| Recently, the class of new technologies based on the multiple-input-multiple-output (MIMO) system has emerged as a major breakthrough in the area of wireless communication. Among these new technologies, which promise a multiple-fold increase in spectral efficiency, the single-user optimization plays the dominant role. The present work in this thesis departs from this traditional perspective by introducing the concept of bandwidth-efficient space-time multiple access or multiuser optimization.; When the forward link is considered, a new multiplexing framework called the Spread Space-Spectrum Multiple Access (SSSMA) is proposed. One main objective is to increase the number of users per unit of time. In this framework, the coded data streams from independent users are modulated with a set of distinct spreadtime spreading sequences. Code symbols from different users are multiplexed over the same spreading period, while the code symbols from the same user are transmitted sequentially over different spreading periods. Within the spreading period, the multiple access interference (MAI) is minimized by using the proposed space-time-diagonal spreading sequences. This set of sequences is shown to be the best linear modulation scheme for linear receiver. It delivers a fading-averaging effect which is shown to be very effective against either correlated or independent fading existing across the MIMO channel.; Subsequently, the coded performance of SSSMA is investigated. The appropriate power profile is derived for the case with two transmit-receive antenna pairs, in which the set of STD sequences can be viewed as two groups of Alamouti's space-time-block-codes (STBC). The orthogonality of STBC simplifies the interference cancellation and power allocation process. It is then found that the resulting performance is superior to existing MIMO transmission schemes with same number of antenna pairs.; Upon developing a new MIMO framework for the forward link, attention is turned toward the reverse link which does not permit direct cooperation among transmitters form different users' terminals. A novel approach is proposed by viewing the joint multiuser MIMO system as a single-user MIMO system. This new multiuser signal design viewpoint facilitates the development of a novel transmission scheme named interference-resistant modulation (IRM). (Abstract shortened by UMI.)... |
