[Paper Review] Increasing Indoor Spectrum Sharing Capacity using Smart Reflect-Array

Xin Tan, Zhi Sun+2 more|arXiv (Cornell University)|Oct 29, 2015

Advanced Wireless Communication Technologies10 references13 citations

TL;DR

This paper proposes a smart reflect-array system to increase indoor spectrum sharing capacity by dynamically controlling phase shifts to enhance desired signals and suppress interference, enabling multiple users to share the same frequency band simultaneously. Experimental and simulation results show up to a 0.5×10⁶ bits·m/s improvement in transport capacity with multiple reflect-arrays, without modifying user devices.

ABSTRACT

The radio frequency (RF) spectrum becomes overly crowded in some indoor environments due to the high density of users and bandwidth demands. To accommodate the tremendous wireless data demands, efficient spectrum-sharing approaches are highly desired. To this end, this paper introduces a new spectrum sharing solution for indoor environments based on the usage of a reconfigurable reflect-array in the middle of the wireless channel. By optimally controlling the phase shift of each element on the reflect-array, the useful signals for each transmission pair can be enhanced while the interferences can be canceled. As a result, multiple wireless users in the same room can access the same spectrum band at the same time without interfering each other. Hence, the network capacity can be dramatically increased. To prove the feasibility of the proposed solution, an experimental testbed is first developed and evaluated. Then, the effects of the reflect-array on transport capacity of the indoor wireless networks are investigated. Through experiments, theoretical deduction, and simulations, this paper demonstrates that significantly higher spectrum-spatial efficiency can be achieved by using the smart reflect-array without any modification of the hardware and software in the users' devices.

Motivation & Objective

• To address the growing spectrum congestion in high-density indoor environments such as conference halls and shopping malls.
• To overcome limitations of existing spectrum-sharing techniques like cognitive radio and beamforming, which require costly hardware upgrades or large antenna arrays.
• To enable simultaneous, non-interfering communication among multiple indoor users on the same frequency band without modifying their devices.
• To demonstrate the feasibility and performance gains of using reconfigurable smart reflect-arrays for spatial multiplexing in indoor wireless networks.

Proposed method

• Deploying reconfigurable reflect-arrays on walls to control the phase shift of each reflector element, thereby shaping the wireless propagation environment.
• Using optimal phase control to enhance desired signals at intended receivers while nullifying interference at unintended receivers.
• Designing and implementing a proof-of-concept testbed with 24, 36, and 48 patch reflectors to validate the system in real indoor conditions.
• Deriving theoretical upper bounds and achievable transport capacity using signal-to-interference-plus-noise ratio (SINR) and path loss models with α = 3.
• Simulating various network configurations with multiple reflect-arrays placed at strategic locations (e.g., (D/2, 0), (0, D/2)) to optimize spatial multiplexing.
• Employing a phase search algorithm with steps from −π to π in increments of π/180 to find optimal phase configurations for maximum capacity.

Experimental results

Research questions

• RQ1 Can a smart reflect-array system enable multiple indoor wireless users to share the same spectrum band simultaneously without mutual interference?
• RQ2 To what extent can transport capacity be improved using reflect-arrays compared to conventional spectrum sharing without such arrays?
• RQ3 How does the number of reflector patches and the number of communication pairs affect the achievable transport capacity?
• RQ4 What is the performance gain of deploying multiple reflect-arrays at different positions in a room?
• RQ5 How close can the achievable transport capacity come to the theoretical upper bound under optimal phase control?

Key findings

• The transport capacity increased by approximately 0.2×10⁶ bits·m/s when the number of reflector patches increased from 24 to 48.
• With a single reflect-array, the achievable transport capacity improved by up to 0.5×10⁶ bits·m/s when four reflect-arrays were deployed compared to a single array.
• The theoretical upper bound of transport capacity was consistently higher than the achievable bound due to idealized node deployment assumptions.
• Increasing the room edge length from 5 m to 10 m led to a measurable increase in transport capacity, as interference nodes could be placed further from receivers.
• The use of two reflect-arrays improved capacity by 0.2×10⁶ bits·m/s compared to a single array, and further gains were observed with three and four arrays.
• The experimental testbed successfully validated the feasibility of the proposed solution for two-user simultaneous transmission in a real indoor environment.