Receiver I/Q Impairment Measurement Using Filter Matrix Compensation
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Solution Overview
Problem
Existing systems face challenges in accurately measuring and compensating for I/Q impairments in transmitter and receiver devices, which lead to unwanted energy and noise in communication signals due to gain and phase imbalances between the I and Q channels.
Innovation Solution
A method involving a 2×2 matrix of digital filters is used to compensate for I/Q impairments by computing frequency responses based on measurements of gain and phase imbalances at both positive and negative frequencies, applied in both transmitters and receivers to pre- or post-compensate for these impairments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a receiver estimates transmitter I/Q impairments based on received signal, then the estimation process can be performed, but the receiver's I/Q demodulator corrupts the estimates with its own I/Q impairments
Solution Approach 1:
The patent introduces a signal path characterization process that acts as an intermediary to separate and account for the receiver's I/Q impairments. By measuring the signal path response and using it to correct the estimates, the system isolates the harmful effect of receiver impairments from the measurement process, enabling accurate transmitter impairment estimation despite the receiver's own distortions.
Solution Approach 2:
The system employs feedback mechanisms where the receiver measures its own signal path characteristics and uses this information to correct subsequent measurements. The signal path characterization is fed back into the estimation process, allowing the system to compensate for receiver I/Q impairments and improve measurement accuracy.
2Productivity
If the signal path between transmitter and receiver is used for transmission, then communication can occur, but the signal path introduces distortion to the I/Q impairment estimates
Solution Approach 1:
The patent extracts the signal path distortion characteristics by measuring the response to known test signals. By separating and characterizing the signal path effects independently, the system can remove these distortions from subsequent impairment measurements, allowing both communication functionality and accurate measurement to coexist.
Solution Approach 2:
The system performs preliminary signal path characterization before actual communication or measurement. By pre-measuring the signal path response to known test signals and storing this information, the system prepares correction data that can be applied to subsequent measurements, eliminating the need to disrupt normal communication operations.
3Object-generated harmful factors
If I/Q impairments are not compensated, then device complexity remains low, but unwanted energy and noise are introduced into communication signals
Solution Approach 1:
The patent implements compensation by adjusting key parameters including gain imbalance, phase skew, and image rejection. These parameter adjustments are applied through digital signal processing operations that modify the I and Q channel characteristics. By changing these parameters dynamically or through calibration, the system reduces unwanted energy and noise while maintaining manageable device complexity through software-based correction rather than hardware redesign.
Data Source
AI summary
Systems and methods for measuring transmitter and/or receiver I/Q impairments are disclosed, including iterative methods for measuring transmitter I/Q impairments using shared local oscillators, iterative methods for measuring transmitter I/Q impairments using intentionally-offset local oscillators, and methods for measuring receiver I/Q impairments. Also disclosed are methods for computing I/Q impairments from a sampled complex signal, methods for computing DC properties of a signal path between the transmitter and receiver, and methods for transforming I/Q impairments through a linear system.