Selective Interference Cancellation in Spread Spectrum Receivers

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Solution Overview

Problem

Conventional interference cancellation systems in spread spectrum communication systems often result in poorer signal-to-noise ratios for desired signal paths, as they do not provide for flexible application and can drown out weaker signals from distant sources, limiting signal diversity and reliability.

Innovation Solution

A method and apparatus for selectively applying interference cancellation by identifying and canceling signal paths that interfere with desired signals only if the cancellation improves the signal-to-noise ratio, using a cancellation controller to determine whether interference cancellation enhances the desired signal strength and providing either interference-canceled or raw signal streams to demodulation fingers based on this assessment.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If interference cancellation is applied to remove extraneous signal paths, then the signal quality of strong interfering signals is improved, but weaker desired signals from distant sources are drowned out and lost

Engineering Contradiction:

Improveinterference from strong signalsVSAvoiddetection of weak signals

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The system dynamically adjusts the application of interference cancellation based on real-time signal conditions. The controller monitors signal paths and selectively applies cancellation only when beneficial, transitioning between cancellation and non-cancellation modes to optimize both interference rejection and weak signal detection

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system changes the parameter of signal processing mode by adjusting the cancellation control signal, which modifies the gain or application state of the interference cancellation filter. This parameter change allows the system to adapt between aggressive cancellation and conservative preservation of weak signals

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If conventional interference cancellation schemes are applied, then strong interfering signals are removed, but the signal-to-noise ratio of desired signal paths deteriorates

Engineering Contradiction:

Improveinterfering signal pathsVSAvoidsignal-to-noise ratio

Core Design Contradiction:

Object-affected harmful factorsVSMeasurement precision

Solution Approach 1:

The system employs feedback by monitoring the signal-to-noise ratio before and after interference cancellation. The controller uses this feedback to determine whether cancellation improved or degraded the desired signal, and adjusts subsequent cancellation operations accordingly to maintain optimal SNR

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

Instead of applying full interference cancellation unconditionally, the system applies partial cancellation only to the extent that it improves the desired signal. The cancellation is moderated to avoid excessive removal that would harm the desired signal path

Inventive Principle:

Principle #16Partial or excessive action

3Reliability

If signal power is controlled to address near-far problem, then distant signals become more detectable, but the system complexity increases with beam steering and smart antenna applications

Engineering Contradiction:

Improvesignal detection capabilityVSAvoidbeam steering and smart antenna systems

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The system extracts and removes only the specific interfering signal components that harm the desired signal, rather than implementing complex beam steering or smart antenna systems. This targeted extraction approach achieves near-far problem mitigation with simpler processing

Inventive Principle:

Principle #2Taking out (Extraction)

4Object-affected harmful factors

If interference cancellation is applied without selective control, then interference is removed, but flexible adaptation to different signal conditions is lost

Engineering Contradiction:

Improveinterference cancellationVSAvoidflexible application to signal conditions

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The system transitions from static interference cancellation to dynamic adaptive cancellation. The controller continuously monitors signal conditions and adjusts the cancellation operation in real-time, enabling the system to adapt to varying signal environments and optimize performance for different scenarios

Inventive Principle:

Principle #15Dynamics

Data Source

PatentUS7787518B2Method and apparatus for selectively applying interference cancellation in spread spectrum systems

Publication Date: 2010.08.31 III HOLDINGS 1 LLC

AI summary

The present invention is directed to the selective provision of interference canceled signal streams to demodulating fingers in a communication receiver. According to the present invention, potential interferer signal paths are identified. Signal streams having one or more potential interferer signals removed or canceled are created, and a correlation is performed to determine whether the strength of a desired signal path increased as a result. If the correlation indicates that the strength of a desired signal path was increased by the signal cancellation, the interference canceled signal stream is provided to the demodulation finger assigned to track the desired signal path. If the correlation determines that the strength of the desired signal path did not increase as a result of performing interference cancellation, the raw or a different interference canceled signal stream is provided to the demodulation finger.