Crest Factor Reduction in Multiband Transmitters

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Solution Overview

Problem

In multiband communication systems, the high peak-to-average power ratio (PAPR) of combined signals leads to high power consumption and increased costs due to nonlinear amplifier characteristics, while clipping to reduce PAPR introduces noise and reduces transmitter performance, making it challenging to balance bandwidth efficiency and transmission power efficiency.

Innovation Solution

A method for crest factor reduction in multiband transmitters involves clipping the superposed signal, projecting clipping errors into sub-band components, filtering, and adding the projected errors back to the signal, while spectrally shaping noise to comply with adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM) parameters, using an integrated circuit with specific combiner and filtering circuits to achieve PAPR control.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Use of energy by moving object

If clipping is applied to reduce PAPR, then power consumption is reduced, but transmitter performance deteriorates due to noise introduction and EVM reduction

Engineering Contradiction:

Improvepower consumptionVSAvoidtransmitter performance

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The patent introduces an intermediary signal processing chain that captures the clipping error, projects it into sub-band components, filters it, upconverts it, and adds it back to the superposed signal. This intermediary processing allows the clipping error to be transformed into a controlled form that reduces PAPR while minimizing degradation of transmitter performance metrics such as EVM and ACLR.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent extracts the clipping error from the clipped signal and processes it separately through projection, filtering, and upconversion stages. By taking out the error component and handling it independently, the system can optimize its treatment to reduce harmful effects while maintaining the beneficial PAPR reduction.

Inventive Principle:

Principle #2Taking out (Extraction)

2Productivity

If clipping is applied to reduce PAPR, then bandwidth efficiency improves, but noise is introduced in other sub-bands increasing ACLR

Engineering Contradiction:

Improvebandwidth efficiencyVSAvoidnoise in other sub-bands

Core Design Contradiction:

ProductivityVSObject-generated harmful factors

Solution Approach 1:

The patent applies local quality by processing the clipping error differently for each sub-band. The error is projected into individual sub-band components, each of which is then filtered with sub-band specific filters before being upconverted and combined. This localized processing ensures that noise is minimized in each specific frequency band rather than uniformly across all bands.

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent introduces intermediary processing stages including projection into sub-band components, filtering, and upconversion. These intermediary steps transform the broadband clipping error into frequency-localized components that can be controlled to minimize ACLR while maintaining bandwidth efficiency.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Loss of energy

If PAPR is reduced through clipping, then transmission power efficiency improves, but EVM is reduced indicating lower signal quality

Engineering Contradiction:

Improvetransmission power efficiencyVSAvoidsignal quality

Core Design Contradiction:

Loss of energyVSMeasurement precision

Solution Approach 1:

The patent introduces an intermediary processing chain that captures the clipping error, projects it into sub-band components, filters it, upconverts it, and adds it back to the superposed signal. This intermediary processing allows the clipping error to be transformed into a controlled form that reduces PAPR while minimizing degradation of transmitter performance metrics such as EVM and ACLR.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent implements feedback by capturing the clipping error and feeding it back through a processing chain that includes projection, filtering, and upconversion. The processed error is then added back to the signal, creating a feedback loop that compensates for the distortion introduced by clipping and helps maintain signal quality.

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS7313373B1Crest factor reduction for use in a multiband transmitter

Publication Date: 2007.12.25 XILINX INC

AI summary

Crest factor reduction in a multiband transmitter is described. Component signals (xi[n]) are respectively obtained from constituent signals. The component signals (xi[n]) are respectively associated with sub-bands. A superposed signal associated with the component signals (xi[n]) is clipped to obtain a clipping noise error signal. The clipping noise error signal is applied to the component signals (xi[n]) using a least squares estimation to project clipping noise error onto the sub-bands.