Channel Capacity Optimization Using Reconfigurable Intelligent Surfaces in Indoor mmWave Environments
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Indoor millimeter-wave (mmWave) environment channels are typically sparsely-scattered and dominated by a strong line-of-sight (LOS) path. Hence, any system optimization that is not centered around the transmission via the direct LOS path usually gives only limited gains. The recent introduction of reconfigurable intelligent surfaces (RISs), which have the potential to influence the propagation environment in a controlled manner, tends to change the previous paradigm. Motivated by this, we study the channel capacity optimization utilizing RISs in indoor mmWave environments. More precisely, we propose two optimization schemes that exploit the customizing capabilities of the RIS reflection elements to enhance the channel capacity. The first optimization scheme exploits only the adjustability of the RIS reflection elements; for this scheme we derive an approximate expression which explains the connection between the channel capacity gains and the system parameters. The second optimization scheme jointly optimizes the RIS reflection elements and the transmit phase precoder; for this scheme, we propose a low-complexity technique called global co-phasing to determine the phase shift values for use at the RIS. Simulation results show that the proposed optimization schemes achieve very significant channel capacity gains in systems with a large number of RIS elements.
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