Performance analysis of downlink W-CDMA systems in Weibull, Lognormal and Nakagami fading channels

Abstract

Wideband Code Division Multiple Access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds to mobile and portable wireless devices than those which are commonly offered in todayʼs market. In W-CDMA systems transmitting over multipath channels, both Inter Symbol Interference (ISI) as a result of Inter Chip interference (ICI) and Multiple Access Interference (MAI) cannot be easily eliminated. Although it is possible to design multiuser detectors that suppress MAI and ISI, these detectors often require explicit knowledge of at least the desired usersʼ signature waveform. Torlak and Xu proposed a blind estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiuser channels (Torlak and Xu, 1997 [1]). In our work, we study a similar blind channel estimation scheme for downlink W-CDMA systems that provides estimates of the multiuser channels by exploiting the structural information of the data output. In particular, we show that the subspace of the (data + noise) matrix contains sufficient information for unique determination of channels, and hence, the signature waveforms and signal constellations. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for the Weibull and Lognormal fading channels. Estimated signal constellations under the Weibull, Lognormal and Nakagami fading channels are also plotted.