OFDM Receiver Channel Estimation via Impulse Response Truncation
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Solution Overview
Problem
Current OFDM receivers face challenges in accurately estimating the wireless channel before demodulation, leading to suboptimal performance and higher receiver sensitivity due to noise in received samples and the presence of null sub-carriers.
Innovation Solution
The proposed solution involves an OFDM receiver circuit with an FFT circuit and a smoothing circuit that performs iterative or least-square time-domain truncation algorithms to estimate channel coefficients, mitigate noise, and handle null sub-carriers, enabling improved channel estimation by truncating impulse responses and applying inverse FFT and matrix operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional channel estimation is used in OFDM receivers, then the system can operate with standard receiver sensitivity requirements, but the channel estimation accuracy is degraded due to noise in received samples and presence of null sub-carriers
Solution Approach 1:
The channel estimation process is segmented into multiple stages: initial channel frequency response estimation from received OFDM symbols, transformation to time domain via IFFT, truncation to remove multipath components beyond delay spread, and transformation back to frequency domain via FFT. This segmentation allows targeted processing of different signal components to improve estimation accuracy while managing complexity.
Solution Approach 2:
The patent applies preliminary action by performing IFFT transformation and impulse response truncation before the final channel estimation is completed. By pre-processing the channel frequency response to remove noise and null sub-carrier effects in the time domain, the subsequent frequency domain estimation benefits from cleaner data, improving overall accuracy.
2Reliability
If noise mitigation techniques are applied to improve receiver sensitivity, then the minimum input power requirement increases, but the processing complexity and computational load increase
Solution Approach 1:
The patent extracts and removes harmful components from the channel estimation process by identifying and eliminating the effects of null sub-carriers and truncating impulse response portions that correspond to delays beyond the channel delay spread. This extraction of unwanted elements improves reliability by reducing noise impact without requiring excessive computational energy.
Solution Approach 2:
The patent changes parameters by transforming the channel estimation from direct frequency domain processing to time domain processing via IFFT, applying truncation based on channel delay spread characteristics, then transforming back. This parameter transformation allows the system to adapt to different channel conditions while managing computational energy consumption efficiently.
3Measurement precision
If iterative extrapolation methods are used to improve channel equalization performance, then the channel estimation accuracy improves, but the processing time and computational complexity increase
Solution Approach 1:
The patent applies preliminary action by performing IFFT transformation and impulse response truncation before the final channel estimation is completed. By pre-processing the channel frequency response to remove noise and null sub-carrier effects in the time domain, the subsequent frequency domain estimation benefits from cleaner data, improving overall accuracy.
Solution Approach 2:
The patent transitions from purely frequency domain processing to time domain processing by applying IFFT, performs truncation in the time domain to remove multipath components, then transforms back to frequency domain using FFT. This dimensionality change enables more effective noise mitigation and handles null sub-carriers more efficiently, improving equalization performance while controlling processing time.
Data Source
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AI summary
Embodiments of the present disclosure include an OFDM receiver circuit, which includes an FFT circuit configured to calculate an FFT of a plurality of sample values received by the receiver circuit, and a smoothing circuit configured to identify equalizer coefficients for the sample values by truncating portions of an impulse response of the FFT.