The uplink of a space-time spreading code-division multiple-access system with dual transmit and dual receive antennas is analyzed with the effect of imperfect channel estimation. With the help of pilot signals, the Rayleigh multipath fading channel experienced by the transmitted signal is estimated by simple correlators, and subsequently used to coherently combine the multipath signals in a RAKE-like space-time 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. Through the derivation of the probability of error in a space-time spreading system with channel-estimation errors, this paper studies the tradeoff between diversity and estimation errors. It is shown that an optimal bandwidth exists and the optimal power allocation for the pilot signals is a function of the quality of the channel estimates.

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.

Bit error rate is evaluated for a multicarrier CDMA system with channel estimation errors. We consider a multicarrier CDMA system with pilot and data channels. The signal experiences independent flat Rayleigh fading on each subcarrier. Simple integrators produce the channel estimates which are used to maximal-ratio-combine the data from all the subcarriers, Keeping the total transmitted energy fixed, as the number of subcarriers increases, the weaker signal in each subcarrier makes channel estimation more difficult and results in larger errors in the combiner weights. We quantify how errors in channel estimation affect a multicarrier CDMA system as the system becomes more wideband. We show that there is a tradeoff between diversity order and SNR available for channel estimation.