Adaptive FIR Filter for OFDM Channel Estimation Noise
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Solution Overview
Problem
Noisy channel estimates due to interpolation of pilot tones in OFDM systems lead to degraded carrier-to-noise (C/N) performance in OFDM-based communication systems, particularly in terrestrial broadcasting scenarios like DVB-T/H mobile TV broadcasting.
Innovation Solution
An adaptive frequency domain equalization method is implemented, where channel estimates are obtained every third bin in the frequency domain through time domain interpolation, and an FIR low-pass filter is applied to estimate the original channel, with the filter's bandwidth adjusted to cover the delay span of the channel impulse response, using criteria such as magnitude and power approaches to maximize noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If interpolation is used to estimate channel frequency response from pilot tones, then channel estimation is achieved, but noise is introduced and C/N performance is degraded
Solution Approach 1:
The patent segments the channel estimation process into two distinct stages: first obtaining noisy channel estimates from pilot tones using interpolation, then applying a FIR low-pass filter to smooth and denoise the estimates. This segmentation allows each stage to serve its specific purpose - the first stage captures channel information while the second stage removes noise artifacts.
Solution Approach 2:
The patent introduces an intermediary FIR low-pass filter between the pilot tone interpolation stage and the final channel equalization stage. This intermediary component processes the noisy channel estimates by applying convolution with the filter impulse response, thereby smoothing the noise while preserving the essential channel characteristics needed for equalization.
2Object-affected harmful factors
If FIR low-pass filter is applied to smooth channel estimates, then noise is reduced, but computational complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating and storing the impulse response of the FIR low-pass filter before the actual channel estimation process. This allows the filter to be efficiently applied during channel equalization without requiring complex real-time computation, as the filter coefficients are already prepared in advance.
Solution Approach 2:
The patent changes the parameter of the FIR filter by adjusting the number of taps (filter length) and the sampling rate to optimize the balance between noise reduction effectiveness and computational complexity. By carefully selecting these parameters, the system achieves adequate noise suppression with minimal additional computational burden.
Data Source
AI summary
An apparatus, system, and method of performing adaptive frequency domain equalization in an Orthogonal Frequency Domain Multiplexing (OFDM) based communication system transmitting data information, wherein the method comprises receiving OFDM symbols comprising scattered pilots; obtaining channel estimates on every third bin of the scattered pilots in a frequency domain, wherein the channel estimates are obtained by performing an interpolation in a time domain across the received OFDM symbols; estimating an original channel based on the channel estimates, wherein the original channel in the time domain is estimated by applying a finite impulse response (FIR) low-pass filter in a frequency domain, wherein the FIR low-pass filter is adaptive according to a delay span of an original channel impulse response and is sufficiently wide to cover the delay span of the original channel impulse response; and dividing the received OFDM symbols by the channel estimate to obtain transmitted data information.