Multi-branch OFDM Receiver Interference Rejection Combining
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Solution Overview
Problem
Existing methods for reducing inter-cell interference in mobile communication systems, such as LTE, face challenges in generating accurate channel and noise estimates, especially when the number of pilot symbols is insufficient, leading to suboptimal performance of interference rejection combining techniques like IRC.
Innovation Solution
A multi-branch OFDM receiver generates first and second channel estimates for serving and non-serving base stations, computes a noise covariance matrix based on these estimates and time offsets, and uses this matrix to combine diversity signals effectively, improving interference rejection combining by accounting for noise across multiple subcarriers and base stations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the number of pilot symbols is increased to improve channel and noise estimation accuracy, then the quality of channel and noise estimates improves, but the signaling overhead increases
Solution Approach 1:
The patent uses non-serving base station channel estimates as an intermediary to infer the noise covariance matrix. Instead of directly estimating noise from pilot symbols, the system leverages channel estimates from neighboring cells to derive noise characteristics, thereby obtaining accurate noise information without requiring additional pilot symbols from the serving cell.
Solution Approach 2:
The patent copies channel estimate information from non-serving base stations to serve the noise estimation purpose. By utilizing channel estimates from neighboring cells (which are already available at the mobile terminal), the system creates a copy of the noise covariance matrix without needing separate noise pilot symbols, thus avoiding increased signaling overhead.
2Loss of information
If the number of pilot symbols is decreased to reduce signaling overhead, then the signaling overhead is reduced, but the quality of channel and noise estimates deteriorates
Solution Approach 1:
The patent introduces non-serving base station channel estimates as an intermediary resource. These channel estimates serve as a mediator that enables accurate noise covariance matrix computation without requiring additional pilot symbols from the serving cell, thus maintaining estimation accuracy while reducing signaling overhead.
Solution Approach 2:
The patent changes the approach from estimating noise directly using serving cell pilots to inferring noise parameters from non-serving cell channel estimates. This parameter transformation allows the system to obtain accurate noise covariance information through existing channel estimate data, avoiding the need for more pilot symbols.
3Reliability
If interference rejection combining is applied to improve signal-to-noise ratio, then the signal-to-noise ratio improves, but the system becomes more complex
Solution Approach 1:
The patent performs preliminary computation of the noise covariance matrix using non-serving base station channel estimates before executing the interference rejection combining. By pre-computing the noise covariance matrix from available channel estimates, the system prepares the necessary noise information in advance, simplifying the subsequent combining operation and reducing real-time computational complexity.
Solution Approach 2:
The patent enables the mobile terminal to self-compute the noise covariance matrix using channel estimates from non-serving base stations that are already available at the terminal. This self-service approach eliminates the need for complex noise estimation procedures and reduces the overall system complexity by leveraging existing resources at the mobile terminal.
Data Source
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AI summary
A multi-branch OFDM receiver combines diversity signals received over different receiver branches using interference rejection combining. The receiver generates first channel estimates associated with a serving base station, second channel estimates associated with at least one non-serving base station, and a time offset between the serving base station and non-serving base station. The receiver computes a noise covariance matrix based on the second channel estimates and the time offset, and then combines the diversity signals received over different branches using the first channel estimates and the noise covariance matrix.