Hybrid precoded index modulation in downlink mmWave MU-MIMO systems

Abstract

We explore the problem of downlink spatial modulation in mmWave MU-MIMO systems, where the spatial information is conveyed by the indices of the receiving inphase/quadrature streams. Four hybrid precoder/combiner designs are described: two already proposed in the literature, HBA-MMSE - based on the MMSE precoder for the digital part of the hybrid beamforming (HB) and on the singular value decomposition of the channel for the HB' analog part -, and HB-A*-BD - it performs an optimization on the equivalent baseband channel and applies block diagonalization precoder to HB digital part -. The two others, examined here and referred to as HB-ABD and HB-A*-MMSE, are modified versions of the above HBs obtained by interchanging their digital part designs. Simulation results indicate: (i) the advantages of using MMSE precoder as HB digital part; (ii) significant bit error rate performance improvement can be obtained with the proposed HB-A*-MMSE in a multiuser scenario; (iii) performing the hybrid precoded streaming spatial modulation in downlink mmWave MU-MIMO system is a good strategy for reducing the required transmit energy in the base station; and (iv) a simple detection approach can be used for data estimation when the number of users is not large.