Self-Interference Cancellation With IQ Imbalance
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Solution Overview
Problem
Existing wireless full-duplex systems face limitations in self-interference cancellation, particularly when IQ imbalance is present, as existing digital interference cancellation technologies struggle to effectively cancel self-interference signals, leading to poor performance and inability to cancel interference greater than 40 dB.
Innovation Solution
A signal processing method and apparatus that acquires digital baseband and self-interference reference signals, estimates comprehensive responses, and calculates a self-interference signal using formulas such as Z(f)=H1(f)S(f)+H2(f)S*(−f) to perform self-interference cancellation, improving digital interference cancellation performance even in the presence of IQ imbalance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing digital interference cancellation technology is used, then the system can operate with simple architecture, but self-interference cancellation performance is limited and cannot cancel interference greater than 40 dB
Solution Approach 1:
The patent segments the self-interference signal into two distinct components: the main self-interference signal and the image self-interference signal caused by IQ imbalance. By separating these components and estimating their respective channel responses (H1 for main signal, H2 for image signal), the system can apply targeted cancellation strategies to each component, thereby improving overall cancellation performance while maintaining manageable processing complexity.
Solution Approach 2:
The patent performs preliminary channel estimation for both the main self-interference path and the image interference path before the actual cancellation process. By pre-calculating the channel responses H1 and H2 and the corresponding self-interference signals, the system prepares all necessary components in advance, enabling effective cancellation during the reception phase without adding real-time processing burden.
2Reliability
If analog interference cancellation is used, then the main self-interference signal can be eliminated, but the image interference signal caused by IQ imbalance remains uncanceled
Solution Approach 1:
The patent introduces an intermediary digital signal processing stage that operates on the received signal after analog cancellation. This digital processing intermediary estimates and subtracts the image self-interference component that was not removed by analog cancellation, thereby completing the interference removal process without requiring additional analog hardware components.
Solution Approach 2:
The patent replaces the need for additional analog interference cancellation hardware with a digital signal processing approach. By using mathematical models and digital computations to estimate and cancel the image interference signal, the system achieves more complete cancellation without increasing the physical complexity of the analog front-end.
3Productivity
If FDD or TDD technology is used, then self-interference is avoided by using different frequency bands or time periods, but spectral efficiency is reduced by half
Solution Approach 1:
The patent converts the harmful self-interference signal into a useful estimation resource. By deliberately estimating the self-interference signal components (both main and image signals) based on the transmitted signal and channel responses, the system transforms what was previously a destructive interference into a predictable and cancellable component, enabling full-duplex operation with high spectral efficiency.
Data Source
AI summary
The present embodiments relate to the field of communications, and discloses a signal processing method and apparatus, which can implement self-interference cancellation when in-phase quadrature (IQ) imbalance exists in a communications system. An embodiment is acquiring, a digital baseband reference signal, a self-interference reference signal, and a frequency-domain baseband signal. The method also includes obtaining, according to the digital baseband reference signal, a basic reference signal and an image reference signal that are image to each other and estimating an estimated value of a first comprehensive response and an estimated value of a second comprehensive response according to the basic reference signal, the image reference signal, and the self-interference reference signal. Additionally, the method includes calculating a self-interference signal according to the estimated value of the first comprehensive response, the estimated value of the second comprehensive response, the basic reference signal, and the image reference signal, so as to perform self-interference cancellation on the frequency-domain baseband signal.