Abstract
Most algorithms developed for the optimization of Intelligent Reflecting Surfaces (IRSs) so far require knowledge of full Channel State Information (CSI). However, the resulting acquisition overhead constitutes a major bottleneck for the realization of IRS-assisted wireless systems in practice. In contrast, in this letter, focusing on downlink transmissions from a Base Station (BS) to a Mobile User (MU) that is located in a blockage region, we propose to optimize the IRS for illumination of the area centered around the MU. Hence, the proposed design requires the estimation of the MU’s position and not the full CSI. For a given IRS phase-shift configuration, the end-to-end BS-IRS-MU channel can then be estimated using conventional channel estimation techniques. The IRS reconfiguration overhead for the proposed scheme depends on the MU mobility as well as on how wide the coverage of the IRS illumination is. Therefore, we develop a general IRS phase-shift design, which is valid for both the near- and far-field regimes and features a parameter for tuning the size of the illumination area. Moreover, we study a special case where the IRS illuminates the entire blockage area, which implies that the IRS phase shifts do not change over time leading to zero overhead for IRS reconfiguration.
Highlights
Intelligent Reflecting Surfaces (IRSs) have attracted significant attention as an enabling technology for the realization of smart radio environments in future sixth generation (6G) wireless systems [1], [2]
Regardless of which of the above Channel State Information (CSI) acquisition schemes is adopted, the common drawback of optimizing the IRS based on CSI is that, since channel gains change quickly, the IRS should be in principle frequently reconfigured
We focus on downlink transmissions from a Base Station (BS) to an Mobile User (MU) that is located in a blockage region
Summary
Intelligent Reflecting Surfaces (IRSs) have attracted significant attention as an enabling technology for the realization of smart radio environments in future sixth generation (6G) wireless systems [1], [2]. The ON/OFF protocol proposed in [5] comprises Q stages, where in each stage, only one reflecting element is ON and the corresponding cascaded Base Station (BS)-IRS-Mobile User (MU) channel is estimated. In [7], the authors proposed an algorithm which estimates the BS-IRS and IRS-MU channels on two different time scales. Regardless of which of the above CSI acquisition schemes is adopted, the common drawback of optimizing the IRS based on CSI is that, since channel gains change quickly, the IRS should be in principle frequently reconfigured (e.g., typical channel coherence times are on the order of milliseconds [10]). The frequency of IRS reconfiguration does not explicitly depend on the channel coherence time, but on the mobility of the user, the size of the area illuminated by the IRS, and the MU QoS requirement. We study an interesting special case where the IRS illuminates the entire blockage area, avoiding the need for IRS reconfiguration
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