Digital Feedforward Transmitter Noise Cancellation Subsystem

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Solution Overview

Problem

Current transmitter noise suppression methods, such as feedforward TX noise cancellation subsystems, are limited in bandwidth and unsuitable for wideband or high-power applications, leading to inadequate cancellation of thermal noise and intermodulation distortion (IMD) in co-located receivers.

Innovation Solution

A digital feedforward transmit noise cancellation subsystem that includes a nonlinear transmitter model and a linear model to generate a digital transmitter noise cancellation signal, suitable for wideband applications, by processing the digital transmit signal to suppress transmitter noise in the receive band of a co-located receiver, using adaptive digital filters and couplers to minimize insertion losses.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If a feedforward TX noise cancellation subsystem is used to suppress transmitter noise, then transmitter noise cancellation is achieved, but the bandwidth is limited and unsuitable for wideband applications

Engineering Contradiction:

Improvetransmitter noiseVSAvoidbandwidth

Core Design Contradiction:

Object-affected harmful factorsVSAdaptability or versatility

Solution Approach 1:

The patent replaces the traditional analog feedforward cancellation system with a digital signal processing approach. The digital signal processor implements adaptive filtering algorithms that can operate across wide bandwidths, substituting the mechanical/analog limitations with digital flexibility to achieve both noise cancellation and wideband operation

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention changes the operating parameters of the cancellation system by using digital signal processing with adjustable filter coefficients and adaptive algorithms. This allows the system to adapt to different bandwidth requirements and optimize performance across wide frequency ranges, unlike fixed analog systems

Inventive Principle:

Principle #35Parameter changes

2Object-affected harmful factors

If the transmit band filter is designed with a deep stop-band to reduce thermal noise and residual IMD, then transmitter noise leakage is reduced, but the number of resonators increases and tuning time increases

Engineering Contradiction:

Improvethermal noise and residual IMD leakageVSAvoidnumber of resonators

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent replaces the complex physical filter with multiple resonators with a digital signal processing approach. The digital filter implemented in the signal processor achieves the same noise rejection function without requiring multiple physical resonators, thereby reducing device complexity and tuning time while maintaining deep stop-band performance

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The invention introduces a digital signal processor as an intermediary between the analog filter and the receiver. This digital intermediary actively cancels transmitter noise through adaptive filtering, allowing the analog filter to have relaxed specifications with fewer resonators while still achieving the required noise suppression

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If the transmit band filter is designed with a deep stop-band to reduce transmitter noise leakage, then noise suppression is improved, but insertion loss increases

Engineering Contradiction:

Improvetransmitter noise leakageVSAvoidinsertion loss

Core Design Contradiction:

Object-affected harmful factorsVSLoss of energy

Solution Approach 1:

The patent introduces a digital signal processor as an intermediary that actively cancels transmitter noise through adaptive filtering. This digital cancellation mechanism provides noise suppression without the need for a physically deep stop-band filter, thereby reducing insertion loss while maintaining effective noise suppression

Inventive Principle:

Principle #24Intermediary (Mediator)

4Object-affected harmful factors

If more resonators are added to the transmit band filter to achieve deep stop-band, then noise suppression is improved, but manufacturing cost increases

Engineering Contradiction:

Improvetransmitter noise leakageVSAvoidmanufacturing cost

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The patent replaces the need for multiple expensive physical resonators with a digital signal processing implementation. The digital filter algorithms running on the signal processor achieve the same noise rejection performance without the manufacturing costs associated with designing, fabricating, and tuning multiple precision resonators

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Data Source

PatentEP3229375B1Digital suppression of transmitter intermodulation in receiver

Publication Date: 2020.11.18 TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

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AI summary

A system and a method for digital transmitter noise cancellation are disclosed. In one embodiment, a system comprises a digital feed forward transmit noise cancellation subsystem. The subsystem is configured to generate a digital transmitter noise cancellation signal representative of transmitter noise in a receive band of a main receiver at an output of the main receiver based on a digital transmit signal. The subsystem is further configured to subtract the digital transmitter noise cancellation signal from a digital receive signal output by the main receiver to provide a compensated digital receive signal.