Frequency-Domain I/Q Balance Compensation for Zero-IF Spurious Rejection
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Solution Overview
Problem
Existing techniques for correcting I/Q balance in Zero-IF receivers are inadequate in addressing spurious signals due to amplitude and phase imbalances, particularly at high sample rates, and fail to account for frequency-dependent errors and edge effects, leading to inefficient FIR filter architectures.
Innovation Solution
A method and system for correcting spurious signals by measuring I/Q imbalances in the frequency domain, calculating frequency-dependent calibration coefficients, converting to the time domain, and applying them to correct amplitude and phase variations using Fast Fourier Transforms and Inverse Fast Fourier Transforms, combined with overlap-and-save algorithms to optimize processor utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital correction mechanism is used to correct I/Q imbalance, then spurious signal rejection is improved, but processing complexity and resource requirements increase
Solution Approach 1:
The correction process is divided into separate stages: calibration phase where I/Q imbalance characteristics are measured and stored, and operational phase where pre-calculated coefficients are applied. This segmentation allows complex correction to be performed offline, reducing real-time processing complexity while maintaining high spurious signal rejection.
Solution Approach 2:
I/Q imbalance calibration coefficients are calculated and stored in advance during a calibration phase, before actual signal processing begins. This preliminary action transfers the computational burden from real-time operation to setup time, enabling efficient real-time correction with reduced processing complexity.
2Measurement precision
If high sample rate data is processed in real-time, then signal processing accuracy is improved, but processing speed and resource utilization deteriorate
Solution Approach 1:
Processing is segmented into calibration (offline) and operation (real-time) phases. High-precision coefficient calculation is performed offline during calibration, while real-time processing applies these coefficients efficiently, maintaining accuracy while improving processing speed and resource utilization.
Solution Approach 2:
The patent replaces complex real-time mechanical/computational processing with pre-calculated mathematical coefficients stored in memory. This substitution transforms the problem from real-time computation to memory retrieval and simple multiplication, dramatically improving processing speed while maintaining accuracy.
3Measurement precision
If FIR filters are used for I/Q correction, then amplitude and phase imbalance correction is improved, but processor efficiency and implementability deteriorate
Solution Approach 1:
Instead of applying FIR filters directly in the time domain, the patent transforms the correction approach to the frequency domain using FFT, applies correction coefficients, and transforms back. This inversion of the processing domain improves processor efficiency by leveraging the computational advantages of frequency domain operations for this specific correction task.
Solution Approach 2:
The patent substitutes complex FIR filter implementation with a simpler coefficient-based correction method using FFT. This replacement maintains I/Q correction accuracy while dramatically improving processor efficiency and ease of implementation by avoiding the computational burden of long FIR filters.
4Measurement precision
If frequency domain coefficients are converted directly to time domain using FIR filter approach, then I/Q balance correction is achieved, but edge effects and Gibbs phenomenon deteriorate correction quality
Solution Approach 1:
The patent applies windowing functions to the frequency domain coefficients before transformation, as a preliminary measure to prevent Gibbs phenomenon and edge effects. This anti-action taken in advance eliminates correction quality deterioration that would otherwise occur with direct time domain conversion.
Solution Approach 2:
Rather than converting frequency domain coefficients directly to time domain (which causes Gibbs phenomenon), the patent inverts the approach by working in the frequency domain throughout the correction process, applying corrections to FFT-transformed signals, then transforming back. This avoids the mathematical operations that generate edge effects and improves correction reliability.
Data Source
AI summary
Spurious signals in a receiver are rejected using a method of correcting amplitude and phase imbalances in the received signal. A system implementing the method can be built into the receiver or can be used during assembly of the receiver.