CSI Feedback Overhead Reduction via Uplink Reciprocity
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Solution Overview
Problem
In communications systems, especially those using MIMO technology, the mismatch between the number of transmit and receive antennas in terminal devices leads to incomplete downlink channel state information, resulting in reduced data transmission rates and system performance due to inaccurate CSI feedback.
Innovation Solution
The terminal device sends a sounding reference signal through a subset of transmit antennas to allow the network device to determine a partial uplink channel matrix, which is then used to infer a complete downlink channel matrix, reducing the need for precise PMI feedback and minimizing feedback overheads by only reporting CQI and RI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the terminal device feeds back complete downlink CSI (PMI, CQI, RI) to improve CSI accuracy, then the CSI feedback precision increases, but the uplink time-frequency resources occupied increase, resulting in increased feedback overheads
Solution Approach 1:
The patent extracts and removes the PMI from the CSI feedback content, keeping only CQI and RI. This is achieved by having the network device obtain downlink channel matrix through uplink channel reciprocity calibration, making PMI feedback unnecessary. The terminal device only feeds back CQI and/or RI, significantly reducing feedback overhead while maintaining sufficient CSI accuracy for precoding and modulation/coding scheme determination.
2Device complexity
If the terminal device has fewer transmit antennas than receive antennas, then the device complexity is reduced, but the network device cannot obtain complete downlink channel matrix, resulting in incomplete CSI
Solution Approach 1:
The network device performs self-service by obtaining the downlink channel matrix through uplink channel reciprocity calibration. Instead of relying on the terminal device to feed back complete channel state information, the network device autonomously derives the downlink channel matrix from uplink channel measurements, eliminating the need for the terminal to have matching transmit antenna configurations.
3Measurement precision
If the terminal device sends SRS through all receive antennas to obtain complete downlink channel matrix, then the CSI accuracy improves, but the device complexity and cost increase
Solution Approach 1:
The patent applies universality by making the receive antennas serve dual purposes: both receiving downlink data and transmitting uplink SRS for channel reciprocity calibration. This multi-functionality allows the network device to obtain complete downlink channel matrix information without requiring separate transmit antenna configurations, reducing device complexity while maintaining measurement accuracy.
Data Source
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AI summary
Embodiments of this application provide a channel state information transmission method, a terminal device, and a network device. The method includes: sending, by a terminal device, a first reference signal through a first antenna port set, where the first antenna port set includes n antenna ports; receiving, by the terminal device, a second reference signal through a second antenna port set, where the second antenna port set includes N antenna ports, and the first antenna port set is a proper subset of the second antenna port set; and sending, by the terminal device, channel state information, where content of the channel state information is associated with a rank indicator RI, and the channel state information and the RI are determined based on the second reference signal. In the embodiments of this application, the terminal device determines the CSI content based on a value of the RI, so that feedback overheads for the channel state information can compromise with feedback precision of the channel state information, and this is more flexible. Therefore, the method improves accuracy of the channel state information , reduces the feedback overheads for the channel state information, and improves system performance.