Multi-dimensional amplitude control for DS-CDMA

A jointly adaptive transmitter/receiver scheme is proposed for the reverse link of a DS-CDMA system with short spreading codes. The scheme allows a tradeoff between performance and the bandwidth of the feedback channel required for transmitter adaptation. Each spreading code is expressed as a linear combination of mutually orthogonal vectors, which are adaptively combined to minimize mean squared error at the receiver. Numerical results are presented that illustrate the performance of the proposed scheme assuming additive Gaussian noise, log-normal shadowing, and coefficient estimation error. These results show that adaptation of relatively few combining coefficients leads to significant performance improvements. Stochastic gradient and least squares adaptive algorithms are derived for estimation of the combining coefficients. Convergence curves are presented assuming both recursive and block adaptation with a matched-filter receiver.