Intelligent Reflecting Surface-Aided Wireless Relaying Communication: Active or Passive?

In this letter, we consider an intelligent reflecting surface (IRS)-aided relay system, where an active or passive IRS is integrated with a half-duplex decode-and-forward relay to aid its data relaying from an access point to a user. First, we jointly optimize the IRS beamforming and the power allocation for all the transmission nodes to maximize the achievable rate for the relay system with an active or passive IRS, subject to a given power budget over two separate transmission phases. Moreover, for different relay/IRS deployment strategies, we analyze the achievable rates for both the active and passive IRS-aided relay systems and obtain the approximate conditions on the number of reflecting elements under which a passive IRS-aided relay system outperforms its active counterpart. Our simulation results show that given the same total power budget, the active IRS-aided relay system can achieve better rate performance than the passive counterpart when the number of IRS elements is not too large.