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This paper focuses on the non-convex joint optimization with a dynamic resource of multi-user for an intelligent reflecting surface-enhanced mmWave system, where all users have individual rates or quality of service requirements. Firstly, the objective function of the above non-linear problem is converted into a quadratic programming form under the quality of service constraints. Further, a multi-blocks alternating optimization framework with dynamic power allocation is proposed to obtain the maximum sum-rate, where the relaxed ADMM algorithm is adopted to tackle the optimal full-digital precoder and the corresponding passive reflecting matrix is obtained by the gradient-projection. The numerical results verify that beam optimization should be emphasized in high SNR, but joint dynamic resource allocation can further improve system performance even if the hardware dimensions reaches the limit. [ABSTRACT FROM AUTHOR]

In this paper, novel ergodic capacity (EC) performance evaluation results of a power beacon (PB)-assisted multi-input multi-output (MIMO) wireless powered communication network are presented. In the considered system, the energy harvesting node harvests energy from the radio-frequency signals sent by the dedicated PB and uses this energy to communicate with the destination node. To accurately model the combined effect of multi-path fading and shadowing, it is assumed that the energy transfer link is subject to $\kappa$ - $\mu$ shadowed fading. Performance evaluation results are presented for two cases, depending upon the availability of channel state information (CSI) at the PB, namely, $no$ CSI and $full$ CSI. In the former case, equal power allocation is assumed, whereas, in the later case, energy beamforming is employed to increase energy transfer efficiency. For the performance evaluation of EC under $full$ CSI, a closed-form approximation for the probability density function of the maximum eigenvalue of a $\kappa$ - $\mu$ shadowed distributed random matrix is derived. For both $no$ CSI and $full$ CSI cases, lower and upper bounds on the achievable EC are derived in closed-form. Moreover, in order to obtain further insights on the impact of key parameters on the system performance, asymptotic EC expressions which become very tight at low- and high-signal-to-noise ratio regimes, are obtained. Using the proposed EC lower bound as well as these asymptotic results, simple closed-form expressions for the optimal time split that maximize the achievable EC are derived. Numerically evaluated results accompanied with Monte-Carlo simulations are further presented to corroborate the theoretical analysis. [ABSTRACT FROM AUTHOR]

This paper presents a non-orthogonal multiple access (NOMA) scheme with group detection for uplink multiple-input multiple-output (MIMO) systems, for which an effective precoder design is developed. In the scheme, users are divided into groups in accordance with their locations for detection at the base station. The inter- and intra-group interferences are mitigated by successive interference cancellation (SIC) and transceivers, respectively. Based on a derived approximate signal-to-interference-plus-noise ratio (SINR) for using zero-forcing detection, an iterative power and beamforming update procedure is developed for obtaining the user precoders. The precoder design effectively mitigates the intra-group-inter-user correlation making the adopted approximate SINR represent the original SINR accurately. The proposed multi-group MIMO-NOMA scheme can work under more practical transmit-receive antenna configurations and is shown to outperform upon existing cluster-based MIMO-NOMA schemes in terms of total transmit power for various system configurations. The impact of SIC residuals on the multi-group MIMO-NOMA scheme is investigated. Feasibility conditions for the design under imperfect SIC based on the fractional cancellation error model are developed. [ABSTRACT FROM AUTHOR]

Cache-enabled small base stations (SBS) are capable of relieving the heavy burden of the backhaul link and reducing the transmission latency. The hit probability depends on the coverage probability and caching placement probabilities. However, the interference in the small-cell networks may significantly degrade the coverage probability. In this paper, for MIMO small-cell networks consisting of SBS and users, where both of them are equipped with multiple antennas, a joint interference alignment (IA) and probabilistic caching (JIA-ProbC) scheme is proposed. Using tools from stochastic geometry, the $K$ -th order Voronoi cells are constructed to form clusters, where $K$ SBSs cooperatively serve users within each of the $K$ -th order Voronoi cells. Then, the IA scheme for MIMO interference channel (IC) is employed to cancel the intra-cluster interference within each $K$ -th order Voronoi cell. By exploiting the advantage of multiples antennas at users, the IA scheme can simultaneously support more users interference-free than both the zero forcing (ZF) based interference cancellation scheme for MISO systems and SISO systems without interference management, as more interference can be canceled. Furthermore, the coverage probability is analytically approximated by the a closed-form expression. Moreover, the optimal caching placement probability is analytically derived. Numerical Simulation results show that the proposed JIA-ProbC can significantly outperform the existing joint ZF and probabilistic caching (JZF-ProbC) scheme for MISO systems and SISO probabilistic caching (SISO-ProbC) scheme as well as the joint IA and most popular caching (JIA-MPC) caching scheme. [ABSTRACT FROM AUTHOR]

This paper proposes a stochastic-robust constructive interference (CI) precoding scheme for downlink multi-user MISO systems, assuming that channel state information (CSI) at the transmitter side (CSIT) is contaminated by Gaussian-distributed uncertainties. Our objective is to minimize the total transmit power under users’ quality-of-service constraints: formulating CI at each user with high probabilities for a given target signal-to-noise ratio (SINR). We first analyze the probability of CI under imperfect CSIT. A series of approximations are then developed, transforming the intractable stochastic CI constraints into determined convex constraints. The non-convex stochastic-robust CI power minimization (CIPM) problem is then converted into second-order cone programming. We show that we could create tightened or relaxed approximations by changing the parameters, enabling us to find upper-bounds and lower-bounds for the original stochastic CIPM problem. The best parameter values corresponding to the tightest upper and lower bounds are also discussed and obtained. Simulation results show that the proposed methods reasonably approximate the stochastic CIPM problem. Using the given parameter values, it can guarantee the required probability of CI for each user under acceptable channel uncertainties and outperform the existing robust CI precoding in terms of both transmit power and feasibility rate. The small gap between the upper and lower bounds also shows that the proposed method does not cause too much performance loss. [ABSTRACT FROM AUTHOR]

Vector perturbation (VP) is a nonlinear precoding technique that achieves near-capacity performance in multiuser multiple-input multiple-output systems at the expense of large complexity due to the search for the optimum perturbation vector. In this paper, we present the hybrid Tomlinson–Harashima VP (TH-VP) algorithm, a novel zero-forcing precoding scheme, which combines TH precoding to remove interuser interference, and VP precoding to equalize each user's multiple spatial streams. We show that the two nonlinear techniques can be integrated in a single optimization and that the proposed algorithm has lower computational requirements than any other. The performance of TH-VP is analyzed and simulation results show that TH-VP outperforms conventional zero-forcing VP and approaches the performance of dirty paper coding. [ABSTRACT FROM AUTHOR]

Convergence and density evolution of a low-complexity iterative multiple-input multiple-output detection based on belief propagation over a ring-type pairwise graph are presented for binary data. The detection algorithm to be considered is effectively a forward–backward recursion and was originally proposed by Yoon and Chae in a work published in 2014, in which link-level performance, computational complexity, and convergence for Gaussian input were analyzed in detail. This paper presents the convergence proof and the density evolution framework for binary input to give an asymptotic performance in terms of average signal-to-interference-plus-noise ratio and bit error rate (BER) without channel coding. The BER curve obtained via density evolution shows a good match with the simulation results for uncoded BER in the paper by Yoon and Chae verifying the effectiveness of the analysis provided and the performance of the detection algorithm. [ABSTRACT FROM AUTHOR]

In this paper, we propose an optimal random beamforming technique in mmWave MIMO-NOMA transmission systems. In our model, we consider a NOMA system with a user pairing scheme that works based on the distance between the cellular base station (BS) and the active mobile users. The aim of this is to reduce the system overall overhead for massive connectivity and achieve the desired Quality of Service (QoS). We present an optimization problem with the aims to find the optimal random beamforming coefficients by minimizing the outage probability. We analyze the convexity of the outage probability for three user pairing schemes and prove that the proposed optimal random beamforming is convex in high signal-to-noise ratio (SNR). We utilize the gradient-based algorithm namely the gradient descent algorithm to find optimal random beamforming coefficients. Our simulation results demonstrate that the proposed transmission schemes reduce the outage probability and improve network performance compared to previous works. [ABSTRACT FROM AUTHOR]

Orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) are wireless radio technologies adopted by the new Fifth Generation (5G) of mobile communications. A very large number of antennas (massive MIMO) is used to perform the beam-forming of the transmitted signal, either to reduce the multi-user interference (MUI), when spatially multiplexing several users, or to compensate the path-loss when higher frequencies than microwave are used, such as the millimeter-waves (mm-Waves). Usually, a coherent demodulation scheme (CDS) is used in order to exploit MIMO-OFDM, where the channel estimation and the pre/post-equalization processes are complex and time consuming operations, which require a considerable pilot overhead and also increase the latency of the system. As an alternative, non-coherent techniques based on a differential modulation scheme have been proposed for the up-link (UL). However, it is not straightforward to extend these proposals to the down-link (DL) due to the (usually) reduced number of antennas at the receiver side. In this paper we overcome this problem, and assuming that each user equipment (UE) is only equipped with one single antenna, we propose the combination of beam-forming with a differential modulation scheme for the DL, enhanced by the frequency diversity. The new transmission and reception schemes are described, and the signal-to-interference-plus-noise ratio (SINR) and the complexity are analysed. The numerical results verify the accuracy of the analysis and show that our proposal outperforms the existing CDS with a significant lower complexity. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the system outage performance of full-duplex (FD) two-way relay networks where all nodes are equipped with FD multiple-input multiple-output (MIMO) capability and two sources exchange information via decode-and-forward (DF) relay protocol in two consecutive time slots. In order to completely separate the desired signal and interference, we consider a finite size of buffer at the relay. We propose zero-forcing based beamforming schemes for two different cases of the buffer-aided relay and non-buffer-aided relay. We derive exact closed-form expression and lower bound of the outage probability for those two-way relay system, respectively. Numerical results show that the proposed buffer-aided relay scheme significantly improves the system performance over the conventional scheme in terms of outage probability. [ABSTRACT FROM AUTHOR]

This paper studies the deployment of multiple-input multiple-output (MIMO) full-duplex (FD) relaying systems in a multicell environment, where the source and destination nodes are equipped with a single antenna and communicating via a dual-hop amplify-and-forward (AF) relay station with multiple receive and transmit antennas in the presence of co-channel interference (CCI). This paper addresses the fundamental challenges of loopback self-interference (LI) and CCI when incorporating FD relaying in cellular systems. Due to the higher frequency reuse in FD relaying compared to its half-duplex (HD) relaying counterpart, the CCI is expected to double as the FD relay station simultaneously schedule uplink and downlink transmission on the same channel. The optimal design of relay receive and transmit precoding weight vectors, which maximizes the overall signal-to-interference-plus-noise ratio (SINR) is formulated by a proper optimization problem, and then, a closed-form suboptimal solution based on null space projection is proposed. The proposed precoding vectors are based on the added receive and transmit zero-forcing (ZF) constraints used to suppress the CCI and LI, respectively. To this end, exact closed-form expressions for the outage probability and ergodic capacity are derived, where simpler lower bound expressions are also presented. In addition, the asymptotic high signal-to-noise ratio (SNR) outage probability approximation is also considered, through which the diversity order of the null space projection (ZF/ZF) scheme is found to achieve \mathrmmin(NR-M,\, NT-1), where NR and NT are the number of relay receive and transmit antennas, respectively, and $M$ is the number of CCI interferers. Numerical results sustained by Monte Carlo simulations show the exactness of the proposed analytical expressions, as well as the tightness of the proposed lower bound expressions. In addition, simulation results for the minimum mean square error (MMSE)/ZF scheme is also considered for comparison purposes. Our results reveal that MIMO FD relaying could substantially boost the system performance, compared to its conventional MIMO HD relaying counterpart. [ABSTRACT FROM AUTHOR]

This paper analyzes the performance of the recently proposed quadrature spatial modulation (QSM) multiple-input–multiple-output (MIMO) system over Nakagami- $m$ fading channel. In the analysis, the general distribution of the Nakagami- m$ channel phase is considered. In the literature, performance analysis of spatial modulation (SM) over Nakagami- m$ channel with uniform phase is conducted. However, apart from the very special case of , where Nakagami- $m$ fading corresponds to Rayleigh fading, the phase of the Nakagami- $m$ distribution is not uniformly distributed. It is shown in this paper that the phase of the channel has major impact on the performance of spatial multiplexing MIMO systems such as SM and QSM systems. A general upper bound expression for the average bit error ratio (ABER) performance of QSM is derived, and the impact of different channel parameters is studied. Monte Carlo simulation results are provided to corroborate the exactness of the derived analysis. [ABSTRACT FROM PUBLISHER]

In this paper, we address the ordering of transmit antennas according to reliability for unequal error protection (UEP) in spatially multiplexed (SM) multiple-input multiple-output (MIMO) systems with joint detection at the receiver. When zero-forcing (ZF) detection is adopted, the reliabilities of transmit antennas are explicitly expressed as postequalization signal-to-noise ratios (SNRs). Thus, multiantenna UEP can be implemented by assigning data of high priority to transmit antennas with a high postequalization SNR. Unfortunately, the overall error performance is generally unsatisfactory. Various joint signal detection techniques that achieve maximum likelihood (ML) or near-ML performance have been developed as alternatives to ZF, but it is not obvious how to discriminate the reliabilities of the transmit antennas or the jointly detected symbols. Recently, an ordering technique for antenna reliabilities was proposed that exploits the structure of the previous near-optimal QR-decomposition-based least-reliable-layer joint detection. In this paper, we divide the log-likelihood ratio of each symbol into collaborative and individual components, assuming joint ML detection. We derive a statistical connection between the magnitude order of each component of the multiple symbols (or the corresponding transmit antennas) and the post-ZF-equalization SNRs. Based on the statistical connections, we propose the use of post-ZF-equalization SNR as a criterion for antenna reliability ordering of SM MIMO with various near-optimal, as well as optimal, joint detections. The differentiated error performance of transmit antennas is also shown to be mainly attributed to the difference of individual components, and the tendency becomes stronger as the constellation size increases. Simulations demonstrate that the proposed ordering technique better meets the UEP requirement with lower computational complexity than the conventional ordering. Assuming N_t \times N_t MIMO systems, the previous ordering and the proposed ordering require \mathcal{O}(N_t^3)+\sum_{N=2}^{N_t-1}\mathcal{O}(NN_t^2+N^3) and \mathcal{O}(N_t^3)$, respectively. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a novel receiver scheme for multiple-input–multiple-output (MIMO) single-carrier frequency-division multiple access (SC-FDMA) systems. Various optimal and near-optimalMIMO detection techniques developed for flat-fading channels are not readily applied to MIMO SC-FDMA systems due to the large dimensions of the effective channels. Recently, the system equation of single-input–single-output (SISO) SC-FDMA systems was divided into a number of disjoint subsystems with moderate dimensions, and a previous MIMO detection technique was applied to the subsystems. In this paper, instead of naively extending the previous scheme for SISO SC-FDMA to MIMO SC-FDMA systems, we first express the large system equation of MIMO SC-FDMA, such that the effective channels are block circulant for an arbitrary number of transmit and receive antennas. The block circulant channel structure is then exploited to lower the computational complexity of projections to construct nonoverlapping subsystems. The proposed circulant projection also takes advantage of the sparse channel structure, offering higher postprojection signal-to-noise ratios (SNRs) of the resulting subsystems than those of a naive projection that does not exploit the channel structure. The simulations confirm the desirable performance of the proposed scheme when a relatively small number of subcarriers are used. The proposed technique is also compared with the previous iterative block decision feedback equalization (IB-DFE) and minimum-mean-square-error–prewhitened-maximum-likelihood (MMSE-prewhitened-ML) detection techniques. [ABSTRACT FROM PUBLISHER]

Low-complexity linear precoders are known to be close to optimal for massive multiple-input multiple-output (M-MIMO) systems. However, the large number of antennas at the transmitter imposes a high computational burden and high hardware overloads. In line with this, in this paper, we propose a low-complexity antenna selection (AS) scheme that selects the antennas that maximize constructive interference between the users. Our analyses show that the proposed AS algorithm, in combination with a simple matched-filter (MF) precoder at the transmitter, is able to achieve better performances than systems equipped with a more complex channel inversion (CI) precoder and computationally expensive AS techniques. First, we give an analytical definition of constructive and destructive interference, based on the phase of the received signals from phase-shift-keying-modulated transmissions. Then, we introduce the proposed AS algorithm, which identifies the antenna subset with the highest constructive interference, maximizing the power received by the user. In our study, we derive the computational burden of the proposed technique with a rigorous and thorough analysis, and we identify a closed-form expression of the upper bound received power at the user side. In addition, we evaluate in detail the power benefits of the proposed transmission scheme by defining an efficiency metric based on the achieved throughput. The results presented in this paper prove that AS and green radio concepts can be jointly used for power-efficient M-MIMO, as they lead to significant power savings and complexity reductions. [ABSTRACT FROM AUTHOR]

In this paper, we propose regularized block diagonalization (RBD) precoding using artificial noise (AN) for physical layer security in downlink multi-user MIMO wireless networks. We derive secrecy sum rate and asymptotic secrecy sum rate for the proposed scheme. The optimum power allocation for legitimate users and the AN signal are derived in closed form for optimal asymptotic secrecy sum rate. Our analysis shows that to achieve best performance, it is more efficient to degrade the performance of the eavesdropper than improving legitimate users’ rates. We also study the impact of error in channel estimation on the system and derive closed-form SINR and secrecy sum-rate expressions for this case. Simulations show that the secrecy sum rate of RBD precoding outperforms the secrecy sum rate of regularized channel inversion by 0.5 bits/s/Hz. We also show that in the presence of channel estimation error, our approximate closed forms for secrecy sum rate are very closed to the actual secrecy sum rate over a wide range of SNR and channel estimation error values. [ABSTRACT FROM AUTHOR]

In this paper, we study the transmission of orthogonal space–time block codes (OSTBCs) over a shadowed Rician (SR) land mobile satellite (LMS) link. Specifically, we derive the symbol error rate (SER), diversity order, and the average capacity of the OSTBC-transmission-based scheme over the SR fading LMS communication systems. First, we consider the independent and identically distributed (i.i.d.) SR fading channels and derive the expressions of moment-generating function (mgf) in terms of the Meijer-G function. By substituting the Meijer-G function in terms of hypergeometric function and then by considering the asymptotic approximation of hypergeometric function, the analytical diversity order of the scheme is obtained. The ergodic capacity of the scheme is derived by using the mgf-based approach. The effect of elevation angles over the SER performance of the scheme is analyzed, and it is observed that the performance of the system is improved with increasing values of elevation angles. Next, we consider the OSTBC transmission over correlated SR fading channels and derive the expressions of mgf, SER, diversity order, and average capacity of the considered setup. In particular, it is demonstrated in this paper that, by employing an additional transmit antenna at the satellite along with Alamouti code, the error rate of the LMS communication system can be significantly improved. It is also shown that the correlation has no impact on the diversity order of the system, but it adversely affects the capacity of the system. [ABSTRACT FROM AUTHOR]

In this paper, we consider a single-relay-based decode-and-forward (DF) cooperative multiple-input multiple-output (MIMO) system in which the source, the relay, and the destination are equipped with Ns, Nr, and Nd antennas, respectively. We propose a joint antenna and path selection scheme, which jointly selects the single-transmit and single-receive antenna pairs, along with the selection of either a direct path that consists of source–destination channels or a cooperative path that consists of source–relay and relay–destination channels. The proposed selection scheme is based on the maximization of minimum of maximums (max-min-max) criterion of instantaneous signal-to-noise ratio (SNR). The analysis in this paper is based on the assumptions that all the channels follow independent Rayleigh fading. A closed-form expression of the symbol error rate (SER) for the proposed scheme in a cooperative MIMO system with M-ary phase-shift keying is derived. We extract the analytical diversity order from the derived SER and show that the proposed selection scheme achieves the diversity order of N_{s}N_{d}+N_{r}\mathrm{min}(N_{s},N_{d}) in the considered cooperative MIMO system. Closed-form expressions of bandwidth efficiency (BE) and ergodic capacity (C_{t})$ are derived for the proposed scheme. An optimized selection parameter from the specific set of values is numerically evaluated by maximizing a heuristic utility function (C_{t}\times \mbox{BE}/\mbox{SER}). By using the already-gathered information about the maximum instantaneous SNR of every hop, a power adaptation scheme that maximizes the instantaneous SNR in the cooperative path is proposed and analyzed. The proposed power adaptation scheme, which is applied only in the event of selection of a cooperative path, outperforms the uniform-power-distribution-based DF cooperative MIMO system. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of decoding in large-scale multiple-input–multiple-output (MIMO) systems. In this case, the optimal maximum-likelihood (ML) detector becomes impractical due to an exponential increase in the complexity with the signal and the constellation dimensions. This paper introduces an iterative decoding strategy with a tolerable complexity order. We consider a MIMO system with finite constellation and model it as a system with sparse signal sources. We propose an ML relaxed detector that minimizes the Euclidean distance with the received signal while preserving a constant \ell1 -norm of the decoded signal. We also show that the detection problem is equivalent to a convex optimization problem, which is solvable in polynomial time. Two applications are proposed, and simulation results illustrate the efficiency of the proposed detector. [ABSTRACT FROM PUBLISHER]

This paper proposes a new multiple-input–multiple-output (MIMO) technique called quadrature spatial modulation (QSM). QSM enhances the overall throughput of conventional SM systems by using an extra modulation spatial dimension. The current SM technique uses only the real part of the SM constellation, and the proposed method in this paper extends this to in-phase and quadrature dimensions. It is shown that significant performance enhancements can be achieved at the expense of synchronizing the transmit antennas. Additionally, a closed-form expression for the pairwise error probability (PEP) of generic QSM system is derived and used to calculate a tight upper bound of the average bit error probability (ABEP) over Rayleigh fading channels. Moreover, a simple and general asymptotic expression is derived and analyzed. Obtained Monte Carlo simulation results corroborate the accuracy of the conducted analysis and show the significant enhancements of the proposed QSM scheme. [ABSTRACT FROM PUBLISHER]

In this paper, amplify-and-forward (AF)-based cooperation in a multiple-antenna-based wireless communication system is studied. In particular, we address the problem of hop-by-hop beamforming and combining in a dual-hop AF multiple-input–multiple-output (MIMO) relay network with two antennas at each node over Nakagami- $m$ fading channels for any integer values of $m$. The beamforming and combining vectors are calculated by using a maximum-eigenvalue-based criterion. A moment-generating-function (mgf)-based approach is used for the analysis. We derive a closed-form expression of mgf of the instantaneous received signal-to-noise ratio (SNR) of the considered cooperative scheme. In addition, diversity order analysis of the beamforming-and-combining-based AF MIMO relay system is performed for three cases. It is deduced on the basis of this paper that the diversity order of the hop-by-hop beamforming and combining in an AF MIMO relay system linearly depends upon the minimum of the Nakagami parameters of both hops. [ABSTRACT FROM PUBLISHER]

Channel state information (CSI) is critical for the performance of cooperative multicell transmission. In this paper, the performances of cooperative multicell precoding under global CSI and local individual CSI are analyzed and compared in the large dimensional regime. Using theoretical results from large random matrix theory, we derive large dimensional approximations of signal-to-interference-plus-noise ratio for both precoding cases. Such approximations depend only on the slow fading channel statistics instead of the fast fading channel realizations. It is easy to quantify the performance loss caused by local individual CSI in the large dimensional regime. Two different massive MIMO scenarios are considered. When the number of antennas and that of users go large at the same rate, there is a constant gap between the two CSI cases. When the number of antennas goes large, while the number of users is fixed, the performances of both CSI cases are the same. This means that the impact of limited local individual CSI vanishes. Numerical results validate the theoretical analysis and show that there is constant performance loss due to the price of limited CSI. Also, the performance of precoding with local individual CSI almost decreases linearly with the increased number of BSs for the first scenario. [ABSTRACT FROM PUBLISHER]

We investigate the performance of multiuser multiple-input-single-output (MU-MISO) downlink in the presence of the mutual coupling effect at the transmitter. Contrary to traditional approaches that aim at eliminating this effect, in this paper we propose a joint analog–digital (AD) beamforming scheme that exploits this effect to further improve the system performance. A jointly optimal AD beamformer is first obtained by iteratively maximizing the minimum received signal-to-interference-plus-noise ratio in the digital domain, followed by an optimization on the load impedance of each antenna element in the analog domain. We further introduce a decoupled low-complexity approach, with which existing closed-form beamforming schemes can also be efficiently applied. For the consideration of hardware imperfections in practice, we study the case where the analog load values are quantized, and propose a sequential search scheme based on greedy algorithm to efficiently obtain the desired quantized load values. Moreover, we also investigate the imperfect channel state information (CSI) scenarios, where we prove the optimality for closed-form beamformers, and further propose the robust schemes for two typical CSI error models. Simulation results show that with the proposed schemes the mutual coupling effect can be exploited to further improve the performance for both perfect CSI and imperfect CSI. [ABSTRACT FROM PUBLISHER]

In this paper, we study multiple-input multiple-output (MIMO) systems with a large number of antennas at a base station serving a number of users in a cell. The antennas at the base station are assembled into multiple antenna arrays (MAA), which are well separated to keep independence between the arrays, but in each array, antennas are densely installed. The MAA can be viewed as a flexible configuration of multiple antennas to reduce the space for installing the antennas and benefit from beamforming. In order to determine how dense the MAA can be designed, we define antenna area efficiency, that is the ratio of the achievable rate and the 2-D space required for installing the antennas. Then, we analyze the achievable rate of the massive MIMO system with $K$ uplink users and NM$ antenna elements at the base station placed in N$ square arrays and each array having antennas densely deployed. Specifically, the analytical uplink sum rate is first derived. Then, the sum rate in the low-SNR and high-SNR regimes is studied. A case study is provided to show how dense MAA can be designed in a massive MIMO system. Our analytical and simulations results show that, for ten users in low SNR, a single dense antenna array with $11\times 11$ antennas in a square requires only $1/200$ of the area of conventional 100 independent antennas to achieve the same rate. For ten users in high SNR, we find that two $8\times 8$ square arrays can achieve the highest antenna area efficiency in comparison with one $16\times 16$ antenna array, four $5\times 5$ antenna arrays, and 100 independent antennas. [ABSTRACT FROM PUBLISHER]

This paper presents a two-phase process consisting of advantage distillation (AD) and information reconciliation for achieving secret sharing over a wiretap channel. By using the feedback bits from the legitimate receiver to transmitter, we propose a novel AD scheme for multiple-input multiple-output (MIMO) wiretap (MIMO-WT) channels. We first generalize the extended orthogonal space-time block codes (EO-STBCs). Then, based on the generalized EO-STBCs (GEO-STBCs) and channel state information (CSI), the feedback bits transmitted from the legitimate receiver to the transmitter are generated to increase the signal-to-noise ratio (SNR) gap between the legitimate receiver and the eavesdropper. Simulation results show that the feedback performance gain of the proposed AD scheme increases rapidly with the number of transmit antennas and the value of SNR. A bit error rate (BER) performance gain up to 5.5 dB is obtained by the legitimate receiver over the eavesdropper at the BER of 10^-5. Moreover, it is also shown that the secrecy capacity of two-way MIMO-WT channels with feedback grows rapidly in low SNR regime and grows slowly in high SNR regime. [ABSTRACT FROM AUTHOR]

This paper investigates the secrecy outage performance of buffer-aided multirelay multiple-input multiple-output cooperative systems in the presence of a passive eavesdropper. Due to the unavailability of the channel state information of eavesdropper's channel, a buffer-aided joint transmit antenna and relay selection scheme based on the main channel is proposed to enhance the secrecy performance. Specifically, we model the evolution of the relay buffers as a Markov chain and derive new exact and asymptotic closed-form expressions for the secrecy outage probability, which provides an efficient way to assess the effect of system parameters on the secrecy outage probability. Moreover, simple asymptotic results are further exploited under two special scenarios, i.e., $L \rightarrow \infty$ and L \not\rightarrow \infty$ (where L$ denotes the size of the relay buffers), for characterizing the achievable secrecy diversity gain, the secrecy coding gain, and the secrecy diversity-multiplexing tradeoff. Our results reveal that: 1) a secrecy diversity gain of is achieved when $L \not\rightarrow \infty$, however, when $L \rightarrow \infty$, the secrecy diversity gain increases to $N_RM(N_S+N_D)$, where $N_S$, $N_R$ , and $N_D$ represent the number of antennas at the source, each of $M$ relays and the destination, respectively. 2) The eavesdropper's channel does not affect the secrecy diversity gain but only the secrecy coding gain in both the two scenarios. [ABSTRACT FROM AUTHOR]

To leverage the benefits of multiple-input multiple-output in high-mobility communications, this paper proposes a broad beamforming approach (BBA), which focuses a broad beam on a moving user on the basis of the moving user's current location and velocity information. So, the moving user can be covered and tracked by the broad beam and is able to achieve high received signal-to-noise ratio (SNR). An optimization problem is formulated to minimize the required power by jointly optimizing the transmit and the receiving beam vectors, while guaranteeing the desired information rate of the moving user. Since the problem is with infinite constraints and has no known solution, we design an efficient algorithm to solve it, where the transmit and receiving beam vectors are optimized by using semidefinite relaxation alternatively in an iterative manner. Simulation results show that by using our proposed BBA, the desired information rate of the high-mobility user can be guaranteed. Compared with existing schemes, with the same power consumption, our proposed scheme can enhance the SNR greatly within the moving region of interest. Besides, by increasing the number of transmit antennas, the required power can be further decreased. [ABSTRACT FROM PUBLISHER]

This paper provides a comprehensive scaling law-based performance analysis for multicell multiuser massive multiple-input-multiple-output (MIMO) downlink systems. Imperfect channel state information (CSI), pilot contamination, and channel spatial correlation are all considered. First, a sum-rate lower bound is derived by exploiting the asymptotically deterministic property of the received signal power, while keeping the random nature of other components in the signal-to-interference-plus-noise-ratio (SINR) intact. Via a general scaling model on important network parameters, including the number of users, the channel training energy and the data transmission power, with respect to the number of base station antennas, the asymptotic scaling law of the effective SINR is obtained, which reveals quantitatively the tradeoff of the network parameters. More importantly, pilot contamination and pilot contamination elimination (PCE) are considered in the analytical framework. In addition, the applicability of the derived asymptotic scaling law in practical systems with large but finite antenna numbers are discussed. Finally, sufficient conditions on the parameter scalings for the SINR to be asymptotically deterministic in the sense of mean square convergence are provided, which covers existing results on such analysis as special cases and shows the effect of PCE explicitly. [ABSTRACT FROM PUBLISHER]

The evaluation of the coverage probability of multistream multiple-input multiple-output (MIMO) communications in HetNets subject to noise, fading, and intercell interference is undoubtedly intricate. Unfortunately, the current literature misses its comprehensive evaluation, as the effects of noise and cross-stream correlation are often overlooked. Furthermore, computationally friendly expressions of the coverage probability allowing engineering insights and adaptive system design are lacking. For multistream MIMO zero-forcing beamforming, in this paper we tackle these issues by considering scenarios where a receiver is in the coverage if all of its data-streams are successfully decoded. Assuming the max signal-to-interference-plus-noise ratio (SINR) cell association (CA), we adopt the stochastic geometry tools to provide an upper bound and an easy-to-compute closed-form lower bound on the coverage probability, while their accuracies are confirmed against extensive simulations. Our contributions are as follows. We prove that full correlation of data streams of a given link slightly reduces the coverage performance. We show that from a coverage probability perspective, the single stream communication is preferable. We exploit our analysis to explore several pertinent design issues, which have not fully discussed in the literature. Our results demonstrate tradeoffs between densification and multiplexing gains. We, further, see that by appropriately designating feedback channel with modest capacity 8 bits per frame per user, the spatial throughput grows by nearly 180 $\%$ over the conventional 1-bit feedback scenario. Finally, We present important extensions of our analysis to underlay spectrum sharing, practical aspects of the max-SINR CA, and a nonhomogeneous path loss environment. [ABSTRACT FROM PUBLISHER]

Cognitive radio (CR) in conjunction with multiple-input multiple-output (MIMO) orthogonal frequency-division multiple access is a candidate technology for future mobile radio networks. The short communication range of underlay CR systems is commonly a major limiting factor. In this paper, we propose a computationally and spectrally efficient resource allocation scheme for multiuser MIMO orthogonal-frequency-division-multiplexing-based underlay CR networks to provide good spectral efficiency gain and, therefore, increased communication range. Since the formulated optimization problem defines a mixed-integer programming (combinatorial task) that is hard to solve, we propose a two-phase scheme to produce efficient solutions for both the downlink and the uplink. Particularly, the first procedure elaborates on an adaptive precoding that is characterized by spectral efficiency due to the degrees of freedom it can provide. The second procedure develops a fast subcarrier mapping algorithm, which can be worked out through optimal power distribution among the CR users. The proposed scheme is optimal for the downlink but, however, near-optimal for the uplink. Simulation results demonstrate the bandwidth and computational efficiencies of the proposed scheme compared with the state of the art. [ABSTRACT FROM AUTHOR]

The recent concept of beamspace multiple input multiple output (MIMO) with discrete lens array can utilize beam selection to reduce the number of radio-frequency chains (RF) required in terahertz (THz) massive MIMO systems. However, to achieve the capacity-approaching performance, beam selection requires information on a beamspace channel of large size. This is difficult to obtain since the user mobility usually leads to the fast variation of THz beamspace channels, and the conventional real-time channel estimation schemes involve unaffordable pilot overhead. To solve this problem, in this paper, we propose the a priori aided (PA) channel tracking scheme. Specifically, by considering a practical user motion model, we first excavate a temporal variation law of the physical direction between the base station and each mobile user. Then, based on this law and the special sparse structure of THz beamspace channels, we propose to utilize the obtained beamspace channels in the previous time slots to predict the prior information of the beamspace channel in the following time slot without channel estimation. Finally, aided by the obtained prior information, the time-varying beamspace channels can be tracked with low pilot overhead. Simulation results verify that to achieve the same accuracy, the proposed PA channel tracking scheme requires much lower pilot overhead and signal-to-noise ratio (SNR) than the conventional schemes. [ABSTRACT FROM AUTHOR]

Line-of-sight (LoS) multiple-input multiple-output (MIMO) gives full spatial-multiplexing gain when the antenna array geometry and orientation are designed based on the interterminal distance. These known design methodologies that hold for antenna arrays with fixed orientation do not provide full MIMO gains for arbitrary array orientations. In this paper, we study LoS MIMO channels with random array orientations when the number of transmit antennas used for signaling is 2. We study the impact of common array geometries on error probability, and identify the code design parameter that describes the high signal-to-noise ratio (SNR) error performance of an arbitrary coding scheme. For planar receive arrays, the error rate is shown to decay only as fast as that of a rank 1 channel, and no better than SNR^-3 for a class of coding schemes that includes spatial multiplexing. We then show that for the tetrahedral receive array, which uses the smallest number of antennas among nonplanar arrays, the error rate decays faster than that of rank 1 channels and is exponential in SNR for every coding scheme. Finally, we design a LoS MIMO system that guarantees a good error performance for all transmit/receive array orientations and over a range of interterminal distances. [ABSTRACT FROM AUTHOR]

Distributed multiple-input multiple-output (D-MIMO) is a promising technique for next-generation wireless networks, which offers a remarkable spectral efficiency gain over the conventional colocated MIMO (C-MIMO). In contrast to C-MIMO, which can be regarded as a special case of D-MIMO, performance analysis of D-MIMO is a challenging problem. This is because radio channels between a user and the distributed radio ports (RPs) are characterized by nonidentical path-loss and shadowing effects that render the classical analytical methods nontractable. In this paper, new accurate expressions for the uplink spectral efficiency of D-MIMO and C-MIMO systems are presented and compared for given large-scale coefficients. We further consider the uplink spectral efficiency for a single-cell distributed large-scale MIMO (D-LMIMO) system with linear zero-forcing (ZF) receivers that account for path loss along with shadow fading and multipath fading effects. Exact expressions for the average spectral efficiency over shadow fading in the asymptotically very large number of RPs antenna regime is explicitly derived, and a tight closed-form lower bound on the asymptotic spectral efficiency is presented. We demonstrate that, the transmit power of each user in D-LMIMO can be scaled down proportionally to the inverse of the number of RP antennas with no performance reduction. Moreover, we study the spectral efficiency of a D-MIMO in a multicell environment taking into account accurate cochannel interference (CCI) models. These expressions provide meaningful insights into the impact of signal-to-noise ratio (SNR), RPs and user positions, number of RPs antennas, shadow fading, and out-of-cell interference on the spectral efficiency of D-MIMO over practical scenarios. Finally, numerical results are validated by simulation to confirm our analysis. [ABSTRACT FROM AUTHOR]

In this paper, we study a multihop distributed relay network consisting of a single source–destination pair and multiple nonregenerative single-antenna relay nodes, which are arranged in different layers. Due to the distributed deployment, the amplifying matrix of the relay nodes at each layer has to be a diagonal matrix. We adopt a layer-by-layer approach to compute the relay amplifying matrices with the objective of maximizing the end-to-end transmission rate. The amplifying matrix of each layer is derived from a per-layer sum-rate maximization problem. When there is only one receiving node at the direct forward layer, the nonconvex per-layer sum-rate maximization problem is equivalently converted into a convex quadratically constrained quadratic program and could be efficiently solved. When there are multiple receiving nodes at the direct forward layer, the nonconvex per-layer sum-rate maximization problem is more challenging. We then transform it into a difference-of-convex program and design iterative convex programing to yield an approximate solution. The analysis shows that the proposed iterative algorithm will converge to local optima of the per-layer sum-rate maximization problem. Simulation results confirm that the proposed scheme outperforms the existing works in terms of the end-to-end transmission rate and is more effective in suppressing noise propagation. [ABSTRACT FROM AUTHOR]

In uplink device-to-device (D2D) underlay cellular systems, massive multiple-input multiple-output (MIMO) seems promising as the large antenna array at the base station (BS) can nearly null the D2D-to-cellular interference. However, the channel-state information (CSI) from all users is required to obtain this advantage. For the orthogonal training scheme, the pilot overhead increases with the number of D2D users, leading to a loss of the achievable spectral efficiency. In this paper, we propose a pilot scheduling scheme for D2D underlay massive MIMO systems, which allows D2D users to reuse the pilots of cellular users so that the pilot overhead can be reduced. Moreover, a novel interference-aided minimum mean square error (MMSE) detector is proposed to suppress the D2D-to-cellular interference, utilizing the estimated CSI from not only cellular users but D2D users as well. Furthermore, we derive the large-scale approximations of the signal-to-interference-plus-noise ratios (SINRs), which are asymptotically tight and accurate, even for a small number of BS antennas. Based on these SINR approximations, performance analyses are given to provide more insights. Simulation results show that the proposed pilot reuse scheme and detector significantly increase the achievable sum spectral efficiency, as compared with the conventional massive MIMO and other baseline schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the performance of a dual-hop multiple-input–multiple-output (MIMO) amplify-and-forward (AF) relay network, where the source, relay, and destination are all equipped with multiple antennas. By using maximum ratio transmission (MRT) at the transmitter and maximum ratio combining (MRC) at the receiver, we first obtain the output signal-to-interference-plus-noise ratio (SINR) of the dual-hop AF relay system, considering multiple cochannel interferences (CCIs), as well as noise at the relay. Then, we derive an exact closed-form expression for the outage probability (OP), and the asymptotic result of OP at high SNR, which can be used to calculate the array gain and diversity order. Finally, computer simulations are conducted to validate the performance analysis. Our new analytical expressions not only provide a fast and efficient method to evaluate the system performance but enable us to gain valuable insights into the effects of key parameters on the MIMO AF relaying network performance that benefits from implementing multiple antennas at each of the three nodes as well. [ABSTRACT FROM PUBLISHER]

In this paper, the performance of a nonregenerative relaying network of multiple-antenna terminal nodes is analyzed with respect to the power allocation issue. Assuming that complete channel state information (CSI) of all links is known at the destination terminal, an optimal power allocation (OPA) approach is investigated subject to constant total power with the objective of maximizing the instantaneous signal-to-noise ratio (SNR) at the destination. Generally, by this OPA approach, the total available power in the system is appropriated to source and relay nodes proportional to channel properties with the aim of coordinating the source–relay and relay–destination hop quality. Closed-form expressions for the outage probability are analytically derived, considering both conventional and maximized SNRs. It is shown that OPA outperforms the conventional uniform power allocation, although the achieved improvement is more significant if the number of destination antennas is less than the number of source antennas. Moreover, the results indicate that the effect of OPA on the performance improvement is significant if the relay node is close to the source terminal. Moreover, it is seen that the minimum number of the source and destination antennas is a determinant parameter in the evaluation of the outage probability. Hence, it is demonstrated that for an efficient system design, the number of source antennas should be as close as possible to that of the destination antennas. In addition, the relay selection scheme is considered to further improve the performance of the system. Finally, simulation results are presented, which confirms the validity of the analysis. [ABSTRACT FROM PUBLISHER]

Joint source/relay precoding has been considered an effective method to improve the system performance of dual-hop amplify-and-forward (AF) multiple-input–multiple-output (MIMO) relay systems. For practical implementations, the codebook-based limited-feedback precoding is widely exploited since the feedback bits can be effectively limited. As known, system performance strongly depends on the codeword selection criterion. In this paper, we will explore how to design the selection criterion when successive interference cancellation (SIC) receivers are adopted at the destination. Starting from the QR-SIC receiver, we first propose a centralized selection scheme by maximizing the minimum postprocessing signal-to-noise ratio (SNR). Next, a decentralized selection scheme is further developed to reduce the computational complexity. Furthermore, we demonstrate that our methods can be directly extended to the system with the minimum mean square error (MMSE)-SIC receiver. Simulation results show that the proposed designs can significantly improve system performance. [ABSTRACT FROM PUBLISHER]

In this paper, nonorthogonal multiple access (NOMA) is applied to large-scale underlay cognitive radio (CR) networks with randomly deployed users. To characterize the performance of the considered network, new closed-form expressions of the outage probability are derived using stochastic geometry. More importantly, by carrying out the diversity analysis, new insights are obtained under the two scenarios with different power constraints: 1) fixed transmit power of the primary transmitters (PTs); and 2) transmit power of the PTs being proportional to that of the secondary base station. For the first scenario, a diversity order of $m$ is experienced at the $m$th-ordered NOMA user. For the second scenario, there is an asymptotic error floor for the outage probability. Simulation results are provided to verify the accuracy of the derived results. A pivotal conclusion is reached that by carefully designing target data rates and power allocation coefficients of users, NOMA can outperform conventional orthogonal multiple access in underlay CR networks. [ABSTRACT FROM PUBLISHER]

We consider a cellular system with amplify-and-forward (AF) nonconcurrent two-way relaying (ncTWR), where a base station serves a transmit-only user and a receive-only user. Most of the state-of-the-art transceiver designs for AF multiple-input multiple-output (MIMO) ncTWR optimize a system-wide objective function subject to the transmit power constraints. Transceiver designs that incorporate quality-of-service (QoS) constraints are not well investigated in ncTWR literature. In this paper, we design a MIMO AF transceiver that maximizes weighted sum-rate (WSR) while guaranteeing the QoS constraints that are cast as per-stream rate required by two ncTWR users. The WSR maximization is a nonconvex problem due to its nonconvex objective. We solve this problem by separately approximating the objective at low and high signal-to-noise ratios (SNRs), with each approximation cast as a geometric program. With extensive numerical evaluations, we first demonstrate the improved performance of the proposed transceiver over existing designs without QoS constraints. We later investigate the effect of QoS constraints on the system WSR. [ABSTRACT FROM PUBLISHER]

In this paper, we provide a practical downlink transmission approach for single-cell full-dimension multiple-input–multiple-output (FD-MIMO) systems with large-scale uniform planar antenna array at the base station (BS). Under the assumption of only statistical channel state information (CSI) at the BS, we derive the optimal beamforming vector of each user by maximizing a lower bound on the average signal-to-leakage-plus-noise ratio. Some main guidelines for user scheduling are also derived under this criterion. Based on these results, a low-complexity 3-D beamforming space-division multiple-access (SDMA) transmission algorithm exploiting only the statistical CSI of each user is proposed. Furthermore, the ergodic sum rate of the proposed algorithm is analyzed, and a closed-form expression, as well as a low signal-to-noise ratio (SNR) approximation and a high-SNR approximation, are derived. Simulation results show that the proposed algorithm performs well in terms of achievable sum rate, and the analytical results on its achievable sum rate are validated. [ABSTRACT FROM AUTHOR]

Zheng and Tse were the first to discover the fundamental diversity–multiplexing tradeoff (DMT) that occurs in multiple-input multiple-output (MIMO) systems. Their research was limited to infinite signal-to-noise ratio (SNR) situations. Later, research was also conducted on finite-SNR situations; however, this research had significant problems with coarse approximation. In this paper, we propose more accurate approximations of the finite-SNR DMT and the outage probability for Rayleigh fading MIMO channels to solve these problems. The proposed formulas provide more general solutions that are applicable not only to uncorrelated and semicorrelated channels but also to fully correlated channels, which have not been considered in the literature. Utilizing the proposed finite-SNR DMT, we further investigate the influence of the deviation of the finite-SNR DMT on system performance. We also derived an accurate SNR offset quantity, which provides a link for transformation of finite-SNR DMT to actual outage probability. Finally, we present computer simulation results for illustration and comparison to confirm the validity of our research work. [ABSTRACT FROM PUBLISHER]

Cooperative diversity systems with optimal and suboptimal antenna and relay selection have been paid significant attention for more than half a decade. However, optimal antenna and relay selection strategies require global channel state information (CSI), which is a cumbersome process. In this paper, we propose a diversity-optimal and three suboptimal transmit–receive antenna and relay selection strategies, named S1, S2, and S3, for decode-and-forward cooperative relaying systems, equipped with Nt and Nr antennas at the source (S) and the destination (D), respectively, and considering a multirelay scenario. Furthermore, we study the symbol error probability (SEP) for these strategies, assuming M-ary phase-shift keying signaling over Rayleigh fading channels. In addition, we perform diversity order analysis through closed-form asymptotic SEP expressions. Since the proposed suboptimal strategies, i.e., S2 and S3, involve the so-called switch-and-examine combining scheme, we compare the complexity of S1, S2, and S3 in terms of the average number of CSI required at D to select the best transmit–receive antenna pair and relay. From the derived SEP expressions, it can be concluded that all three suboptimal strategies achieve the same diversity order of N_{t}N_{r}+N, where N$ is the number of relays, except for the case when the switching threshold signal-to-noise ratio (SNR) is much lower than the average SNR in S2 and S3. Finally, the diversity-optimal strategy achieves full diversity order of N_{t}N_{r}+N\min(N_{t},N_{r}). [ABSTRACT FROM AUTHOR]

In this paper, we consider a distributed multiple-input–multiple-output (D-MIMO) system, where the channel is flat fading and may be correlated, and experiences both small- and large-scale fading. We assume that full knowledge of channel state information (CSI) is available at the receiver and that only the first-and second-order statistics of the channel are available at the transmitter. For such a system with square quadrature amplitude modulation (QAM), an asymptotic symbol error probability (SEP) is derived for the linear zero-forcing (ZF) receiver. Then, we propose an optimal diagonal power loading (PL) strategy that minimizes the dominant term of the asymptotic SEP subject to either a total transmission power constraint when the total power normalization coefficient can be fed back to the transmitter from the receiver or an individual transmission power constraint. A simple closed-form solution is obtained. Computer simulations show that our presented optimal system attains significant performance gains over the currently available equal PL system. [ABSTRACT FROM PUBLISHER]

Current and future mobile network access technologies increasingly rely on multiantenna transmission techniques and on cell miniaturization to achieve orders-of-magnitude gains in capacity. In this paper, we propose and evaluate the idea of multiuser multiple-input–multiple-input-based (MU-MIMO) cell reassignments. Dense small-cell deployments make it possible to pair user equipment units (UEs), which were originally assigned to different cells, enabling multiuser MIMO (MU-MIMO) and resulting in performance improvements to both UEs. We discuss how such pairings can be accomplished, and we assess the potential gains in the resulting spectral efficiency and MU-MIMO usage. These are assessed through both discussion of performance bounds and detailed system-level simulation in a realistic outdoor small-cell scenario. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a dual-hop amplify-and-forward (AF) multiple-input–multiple-output (MIMO) relay network, where the source, relay, and destination are each equipped with multiple antennas. The relay is untrusted if it is willing to forward the signal to the destination and, at the same time, acts as a potential eavesdropper to interpret the message from the source. Since there exists no direct link between the source and the destination, a positive secrecy rate cannot be obtained. Addressing this issue, we propose a joint destination-aided cooperative jamming and precoding at both the source and the relay scheme: joint source, relay, and destination precoding (JP). We target at maximizing the secrecy rate by jointly designing the source, relay, and destination precoding matrices and propose an alternating iterative optimization algorithm to tackle the nonconvex problem. Then, a comprehensive study on the asymptotic performance is conducted in a high signal-to-noise ratio (SNR) regime. In particular, we present simple closed-form expressions for the two key performance parameters in the asymptotic secrecy rate, i.e., the high-SNR slope and the high-SNR power offset. Finally, numerical results are conducted to demonstrate the validity of the proposed secure scheme and its performance analysis. [ABSTRACT FROM PUBLISHER]

In this paper, we consider a cellular two-way relay channel (cTWRC) where multiple mobile stations (MSs) exchange information with a base station (BS) via a relay station (RS). Both the BS and the RS are equipped with a very large-scale antenna array, whereas each MS is equipped with a small number of antennas. We investigate two zero-forcing (ZF)-based nonregenerative relaying schemes for cTWRCs, namely, signal-alignment-based ZF (SA-ZF) and antenna-selection-based ZF (AS-ZF). We focus on analyzing the impact of large antenna arrays on the performance of these low-complexity nonregenerative relaying protocols, and we derive closed-form asymptotic expressions for the signal-to-interference-plus-noise ratio (SINR) and the achievable sum rate when the numbers of antennas at the BS and the RS go large simultaneously. We show that with large-scale antenna arrays, ZF-based relaying can achieve the sum-rate capacity of the cTWRC, either when the RS is located much closer to the BS than to the MSs or when the number of antennas at the BS far exceeds that at the RS. We further show that, with large-scale antenna arrays, the transmit power of the BS and each MS can be made inversely proportional to the number of relay antennas while maintaining a given achievable rate for each end node. Numerical results are provided to verify our analysis. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the space–time network coding (STNC) with antenna selection (AS) in the cooperative multiple-input–multiple-output (MIMO) network, where $U$ users communicate with a common destination D$ with the aid of R$ decode-and-forward (DF) relays. In this network, the best transmit/receive antenna pair with the highest signal-to-noise (SNR) ratio is selected to perform the signal transmission and reception over the user–destination and relay–destination links. To quantify the performance degradation of STNC with AS due to time delay between instants of channel state information (CSI) estimation and data transmission, we derive the symbol error rate (SER) and capacity expressions over flat Rayleigh fading channels. The asymptotic SER expression reveals that STNC with AS guarantees full diversity order of , where N_u$, N_r$, and are the antenna numbers of user u$, relay r$, and the destination D. We also examine the effect of spatial correlation on the performance of STNC with AS by obtaining new closed-form expression for the asymptotic SER, which indicates that STNC with AS achieves the full diversity order over flat correlated Rayleigh channels, regardless of the value of spatial correlation coefficient. Numerical and simulation results are provided to demonstrate the accuracy of our theoretical analysis and evaluate the performance of STNC with AS. [ABSTRACT FROM AUTHOR]

In this paper, we examine orthogonal space–time block coding with receiver maximal ratio combining (OSTBC/MRC) and selection combining (OSTBC/SC) in multiple-input–multiple-output (MIMO) decode-and-forward (DF) relay networks with underlay spectrum sharing, considering optimal and suboptimal cases. The secondary network under consideration is equipped with multiple correlated antennas at the source, the relay, and the destination. On the other hand, the primary network is composed of $L$ primary users (PUs), each of which is equipped with multiple correlated antennas. For the considered underlay spectrum sharing, the transmit power condition is related by an interference limit on the primary network and the maximum transmission power in the secondary network. In particular, new exact expressions for the outage probability of the adopted system models are obtained. Moreover, simple asymptotic expressions for the outage probability are provided to enable the characterization of the achievable diversity orders and coding gains. To enhance the secondary network performance, optimal power allocation (PA) between the secondary source and the secondary relay is obtained based on the asymptotic outage probability under the constraints of total allowable transmit power at the secondary user (SU) and maximum allowable interference power limit at the PU. The derived analytical formulas herein are supported by numerical results to clarify the main contributions. [ABSTRACT FROM AUTHOR]

We propose a statistical information-based approach to enhance the performance of the noniterative quasi-maximum-likelihood (QML) receiver (detector plus decoder) recorded at the output of the channel decoder for coded multiple-input–multiple-output (MIMO) systems. As an illustrative example, the QR decomposition with an $M$-algorithm (QRD-M)-based noniterative QML receiver is employed in this paper. We first illustrate that there is a large discrepancy between the amplitude of the raw log-likelihood ratio (LLR) generated by the complexity-constrained QRD-M detector and its reliability, particularly for LLRs with high amplitudes. The discrepancy is shown to be the main underlying cause of degraded performance in coded MIMO systems. Then, we propose a reliability-aware transformation technique, which exploits the statistical relationship between the raw LLR's amplitude and its reliability to adjust the raw LLR's amplitude to a level commensurate with its reliability. By using the proposed statistical knowledge-based technique, the performance of the receiver (detector plus decoder) recorded at the output of the channel decoder is significantly enhanced for high-order modulations. The extension of the proposed method to other QML receivers such as the list sequential (LISS) detector and list sphere detector (LSD)-based receivers is straightforward. [ABSTRACT FROM AUTHOR]