ARIS and PRIS Joint Deployment: A Novel Perspective on Overall Power Constraint

With the rapidly increased number of antennas, even the amplifying power used for the active element of active reconfigurable intelligent surface (ARIS) is very small, such power will have a profound impact on system performance, which is no longer ignored. In this letter, we investigate a communication system jointly assisted by a fixed passive RIS (PRIS) and a movable ARIS, under an overall power constraint that includes the transmit power of base station (BS) and the amplifying power for ARIS. Without loss of generality, two deployment orders of RISs are respectively studied, i.e., ARIS-PRIS and PRIS-ARIS deployments. To better illustrate the impact of ARIS deployment and power allocation on the achievable rate, we derive the closed-form expressions of optimal power allocations for these two deployments. Following the overall power constraint, the numerical results matching our analysis confirm that, when the amplifying power for ARIS is large enough, ARIS should be deployed closer to BS for any deployment orders, to achieve an optimal rate, and vice versa.