In this letter, we study the wireless point-to-point communication from a transmitter (Tx) to a receiver (Rx), which is jointly aided by an active intelligent reflecting surface (AIRS) and a passive IRS (PIRS). We consider two practical transmission schemes by deploying the two IRSs in different orders, namely, Tx$\rightarrow$PIRS$\rightarrow$AIRS$\rightarrow$Rx (TPAR) and Tx$\rightarrow$AIRS$\rightarrow$PIRS$\rightarrow$Rx (TAPR). Assuming line-of-sight channels, we derive the achievable rates for the two schemes by optimizing the placement of the AIRS with the location of the PIRS fixed. Our analysis shows that when the number of PIRS elements and/or the AIRS amplification power is small, the AIRS should be deployed closer to the Rx in both schemes, and TAPR outperforms TPAR with their respective optimized AIRS/PIRS placement. Simulation results validate our analysis and show the considerable performance gain achieved by the jointly optimized AIRS/PIRS deployment over the baseline double-PIRS system under the same power and IRS element budgets.

翻译：在这封信中,我们研究了从一个发报机(Tx)到一个接收器(Rx)的无线点对点通信(Rx),这种通信由活跃的智能反射表面(AIRS)和被动的IRS(PIRS)共同协助,我们考虑了两种实际的传输计划,将两个IRS部署在不同的订单上,即:Tx$\rightrorrow$PIRS$\rightrorrowor $AIRS$\rightrroror$AIRS$\rightrorom$PIRS$\right-rightror$PIRRS$\right-rorrow$Rx(TAPR),我们的分析表明,当PIRS元素和(或)AIRSARS的放大能力小的时候,应该将AIRS/PIRS在两个计划中都更接近R(TRAS)的配置,而TRARS/PIRS的定位是各自优化的优化的ARS/PIRS。