OFDM Signal Processor ICI Mitigation via Dynamic Weighted Combining
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Solution Overview
Problem
OFDM systems are sensitive to mobility-induced Doppler spreading, leading to inter-carrier interference (ICI) that increases bit error rates in mobile environments, as conventional antenna selection mechanisms fail to effectively mitigate ICI in time-varying channels.
Innovation Solution
A processor is designed to combine multiple instances of the same symbol received by different antennas or subcarriers using weighted combinations based on estimated channel gains and ICI contributions, primarily focusing on nearest neighbor subcarriers to reduce ICI, with metrics like SINR and MMSE used to optimize the combination process, thereby reducing ICI contributions and improving bit error rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional SNR-based antenna selection is used, then spatial diversity is provided in time-invariant channels, but ICI mitigation capability is limited in time-varying channels
Solution Approach 1:
The invention transitions from static SNR-based antenna selection to dynamic ICI-aware antenna selection and signal combining. The system adapts to time-varying channels by estimating ICI contributions and adjusting combining weights based on current channel conditions, making the selection mechanism responsive to mobility-induced Doppler spreading.
Solution Approach 2:
The invention changes the selection criterion from SNR to ICI contribution metrics. By estimating the ICI contribution of each antenna signal and using these estimates as combining weights, the system optimizes performance in time-varying channels where ICI is the dominant impairment rather than noise.
2Reliability
If ICI compensation is implemented, then bit error rate is reduced in mobile environments, but computational complexity increases
Solution Approach 1:
The invention applies partial ICI compensation by using only the estimated ICI contributions as combining weights rather than implementing full ICI cancellation. This partial action approach achieves significant BER improvement while avoiding the excessive computational complexity of complete ICI removal algorithms.
Solution Approach 2:
The invention uses pilot symbols to estimate channel responses and ICI contributions, creating simplified copies of the actual channel conditions. These estimated parameters are then used for antenna selection and signal combining, reducing the need for complex real-time ICI calculation.
3Reliability
If multiple antenna signals are combined, then signal diversity is improved, but ICI contribution from multiple sources increases
Solution Approach 1:
The invention applies different combining strategies to different antenna signals based on their local ICI characteristics. Each antenna signal is evaluated individually for its ICI contribution, and combining weights are assigned locally to minimize the total ICI in the combined output while maintaining signal diversity.
Solution Approach 2:
The invention converts the harmful ICI contributions into useful selection criteria. By estimating the ICI contribution of each antenna signal and using these estimates as combining weights, the system transforms the previously harmful parameter into a beneficial guide for optimal signal combination.
Data Source
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AI summary
A processor (110) is disclosed for processing a plurality of Fourier-transformed instances of a symbol, each instance being comprised in one of a plurality of frequency-divided multiplexed subcarriers, said processor being arranged to estimate, for each instance, the channel gain and the inter-carrier interference contribution to said symbol from neighboring subcarriers due to a time-varying channel response of the received signal,; and combine the instances into a single representation of said symbol based on the estimated channel gain and the inter-carrier interference contributions. A receiver comprising such a processor and a method for processing such signals are also disclosed.