Codebook Subset Restriction Signaling for Low-Overhead Precoding
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Solution Overview
Problem
The conventional method of signaling codebook subset restrictions in wireless communication systems is inefficient, particularly for large antenna arrays and two-dimensional antenna systems, due to high overhead and limited flexibility in configuring different codebook subset restrictions, especially when frequent updates or multiple users are involved.
Innovation Solution
A method that generates rank-agnostic codebook subset restriction signaling by jointly restricting precoders based on common components, such as beam precoders, using techniques like Kronecker products and bitmaps, to reduce the number of bits required for signaling, thereby lowering overhead while maintaining flexibility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a bitmap of length N is used to signal codebook subset restriction for each precoder in the codebook, then full flexibility to restrict every possible subset is achieved, but signaling overhead becomes very large for large antenna arrays
Solution Approach 1:
The codebook is divided into multiple groups, and restriction signaling is performed at the group level rather than individual precoder level. This segmentation allows the system to manage large codebooks by handling smaller subsets independently, reducing the total signaling bits required while maintaining the ability to restrict specific precoders through group selection.
Solution Approach 2:
Instead of providing full individual control over every precoder (excessive action), the system applies restriction at the group level (partial action). This partial control approach is sufficient for most practical scenarios where entire groups of precoders can be restricted together, significantly reducing signaling overhead while maintaining adequate flexibility.
2Productivity
If codebook subset restriction is frequently updated to adapt to changing channel conditions, then system performance is improved, but signaling overhead and processing complexity increase
Solution Approach 1:
By segmenting the codebook into groups with stable geometric relationships, the system enables frequent updates of restriction patterns without requiring complete re-signaling of individual precoder restrictions. The grouped structure allows efficient representation of dynamic restriction patterns, supporting frequent adaptations to changing channel conditions.
Solution Approach 2:
The codebook groups are pre-configured with specific geometric relationships (e.g., rectangular regions in angular space) before operation begins. This preliminary organization allows the system to quickly apply restrictions by simply indicating which pre-defined groups to restrict, enabling fast adaptation to changing conditions without complex real-time calculations.
3Measurement precision
If a large codebook is used to provide fine angular resolution for two-dimensional antenna arrays, then coverage and precision are improved, but the number of bits required for restriction signaling increases quadratically
Solution Approach 1:
The large codebook for two-dimensional antenna arrays is segmented into multiple smaller groups, each representing a specific angular region or beam sector. This segmentation allows the system to maintain fine angular resolution across the entire coverage area while restricting only the necessary groups rather than individually managing every precoder, reducing signaling bits from quadratic to linear scaling.
Solution Approach 2:
The codebook groups are organized in a two-dimensional angular space structure, where groups can be identified and restricted based on their spatial coordinates. This geometric organization allows efficient representation of restriction patterns by referencing group positions in the angular dimension, reducing the signaling overhead compared to flat enumeration of individual precoders.
Data Source
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AI summary
A network node (10) signals to a wireless communication device (14) which precoders in a codebook are restricted from being used. The network node (10) in this regard generates codebook subset restriction signaling that, for each of one or more groups of precoders, jointly restricts the precoders in the group by restricting a certain component (e.g., a certain beam precoder) that the precoders in the group have in common. This signaling may be for instance rank-agnostic signaling that jointly restricts the precoders in a group without regard to the precoders' transmission rank. Regardless, the network node (10) sends the generated signaling to the wireless communication device (14).