Abstract
Cellular networks are multi-user communication systems that consist of three basic elements: interference, cooperation, and feedback. A fundamental goal of multi-user systems research is to find out the capacity limit and its achievability of a general model that consists of many senders, receivers, and intermediate nodes. In the past 60 years, a huge amount of research efforts have been paid towards five special problems of multi-user systems: multiple-access channel, broadcast channel, relay channel, crosstalk channel, and feedback channel. Although most of those problems have not received a satisfactory answer yet, rapid development of cellular networks have motivated communication-theoretic research about cooperation in those special channels. The primary objective of this thesis is to study the cooperation theory in relay and crosstalk channels. The overall organisation of this thesis is based on our new vision about cooperative behaviour in communication networks. This new vision indicates that cooperative behaviour in relay and crosstalk networks can be classified into three groups, namely. Postman, Host, and Synergy. The classification is based on how a cooperative node utilises the multi-user side information such as channel quality information (CQI), codebook, message, in various communication scenarios. Specifically, major contributions of this thesis are summarised as follows. The Postman describes cooperative behaviour in relay networks, where a cooperative node offers cooperation by delivering other's message to its desired destination. Our first work in this category is about doubly differential cooperative relaying scheme proposed for mobile communication over rapidly time-varying channel. It is shown that the proposed scheme can enjoy full cooperative diversity-gain without need of full channel state information. The other work in this category is about adaptive bit-power allocation for orthogonal frequency-division multiplexing (OFDM)-based relay networks. Provided full knowledge of CQI, a number of sub-optimum approaches have been proposed to improve the power efficiency through multi-link optimisation. The Host describes cooperative behaviour in cognitive interference networks, where a primary user offers cooperation to a secondary user by opening its own spectrum and sharing knowledge of side information. The work in this category is about overlay and underlay cognitive radio channels, where the primary user broadcasts its private codebook and knowledge of CQI, so that the secondary user can perceive the primary user's message and interference state. Capacity theorem of two-user Gaussian cognitive interference channels have been carefully investigated, based on which power allocation and spectrum access approaches have been proposed in terms of power and spectrum efficiency. The Synergy describes cooperative behaviour in crosstalk channels. A typical example is the cooperative bit-power allocation between two individual transmitter-receiver pairs. One cooperative behaviour is sharing of codebook and CQI between two transmitter-receiver pairs. The purpose of sharing is to maximize their common profit and to allow an optimal treatment of mutual interference. Provided full knowledge of multi-user CQI at transmitters, two transmitter-receiver pairs first perform iterative rate-adaptation to maximize the sum-rate, and then employ proportional fairness for rate allocation.