Beam Direction-Based Modulation for Millimeter-Wave Communication Systems: Design and Optimization

In this paper, we investigate a novel beam direction-based modulation transmit scheme for millimeter-wave (mmWave) communication systems equipped with distributed antennas, and propose an enhanced space-domain index modulation (ESDIM) scheme, in which the number of beamforming directions (BDs) for transmitting information bits can be one or two. The ESDIM system jointly utilizes the combination of the index of BDs and signal constellations to transmit information bits, in which one or two beam directions are considered. In addition, we propose power allocation (PA) aided schemes for ESDIM to further improve the system reliability by reducing the system symbol error rate (SER), where three constraints to the transmit power for beamforming are investigated. To be specific, a total transmit power constraint (TTPC) and two per-beamforming power constraints (PBPC) are considered. We first propose a suboptimal PA algorithm for the TTPC-PA aided ESDIM scheme using a powerful solver based on advanced algebra theories, which only considers the PA aspects for a given selected beamforming pair. Then, we extend the TTPC-PA aided scheme to the average per-beamforming power constraint (APBPC)-PA aided scheme and the strict per-beamforming power constraint (SPBPC)-PA aided scheme. Simulation results show that the proposed schemes improve the system SER performance compared to other existing counterparts.