Adaptive Filter for Transmit Leakage Rejection in Full-Duplex Systems
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Solution Overview
Problem
In wireless full-duplex communication systems, transmit signal leakage causes interference in the receive path due to second-order distortion and cross-modulation distortion, leading to potential degradation of the desired received signal, despite filtering efforts.
Innovation Solution
An adaptive filter circuit is introduced in the RF receiver, which estimates and subtracts the transmit leakage signal using a reference signal at the carrier frequency, effectively reducing or eliminating distortion by canceling at least a portion of the transmit leakage signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If filtering is applied to remove TX signal leakage, then some TX leakage is reduced, but residual TX leakage remains causing distortion
Solution Approach 1:
The patent implements an adaptive filter that uses feedback from the received signal to estimate and cancel TX leakage. The filter continuously adjusts its parameters based on the residual leakage detected in the RX path, creating a closed-loop system that dynamically compensates for leakage variations and maintains high rejection performance.
Solution Approach 2:
The patent introduces an adaptive filter as an intermediary component between the duplexer and the RX signal processing chain. This filter acts as a mediator that selectively removes TX leakage components from the composite signal without affecting the desired RX signal, thereby resolving the contradiction between leakage reduction and signal quality preservation.
2Object-affected harmful factors
If adaptive filtering is applied to cancel TX leakage, then TX leakage distortion is reduced, but device complexity increases
Solution Approach 1:
The adaptive filter is configured to automatically estimate and cancel TX leakage without requiring manual intervention or complex external control systems. The filter uses the available RX signal and reference signals to self-adjust its parameters, thereby reducing leakage distortion while minimizing the need for additional complex control circuitry.
Solution Approach 2:
The patent employs parameter changes in the adaptive filter coefficients to achieve TX leakage cancellation. By dynamically adjusting filter parameters based on signal conditions rather than using a fixed complex structure, the system achieves effective leakage rejection with relatively simple circuit implementation.
Data Source
AI summary
This disclosure describes techniques for reducing adverse effects of transmit signal leakage in a full-duplex, wireless communication system. The disclosure describes techniques for reducing adverse effects of second order distortion and cross-modulation distortion of transmit signal leakage from a transmitter via a duplexer. The techniques may be effective in rejecting at least a portion of a transmit leakage signal, thereby reducing or eliminating distortion. The adaptive filter may include an estimator circuit that generates a transmit leakage signal estimate. A summer subtracts the estimate from the received signal to cancel transmit leakage and produce an output signal. The estimator circuit generates the transmit leakage signal estimate based on a reference signal and feedback from the output signal. The reference signal approximates the carrier signal used to generate the transmit signal in the transmitter. The reference signal may be provided by the same oscillator used to produce the transmit carrier signal.