Adaptive Channel Equalizer for OFDM Multi-Path Compensation
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Solution Overview
Problem
OFDM receivers face challenges in accurately estimating channels due to multi-path channel effects, which lead to distortion and noise in the demodulation process, making it difficult to compensate for the variations in transmission path environments.
Innovation Solution
A channel equalizer method that uses a combination of low pass and band pass filters to generate and estimate channel impulse responses in the frequency domain, improving channel estimation accuracy by filtering and compensating for subcarriers, with the filtering bandwidth of the band pass filter being variable and adaptive based on the communication environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a typical equalizer with adaptive function is used to compensate for multi-path distortion, then the receiver can handle variations in transmission path environments, but the channel estimation accuracy deteriorates due to delay times of signals received through multi-path channels
Solution Approach 1:
The patent segments the channel impulse response estimation into two distinct parts: first estimating the delay time using correlation processing to identify peak positions, then using this delay information to guide frequency domain interpolation. This segmentation allows the system to handle multi-path effects systematically by separating the delay estimation function from the channel response interpolation function, thereby maintaining accuracy despite multi-path delays
Solution Approach 2:
The patent performs preliminary estimation of delay time before conducting channel impulse response estimation. By first identifying the delay characteristics through correlation processing and peak detection, the system prepares the necessary timing information in advance. This preliminary action enables subsequent frequency domain interpolation to be performed with accurate delay compensation, resolving the accuracy issue caused by multi-path delay times
2Reliability
If frequency domain interpolation is used to estimate channel impulse responses for all subcarriers, then the equalizer can compensate for channel distortion, but noise from multi-path channels reduces the accuracy of the estimation
Solution Approach 1:
The patent introduces delay time estimation as an intermediary step between receiving the OFDM signal and performing frequency domain interpolation. The correlation processing and peak detection mechanisms serve as intermediaries that extract timing information from the noisy multi-path signal. This intermediary delay information then guides the interpolation process, enabling accurate channel estimation despite the presence of multi-path noise
Solution Approach 2:
The patent employs feedback through correlation processing where the received signal is correlated with a reference signal to identify peak positions corresponding to delay times. This feedback mechanism continuously monitors the signal characteristics and adjusts the delay estimation accordingly, thereby maintaining accurate channel impulse response estimation even in noisy multi-path environments
Data Source
AI summary
A channel equalizer obtains channel impulse responses (CIRs) for all subcarriers by way of filtering channel impulse responses of specific subcarriers using at least two filters. One of the two filters may be a low pass filter. At least one other of the at least two filters is implemented as a band pass filter having a variable filtering bandwidth, being available to establish various filtering bandwidths in response to various multi-path channel environments. By improving the performance of channel estimation, equalization may be improved.