressions of the PDF are obtained for special cases. The derived results show that the PDFs of CCI are with a heavy tail, and significantly deviate from the Gaussian distribution. Then, based on the derived statistical properties of CCI, the downlink spectral efficiency is derived. Numerical and simulation results justify the derived statistical CCI model and spectral efficiency.

Most researches on relay selection (RS) in bidirectional relay network typically assume perfect channel state information (CSI). However, outdated CSI, which is caused by the the time-variation of channel, cannot be ignored in the practical system, and the performance of the conventional bidirectional RS scheme degrades greatly with outdated CSI. In this paper, to improve the performance of RS with outdated CSI, we propose a weighted bidirectional RS scheme, in which a deterministic weight factor decided by the correlation coefficient of outdated CSI, is introduced in the selection process. The outage probability bound of the weighted bidirectional RS is derived and verified, along with the asymptotic expression in high signal-to-noise ratio (SNR). Based on the analytical expressions, the optimal weight factor and the optimal power allocation scheme in minimizing the outage probability are obtained. Simulation results reveal that when the CSI is outdated, the diversity order reduces from full diversity to one. Furthermore, the weighted bidirectional RS scheme with the optimal weight factor yields a significant performance gain over the conventional bidirectional RS scheme, especially in high SNR.

Recently, cardiovascular disease (CVD) has become one of the leading death causes worldwide, and it contributes to 41% of all deaths each year in China. This disease incurs a cost of more than 400 billion US dollars in China on the healthcare expenditures and lost productivity during the past ten years. It has been shown that the CVD can be effectively prevented by an interdisciplinary approach that leverages the technology development in both IT and electrocardiogram (ECG) fields. In this paper, we present WE-CARE , an intelligent telecardiology system using mobile 7-lead ECG devices. Because of its improved mobility result from wearable and mobile ECG devices, the WE-CARE system has a wider variety of applications than existing resting ECG systems that reside in hospitals. Meanwhile, it meets the requirement of dynamic ECG systems for mobile users in terms of the detection accuracy and latency. We carried out clinical trials by deploying the WE-CARE systems at Peking University Hospital. The clinical results clearly showed that our solution achieves a high detection rate of over 95% against common types of anomalies in ECG, while it only incurs a small detection latency around one second, both of which meet the criteria of real-time medical diagnosis. As demonstrated by the clinical results, the WE-CARE system is a useful and efficient mHealth (mobile health) tool for the cardiovascular disease diagnosis and treatment in medical platforms.

Data dissemination is a promising application for the vehicular network. Existing data dissemination schemes are generally built upon some random-access protocol, which results in the unavoidable collision problem. To address this problem, in this paper we design a novel data dissemination strategy from the scheduling perspective. A data dissemination scheduling framework is then proposed. In the proposed framework, the main challenge is how best to assign the transmission opportunity to nodes with maximum dissemination utility and to avoid the collision problem. We then propose a novel and practical relay selection strategy and adopt the space-time network coding (STNC) with low detection complexity and space-time diversity gain to improve the dissemination efficiency. Compared with the random-access dissemination such as CodeOn-Basic and the noncooperative transmission, our proposed data dissemination strategy performs better in terms of the dissemination delay. In addition, the proposed strategy works even better in the dense network than the sparse scenario, benefitting from the space-time diversity gain of STNC and no-collision transmissions. This is in sharp contrary to the CodeOn-Basic method.

The full duplex (FD) technique, which allows the communication node to transmit and receive signals over the same frequency band simultaneously, has the potential to double the spectral efficiency in comparison with the traditional half duplex (HD) technique. However, self-interference, leaking from the FD node's transmission to its own reception, has the detrimental impact on the performance of FD communication. In this paper, we analyze and optimize the two-way FD relay system using amplify-and-forward protocol, when the multi-relay scenario is considered. The optimal relay selection scheme in maximizing the effective signal-to-interference and noise ratio is proposed, which significantly improves the system performance than a single relay network. Furthermore, to facilitate the comparisons with the traditional two-way HD relay, the analytical expressions of the two-way FD relay are derived in a closed form, including bit error rate (BER), ergodic capacity, and outage probability. Based on the analytical expressions, the optimal power allocation and the optimal choice of duplex mode, i.e., FD and HD, are obtained by minimizing the outage probability. Monte-Carlo simulations are fulfilled to verify the analytical expressions. The results reveal that the residual self-interference after interference suppression limits the performance of two-way FD relay: when the residual interference is small, the FD mode has lower BER/outage probability and higher ergodic capacity since it utilizes the resources effectively; otherwise, the HD mode achieves lower BER/outage probability and higher ergodic capacity since it can completely cancel the self-interference at the cost of lower resource utilization.

In this paper, we investigate the performance of multi-pair two-way relaying, in which multiple pairs of users exchange information within pair, with the help of a shared relay. Each user has a single antenna, and the relay is equipped with very large number of antennas. The relay adopts the amplify-and-forward protocol, and the beamforming matrixes of maximum-ratio combining/maximum ratio transmission and zero-forcing reception/zero-forcing transmission are both considered. Due to array gain of antenna array, the power of each user or the relay (or both) can be made inversely proportional to the number of relay antennas, without compromising the performance. Thus, three power-scaling schemes are studied. Furthermore, the asymptotic spectral and energy efficiencies of the system are obtained analytically, when the number of relay antennas approaches to infinity. The asymptotic results are beneficial to provide more insightful understandings for the fundamental limits of the very large antenna system, and verified by the Monte-Carlo simulations. The analytical and simulation results reveal that very large antenna arrays in such system can average the small-scale fading, eliminate the inter-pair interference, and reduce the total power consumption.

In this paper, by considering the case of two transmit antennas, we propose a novel approach for introducing differential signaling into Spatial Modulation (SM)/Space-Shift Keying (SSK) and thus develop a differential SM/SSK (DSM/DSSK) scheme, where neither the transmitter nor the receiver has access to channel state information. The proposed approach can be applied to any equal energy signal constellations. Performance analysis of the proposed DSM is developed analytically and demonstrated via simulations, leading to some interesting observations and useful conclusions. It is shown that the performance degradation of DSM over SM can be less than 3dB and that the loss decreases as the number of receive antennas decreases.

In this paper, we for the first time consider the space-time network coding (STNC) to propose a novel cooperative data dissemination strategy in the time-division multiple access (TDMA) manner for the vehicle network, to overcome the shortcomings of the traditional network coding (NC) techniques with carrier sense multiple access/collision avoidance (CSMA/CA) protocol, i.e, high signal detection complexity and channel collision problem. An optimal relay selection strategy in the procedure of cooperative data dissemination is proposed to maximize the average system capacity for the data dissemination. In a addition, a suboptimal relay selection strategy is put forward to reduce the computation complexity and thus makes the developed data dissemination strategy more practical. Compared with the non-cooperative data dissemination, the proposed cooperative data dissemination via STNC has better performance in terms of the average system capacity, the average user equipment (UE) capacity, and the average data dissemination delay.

Dual-polarized antenna systems have received more and more attention due to its potential to double the channel capacity compared with omnidirectional single-input single-output (SISO) systems. However, the implementation of dual-polarized systems into real three-dimensional (3-D) environments may result in the power loss from the third polarization direction. Therefore, the channel capacity of dual-polarized systems in real 3-D scenarios will be significantly affected by the power loss. Based on the newly proposed 3-D two-spheric double-bounced geometry-based stochastic channel model, this paper for the first time analyzes this impact of the power loss on the channel capacity and demonstrates the critical maximum elevation spread, where the channel capacity of dual-polarized systems is equal to that of omnidirectional SISO system. The work in this paper is significant for the guidance of the proper application of dual-polarized systems in the future.

Two-path transmission schemes have attracted much attention due to its effectiveness in suppressing intercarrier interference (ICI) in orthogonal frequency-division multiplexing (OFDM) systems. This paper proposes a general implementation framework for the existing two-path transmission schemes, which not only reveals the underlying relationship between the existing two-path transmission schemes and the mirror-subcarrier-mapping based ICI self-cancellation technique but also owns the advantage of backward compatibility with normal OFDM systems. Moreover, using the proposed framework, new two-path transmission schemes can be easily developed. With insights provided by this framework, the carrier-to-interference power ratio (CIR) and the bit error probability (BEP) achieved by the existing two-path transmission schemes are further analytically investigated. Monte Carlo simulations validate the analysis.

In Long Term Evolution-Advanced (LTE-A) networks, the quasi-static configuration of Control Channel Element (CCE) creates multiple challenges to real-time mobile health (mHealth) applications. To handle these challenges, we propose a novel solution, Service-oriented Self-adaptive CCE (S2-CCE) configuration mechanism. This proposal can dynamically configure the just-enough number of CCEs for mHealth users according to their scenarios, which can avoid the overutilization of the limited CCE resources. Furthermore, this self-adaptive CCE configuration is also self-aware to service quality from an mHealth user, which can solve the time-sensitive concern in mHealth applications, for example, emergency call and Consultation Video for the point of care. Consequently, we conceive an algorithm to implement the S2-CCE mechanism, in which the initial CCE configuration is based on the Channel Quality Indicator (CQI) reported by an mHealth user from a real deployment, and then this initialized CCE configuration can be intelligently adjusted according to QoS (Quality of Service) requirements from the mHealth user by introducing a concept of Service-Aware Degree (SAD). Our LTE-A system-level simulation experiments demonstrate that the S2-CCE can reduce average delay remarkably for mHealth applications (including HL7, DICOM mHealth users achieving 50% lower delay in contrast with non-service-aware method when there are 50 mHealth users in the cell). And it achieves high user satisfaction (almost 100%) in multi-user scenarios given a milder relaxation to user fairness.

Cardiovascular disease (CVD), principally heart disease and stroke, has become the worldwide leading killer for people of all racial and ethnic groups. In China, this disease contributes 41% to all deaths each year, and it costs the country more than 400 billion US dollars in last decade, including health expenditures and lost productivity, which continues to grow as the population size increases. Recent research findings indicate that CVD can be effectively prevented to some extent by an interdisciplinary approach that combines ICT (Information and Communication Technology) and healthcare applications. Based on this motivation, we developed WE-CARE, a Wearable Efficient teleCARdiology systEm using mobile 7-lead ECG devices. Our WE-CARE system surpasses existing resting ECG systems that reside in hospitals owing to its improved mobility brought by wearable and mobile ECG devices. Meanwhile, it outperforms those conventional dynamic 1-lead or 3-lead ECG systems for mobile users in terms of the appropriate ECG information required for clinical proposes. We carried out clinical trials by deploying the WE-CARE systems at People Hospital of Peking University. The results showed that our solution achieves a high detection rate over 95% against common types of anomalies in ECG signals, while its risk alert delay is limited around one second, both of which match the criteria of real-time healthcare monitoring very well. As demonstrated by the results, the WE-CARE system is a useful and efficient tool for the cardiovascular disease prevention and daily monitoring.

In this paper, we propose a novel multihop transmission scheme using selective network coding (NC) and differential modulation (SNC-DM) for two-way relay networks (TWRNs) when neither the source nodes nor the relay nodes know the channel state information (CSI). We first develop a bidirectional transmission scheme using NC where the information exchange in a two-way multihop relay network with the arbitrary number of hops can be completed in four transmission phases. As a result, the maximum achievable throughput does not decrease as the number of hops increases. To overcome the error propagation in the multihop transmission with decode-and-forward (DF) protocol in wireless fading channels, a selective NC scheme is proposed. In addition, we apply differential modulation in the proposed scheme to avoid channel estimation in the multihop networks. The performance of the proposed scheme is analyzed, and a closed-form frame error rate (FER) expression is derived. It is shown that the proposed scheme achieves significant improvements in both FER performance and network throughput compared to the conventional multihop DF scheme in TWRNs. The analytical results are verified through numerical simulations.

This paper for the first time considers a low complexity multiple-input multiple-output (MIMO) mode switching technique between the conventional MIMO and distributed MIMO. By considering the conventional space-time block coding (STBC) and the distributed STBC (DSTBC), we propose a novel mode switching scheme between them to maximize the capacity performance. Since the difference between the STBC and D-STBC mainly comes from the three-directional (3D) distances, the proposed mode switching scheme is based on the jointly consideration of the received signal-to-noise ratio (SNR) at the user equipment (UE) and the 3D distances. Compared with non-adaptive MIMO modes, the proposed adaptive scheme has better capacity performance and thus is more energy-efficient.

To provide healthcare services in mobile networks, GBR (Guaranteed Bit Rate)-oriented mechanism is expected to offer stable transmission for vital life and health information. Unfortunately, a kind of GBR-based applications is aggressive to exhaust limited bandwidths in a mobile network. To facilitate such a GBR-driven application, radio bandwidth scheduling should be agile and flexible. Motivated by this trend, we propose a Best-fit Carrier Dial-up (BCD) algorithm, which can dynamically schedule demanded bandwidth for GBR-oriented healthcare applications. In fact, this proposal is developed on the basis of Carrier Aggregation (CA), which is the typical new feature in LTE-A (Long Term Evolution-Advanced) networks. Compared with the CA technology, our proposal has two favorable properties: (1) the BCD algorithm uses the LTE-A own system information to select the best-fit carrier in order to avoid extra signaling overhead. Thus it is suitable for healthcare services which are time-sensitive; (2) the BCD algorithm can dial-up bandwidth on demand at a small-scale granularity. Most valuably, this proposal is backward compatible with CA standards seamlessly. In this study, medical image and consulting video are chosen for simulation experiments. Results verify that our proposal can finely tailor radio bandwidth allocation for the time-sensitive and stable healthcare services at a required GBR level.

In this paper, we investigate the resource sharing problem to optimize the system performance in device-to-device (D2D) communications underlaying cellular networks from a distributed and cooperative perspective. Specifically, we formulate a coalitional game with transferable utility, in which each user intends to maximize its own utility and has the incentive to cooperate with other users to form a strengthened user group that can increase the opportunity to win its preferred spectrum resources. Furthermore, we propose a distributed merge-and-split based coalition formation algorithm based on a new defined Max-Coalition order to effectively process the resource allocation problem. Simulation results confirm that, with much lower computational complexity, the proposed scheme achieves an approaching performance in terms of network sum-rate compared with the centralized optimal resource allocation scheme obtained via exhaustive search.

Device-to-device (D2D) communications underlaying cellular networks have recently been considered as a promising means to improve the resource utilization of the cellular network and the user throughput between devices in proximity to each other. In this paper, we investigate the resource sharing problem to optimize the system performance in such a scenario. Specifically, we formulate the interference relationships among different D2D communication links and cellular communication links as a novel interference-aware graph, and propose an interference-aware graph based resource sharing algorithm that can effectively obtain the near optimal resource assignment solutions at the base station (BS) but with low computational complexity. Simulation results confirm that, with markedly reduced complexity, our proposed scheme achieves a network sum rate that approaches the one corresponding to the optimal resource sharing scheme obtained via exhaustive search.

In this paper, we propose a new regular-shaped geometry-based stochastic model (RS-GBSM) for non-isotropic scattering wideband multiple-input multiple-output vehicle-to-vehicle (V2V) Ricean fading channels. By correcting the unrealistic assumption widely used in current RS-GBSMs, the proposed model can more practically study the impact of the vehicular traffic density on channel statistics for different time delays. From the proposed model, we derive the Doppler power spectral density (PSD) and find that highly dynamic Doppler spectrum appears for V2V channels. Excellent agreement is achieved between the derived Doppler PSD and measured data, demonstrating the utility of the proposed model. To combat the intercarrier interference (ICI) caused by highly dynamic Doppler spectrum in real orthogonal frequency division multiplexing based V2V systems, this paper proposes a new type of ICI cancellation scheme, named as precoding based cancellation (PBC) scheme. The proposed scheme can be easily implemented into real V2V systems with the same ICI mitigation performance as the current best ICI cancellation scheme that has high complexity. To further improve the performance of the proposed PBC scheme, a new phase rotation aided (PRA) method, namely constant PRA (CPRA) method, is proposed. Compared with the existing PRA method, the CPRA method has better performance and much less implementation complexity. Therefore, the proposed PBC scheme with the CPRA method is the best ICI cancellation scheme for real V2V systems.

Driven by both safety concerns and commercial interests, vehicular ad hoc networks (VANETs) have recently received considerable attentions. In this paper, we address popular content distribution (PCD) in VANETs, in which one large popular file is downloaded from a stationary roadside unit (RSU), by a group of on-board units (OBUs) driving through an area of interest (AoI) along a highway. Due to high speeds of vehicles and deep fadings of vehicle-to-roadside (V2R) channels, some of the vehicles may not finish downloading the entire file but only possess several pieces of it. To successfully send a full copy to each OBU, we propose a cooperative approach based on coalition formation games, in which OBUs exchange their possessed pieces by broadcasting to and receiving from their neighbors. Simulation results show that our proposed approach presents a considerable performance improvement relative to the non-cooperative approach, in which the OBUs broadcast randomly selected pieces to their neighbors as along as the spectrum is detected to be unoccupied.

Peer-to-peer communication has been recently considered as a popular issue for local area services. An innovative resource allocation scheme is proposed to improve the performance of mobile peer-to-peer, i.e., device-to-device (D2D), communications as an underlay in the downlink (DL) cellular networks. To optimize the system sum rate over the resource sharing of both D2D and cellular modes, we introduce a reverse iterative combinatorial auction as the allocation mechanism. In the auction, all the spectrum resources are considered as a set of resource units, which as bidders compete to obtain business while the packages of the D2D pairs are auctioned off as goods in each auction round. We first formulate the valuation of each resource unit, as a basis of the proposed auction. And then a detailed non-monotonic descending price auction algorithm is explained depending on the utility function that accounts for the channel gain from D2D and the costs for the system. Further, we prove that the proposed auction-based scheme is cheat-proof, and converges in a finite number of iteration rounds. We explain non-monotonicity in the price update process and show lower complexity compared to a traditional combinatorial allocation. The simulation results demonstrate that the algorithm efficiently leads to a good performance on the system sum rate.

To ensure security in data transmission is one of the most important issues for wireless relay networks, and physical layer security is an attractive alternative solution to address this issue. In this paper, we consider a cooperative network, consisting of one source node, one destination node, one eavesdropper node, and a number of relay nodes. Specifically, the source may select several relays to help forward the signal to the corresponding destination to achieve the best security performance. However, the relays may have the incentive not to report their true private channel information in order to get more chances to be selected and gain more payoff from the source. We propose a Vickey-Clark-Grove (VCG) based mechanism and an Arrow-d'Aspremont-Gerard-Varet (AGV) based mechanism into the investigated relay network to solve this cheating problem. In these two different mechanisms, we design different "transfer payment" functions to the payoff of each selected relay and prove that each relay gets its maximum (expected) payoff when it truthfully reveals its private channel information to the source. And then, an optimal secrecy rate of the network can be achieved. After discussing and comparing the VCG and AGV mechanisms, we prove that the AGV mechanism can achieve all of the basic qualifications (incentive compatibility, individual rationality and budget balance) for our system. Moreover, we discuss the optimal quantity of relays that the source node should select. Simulation results verify efficiency and fairness of the VCG and AGV mechanisms, and consolidate these conclusions.

In this paper, we consider general two-way relay networks (TWRNs) with two source and N relay nodes when neither the source nodes nor the relay nodes have access to channel-state information (CSI). A distributed differential space time coding with analog network coding (DDSTC-ANC) scheme is proposed. A simple blind estimation and a differential signal detector are developed to recover the desired signal at each source. The pairwise error probability (PEP) and block error rate (BLER) of the DDSTC-ANC scheme are analyzed. Exact and simplified PEP expressions are derived, which can be used for power allocation between the source and relay nodes. The analytical results are verified through simulations.

In this paper, we present an analytical study of the bit error rate (BER) for interleaved single-carrier frequency-division multiple access (SC-FDMA) systems over independent but not necessarily identically distributed (i.n.i.d.) Nakagami-m fading channels with fading parameters {m} being integers when minimum mean-square error frequency-domain equalization (MMSE-FDE) is applied. Under the assumption of independent fading characteristics among channel frequency responses (CFRs) at the allocated subcarriers for a specific user, accurate numerical BER computation for square M-ary quadrature amplitude modulation (M-QAM) is developed by exploiting the statistics of the equalized noise. More importantly, the BER derivation is based on the real distribution of the CFRs without applying the widely used approximation of the CFRs in previous literature, resulting in a more accurate BER analysis. Monte-Carlo simulations are conducted to validate the analysis.

An innovative auction-based allocation scheme is proposed to improve the performance of device-to-device (D2D) communications as an underlay in the downlink (DL) cellular networks. To optimize the system sum rate over the resource sharing of both D2D and cellular modes, we introduce a reverse iterative combinatorial auction as the allocation mechanism. In the auction, all the spectrum resources are considered as a set of resource units, which compete to obtain business as bidders while packages of D2D pairs are auctioned off as goods in each auction round. We first formulate the valuation of each resource unit for packages of D2D links. And then a detailed non-monotonic descending price auction algorithm is explained. Further, we prove that the proposed scheme is cheat-proof, converges in a finite number of iteration rounds, and has lower complexity compared to a traditional combinatorial allocation. The simulation results demonstrate that the algorithm efficiently leads to a good performance on the system sum rate.

In this paper, we propose an interference-avoidance pilot design scheme using Zero-Correlation Zone (ZCZ) sequences for multi-cell MIMO-OFDM systems. In the proposed scheme, the ZCZ sequences from the same family set are designed as the time-domain (TD) pilot symbols and are Code-Division Multiplexing (CDM) for different transmit antennas in adjacent cells. Due to the perfect auto-correlation and cross-correlation properties of the ZCZ sequences within a certain correlation zone that is designed equal to or a little larger than the Cyclic Prefix (CP) length, the inter-cell interference of the pilot symbols can be effectively eliminated by utilizing a time-domain correlation-based channel estimation method. Simulation results show that the proposed scheme achieves near optimal normalized Mean Square Error (MSE) performance of channel estimation in a multi-cell environment.

Today, IT technology plays a key role in promoting health services which provide medical information over a digital information system. Unfortunately, the digitized data may be not understood by medical professionals due to the limitation of conventional medical signal recognition. To deal with this challenge, we design a 3R (Retiming, Regeneration, Reshaping) dataflow engine that can restore electrophysiological data into its original medical patterns. We carried out clinical trials on our cloud platform in PKU's People Hospital. Clinical results proved that our solution produces high playback accuracy and matches with medical diagnosis criteria very well. With the proof of our clinical tests, this solution can be a very useful tool for clinical treatment and diagnosis in medical platforms.

We consider a cognitive radio network in which multiple pairs of secondary users (SUs) communicate by a one-way relay node over orthogonal channels with the existence of an eavesdropper close to the destination. The transmit power of the relay needs efficient distribution for maximizing the sum secrecy rate of the SU pairs, meanwhile satisfying the interference constraint at the single primary user (PU). Specifically, we introduce two multi-object auctions, i.e. the Vickrey auction and the sequential first-price auction, to perform this power allocation problem. We prove the existence and give the general form of the only equilibrium for each auction. We also propose two algorithms based on the equilibriums, respectively. From the simulation results, we see that the system secrecy rate curve of the Vickrey auction gradually coincides with that of the optimal allocation with increasing power units, while the sequential first-price auction reflects more fairness.

An innovative resource allocation scheme is proposed to improve the performance of device-to-device (D2D) communications as an underlay in the downlink (DL) cellular networks. To optimize the system sum rate over the resource sharing of both D2D and cellular modes, we introduce a sequential second price auction as the allocation mechanism. In the auction, all the spectrum resources are considered as a set of resource units, which are auctioned off by groups of D2D pairs in sequence. We first formulate the value of each resource unit for each D2D pair, as a basis of the proposed auction. And then a detailed auction algorithm is explained using a N-ary tree. The equilibrium path of a sequential second price auction is obtained in the auction process, and the state value of the leaf node in the end of the path represents the final allocation. The simulation results show that the proposed auction algorithm leads to a good performance on the system sum rate, efficiency and fairness.

Interference alignment (IA) has been well recognized as an efficient approach to reduce interference at high signal to noise ratio (SNR). However, it demands global channel state information (CSI) at both transmitters and receivers for preceder design in order to maximize the multiplexing gain. In this paper, we discuss IA with delayed differential CSI feedback for time-correlated multiple input multiple output (MIMO) block fading channels. We consider the impact of distortion caused by channel estimation errors and quantized CSI feedback delay, and thus, find an optimal feedback interval to minimize this distortion, as well as the sum rate performance. Specifically, we derive the minimum differential feedback rate. And with the feedback-channel capacity constraint, we further study the relationship between the average sum rate and the feedback interval. Analytical results are verified by simulations.

In this paper, a novel unified channel model framework is proposed for cooperative multiple-input multiple-output (MIMO) wireless channels. The proposed model framework is generic and adaptable to multiple cooperative MIMO scenarios by simply adjusting key model parameters. Based on the proposed model framework and using a typical cooperative MIMO communication environment as an example, we derive a novel geometry-based stochastic model (GBSM) applicable to multiple wireless propagation scenarios. The proposed GBSM is the first cooperative MIMO channel model that has the ability to investigate the impact of the local scattering density (LSD) on channel characteristics. From the derived GBSM, the corresponding multi-link spatial correlation functions are derived and numerically analyzed in detail.

It has been well recognized that channel state information (CSI) feedback is of great importance for downlink transmissions of closed-loop wireless networks. However, the existing work typically researched the CSI feedback problem for each individual mobile station (MS), and thus, cannot efficiently model the interactions among self-interested mobile users in the network level. To this end, in this paper, we propose an alternative approach to investigate the CSI feedback-rate control problem in the analytical setting of a game theoretic framework, in which a multiple-antenna base station (BS) communicates with a number of co-channel MSs through linear precoder. Specifically, we first present a non-cooperative feedback-rate control game (NFC), in which each MS selects the feedback-rate to maximize its performance in a distributed way. To improve efficiency from a social optimum point of view, we then introduce pricing, called the non-cooperative feedback-rate control game with price (NFCP). The game utility is defined as the performance gain by CSI feedback minus the price as a linear function of the CSI feedback-rate. The existence of the Nash equilibrium of such games is investigated, and two types of feedback protocols (FDMA and CSMA) are studied. Simulation results show that by adjusting the pricing factor, the distributed NFCP game results in close optimal performance compared with that of the centralized scheme.

The hybrid relay selection (HRS) scheme, which adaptively chooses amplify-and-forward (AF) and decode-and-forward (DF) protocols based on the decoding results at the relay, is very effective to achieve robust performance in wireless relay networks. This paper analyzes the frame error rate (FER) of the HRS scheme in general wireless relay networks without and with utilizing error control coding at the source node. We first develop an improved signal-to-noise ratio (SNR) threshold-based FER approximation model. Then, we derive an analytical average FER expression as well as a high SNR asymptotic expression for the HRS scheme and generalize to other relaying schemes. Simulation results exhibit an excellent agreement with the theoretical analysis, which validates the derived FER expressions.

In this paper, we investigate the differential channel state information (CSI) feedback problem for a general multiple input multiple output (MIMO) system over time-correlated Rayleigh block-fading channels. Specifically, we derive the closed-form minimum differential feedback rate in the presence of channel estimation errors and quantization distortion. With the feedback-channel capacity constraint, we further study the ergodic capacity in a periodic feedback system in terms of the minimum differential feedback rate and the feedback interval. Through theoretical analysis, we find that there exists an optimal differential feedback interval to achieve the maximum ergodic capacity. Analytical results are verified by simulations in a practical periodic differential feedback system employing water-filling precoder and Lloyd's quantization algorithm.

In this paper, we investigate joint relay and jammer selection in two-way cooperative networks, consisting of two sources, a number of intermediate nodes, and one eavesdropper, with the constraints of physical-layer security. Specifically, the proposed algorithms select two or three intermediate nodes to enhance security against the malicious eavesdropper. The first selected node operates in the conventional relay mode and assists the sources to deliver their data to the corresponding destinations using an amplify-and-forward protocol. The second and third nodes are used in different communication phases as jammers in order to create intentional interference upon the malicious eavesdropper. First, we find that in a topology where the intermediate nodes are randomly and sparsely distributed, the proposed schemes with cooperative jamming outperform the conventional nonjamming schemes within a certain transmitted power regime. We also find that, in the scenario where the intermediate nodes gather as a close cluster, the jamming schemes may be less effective than their nonjamming counterparts. Therefore, we introduce a hybrid scheme to switch between jamming and nonjamming modes. Simulation results validate our theoretical analysis and show that the hybrid switching scheme further improves the secrecy rate.

In this paper, we investigate joint relay and jammer selection in a two-way relay network with secrecy constraints, in which there are two sources, a cluster of intermediate nodes, and one eavesdropper. Under a decode-and-forward (DF) protocol, the considered two-way relay network implements a complete transmission in three phases. An intermediate node is selected as conventional relay and another two are selected as jammers during these phases, in order to improve security against the malicious eavesdropper. We find that when the jamming power is higher than that of source nodes, the proposed scheme has a better and more stable secrecy performance than the conventional non- jamming schemes. In addition, the system's security status gets increasingly better when more intermediate nodes are added into the relay/jamming cluster.

Orthogonal Frequency Division Multiplexing (OFDM) systems may suffer from both carrier frequency offset (CFO) and in-phase/quadrature-phase (I/Q) imbalance at the receiver front end. In this paper, a novel type of intercarrier interference (ICI) self-cancellation method using mirror mapping is proposed to combat these impairment. Based on the proposed novel method and by adopting two widely used mapping operations, we altogether derive two different mirror mapping schemes. Analysis and simulation results verify that the proposed mirror mapping schemes not only inherit the efficiency of the existing self-cancellation schemes in suppressing ICI caused by CFO but also have the ability of compressing or even eliminating IQ imbalance.

Interference alignment (IA) has been well recognized as a promising technique to obtain large multiplexing gain in multiple input multiple output (MIMO) interference channels. Most of the existing IA schemes require global channel state information (CSI) at the transmitter to design precoding vectors, which causes high amount of feedback bits. To reduce the feedback overhead, in this paper, we investigate the IA scheme employing differential CSI feedback over time-correlated MIMO channels. Specifically, we analyze the achievable sum-rate performance, and derive the minimum differential feedback rate to preserve the maximum multiplexing gain. In addition, we use the general alternating-minimization precoder design scheme to verify the analytical results.

In this paper, we investigate joint relay and jammer selection in two-way cooperative networks, consisting of two sources, a number of intermediate nodes, and one eavesdropper, with secrecy constraints. Specifically, the proposed algorithms select two or three intermediate nodes to enhance security against the malicious eavesdropper. The first selected node operates in the conventional relay mode and assists the sources to deliver their data to the corresponding destinations via the amplify-and-forward protocol. The second and third nodes are used in different communication phases as jammers in order to create intentional interference upon the eavesdropper node. Firstly, we find that in a topology where the relay and jamming nodes are randomly and sparsely distributed, the proposed schemes with cooperative jamming outperforms the conventional non-jamming schemes within a certain transmitted power regime. We also find that, in the scenario in which the intermediate nodes gather as a close cluster, the jamming schemes may be less effective than their non-jamming counterparts. Therefore, we introduce a hybrid scheme to switch between jamming and non-jamming modes. Simulation results validate our theoretical analysis that the hybrid switching scheme further improves the secrecy rate.

It has been well recognized that channel state information (CSI) feedback is important for dowlink transmissions of closed-loop wireless networks. In this paper, we investigate the CSI feedback rate control problem in the analytical setting of a game theoretic framework, where a multiple-antenna base station (BS) communicates with a number of co-channel mobile stations (MS) through a minimum mean square error (MMSE) precoder. Specifically, we present a non-cooperative feedback-rate control game with price (NFCP) over orthogonal feedback channels with a total bandwidth constraint. The game utility is defined as the performance gain by CSI feedback minus the price as a linear function of the CSI feedback rate, subject to an overall bandwidth constraint. The existence of the Nash equilibrium of such a game is investigated. Simulation results show that the distributed game approach results in close optimal performance compared with the centralized scheme.

In this paper, we investigate cooperation of conventional relays and friendly jammers subject to secrecy constraints for cooperative networks consisting of one source node, one corresponding destination node, one malicious eavesdropper node, and several intermediate nodes. In order to obtain a higher secrecy rate, the source selects one conventional relay and several friendly jammers from the intermediate nodes to assist message transmission, and in return, it needs to make a payment. Each intermediate node here has two possible identities to choose, i.e., to be a conventional relay or a friendly jammer, which results in a direct impact on the final utility of the intermediate node. After the intermediate nodes determine their identities, they seek to find optimal partners forming coalitions, which improves their chances to be selected by the source and thus to obtain the payoffs in the end. We formulate this cooperation as a coalitional game with transferable utility and also study its properties. Furthermore, we define a Max-Pareto order for comparison of the coalition value, based on which we employ the merge-and-split rules. We also construct a distributed merge-and-split coalition formation algorithm for the defined coalition formation game. The simulation results verify the efficiency of the proposed coalition formation algorithm.

A solution to the power leakage minimization problem in discrete Fourier transform (DFT) based communication systems is presented. In a conventional DFT based system, modulated subcarriers exhibit high sidelobe levels, which leads to significant out-of-band power leakage. Existing techniques found in the literature either do not achieve sufficient sidelobe suppression or suffer from significant spectral efficiency loss. Precoding can be seen as a general linear processing method for power leakage reduction, however, how to design the optimal linear precoder is still an open problem. In this paper, the power leakage suppression is first treated as a matrix Frobenius norm minimization problem, and then the optimal orthogonal precoding matrix design for the power leakage suppression is proposed based on singular value decomposition (SVD). By further exploiting the extra degrees of freedom in the precoding matrix, two kinds of optimized precoding matrices, one with multi-carrier property and the other with single-carrier property, are developed to take the advantages of orthogonal frequency division multiplexing (OFDM) and single carrier frequency division multiple access (SC-FDMA), respectively. Simulation results show that both the multi-carrier and the single-carrier precoding schemes achieve significant power leakage suppression, and have similar peak-to-average power ratio (PAPR) and bit-error-rate (BER) to those of OFDM and SC-FDMA systems, respectively.

Abstract High‐frequency (HF) vehicular communication system works with the frequency‐selective fading channel, thereby the coherence bandwidth is limited due to the multipath time dispersive effect, which imposes the difficulty for achieving the high‐data rate transmission. The present paper investigates the antenna array technique for its ability in reducing the multipath delay spread of the ionosphere channel and, thus, increasing possibly the bandwidth of the HF system. To enable fast moving speed of the vehicular receiver, we propose to use single antenna at the receiver and the adaptive array at the transmitter. The adaptive beamforming is driven based on the protocol design and reciprocity principle of channel. In order to evaluate the performance of array system, a statistical HF double‐directional channel model, which includes angular information at both the transmitter and receiver, is presented. The explicit expressions are obtained for calculating the coherence bandwidth. The numerical results show the efficiency of this approach for mid‐latitude mid‐range channel. Copyright © 2009 John Wiley & Sons, Ltd.

Welcome to this special issue of Wiley Journal of Wireless Communications and Mobile Computing (WCMC).To date, wireless vehicular communications have attached much attention for improving road safety, intelligent management and data exchange services, and providing Internet access on the move to ensure wireless pervasive and ubiquitous connectivity.The field of wireless vehicular communications can be typically identified as vehicle-to-person communications, vehicle-to-infrastructure communications, vehicle-to-vehicle communications, and vehicular communication networks.The combination of unique features of wireless vehicular communications and networking issues opens new opportunities for many interesting research areas, for example, real time safety applications, and intelligent diver information services.The goal of this special issue is to present good-performance, highly scalable, robust, and secure vehicular technologies for universal realization of wireless vehicular communications.To guarantee the quality, in this special issue, we have selectively collected 15 papers out of over 60 submissions, and clustered them in four groups: three are survey papers, four papers deal with channel modeling and physical layer issues, six papers investigating MAC and network layer issues, and two papers focusing on applications.Detailed overview of the selected works is given below.The first group includes three papers, which survey recent advances in wireless vehicular communications.The first paper, by Chen et al., provides recent results for data dissemination in vehicular ad hoc networks (VANETs).This paper also discusses security challenges in this field and the need of supporting technologies to enable efficient data dissemination for automotive applications.The paper by Leng et al. gives a global review of media access control techniques for VANETs.This paper summarizes recent work in this domain including MAC standardization activities, wireless channel resource management, QoS capability enhancement in MAC layer, and reliable MAC broadcasting strategies.The third paper, by Martinez et al., makes a survey of several publicly available mobility generators, network simulators, and VANET simulators.This paper contrasts their software characteristics, graphical user interface, popularity, ease of use, input requirements, output visualization capability, and accuracy of simulation.

The incremental hybrid relay selection (IHS) scheme has recently attracted great attention for its high spectrum efficiency and robust performance. In this paper, we study the analytical frame error rate (FER) performance of the IHS scheme with and without applying channel coding at the source node. Specifically, we consider a multiple-relay cooperative network with a direct source-destination link, under dissimilar network settings, i.e., the channels of different relay branches experience Rayleigh block fading with different variances. We first develop an improved SNR threshold-based FER model for the general MIMO system. Using this model, we then derive the closed-form FER expression, and further make simplification at high SNRs. Monte- Carlo simulations are performed to validate the analytical results.

The cyclic prefix comb spectrum code division multiple access (CP-CS-CDMA) has comb spectrum in frequency domain. Its different code groups can be separated with a simple hopping accumulator. In the paper, we combine OFDMA and CP-CS-CDMA, and propose a new multiple access scheme, hybrid multiple access (HMA). Then we propose a new reuse partitioning system with HMA. The cell of the system has two regions: the inner region with OFDMA and the outer region with CP-CSCDMA. The proposed system makes full use of the advantages of OFDMA and CDMA to improve the performance. Theoretical analysis and simulation results have verified that our HMA and the new reuse partitioning system significantly increase the capacity compared with the conventional OFDMA system.

In this paper, we consider a two-way relay network where two sources can communicate only through an unauthenticated intermediate relay node. We investigate secure communications of this two-way relay scenario using physical layer security. Specifically, we treat the relay node as an eavesdropper from whom the information transmitted by the sources needs to be kept secret, despite the fact that its cooperation in relaying this information is essential. We first find that a non-zero secrecy rate is indeed achievable in this two-way relay network even without external jammers. Further still, with the help of friendly jammers who can transmit jamming signals to distract the malicious relay, a positive gain of the secrecy rate can be realized. In order to obtain the maximum secrecy rate, we define and then analyze an optimization problem. Finally, an optimal solution of jamming power allocation is provided for the system with friendly jammers.

In this paper, we investigate the differential channel state information (CSI) feedback problem for a general multiple input multiple output(MIMO) system over time-correlated Rayleigh block-fading channels. Specifically, we first derive the analytical minimum differential feedback rate in the presence of channel estimation errors and quantization distortion. With the feedback-channel capacity constraint, in the periodic feedback system, we further study the relationship between the ergodic capacity and the feedback interval. We find that there exists an optimal feedback interval to maximize the ergodic capacity. Analytical results are verified by simulations in a practical differential feedback system employing Lloyd's quantization algorithm.

In this paper, we consider a general bi-directional relay network with two sources and N relays when neither the source nodes nor the relays know the channel state information (CSI). A bi-directional relay selection scheme is proposed using differential analog network coding (BRS-DANC), and a simple linear detector is given to recover the received signals. In the proposed scheme, we provide an optimal and a sub-optimal methods to select the relay node from a single source by minimizing the average symbol error rate (SER). The performance of the proposed BRS-DANC scheme is analyzed, and a simple asymptotic SER expression is derived. It is shown that the SER performance of the proposed differential scheme is about 3 dB away from that of the coherent detection scheme.

This paper presents a systematic solution to enable the code division duplex (CDD) system that allows the uplink- and downlink channel to work on the same frequency at the same time but with different smart codes. CDD is considered to be most spectral efficient among all other duplex systems. However, in comparison with the frequency division duplex (FDD) system, a CDD mobile station (MS) receiver can suffer from an additional interference transmitted from other MSs in its vicinity, and the Base Station (BS) receiver can suffer from another additional interference delivered from the BS transmitter. Also the BS may have interference caused by the neighboring BS. In the proposed system, the MS to MS interference is reduced using a scheduling method which separates the desired MS from the interference MSs in distance, and the BS to BS interference is effectively alleviated by the use of distributed receive antennas and, furthermore, it can be reduced by the proposed interference cancellation technique. The theoretical calculations show that the CDD system has about twice large capacity compared to the FDD system.

A new methodology that applies frequency orthogonality to the spreading code design has been presented. The main purpose is to reduce the receiver complexity of the cyclic prefix code division multiple access (CP-CDMA) over the downlink channel and to enable parallel transmission over the uplink channel. The receiver complexity has been found for requiring full-band FFT and IFFT calculations in the channel equalizer. To handle this problem, we developed the comb spectrum codes organized in frequency orthogonal groups, in each of which the codes have time correlation orthogonality. For the downlink channel, the reduction of complexity in signal processing of a CSCDMA receiver is due to that the separation of groups is simple and each separated group is in the form of a narrower bandwidth CP-CDMA. Thus, the full-band FFT and IFFT can be replaced by the partial FFT and partial IFFT as shown in this proposed approach. For the uplink channel, we assign the code groups to different users to form a group division multiple access (GDMA) for enabling an independent channel equalization of each user at base station. The theoretical analysis and the simulation results agree well with each other and both confirm the effectiveness of this approach.

This paper develops a dual-window technique to reduce the sensitivity to carrier frequency offset (CFO) of orthogonal frequency-division multiplexing. We define two windows and use them alternately onto the subcarriers one another in adjacent for pulse shaping at the transmitter. The receiver selects one of the two windows to maximize the output of the desired subcarriers and suppresses the others by window- matching and anti-matching functions respectively. The efficiency of the proposed method is demonstrated in the theoretical analysis and in the simulations as well.

In the conventional pilot symbol assisted modulation design, a data block is composed of a pilot set and an information data set. For improving the quality of the channel estimates, some iteration methods use the detected information symbols as the additional pilots. We work on orthogonal frequency division multiplexing (OFDM) system to divide the information data set into several segments and assign them with different data rates for exploiting the potential of the iterative channel estimation. The averaged data rate can be increased by the proposed scheme with the minimum mean-square error channel estimator. The simulation results confirm this approach.

In this paper, a novel decoding algorithm using perturbation techniques for LDPC concatenated with CRC (LDPC-CRC) is proposed. The CRC is used to check the residual error of the BP algorithm, while a new parameter is introduced to LDPC decoding to describe the reliability of each bit in the iterative decoding algorithm. Upon an error is detected, re-decoding process with perturbation method will be aroused. Simulation results show that this method lowers the error floor for codeword length of several hundred bits effectively.

In this paper, we propose a new decoding method for LDPC aided by CRC and perturbation for improving FER performance. The CRC is used to check the decoding error of BP algorithm. Once an error is found, the perturbation method will be used to start re-decoding processing. Simulation results show that this method performs within about 1.2 dB of the sphere-packing bound for codeword length of several hundred bits.

In this paper, we consider the capacity behaviors of MC-CDMA and CP-CDMA systems by the uses of MMSE receivers. The averaged capacities are derived for the two systems, having a finite spreading factor, in Rayleigh fading environment. The closed-form solutions have been obtained, which show that the capacity of the MC-CDMA is slightly larger than that of the CP-CDMA. The theoretical predictions are confirmed by the simulation results.