Hybrid RIS-Assisted Communications: Optimal Allocation Under a Total Power Constraint

In this letter, we investigate the wireless communication system assisted by hybrid intelligent reflecting surface (RIS), which is composed of both passive and active elements integrated reflection-type amplifiers. Different from conventional hybrid RIS system, the amplifying power used at active RIS is considered as one part of the total power for overall system. Under this condition, we present the exact closed-form expression of the outage probability (OP) and investigate the optimal allocations of the RIS elements and power budget for signal-to-interference-plus-noise ratio (SINR) maximization. In addition, we analyze the amplification factor and corresponding dynamic noise, as well as derive the threshold of the amplification factor for the proposed scheme. Finally, simulation and numerical results show that the proposed hybrid RIS scheme is significantly preferable over the conventional RIS scheme if the amplification factor of the proposed scheme is smaller than that of the threshold.