Distributed RIS Positioning for Higher-Rank Wireless Channels
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Solution Overview
Problem
The use of a single Reconfigurable Intelligent Surface (RIS) to extend wireless communication coverage can limit the number of user terminals that can be spatially multiplexed due to a low rank propagation channel, particularly at high frequencies, and direct line of sight conditions, restricting spatial multiplexing gains.
Innovation Solution
Positioning a plurality of RISs, including a main RIS and intermediate RISs, to create multiple indirect paths between a base station and user terminals, optimizing their placement to maximize path gain by determining positioning data that consider distances and angles of signals, using algorithms like constrained gradient descent.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single RIS is deployed to extend wireless coverage, then coverage extension is achieved, but the rank of propagation channel remains low limiting spatial multiplexing gains
Solution Approach 1:
The single RIS is segmented into multiple distributed RIS units (first RIS, second RIS, third RIS, fourth RIS) positioned at different locations. Each RIS unit independently reflects signals to user terminals, creating multiple independent propagation paths. This segmentation increases the rank of the propagation channel matrix, enabling higher spatial multiplexing gains while maintaining extended coverage area.
2Use of energy by moving object
If RIS reflects signals passively without amplification, then energy consumption is minimized, but signal power level at receiver is reduced
Solution Approach 1:
Multiple RIS units are merged to work cooperatively, each reflecting signals to the same user terminals. The reflected signals from multiple RIS units combine constructively at the receiver, increasing the overall signal power level. This merging approach maintains passive operation (low energy consumption) while achieving higher received power through signal combining.
Solution Approach 2:
The system transitions from a single RIS providing one reflection path to multiple RIS units providing multiple reflection paths through different spatial dimensions. This dimensional expansion creates diverse propagation paths that arrive at the receiver with different phases and amplitudes, enabling constructive combining to boost signal power while keeping individual RIS units passive and energy-efficient.
3Reliability
If direct line of sight paths are obstructed by buildings, then signal attenuation increases, but deploying RIS requires additional infrastructure
Solution Approach 1:
Multiple RIS units are deployed as intermediary elements between the base station and user terminals in areas with obstructed direct paths. Each RIS unit acts as a mediator that receives signals from the base station, reflects them towards user terminals, and enables reliable communication in non-line-of-sight conditions. The distributed deployment of multiple intermediaries provides redundancy and improves reliability without requiring complex single-point infrastructure.
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, allowing more user terminals to be served with sufficient quality, especially at high frequencies, and optimizing spatial multiplexing gains.
Implementation Method 1
a RIS comprises a large number of low-cost passive reflecting elements, hereinafter named 'reflective elements'
Implementation Method 2
By modifying the reflective properties of each reflective element of the RIS, typically by individually modifying the phase shift introduced by each of these reflective elements
Implementation Method 3
the signals reflected by the RIS may be combined constructively to improve the level of power of the signal received by a receiver
Data Source
AI summary
A method for positioning a set of reconfigurable intelligent surfaces associated with an access point of a telecommunications network. The set includes at least one reconfigurable intelligent surface, called an “intermediate surface” and at least one other reconfigurable intelligent surface, called a “main surface”. The method particularly includes determining positioning data of the intermediate and main surfaces such that signals emitted by the access point are reflected by the intermediate surface toward the main surface to exchange data with at least one user terminal situated in the geographical area served by the main surface, but also such that a path gain of a path taken by said signals between the access point and this user terminal is greater than a predetermined threshold or maximized.