Coded direct sequence spread spectrum systems over satellite channels using an adaptive receiver

This paper examines the performance of a direct sequence spread spectrum multiple access (DS-SSMA) system used over two typical, frequency-selective, fading channels for intermediate circular orbit (ICO) satellites. In an attempt to increase the system efficiency, a timing and phase synchronisation insensitive, adaptive receiver described by Rapajic and Vucetic (1994) has been implemented. The receiver is a least-mean-squares (LMS) implementation of a minimum mean square error (MMSE) receiver. This system has been combined with soft-decision convolutional coding in order to improve the system performance under the fading conditions relative to the uncoded system and to allow as many simultaneous users as possible. Various code rates have been examined and the results are given. This paper specifically focuses on DS-SSMA systems with low spreading ratios. The satellite channels used in this paper were produced by models developed as a result of experimental measurements.