Adaptive IM2 Cancellation in Full-Duplex Receive Channels

Solution Overview

Problem

Conventional transceiver architectures in mobile communication devices suffer from second-order inter-modulation interference due to transmitter leakage, which is not effectively addressed without the use of SAW filters, leading to interference in the receive signal.

Innovation Solution

A digital signal canceller is introduced, comprising a delay estimator and a signal adjuster, which generates an estimate of the transmit leakage signal's second-order inter-modulation and removes it from the received signal before processing, thereby reducing interference in the receive channel.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If SAW filters are used to reduce transmitter leakage, then interference in the receive signal is reduced, but device complexity and cost increase

Engineering Contradiction:

Improvetransmitter leakage interferenceVSAvoidfilter architecture complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces the mechanical SAW filter system with a digital signal processing system. An adaptive finite impulse response (FIR) filter is implemented in the digital domain to cancel second-order inter-modulation products generated by transmitter leakage. This substitution eliminates the need for complex analog filter hardware while achieving the same interference reduction goal through digital adaptive filtering techniques.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an adaptive FIR filter as an intermediary component between the received signal and the baseband processor. This intermediary digitally processes the received signal to cancel out the harmful second-order inter-modulation products caused by transmitter leakage, thereby reducing interference without requiring additional analog filter hardware in the RF path.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If SAW filters are removed to reduce device size and cost, then device complexity decreases, but second-order inter-modulation interference increases

Engineering Contradiction:

Improvefilter architecture complexityVSAvoidsecond-order inter-modulation interference

Core Design Contradiction:

Device complexityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces the mechanical SAW filter system with a digital signal processing system. An adaptive finite impulse response (FIR) filter is implemented in the digital domain to cancel second-order inter-modulation products generated by transmitter leakage. This substitution eliminates the need for complex analog filter hardware while achieving the same interference reduction goal through digital adaptive filtering techniques.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent employs an adaptive filtering system that uses feedback to continuously adjust and optimize the cancellation of second-order inter-modulation products. The adaptive FIR filter monitors the received signal and dynamically adjusts its coefficients to effectively cancel the interference caused by transmitter leakage, maintaining performance without requiring fixed analog filter hardware.

Inventive Principle:

Principle #23Feedback

3Device complexity

If conventional transceiver architecture is used without additional filtering, then device simplicity is maintained, but signal quality deteriorates due to inter-modulation interference

Engineering Contradiction:

Improvetransceiver architecture simplicityVSAvoidreceive signal quality

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent replaces the mechanical SAW filter system with a digital signal processing system. An adaptive finite impulse response (FIR) filter is implemented in the digital domain to cancel second-order inter-modulation products generated by transmitter leakage. This substitution eliminates the need for complex analog filter hardware while achieving the same interference reduction goal through digital adaptive filtering techniques.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an adaptive FIR filter as an intermediary component between the received signal and the baseband processor. This intermediary digitally processes the received signal to cancel out the harmful second-order inter-modulation products caused by transmitter leakage, thereby reducing interference without requiring additional analog filter hardware in the RF path.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS8855029B2LMS adaptive filter for digital cancellation of second order inter-modulation due to transmitter leakage

Publication Date: 2014.10.07 SKYWORKS SOLUTIONS INC

AI summary

A transmit signal second-order inter-modulation (IM2) canceller for a portable handset using a full duplex mode of operation (e.g., WCDMA) is used to controllably reduce IM2 introduced by a transmit signal that appears in a received signal in a receive channel of the portable handset. The transmit signal IM2 canceller includes a delay estimator and a digital signal adjuster. The delay estimator receives a first input from a receive channel and a second input from a transmit channel. The delay estimator generates an estimate of the IM2 that the transmit channel introduces in the receive channel. The digital signal adjuster removes the estimate of the IM2 before forwarding a modified receive channel signal to a baseband subsystem of the portable handset.