Quotient Quadrature Amplitude Modulation (QQAM) for Fading Channels

摘要

Multiplicative Rayleigh fading is a frequent problem in wireless communications.If the channel is relatively benign and fading is not severe, one may obtain higher bit rates for an equivalent bandwidth by using M-ary Quadrature Amplitude Modulation (MQAM). A variation, used to combat channel fading while still retaining MQAM, is differential MQAM (i.e., DQAM). The term differential refers to the phase that is coded exactly as in DPSK; however, the amplitude is still subject to distortion by the fading channel. In this paper, we propose a technique called quotient coding, which is designed to remove channel effects from the symbol amplitude as well as its phase. In particular, we shall apply it to MQAM, resulting in modulation that we term Quotient Quadrature Amplitude Modulation (QQAM). In contrast to DQAM, QQAM is just as effective at suppressing the effects of channel fading with respect to the entire symbol as DPSK is for the phase alone. Furthermore, it can be applied to arbitrary MQAM configurations.