[Paper Review] How to Deploy Intelligent Reflecting Surfaces in Wireless Network: BS-side, User-side, or Both Sides?

Changsheng You, Beixiong Zheng+2 more|arXiv (Cornell University)|Dec 7, 2020

Advanced Wireless Communication Technologies17 citations

TL;DR

This paper proposes a hybrid intelligent reflecting surface (IRS) deployment strategy that combines base station (BS)-side and user-side IRSs to maximize network performance. By enabling cooperative passive beamforming and flexible user-IRS association, the hybrid approach achieves superior min-rate performance—especially with large IRS aperture sizes—outperforming single-sided deployments due to enhanced coverage and beamforming gain from double-reflection links.

ABSTRACT

The performance of wireless communication systems is fundamentally constrained by the random and uncontrollable wireless channel. By leveraging the recent advance in digitally-controlled metasurface, intelligent reflecting surface (IRS) has emerged as a promising solution to enhance the wireless network performance by smartly reconfiguring the radio propagation environment. Despite the substantial research on IRS-aided communications, this article addresses the important issue of how to deploy IRSs in a wireless network to achieve its optimum performance. We first compare the two conventional strategies of deploying IRS at the side of base station or distributed users in terms of various communication performance metrics, and then propose a new hybrid IRS deployment strategy by combining their complementary advantages. Moreover, the main challenges in optimizing IRS deployment as well as their promising solutions are discussed. A case study is also presented to compare the performance of different IRS deployment strategies and draw useful insights for practical design.

Motivation & Objective

• To address the critical design challenge of where to deploy intelligent reflecting surfaces (IRS) in wireless networks to maximize performance.
• To compare conventional one-sided IRS deployments (BS-side or user-side) in terms of coverage, beamforming gain, and signaling overhead.
• To propose a novel hybrid IRS deployment strategy that combines the complementary advantages of both one-sided approaches.
• To analyze the key optimization challenges in hybrid IRS deployment, including user-IRS association, channel estimation, and reflecting element allocation.
• To provide quantitative insights into the performance gains of hybrid IRS deployment over one-sided strategies under various network conditions.

Proposed method

• Proposes a hybrid IRS deployment model with both BS-side and user-side IRSs to enable cooperative passive beamforming.
• Introduces a joint optimization framework for IRS-user association and reflecting element allocation to maximize the system's minimum rate (min-rate).
• Uses a double-reflection link model to exploit channel gains from signals reflected via both BS-side and user-side IRSs.
• Applies exhaustive search for optimal user-IRS association and compares performance across different IRS deployment configurations.
• Employs a signal model that accounts for path loss, phase shifts, and channel statistics in IRS-aided wireless systems.
• Conducts numerical evaluations using a 3-user scenario with varying total reflecting elements (M) to compare performance across deployment strategies.

Experimental results

Research questions

• RQ1 How does the performance of BS-side IRS deployment compare to user-side IRS deployment in terms of network coverage and min-rate?
• RQ2 What are the key advantages and limitations of one-sided IRS deployment (BS-side or user-side) in practical wireless networks?
• RQ3 Can a hybrid IRS deployment strategy combining both BS-side and user-side IRSs achieve better performance than one-sided deployments?
• RQ4 How does the number of reflecting elements (M) affect the performance gain of different IRS deployment strategies?
• RQ5 What is the impact of double-reflection links (via both IRSs) on the achievable rate and system fairness in hybrid IRS deployment?

Key findings

• The hybrid IRS deployment strategy achieves the highest min-rate across all tested configurations, especially when the total number of reflecting elements M exceeds 1200.
• For M < 1000, the BS-side IRS deployment outperforms the hybrid strategy due to stronger single-reflection links, but the hybrid strategy surpasses it when M > 1200.
• User-side IRS deployment shows marginal performance gains with increasing M, as many users remain outside the local coverage of individual IRSs.
• The hybrid strategy enables all users to be served by at least one IRS, eliminating coverage holes present in one-sided deployments.
• User 2 benefits from a higher-order passive beamforming gain via a double-reflection link, enabling more flexible rate balancing in the system.
• The hybrid deployment achieves significant performance gains by exploiting inter-IRS cooperative beamforming, particularly when M is large.