The reconfigurable intelligent surface-aided multi-node IoT downlink: beamforming design and performance analysis

Abstract

Reconfigurable intelligent surfaces (RIS) are capable of enhancing the wireless propagation environment of the future Internet of Things (IoT). Recently, they have also been configured as a transmitter to realize information modulation at low hardware complexity. In this paper, we conceive a transmitter relying on a single radio frequency (RF) chain for low-complexity RIS-aided multi-user downlink communication. More explicitly, in the proposed architecture, the multi-user information is transmit precoded and modulated at the RIS by appropriately configuring the phase shift and amplitude of each RIS element. We assume that the distribution of multiple users obeys on a Poisson point process (PPP), where we jointly optimize the total power reflected from the RIS and the power allocation fraction assigned to each user, under the practical constraint of a realistic amplitude limitation of each RIS element. Additionally, we theoretically analyse the ergodic rate, symbol error probability, outage probability and coverage range of the proposed RIS-aided single-RF downlink and confirm the accuracy of our analysis by simulations. Finally, we compare its performance to that of the conventional multiple-input-multiple-output (MIMO) systems employing multiple RF-chains.