Baseband Intermodulation Cancellation via Nonlinear Reconstruction

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Solution Overview

Problem

Conventional full-duplex communication devices face interference issues due to leaked transmit signals and jammer signals, which are not effectively filtered out by traditional methods, leading to difficulty in detecting intended receive signals.

Innovation Solution

An apparatus and method for canceling intermodulation interference at baseband using a reconstruction circuit that approximates the nonlinear characteristics of the receiver and subtracts a reconstructed interference signal from the composite signal, including a look-up table to mimic the transmitter power amplifier and an adaptive filter to approximate the receiver's gain stage, allowing for interference cancellation without external filters.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional filtering methods are used to remove leaked transmit signals, then frequency separation can be maintained, but nonlinear mixer characteristics cause intermodulation products to fall into the receive band making filtering ineffective

Engineering Contradiction:

Improvesignal detection reliabilityVSAvoidreceiver circuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The invention performs preliminary action by reconstructing the intermodulation interference signal before it combines with the desired receive signal. The interference cancellation signal is generated by processing the leaked transmit signal through nonlinear characteristics approximation (look-up table) and adaptive filtering, then subtracting it from the composite signal. This preliminary cancellation prevents the interference from corrupting the receive signal detection, resolving the contradiction between reliable signal detection and circuit complexity.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If external SAW filters are used to remove leaked transmit signals, then frequency separation is maintained, but the filters are costly and do not remove jammer signals

Engineering Contradiction:

Improveinterference removal effectivenessVSAvoidmanufacturing cost

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention substitutes mechanical/physical filtering (external SAW filters) with a signal processing approach using nonlinear characteristics approximation and adaptive filtering. Instead of relying on physical frequency-selective components, the system reconstructs the interference signal in the time domain by modeling the receiver's nonlinear response and adaptively canceling it. This replaces expensive external filters with programmable signal processing, reducing manufacturing cost while improving interference removal effectiveness by also eliminating jammer signals.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Reliability

If highly linear mixers are used to prevent intermodulation, then frequency separation is maintained, but power consumption increases and cost increases

Engineering Contradiction:

Improvefrequency separation maintenanceVSAvoidpower consumption

Core Design Contradiction:

ReliabilityVSUse of energy by moving object

Solution Approach 1:

The invention uses copying by creating a model of the receiver's nonlinear characteristics through a look-up table that stores pre-measured or pre-calculated nonlinear response data. Instead of using expensive highly linear mixers to prevent intermodulation, the system copies the nonlinear behavior in a controlled manner to generate the interference cancellation signal. This allows the use of standard, lower-power mixers while maintaining frequency separation through digital signal processing, significantly reducing power consumption.

Inventive Principle:

Principle #26Copying

4Power

If the transmitted signal is amplified by power amplifiers to overcome attenuation, then the signal reaches the destination, but the amplified signal leaks into the receiver path causing interference

Engineering Contradiction:

Improvetransmit signal powerVSAvoidreceiver interference

Core Design Contradiction:

PowerVSObject-affected harmful factors

Solution Approach 1:

The invention converts the harmful leaked transmit signal into a beneficial reference for interference cancellation. By using the known transmitted signal as an input to the nonlinear characteristics approximation and adaptive filter, the system reconstructs the interference that would otherwise corrupt the receive signal. The leaked signal, which was previously harmful, becomes the basis for generating the cancellation signal, effectively turning the problem into part of the solution and enabling successful receive signal detection despite high transmit power.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS8170487B2Baseband transmitter self-jamming and intermodulation cancellation device

Publication Date: 2012.05.01 QUALCOMM INC

AI summary

Some embodiments provide a method, system, and apparatus for interference cancellation at the baseband of a receiver. A wireless communication device, having a transmitter and receiver, is provided with an adaptive circuit that cancels interference caused by transmit signals (or other signals) leaked or bled onto the receiver at baseband to facilitate detection of a received signal of interest. Some implementations provide for a circuit that approximately reconstructs the second and third order components caused by the nonlinear response of the down-conversion chain of a receiver. This reconstructed signal is then subtracted from the composite received signal to obtain a received signal of interest.