Spatial Path Index Modulation for RIS-Aided Massive MIMO

The next generation wireless networks focus on improving the energy and spectral efficiency (SE/EE) of the communication systems in response to the demand for massive number of users and data rate. In this work, we aim to achieve the enhancement of SE and EE by employing index modulation (IM) techniques for reconfigurable intelligent surface (RIS)-aided communication systems. While RIS offers the network efficiency and improve the coverage, IM provides SE improvement by the transmission of additional index bits. In IM, we utilize the indices of the spatial paths between the base station and the user through the RIS. We introduce a low complexity approach for the design of hybrid beamformers, which are constructed by the steering vectors corresponding to the selected spatial path indices for IM. Via numerical experiments, we show that the proposed approach presents an improved SE performance, even higher than that of the use of fully-digital beamformers while using a few RF chains.