MIMO Precoding Matrix Determination via Channel Reciprocity

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Solution Overview

Problem

In wireless communication systems, the feedback overhead for MIMO transmissions is high due to the need to send both precoding matrices and CQI/MCS information, which increases the burden on the communication channel.

Innovation Solution

Both the transmitter and receiver determine the precoding matrix using channel reciprocity in TDD systems, reducing the need to send the precoding matrix and thereby reducing feedback overhead by only sending CQI/MCS information.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the receiver sends feedback information including both precoding matrix and CQI/MCS information, then the transmitter can achieve good MIMO transmission performance, but the feedback overhead increases

Engineering Contradiction:

ImproveMIMO transmission performanceVSAvoidfeedback overhead

Core Design Contradiction:

ReliabilityVSLoss of information

Solution Approach 1:

The patent extracts the precoding matrix determination function from the receiver and assigns it to the transmitter. The transmitter now independently determines the precoding matrix using channel reciprocity, while the receiver only sends feedback for CQI/MCS information, thereby removing the large feedback overhead associated with transmitting the precoding matrix.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent applies preliminary action by having the transmitter pre-determine the precoding matrix before the feedback exchange. The transmitter uses downlink reference signals to estimate the channel response and determine the precoding matrix in advance, so that during the feedback phase, only lighter CQI/MCS information needs to be transmitted.

Inventive Principle:

Principle #10Preliminary action

2Loss of information

If both transmitter and receiver determine the precoding matrix independently, then feedback overhead is reduced, but channel reciprocity must be exploited which requires TDD system configuration

Engineering Contradiction:

Improvefeedback overheadVSAvoidsystem configuration requirement

Core Design Contradiction:

Loss of informationVSDevice complexity

Solution Approach 1:

The patent makes the TDD system configuration serve multiple functions: it enables channel reciprocity for precoding matrix determination, allows time-division between downlink and uplink transmissions, and facilitates the feedback mechanism. This multi-functionality justifies the system configuration requirement by delivering multiple benefits from a single design choice.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8798183B2Feedback and rate adaptation for MIMO transmission in a time division duplexed (TDD) communication system

Publication Date: 2014.08.05 QUALCOMM INC

AI summary

Techniques for sending a MIMO transmission in a wireless communication system are described. In one design, a transmitter sends a first reference signal to a receiver. The receiver selects a precoding matrix based on the first reference signal and in accordance with a selection criterion. The receiver estimates noise and interference at the receiver and determines channel quality indicator (CQI) or modulation and coding scheme (MCS) information based on the precoding matrix and the estimated noise and interference. The receiver sends the CQI or MCS information and a second reference signal to the transmitter. The transmitter selects the precoding matrix based on the second reference signal and in accordance with the same selection criterion used by the receiver. The transmitter then sends a MIMO transmission to the receiver based on the CQI or MCS information obtained from the receiver and the precoding matrix selected by the transmitter.