Power-Aware Sparse Reflect Beamforming for Active RIS-aided Interference Channels

In an active reconfigurable intelligent surface (RIS), each reflecting element (RE) reflects the incident signal with not only reconfigurable phase shift but also controllable amplitude amplification. In this paper, we are interested in active RIS-aided interference channels in which
$K$
user pairs share the same time and frequency resources with the help of the active RIS. Thanks to the promising amplitude amplification capability, activating a moderate number of REs, rather than all of them, is sufficient for the active RIS to mitigate the cross channel interferences. Motivated by this, we propose a power-aware sparse reflect beamforming design for the active RIS-aided interference channels, which allows the active RIS to flexibly adjust the number of activated REs for the sake of saving power. Specifically, we first establish the power consumption model in which only those activated REs consume the biasing and operation power that supports the amplitude amplification. Based on the proposed model, we formulate a problem to maximize the sum rate of the
$K$
user pairs by designing the sparse reflect beamforming vector under the maximum amplification gain and the limited power budget constraints on the active RIS. Towards this end, we propose an iterative reweighted
$\ell_{1}$
-norm method in combination with fractional programming to find a sparse solution for the reflect beamforming vector. Numerical results show that the proposed sparse design can notably increase the sum rate of the
$K$
user pairs in interference channels even with the limited power budget.