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Multi-User Reconfigurable Intelligent Surface-Aided Communications Under Discrete Phase Shifts
  • Wei Jiang ,
  • Hans Dieter Schotten
Wei Jiang
German Research Center for Artificial Intelligence (DFKI)

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Hans Dieter Schotten
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Reconfigurable intelligent surface a.k.a intelligent reflecting surface (IRS) has recently drawn considerable attention because of its potential to achieve high spectral and energy efficiencies in a cost-effective way. Due to its disruptive ability to manipulate wireless environments, IRS imposes fundamental particularities on multi-user communications.
This paper focuses on studying  orthogonal and non-orthogonal multiple access in IRS-aided systems. Unlike most prior works assuming continuous phase shifts, we employ the practical setup where only a finite number of discrete phase shifts are available. To maximize the sum rate, active beamforming and discrete reflection need to be jointly optimized. We therefore propose an alternative optimization method to get the optimal continuous phase shifts iteratively, and then quantize each phase shift to its nearest discrete value. The sum-rate maximization of different schemes is theoretically analyzed and numerically evaluated with different numbers of phase-control bits.