MMSE Demodulation Using Estimated Interferer Precoders
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Solution Overview
Problem
In multi-user MIMO communication systems, the suboptimal Maximum Ratio Combining (MRC) demodulation method is used due to unknown precoding weights for interfering data streams, leading to performance loss, especially at high signal-to-noise ratios, when interference is correlated.
Innovation Solution
The receiving terminal estimates the precoding weights for interfering data streams and uses both the known precoder for the desired data stream and the estimated precoders for the interfering data streams to perform Minimum Mean Squared Error (MMSE) demodulation, improving receiver performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If Maximum Ratio Combining (MRC) demodulation is used, then the demodulation process is simple, but the receiver performance deteriorates when interference is correlated
Solution Approach 1:
The patent changes the demodulation parameters from simple MRC combining to MMSE combining, which uses minimum mean squared error optimization to determine combining weights. This parameter change allows the receiver to account for correlated interference from other users while maintaining computational feasibility through iterative optimization of the combining weights based on channel state information.
2Reliability
If MMSE demodulation with estimated precoders is used, then the signal-to-noise ratio is improved, but the computational complexity increases
Solution Approach 1:
The patent applies preliminary action by having the transmitter pre-calculate and signal the precoding matrices to be used for interfering data streams before the actual data transmission. This allows the receiver to have advance knowledge of the interference structure and pre-compute the MMSE combining weights, reducing the real-time computational burden during actual demodulation operations.
Solution Approach 2:
The patent uses copying by having the transmitter signal the precoding matrices (or their indices) to the receiver through downlink control information. This copied information about the interfering streams' precoders enables the receiver to replicate the transmitter's precoding knowledge and perform accurate MMSE combining without requiring complex real-time estimation of interference characteristics.
3Ease of manufacture
If only the desired data stream precoder is known, then the system is easy to implement, but the demodulation accuracy deteriorates due to correlated interference
Solution Approach 1:
The patent introduces an intermediary mechanism where the transmitter acts as a mediator by signaling the precoding matrices for interfering data streams to the receiver through downlink control information. This intermediary information transfer enables the receiver to acquire knowledge about interference precoders without requiring direct estimation, thus improving demodulation accuracy while maintaining implementation simplicity through standardized control channel communication.
Data Source
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AI summary
A method and apparatus is provided for demodulating a desired data stream in a MU-MIMO communication system where only the precoder for the desired data stream is known a priori. The receiving terminal according to various embodiments of the present invention estimates the precoder for one or more interfering data streams. The receiving terminal can then use the known precoder for the desired data stream and the estimated precoders for the interfering data streams to perform MMSE demodulation.