ABSTRACT OF THE DISSERTATION Interference Avoidance for Wireless Systems

OF THE DISSERTATION Interference Avoidance for Wireless Systems by Dimitrie C. Popescu Dissertation Director: Professor Christopher Rose The study of interference avoidance for wireless communications is motivated by recent developments in telecommunications industry which demands new solutions for personal communications. Radios are becoming more sophisticated, and one can presently think of adjusting transmission/reception methods to suit the environment in which the communication system is operating. As a main application of interference avoidance techniques we see communication in unlicensed bands, where independent systems that interfere with each other will have to coexist without central control or coordination. 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. Each user sends frames containing multiple symbols (at least as many as there are signal space dimensions) and each symbol is assigned a signature waveform. Under the assumption that the frame duration is long enough, a common set of signal space basis functions consisting of real sinusoids is shared