Common-LO Self-Interference Cancellation for FDD Transceivers
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Solution Overview
Problem
Frequency division duplexing (FDD) systems face significant interference due to self-interference from transmitter leakage, which desensitizes the receiver and degrades signal quality, and current methods to mitigate this, such as using high-quality local oscillator (LO) signals, are power-consuming and costly.
Innovation Solution
The implementation of a self-interference cancellation system that uses a common LO signal for both up-conversion and down-conversion, along with an auxiliary path to shift and conjugate phase-noise mixing products, effectively cancels phase-noise interference by correlating the LO signals and leveraging the duplexer's duplex offset frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If high-quality local oscillator (LO) signals are used to reduce phase-noise mixing products, then signal quality is improved, but power consumption increases
Solution Approach 1:
The patent converts the harmful phase-noise mixing products into a beneficial cancellation mechanism by deliberately generating identical phase-noise products in an auxiliary path and subtracting them from the main signal path. Instead of trying to eliminate phase-noise through high-quality LO signals, the system exploits phase-noise correlation to cancel self-interference, thereby reducing power consumption while maintaining signal quality.
Solution Approach 2:
The patent segments the signal processing into two separate paths: a main path for normal signal reception and an auxiliary path for phase-noise cancellation. The auxiliary path processes a copy of the transmitted signal through identical operations to generate correlated phase-noise mixing products, which are then subtracted from the main path output. This segmentation allows independent optimization of each path and enables cancellation without requiring high-power LO signals.
2Reliability
If self-interference cancellation is implemented to reduce receiver desensitization, then receiver sensitivity is improved, but device complexity increases
Solution Approach 1:
The auxiliary LO signal generator serves multiple functions: it generates the LO signal for the auxiliary path, produces phase-noise mixing products for cancellation, and can be derived from the same source as the main path LO. This multi-functionality reduces the need for separate dedicated components and simplifies the overall system architecture while maintaining effective self-interference cancellation.
Solution Approach 2:
The patent introduces an auxiliary path as an intermediary mechanism that mediates between the transmitted signal and the received signal. Rather than directly canceling interference in the main path, the auxiliary path generates correlated interference products that act as a mediator to cancel the self-interference when subtracted from the main signal, thereby improving receiver sensitivity with manageable complexity.
3Object-generated harmful factors
If duplexer isolation is increased to reduce transmitter leakage, then self-interference is reduced, but insertion loss increases
Solution Approach 1:
The patent implements a feedback mechanism where a copy of the transmitted signal is processed through the same RF chain operations to generate an estimate of the self-interference. This estimated interference is then fed back and subtracted from the received signal to cancel the leakage. This active cancellation approach replaces passive duplexer isolation, reducing insertion loss while effectively eliminating transmitter leakage.
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 reduces receiver desensitization and noise-figure degradation, providing improved signal quality by suppressing transmitter leakage and phase-noise mixing products without the need for high-power, low-phase-noise LO signals.
Implementation Method 1
correlating the LO signals and leveraging the duplexer's duplex offset frequency
Implementation Method 2
shift the phase-noise mixing product in the corrected received signal by twice the duplex offset frequency
Implementation Method 3
conjugate the shifted signal to flip the spectrum
Data Source
AI summary
Systems, methods, and circuitries are disclosed for performing self-interference cancellation in a transceiver. In one example, a self-interference cancellation system includes a cancellation signal circuitry, cancellation circuitry, down-conversion circuitry, and an LO derivation circuitry. The cancellation signal circuitry is configured to use a cancellation transmit (TX) local oscillator (LO) signal to up-convert a baseband transmit leakage replica signal to generate a cancellation signal. The cancellation circuitry is configured to combine the cancellation signal with a received signal to generate a corrected received signal. The down-conversion circuitry is configured to use a receive (RX) LO signal to down-convert the corrected received signal to generate a baseband received signal. The LO derivation circuitry is configured to derive the cancellation TX LO signal and the RX LO signal from a common LO signal.