Adaptive diversity combination of space-time block coding in OFDM-CDMA systems with pilot-based channel estimation

We investigate the transmit diversity for orthogonal frequency division multiplexing code division multiple access (OFDM-CDMA). Diversity transmission at the base station is an effective technique to combat channel fading. Space-time (ST) coding has been proposed as coding technique to improve the system performance with additional gains. By combing the spatial transmit diversity with the space-time codes for OFDM systems it shows high performance improvement. But it is important to remark that ST decoding requires multichannel state information at the receiver. Thus the achievable diversity gain comes at the price of proportional increase in the amount of training or computation complexity, which incurs efficiency loss especially in a rapidly varying environment. In an OFDM system, there exist pilots used for frame detection, carrier frequency offset estimation and channel estimation. We proposed a receive scheme, which use the pilot structure to estimate the multichannel state information and use the CMA-based channel tracking in the space-time coded transmit diversity OFDM-CDMA systems. Numerical simulations illustrate the effectiveness of this algorithm.