OFDM Reverse Link Interference Estimation via Linear Filtering
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Solution Overview
Problem
In OFDM wireless communication systems, accurately estimating carrier-to-interference ratio (CIR) for reverse link transmissions is challenging due to unpredictable interference from mobile stations, which affects adaptive modulation coding and scheduling.
Innovation Solution
A method and apparatus for determining an interference estimate of an OFDM signal received from a mobile station, using this estimate to calculate the CIR for sub-carriers and sub-channels, by averaging interference levels over time and using linear filtering to generate stable interference predictions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interference estimation is performed for reverse link OFDM signals, then CIR estimation accuracy is improved, but system complexity increases
Solution Approach 1:
The patent performs interference estimation in advance before CIR calculation using pre-established filtering mechanisms. The linear filter is configured beforehand to average interference levels over specific time periods, allowing the system to predict interference patterns proactively rather than reactively, thus improving measurement precision while managing complexity through pre-computation
Solution Approach 2:
The patent introduces an interference estimator as an intermediary component between signal reception and CIR calculation. This intermediary uses linear filtering to process raw interference signals and generate smoothed interference level estimates, which then feed into the CIR estimation process, effectively decoupling the complexity of interference analysis from the core CIR calculation
2Stability of the object's composition
If interference levels are averaged over time using linear filtering, then CIR estimation stability is improved, but response time to interference changes increases
Solution Approach 1:
The patent implements dynamic averaging where the linear filter adapts its time constant based on observed interference characteristics. When interference varies rapidly, the filter uses shorter averaging periods to maintain responsiveness; when interference is stable, longer averaging periods enhance smoothing. This dynamic adjustment allows the system to balance stability and response time according to actual channel conditions
Solution Approach 2:
The patent changes the filtering parameters (time constant, averaging window size) based on the statistical properties of the interference signal. By monitoring interference variance and adjusting filter coefficients accordingly, the system optimizes the trade-off between stability and response time, using longer filters for stable interference conditions and shorter filters for rapidly changing interference environments
Data Source
AI summary
A new method of performing interference estimation to allow the data packets to be efficiently delivered in an OFDM system. The interference estimation is performed on average over each frame for each mobile station individually in both frequency and time domains. Based on the estimated interference, the CIR can be determined by the BTS based on channel response estimates made by the BTS, or by the MS based on channel response estimates made for the uplink assuming a symmetrical channel. Numerical results show that the CIR estimation error could be very small if a sub-channel is considered as the minimum transmission unit. In terms of the aggregate throughput, the interference estimation method can provide a significant gain.