In this letter, we consider an intelligent reflecting surface (IRS)-aided wireless communication system, where an active or passive IRS is employed to assist the communication between an access point and a user. First, we consider the downlink/uplink communication separately and optimize the IRS placement for rate maximization with an active or passive IRS. We show that the active IRS should be deployed closer to the receiver with the IRS's decreasing amplification power; while in contrast, the passive IRS should be deployed near either the transmitter or receiver. Moreover, with optimized IRS placement, the passive IRS is shown to outperform its active counterpart when the number of reflecting elements is sufficiently large and/or the active-IRS amplification power is too small. Next, we optimize the IRS placement for both active and passive IRSs to maximize the weighted sum-rate of uplink and downlink communications. We show that in this case, the passive IRS is more likely to achieve superior rate performance. This is because the optimal active-IRS placement needs to balance the rate performance in the uplink and downlink, while deploying the passive IRS near the transmitter or receiver is optimal regardless of the uplink or downlink.
翻译:在本信里,我们考虑的是智能反射表面(IRS)辅助无线通信系统,即使用主动或被动IRS来协助接入点与用户之间的通信。首先,我们单独考虑下行/上行通信,优化IRS用于使用主动或被动IRS实现最高比率的定位。我们表明,主动IRS应随着IRS的扩增能力下降而更接近接收器部署;相反,被动IRS应部署在发射机或接收器附近。此外,由于IRS的优化定位,当反射元素的数量足够大和(或)主动-IRS增缩能力太小时,被动IRS显示被动的IRS优于其主动对应方。接下来,我们优化对主动和被动IRS的配置,以最大限度地增加IRS上行和下行通信的加权总和率。我们表明,在这种情况下,被动IRS更可能实现更优的性性性能。这是因为最佳的主动-IRS定位需要平衡上行和下行的上行速度,同时部署IRS的被动式IMS上下行或最优性链路。