Distributed RIS Phase Control for Spatial Multiplexing Gains
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Solution Overview
Problem
The use of a single reconfigurable intelligent surface (RIS) to create an indirect path between a base station and a geographical area may not be sufficient to serve multiple user terminals with sufficient quality of service, particularly at high frequencies, due to a low rank of the propagation channel matrix and direct line of sight conditions, limiting spatial multiplexing gains.
Innovation Solution
Implementing a plurality of RISs, including a main RIS and intermediate RISs, and controlling the phase shifts of intermediate RISs to enhance signal directivity and concentration towards the main RIS and access point, optimizing communication performance criteria.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single RIS is used to create an indirect path between base station and geographical area, then the energy consumption is negligible and installation is simpler, but the quality of service for multiple user terminals is insufficient due to low rank of propagation channel matrix
Solution Approach 1:
The patent divides a single large RIS into multiple smaller RISs (first RIS, second RIS, third RIS) that work together to form a distributed RIS system. Each RIS has its own reflective elements and can be independently controlled, allowing the system to achieve higher service quality through cooperative reflection while maintaining individual simplicity and low energy consumption.
Solution Approach 2:
The patent introduces spatial distribution as a new dimension by deploying multiple RISs at different locations (first RIS at first location, second RIS at second location, third RIS at third location) rather than using a single centralized RIS. This spatial dimensionality increase enables the system to serve multiple user terminals simultaneously with improved quality of service.
2Adaptability or versatility
If a single RIS is used, then the device is simpler to install and operates passively without amplification, but it cannot provide sufficient spatial multiplexing gains for multiple user terminals
Solution Approach 1:
The system segments the RIS functionality across multiple distributed units, each capable of independent phase shift control. This segmentation enables spatial multiplexing by allowing different RISs to serve different user terminals or groups of terminals simultaneously, thereby increasing adaptability without requiring each individual RIS to be overly complex.
Solution Approach 2:
Each RIS in the distributed system maintains the universal passive reflection capability while the collective system achieves multi-functionality by serving multiple user terminals with different spatial requirements. The distributed architecture allows the same basic RIS structure to be universally deployed at multiple locations to achieve diverse service functions.
3Reliability
If intermediate RISs are added to improve signal directivity and concentration, then communication performance is optimized, but the system complexity increases
Solution Approach 1:
The patent introduces intermediate RISs (second RIS and third RIS) as mediators between the base station and user terminals, or between different RISs. These intermediate elements enhance signal directivity and concentration by providing additional reflection paths with controllable phase shifts, thereby optimizing communication performance without requiring direct line-of-sight or overly complex single-point architecture.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the quality of service by increasing the rank of the propagation channel matrix and reducing interference, allowing effective communication with user terminals in the geographical area.
Implementation Method 1
By modifying the reflective properties of each element of the RIS, for example by individually modifying the phase shift introduced by each of these reflective elements
Implementation Method 2
such an RIS is intended to reflect incident radio signals in a passive manner
Data Source
AI summary
A method for controlling at least one reconfigurable intelligent surface, called an “intermediate surface”, positioned between an access point and at least one other reconfigurable intelligent surface, called a “main surface”, configured to serve a given geographical area. The method includes: determining respective phase shifts of reflective elements of the intermediate surface such that: signals emitted by the access point to exchange data with at least one user terminal situated in the geographical area are reflected by the intermediate surface toward the at least one main surface, and the power of the signals reflected is greater than a given threshold or maximized; and controlling the reflective elements of the intermediate surface by using the determined phase shifts.