Constant-Power Adaptive QAM in High Delay Spread Environments

Constant-power constant-symbol-rate adaptive quadrature amplitude modulation (AQAM) system with four modes is analyzed in high delay spread environments. The ratio of rms delay spread to symbol period is from 0.02 to 0.2. The average bit-error-rate (BER) and throughput are investigated subject to the instantaneous BER constraint and the average BER constraint. Results show that an increase in power or a reduction in delay spread will lead to the increase of the average throughput under the two constraints, whereas they will not necessarily result in a decrease in the average BER under the instantaneous BER constraint. The superiority to individual QPSK mode is investigated in the delay spread immunity at last.