Subspace based downlink channel estimation for W-CDMA systems

Abstract

Wideband code division multiple access (W-CDMA) is a third generation (3G) mobile wireless technology that promises much higher data speeds for 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 (1997) [1] proposed a subspace based channel estimation algorithm for Asynchronous CDMA (A-CDMA) systems to estimate the multiple usersʼ symbols. In our work, we study a similar subspace based channel estimation scheme for downlink W-CDMA systems that provide estimates of the subchannels of multiple users 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 constellation. Performance measures like Bit Error Rate (BER) and Root Mean Square Error (RMSE) are plotted for Rayleigh and Rician fading channels.