LTE Rank Information Report Control for CoMP High Rank Transmission
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Solution Overview
Problem
In modern mobile communications systems like LTE, conventional Rank Information (RI) reports are not applicable for high rank transmission in CoMP (Coordinated Multi-Point) transmission, which limits network configuration and performance, especially in dynamic point selection or dynamic point blanking scenarios.
Innovation Solution
A method is introduced to support high rank transmission by determining a CSI report set with multiple CSI feedback modes, sending RRC signaling indicating precoding codebook subsets and rank restrictions using bitmap parameters, allowing UE to determine rank characteristics based on received signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional RI report is used in CoMP transmission, then the system maintains compatibility with existing LTE protocols, but high rank transmission cannot be supported which limits coverage area and cell edge throughput
Solution Approach 1:
The invention segments the RI reporting mechanism into multiple CSI feedback modes (CSI processes), where each mode can be independently configured with specific precoding codebook subsets and rank restrictions. This allows different RI reporting behaviors for different CSI processes, enabling high rank transmission support in certain modes while maintaining conventional RI reporting in others, thus resolving the contradiction between supporting high rank transmission and maintaining conventional RI report compatibility.
Solution Approach 2:
The invention introduces dynamic configurability of RI report modes through RRC signaling, which can indicate different CSI feedback modes and their associated precoding codebook subset restrictions. This dynamic adaptation allows the system to switch between conventional RI reporting and high rank transmission support based on channel conditions and network requirements, resolving the contradiction between fixed conventional RI report limitations and the need for flexible high rank transmission support.
2Adaptability or versatility
If multiple CSI feedback modes are configured for CoMP, then high rank transmission and rank selection are enabled, but signaling complexity increases due to additional RRC signaling and bitmap parameters
Solution Approach 1:
The invention creates a universal CSI feedback mode framework where a single RRC signaling mechanism can configure multiple CSI processes with different feedback modes. The same signaling structure (bitmap parameters for precoding codebook subset restriction) serves multiple functions: it configures conventional RI reporting, supports high rank transmission, and enables rank selection across different CSI processes. This multi-functionality reduces the need for separate signaling mechanisms, thereby managing complexity while providing versatile rank selection capability.
3Adaptability or versatility
If precoding codebook subset restriction is applied per CSI feedback mode, then network configuration flexibility for high rank transmission is improved, but processing complexity at base station and UE increases
Solution Approach 1:
The invention applies precoding codebook subset restriction locally to each CSI feedback mode independently through bitmap parameters. Each CSI process can have its own specific codebook subset configuration tailored to its requirements (e.g., certain modes restricted to rank 1, others allowing high rank). This localized configuration approach provides fine-grained network configuration flexibility for high rank transmission while avoiding the need to process and configure a single complex global configuration, thereby managing processing complexity at both base station and UE.
Data Source
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AI summary
The present invention relates to a method and an apparatus for controlling a rank information (RI) report. According to an embodiment of the present invention, a method for controlling an RI report of a User Equipment (UE) in a base station of a Long Term Evolution (LTE) mobile communications network is provided. The method includes the following steps: determining a Channel State Information (CSI) report set for a UE, where the CSI report set includes multiple CSI feedback modes (CSI processes); sending to the UE Radio Resource Control (RRC) signaling indicating the CSI report set; and sending to the UE signaling indicating a precoding codebook subset and/or rank restriction of each CSI feedback mode in the CSI report set. According to the above embodiment, rank selection and high rank transmission are supported for coordinated multi-point (CoMP) transmission in the LTE mobile communications network.