Frequency-Selective IQ Correction for DPD Feedback Mismatch
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Solution Overview
Problem
Conventional IQ compensation filters in digital predistortion systems are inadequate in eliminating image signals due to inaccurate estimation of channel responses, particularly in out-of-band regions, and introduce substantial out-of-band ripple when attempting to correct in-phase and quadrature mismatches.
Innovation Solution
An IQ correction filter that employs a signal band detector, IQ estimator, and IQ compensator to apply a correction function derived from the pseudoinverse of a sub-matrix of the discrete Fourier transform matrix indexed by a mask, specifically targeting the signal band to provide accurate compensation without introducing out-of-band errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional IQ compensation filters are used to correct in-phase and quadrature mismatches, then image signal elimination is attempted, but out-of-band ripple is introduced and estimation accuracy deteriorates in out-of-band regions
Solution Approach 1:
The patent segments the frequency spectrum into signal band and out-of-band regions using a mask. The mask identifies which frequency components correspond to the actual signal band, allowing the filter to process only the relevant frequency components and ignore out-of-band regions, thereby avoiding out-of-band ripple while maintaining estimation accuracy in the signal band
Solution Approach 2:
The patent applies frequency-selective correction by using a mask to apply different correction qualities to different frequency regions. Within the signal band (where mask=1), accurate channel response estimation and correction are applied. In out-of-band regions (where mask=0), no correction is applied, avoiding the introduction of out-of-band ripple while maintaining overall system performance
2Object-generated harmful factors
If full-band IQ correction is applied across all frequency points, then in-band image signals are reduced, but out-of-band errors are introduced due to random frequency points
Solution Approach 1:
The patent segments the frequency domain into signal band and out-of-band regions using a mask. By applying IQ correction only where mask=1 (signal band) and not where mask=0 (out-of-band), the system eliminates image signals in the relevant band while avoiding the introduction of out-of-band errors from random frequency point processing
Solution Approach 2:
The patent changes the parameter of correction application from uniform full-band correction to frequency-selective correction based on the mask parameter. This parameter change allows the system to adaptively apply correction only where needed (signal band) and avoid correction where it would be harmful (out-of-band regions), thereby reducing image signals without introducing out-of-band errors
Data Source
AI summary
In conventional radio frequency (RF) systems, transmitters will usually convert baseband signals to RF so as to be transmitted. As part of the conversion process, the transmitters will perform digital predistortion (DPD), which uses feedback from a power amplifier. However, there are usually mismatches between the in-phase (I) and quadrature (Q) paths within with feedback loop. Traditional IQ correction filters were ineffective at providing adequate compensation for these mismatches, but here a filter is provided that provides adequate out-of-band compensation by use of frequency selectivity.