Abstract
Reconfigurable intelligent surface (RIS) has been expected to be a promising technology for next generation communication systems based on its capability of tailoring propagation environments. At the same time, hybrid analog and digital precoding is also a key technology for improving the energy efficiency of millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) wireless systems. The requirements of low cost and power consumption for future wireless systems can be met by combining these two technologies. In this paper, we formulate the problem of jointly designing the hybrid precoding at the base station (BS) and the phase shifts at the RIS for both single-cell and multi-cell scenarios to maximize the achievable sum rate. For the single-cell scenario, we propose an improved sparse precoding (ISP) scheme for analog transmit precoding (TPC) design while considering the beam squint effect, and utilize the two-stage digital TPC scheme to reduce the computational complexity. Inspired by the two-stage digital TPC design, we propose the three-stage digital TPC design for the multi-cell scenario, which handles inter-cell and intra-cell interference, and power allocation respectively. Finally, simulation results demonstrate that the proposed scheme has better performance than existing hybrid precoding schemes.
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