With the fast development of today’s multimedia services, engineers face a huge hurdle that is, the overwhelming need of highly reliable communication over long distances. Cooperative communication is a novel concept which tackles this problem effectively. The direct link is assisted by nodes called relays, which also reduce shadowing and pathloss effects in wireless networks. An added advantage of such a cooperative communication network is that when combined with multiple-input multiple-output (MIMO) antenna systems and cognitive radio networks (CRN), the system performance in terms of spectral efficiency and reliability, can be extremely enhanced without any extra power and spectrum.The concept of cooperative communications in MIMO and CRN systems has gained immense interest in the literature. Most of the research works have assumed Rayleigh fading conditions. In this thesis, the performance of cooperative communications with practical constraints of shadowing is studied. Analytical expressions for the outage probability of cooperative networks under different relaying protocols with selection combining are presented under the assumption of κ − µ shadowing fading. Specifically, the relaying protocols that are investigated are incremental relaying, opportunistic relaying, adaptive amplify-and-forward and decode-and-forward. Furthermore, this system model is simulated and the simulation results are compared with the analytical results. Mathematica, a technical computing tool, is used for numerical estimations using stochastic processes and probability theory. Simulation is done in MATLAB.In this thesis, along with the analytical framework for evaluating outage probability for the system is presented. Simulations are performed for various fading parameters and the results closely match with analytical results which validate the derivations.

" In telecommunications, a cooperative scheme refers to a method where two or more users share or combine their information in order to increase diversity gain or power gain. In contrast to conventional point-to-point communications, cooperative communications allow different users in a wireless network to share resources so that instead of maximizing the performance of its own link, each user collaborates with its neighbours to achieve an overall improvement in performance. In this dissertation, we consider different models for transmission and reception and explore cooperative techniques that increase the reliability and capacity gains in wireless networks, with consideration to practical issues such as channel estimation errors and backhaul constraints. This dissertation considers the design and performance of cooperative communication techniques. Particularly, the first part of this dissertation focuses on the performance comparison between interference alignment and opportunistic transmission for a 3-user single-input single- output (SISO) interference channel in terms of average sum rate in the presence of channel estimation errors. In the case of interference alignment, channel estimation errors cause interference leakage which consequently results in a loss of achievable rate. In the case of opportunistic transmission, channel estimation errors result in a non-zero probability of incorrectly choosing the node with the best channel. The effect of these impairments is quantified in terms of the achievable average sum rate of these transmission techniques. Analysis and numerical examples show that SISO interference alignment can achieve better average sum rate with good channel estimates and at high SNR whereas opportunistic transmission provides better performance at low SNR and/or when the channel estimates are poor. We next considers the problem of jointly decoding binary phase shift keyed (BPSK) messages from a single distant transmitter to a cooperative receive cluster connected by a local area network (LAN). An approximate distributed receive beamforming algorithm is proposed based on the exchange of coarsely- quantized observations among some or all of the nodes in the receive cluster. By taking into account the differences in channel quality across the receive cluster, the quantized information from other nodes in the receive cluster can be appropriately combined with locally unquantized information to form an approximation of the ideal receive beamformer decision statistic. The LAN throughput requirements of this technique are derived as a function of the number of participating nodes in the receive cluster, the forward link code rate, and the quantization parameters. Using information-theoretic analysis and simulations of an LDPC coded system in fading channels, numerical results show that the performance penalty (in terms of outage probability and block error rate) due to coarse quantization is small in the low SNR regimes enabled by cooperative distributed reception. An upper/lower bound approximation is derived based on a circle approximation in the channel magnitude domain which provides a pretty fast way to compute the outage probability performance for a system with arbitrary number of receivers at a given SNR. In the final part of this dissertation, we discuss the distributed reception technique with higher- order modulation schemes in the forward link. The extension from BPSK to QPSK is straightforward and is studied in the second part of this dissertation. The extension to 8PSK, 4PAM and 16QAM forward links, however, is not trivial. For 8PSK, two techniques are proposed: pseudobeamforming and 3-bit belief combining where the first one is intuitive and turns out to be suboptimal,the latter is optimal in terms of outage probability performance. The idea of belief combining can be applied to the 4PAM and 16QAM and it is shown that better/finer quantizer design can further improve the block error rate performance. Information-theoretic analysis and numerical results are provided to show that significant reliability and SNR gains can be achieved by using the proposed schemes. "

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Multihop routing is an effective method for establishing connectivity between the nodes of a network. End-to-end outage probability and total power consumption are applied as the optimization criteria for routing protocol design in multihop networks based on the local channel state information measurement at the nodes of a network. The analysis shows that employing instantaneous channel state information in routing design results in significant performance improvement of multihop communication, e.g., achieving full diversity order when the optimization criterion is outage performance. The routing metrics derived from the optimization problems cannot be optimized in a distributed manner. Establishing an alternate framework, the metrics obtained are converted into new composite metrics, which satisfy the optimality and convergence requirements for implementation in distributed environments. The analysis shows that the running time of the proposed distributed algorithm is bounded by a polynomial. / Communications

Spectral efficiency is one of the most important measures of the performance of wireless communication systems owing to scarcity and cost of the radio spectrum. The increase in spectral efficiency provides higher data rates to the user, lower network cost to the operator, coverage extension and higher service reliability as well. Intercell interference due to frequency reuse is one of the key impairments in wireless systems. Multiple-input multiple-output (MIMO) technique has been developed to enhance the desired signal power (and hence mitigating the effects of intercell interference) and with employing simple linear signal processing technique, can strongly mitigate the interference resulting from co-channel users. This technique is mainly used to achieve spatial diversity for boosting the communication link reliability by combating fading, and providing spatial multiplexing to increase data rates without extra bandwidth by exploiting multipath. Distributed antenna system (DAS) has recently gained substantial interest due to its ability to reduce transmitted power thereby lowering the out-of-cell interference effects, maximise the coverage and improve the spectral efficiency. The combination of MIMO techniques with DAS, so-called distributed MIMO (D-MIMO) systems, is now being exploited and largely succeeded to fulfil the services of the fourth generation (4G) wireless systems. Very recently, one of crucial significance approach to reducing the radiated power and improving spectral efficiency to cope with fifth generation (5G) wireless systems is the use of large-scale MIMO (also referred to as massive MIMO) technology, which utilizes a large number of antennas, i.e., tens to hundreds, typically at the base station (BS) side. Presently, in the light of the rapid evolution of wireless systems into 5G, the integration of wireless power transfer (WPT) with newly wireless systems has seen a great deal of attention as a potential solution for powering energy-constrained wireless systems, especially with shortening communication links by emerging new technologies, e.g., D-MIMO and massive MIMO. This thesis is devoted to investigating and comparing the performance of three different MIMO systems. More specifically, the thesis focuses on analysing the spectral efficiency of a comprehensive model of self-powered MU-MIMO systems employing linear ZF technique at the BS for both perfect and imperfect channel state information (CSI) cases. The results demonstrate the impact of practical channel impairments, e.g., spatial correlation, shadowing and co-channel interference (CCI), and system parameters, e.g., the number of BS and user antennas, signal to noise ratio (SNR) and channel estimation error, on the spectral efficiency of the system. Besides, from a spectral efficiency perspective, a proposed model of a combination of MIMO and massive MIMO technologies with DAS in the presence of linear receivers at the processing unit (PU) is considered and compared to a centralised MIMO (CMIMO) system. The obtained results provide a wide range of insights into the effects of system parameters on the spectral efficiency and reveal that the proposed distributed MIMO system outperforms the C-MIMO system. In the context of wireless powered MIMO systems, this work investigates the performance of a power beacon (PB)-assisted wireless powered C-MIMO system, including one multi-antenna BS and a number of single-antenna users powered by randomly deployed PBs in the presence of ZF receiver at the BS. Also, two modes for radiation from the PBs are assumed and compared, one is the beamforming radiation mode (BRM), and the other is the isotropic radiation mode (IRM).

Cognitive radio (CR) is a cutting-edge wireless communication technology that adopts several existing communication concepts in order to efficiently utilize the spectrum and meet the users demands of high throughput and real-time systems. Conventionally, high throughput demands are met through adopting broadband and multi-antenna technologies such as, orthogonal frequency division multiplexing (OFDM) and Multi-Input Multi-Output (MIMO). Whereas, real-time application demands are met by analyzing metrics which characterize the delay limited channels, such as, outage probability over block-fading channels. Being an environmental friendly technology, energy efficiency metrics should be considered in the design of a CR application. This thesis tackles the energy efficiency of CR system from different aspects, utilizing different measuring metrics and constrains. Under the single-input single-output (SISO) OFDM we minimized the energy per goodbit (EPG) metric subject to several power and Quality of Service (QoS) constraints. In this approach, the minimum EPG metric is optimized via proposing two optimal and sub-optimal resource allocation schemes. We consider several parameters as optimization variables, such as, power policy, sensing threshold, and channel quality threshold. We also captured the impact of involving the media access control (MAC) layers parameters, such as, frame length, in the minimization of a modified EPG metric. Also, a MAC protocol, i.e., hybrid automatic repeat request (HARQ), and the associated power consumption of the retransmission mechanism is considered in the formulation of the problem. In this context, the optimal power and frame length are derived to minimize the modified EPG while considering several spectrum-sharing scenarios, which depend on sensing information. In MIMO based CR system, we maximized capacity to power ratio (CPR) (as an energy efficiency (EE) metric) subject to several power and QoS constraints. In this context, the impact of sensing information with imperfect channel state information (CSI) of the secondary channel has been considered. To realize a CR system with real-time applications we minimized the outage probability over M block-fading channel with several long-term and short-term energy constrains. We derive the minimum outage region and the associated optimal power. Tractable expressions to lower and upper bound the outage probability are derived. We then analyze the impact of utilizing the sensing process of primary user activity.

This thesis presents new methodologies to improve performance of wireless cooperative networks using the Golden Code. As a form of space-time coding, the Golden Code can achieve diversity-multiplexing tradeoff and the data rate can be twice that of the Alamouti code. In practice, however, asynchronism between relay nodes may reduce performance and channel quality can be degraded from certain antennas. Firstly, a simple offset transmission scheme, which employs full interference cancellation (FIC) and orthogonal frequency division multiplexing (OFDM), is enhanced through the use of four relay nodes and receiver processing to mitigate asynchronism. Then, the potential reduction in diversity gain due to the dependent channel matrix elements in the distributed Golden Code transmission, and the rate penalty of multihop transmission, are mitigated by relay selection based on two-way transmission. The Golden Code is also implemented in an asynchronous one-way relay network over frequency flat and selective channels, and a simple approach to overcome asynchronism is proposed. In one-way communication with computationally efficient sphere decoding, the maximum of the channel parameter means is shown to achieve the best performance for the relay selection through bit error rate simulations. Secondly, to reduce the cost of hardware when multiple antennas are available in a cooperative network, multi-antenna selection is exploited. In this context, maximum-sum transmit antenna selection is proposed. End-to-end signal-to-noise ratio (SNR) is calculated and outage probability analysis is performed when the links are modelled as Rayleigh fading frequency flat channels. The numerical results support the analysis and for a MIMO system maximum-sum selection is shown to outperform maximum-minimum selection. Additionally, pairwise error probability (PEP) analysis is performed for maximum-sum transmit antenna selection with the Golden Code and the diversity order is obtained. Finally, with the assumption of fibre-connected multiple antennas with finite buffers, multiple-antenna selection is implemented on the basis of maximum-sum antenna selection. Frequency flat Rayleigh fading channels are assumed together with a decode and forward transmission scheme. Outage probability analysis is performed by exploiting the steady-state stationarity of a Markov Chain model.

Over time, wireless technology advancements in the field of communications have been attracting every individual to turn into a wireless user. To accommodate the increasing number of users and to avoid the problem of spectrum scarcity, the concept of Cognitive Radio Network (CRN) has been developed. Cognitive Radio (CR) is an intelligent radio which efficiently detects and allocates the spectrums of primary licensed users (PUs) to the secondary unlicensed users (SUs). The SUs can utilize these spectrums as long as they do not cause harmful interfere to the PUs. Interference may occur because of the following reasons: misdetection of spectrum availability, the high transmission power of SU when both SU and PU are present in the same channel at the same time. In order to avoid interference, the radio has to have a very accurate spectrum sensing method, transmit power at SU should be constrained by the peak interference power of PU and the CR should continuously sense the presence of PUs. To increase the wireless coverage area and reliability of CRN, a new technology called Cooperative Cognitive Radio Network (CCRN), which is a combination of CRN and cooperative communications was developed. A CCRN not only increases the reliability and wireless coverage area of CR but also improves the overall performance of the system. In this context, the main objective of this research work is to evaluate the outage performance of a CCRN in an environment where fading and shadowing also come into the picture and to study the importance of relay networks in CRN. To fulfill the objectives of this research work, a two-hop decode-and-forward CCRN is considered. The recently introduced κ − µ shadowed fading channel is employed over the CCRN to generate a realistic environment.  In order to implement such system as a whole, a deep literature study is performed beforehand. Analytical expressions for the Probability Density Function (PDF) and Cumulative Distribution Function (CDF) of the Signal-to-Noise Ratio (SNR) are obtained. The analytical expressions and simulation results for Outage Probability (OP) are obtained and compared under different fading parameters. The importance of a multiple-relay system in CRN is presented. From the results obtained in this research work, we can conclude that the OP decreases with increase in allowable peak interference power at the PU. The transmit power at SU should always be constrained by the peak interference power at the PU to avoid interference. The overall system performance increases with increasing number of relays.

With the rapid growth of wireless communications, the demand for the various multimedia services is increasing day by day leading to a deficit in the frequency spectrum resources. To overcome this problem, the concept of cognitive radio technology has been proposed which allows the unlicensed secondary user (SU) to access the licensed spectrum of the primary user (PU), thus improving the spectrum utilization. Cooperative communications is another emerging technology which is capable of overcoming many limitations in wireless systems by increasing reliability and coverage. The transmit and receive diversity techniques such as orthogonal space–time block codes (OSTBCs) and selection combining (SC) in multiple-input multiple-output (MIMO) cognitive amplify and forward relay networks help to reduce the effects of fading, increase reliability and extend radio coverage.   In this thesis, we consider a MIMO cognitive cooperative radio network (CCRN) with multiple relays. The protocol used at the relays is an amplify and forward protocol. At the receiver, the SC technique is applied to combine the signals. Analytical expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the signal-to-noise ratio (SNR) are derived. On this basis, the performance in terms of outage probability is obtained. Mathematica has been used to generate numerical results from the analytical expressions. The system model is simulated in MATLAB to verify the numerical results. The performance analysis of the system model is hence done in terms of outage probability.