Diversity and adaptation in frequency-hopped spread-spectrum multiple access communications

Abstract

In this thesis, we consider diversity and adaptation in frequency-hopped spread-spectrum multiple access (FH/SSMA) communications. We propose a simple and efficient diversity combining scheme and a bandwidth efficient diversity transmission scheme for FH/SSMA communications. In addition, we investigate the performance of combined power/code rate adaptation in comparison with the adaptive power control and adaptive code rate control schemes. First, we propose the logical AND diversity combining scheme in slotted FH/SSMA packet radio networks. The proposed diversity scheme employes the symbol-by-symbol logical AND operation between the currently received packet and the previously combined packet. Our results show that the proposed low-complexity diversity combining scheme provides a much more significant performance improvement over existing much more complex diversity combining schemes using perfect side informations on channels or soft decision demodulation outputs as the number of combined packets or the modulation alphabet size increases. Second, we propose a bandwidth efficient diversity scheme for FH/SSMA systems, where the diversity order is independent of the hopping rate. The proposed scheme reduces the hardware complexity for the frequency synthesizer for frequency hopping in comparison with the conventional fast frequency-hopping scheme and the multihopping scheme. Numerical results show that the proposed scheme yields a much lower bit error probability in comparison with the fast frequency-hopping scheme and the multihopping scheme using same bandwidth, and that the performance improvement becomes more significant as signal-to-noise ratio or bandwidth increases. Third, we consider combined power/code rate adaptation in FH/SSMA communications, where both transmission power and code rate are adapted simultaneously relative to the channel traffic and/or the channel fading. We investigate the optimal pair of transmission power and code rate that minimi...