Performance of Multiuser-Coded CDMA Systems With Transmit Diversity Over Nakagami- $m$ Fading Channels

The performance of a multiple-input-multiple-output (MIMO) code-division multiple-access (CDMA) system, using space-time spreading (STS), is analyzed over a frequency-flat Nakagami-
m
fading channel. The convolutionally space-time coded system employs a decorrelator detector with
N
= 2 and
L
antennas at the user side and base station (BS), respectively. Assuming independent Nakagami fading channels between transmit and receive antennas, we determine the probability density function (pdf) of the signal-to-interference-plus-noise ratio (SINR) at the output of the multiuser detector and after signal combining. Considering binary phase-shift keying (BPSK) transmission, we then evaluate the pairwise error probability and the corresponding bit-error-rate (BER) upper bounds over fast-fading channels. The derived error bounds, when compared to system simulations, are shown to be accurate at all signal-to-noise ratios (SNRs) of interest. Examining the asymptotic performance of the underlying space-time multiuser system, at high SNRs, we evaluate the overall diversity gain as a function of the number of transmit and receive antennas and the minimum free distance of the convolutional code.