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Abstract: Today’s wireless networks face scarcity and expense of the radio spectrum, unprecedented increase in data traffic, and excessive energy consumption. The vision of the next generation of wireless networks is to overcome these challenges and provide seamless and ubiquitous wireless connectivity. Cooperative communication (CC) and network coding (NC), referred to as network-coded cooperation (NCC), appears to be the ideal architecture for future wireless networks. The main focus of this thesis is to propose and analyze new NCC transmission strategies and study their performance under practical implementation issues. The first part of this thesis focuses on design and analysis of new transmission strategies in single-antenna NCC systems. Firstly, we propose a two-step user-relay selection in multiuser multirelay NCC systems to exploit both multiuser diversity (MUD) and cooperative diversity (CD). Taking into account practical constraints, we suggest the most generalized user-relay selection (GURS) scheme. It selects any arbitrary subsets of users and any arbitrary subsets of relays. Our analytical results and design guidelines generalize and subsume all existing results as special cases. Secondly, we investigate the performance of a NCC system in an underlay cognitive radio network (CRN). Compared to the existing literature, the proposed CRN NCC has four main distinguishable features: i) it is applicable to general CRN NCC network settings with arbitrary number of sources and relays; ii) it considers general relay selection (RS) and independent and non-identically distributed (i.n.i.d.) Nakagami-m fading channels; iii) it accounts for maximum transmit power at the secondary network (SN) and assumes secondary-to-primary (S2P) and primary-to-secondary (P2S) interference links; and iv) it provides a generalized version of previous works and includes existing results in the literature as special cases. Despite the rich literature on NCC, all existing works have predominantly been focused on relay networks with single-antenna terminals. The applications of multiple-input multiple-output (MIMO) techniques on NCC networks are also interesting, which have been lacking in the literature. Furthermore, not only MIMO NCC is not studied in the literature, but also the existing NCC RS strategies rely on the “max-min” end-to-end (E2E) criterion. This RS strategy will be too complicated even for a network with single-antenna terminals as it requires global channel state information (CSI). Such high signaling overhead leads to difficult implementation of NCC system with RS, especially for a network with a large number of branches. Attracted by the benefits of multi antenna techniques in enhancing NCC system performance, in the second part of the thesis, we firstly extend single-antenna NCC to a multi-antenna scenario. A new RS strategy for NCC systems is also proposed and analyzed. It can substantially reduce the required signaling overhead for RS-based NCC, without sacrificing the performance. Secondly, we investigate the performance of RS MIMO NCC systems under practical implementation issues such as co-channel interference (CCI) and outdated CSI.

An analysis of the diversity gain for bit-interleaved coded multiple beamforming (BICMB) method and BICMB with perfect coding (BICMB-PC) in millimeter-wave (mm-Wave) massive multiple-input multiple-output (MIMO) systems is carried out for both the single-user and multi-user scenarios. We show that full diversity gain and full spatial multiplexing order can be achieved in both scenarios. Also, we show that the diversity gain becomes independent of the number of transmitted data streams and the number of antennas in each remote antenna unit (RAU) at the transmitter and the receiver. Furthermore, in the multi-user scenario, the diversity gain is independent from the number of users in the system, when BICMB or BICMB-PC is utilized. Furthermore, we study BICMB with orthogonal frequency division multiplexing (OFDM) in order to achieve maximum diversity gain in mm-Wave massive MIMO distributed antenna subarray systems. The assumption here is that the channel state information (CSI) is known at both sides of the transmitter and the receiver and the number of antennas in each RAU tends to infinity. This latter assumption can be relaxed by a large number of antennas in each RAU, similar to the case for all massive MIMO research. Simulation results show that when the perfect CSI assumption is satisfied, the use of BICMB results in the diversity gain values predicted by the analysis.

Time asynchrony inherently exists in many wireless communication systems, specially in multiuser scenarios where the signals come from different locations. Different locations and paths impose different delays on the received signals, resulting in asynchronous reception at the receiver. In most of the works in the literature, perfect synchronization is a com- mon presumption. However, it might be impossible to synchronize all the nodes even if an ideal infrastructure with signal overheads is considered. For example, if the receiver encom- passes multiple receive antennas or there are multiple distributed base stations, then, the synchronization can be realized at one of them at most. Thus, it is of great importance to investigate the effect of the time asynchrony in the wireless systems. One natural question is that how to eliminate the time asynchrony and make all the received signals aligned at the receiver. This question is analyzed under the notion of time synchronization. There are many methods in literature trying to achieve this goal. However, the other question which is atypical but even more important is that, is synchronizing the received signals necessary? does the time asynchrony degrade the performance?When the receiver is designed with the presumption of having perfect synchronization, YES, the time asynchrony will degrade the performance. Nevertheless, what if we design the system and the receiver structure with TIME ASYNCHRONY in mind. Does the system that is designed based on the time asynchrony provide worse performance compared to the synchronous one? We will thoroughly investigate this question in this thesis. In a nutshell, we show that by investigating inherent time delays between different users in a multiuser/multi- antenna scenario, we are able to improve the performance. By using proper transmission and receiver design, time asynchrony provides additional degrees of freedom in a time limited communication settings which can be exploited to improve the performance.In Chapter one, more details about time synchronization and the problem of time asynchrony are presented. Then, we introduce the proper structure for exploiting time asynchrony and present the resulting system model. We also explain the reason behind possible advantages of time asynchrony. In Chapter two, we show implementation of different detection methods based on the asynchronous system model. We include different methods like maximum likelihood sequence detection (MLSD), successive interference cancellation (SIC) and Zero Forcing (ZF). In Chapter three, we analytically analyze the achievable performance by the asynchronous transmission and compare it with the conventional synchronous transmission. Two performance criteria are considered. One is the bit error rate (BER) in a fading channel. The other one is the achievable rate in an additive white Gaussian noise (AWGN) channel. The diversity gain of the BER performance and the multiplexing gain of the achievable rates are also derived. Finally, in Chapter 4, simulation results, some discussions and future work are presented.

In modern communication systems, different users have different requirements for quality of service (QoS). In contrast to existing QoS schemes, there is currently no framework in information theory concerning QoS in multi-user systems. In this work an information-theoretic groundwork is proposed to study communication systems which provide heterogeneous reliabilities for the users. This is done by defining individual codeword error probabilities for the users in the network and obtaining their fundamental tradeoff. This tradeoff is quantified by introducing the concept of the error exponent region. Using this framework, a system can be realized, which can provide a tradeoff of reliabilities among the users for a fixed vector of users' rates. This adds a completely new dimension to the performance tradeoff in such networks, which is unique to multi-terminal communication systems, and is beyond what is given by the conventional performance-versus-rate tradeoff in single-user systems. Although this is a very general concept and can be applied to any multi-terminal communication system, in this work we focus on broadcast and multiple access channels. We show the existence of a tradeoff among the users' error exponents by deriving inner and outer bounds for the error exponent region.

Mobile arrays employing diversity combining and adaptive beamforming techniques overcome multipath fading, improve coverage, and increase capacity in wireless communications systems. In this thesis, diversity combining and adaptive beamforming performance of different four element arrays for mobile (vehicular speed) and portable (pedestrian speed) terminals is investigated. The performance of four element arrays with different configurations and with different element patterns is compared using the square array of four half-wave dipole elements as the baseline. Results from diversity and beamforming measurements, performed in urban and suburban environments for both line-of-sight (LOS) and obstructed multipath channels are used to analyze and compare the performances of different four element arrays. At cumulative probabilities of 10%, 1% and 0.1%, diversity gain and improvement in signal-to-interference-plus-noise-ratio (SINR) are calculated from the diversity combining measurements and interference rejection measurements respectively. Experimental results illustrating the dependence of diversity gain on power imbalance, envelope correlation and diversity-combining scheme are presented. Measurements were performed at 2.05 GHz using the handheld antenna array testbed (HAAT). Low profile linear arrays are shown to provide diversity gain values of 5 to 8 dB and 11 to 16 dB, respectively for switched and maximal ratio combining at the 99% reliability level in non-line-of-sight urban channel. Interference cancellation of 24 to 28 dB was recorded in urban and suburban line-of-sight (LOS) channels for the sectorized square array. Results of vehicular measurements with the arrays mounted on a ground plane supported above the vehicle roof are also reported.

This report, presents an analytical framework for analyzing two-branch diversity systems for a Rayleigh fading channel. In many cases the fading received at both branches (i.e. a two-antenna element system) is correlated because of the proximity of the antenna elements to each other. It is also not uncommon for a diversity system to use antennas with different patterns or polarizations, this usually results in differences in average signal-to-noise ratios at both branches depending on which element is better matched to the signal environment. As will be shown, the performance of a diversity system depends greatly on the envelope correlation, average power imbalance and the combining scheme used on both branches. An analytical expression for the probability density function of the signal-to-noise ratio at the output of a two-branch maximal ratio and selection diversity system is developed in this report. The two branches are assumed to be Rayleigh fading, correlated, as well as of unequal signal-to-noise ratios. Measurements were made in Rayleigh fading channels and compared to the analytical results. The analytical cumulative distribution functions (derived using probability distributions) were found to be within 1 dB of the measured results (statistics obtained from time combining) for both maximal ratio and selection diversity attesting to the validity of the analytic results. Also developed in this report are the exact analytical average probabilities of symbol error for coherent BPSK and coherent QPSK before and after maximal ratio combining for this environment. The diversity gain for selection, maximal ratio, and equal gain combining for the 10% probability level is presented as a function of power imbalance and correlation between branches for a two-branch Rayleigh diversity system