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We propose a cooperative nonorthogonal multicast scheme for multiple-input–single-output (MISO) systems, where the transmitter sends the superimposed signal to two multicast groups. After successfully detecting all signals, the cell-center users (CCUs) in one multicast group help relay signal to the cell-edge users (CEUs) in another group to enhance signal reception. Simultaneous wireless information and power transfer is adopted at CCUs to assist information relaying. In such a system, to minimize the transmission power of the system while satisfying the quality of service requirements of all the users, an optimization problem is formulated to jointly design the transmitter beamformers, distributed CCUs beamformer, as well as the power-splitting (PS) ratios. To solve the nonconvex problem, we first equivalently transform it into a difference of convex (DC) programming. Then, a low-complexity iterative algorithm based on the constrained concave convex procedure (CCCP) is proposed to solve the DC programming one. In addition, a robust joint beamforming and PS scheme is proposed by assuming imperfect channel state information (CSI). The infinite constraints caused by CSI uncertainties are converted into finite ones utilizing the S-procedure. To obtain a rank-one locally optimal solution, the penalty function method and CCCP algorithm are adopted. The simulation results reveal that the proposed cooperative scheme can greatly reduce the transmission power and outperform the baselines within a certain range. Moreover, the robustness and effectiveness of the robust design under imperfect CSI case have been validated.

Spatial modulation (SM) with high spectrum and energy efficiencies is promising for future massive connectivity communication networks, in which user activities are often sporadic and SM signals are sparse. Such characteristics, if exploited in the detection process, will lead to gains in terms of receiver complexity and performance. This letter proposes a compressive sensing (CS) algorithm for multiuser detection in SM-MIMO systems to efficiently exploit such characteristics. Specifically, the temporal correlation of the user activities and the random transmission nature of SM signals are used to improve detection performance without requiring prior knowledge of the user sparsity level. In addition, the proposed algorithm requires a lower number of BS receive and transmit antennas in each user compared with existing CS-based detection algorithms and has a significantly lower computational complexity.

This paper focuses on the secure transmission of wireless-powered relay systems with the imperfect eavesdropper channel state information. For efficient energy transfer and information relaying, a novel two-phase protocol is proposed, in which the relay operates in a full-duplex (FD) mode to achieve the simultaneous wireless power and information transmission. Compared with those existing protocols, the proposed design possesses two main advantages: 1) it fully exploits the available hardware resource (antenna element) of relay and can offer a higher secrecy rate and 2) it enables the self-energy recycling (S-ER) at relay, in which the loopback interference generated by the FD operation is harvested and reused for information relaying. To maximize the worst-case secrecy rate (WCSR) through jointly designing the source and relay beamformers coupled with the power allocation ratio, an optimization problem is formulated. This formulated problem is proved to be non-convex and the challenge to solve it is how to concurrently solve out the beamformers and the power allocation ratio. To cope with this difficulty, an alternative approach is proposed by converting the original problem into three subproblems. By solving these subproblems iteratively, the closed-form solutions of robust beamformers and power allocation ratio for the original problem are achieved. Simulations are done and results reveal that the proposed S-ER -based secure transmission scheme outperforms the traditional time-switching based relaying scheme at a maximum WCSR gain of 80%. Results also demonstrate that the WCSR performance of the scheme reusing all antennas for information reception is much better than that of schemes exploiting only one antenna.

A non-coherent spatial modulation scheme assuming no channel state information (CSI) at the receiver is proposed in this letter. Different from the differential spatial modulation, in which the difference between the previous information block and the current information block is employed, the proposed scheme only utilizes the estimation of the previous transmission block to eliminate the restriction of CSI. Moreover, a generalized multi-ring amplitude phase shift keying (APSK) constellation with arbitrary modulation order of PSK on each circle is used in the scheme, and the optimal one is found through the design method proposed in this letter. Simulation results show that, at the same spectral efficiency, the proposed scheme with optimal constellation outperforms the scheme with traditional PSK, QAM, and existing APSK in Rayleigh fading channel.

This letter investigates the downlink achievable rates of massive multiple-input-multiple-output (MIMO) enabled simultaneous wireless information and power transfer (SWIPT) systems. Since the transmission range of massive MIMO SWIPT systems is quite short, the transmission channels are generally of line-of-sight. Therefore, by assuming Rician fading channels, this letter theoretically derives the approximate expressions of harvested energy and achievable rate. In addition, the corresponding asymptotic expressions are presented for large number of transmit antennas case. Simulation results are provided to demonstrate the accuracy of the derived expressions.

This paper focuses on the secure transmission of wireless-powered full-duplex (FD) relay systems, where a multiantenna source communicates with a single-antenna destination with the help of a FD relay in the presence of a single-antenna eavesdropper. It is assumed that the FD relay is wireless energy harvesting-enabled, adopting both transmit and receive antennas to harvest energy in a time switching (TS) mode. As the objective of this paper is to maximize the system secrecy rate through jointly designing the energy beamforming vector, the information beamforming vector and the TS coefficient, an optimization problem is formulated. The formulated problem is proved to be nonconvex and the challenge to solve which is to concurrently solve out the three variables. To cope with this difficulty, an iterative algorithm is proposed to convert the formulated optimization problem into three convex subproblems, based on which the closed form solutions for the beamforming vectors are derived and the TS coefficient is obtained. Convergence property of the iterative method is analyzed. Simulations are also done to verify the theoretical derivations in terms of the convergence speed and the secrecy rate. Results reveal that the secrecy rate performance of exploiting transmit antenna together with receive antenna for energy harvesting at the FD relay outperforms only receive antenna case. Moreover, although there exists loopback interference between antennas, the FD relaying can always substantially boost the secrecy rate compared with half-duplex relaying architecture.

The bits-to-antenna-index (BAI) and bits-to-modulated-symbol (BMS) mappings play important roles in determining the bit error rate (BER) of spatial modulation (SM). To minimize the BER, a plenty of work has paid much attention on optimizing the noise-free receive signal constellation diagram via adaptive power allocation, phase ration, precoding, etc, but overlooked the impact of the BAI and BMS mappings. To fill in this gap, this paper investigates the adaptive mapper design for SM, and proposes a mapper solution named brute forth mapper (BFM). Through adjusting the binary labels of all the closest symbol-pairs to be of one bit difference in a brute force way, BFM achieves the optimal BER in high signal-to-noise-ratio (SNR) regime. The feasibility of BFM is proved over random fading channels, and the performance improvement brought by BFM in terms of BER enhancement and SNR gain as well as the computational complexity and feedback overhead are quantitatively analyzed. Both analysis and simulations show that the proposed adaptive mapper significantly improves the BER performance with lightweight feedback overhead.

This paper studies the joint transceiver design and power splitting (JTDPS) for a downlink multiuser multiple-input multiple-output (MU-MIMO) simultaneous wireless information and power transfer (SWIPT) system. Aiming to minimize the transmit power by jointly optimizing the transmitter at a base station, the power splitting (PS) factors, and information decoding receivers at mobile stations (MSs) subject to both the predefined mean-square error (MSE) and the given energy harvesting (EH) constraints. The formulated problem is a nonconvex JTDPS optimization problem, which cannot be solved directly. To solve it, an iterative optimization framework composed of joint transmitter and PS factor optimization (JTxPS) subproblem and a receiver side minimum mean-square error (MMSE) minimization subproblem is proposed. By iteratively solve the two subproblems, the original optimization problem is solved. The sufficient and necessary conditions for the feasibility of the formulated JTDPS and the JTxPS problems are analyzed. Theoretical analysis shows that the JTxPS subproblem is also nonconvex and can be solved by using convex semidefinite programming (SDP). Considering the high computational complexity of the SDP-based scheme, a low-complexity suboptimal scheme based on the traditional MMSE transceiver design is also proposed. Simulations are done to validate the theoretical analysis, and results show the effectiveness of the proposed schemes.

A differential spatial modulation (DSM) with binary phase shift keying (BPSK) scheme is designed for two-way relay (TWR) wireless communications that use the denoise-and-forward (DNF) protocol without requiring channel state information at the sources and relay. The key area to make this scheme work is a multiple-to-one mapping method for DSM at the relay, as well as the DSM matrix design at the sources, which are proposed and derived in this letter. Simulation results show that the proposed system achieves significant gains in BER performance over traditional differential modulation with BPSK in DNF-TWR systems when both operate at the same spectral efficiency.

A multi-relay cooperative quadrature spatial modulation (QSM) system with decode-and-forward (DF) scheme is proposed in this paper, which improves the system spectral efficiency via the transmission of the extra information bits to select the relay node. The source jointly selects the relay node, the transmit antennas, and the signal constellation symbol. For the proposed scheme, only one relay with DF protocol can be activated during one communication process and the optimal maximum likelihood (ML) detection is employed without direct link. Simulation results verify that the cooperative QSM system with multiple DF relays can effectively increase the system spectral efficiency and improve the system average bit error probability (ABEP) performance compared with the non-cooperative QSM scheme and the traditional cooperative spatial modulation (SM) system with multiple DF relays.

A multi-relay cooperative quadrature spatial modulation (QSM) system is proposed in this paper. The distinguishable feature of the multi-relay cooperative QSM lies in the enlarged aggregate throughput of the system since extra information bits at the source can be transmitted through the selection of the relays. During the communication process, only one relay is activated which adopts the amplify-and-forward (AF) relaying protocol. Furthermore, a closed-form expression of the average pairwise error probability (APEP) of the proposed multi-relay cooperative QSM system is given and employed to derive the tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. Monte-Carlo simulation shows that the proposed multi-relay cooperative QSM system achieves better ABEP performance compared with the traditional multi-relay cooperative spatial modulation (SM) system.

This paper investigates the downlink transmission of massive multiple-input-multiple-output (MIMO) simultaneous wireless information and power transfer (SWIPT) systems. The base station (BS) is equipped with large scale antenna array to provide users with concurrent information and energy supplies. Considering the short communication range between users and the BS in SWIPT systems, the transmission channels are modeled as Rician fading channels to capture both the line-of-sight (LOS) and non-LOS propagations. The approximate and asymptotic expressions of the achievable rate are first derived, and a sum achievable rate optimization problem is formulated based on the asymptotic expression subject to the quality-of-service (QoS) and transmit power constraints. An iterative optimization framework is proposed to solve the original non-linear non-convex problem, and iterative successive convex approximation (SCA) method is introduced in the framework to transmit the non-convex subproblem into convex form. The convergence and effectiveness of the proposed framework are analyzed and proved through analysis and intensive simulations. Results show that the proposed framework can achieve the optimal system performance as the exhaustive search method does.

This paper studies the impact of channel error on the achievable rate of symmetrical K-user multiple-input multiple-output linear interference alignment (IA) networks. The upper and lower bounds of the achievable sum rate are derived analytically with the assumption of orthonormal transmit precoders and receive filters designed from imperfect channel state information (CSI) over both the uncorrelated and correlated channels. For uncorrelated channels, quite tight lower and upper bounds are obtained. The impact of channel error on the degrees of freedom (DoF) and the DoF persistence conditions are also investigated. Results show that the DoF of IA networks persists only if the channel error decreases in an order higher than the signal-to-noise ratio. For correlated channel, the lower and upper bounds for one realization of IA are derived. The derived upper bound can be used to characterize the achievable rate approximately. Simulation results indicate that the achievable rate of IA network is influenced significantly by CSI uncertainty. The obtained analytical bounds provide an intuitive way to show the impact of channel error on the achievable rate and thus can help practical systems deign.

This work focuses on the design and analysis of link-adaptive bits-to-antenna-indexes mapping for closed-loop space-shift keying (SSK)-modulated multiple-input multiple-output (MIMO) systems. With the aim of achieving a lower bit error rate (BER), optimal mappers are designed under different transmission conditions. Assuming that perfect channel state information (CSI) is available at the transceivers, an original binary switch algorithm (OBSA) is proposed. For the case in which there is no CSI at the transmitter and the feedback channel is bandwidth limited, a restricted binary switch algorithm (RBSA)-based mapping design is proposed. Both of the proposed algorithms can bring considerable performance gains but are of high computational complexity if there are a large number of transmit antennas. To overcome this, algorithms with reduced computational complexity are proposed and investigated, which are named partial OBSA and partial RBSA. The performance improvement brought by all of the proposed mapping schemes in terms of BER performance enhancement and signal-to-noise ratio (SNR) gain in a high-SNR regime is theoretically given. Simulations are done to validate the theoretical analysis, and results show that the proposed schemes can improve BER performance considerably in a wide range of SNR regimes. In addition, all of the proposed mapping schemes can cowork with those existing transmit processing techniques and bring additional performance gain without incurring any extra cost on physical components (e.g., additional phase shifters or power amplifiers). All these make the proposed mapping schemes promising choices for the link-adaptive design of closed-loop SSK MIMO systems.

An interference alignment (IA) transceiver design scheme for multiple-input–multiple-output (MIMO) multicell multiuser wireless communication systems is proposed by minimizing the maximum mean square error (MSE) of the received symbols to improve fairness among users. The formulated Min-Max MSE optimization problem is not jointly convex on the transmit precoders and receive filters and, thus, is very difficult to solve directly. An iterative method is proposed to solve the optimization problem to get a suboptimal solution instead. Considering that if the receive filters are fixed, the Min-Max MSE problem can be reformulated as a second-order cone programming problem, and if the transmit precoders are fixed, the closed-form receive filters minimizing the receive MSE can be easily obtained, and the formulated Min-Max MSE problem is solved by alternatively optimizing the transmit precoders and the receive filters. The convergence of the proposed algorithm is proved, which shows its feasibility. Furthermore, a robust Min-Max MSE algorithm is proposed to counter the channel uncertainty. Simulation results show that the proposed Min-Max MSE algorithm can achieve IA when the antennas are configured to be strong IA proper and when the users in the network are of the same signal-to-noise ratio (SNR). Analysis indicates that the proposed Min-Max IA transceiver design scheme can significantly improve user fairness with a possible cost of sum-rate reduction. Results also show that the proposed robust design algorithm provides better performance when lacking perfect channel state information (CSI).

In this paper, we propose and analyze a new relaying scheme for the three-node cooperative relaying system, named as incremental hybrid decode-amplify-forward relaying (IHDAF), where the relay may choose to keep silent or transmit message in decode-and-forward (DF) or amplify-and-forward (AF) mode based on the qualities of the channels among the source, relay, and destination. Closed-form expressions of the outage probability and bit error rate (BER) of the proposed IHDAF protocol are derived. The optimal relationship of the two important signal-to-noise ratio (SNR) thresholds at the relay and destination to decide whether cooperation is necessary and the cooperative mode has been achieved. Moreover, the effects of the power allocation schemes, SNR thresholds, and relay locations on the outage probability and BER of the IHDAF protocol are studied. Theoretical analysis and simulation results show that the IHDAF relaying scheme outperforms the incremental-selective DF (ISDF), incremental DF (IDF), and cooperative STBC schemes, especially when the relay is close to the destination.

This paper considers power splitting (PS)-based simultaneous wireless information and power transfer (SWIPT) for multiple-input multiple-output (MIMO) interference channel networks where multiple transceiver pairs share the same frequency spectrum. As the PS model is adopted, an individual receiver splits the received signal into two parts for information decoding (ID) and energy harvesting (EH), respectively. Aiming to minimize the total transmit power, transmit precoders, receive filters and PS ratios are jointly designed under a predefined signal-to-interference-plus-noise ratio (SINR) and EH constraints. The formulated joint transceiver design and power splitting problem is non-convex and thus difficult to solve directly. In order to effectively obtain its solution, the feasibility conditions of the formulated non-convex problem are first analyzed. Based on the analysis, an iterative algorithm is proposed by alternatively optimizing the transmitters together with the power splitting factors and the receivers based on semidefinite programming (SDP) relaxation. Moreover, considering the prohibitive computational cost of the SDP for practical applications, a low-complexity suboptimal scheme is proposed by separately designing interference-suppressing transceivers based on interference alignment (IA) and optimizing the transmit power allocation together with splitting factors. The transmit power allocation and receive power splitting problem is then recast as a convex optimization problem and solved efficiently. To further reduce the computational complexity, a low-complexity scheme is proposed by calculating the transmit power allocation and receive PS ratios in closed-form. Simulation results show the effectiveness of the proposed schemes in achieving SWIPT for MIMO interference channel (IC) networks.

Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) have been widely accepted as key techniques of the current and future wireless communication systems. In this paper, an open access MIMO testbed is presented, on which the researchers can demonstrate and evaluate their baseband algorithms over the real wireless channel, without knowing much details about the hardware of the testbed. Moreover, an IEEE 802.11n transmission scheme is implemented as a design example to validate this testbed as well as demonstrate the transmission characteristics of MIMO-OFDM.

This paper proposes a spatial modulated simultaneous wireless information and power transfer (SM SWIPT) scheme to save multiple radio frequency (RF) chains at the transmitter. As SM is adopted, only one RF chain is equipped at the transmit side. To harvest energy and in the same time to transfer information, the received signal is split into two parts according to the defined power splitting factors. The power splitting factors are determined by maximizing the throughput of the information decoding (ID) receiver under the given energy harvesting (EH) constraint. An iterative power splitting algorithm (ISPA) is developed to solve the maximization problem. Its performance is investigated through simulations. In addition, the computational complexity of the proposed algorithm is analyzed. Results show the superiority of the proposed SM SWIPT in throughput through comparison with single-input multiple-output (SIMO) SWIPT and beamformed MIMO SWIPT. What is more, unlike the conventional beamformed MIMO SWIPT that requires perfect channel state information at the transmitter (CSIT), the proposed scheme is open loop and requires no any CSIT, thus can further enhance the superiority in energy efficiency.

In this paper, we present a novel user grouping method for grouped OFDM-IDMA systems. Aiming at maximizing the system capacity, we adaptively distribute users among the pre-allocated subcarrier groups according to their respective channel conditions. Using the notion of SNR evolution function, we first analyze the achievable capacity of the system and formulate the optimization problem as a weighted bipartite matching problem. Due to the analytically intractability of the SNR evolution function, we opt to use either the worst case or best case of the achievable capacity to approximate the original problem. Then Kuhn-Munkres method is employed to solve the approximated problems. The performance of the proposed scheme is evaluated by both theoretical analyses and simulations. Results show that with our proposed algorithm, the system capacity is markedly improved and is very close to the theoretical capacity upper bound.

This paper proposes a power allocation scheme to maximize the sum capacity of all users for signal-to-leakage-and-noise ratio SLNR precoded multiuser multiple-input single-output downlink. The designed scheme tries to explore the effect of the power allocation for the SLNR precoded multiuser multiple-input single-output system on sum capacity performance. This power allocation problem can be formulated as an optimization problem. With high signal-to-interference-plus-noise ratio assumption, it can be converted into a convex optimization problem through the geometric programming and hence can be solved efficiently. Because the assumption of high signal-to-interference-plus-noise ratio cannot be always satisfied in practice, we design a globally optimal solution algorithm based on a combination of branch and bound framework and convex relaxation techniques. Theoretically, the proposed scheme can provide optimal power allocation in sum capacity maximization. Then, we further propose a judgement-decision algorithm to achieve a trade-off between the optimality and computational complexity. The simulation results also show that, with the proposed scheme, the sum capacity of all the users can be improved compared with three existing power allocation schemes. Meanwhile, some meaningful conclusions about the effect of the further power allocation based on the SLNR precoding have been also acquired. The performance improvement of the maximum sum capacity power allocation scheme relates to the transmit antenna number and embodies different variation trends in allusion to the different equipped transmit antenna number as the signal-to-noise ratio SNR changes.Copyright © 2013 John Wiley & Sons, Ltd.

For simulations of multiple-input multiple-output (MIMO) vehicle-to-vehicle (V2V) Rayleigh fading channels under more realistic non-isotropic scattering scenarios, we propose a new parameter computation method for the design of sum-of-sinusoids (SoS) simulation models. Compared with the existing relevant methods, the proposed method has the same simulation efficiency but provides a better approximation to the desired statistical properties of the theoretical reference model.

This paper studies the joint transceiver design and power splitting (PS) for a downlink multiuser multiple-input multiple-output (MU-MIMO) simultaneous wireless information and power transfer (SWIPT) system. The objective of this work is to minimize transmit power by jointly optimizing the transmitter at a base station (BS), the PS factors and information decoding (ID) receivers at mobile stations (MSs) subject to both the mean-square-error (MSE) and energy harvesting (EH) constraints. To solve the formulated nonconvex optimization problem, a framework is proposed to iteratively solve a joint transmitter and PS factors optimization (JTxPS) sub-problem and a receiver side minimum mean-square error (MMSE) minimization subproblem. The nonconvex JTxPS sub-problem is reformulated as a convex semidefinite programming (SDP) and thus solved. Simulation results show the effectiveness of the proposed scheme.

In this paper, a novel closed-loop multiple antennas transmission scheme suitable for M = 2p(p ⩾2) transmit antennas is proposed on the basis of the extended orthogonal space–time block codes. And, all 2p transmit antennas are divided into p groups, and each group includes two antennas, and Alamouti orthogonal space-time block code is adopted. All p groups are used to transmit the same source symbols, and each group is scaled by one scale matrix before transmission. The elegantly designed scale matrix takes both power allocation and phase rotation into account to optimise the antenna array gain and exploit full transmit diversity while maintaining low linear decoding complexity provided by Alamouti code. By formulating the problem as a convex optimisation problem, the optimal solution for the scale matrix is achieved. In addition, several practical feedback codebook design methods are proposed, and their advantages over the existing closed-loop extended orthogonal space–time block code schemes are clearly demonstrated by both analysis and simulation results. Copyright © 2012 John Wiley & Sons, Ltd.

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.

A simple iterative receiver for general nonorthogonal unitary space-time constellations (NOUSTC) is proposed. The output of the conventional noncoherent detector is used to initialize the receiver. In each iteration, the decision from last iteration is used to transform the received signals to derive new signals that bear channel state information (CSI), which are then employed to estimate the CSI using a Wiener filter, following a coherent detector is implemented. In our scheme, for each time block we can use not only the past and the present CSI-bearing signals, but also the future ones, to estimate the CSI, thus resulting in a relatively refined channel estimate and ultimately a receiver with good performance. Simulation results verify the performance of the proposed receiver.

New partial relay selection schemes for cooperative diversity based on amplify-and-forward (AF) relaying are proposed in Nakagami-m fading channels. Their performances are compared with the conventional partial selection scheme. Numerical results show that the new schemes have performance gains of up to 5 dB over the conventional scheme. In some cases, their performances are indistinguishable from the full selection scheme, but they have much simpler structures. Numerical results also show that it is more important to choose the idle user for the hop with a small average signal-to-noise ratio (SNR) or an m parameter in partial selection. Based on this observation, a new adaptive partial selection scheme based on the average SNR, and the m parameter is derived. A complexity analysis also shows that the new schemes reduce the complexity in some cases.

This paper proposes a joint precoding and power allocation strategy to maximize the sum rate of multiuser multiple-input multiple-output (MIMO) relay networks. A two-hop relay link working on amplify-and-forward (AF) mode is considered. Precoding and power allocation are designed jointly at the base station (BS). It is assumed that there are no direct links between the BS and users. Under individual power constraints at the BS and relay station, precoders designed based on zero forcing, minimum mean-square error and maximum ratio transmission are derived, respectively. Optimal power allocation strategies for these precoders are given separately. To demonstrate the performance of the proposed strategies, we simulate the uncoded bit error rate performance of the underlined system. We also show the difference of the sum rate of the system with the optimal power allocation strategies and with average power transmission. The simulation results show the advantages of the proposed joint precoding and power allocation strategies as expected. Copyright © 2011 John Wiley & Sons, Ltd.

In this paper, we propose a quasi-orthogonal space-time block coding (QO-STBC) orthogonal frequency-division multiplex (OFDM) scheme for its application in frequency-selective channels. A novel decoding approach for QO-STBC OFDM is introduced, and it works based on an array-processing technique. The received QO-STBC OFDM symbol array is decomposed by null spaces of the split-up channel matrices, followed by a parallel decoding unit, as an effort to reduce the computational complexity and latency induced by the decoding process. The performance of the proposed system is evaluated over frequency-selective channels by both analysis and computer simulations to show the effectiveness of the scheme.

We present a system for multiuser multiple-input-multiple-output (MIMO) multistream downlink transmission, which employs covariance-based linear precoders at the transmitter and a minimum-mean-square-error (MMSE) equalizer at each receiver. Antennas of user equipment are arranged to receive different streams bound to this user. Furthermore, these antennas receiving different streams are allowed to cooperate with each other through a joint equalizer, leading to a multiuser MIMO multistream transmission link. The precoders are designed per stream based on the covariance channel state information (CSI). Numerical analysis shows the feasibility and usefulness of the presented system. With the proposed approach, the covariance-based precoding concept for multiuser multiple-input-single-output (MISO) single-stream transmission can effectively be extended to a multiuser MIMO multistream transmission link.

In this paper, we investigate the multiple input multiple output (MIMO) direct sequence bipolar pulse amplitude modulation (DS-BPAM) ultra wideband (UWB) system over indoor multipath fading channels based on the research of Alamouti space-time block codes (STBC) and DS-BPAM UWB system. Selective Rake (SRake) receiver is employed in this paper in order to deal with the multipath effects. Theoretical bit error probability of the MIMO DS-BPAM UWB system with SRake receiver is derived. Simulation results of the MIMO DS-BPAM UWB system with SRake receiver and conventional coherent receiver over multipath fading channels are provided. The results show the efficiency of the MIMO DS-BPAM UWB system with SRake receiver.

In this paper, we study the transmit diversity of the cooperative relay system employing multiple-input multiple-output (MIMO) technology, especially for the Alamouti space-time block codes (STBC), over slow Rayleigh fading channel. The transmit diversity gain is achieved by STBC and cooperative technology. Maximum ratio combining (MRC) and maximum likelihood detection (MLD) are applied in the destination node. Two typical relay protocols, generation relay and non-generation relay with two cooperative implementation schemes are studied in this paper. Our attention is paid to the realization and signal processing algorithms of different STBC coded cooperative systems. System bit error probabilities of these cooperative systems are provided in the simulation. Compared with the conventional non-cooperative system and Alamouti STBC scheme, the STBC coded cooperative system obtains two inherent benefits, achieving the spatial diversity offered by the relay channel and also the ability to exert the characteristics of STBC into the relay system.

In this paper, we propose a cross-layer design framework combining adaptive modulation and coding (AMC) with hybrid automatic repeat request (HARQ) based on rate-compatible low-density parity-check codes (RC-LDPC) in multiple-input multiple-output (MIMO) fading channels with estimation errors. First, we propose a new puncturing pattern for RC-LDPC codes and demonstrate that the new puncturing pattern performs similar to the random puncturing but is easier to apply. Then, we apply RC-LDPC codes with the new puncturing pattern to the cross-layer design combing AMC with ARQ over MIMO fading channels and derive the expressions for the throughput of the system. The effect of channel estimation errors on the system throughput is also investigated. Numerical results show that the joint design of AMC and ARQ based on RC-LDPC codes can achieve considerable spectral efficiency gain.

The generation of multiple uncorrelated Rayleigh fading waveforms is often demanded for simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels. In this letter, an improved deterministic sum-of-sinusoids (SoS) channel simulator with a new parameter computation method is proposed to simulate a large number of uncorrelated Rayleigh fading processes. Compared with the existing SoS channel simulators, the proposed deterministic SoS model yields a much better simulation efficiency while still preserving satisfactory approximations to the desired statistical properties of the reference model.

Simulating wideband fading channels, multiple-input multiple-output (MIMO) channels, and diversity-combined fading channels often demands the generation of multiple uncorrelated Rayleigh fading waveforms. In this letter, two appropriate parameter computation methods, namely the method of exact Doppler spread (MEDS) and Lp -norm method (LPNM), for deterministic sum-of-sinusoids (SoS) channel simulators are investigated to guarantee the uncorrelatedness between different simulated Rayleigh fading processes. Numerical and simulation results show that the resulting deterministic SoS channel simulator can accurately and efficiently reproduce all the desired statistical properties of the reference model.

Cognitive radio (CR) is considered one of the prominent techniques for improving the utilization of the radio spectrum. A CR network (i.e., secondary network) opportunistically shares the radio resources with a licensed network (i.e., primary network). In this work, the spectral-energy efficiency trade-off for CR networks is analyzed at both link and system levels against varying signal-to-noise ratio (SNR) values. At the link level, we analyze the required energy to achieve a specific spectral efficiency for a CR channel under two different types of power constraint in different fading environments. In this aspect, besides the transmit power constraint, interference constraint at the primary receiver (PR) is also considered to protect the PR from a harmful interference. Whereas at the system level, we study the spectral and energy efficiency for a CR network that shares the spectrum with an indoor network. Adopting the extreme-value theory, we are able to derive the average spectral and energy efficiency of the CR network. It is shown that the spectral efficiency depends upon the number of the PRs, the interference threshold, and how far the secondary receivers (SRs) are located. We characterize the impact of the multi-user diversity gain of both kinds of users on the spectral and energy efficiency of the CR network. Our analysis also proves that the interference channels (i.e., channels between the secondary transmitter and PRs) have no impact on the minimum energy efficiency.

For the narrow band Wireless Code Division Multiple Access (WCDMA) system, there are some channel coding schemes proposed and applied like Turbo code and convolutional codes. But for the 4G Code Division Multiple Access (CDMA) wideband systems, we have to use new channel coding schemes with high bandwidth efficiency. In this case, multilevel coding (MLC) scheme is easy to map to Multiple Quardrature Amplitude Modulation (MQAM) modulation strategy to be used for 4G, and MLC+MQAM will be a potential channel coding scheme for the error correcting of next generation of mobile systems. A novel criterion, that is ‘capacity rule’ plus ‘mapping rule’, for the design of the optimum MLC scheme for radio systems over Rayleigh fading channels is proposed in this paper. Based on this theory, a few of key issues related to design an optimum MLC system are investigated. These include a novel optimum design criterion proposed, different mapping strategies, different decoding methods of MLC/MSD and MLC/Parallel Decoding on Levels (PDL) and their performance comparison over Additive White Gaussian Noise (AWGN) and Rayleigh fading channels respectively. Copyright © 2003 John Wiley & Sons, Ltd.

The mutual information of spatial modulation (SM) based multiple input and multiple output (MIMO) systems with arbitrary number of transceiver antennas is investigated. An expression of the system mutual information is derived. The expression is not in a closed form and may lead to difficulties when trying to optimize the mutual information. To solve this, based on Jensen Inequality we propose an approximation for mutual information, which is in a closed form. We show that the approximation is accurate in both low and high SNR regimes. In addition, based on the approximated version of the system mutual information, two constellation design critera are proposed to maximize the system mutual information with finite alphabet. Numerical results show that both of the two criteria perform well.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. The recent development of high-speed trains (HSTs), as a high-mobility intelligent transportation system, and the growing demands of broad-band services for HST users, introduce new challenges to wireless communication systems for HSTs. The deployment of mobile relay stations on top of the train carriages is one of the promising solutions for HST wireless systems. For a proper design and evaluation of HST wireless communication systems, we need accurate channel models that can mimic the underlying channel characteristics for different HST scenarios. In this paper, a novel nonstationary geometry-based stochastic model (GBSM) is proposed for wideband multiple-input multiple-output HST channels in rural macrocell scenarios. The corresponding simulation model is then developed with angle parameters calculated by the modified method of equal areas. Both channel models can also be used to model nonstationary vehicle-to-infrastructure channels in vehicular communication networks. The system functions and statistical properties of the proposed channel models are investigated based on a theoretical framework that describes nonstationary channels. Numerical and simulation results demonstrate that the proposed channel models have the capability to characterize the nonstationarity of HST channels. The statistical properties of the simulation model, verified by the simulation results, can match those of the proposed theoretical GBSM. An excellent agreement is achieved between the stationary intervals of the proposed simulation model and those of relevant measurement data, demonstrating the utility of the proposed channel models.

In this work, we propose a novel interference alignment (IA) scheme for two-cell MIMO downlink channels. With this scheme the interference will be aligned to the same directions with the desired signals when the transmitters are sending out the same symbols, otherwise, the interference will be aligned to the orthogonal directions of the desired signals as the traditional IA scheme does. As a result, it outperforms the traditional IA schemes in terms of capacity and mutual information, which is verified by simulation results. Numerical results also show that the mutual information improvement will decrease as the modulation level goes high.

In this paper, a novel trellis coded generalized spatial modulation (TCGSM) scheme is presented and analyzed. Similar to that of the traditional generalized spatial modulation (GSM), a subset of the entire transmit antennas is selected for transmission at each time slot. Nevertheless, in the proposed TCGSM scheme, the bits in the spatial domain are first coded by the trellis encoder before antenna selection. The purpose is to combat the correlation of the MIMO channel and hence improve the system performance. We give the detailed system model as well as the trellis encoding/decoding algorithm for the proposed scheme. The performance of the scheme is evaluated through both theoretical analysis and simulations. The results indicate that the proposed scheme is spectral efficient and robust against the channel correlation.

This paper investigates multi-carrier relay selection schemes in cognitive radio system. As the wireless spectrum resources allocated to primary users cannot be occupied all the time, there are variable available idle sub-channels left for the secondary users (the cooperative communication system in this paper). Two kinds of relay selection schemes are proposed and the system throughput is addressed and analyzed.

Interference alignment (IA) is a promising interference management technique to efficiently eliminate multiuser interference in a K-user interference network. However, channel state information (CSI) at the transmitter is indispensable for the interference alignment precoding matrices design. In spite of the fact that the CSI can be obtained through feedback from receivers to transmitters in a frequency-division duplex (FDD) system or through the reciprocity in a time-division duplex (TDD) system, it may be imperfect for the reason such as estimation inaccuracy, feedback delay and time-varying of channel. In this paper, the impact of imperfect CSI on the achievable sum rate of interference alignment network is considered and a channel prediction technique based on Kalman filtering is proposed to verify the theoretical analysis. Through analysing, we find that the sum rate performance of an interference aligned network is affected by an integrated parameter, i.e., the product of user number, transmit power and channel error variance. Simulation results reveal that the performance of interference alignment is more sensitive to the uncertainty of CSI at high signal-to-noise ratio (SNR) regime than that at low SNR regime. It is also verified that the performance can be improved through channel prediction, comparing with interference alignment based on the delayed feedback CSI.

Hybrid Automatic Retransmission reQuest (HARQ) is an effective technique to improve the reliability of wireless communication systems by detecting, correcting, and retransmitting the erroneous packets. Packet-level error sequences obtained from physical layer wireless communication systems are important for the design and performance evaluation of high layer protocols, e.g., HARQ. In this paper, we utilize the open source Vienna long-term evolution (LTE) simulator to study the impact of HARQ on the burst error statistics of packet-level error sequences. Moreover, we propose a generative model that can generate packet-level error sequences with predicted burst error statistics similar to those of error sequences obtained from wireless systems with HARQ. Simulation results demonstrate that the proposed generative model is accurate and efficient in predicting the behavior of HARQ in terms of a set of burst error statistics rather than predicting the packet error rate (PER) only.

A novel spatial modulation (SM) scheme suitable for correlated Rician fading scenario is proposed with the help of the key idea of Ungerboeck's set partitioning. The motivation is based on the fact that the different error performance exists between the antenna domain and modulation signal domain in the traditional SM scheme. And the total system error performance is mainly determined by the worse case. We analyze the unequal error protection (UEP) performance and find that the error performance of the antenna selection is mainly determined by the correlation coefficient and Rician factor. If the correlation coefficient or Rician factor is large, the error performance will be bad. Considering the error performance of the modulation signal domain is mainly determined by the minimum Euclidean distance between pair of signal points, the error performance of two domains will differ significantly over the fading channels with strong correlation or large Rician factor. The main idea of the novel scheme is to establish the relationship between the antenna domain and modulation signal domain by expanding the signal constellation to carry all the input information bits. The expanded constellation is then partitioned into subsets by using Ungerboeck's set partitioning. The bits mapping to the antenna index are also used to select the partitioned subset, while the remaining bits are used to determine the transmit signal in the selected partitioned subset. In this way, the error performance of the bits mapping to the antenna index is improved, while the error performance of the other bits is preserved by maximizing the minimum Euclidean distance between any pair of signal points in the partitioned subset. Performance analysis and simulation results show that the novel SM scheme could improve the error system performance greatly when the correlation coefficient or Rician factor become larger.

In this paper, a non-stationary wideband geometry-based stochastic model (GBSM) is proposed for multiple-input multiple-output (MIMO) high-speed train (HST) channels. The proposed model employs multiple confocal ellipses model, where the received signal is a superposition of the line-of-sight (LoS) and single-bounced rays. Because of the time-varying feature of angles of arrival (AoAs), angles of departure (AoDs), and LoS angle, the proposed GBSM has the ability to investigate the non-stationarity of HST environment caused by the high speed movement of the receiver. From the proposed model, the local spatial cross-correlation function (CCF) and the local temporal autocorrelation (ACF) are derived for different taps. Numerical results and analysis show that the proposed channel model is capable of characterizing the time-variant HST wireless channel.

In this paper, we present a novel user grouping method for grouped OFDM-IDMA systems. Aiming at maximizing the system capacity, we adaptively distribute the users among the pre-allocated subcarrier groups according to their respective channel conditions. We analyze the achievable capacity of the system and formulate the optimization problem as a weighted bipartite matching problem. Kuhn-Munkres method is employed to solve the problem. The performance of the proposed scheme is evaluated through both theoretical analysis and simulation. It shows that with our proposed algorithm, the system throughput is greatly improved and is very close to the theoretical upper bound.

Cognitive radio (CR) has great potential to improve the spectral efficiency of future wireless networks. This paper focuses on maximizing the sum-capacity of cognitive wireless networks based on signal to leakage noise ratio (SLNR) precoding and hybrid opportunistic spectrum access scheme. We propose a globally optimal power allocation scheme based on a combination of the Branch and Bound framework (B&B) and convex relaxation technique to maximize the sum capacity of all secondary users (SUs). Simulation results indicate that, with the proposed power allocation scheme, the sum capacity of the secondary network can be improved compared to conventional SLNR-precoding-based power allocation schemes.

This paper studies multiple relay selection scheme in cognitive relay network to maximize the signal-to-noise ratio (SNR) of the secondary receiver. We first formulate the relay selection problem as a 0-1 integral programming problem, then propose an iterative relay selection scheme, which is suboptimal but simple. Numerical results indicate that the proposed iterative scheme can always achieve the near-optimal SNR performance.

In this paper, we consider a two-way relay network, where multiple pairs of users exchange their information with the help of a multi-antenna relay station by means of two-way relaying. A relay processing scheme based on minimum mean square error (MMSE) criterion is employed at the relay station to suppress inter- and intra-pair interference. We formulate the optimization problem of minimizing the total transmit power of all users under the relay transmit power constraint and the given sum rate constraint. To solve the optimization problem and get the joint relay processing and power control policy, we propose an iteration algorithm. Simulation results show the performance of the proposed schemes and are coherent with what we expected.