The performance of a space-time spreading CDMA system with channel estimation errors

Transmit diversity has been studied recently as an effective technique to provide high-performance wireless transmission. Space-time spreading is a transmit diversity scheme that achieves full spatial diversity while maintaining high spectral efficiency. This paper analyzes how channel estimation errors in diversity combining affects the uplink of a space-time spreading CDMA system with two transmit and two receive antennas. Pilot and data from K asynchronous users are transmitted through a Rayleigh multipath fading channel. The channel estimates are obtained at the outputs of correlators and are used in the RAKE combiner. As a system becomes more wideband, more multipaths are resolved, and the energy in each path is reduced. This reduction in signal strength causes increased estimation error and impacts the system performance. This paper studies the tradeoff between diversity and estimation errors.