[Paper Review] On the Enabling of Multi-receiver Communications with Reconfigurable Intelligent Surfaces

Hamidreza Taghvaee, Akshay Jain+4 more|arXiv (Cornell University)|Jun 12, 2021

Advanced Wireless Communication TechnologiesEngineering52 references25 citations

TL;DR

This paper proposes a phase-only reconfigurable intelligent surface (RIS) technique for multi-receiver mmWave communications, enabling independent beam control without amplitude tuning. It achieves up to 2 Gbps throughput in indoor offices and over 0.5 Gbps per user in urban microcells, outperforming amplitude-phase methods by 0.8 Gbps with 8 users due to reduced hardware complexity and loss.

ABSTRACT

The reconfigurable intelligent surface is a promising technology for the manipulation and control of wireless electromagnetic signals. In particular, it has the potential to provide significant performance improvements for wireless networks. However, to do so, a proper reconfiguration of the reflection coefficients of unit cells is required, which often leads to complex and expensive devices. To amortize the cost, one may share the system resources among multiple transmitters and receivers. In this paper, we propose an efficient reconfiguration technique providing control over multiple beams independently. Compared to time-consuming optimization techniques, the proposed strategy utilizes an analytical method to configure the surface for multi-beam radiation. This method is easy to implement, effective and efficient since it only requires phase reconfiguration. We analyze the performance for indoor and outdoor scenarios, given the broadcast mode of operation. The aforesaid scenarios encompass some of the most challenging scenarios that wireless networks encounter. We show that our proposed technique provisions sufficient improvements in the observed channel capacity when the receivers are close to the surface in the indoor office environment scenario. Further, we report a considerable increase in the system throughput given the outdoor environment.

Motivation & Objective

• Address the high cost and complexity of RIS systems requiring amplitude and phase control for multi-beam applications.
• Enable efficient, low-complexity multi-receiver communication in mmWave bands using only phase reconfiguration of RIS unit cells.
• Improve system throughput and channel capacity in challenging indoor and urban line-of-sight (LoS) and non-LoS (NLoS) environments.
• Demonstrate that phase-only RIS reconfiguration can achieve comparable or better performance than amplitude-phase control with reduced hardware overhead.
• Validate the method in realistic indoor office and urban microcell (UMi) scenarios under broadcast/multicast transmission mode.

Proposed method

• Propose an analytical phase-only beamforming method to control multiple independent beams via RIS, avoiding complex amplitude tuning.
• Use a mathematical formulation based on Fourier transform principles to derive phase profiles that generate desired multi-beam radiation patterns.
• Apply the method to both indoor (28 GHz, 30 dBi gain) and outdoor (3.55 GHz, 17 dBi gain) scenarios with fixed base stations and mobile users.
• Model path loss using realistic exponents (e.g., 1.7 for LoS, 3.8 for NLoS) and compute SNR and throughput across varying user distances from the RIS.
• Compare performance against amplitude-phase RIS and direct transmission (MCBS/SCBS) in terms of total and per-user throughput.
• Validate results using simulations with 8 users at varying distances (3–7 m) from the RIS in both environments.

Experimental results

Research questions

• RQ1 Can phase-only RIS reconfiguration achieve effective multi-beam control for multiple receivers without amplitude tuning?
• RQ2 How does phase-only RIS beamforming compare to amplitude-phase RIS in terms of system throughput and per-user data rate?
• RQ3 What is the performance gain of RIS in indoor office and urban microcell (UMi) environments under broadcast/multicast operation?
• RQ4 How does user distance from the RIS affect SNR and throughput in both indoor and outdoor scenarios?
• RQ5 To what extent can RIS compensate for NLoS blockage and path loss in mmWave communications?

Key findings

• The proposed phase-only RIS configuration achieves up to 2 Gbps total throughput in the indoor office scenario with 8 users, providing approximately 0.33 Gbps per user.
• For 8 users, the phase-only method provides 0.8 Gbps higher total throughput than the amplitude-phase method, demonstrating significant performance gain.
• In the UMi scenario, the RIS-based system provides over 0.5 Gbps per user, while direct MCBS transmission offers negligible throughput due to NLoS blockage.
• When users are within 1–2 meters of the RIS, they experience at least 0.5 Gbps data rates, with a peak of ~2.2 Gbps in the indoor scenario.
• The system achieves over one order of magnitude higher channel capacity with 7 users in the UMi environment compared to direct MCBS communication.
• SNR degrades significantly with increasing distance from the RIS, confirming that RIS is most effective for short-range, close-proximity user deployments.