Large System Performance of Signature Quantization in CDMA

In this paper, we analyze the performance of a signature quantization scheme for reverse-link Direct Sequence (DS)Code Division Multiple Access (CDMA). Assuming perfect estimates of channel and interference covariance, the receiver selects the signature that maximizes signal-to-interference plus noise ratio (SINR) for a desired user from a signature codebook. The codebook index corresponding to the optimal signature is then relayed to the user with finite number of bits via a feedback channel. Previously, we showed that a Random Vector Quantization (RVQ) codebook, which contains independent isotropically distributed vectors, is optimal (i.e., maximizes SINR) in a large system limit in which number of interfering users, processing gain, and feedback bits tend to infinity with fixed ratios. Dai et al. have analyzed the large system SINR for a matched filter with nonfading channel. Here we extend the results to linear minimum mean squared error (MMSE) receiver and multipath fading channel. Numerical examples show that the derived large system results give a good approximation to the performance of finite-size system.