Design of space-time coded DS/CDMA systems

Abstract

In multi-path fading channels, direct sequence code division multiple access (DS/CDMA) technique is often employed because of its capability to resolve signals from different paths and realize path diversity at the receiver. This advantage of DS/CDMA, however, is realized only when the time difference of the propagation delay between paths is greater than a chip duration. This thesis considers the application of space-time coding techniques to DS/CDMA communication systems with multiple transmit antennas for slow, frequency nonselective fading. Space-time codes are constructed over the set of possible pseudo random (PN) sequences rather than over some standard 2-D signal dimension. Several design examples of these codes of the different number of PN sequences and states are presented, and possible methods of implementation are suggested. Simulation results indicate that the proposed space-time coded systems provide a significant performance improvement over the conventional transmitter diversity system. The performance improvement is more significant with two receive antennas.