Interference avoidance for wireless systems

The study of interference avoidance for wireless communications is motivated by recent developments in telecommunications industry which demands new solutions for personal communications.; Our purpose is to provide insight into a class of distributed iterative algorithms that produce optimal codeword ensembles which maximize sum capacity in a multiuser system and minimize interference. Also known as interference avoidance algorithms they have been introduced in the context of chip-based CDMA systems but have been subsequently framed in a general signal space formulation so as to make them applicable to a wide variety of communication scenarios.; After an introduction to basic interference avoidance (IA) concepts and a review of previous work on IA, we describe how IA can be applied to codeword optimization in the uplink of a CDMA system in which the channel between each user and the basestation is assumed to be known.; Application of interference avoidance to general multiaccess vector channels is also presented. It is shown that application of greedy interference avoidance increases sum capacity for multiaccess vector channels. Application of the eigen-algorithm is generalized for multiaccess vector channels and it is shown that sequential application of the eigen-algorithm for interference avoidance by all users in a multiuser system is equivalent to iterative water filling and always yields codeword ensembles that maximize the sum capacity of the multiaccess vector channel.; Using this general result, application of interference avoidance to multiuser systems with multiple inputs and multiple outputs (MIMO), and asynchronous CDMA systems is also presented. Multiuser MIMO systems are associated with the uplink of a wireless system in which users and the basestation have multiple antennas, while for asynchronous systems symbol intervals corresponding to different users are not necessarily synchronized at the receiver. In both cases a multiaccess vector channel model is derived for which application of interference avoidance becomes straightforward.; Empirical studies on various issues of the eigen-algorithm for interference avoidance are also performed. Codeword representation with finite precision and complexity issues are also explored. (Abstract shortened by UMI.)...