Self-Interference Channel Estimation for Filterless RF Isolation
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Solution Overview
Problem
Conventional radio frequency (RF) front end subsystems face challenges in self-interference cancellation, particularly in frequency division duplex systems, due to nonlinearities and exact group delay control issues, which affect the isolation between transmit and receive bands.
Innovation Solution
A method and system that utilize a swept tone and an infinite impulse response (IIR) filter to characterize the self-interference channel, enabling effective cancellation through feed-forward and digital residual interference cancellation techniques, which can eliminate the need for traditional filters and allow for band-independent transceivers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional balun-based cancellers are used to provide 180° out-of-phase interference samples, then self-interference cancellation is achieved, but exact group delay control becomes difficult and system complexity increases
Solution Approach 1:
The patent replaces mechanical balun-based phase shifting with digital signal processing. An IIR filter is used to generate the cancellation signal by processing a tapped version of the transmit signal, eliminating the need for precise mechanical or electrical phase shifters and group delay control circuits.
Solution Approach 2:
The patent changes the approach from fixed hardware-based phase shifting to adaptive digital filtering. The IIR filter parameters are optimized to achieve the desired phase and amplitude characteristics for self-interference cancellation, providing flexibility without additional hardware complexity.
2Reliability
If traditional filters are used to separate transmit and receive bands, then frequency isolation is achieved, but device size and cost increase
Solution Approach 1:
The patent extracts the frequency isolation function from physical filters and implements it through digital signal processing. By using an IIR filter to generate cancellation signals and subtracting them from the received signal, the system achieves frequency isolation without requiring large, expensive traditional filters.
Solution Approach 2:
The patent substitutes physical filter-based frequency separation with digital filtering and signal cancellation techniques. This replacement reduces the need for bulky RF components while maintaining effective isolation between transmit and receive bands.
3Productivity
If FDD systems use separate frequencies for transmit and receive, then simultaneous operation is enabled, but self-interference from power amplifier nonlinearities affects receive band quality
Solution Approach 1:
The patent takes the harmful self-interference signal and converts it into a useful cancellation reference. By tapping the transmit signal before the power amplifier and processing it through an IIR filter, the system generates a cancellation signal that matches the interference characteristics, then subtracts it from the received signal to eliminate the harmful effects.
Solution Approach 2:
The patent applies preliminary anti-action by generating the cancellation signal in advance from the transmit signal path. The IIR filter processes the tapped transmit signal to predict and prepare the cancellation signal before it needs to counteract the self-interference in the receive band.
Data Source
AI summary
The present application describes a self-interference channel estimation system. The system includes a signal generator configured to generate a swept tone having a frequency ranging from an upper edge of a reception band to a lower edge of the reception band, and configured to generate a message signal. The system includes an infinite impulse response (IIR) filter configured to determine an infinite impulse response of a self-interference channel based upon the swept tone. The system includes a processor configured to characterize the self-interference channel based upon the infinite impulse response.