Signature optimization for DS-CDMA with limited feedback

We examine a Direct Sequence (DS)-Code Division Multiple Access (CDMA) system with signature optimization for interference avoidance. Reduced-rank signature optimization, in which each signature is constrained to lie in a lower-dimensional subspace, is analyzed with a matched filter receiver. Performance is studied assuming that the signature coefficients are quantized for transmission over a feedback channel with limited bandwidth. Assuming scalar quantization of each reduced-rank coefficient, the dimension which maximizes the output Signal-to-Interference Plus Noise Ratio depends on the load and number of feedback bits, and can be much less than the number of signature coefficients. The performance of quantized reduced-rank signature optimization is compared with a random vector quantization scheme, which gives an upper bound on performance.