RF Interference Cancellation Circuit for Full-Duplex Systems
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Solution Overview
Problem
In full-duplex communication systems, the interference from transmitted signals to the receive system is significant due to shared frequency bands, making it difficult to achieve effective isolation, especially in broadband systems where traditional filtering and passive cancellation methods are impractical, and existing active cancellation circuits are challenging to design for multiple simultaneous signals.
Innovation Solution
An apparatus with a cancellation circuit that taps and adjusts the phase and amplitude of the transmit signal to cancel interference in the receive path, using a combination of tappers, amplifiers, phase-shifters, and feedback loops to address both leakage and reflection issues, allowing for effective cancellation of multiple simultaneous signals with varying frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a narrow bandpass filter is applied before the receiver to reject other frequencies, then interference from transmit signals is avoided, but the system cannot be applied to broadband systems where transmit and receive frequencies are in the same frequency band
Solution Approach 1:
A cancellation circuit is introduced as an intermediary element between the receive antenna and the LNA. This circuit generates a cancellation signal that is the negative of the interfering transmit signal, thereby eliminating the interference without requiring frequency separation or narrow bandpass filtering, enabling broadband operation.
Solution Approach 2:
The cancellation circuit performs preliminary anti-action by generating and injecting the negative of the interfering signal before it reaches the LNA. This pre-cancellation prevents the interfering signal from saturating the LNA, allowing the receiver to process weak signals even in the presence of strong transmit signals in the same frequency band.
2Object-affected harmful factors
If isolation between transmit antenna and receive antenna is provided, then interference is reduced, but space and weight increase
Solution Approach 1:
The cancellation circuit serves as an intermediary that electronically eliminates interference without requiring physical separation between transmit and receive antennas. By injecting the cancellation signal in the receive path, the system achieves interference rejection while maintaining a compact, single-antenna configuration, thereby reducing weight compared to dual-antenna isolated systems.
3Device complexity
If a passive cancellation circuit is used with fixed phase and amplitude, then the circuit is simple, but it cannot compensate for temperature variations and frequency changes
Solution Approach 1:
The cancellation circuit is made dynamic by introducing adjustable phase and amplitude control mechanisms. These controls allow the cancellation signal parameters to be adapted in real-time to compensate for temperature variations and frequency changes, maintaining effective cancellation across varying operating conditions without requiring a completely complex system redesign.
Solution Approach 2:
A feedback mechanism is implemented to monitor the effectiveness of the cancellation and adjust the phase and amplitude of the cancellation signal accordingly. This feedback loop ensures that the cancellation remains effective despite temperature drifts and frequency variations, improving reliability while keeping the overall circuit architecture relatively simple.
4Reliability
If the cancellation signal is added before the LNA, then LNA saturation is prevented, but the phase and amplitude of the cancellation signal must be precisely controlled
Solution Approach 1:
The cancellation circuit acts as an intermediary stage before the LNA, generating a signal that precisely counteracts the interfering transmit signal. By controlling the phase and amplitude of this intermediate cancellation signal, the system prevents LNA saturation while maintaining the ability to process weak receive signals, with the control complexity concentrated in the cancellation circuit rather than the entire receive chain.
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
The solution provides robust cancellation of interference from both leakage and reflection, ensuring receiver sensitivity and preventing LNA saturation, even in systems with multiple simultaneous transmit signals and frequency changes, by dynamically adjusting the cancellation signals based on frequency and phase variations.
Implementation Method 1
The principle is that a signal is added in the receive path. This signal is equal to the unwanted interference signal, but has opposite phase, such that the two signals cancel each other.
Data Source
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AI summary
There is disclosed an apparatus for emitting and receiving radio-frequency signals, the apparatus comprising a circuit to cancel interferences. It comprises means for transmitting at least one signal by virtue of an antenna, means for receiving signals by the same antenna and means for isolating the means for transmitting from the means for receiving. The apparatus comprises also: - means for tapping a first part of the signal to be transmitted; - means for controlling the amplitude and the phase of the first part of the signal; - means for introducing the first part of the signal in the means for receiving after said first part of the signal has been amplified and phase-shifted, such as to cancel in the means for receiving interferences due to portions of the signal that unwantedly have entered the means for receiving.