Adaptive coding for high-rate direct-sequence spread spectrum

High-rate direct-sequence (DS) spread spectrum is a modulation technique in which most or all of the spreading is provided by nonbinary data modulation. For applications to mobile ad hoc wireless networks, the limited processing gain of high-rate DS spread spectrum gives only modest protection against multiple-access or multipath interference, but increased interference rejection capability can be obtained from error-control coding. In this paper, we evaluate the performance of high-rate DS spread spectrum with turbo product codes. The utility of the Gaussian approximation for the design of adaptive coding systems is illustrated. An adaptive coding algorithm is described and its performance is compared with that of fixed-rate codes for channels with unknown propagation loss. The algorithm is based on statistics obtained in the receiver, and no external side information is employed.