Signature Quantization in Fading CDMA With Limited Feedback

TL;DR

This paper evaluates a signature quantization scheme for CDMA systems with limited feedback, analyzing its performance in large systems and showing near-optimal results with minimal feedback bits.

Contribution

It introduces an analysis of RVQ-based signature quantization in CDMA with fading, deriving SINR expressions and demonstrating near-optimal performance with minimal feedback.

Findings

Large system SINR approximations match finite system performance

MMSE receiver achieves near single-user performance with one feedback bit

Performance analysis extends to fading and non-fading channels

Abstract

In this work, we analyze the performance of a signature quantization scheme for reverse-link Direct Sequence (DS)- Code Division Multiple Access (CDMA). Assuming perfect estimates of the channel and interference covariance, the receiver selects the signature that minimizes interference power or 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 a finite number of bits via a feedback channel. Here we are interested in the performance of a Random Vector Quantization (RVQ) codebook, which contains independent isotropically distributed vectors. Assuming arbitrary transmit power allocation, we consider additive white Gaussian noise (AWGN) channel first with no fading and subsequently, with multipath fading. We derive the corresponding SINR in a large system limit at the output of matched filter and linear minimum mean squared error (MMSE) receiver. Numerical examples show that the derived large system results give a good approximation to the performance of finite-size system and that the MMSE receiver achieves close to a single-user performance with only one feedback bit per signature element.