IQ Mismatch Compensation Filter Calibration for Image Rejection
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Solution Overview
Problem
IQ mismatches and imbalances in wireless communication receivers lead to image signal interference, degrading performance, especially at high data rates, as existing compensation techniques fail to meet the demands of emerging applications.
Innovation Solution
A method and apparatus for IQ mismatch compensation using a compensation filter with estimated filter coefficients and time delay, where single tone signals are sent across a frequency range to determine frequency responses and generate time-domain filter taps, and an adaptive filter is used during signal reception to refine the time delay tap coefficients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If iterative adaptive filter techniques are used to find filter coefficients, then the compensation can adapt to varying conditions, but the convergence speed and accuracy are insufficient for high data rate applications
Solution Approach 1:
The patent applies preliminary action by performing a fast Fourier transform (FFT) based frequency response estimation before the iterative adaptive filtering process. This preliminary step provides an initial estimate of the frequency response that accelerates convergence of the subsequent iterative algorithm, thereby resolving the contradiction between accuracy and convergence speed for high data rate applications
2Measurement precision
If comprehensive frequency response estimation is performed across the entire frequency range, then accurate compensation filter coefficients are obtained, but the calibration time and computational complexity increase
Solution Approach 1:
The patent applies partial action by estimating the frequency response at selected frequency points using FFT rather than continuously across the entire frequency range. This selective sampling approach maintains sufficient accuracy for compensation while significantly reducing calibration time and computational complexity
Solution Approach 2:
The patent substitutes traditional time-domain iterative measurement methods with frequency-domain FFT-based estimation. This substitution enables rapid frequency response characterization without requiring extensive time-domain sweeping, thereby reducing calibration time while maintaining measurement precision
3Object-affected harmful factors
If time delay is adjusted to optimize compensation performance, then image signal interference is reduced, but the system complexity and adjustment requirements increase
Solution Approach 1:
The patent applies feedback by using the estimated frequency response to automatically determine optimal time delay values. The system measures the actual frequency response, compares it with the ideal response, and adjusts the time delay accordingly to minimize image signal interference, thereby reducing system complexity through automated feedback-based optimization
Data Source
AI summary
A method for providing IQ mismatch (IQMM) compensation includes: estimating an overall frequency response of a compensation filter by stepping through a frequency range starting at an initial frequency and performing (1) through (3) at each step, a selected frequency at each step being a multiple of a subcarrier frequency of the initial frequency: (1) sending a single tone signal at the selected frequency, (2) determining a first response of a mismatched signal at the selected frequency and a second response of the mismatched signal at an image frequency of the selected frequency, and (3) estimating a frequency response of the compensation filter at the selected frequency based on the first response and the second response; generating time-domain filter taps based on the estimated overall frequency response of the compensation filter; determining a time delay based on the time-domain filter taps; and generating a compensated signal based on the time delay.