Energy-Efficient M-QAM Precoder Design with Spatial Peak Power Minimization for MIMO Directional Modulation Transceivers

Spectrally efficient multi-antenna wireless communications is a key challenge as service demands continue to increase. At the same time, powering up radio access networks increases CO2 footprint. Hence, for an efficient radio access design, we design a directional modulation precoder for M QAM modulation with M = 4, 8, 16, 32. First, extended detection regions are defined in these constellations using analytical geometry. Then, constellation points are placed in the optimal positions of these regions while the minimum Euclidean distance to neighbor constellation points and detection region boundary is kept as in the conventional M -QAM modulation. For further energy-efficiency, relaxed detection regions are modeled for inner points of M = 16, 32 constellations. The modeled extended and relaxed detection regions as well as the modulation characteristics are utilized to formulate convex symbol-level precoder design problems for directional modulation to minimize the transmission power while preserving the minimum required SNR at the destination. In addition, the extended and relaxed detection regions are used for precoder design to minimize the output of each power amplifier. Results show that compared to the benchmark schemes, the proposed methods perform better in terms of power and peak power reduction as well as symbol error rate reduction for a long range of SNRs. Keywords—Directional modulation, energy efficiency, extended detection region, spatial peak power, M -QAM modulation, symbollevel precoding.