Space-time coded CDMA systems: Blind channel identification and system performance

This dissertation considers the problem of applying space-time (ST) coding scheme to code division multiple access (CDMA) systems in frequency selective fading environments to achieve transmit diversity. Space-time coding techniques have received a great deal of attention in recent years due to promising features such as increasing system capacity, providing diversity and coding gain, and combating channel fading. However, most of previous studies on ST coding were concentrated on code design, assuming either the knowledge of the underlying channel is perfectly known or the channel is flat (frequency-nonselective). This, however, is hardly the case in reality, where mobile radio channels are characterized by time/frequency selective fading and interference. In this dissertation, we relax the assumptions on the channel and apply subspace-based blind channel identification technique to CDMA systems in frequency selective channels. There are mainly two parts in this dissertation. In the first part, we propose a blind channel identification algorithm which utilizes the second order statistics of the received signal to identify the frequency selective channel in a space-time coded CDMA (STC-CDMA) system without requiring any training sequence. The performance of the algorithm, subspace-based blind channel identification algorithm, is compared with a closed form Cramér-Rao lower bound, which serves as the benchmark on the channel estimation error. The second part of this dissertation studies a multicarrier CDMA system with space-time coding (STC-MC-CDMA). In the STC-SIC-CDMA system, we effectively combine the multicarrier modulation technique, commonly known as orthogonal frequency division multiplexing (OFDM), with a space-time coded CDMA system. For the STC-MC-CDMA system, we again apply the subspace-based channel identification algorithm to obtain the channel information, which is required by the receiver for coherent signal detection. In addition, this dissertation also includes some background information on space-time coding, OFDM modulation, and multicarrier CDMA systems.