On the Performance of RIS Transmitter with Receive Combining Techniques
In this paper, we investigate the impact of practical phase-shift constraint of reconfigurable intelligent surface (RIS) on multi-antenna systems employing maximal ratio combining (MRC) and receive antenna selection (RAS). Since each element of RIS can apply only a single phase-shift at a given time, the system performance degrades substantially when multiple receive antennas are active simultaneously. To quantify this effect, closed-form outage probability expressions are derived and asymptotic analyses are carried out over Rician fading channels. We show that the practical phase-shift constraint of RIS degrades the diversity order of MRC and in addition, RAS outperforms MRC, contrary to the conventional performance ordering of these techniques.