Prediction Filter Mitigates Lowpass Group Delay
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Solution Overview
Problem
Lowpass filters in wireless communication systems introduce group delay, leading to systematic channel estimation errors that affect the accuracy of channel impulse response estimation.
Innovation Solution
A device and method utilizing a prediction filter with adjustment circuitry to compensate for the group delay of lowpass filters, which includes downsampling, delaying, and interpolating the lowpass filtered channel coefficients to generate a prediction value with a reduced group delay, thereby mitigating estimation errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If lowpass filtering is applied to suppress high frequency estimation error components, then measurement precision is improved, but group delay is introduced causing systematic channel estimation errors
Solution Approach 1:
The patent applies preliminary action by predicting future channel coefficients based on past and present lowpass filtered coefficients. The prediction mechanism compensates for the group delay by estimating what the channel coefficient should be at the current time, effectively counteracting the time loss introduced by lowpass filtering before it affects channel estimation accuracy
2Reliability
If pilot symbol rate is increased to track channel variations at high speeds, then reliability is improved, but device complexity increases
Solution Approach 1:
The prediction mechanism performs preliminary action by computing expected channel coefficients in advance using a linear predictor. This allows the system to maintain reliable channel tracking at high speeds without requiring proportionally higher pilot symbol rates, as the prediction fills in the gaps between pilot symbols, reducing the overall processing complexity
Solution Approach 2:
The patent uses copying by creating predicted copies of channel coefficients based on the lowpass filtered values. Instead of requiring every pilot symbol to capture rapid channel variations, the system creates predicted copies that follow the channel evolution, maintaining tracking reliability while reducing the burden on pilot symbol density and processing complexity
Data Source
AI summary
A device for mitigating a first group delay of a lowpass filter configured to lowpass filter a first channel coefficient of a set of channel coefficients with respect to time, includes a prediction filter configured to filter a data sequence derived from a lowpass filtered first channel coefficient to generate a prediction value of the lowpass filtered first channel coefficient; and an adjustment circuitry configured to adjust the prediction filter to generate the prediction value having a second group delay that is less than the first group delay.