Self-Interference Cancellation Using Impedance Mismatch Terminal
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Solution Overview
Problem
In-Band Full-Duplex communication systems face challenges in reducing self-interference signals, particularly in single-antenna configurations, due to the difficulty in accurately estimating and canceling the self-interference signal, which limits spectrum efficiency and increases complexity and cost.
Innovation Solution
The implementation of an analog self-interference cancellation technique using an impedance mismatch terminal (IMT) circuit that generates and modifies a secondary self-interference signal to cancel the primary self-interference signal, leveraging the circulator's inherent properties to reduce interference without the need for additional RF components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple antennas are used for spatial isolation, then self-interference cancellation is improved, but device complexity and form factor are worsened
Solution Approach 1:
The patent combines multiple cancellation functions (passive isolation, active cancellation, and digital processing) into a single integrated circuit architecture, eliminating the need for multiple separate antennas while achieving equivalent or superior self-interference cancellation performance
Solution Approach 2:
The single antenna is designed to perform multiple functions simultaneously: transmission, reception, and self-interference cancellation through integrated circuitry, making the system as effective as multi-antenna systems without the complexity
2Reliability
If analog cancellation circuitry is added, then self-interference cancellation is improved, but hardware complexity and cost are worsened
Solution Approach 1:
The system uses the transmitted signal itself to generate the cancellation signal through the circulator's inherent properties, eliminating the need for external analog cancellation circuitry or additional RF components
Solution Approach 2:
The circulator naturally creates a copy of the transmitted signal that can be used for cancellation, leveraging the circulator's inherent signal routing properties rather than requiring separate cancellation hardware
3Measurement precision
If precise SI signal estimation is attempted, then cancellation accuracy is improved, but system complexity increases
Solution Approach 1:
The circulator pre-processes the transmitted signal to create a naturally synchronized cancellation signal before it reaches the receiver, eliminating the need for complex real-time estimation algorithms
Solution Approach 2:
The system uses feedback from the circulator's signal routing to automatically adjust and maintain accurate cancellation without requiring complex control algorithms or additional sensing hardware
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach achieves up to 90 dB cancellation in narrowband systems and 40 dB in wideband systems, doubling the usable capacity of the electromagnetic spectrum and reducing hardware complexity and cost, while being robust to antenna impedance variations and fabrication errors.
Implementation Method 1
providing the IBFD system consisting of a single antenna and comprising a circulator having at least a transmitter port, a receiver port, and an impedance mismatch terminal (IMT) port
Implementation Method 2
an IMT circuit connected to the IMT port and operating between the antenna and the circulator; and configuring the IMT circuit to collect a secondary self-interference signal of the circulator
Data Source
AI summary
An analog self-interference cancellation technique for In-Band Full-Duplex (IBFD) systems generates an inherent secondary self-interference (SI) signal of a circulator and uses that signal to cancel a primary SI signal leaked from a transmitter port within a communication device. The communication device manipulates the phase and angle of this secondary SI, using an adjustable Impedance Mismatch Terminal (IMT) circuit. The result is an efficient SI cancellation technique in the analog domain, which uses the circulator inherent SI signals.