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Rate-Splitting Multiple Access (RSMA) is a robust multiple access scheme for downlink multi-antenna wireless networks. In this work, we investigate a novel application of RSMA for joint communications and jamming with a Multi-Carrier (MC) waveform in Multiple Input Single Output (MISO) Broadcast Channel (BC). Our aim is to simultaneously communicate with Information Users (IU) and jam Adversarial Users (AU) to disrupt their communications in a setting where all users perform broadband communications by MC waveforms in their respective networks. We consider the practical setting of imperfect CSI at transmitter (CSIT) for the IUs and statistical CSIT for AUs. The optimal information and jamming precoders are designed to maximize the sum-rate under jamming power constraints on the pilot subcarriers of AUs, a jamming method considered to be among the most destructive methods for MC waveforms under the considered system model. We compare the sum-rate performance of RSMA and Space Division Multiple Access (SDMA) schemes by numerical results to demonstrate that RSMA achieves a significant sum-rate gain compared to SDMA.

Rate-splitting multiple access (RSMA) is a promising technique for downlink multi-antenna communications owning to its capability of enhancing the system performance in a wide range of network loads, user deployments and channel state information at the transmitter (CSIT) inaccuracies. In this paper, we investigate the achievable rate performance of RSMA in a multi-user multiple-input single-output (MU-MISO) network where only slow-varying statistical channel state information (CSI) is available at the transmitter. RSMA-based statistical beamforming and the split of the common stream is optimized with the objective of maximizing the minimum user rate subject to a sum power budget of the transmitter. Two statistical CSIT scenarios are investigated, namely the Rayleigh fading channels with only spatial correlations known at the transmitter, and the uniform linear array (ULA) deployment with only channel amplitudes and mean of phase known at the transmitter. Numerical results demonstrate the explicit max min fairness (MMF) rate gain of RSMA over space division multiple access (SDMA) in both scenarios. Moreover, we demonstrate that RSMA is more robust to the inaccuracy of statistical CSIT., conference

In the presented work, a comparative analysis of the bandwidth of information networks of mobile communications is carried out, with a change in the frequency resource of the network and the spatial selectivity of the antenna systems of base stations. It was shown that the use of adaptive antenna systems at the base station allows to achieve a significantly larger increase in network bandwidth compared to an increase in the frequency resource. It is also possible to implement parallel data reception with simultaneous suppression of interfering signals and to coordinate the maximum coverage area of the base station both in the downlink and in the uplink. This allowed us to propose methods to increase the bandwidth of the information network, based on spatial and random methods, in which complex signals are used to coordinate the energy budgets of the downlink and uplink.

In this paper, the performance of non-orthogonal multiple access (NOMA) is investigated and optimized in a downlink space division multiple access network with a multi-antenna base station and randomly deployed users, under a general channel state information (CSI) limited feedback framework. We first propose a dynamic user scheduling and grouping strategy by leveraging limited feedback. Based on that, an analytical framework is proposed to obtain the outage probability of the network in closed form. The diversity order and the impacts of the number of feedback bits on the outage performance of NOMA are analyzed. Furthermore, the net throughput, which captures the network-wide throughput with the uplink feedback cost considered, is maximized by optimizing the number of feedback bits. Numerical results are demonstrated to verify our analytical findings and show that different from the perfect CSI case, there always exists a performance floor of outage probability in the considered network due to limited feedback. Moreover, the optimal number of feedback bits for net throughput maximization increases as the channel coherence time becomes longer.

We present a three-dimensional switched beam antenna suitable for the Space Division Multiple Access paradigm. The antenna is arranged on an half-dodecahedron and its elements operates in circular polarization, hence it is suitable for indoor operation. When hanging from the ceiling, the proposed antenna is the key-component for MIMO system and for position estimation in indoor scenarios. The paper describes the antenna design and the corresponding simulated results.

Massive multiple-input multiple-output (MIMO) wireless communication refers to the idea equipping transmitters with a very large number of antennas, and has been shown to potentially allow for orders of magnitude improvement in spectral and energy efficiency by using relatively simple (linear) processing. In a multi-user MIMO (MU-MIMO) spatial multiplexing scheme, multiple users are scheduled in the same resource block (RB). In 3GPP Long Term Evolution (LTE) systems, single user MIMO (SU-MIMO) rank one precoding based channel quality indicator (CQI) reporting mechanism is reused for MU-MIMO. This is optimum for MU-MIMO if single user is served. This paper is to get an insight of the multi user CQI prediction. A method to estimate the multi user CQI from the reported rank 1 single user CQI is proposed for the space division multiple access (SDMA) mode and zero-forcing (ZF) precoding. Simulation results illustrate that the derived asymptotic value of the MU-MIMO CQI is very close to the real value of that.

Underwater visible light communication (UVLC) is a newly emerging technique in the field of wireless communication. Numerous studies indicated that it can achieve high data rate (on the order of Gbps) over tens of meters of communication link. Multiuser multiple-input multiple-output (MU-MIMO) systems have a potential to provide high capacity, interference suppression and space division multiple access. In this paper the performance of an orthogonal frequency division multiplexing (OFDM)-based MU-MIMO system for underwater visible light communication (VLC) is investigated. It is worth to note that MU-MIMO OFDM has been applied for indoor optical communication, however, to the best of our knowledge, it has not been studied for underwater environment yet. The system is considered to be $2\mathrm {x}2$ and the channel gain for each path is calculated with the closed-form expression for weighted double gamma function (WDGF). Zero-forcing precoding scheme is implemented to eliminate multiuser interference.

Wireless powered sensor networks (WPSNs) have emerged as a key development towards the future self-sustainable Internet of Things (IoT) networks. To achieve a good balance between self-sustainability and reliability, partially WPSNs with a mixed power solution are desirable for practical applications. Specifically, most of the sensor nodes are wireless powered but the key sensor node adopts traditional wire/battery power for reliability. As a result, this paper mainly investigates optimal design for the partially WPSNs in which simultaneous wireless information and power transfer (SWIPT) is adopted in the downlink. Two scenarios with space division multiple access (SDMA) and time division multiple access (TDMA) in the uplink are considered. For both the SDMA-enabled and TDMA-enabled partially WPSNs, joint design of downlink beamforming, uplink beamforming and time allocation is investigated to maximize the uplink sum rate while guaranteeing the quality-of-service (i.e., satisfying the downlink rate constraint) at the key sensor node. After analyzing the feasibility of uplink sum rate maximization problems and the influence of the downlink rate constraint, semi-closed-form optimal solutions for both SDMA-enabled and TDMA-enabled WPSNs are proposed with guaranteed global optimality. Complexity analysis is also provided to justify the advantage of the proposed solutions in low complexity. The effectiveness and optimality of the proposed optimal solutions are finally demonstrated by simulations., Comment: 14 pages

The multiuser detection (MUD) at the receiver end of the Space Division Multiple Access aided Orthogonal Frequency Division Multiplexing (SDMA-OFDM) systems is very crucial for receiver design technologies. Due to the detailed search mechanism, the maximum likelihood (ML) MUD that provides optimal performance is limited to a dramatically increased computational complexity. The QR decomposition with M-algorithm maximum likelihood detection (QRM-MLD) MUD reduces the computational complexity compare with the computational complexity of ML MUD. The minimum mean squared error (MMSE) MUD with low complexity exhibit poor performance. MMSE-successive interference cancellation (SIC) MUD with almost the same complexity provides better bit error rate (BER) performance than linear MMSE MUD. In this paper, Hybrid QRM-MLD-MMSE with SIC adaptive multiuser detection has been proposed for signal detection. The simulation results show that the proposed method significantly reduces the complexity of the system and controls the BER performance of the system at the desired level.

To support space division multiple access (SDMA) in the IEEE 802.11n downlink, a joint beamforming based MAC protocol, J-MAC is presented in this paper. An access point (AP) follows J-MAC, which employs multiple array antennas, and user equipments (UEs) follow the IEEE 802.11x standard which employ omni-directional MIMO antennas. J-MAC maintains full compatibility with 802.11x, and UEs do not change any more. In J-MAC, firstly, the AP achieves the weight vector for the array antenna-based beamforming, and updates it periodically. Secondly, before transmitting any data-frame, the AP achieves the weight vector for the MIMO-based beamforming, which should be updated in each transmission. Finally, after getting the joint beamforming, the AP transmits its data-frames to multiple UEs simultaneously. Simulation results show that J-MAC can support the joint beamforming effectively and provide much higher network throughput, lower delay, jitter and packet-loss-rate than DCF does.

A novel space-division multiple-access (SDMA) method is proposed by the multibeam characteristic of the time-modulated array (TMA). The TMA generates the fundamental and harmonic components pointing to different directions. For the uplink, the users in different directions transmit the signals with the same carrier frequency to the base station with the TMA. Then, the base station distinguishes the users by the generated harmonic components. For the downlink, signals of different users are modulated to different carrier frequencies beforehand. Because of the modulation of the TMA, the downlink signals are transmitted to different directions with the same carrier frequency. Compared to the traditional SDMA systems implemented by the Butler matrix beamforming or the digital beamforming, the proposed method implements the SDMA with a single RF channel, which has advantage in the hardware complexity and cost. The uplink and downlink schemes are analyzed, and their drawbacks are discussed. A simple TMA is constructed to verify its effectiveness.

In this paper we analyze and design a Heterogenous cellular networks (HetNets) where base stations (BSs) are equipped with multi-antennas, serving a number of singleantenna user equipments (UEs) in downlink. We focus of space division multiple access (SDMA) whereby (i) zero-forcing beamforming vectors at the BSs are chosen based on the quantized channel direction information (CDI) and (ii) scheduled data rates are specified adaptively based on the quantized channel quality information (CQI). Adopting tools of stochastic geometry, we firstly, provide a tight approximation of the coverage performance of quantized SDMA beamforming in a closed-form that encompasses impacts of feedback capacity, density of BSs, and SIR thresholds under max-SIR cell association rule. Assuming CQI of each UE is its experienced SIR, we then exploit our analysis to devise a proper optimization problem to adaptively share feedback capacity between tiers, and also between CDI and CQI feedback. We do so by introducing net spatial throughput (NST) as the main performance metric, which is defined as the spatial throughput minus uplink penalty of feedback capacity per area per frame. Our numerical results show that serving more UEs calls for higher capacity of feedback channel without delivering strong NST. We further observe that one way to coup with such a weak performance is to densify the network in tier 2 wherever path-loss exponent is adequately large, e.g., installing many femto-cells in indoor.

Given the critical dependence of broadcast channels by the accuracy of channel state information at the transmitter (CSIT), we develop a general downlink model with zero-forcing (ZF) precoding, applied in realistic heterogeneous cellular systems with multiple antenna base stations (BSs). Specifically, we take into consideration imperfect CSIT due to pilot contamination, channel aging due to users relative movement, and unavoidable residual additive transceiver hardware impairments (RATHIs). Assuming that the BSs are Poisson distributed, the main contributions focus on the derivations of the upper bound of the coverage probability and the achievable user rate for this general model. We show that both the coverage probability and the user rate are dependent on the imperfect CSIT and RATHIs. More concretely, we quantify the resultant performance loss of the network due to these effects. We depict that the uplink RATHIs have equal impact, but the downlink transmit BS distortion has a greater impact than the receive hardware impairment of the user. Thus, the transmit BS hardware should be of better quality than user's receive hardware. Furthermore, we characterise both the coverage probability and user rate in terms of the time variation of the channel. It is shown that both of them decrease with increasing user mobility, but after a specific value of the normalised Doppler shift, they increase again. Actually, the time variation, following the Jakes autocorrelation function, mirrors this effect on coverage probability and user rate. Finally, we consider space division multiple access (SDMA), single user beamforming (SU-BF), and baseline single-input single-output (SISO) transmission. A comparison among these schemes reveals that the coverage by means of SU-BF outperforms SDMA in terms of coverage., accepted in IEEE TVT

In this paper, the outage performance of nonorthogonal multiple access (NOMA) is investigated in a downlink space division multiple access (SDMA) network with a multi-antenna base station and randomly deployed users. The NOMA technology is concurrently exploited with SDMA to further improve spectral efficiency. With limited channel state information (CSI) feedback taken into account, an analytical framework is proposed to evaluate outage performance for a given user. An expression for the outage probability is derived in closed form. Moreover, the diversity order and the effect of the number of feedback bits on the outage performance of NOMA are analyzed. Numerical results are demonstrated to verify our analytical findings and show that different from the perfect CSI case there always exists performance floor in the considered network due to limited feedback.

Despite its promising performance gain, the realization of mmWave massive MIMO still faces several practical challenges. In particular, implementing massive MIMO in the digital domain requires hundreds of RF chains matching the number of antennas. Furthermore, designing these components to operate at the mmWave frequencies is challenging and costly. These motivated the recent development of hybrid-beamforming where MIMO processing is divided for separate implementation in the analog and digital domains, called the analog and digital beamforming, respectively. Analog beamforming using a phase array introduces uni-modulus constraints on the beamforming coefficients, rendering the conventional MIMO techniques unsuitable and call for new designs. In this paper, we present a systematic design framework for hybrid beamforming for multi-cell multiuser massive MIMO systems over mmWave channels characterized by sparse propagation paths. The framework relies on the decomposition of analog beamforming vectors and path observation vectors into Kronecker products of factors being uni-modulus vectors. Exploiting properties of Kronecker mixed products, different factors of the analog beamformer are designed for either nulling interference paths or coherently combining data paths. Furthermore, a channel estimation scheme is designed for enabling the proposed hybrid beamforming. The scheme estimates the AoA of data and interference paths by analog beam scanning and data-path gains by analog beam steering. The performance of the channel estimation scheme is analyzed. In particular, the AoA spectrum resulting from beam scanning, which displays the magnitude distribution of paths over the AoA range, is derived in closed-form. It is shown that the inter-cell interference level diminishes inversely with the array size, the square root of pilot sequence length and the spatial separation between paths., Submitted to IEEE JSAC Special Issue on Millimeter Wave Communications for Future Mobile Networks, minor revision

The design of linear precoders or decoders for multiuser multiple-input multiple-output filterbank multicarrier (FBMC) modulations in the case of a strong channel frequency selectivity is presented. The users and the base station (BS) communicate using space division multiple access. The low complexity proposed solution is based on a single tap per-subcarrier precoding/decoding matrix at the BS in the downlink/uplink. As opposed to classical approaches that assume flat channel frequency selectivity at the subcarrier level, the BS does not make this assumption and takes into account the distortion caused by channel frequency selectivity. The expression of the FBMC asymptotic mean squared error (MSE) in the case of strong channel selectivity derived in earlier works is developed and extended. The linear precoders and decoders are found by optimizing the MSE formula under two design criteria, namely zero forcing or minimum MSE. Finally, simulation results demonstrate the performance of the optimized design. As long as the number of BS antennas is larger than the number of users, it is shown that those extra degrees of freedom can be used to compensate for the channel frequency selectivity., SCOPUS: ar.j, info:eu-repo/semantics/published

In this paper, we investigate the user scheduling, transmit beamforming, and receive beamforming of uplink space division multiple access (SDMA) systems where multiple users are allowed to transmit their signal to a base station (BS) using the same frequency band simultaneously. The BS performs a receive beamforming using the predetermined pseudo-random pattern and select users with a specific criterion. Especially, in this paper, we propose the threshold-based transmit power control, in which a user decrease its transmit power according if its generating interference to other users’s signal is larger than a predetermined threshold. Assuming that the TDD system is used, the channel state information (CSI) can be obtained at each user from pilot signals from the BS. Simulation results show that the proposed technique significantly outperforms the existing user scheduling algorithms. 키워드 : 다중안테나, 셀룰라 네트워크, 빔포밍, 전력 제어, 사용자 스케쥴링 Key word : MIMO, cellular networks, beamforming, power control, user schedulingJournal of the Korea Institute of Information andCommunication Engineering

In this contribution we present the performance of a multi-user transmitter preprocessing (MUTP) assisted multiple-input multiple-output (MIMO) space division multiple access (SDMA) system, aided by double space time transmit diversity (DSTTD) and space time block code (STBC) processing for downlink (DL) and uplink (UL) transmissions respectively. The MUTP is invoked by singular value decomposition (SVD) which exploits the channel state information (CSI) of all the users at the base station (BS) and only an individual user’s CSI at the mobile station (MS). Specifically, in this contribution, we investigate the performance of multi-user MIMO cellular systems in frequency-selective channels from a transmitter signal processing perspective, where multiple access interference (MAI) is the dominant channel impairment. In particular, the effects of three types of delay spread distributions on MUTP assisted MIMO SDMA systems pertaining to the Long Term Evolution (LTE) channel model are analyzed. The simulation results demonstrate that MUTP can perfectly eliminate MAI in addition to obviating the need for complex multi-user detectors (MUDs) both at the BS and MS. Further, SVD-based MUTP results in better achievable symbol error rate (SER) compared to popularly known precoding schemes such as block diagonalization (BD), dirty paper coding (DPC), Tomlinson–Harashima precoding (THP) and geometric mean decomposition (GMD). Furthermore, when turbo coding is invoked, coded SVD aided MUTP results in better achievable SER than an uncoded system.

In this paper, a coding algorithm is proposed for multi-user multi-input multi-output (MU-MIMO) systems to improve the reception performance in fading conditions without reducing the bandwidth efficiency. The space division multiple access (SDMA) scheme that is one of the commonly used for MU-MIMO systems is vulnerable to the fading. The space time block code (STBC) scheme that is used to overcome the fading has a disadvantage of reduced throughput. The proposed MU-MIMO system first encodes transmitted symbols by linear dispersion code (LDC) which is less vulnerable to the fading and increases the throughput in proportional to the number of transmit antennas. Then, the LDC coded symbols are pre-coded by the result of singular value decomposition (SVD) of the estimated channel gain. We evaluate the performance of the proposed scheme compared with the conventional algorithms by computer simulations.

Future wireless systems face challenges in supporting high-rate multimedia streaming with wide coverage area and at low power. Cooperative relaying is investigated in the following context: a single base station with multiple antennas simultaneously transmits different data streams to single-antenna destinations through a set of single-antenna fixed relays, with no direct link transmission between base stations and destinations. Transmission is via space-division multiple access with per-user quality-of-service constraints. The base station performs transmit beamforming (precoding) and relays cooperatively perform distributed beamforming. To address minimum-power source precoding and relay beamforming, the source precoder design with a fixed relay beamformer is first considered. Precoding is also generalized to multiple cooperating base stations. Next, the relay beamformer is optimized for a given source precoder and the process is iterated. The formulation is generalized to account for CSI estimates obtained from pilot symbol training. Simulation results quantify tradeoffs, including numbers of base station antennas and relays, effect of CSI quality on performance, as well as the impact of cooperating base stations.

Coordinated beamforming (CBF) or coordinated scheduling is regarded as an effective means of mitigating the intercell interference (ICI) in orthogonal frequency-division multiplexing (OFDM) systems. In this paper, a new CBF scheme is presented based on leakage-controlled minimum-mean-square-error (LC-MMSE) precoding. We use a regularized factor to maximize the signal-to-interference-plus-noise-ratio (SINR) of LC-MMSE and analyze its achievable throughput loss compared with the conventional minimum-mean-square-error (MMSE) scheme. The results show that the upper bound of the achievable throughput loss increases as the number of serving users grows. A joint frequency and spatial coordination scheme is proposed as an effort to simplify the design of transmit beamforming weights by separating the objective functions that maximize the expected signal strength and minimize the interference leakage in different resource groups. System-level simulation results demonstrate that the proposed scheme can significantly reduce the ICI, and it performs well even with imperfect channel-state information (CSI) at the transmitter.

Multi-user multiple antenna systems have attracted much attention because of large spectral efficiency. However, receiver and transmitter channel state information (CSI) is generally required, especially for the downlink channel. In this study, the authors investigate the ergodic sum rate and present low complexity adaptive transmission scheme for multiple-input single-output downlink multi-user systems with statistical CSI at the base station (BS). The authors derive an approximation of the ergodic sum rate, and the constraint of each user's statistical CSI under which the approximation of the ergodic sum rate is maximised. Then, statistical beamforming space division multiple access transmission is derived through maximising the approximation of the ergodic sum rate, and new adaptive transmission schemes are proposed. The proposed algorithms are shown to perform well and require the BS only to know the statistical CSI of each user.

The most important linear precoding method for frequency-flat MIMO broadcast channels is block diagonalization (BD) which, under certain conditions, attains the same nonlinear dirty paper coding channel capacity. However, BD is not easily translated to frequency-selective channels, since space-time information must be included in the transceiver design. In this paper, we demonstrate that BD is possible in frequency-selective MIMO broadcast channels to eliminate inter-user interference and derive the conditions on the number of transmit antennas and the transmission block length (as functions of the number of users and channel delay spread) for the existence of BD precoders. We also propose three different approaches to mitigate/eliminate inter-symbol interference in block transmissions: time-reversal-based BD (TRBD), equalized BD (EBD), and joint processing BD (JPBD). We show that any transmit-processing-only method (including TRBD and EBD) yields zero diversity and multiplexing gains (high SNR regime). We also demonstrate that JPBD, which uses linear processing at the transmitter and the receiver, approximates full multiplexing gain for a sufficiently large transmit block length, and show its diversity-multiplexing tradeoff. Extensive numerical simulations show that the achievable rate and probability of error performance of all the proposed techniques remarkably improve that of conventional time-reversal beamforming. Moreover, JPBD provides the highest achievable rate region for frequency-selective MIMO broadcast channels.

Massive MIMO is the new emerging technology which can be used to increase the data rate. Massive MIMO reap all benefits of conventional MIMO. In Massive MIMO we use the receiver diversity. In this paper we are proposing Opportunistic space division multiple access technology with beam selection for massive MIMO system technology. OSDMA-S is the technology in which we generate a orthonormal beam which carry the message symbols. In our proposed scheme we are implementing multi antenna for users. In conventional MIMO system we used only one antenna for one receiver, while in the massive MIMO we use a number of antenna at the user to increase the throughput of the system. In this paper we use four antenna four one user. By implementing Massive MIMO we increases the throughput by 100%.

In this paper, we investigate a relay-assisted resource sharing scenario, namely, multi-operator two-way relaying with a MIMO amplify-and-forward (AF) relay. Here, the spectrum and the relay (infrastructure) are shared among multiple operators. We develop the projection based separation of multiple operators (ProBaSeMo) relay transmit strategy, which is inspired by the block diagonalization (BD) and regularized block diagonalization (RBD) schemes that are space-division multiple access (SDMA) approaches for multi-user MIMO systems. If the user terminals are equipped with multiple antennas, appropriate precoding and decoding matrix designs are also proposed. Compared to the time-shared approach where the relay is used by different operators in a time division multiple access (TDMA) manner, we demonstrate that the ProBaSeMO algorithms can provide a significant sharing gain in terms of the sum rate with many antennas at the relay or in the high SNR regime in a two-operator case. For a fixed number of antennas at the relay, an even higher sharing gain can be obtained if the number of operators increases.

In this paper, resource allocation for energy-efficient communication in an orthogonal frequency division multiple access (OFDMA) downlink network with a large number of transmit antennas is studied. The considered problem is modeled as a non-convex optimization problem which takes into account the circuit power consumption, imperfect channel state information at the transmitter (CSIT), and different quality of service (QoS) requirements including a minimum required data rate and a maximum tolerable channel outage probability. The power allocation, data rate adaptation, antenna allocation, and subcarrier allocation policies are optimized for maximization of the energy efficiency of data transmission (bit/Joule delivered to the users). By exploiting the properties of fractional programming, the resulting non-convex optimization problem in fractional form is transformed into an equivalent optimization problem in subtractive form, which leads to an efficient iterative resource allocation algorithm. In each iteration, the objective function is lower bounded by a concave function which can be maximized by using dual decomposition. Simulation results illustrate that the proposed iterative resource allocation algorithm converges in a small number of iterations and demonstrate the trade-off between energy efficiency and the number of transmit antennas.

Research on ultra-wideband (UWB) systems with multiple-input multiple-output (MIMO) configuration has gained a great deal of attention recently. In this article we report a real time experimental UWB MIMO system testbed developed at Tennessee Technological University. We present the architecture, unique capabilities, algorithms development, experimental demonstrations, secure communications scheme with measurement based performances evaluation, and potential applications of the system testbed. Two demonstration cases are used to validate the system. In the first demo case we experimentally investigate UWB MIMO enhanced spatial-temporal focusing property in a harsh RF environment with time reversal waveform precoding technique to take advantage of multipath propagation. In the second demo case UWB MIMO spatial division multiple access (SDMA) in a typical office environment is experimentally verified. In particular, as a physical layer security enhancement, a unique location based security-enhanced communications concept is tested with normal office-area propagation channels, and it is proved to be feasible at certain data rates. First-hand experimental results are collected to support UWB MIMO research.

In this paper, the benefit of rateless codes combining with multi-antenna technique is exploited to provide quality-of-service (QoS) guarantee while maximizing the spectral efficiency in a limited feedback multiuser MIMO downlink. Critical to the design of such a system is the achievement of channel state information (CSI) at the base station (BS) to schedule the optimal users and pre-cancel the interuser interference. In order to reduce feedback amount and decrease scheduling complexity simultaneously, we propose to adopt multi-beam opportunistic beamforming (MOBF) and opportunistic space division multiple access (OSDMA) for the cases of noise and interference limited, respectively. Through theoretical analysis, it is found that, in order to satisfy QoS requirement, the admissible number of users has an upper bound, which is a function of data arrival rate and QoS requirement. With the purpose of balancing the achievable rate and feedback amount, we introduce a new concept, namely netput, as the difference of the above focused factors. By maximizing the netput, we derive the optimal feedback thresholds for the two transmission modes, respectively. Furthermore, according to the characteristics of the considered system, we obtain the optimal switch thresholds for the two modes in terms of the number of users and the SNR, respectively. Finally, our theoretical claims are validated by the numerical results.

The study of multi-user multiple-input multiple-output (MU-MIMO) systems has emerged recently as an important research topic because such systems have the potential to combine the high capacity that can be achieved through MIMO processing with the benefits of spatial-division multiple-access. However, receiver and transmitter channel state information (CSI) is generally required, especially for the downlink channel. In this paper, MU-MIMO downlink transmission systems with statistical CSI at the transmitter are studied for jointly correlated MIMO channels. Eigen-mode space division multiple access transmission is derived based on the maximization of the ergodic sum rate, and two eigen-mode power allocation algorithms are proposed using matrix permanent and convex optimization theory. The new algorithms can overcome the limitations of the existing multi-user downlink transmission algorithm in practical applications.

Improving channel information quality at the base station (BS) is crucial for the optimization of frequency division duplexed (FDD) multi-antenna multiuser downlink systems with limited feedback. To this end, this paper proposes to estimate a particular representation of channel state information (CSI) at the BS through channel norm feedback and a newly developed channel phase codebook, where the long-term channel correlation is efficiently exploited to improve performance. In particular, the channel representation is decomposed into a gain-related part and a phase-related part, with each of them estimated separately. More specifically, the gain-related part is estimated from the channel norm and channel correlation matrix, while the phase-related part is determined using a channel phase codebook, constructed with the generalized Lloyd algorithm. Using the estimated channel representation, joint optimization of multiuser precoding and opportunistic scheduling is performed to obtain an SDMA transmit scheme. Computer simulation results confirm the advantage of the proposed scheme over state of the art limited feedback SDMA schemes under correlated channel environment.

Opportunistic beamforming is a promising technique for downlink channels in cellular systems. When opportunistic beamforming is to support multiple users at a time, it is important to form multiple beams with as little interference as possible. In the conventional approach with limited feedback of channel state information from users, the best beamforming matrix can be selected from a set of multiple beamforming matrices. Thus, at each time when a different set of users are selected by a scheduler, a new beamforming matrix has to be found, which may require excessive complexity. To avoid this problem, in this paper, we propose an opportunistic beamforming approach with a single fixed beamforming matrix for stationary users. Since the beams are fixed, we only need to perform user selection (and power allocation if necessary). It is also shown that the proposed approach is suited for a distributed virtual antenna array built by multiple base station or access point units, since the intercorrelation between the users' channel vectors in this case allows effective opportunistic beamforming based on user classification in conjunction with a single beamforming matrix.

In this paper, for a uplink space division multiple access system named cooperative spatial multiplexing(CSM), radio resource management(RRM) algorithms are proposed based on sharing uplink channel information among a serving base station(BS) and interfering BSs in a uplink coordinated wireless communication system. A constrained maximum transmit power algorithm is proposed for mobile station(MS) to limit uplink inter-cell interference(ICI). And joint scheduling algorithm among coordinated BSs is proposed to enhance uplink capacity through ICI mitigation by using channel information from interfering BSs. It is shown that the proposed RRM algorithm provides a considerable uplink capacity enhancement by effective ICI mitigation only with moderate complexity.

We argue for incorporating Space Division Multiple Access (SDMA) into cooperative relaying, in order to bypass orthogonal relaying transmissions and thus achieve diversity gain without any cost on the available degrees of freedom. In particular, we propose a cooperative relaying scheme that utilizes two single-antenna relays and multiple antennas at the destination terminal, in order to spatially separate the concurrently arriving signals. The whole concept is based upon two key elements: a) To combat the half-duplex constraint by having two relays transmitting alternatively, i.e., the one receiving while the other transmitting and vice versa, and b) to spatially separate the signals arriving concurrently at the destination using the well-known optimum combining technique. Closed-form expressions for the average capacity and outage probability are provided. Numerical results manifest that the proposed model outperforms orthogonal relaying as well as distributed space-time coding in terms of average capacity and outage probability, owing to the former's advantage of higher spectral efficiency.

This paper introduces a novel transmission technique for MIMO broadcasting directional channels, herein called the Angle-of-Departure-Aided Opportunistic Space-Division Multiple Access (AOD-OSDMA) technique. In AOD-OSDMA, the knowledge of angles-of-departure (AODs) at the BS of the strongest signal received by each user is used to design multiple opportunistic beams so that advantage is made of the clustering nature of wireless channels. Compared to the OSDMA-S using 4 × 2 (8 × 2) MIMO system, the proposed technique provides gains in system capacity of up to 50% (160%), and reduces the number of channel directional feedback bits by 33% (55%), when evaluated using MIMO directional channel model such as WINNER.

This work proposes a general equation for the channel reliability (Lc) of turbo code in DS/CDMA systems under flat fading channels and multiple access interference. The proposed reliability equation is suitable for prediction under low, medium as well high signal-noise ratio (SNR) operation system. The channel reliability equation was established as a function of system loading and SNR from fitting of Monte-Carlo simulation (MCS) performance results.

The IEEE 802.16/WiMAX standard has fully embraced multiantenna technology and can, thus, deliver robust performance and high transmission rates. Nevertheless, due to its inherent cost concerns, a WiMAX mobile station (MS) should preferably contain fewer radio frequency (RF) chains than antenna elements. Thus, antenna selection, wherein a subset of antennas is dynamically selected to connect to the limited number of RF chains for transceiving, is a highly appealing performance enhancement technique for multi-antenna WiMAX terminals. In this paper, a novel protocol for antenna selection in space division multiple access (SDMA) transmission is developed for the next-generation IEEE 802.16 mobile stations. Both locally and globally optimal selection rules are considered at the base station (BS). The proposed protocol can readily accommodate various channel situations (e.g., reciprocal and non-reciprocal channels). As demonstrated by analysis and simulation, the proposed protocol delivers considerable performance improvement over conventional IEEE 802.16 terminals that lack antenna selection capability. Moreover, the proposed protocol leverages the existing signaling method defined in IEEE 802.16, thereby incurring a negligible signaling overhead and requiring only minimal modifications of the standard.

In this paper, multi-user multiple input multiple output (MIMO) beamforming techniques with reduced overhead compared to hitherto known works are examined. In previous works, the subscriber station (SS) feeds back the entire channel matrix to the base station (BS) and the BS designs its zero-forcing transmit beamformer and each user's receive beamformer, and feeds forward each user its respective receive beamformer. In this paper, each SS designs its receive beamformer using only its own channel and independent of the other user's channels and feeds back only a vector this framework is called non-collaborative. Assuming zero-forcing beamforming (ZFBF) with a single stream to each SS, we derive the optimal receive beamformer using the average SNR metric and determine the feedback vector based on this optimal receive beamformer. We show that the average receive SNR per user degrades linearly with increasing number of users assuming isotropically distributed MIMO channels and that the dominant right singular vector of the channel matrix is the optimal SS receive beamformer. This optimality holds even when the MIMO channels are correlated. Furthermore, we propose a receive beamformer design in the presence of external interference which can be caused due to aggressive time-frequency reuse in neighboring cells.

The downlink minimum bit error rate (MBER) transmit beamforming is directly designed based on the uplink MBER receive beamforming solution for time division duplex (TDD) space-division multiple-access (SDMA) induced multiple-input multiple-output (MIMO) systems, where the base station (BS) is equipped with multiple antennas to support multiple single-antenna mobile terminals (MTs). It is shown that the dual relationship between multiuser detection and multiuser transmission can be extended to the rank-deficient system where the number of users supported is more than the number of transmit antennas available at the BS, if the MBER design is adopted. The proposed MBER transmit beamforming scheme is capable of achieving better performance over the standard minimum mean square error transmit beamforming solution with the support of low-complexity and high power-efficient MTs, particularly for rank-deficient TDD-SDMA MIMO systems. The robustness of the proposed MBER transmit beamforming design to the downlink and uplink noise or channel mismatch is investigated using simulation.

We consider an ad hoc wireless network consisting of d source-destination pairs communicating, in a pairwise manner, via R relaying nodes. The relay nodes wish to cooperate, through a decentralized beamforming algorithm, in order to establish all the communication links from each source to its respective destination. Our communication strategy consists of two steps. In the first step, all sources transmit their signals simultaneously. As a result, each relay receives a noisy faded mixture of all source signals. In the second step, each relay transmits an amplitude- and phase-adjusted version of its received signal. That is each relay multiply its received signal by a complex coefficient and retransmits the so-obtained signal. Our goal is to obtain these complex coefficients (beamforming weights) through minimization of the total relay transmit power while the signal-to-interference-plus-noise ratio (SINR) at the destinations are guaranteed to be above certain predefined thresholds. Although such a power minimization problem is not convex, we use semidefinite relaxation to turn this problem into a semidefinite programming (SDP) problem. Therefore, we can efficiently solve the SDP problem using interior point methods. Our numerical examples reveal that for high network data rates, our space division multiplexing scheme requires significantly less total relay transmit power compared to other orthogonal multiplexing schemes, such as time-division multiple access schemes.

Herein, we treat Space Division Multiple Access (SDMA) based on partial channel state information and limited feedback. We propose a novel framework utilizing subspace packings, where beamforming, feedback, and scheduling are integrated. Advantages of the proposed framework are that the fed back supportable rates are based on the post-scheduling SINR and that the feedback implicitly contains information about the spatial compatibility of the users. The feasibility region of packings of different dimensions is indicated by the allocation outage probability which is derived. Grassmannian subspace packings, DFT-based packings, and non-orthogonal Grassmannian packings are formulated and studied as candidates. Numerical simulations show better performance for the proposed scheme compared to conventional channel quantization at the receiver with zero-forcing transmission in i.i.d. Rayleigh fading. Finally, we propose and evaluate a beam-graph method to further reduce the feedback load, that can be used in the context of tracking quantized beamformers.

A novel singular value decomposition (SVD)-based joint multiuser transmitter (MUT) and multiuser detector (MUD) aided multiple-input-multiple-output (MIMO) system is proposed, which takes advantage of the channel state information (CSI) of all users at the base station (BS), but only of the mobile station (MS)'s own CSI, to decompose the multiuser (MU) MIMO channels into parallel single-input-single-output (SISO) channels, where each SISO channel corresponds to the singular values of a particular MS's channel matrix. Based on the proposed scheme, the SVD-based transmission carried out in the context of a single user can readily be extended to the MU case for both the uplink (UL) and downlink (DL). As a beneficial application of the proposed scheme, we improve the system's achievable throughput and highlight its future applications.

On the multi-antenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions such as Tomlinson-Harashima precoding are sensitive to CSI inaccuracy. This paper considers a more practical design called per user unitary and rate control (PU2RC), which has been proposed for emerging cellular standards. PU2RC supports multiuser simultaneous transmission, enables limited feedback, and is capable of exploiting multiuser diversity. Its key feature is an orthogonal beamforming (or precoding) constraint, where each user selects a beamformer (or precoder) from a codebook of multiple orthonormal bases. In this paper, the asymptotic throughput scaling laws for PU2RC with a large user pool are derived for different regimes of the signal-to-noise ratio (SNR). In the multiuser-interference-limited regime, the throughput of PU2RC is shown to scale logarithmically with the number of users. In the normal SNR and noise-limited regimes, the throughput is found to scale double logarithmically with the number of users and also linearly with the number of antennas at the base station. In addition, numerical results show that PU2RC achieves higher throughput and is more robust against CSI quantization errors than the popular alternative of zero-forcing beamforming if the number of users is sufficiently large., Comment: 27 pages; to appear in IEEE Transactions on Vehicular Technology

We consider space-time transceiver architectures for space-division multiple-access (SDMA) fading channels with simultaneous transmissions from multiple users. Each user has up to four transmit antennas and employs a space-time orthogonal or a quasi-orthogonal design as an inner code. At the multiple-antenna receiver, efficient successive group interference cancellation strategies based on zero-forcing or minimum mean-square error (MMSE) filtering are employed in some fixed or channel-dependent order. These strategies are efficient in the sense that they exploit the special structure of the inner codes to yield much higher diversity orders than would be otherwise possible, while at the same time preserving what we call the decoupling property of the constituent inner codes which enables the use of low-complexity outer encoders/decoders for each user. Motivated by the special structure of the effective channel matrix induced by the inner codes, we obtain several new distribution results on the QR and eigenvalue decompositions of certain structured random matrices. These results are the key to a comprehensive performance analysis of the proposed multiuser transceiver architectures including the characterization of diversity-multiplexing tradeoff (DMT) curves and exact per-user bit-error rates (BERs) without making simplifying assumptions about error propagation.

The system requirements for IMT-A are currently being specified by the ITU. Target peak data rates of 1 Gb/s in local areas and 100 Mb/s in wide areas are expected to be provided by means of advanced MIMO antenna configurations and very high spectrum allocations (on the order of 100 MHz). For the downlink, OFDMA is unanimously considered the most appropriate technique for achieving high spectral efficiency. For the uplink, the LTE of the 3GPP, for example, employs SCFDMA due to its low PAPR properties compared to OFDMA. For future IMT-A systems, the decision on the most appropriate uplink access scheme is still an open issue, as many benefits can be obtained by exploiting the flexible frequency granularity of OFDMA. In this article we discuss the suitability of using OFDMA or SC-FDMA in the uplink for local area high-data-rate scenarios by considering as target performance metrics the PAPR and multiuser diversity gain. Also, new bandwidth configurations have been proposed to cope with the 100 MHz spectrum allocation. In particular, the PAPR analysis shows that a localized (not distributed) allocation of the resource blocks (RBs) in the frequency domain shall be employed for SC-FDMA in order to keep its advantages over OFDMA in terms of PAPR reduction. Furthermore, from the multiuser diversity gain evaluation emerges the fact that the impact of different RB sizes and bandwidth configurations is low, given the propagation characteristics of the assumed local area environment. For full bandwidth usage, OFDMA only outperforms SC-FDMA when the number of frequency multiplexed users is low. As the spectrum load decreases, instead, OFDMA outperforms SC-FDMA also for a high number of frequency multiplexed users, due to its more flexible resource allocation. In this contex different channel-aware scheduling algorithms have been proposed due to the resource allocation differences between the two blocks chemes.

To achieve high performance, in terms of reliability and throughput, in future multiple-antenna communication systems, it is essential to fully exploit the spatial dimensions of the wireless propagation channel. In multiuser communication systems, the throughput can be significantly increased by simultaneously transmitting to several users in the same time-frequency slot by means of spatial-division multi-access (SDMA). A major limiting factor for downlink SDMA transmission is the amount of channel-state information (CSI) that is available at the transmitter. In most cases, CSI can be measured/estimated only at the user terminals and must be fed back to the base station. This procedure typically constrains the amount of CSI that can be conveyed to the base station. Herein, we develop several low-complexity, as well as optimized, SDMA downlink resource-allocation schemes that are particularly suitable for systems utilizing statistical channel information and partial CSI feedback. A framework is proposed for combining statistical channel information with a class of instantaneous channel norms. It is shown that, in wide-area scenarios, the feedback of such a scalar norm provides sufficient information for the proposed resource-allocation algorithms to perform efficient SDMA beamforming (BF) and scheduling.

In this paper, the mutual information transfer characteristics of several novel turbo multiuser detectors (MUD) employed in space division multiple access (SDMA) aided orthogonal frequency division multiplexing (OFDM) systems are investigated with extrinsic information transfer (EXIT) charts. These novel schemes are the Bayesian, the Soft Interference cancellation aided minimum bit error rate (SIC-MBER) and the reduced-complexity minimum Bit Error Rate (RMBER) turbo MUDs. In order to increase the effective throughput of the system, a powerful MUD has to be employed in the so- called "rank-deficient" scenario, namely when the number of transmit antennas exceeds that of the receiver antennas. The classic minimum mean square error (MMSE) solutions exhibit a low complexity. However, they are overwhelmed in rank-deficient scenarios. In these situations powerful non-linear MUDs are required, which are designed in this treatise.

In this letter a multiuser transmitter preprocessing (MUTP) approach is proposed for downlink wireless communications, such as in spatial-division multiple-access (SDMA) or direct-sequence code-division multiple-access (DS-CDMA) system. In the proposed MUTP the preprocessing matrix is obtained by constructing a subspace that is orthogonal to the interference subspace without relying on eigen-analysis. The proposed MUTP fully removes the downlink multiuser interference, resulting in the zero-forcing (ZF) solution. It is capable of achieving the same bit error rate (BER) performance as the conventional ZF-based MUTP (ZF-MUTP).

Space division multiple access (SDMA) with an antenna array at the transmitter is a promising means for increasing system capacity and supporting rate-demanding services. However, the presence of an antenna array at the physical layer raises significant issues at higher layers. In this paper, we attempt to capture the impact of SDMA on access layer channel allocation, reflected on channel reuse. This impact obtains different twists in TDMA, CDMA and OFDMA due to the different nature of co-channel and cross-channel interference and the different interaction of user spatial channel characteristics with system channels, namely time slots, codes and subcarriers. We consider these access schemes in a generalized unified framework and propose heuristic algorithms for channel allocation, downlink beamforming and transmit power control so as to increase total provisioned system rate and provide QoS to users in the form of minimum rate guarantees. We study the class of greedy algorithms that rely on criteria such as induced or received interference and signal-to-interference ratio (SIR), and a class of SIR balancing algorithms. Results show superior performance for SIR balancing resource allocation and expose the performance benefits of cross-layer design.

We propose a new broadcast strategy for a multiple-input multiple-output (MIMO) system with N transmit antennas at the transmitter and M≤N single antenna receivers. The proposed method, based on dirty-paper coding (DPC), spatially separates the M users but does not suffer from the power loss of classical spatial division multiple access (SDMA). For the special case of M=N=2 and when the two single antenna receivers are assumed to be co-located, the proposed scheme produces a 2 transmit, 2 receiver antenna MIMO transmission system that doubles the symbol rate of MIMO space-time block code (STBC) systems from one to two symbol per transmission time. It is proved theoretically and experimentally that the proposed scheme provides the same performance level as that of MIMO STBC systems (i. e., the Alamouti scheme) for the first symbol, and the same performance as the Bell labs layered space-time (BLAST) system for the second symbol. When compared to the BLAST system, the proposed scheme has the same symbol rate, but achieves significantly better performance, since it provides 2 level diversity per symbol on the first symbol while the BLAST system does not provide any diversity.

This paper considers the use of space division multiple access (SDMA) techniques for the uplink of multi-carrier code division multiple access (MCCDMA) systems, where the transmitted signals face strong nonlinear distortion effects. The signal transmitted by each mobile terminal (MT) is submitted to a nonlinear operation consisting of a clipping device followed by a frequency-domain filtering operation, so as to reduce the envelope fluctuations and peak-to-mean envelope power ratio (PMEPR) while maintaining the spectral occupation of conventional MC-CDMA signals. At the base station, an iterative receiver employing multiple antennas jointly performs turbo multi-user detection and the estimation and cancellation of nonlinear distortion effects. Performance results show that the proposed receiver structures can achieve good performances that are very close to those obtained with linear transmitters, even for high system load and/or when a very low-PMEPR MC-CDMA transmission is intended for each MT.