Space-Time CDMA Systems over Nakagami-M Fast-Fading Channels

The performance of a space-time spreading (STS) transmit diversity scheme is examined over a frequency-flat and fast- fading Nakagami-m channel. Our focus will be on the uplink of the communication system where the STS system employs N=2 and L antennas at the user side and base-station (BS) respectively. Direct-sequence code-division multiple-access (DS-CDMA) is used in order to support many users and a linear decorrelator detector is used in order to combat the effect of multi-user interference. The modulation scheme considered is binary phase-shift keying (BPSK). In our study, we start by determining the probability density function (pdf) of the signal- to-interference and noise ratio (SNR) at the output of the ST combiner at the receiver side. Using this pdf, we derive a closed form expression for the bit error rate (BER) of the underlying system. The accuracy of the BER expression is verified when compared to simulations results for different values of the fading figure m.