Design and analysis of random-like codes for various multiple-input and multiple-output communication systems are addressed in this work. Random-like codes have drawn significant interest because they offer capacity-achieving performance. We first consider the analysis and design of low-density parity-check (LDPC) codes for turbo multiuser detection in multipath CDMA channels. We develop techniques for computing the probability density function (pdf) of the extrinsic messages at the output of the soft-input soft-output (SISO) multiuser detectors as a function of the pdf of input extrinsic messages, user spreading codes, channel impulse responses, and signal-to-noise ratios. Using these techniques, we are able to accurately compute the thresholds for LDPC codes and design good irregular LDPC codes. We then apply the tools of density evolution with mixture Gaussian approximations to optimize irregular LDPC codes and to compute minimum operational signal-to-noise ratios for ergodic MIMO OFDM channels. In particular, the optimization is done for various MIMO OFDM system configurations which include different number of antennas, different channel models and different demodulation schemes. We also study the coding-spreading tradeoff in LDPC coded CDMA systems employing multiuser joint decoding. We solve the coding-spreading optimization based on the extrinsic information SNR evolution curves for the SISO multiuser detectors and the SISO LDPC decoders. Both single-cell and multi-cell scenarios will be considered. For each of these cases, we will characterize the extrinsic information for both finite-size systems and the so-called large systems where asymptotic performance results must be evoked. Finally, we consider the design optimization of irregular repeat accumulate (IRA) codes for MIMO communication systems employing iterative receivers. We present the density evolution-based procedure with Gaussian approximation for optimizing the IRA code ensemble. We adopt an approximation method based on linear programming to design an IRA code with the extrinsic information transfer (EXIT) chart matched to that of the soft MIMO demodulator.

Next generation wireless systems will use multiple antenna technologies, also known as multiple-input multiple-output (MIMO), to provide high data rates and robustness against fading. MIMO communication strategies for single user communication systems and their practical application in wireless networks are by now well known. MIMO communication systems, however, can benefit from multiuser processing by coordinating the transmissions to multiple users simultaneously. For numerous reasons, work on the theory of multiuser MIMO communication has yet to see broad adoption in wireless communication standards. For example, global knowledge of channel state information is often required. Such an unrealistic assumption, however, makes it difficult in practice to implement precoding techniques. Furthermore, the achievable rates of the conventional multiuser MIMO techniques are far from the theoretical performance bounds. These and other factors motivate research on practical multiuser communication strategies for the MIMO broadcast channel (point to multi-point communication) and the analysis of those strategies. The primary contributions of this dissertation are i) the development of four novel low complexity coordinated MIMO transceiver design techniques to approach the theoretical performance bound and ii) the investigation of the optimality of the proposed coordinated wireless MIMO networks. Several coordinated beamforming algorithms are proposed, where each mobile station uses quantized combining vectors or each base station uses limited feedback from the MS. The asymptotic optimality of the proposed coordinated beamforming system for the MIMO Gaussian broadcast channel is next investigated. For multi-stream transmission, a novel block diagonalized vector perturbation is proposed and the achievable sum rate upper bound of the proposed system is derived. Finally, for multi-cell environments, linear and non-linear network CBF algorithms supporting multiple cell-boundary users are proposed. The optimality of network coordinated beamforming in terms of the number of receive antennas is also investigated. / text

The use of multiple antennas to improve the reliability and capacity of wireless communication has been around for a while, leading to the concept of multiple-input multiple-output (MIMO) communications. To enable full MIMO potentials, the precoding design has been recognized as a crucial component. This thesis aims to design multiuser MIMO precoders of practical interest to achieve high reliability and capacity performance under various real-world constraints like inaccuracy of channel information acquired at the transmitter, hardware complexity, etc. Three prominent cases are considered which constitute the mainstream evolving directions of the current cellular communication standards and future 5G cellular communications. First, in a relay-assisted multiuser MIMO system, heavily quantized channel information obtained through limited feedback contributes to noticeable rate loss compared to when perfect channel information is available. This thesis derives an upper bound to characterize the system throughput loss caused by channel quantization error, and then develops a feedback quality control strategy to maintain the rate loss within a bounded range. Second, in a massive multiuser MIMO channel, due to the large array size, it is difficult to support each antenna with a dedicated radio frequency chain, thus making high-dimensional baseband precoding infeasible. To address this challenge, a low-complexity hybrid precoding scheme is designed to divide the precoding into two cascaded stages, namely, the low-dimensional baseband precoding and the high-dimensional phase-only processing at the radio frequency domain. Its performance is characterized in a closed form and demonstrated through computer simulations. Third, in a mmWave multiuser MIMO scenario, smaller wavelengths make it possible to incorporate excessive amounts of antenna elements into a compact form. However, we are faced with even worse hardware challenges as mixed signal processing at mmWave frequencies is more complex and power consuming. The channel sparsity is taken advantage of in this thesis to enable a simplified precoding scheme to steer the beam for each user towards its dominant propagation paths at the radio frequency domain only. The proposed scheme comes at significantly reduced complexity and is shown to be capable of achieving highly desirable performance based on asymptotic rate analysis. / Graduate

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In this work wireless communication systems with multiple co-channel signals present at the receiver are considered. One of the major challenges in the development of such systems is the computational complexity required for the detection of the transmitted signals. This thesis addresses this problem and develops reduced complexity algorithms for the detection of multiple co-channel signals in receivers with multiple antennas. The signals are transmitted from either a single user employing multiple transmit antennas, from multiple users or in the most general case by a mixture of the two. The receiver is assumed to be overloaded in that the number of transmitted signals exceeds the number of receive antennas. Joint Maximum Likelihood (JML) is the optimum detection algorithm which has exponential complexity in the number of signals. As a result, detection of the signals of interest at the receiver is challenging and infeasible in most practical systems. The thesis presents a framework for the detection of multiple co-channel signals in overloaded receivers. It proposes receiver structures and two list-based signal detection algorithms that allow for complexity reduction compared to the optimum detector while being able to maintain near optimum performance. Complexity savings are achieved by first employing a linear preprocessor at the receiver to reduce the effect of Co-Channel Interference (CCI) and second, by using a detection algorithm that searches only over a subspace of the transmitted symbols. Both algorithms use iterative processing to extract ordered lists of the most likely transmit symbols. Soft information can be obtained from the detector output list and can then be used by error control decoders. The first algorithm named Parallel Detection with Interference Estimation (PD-IE) considers the Additive White Gaussian Noise (AWGN) channel. It relies on a spatially reduced search over subsets of the transmitted symbols in combination with CCI estimation. Computational complexity under overload is lower than that of JML. Performance results show that PD-IE achieves near optimum performance in receivers with Uniform Circular Array (UCA) and Uniform Linear Array (ULA) antenna geometries. The second algorithm is referred to as List Group Search (LGS) detection. It is applied to overloaded receivers that operate in frequency-flat multipath fading channels. The List Group Search (LGS) detection algorithm forms multiple groups of the transmitted symbols over which an exhaustive search is performed. Simulation results show that LGS detection provides good complexity-performance tradeoffs under overload. A union bound for group-wise and list-based group-wise symbol detectors is also derived. It provides an approximation to the error performance of such detectors without the need for simulation. Moreover, the bound can be used to determine some detection parameters and tradeoffs. Results show that the bound is tight in the high Signal to Interference and Noise Ratio (SINR) region.

Several efficient low complexity interference management techniques were developed for improving the performance of multiple-input multiple-output (MIMO) networks. Sub-optimal techniques involving optimal antenna selection-aided stream control were proposed for joint optimization of co-channel MIMO links in a space division multiple access (SDMA) network. Results indicated that the use of the SDMA scheme along with partial channel state information at the transmitters significantly reduces the signaling overhead with minimal loss in throughput performance. Next, a mean squared error (MSE) based antenna selection framework was presented for developing low complexity algorithms for finite complexity receivers. These selection algorithms were shown to provide reasonable bit-error rate performance while keeping the overall system complexity low. Furthermore, some new algebraic properties of linear orthogonal space-time block codes (OSTBCs) were utilized to develop a single-stage and minimum MSE optimal detector for two co-channel users employing unity rate real and derived rate-1/2 complex OSTBCs. A sub-optimal space-time interference cancellation (IC) technique was also developed for a spatial-multiplexing link subjected to Alamouti interference. The performance of proposed interference management techniques and their implications for future research are discussed.

Thesis (M. Sc.)--University of Alberta, 2009. / Title from pdf file main screen (viewed on Aug. 14, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science in Communications, Department of Electrical and Computer Engineering, University of Alberta." Includes bibliographical references.

The problem of information-theoretic optimal resource allocation for the synchronous single-cell CDMA Gaussian multiple access channel is investigated. Several different cases are analyzed including: optimal sequence allocation without power control, optimal sequence allocation with optimal power control and optimal sequence allocation without power control with equal single user capacities. In order to simplify the mathematical description of the multiple access capacity region, a Cholesky decomposition characterization is introduced and utilized to find the optimal sequence allocation for equal single user capacities. The case of randomly chosen spreading sequences in a large system model, i.e. when number of users and processing gain increase without bounds while maintaining their ratio fixed, is also analyzed. Using this model, the performance of a conventional decision feedback receiver in flat fading channels is analyzed. A sequence allocation scheme that uses two sets of orthogonal users that can be decoded with a very simple decision feedback receiver is analyzed. It is shown that the spectral efficiency of this scheme is very close to the maximal possible. Finally, the issue of imperfect channel state information available at the receiver is discussed and the spectral efficiency loss compared to the perfect channel state information case is evaluated for the optimal multiuser receiver. / Graduate

Cooperative and cognitive radio systems have been proposed as a solution to improve the quality-of-service (QoS) and spectrum efficiency of existing communication systems. The objective of this dissertation is to propose and analyze schemes for cooperative and cognitive radio systems considering real world scenarios and to make these technologies implementable. In most of the research on cooperative relaying, it has been assumed that the communicating nodes have perfect channel state information (CSI). However, in reality, this is not the case and the nodes may only have an estimate of the CSI or partial knowledge of the CSI. Thus, in this dissertation, depending on the amount of CSI available, novel receivers are proposed to improve the performance of amplify-and forward relaying. Specifically, new coherent receivers are derived which do not perform channel estimation at the destination by using the received pilot signals directly for decoding. The derived receivers are based on new metrics that use distribution of the channels and the noise to achieve improved symbol-error-rate (SER) performance. The SER performance of the derived receivers is further improved by utilizing the decision history in the receivers. In cases where receivers with low complexity are desired, novel non-coherent receiver which detects the signal without knowledge of CSI is proposed. In addition, new receivers are proposed for the situation when only partial CSI is available at the destination i.e. channel knowledge of either the source-relay link or the relay-destination link but not both, is available. These receivers are termed as `half-coherent receivers' since they have channel-state-information of only one of the two links in the system. In practical systems, the CSI at the communicating terminals becomes outdated due to the time varying nature of the channel and results in system performance degradation. In this dissertation, the impact of using outdated CSI for relay selection on the performance of a network where two sources communicate with each other via fixed-gain amplify-and-forward relays is studied and for a Rayleigh faded channel, closed-form expressions for the outage probability (OP), moment generating function (MGF) and SER are derived. Relay location is also taken into consideration and it is shown that the performance can be improved by placing the relay closer to the source whose channel is more outdated. Some practical issues encountered in cognitive radio systems (CRS) are also investigated. The QoS of CRS can be improved through spatial diversity which can be achieved by either using multiple antennas or exploiting the independent channels of each user in a multi-user network. In this dissertation, both approaches are examined and in multi-antenna CRS, transmit antenna selection (TAS) is proposed where as in a multi-user CRS, user selection is proposed to achieve performance gains. TAS reduces the implementation cost and complexity and thus makes CRS more feasible. Additionally, unlike previous works, in accordance with real world systems, the transmitter is assumed to have limited peak transmit power. For both these schemes, considering practical channel models, closed-form expression for the OP performance, SER performance and ergodic capacity (EC) are obtained and the performance in the asymptotic regimes is also studied. Furthermore, the OP performance is also analyzed taking into account the interference from the primary network on the cognitive network.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico / Nesse trabalho, propÃe-se um esquema de seleÃÃo eficiente e de baixa complexidade para redes cooperativas multiusuÃrio multi-relay compostas de um nà fonte, L nÃs destinos e N nÃs relays. O esquema proposto primeiro seleciona o melhor destino baseado na qualidade de canal dos links diretos e entÃo seleciona o melhor relay que provà o melhor caminho da fonte para o destino selecionado. Considerando-se os protocolos de cooperaÃÃo decodifica-e-encaminha e amplifica-e-encaminha, o desempenho do sistema à investigado. ExpressÃes em forma fechada para a probabilidade de bloqueio sÃo obtidas e validadas por simulaÃÃes de Monte Carlo. ComparaÃÃes com o esquema de seleÃÃo Ãtimo sÃo realizadas e demonstram que o desempenho do esquema de seleÃÃo proposto à bem prÃximo ao do esquema Ãtimo, com a vantagem de o primeiro possuir uma complexidade menor que o Ãltimo. AlÃm disso, em nossa anÃlise, a fonte pode ser equipada com uma Ãnica antena ou com M mÃltiplas antenas. Uma anÃlise assintÃtica à realizada e revela que, independentemente da estratÃgia de cooperaÃÃo empregada, a ordem de diversidade à de L+N para o caso da fonte com uma Ãnica antena, enquanto que para o caso multiantena a diversidade à igual a ML+N. Os efeitos do nÃmero de nÃs relays e destinos no desempenho do sistema e sua influÃncia na posiÃÃo Ãtima do relay sÃo examinados. AlÃm disso, um compromisso entre desempenho e eficiÃncia espectral à observado para o caso em que mÃltiplas antenas sÃo empregadas. / On this work, it is proposed an efficient low-complexity selection scheme for multiuser multi-relay downlink cooperative networks comprised of one source node, L destination nodes, and N relay nodes. The proposed scheme first selects the best destination node based on the channel quality of the direct links and then selects the best relay that yields the best path from the source to the selected destination. Assuming both decode-and-forward and amplify-and-forward relaying strategies, the performance of the considered system is investigated. Closed-form expressions for the outage probability are obtained and validated by means of Monte Carlo simulations. Comparisons with the optimal selection scheme are performed and shows that the performance of the proposed scheme is very close to that of the optimal selection scheme, with the proposed scheme having the advantage of lower complexity than the optimal scheme. Furthermore, in our analysis, the source node may be equipped with either a single antenna or M multiple antennas. An asymptotic analysis is carried out, and it reveals that, regardless of the relaying strategy employed, the diversity order reduces to L+N for the single-antenna source case, whereas it is equal to ML+N for the multiple-antenna source case. The effects of the number of relay and destination nodes on the system performance and its influence on the best relay position are examined. In addition, a trade-off concerning the system performance and spectral efficiency is observed when multiple antennas are employed at the source node.