OFDM Receiver Circuit for Channel Estimation and Remnant Offset Correction
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Solution Overview
Problem
OFDM systems, particularly in IEEE 802.11a and 802.11g wireless LAN standards, face challenges in accurately estimating channel impulse response and compensating for remnant frequency offset, leading to performance degradation due to inter-symbol interference and inter-channel interference.
Innovation Solution
A circuit is introduced that includes an equalizer, a remnant frequency compensation module, and an error estimation module to refine channel impulse response estimation by using pilot signals to calculate phase offset coefficients and rotate the phase of signals, thereby improving channel equalization and compensating for remnant frequency offset.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional channel estimation and equalization is used in OFDM receiver, then basic signal reception is achieved, but channel impulse response estimation accuracy is insufficient leading to performance degradation
Solution Approach 1:
The patent implements a feedback mechanism where the equalizer output is fed back to refine channel impulse response estimation. The equalizer compensates for channel distortion using initial channel estimates, and the compensated signal is then used to update and improve the channel estimates iteratively, creating a closed-loop system that continuously enhances estimation accuracy.
Solution Approach 2:
The patent performs preliminary channel estimation using pilot signals before main data reception. This preliminary action establishes initial channel impulse response estimates that are then refined through the feedback process, allowing the system to prepare accurate compensation parameters in advance of processing the actual data symbols.
2Measurement precision
If frequency offset compensation is applied, then carrier frequency alignment is improved, but remnant frequency offset remains causing inter-channel interference
Solution Approach 1:
The patent applies partial compensation by addressing only the remnant frequency offset that remains after conventional compensation. Instead of attempting to compensate for all frequency offset at once, the system first applies standard frequency offset correction, then separately compensates for the remaining partial offset using the equalized signal and pilot information, thereby eliminating residual inter-channel interference.
3Reliability
If equalization is performed to compensate channel distortion, then signal quality is improved, but channel estimation accuracy limitations reduce effectiveness
Solution Approach 1:
The patent creates a feedback loop where the equalizer's output is used to refine the channel impulse response estimates. The equalizer initially compensates for channel distortion using preliminary estimates, and the compensated signal is then fed back to update and improve the channel estimates, making the equalization progressively more effective with each iteration.
Data Source
AI summary
A circuit for improving accuracy of channel impulse response estimation and compensating for remnant frequency offset in a receiver of an orthogonal frequency division multiplexing (OFDM) system is provided. The circuit comprises an equalizer, for compensating a first signal for channel distortion with the channel impulse response estimate to generate a second signal. The circuit also comprises a remnant frequency compensation module, coupled to the equalizer, for rotating a phase of the second signal with a phase angle of an phase offset coefficient calculated according to a plurality of pilot signals of the second signal to generate a third signal. The circuit further comprises a error estimation module, coupled to the remnant frequency compensation module, for generating an error estimate according to the third signal and its hard decision estimate, and the error estimate is further fed back to the equalizer to refine the channel impulse response estimate.