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In this paper, we propose an adaptive MIMO EMTS with a beamspace zero forcing (ZF) interference canceller in Rx and a single channel encoder for all eigenmodes. Generalized BER equations for various constellations applicable for all quality of CSI at Tx are also derived. Each eigenmode is modeled as an AWGN channel, to a Nakagami-Rice fading channel and lastly to a Rayleigh fading channel as the CSI at Tx degrades from perfect to partial and to no CSI. Thus our proposed system provides a smooth transition between the different qualities of CSI and encompasses the perfect, partial and no CSI paradigms with the generalized BER equations. With this smooth transition, it is possible to trade feedback frequency (or overhead) with throughput performance according to the system design and channel conditions. Our proposed system is therefore a robust and practical scheme that has the potential for implementation.

The performance of the MIMO eigenmode transmission system (EMTS) is very sensitive to the accuracy of channel state information and thus it is of practical importance to analyzing its performance when channel state information is corrupted under realistic system and propagation conditions. We lower bound the mutual information of MIMO EMTS with imperfect channel estimation and delayed quantized feedback in a spatially correlated continuous fading channel. Our results show that this lower bound is tight and can serve as a comprehensive guide to the actual performance of MIMO EMTS under practical operating conditions.

Adaptive MIMO eigenmode transmission system is a promising candidate for future high data rate wireless systems. However under practical conditions when channel state information (CSI) is imperfect, the eigenbeams lose their orthogonality and inter-eigenmode interference occurs. No work so far has attempted to consider the effects of inter-eigenmode interference on the adaptive signaling algorithm which is essential in ensuring a practical and robust adaptive system. Thus in this paper, we propose an adaptive algorithm that account for CSI imperfections explicitly. Our results showed that the proposed algorithm is robust and superior to conventional schemes under practical operating conditions. Furthermore, a low complexity look-up table-based computation method is also devised.

In order to evaluate the performance of multi-input multi-output (MIMO) communication systems accurately, MIMO channel sounding is necessary. DINO (Dynamic Integrated platform for multi-dimensional data analysis) is proposed for the systematic analysis of the data from a MIMO channel sounder. In DINO, through the visualization of the obtained data by recreating the propagation channel virtually in a computer, a fundamental link between the measured data and the physical environment is established.

To meet the rapid growth of wireless applications and multimedia services, the development of wireless communications that is able to provide higher data rates and more reliable communications while maintaining satisfactory quality of service is required. Multiple-input multiple-output (MIMO) system has shown tremendous potential to be an excellent approach for solving this problem by providing multiplexing and spatial diversity gains without requiring additional radio resources, such as bandwidth and power. However, the size and complexity limitations of wireless mobile devices mean that MIMO systems may possibly be unfeasible, especially for the uplink. For this reason, cooperative communications has been proposed and its potential benefits have attracted much research attention in the past few years. The idea of this technique is to utilize the broadcast nature of wireless signals by exploiting the fact that a signal intended for a particular destination node can be overheard at neighboring nodes, and thus these nodes can help each other to create a virtual MIMO system. Spectral efficiency (multiplexing gain) and reliability (diversity gain) are the two most important features of cooperative communication protocols. Many cooperative communication protocols are able to achieve full spatial diversity gain, but fail to exploit the multiplexing gain. It is observed in many cases that the multiplexing gain is reduced to one-half due to the half-duplex constraint of the relay. Thus, in this thesis, we investigate cooperative communications protocols that are able to enhance this spectral efficiency (recover multiplexing loss) and improve the corresponding reliability in wireless networks. Specifically, we first analyze the performance of amplify-and-forward (AF) two-path, also known as successive half-duplex, relaying protocol where two-relays are utilized to alternate between transmission and reception modes. This protocol is very interesting, but less studied in the literature due to inter-relay interference inherent in this protocol. DOCTOR OF PHILOSOPHY (EEE)

The explosive growth of wireless applications and steadily increasing demands for higher quality of service have led to a perceived dearth of available radio bandwidth, which necessitates a more efficient utilization of spectrum resources. Both cooperation and cognition in wireless networks have individually been shown to be powerful tools to achieve such a purpose. The objective of this dissertation is to jointly investigate these two techniques and propose practical protocols for spectrum efficiency enhancement in wireless networks. DOCTOR OF PHILOSOPHY (EEE)

Network coding, first proposed in the seminal work by Ahlswede, Cai, Li, and Yeung, has attracted significant interest in the last decade in both academia and the industry due to its versatility and promising potential in improving the performance of communication networks. In contrast to conventional routing architecture which is typical in most computer networks where intermediate nodes of a network can only store-and-forward the received packets, the intermediate nodes are allowed to perform random mapping of the received packets in network coding. With independent information flows intended for different receivers combining at the intermediate nodes, the bottleneck of data communications has shifted from point-to-point links to the whole network topology. Although network coding was originally designed for wireline networks with error-free links, wireless networks provide a fertile ground for various applications based on network coding. DOCTOR OF PHILOSOPHY (EEE)

Scarcity of radio spectrum and inherent inefficiency of current spectrum allocation policies have spurred much research for alternative spectrum access techniques giving birth to the notion of cognitive radios. Recently, cooperative spectrum sharing (CSS) where two wireless systems operate over the same spectrum band albeit with different priorities has been proposed as a viable framework for cognitive radio. However, most of the proposed CSS protocols are interference limited and the performance of the systems are limited by the amount of interference from one system to another. Furthermore, most of the work on CSS can not be validated due to lack of measurement results. In this thesis, we try to resolve the above issues by proposing an interference-free CSS protocol known as orthogonal spectrum sharing scheme (OSSS) and as a proof-of-concept implement a CSS protocol on a RF testbed. The performance of the testbed has been validated by obtaining both quantitative as well as qualitative results. Quantitative results are obtained by measuring the packet error rates for both primary and secondary systems whereas qualitative results are shown by utilizing a CSS protocol to successfully transmit two different images from PT to PR and ST to SR respectively. DOCTOR OF PHILOSOPHY (EEE)

87 p. Most of the spectrum deficiency occurring today is because of fixed spectrum assignment policy in which the spectrum is allocated to certain users who use the spectrum sporadically. These licensed users are called primary users. This inefficient utilization of the available spectrum is the main cause of spectrum deficiency. This problem can be solved by the use of cognitive radio technology. A cognitive radio technology is one in which the available spectrum resources which are not used by the primary users are identified and informed to the nodes in the cognitive radio network. These members which use the spectrum in the absence of the primary users are called the secondary users. By using this technology the spectrum deficiency problem existing today can be solved. But the cognitive radio technology has its own disadvantages like highly fluctuating available spectrum and diverse Quality-Of-Service requirements. ​Master of Science (Communications Engineering)