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Layered space-time multiuser communication systems

Authors Sfar, Sana
Issue Date 2001
Summary Wireless communication systems have become very successful in the market place and it is expected that this success will continue when various interactive services and applications such as the Internet are introduced. The next generation of wireless networks will support multiple classes of traffic with different quality of service requirements such as data rate and bit error rate [l, 2]. In particular, Wideband CDMA has been selected as the air interface standard for third generation systems such as IMT-2000 proposed by ETSI/ARIB, and cdma2000 proposed by TIA, due to their various technical advantages. In addition, it has been recently shown that the use of MIMO systems in a rich scattering wireless channel is capable of enormous theoretical capacity improvement provided the scattering is properly exploited through the use of an appropriate processing architecture [3, 4]. The vertical layered space-time architecture proposed by Foschini [5], known as V-BLAST, is one such approach. In this thesis, we investigate the use of layered space-time scheme for multiuser detection over the uplink of a DS/CDMA communication system. The multiple transmit antennas in V-BLAST are treated as individual mobile station transmitters, while the base station consists of multiple receive antennas. The layered space-time algorithm is then invoked to detect the signals from all users. In addition, CDMA is also applied. Users are organized in different groups and users in a particular group are allocated the same spreading code. Therefore, CDMA spreading technique will remove the interference between the groups and the layered space-time scheme will further remove the remaining interference. A decorrelator-type CDMA receiver based layered space-time detection is proposed for both complex and real constellations. For the latter case, we derive our receiver after evaluating and comparing the performance of two decorrelators based on the V-BLAST scheme. It is demonstrated that a significant performance improvement and increase in system capacity is obtained with very low spreading factors. Further results are also introduced by considering reduced complexity receivers based on Serial Layered Space-Time Group Multiuser detection, and Parallel Layered Space-Time Group Multiuser detection. We are also interested in packet transmission mode. The wireless networks will then present packet radio mobile stations transmitting to a single base station. Our primary aim is to assess the impact of the proposed layered space-time multiuser detection technique, over a packetized random access system based on Slotted ALOHA protocol. A significant improvement in system throughput, delay and capacity are achieved. Finally, we considered wireless circuit switched and packet switched modes integrated CDMA systems. The effect of packet mode users on system performance is considered. Throughput and BER performances of packet and circuit mode users are hence investigated, respectively. The robustness of the proposed detection technique is also demonstrated against transmission power variation of packet mode users.
Note Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2001
Language English
Format Thesis
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