I/Q Impairment Correction Using 2x2 Digital Filter Matrix
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Solution Overview
Problem
Existing communication systems face challenges in accurately measuring and correcting for I/Q impairments in transmitter and receiver devices, which lead to unwanted energy and noise due to gain and phase imbalances between the I and Q channels, complicating signal processing and transmission.
Innovation Solution
A system and method using a 2×2 matrix of digital filters are applied to compensate for I/Q impairments by computing frequency responses based on measurements of gain and phase imbalances at both positive and negative frequencies, allowing for partial compensation of I/Q impairments in both transmitters and receivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If I/Q impairments are corrected using traditional methods, then signal quality improves, but measurement accuracy deteriorates due to corruption by receiver's own impairments and signal path distortion
Solution Approach 1:
The patent introduces a calibration signal as an intermediary that passes through the transmitter's I/Q modulator and receiver's I/Q demodulator. This calibration signal allows measurement of the combined impairments of both devices and the signal path without being corrupted by normal signal processing, thereby enabling accurate measurement while maintaining signal quality improvement
Solution Approach 2:
The patent segments the measurement process into separate calibration phases where known test signals are injected through the system. By separating the measurement of transmitter impairments, receiver impairments, and signal path effects into distinct measurable components, the system can accurately characterize each element without mutual interference
2Measurement precision
If a 2×2 matrix of digital filters is used to compensate for I/Q impairments, then compensation accuracy improves, but device complexity increases
Solution Approach 1:
The patent transforms the I/Q impairment compensation problem from the time domain to the frequency domain by computing the 2×2 matrix of digital filters based on frequency response measurements. This parameter transformation enables accurate compensation across a wide frequency range while providing a systematic method to determine the filter coefficients, balancing accuracy with implementability
3Reliability
If frequency response measurements are computed using both positive and negative frequencies, then compensation effectiveness improves, but measurement and processing time increases
Solution Approach 1:
The patent performs comprehensive frequency response measurements across both positive and negative frequencies in advance during a calibration phase. By pre-computing the complete 2×2 filter matrix based on full frequency spectrum measurements, the system achieves effective wideband compensation without requiring real-time measurements during normal operation, thus reducing operational time loss
Data Source
AI summary
Various embodiments of communication devices and associated methods for reducing I/Q impairments in signals used by the communication devices are described. A transmitter device 206 may perform filtering (or matrix multiplication) on digital I and Q signals to pre-correct them before converting them into analog I and Q signals. The pre-correction may pre-compensate for I/Q impairments which have not been introduced yet, but which will subsequently be introduced during digital to analog conversion, I/Q modulation, or other processing that occurs to produce a transmission signal from the original digital I and Q signals. A receiver device may receive a transmission signal, produce digital I and Q signals from it, and perform filtering on the digital I and Q signals to correct I/Q impairments at a plurality of frequency offsets.