Fading correlation and its effect on the capacity of space-time turbo coded DS/CDMA systems

This paper considers the performance evaluation of a space-time turbo processing system employing a combined turbo coded and antenna transmission diversity scheme for DS/CDMA communication systems. In this combined coding/signalling scenario the turbo coder structure is exploited for a novel space-time processing approach. The binary input data to a rate 1/(M+1) multiple turbo encoder produces M+1 coded bits, which, in turn, are assigned through suitable puncturing patterns to M different antennas and transmitted from each antenna simultaneously. The novelty of the transmission scheme, is that the original single-antenna rate-1/2 turbo coded system is transformed into a more powerful rate-1/(M+1) turbo code. The bit error rate performance of a QPSK DS/CDMA system employing a short-frame space-time turbo-coded transmission scheme and RAKE diversity receiver is studied by means of simulation. It is shown that with the proposed system, employing M transmit antennas and an L-branch RAKE receiver, lower bit error rate performance can be achieved, compared to a conventional single antenna scheme. The latter results are achieved even in the presence of correlated fading conditions