Efficient receivers for SC-FDE with offset modulations

Offset QAM signals (Quadrature Amplitude Modulation) allow good power-bandwidth trade-offs, making them good candidates for broadband wireless systems, especially when combined with SC-FDE schemes (Single-Carrier with Frequency-Domain Equalization). However, FDE receivers designed for nonoffset modulations have poor performance when employed with offset modulations and even FDE receivers specially designed for offset modulations have poor performance when large offset QAM constellations are employed. This is especially serious for non-uniform constellations. In this paper we study the reason behind the poor performance of offset modulations with conventional FDE schemes and present pragmatic FDE receivers for offset modulations that have low complexity but allow excellent performance, even for large and highly non-uniform offset QAM constellations.¹