Cooperative Double-IRS Aided Communication: Beamforming Design and Power Scaling

Abstract

Intelligent reflecting surface (IRS) is a promising technology to support high performance wireless communication. By adaptively configuring the reflection amplitude and/or phase of each passive reflecting element on it, the IRS can reshape the electromagnetic environment in favour of signal transmission. This letter advances the existing research by proposing and analyzing a double-IRS aided wireless communication system. Under the reasonable assumption that the reflection channel from IRS 1 to IRS 2 is of rank 1 (e.g., line-of-sight channel), we propose a joint passive beamforming design for the two IRSs. Based on this, we show that deploying two cooperative IRSs with in total K elements can yield a power gain of order O(K 4 ), which greatly outperforms the case of deploying one traditional IRS with a power gain of order O(K 2 ). Our simulation results validate that the performance of deploying two cooperative IRSs is significantly better than that of deploying one IRS given a sufficient total number of IRS elements. We also extend our line-of-sight channel model to show how different channel models affect the performance of the double-IRS aided wireless communication system.

Cooperative Beam Routing for Multi-IRS Aided Communication

“…Furthermore, we define ϑ 0,j as the AoD from the BS to IRS j, ϕ a j,i /ϕ e j,i as the azimuth/elevation AoA at IRS j from node i, and ϑ a i,j /ϑ e i,j as the azimuth/elevation AoD from IRS i to node j. The above AoAs and AoDs can be estimated based on the geometric relationship of the BS, IRSs and users in the system [7] or by integrating sensors to the IRSs.…”

“…This is because by carefully deploying the IRSs, strong line-of-sight (LoS) channel can be achieved for inter-IRS links, which can provide more pronounced cooperative passive beamforming (CPB) gains over the conventional single-IRS assisted system. Inspired by this, the authors in [7] first proposed a double-IRS system, where a single-antenna BS serves a single-antenna user through a double-reflection link by two IRSs deployed near the BS and user, respectively. It was shown in [7] that this system provides a CPB gain that increases quartically with the total number of IRS reflecting elements, compared to the quadratic growth of the passive beamforming gain in the conventional single-reflection link.…”

RIS-Assisted Coverage Enhancement in Millimeter-Wave Cellular Networks

“…Since the RIS includes a large number of passive elements, it can profit from the angle-of-arrival (AOA) localization technique in [56] to find ϕ when UE identifies itself by broadcasting the response to the paging message from the associated BS. Moreover, assuming the RIS is equipped with received RF chain, as investigated in [13], [26], the RIS can directly obtain the channel state information (CSI) of BS-RIS and RIS-UE paths to achieve the optimal performance.…”

What Role Do Intelligent Reflecting Surfaces Play in Multi-Antenna Non-Orthogonal Multiple Access?

“…Transmissions coming from one IRS can leak to others and cause strong inter-IRS interference, impacting the network performance. Such impairment could be mitigated if those IRSs with exceeding levels of interference could work in cooperative mode, as in [14], instead of operating independently. However, the joint coordination of multiple IRSs can trigger an explosion in signaling and processing overhead, which can potentially impact communication latency.…”