Adaptive coding in direct-sequence spread-spectrum systems for channels with time-varying propagation losses

High-rate direct sequence spread spectrum with error-control coding has been shown to provide high data rates even in the presence of interference, which makes it attractive for inclusion in an adaptive transmission system. In this paper, we evaluate the performance of high-rate waveforms that use binary antipodal modulation, M-ary orthogonal modulation, or M-ary biorthogonal modulation. We demonstrate how to apply channel capacity results and receiver statistics to select appropriate transmission parameters. A power adjustment protocol that attempts to minimize the transmitted power based on feedback from the receiver is described and evaluated. An adaptive coding protocol is presented, and its performance is compared with that of ideal adaptive protocols that are given perfect channel state information