Wideband Generalized Beamspace Modulation (wGBM) for mmWave Massive MIMO Over Doubly-Selective Channels

Generalized beam modulation (GBM) is a recently proposed spectrum efficiency (SE)-enhanced index modulation (IM) scheme for narrowband millimeter wave (mmWave) massive multiple-input multiple-output (mMIMO) systems with hybrid transceivers. Unlike most existing fully-digital IM techniques whose application to wideband channels is straightforward after adopting the orthogonal frequency division multiplexing (OFDM) technique, extending GBM from the narrowband to wideband channels is quite challenging. The reason is that the per-subcarrier process in hybrid OFDM systems is no longer independent across individuals as all subcarriers share a common analog beamformer. Hence, the designed wideband GBM (wGBM) has to be compatible with hybrid OFDM systems while maintaining the SE-enhanced merit of GBM. Towards this objective, a symbol-based instead of the prevalent subcarrier-based paradigm is applied to guide wGBM design. To avoid the high detection complexity in large-scale OFDM systems, we devise a low-complexity detector by transforming the complicated symbol (block) detection into the manageable subcarrier (sub-block) detection. Finally, a simple first-order Doppler compensator is carefully designed to enhance the robustness of wGBM against Doppler. Both theoretical analyses and numerical simulations have been carried out to demonstrate the superiority of wGBM over existing alternatives in terms of error performance and energy efficiency.