RIS Channel Parameter Estimation Using Spherical Wave Assumption
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Solution Overview
Problem
Existing channel estimation algorithms for Reconfigurable Intelligent Surfaces (RIS) in near-field regions assume plane wave propagation, leading to inaccurate characterization of channel parameters, particularly in the RIS near-field region where spherical wavefront propagation characteristics are significant.
Innovation Solution
A method for estimating channel parameters of a reconfigurable intelligent surface channel based on a spherical wave assumption, involving the construction of a signal transmission model, obtaining channel measurement data, and using a space-alternating generalized expectation maximization algorithm combined with maximum likelihood principles to estimate delay, angle, Doppler shift, and polarization matrix parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the RIS size is increased to achieve more accurate directional control and stronger reflected beam gain, then the beam control accuracy and reflected beam gain are improved, but the Rayleigh distance increases causing the transmitter and receiver to be located in the RIS near-field region where plane wave approximation becomes inaccurate
Solution Approach 1:
The patent changes the fundamental wave propagation model parameter from plane wave assumption to spherical wave assumption. This parameter change allows accurate characterization of the near-field region where the transmitter and receiver are located, resolving the contradiction between maintaining large RIS size for beam control and ensuring accurate channel parameter estimation in the near-field region.
2Device complexity
If the plane wave propagation assumption is used for channel estimation, then the estimation algorithm is simple, but the distance parameters and coupling polarization matrix parameters of the RIS in its near-field region cannot be accurately estimated
Solution Approach 1:
The patent applies spherical wavefront propagation characteristics instead of plane wave assumption, introducing curvature to the wave propagation model. This allows accurate estimation of distance parameters and coupling polarization matrix parameters in the RIS near-field region, resolving the contradiction between algorithm simplicity and estimation accuracy.
3Power
If the RIS is designed to carry more electromagnetic reflection unit cells to achieve stronger reflected beam gain, then the beam gain is improved, but the RIS size increases leading to larger Rayleigh distance and near-field effects
Solution Approach 1:
The patent changes the wave propagation model from plane wave to spherical wave, which accounts for the near-field effects that arise when RIS size increases. This parameter change enables the system to maintain large RIS size for high beam gain while accurately characterizing the channel in the near-field region through spherical wave assumption.
Data Source
AI summary
A method for estimating channel parameters of a reconfigurable intelligent surface based on a spherical wave assumption includes the following steps. In Step 1, a signal transmission model of a RIS-assisted near-field communication is constructed based on the spherical wave assumption; in Step 2, channel measurement data in different RIS transmission modes are obtained; in Step 3, a delay, an angle of arrival, an angle of departure, a Doppler shift and a polarization matrix of multipath in channels are estimated based on a space-alternating generalized expectation maximization algorithm, and angle parameters, distance parameters and coupling polarization matrices of the multipath at a RIS end are estimated based on a maximum likelihood principle; and in Step 4, the estimated parameters are updated and iterated subsequently. The method can estimate all important channel parameters in the RIS-assisted near-field communication scenario more accurately.