High-performance 64-QAM OFDM via carrier interferometry spreading codes

摘要

OFDM (orthogonal frequency division multiplexing) is an excellent technology that will almost certainly play a large role in next generation wireless communication systems. However, in OFDM, no frequency diversity is exploited to improve BER performance. Today's OFDM systems attempt to overcome this limitation by application of channel coding and interleaving, which requires a reduction in throughput. In our earlier work, we showed how carrier interferometry (CI) codes may be used to spread OFDM symbols over all N subcarriers to exploit frequency diversity without loss in throughput. However, only BPSK was considered in the earlier work. In this paper, we extend the proposed CI/OFDM (carrier interferometry with OFDM) system by updating it for application with QAM modulation schemes. (For example, minimized mean square error combining (MMSEC) is derived for CI/OFDM with QAM modulation schemes.) Simulation results over multi-path fading channels show that 64QAM CI/OFDM significantly outperforms 64QAM OFDM at the cost of a small increase in complexity.