RIS Subarray Beamforming for Near-Field Gain Limits
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Solution Overview
Problem
Large-sized Reconfigurable Intelligent Surfaces (RIS) panels in millimeter wave communication systems face issues with large near-field ranges and low gain due to traditional beamforming methods, which require complete channel state information and complex phase control.
Innovation Solution
The RIS is divided into subarrays based on the distance between the target device and the panel, with each subarray serving one target device, and a dual-layer codebook is used to converge and disperse beams for improved gain and coverage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a large-sized RIS panel is used to provide sufficient gain to compensate for path loss, then the communication coverage and capacity are improved, but the near field range becomes excessively large causing low gain in the near field
Solution Approach 1:
The patent divides the large-sized RIS panel into multiple subarrays, each with a smaller aperture. This segmentation reduces the near field range of each subarray while maintaining the overall coverage area. The total gain is achieved by coordinating multiple subarrays rather than relying on a single large panel, thus resolving the contradiction between providing sufficient gain and limiting near field range.
2Device complexity
If traditional DFT-based beamforming is used for large-sized RIS, then the system complexity is low, but the gain in the near field is low due to far-field design assumptions
Solution Approach 1:
By segmenting the large RIS into smaller subarrays, each subarray can use simplified DFT-based beamforming appropriate for its smaller aperture. The overall system achieves near field performance through the coordinated operation of multiple subarrays, maintaining low complexity while improving near field gain.
Solution Approach 2:
The patent changes the beamforming parameters (phase shifts, amplitude weights) for each subarray based on the specific near field geometry and target positions. This allows each subarray to optimize its beamforming for near field conditions rather than using far-field assumptions, improving gain while keeping the beamforming method itself simple.
3Power
If coherent beamforming technology is used to improve near field gain, then the signal gain is improved, but complete channel state information is required which is extremely difficult to obtain
Solution Approach 1:
The patent applies segmentation to reduce the information requirement. Each subarray requires channel state information only for its local region and target devices, rather than requiring complete CSI for the entire large panel. This localizes the information requirement, making it practically obtainable while still achieving coherent beamforming benefits within each subarray.
Data Source
AI summary
The present disclosure provides a reconfigurable intelligent surface, including: a receiving unit which receives subarray division setting information sent from a base station; a reconfigurable panel; and a processing unit, which divides, based on the subarray division setting information, the reconfigurable panel into M subarrays, where M is a positive integer greater than 1, wherein, the subarray division setting information is determined based on a distance between a target device and the reconfigurable panel, N subarrays of the M subarrays serve one target device, and N is a positive integer greater than 1 and less than or equal to M.