W-CDMA downlink performance degradation due to multipath interference and channel estimation errors

The aim of this paper is to quantify the performance behaviour of a W-CDMA system in dependency of a given power delay profile (PDP) and channel estimation errors. The analysis extends the previously published work by Adachi [1], which assumes ideal channel estimation and multipath tracking. For the analytical expressions a particular channel estimation technique was taken into account and a practical pilot symbol assisted technique was used to derive the channel estimation error. By combining both, the performance degradation due to multiple access interference (MAI) and due to channel estimation errors, an easy to use conditional SINR is derived. Assuming BPSK data modulation for simplicity, the downlink performance in terms of the average BER-vs.-SINR was evaluated by means of Monte Carlo simulation for different PDPs; a uniform, a negative exponential and three specific UMTS PDPs. It could be shown that the performance severely depends on the power distribution of the multipath components and the available number of pilot symbols, which determines the reliability of the estimated channel necessary to perform coherent demodulation.