Wireless Transmitter Phase Shifting for Intermodulation Mitigation
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Solution Overview
Problem
Existing wireless transmitters face challenges in mitigating intermodulation distortion caused by non-linear hardware components, which leads to contamination of nearby frequency channels and increased costs due to the need for pre-distortion and other linearization techniques.
Innovation Solution
A method involving a wireless transmitter with multiple signal branches, each with a non-linear hardware component, where the input signal is modified by applying specific phase shifts to different parts of the signal spectrum to mitigate intermodulation distortion, allowing for the cancellation or reduction of intermodulation components without the need for pre-distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If pre-distortion is applied to compensate for non-linearity, then intermodulation distortion is reduced, but signal bandwidth must be widened and component requirements become more demanding
Solution Approach 1:
Instead of applying pre-distortion to linearize the non-linear power amplifier, the patent applies post-distortion by intentionally introducing additional non-linearity after the power amplifier. This inverted approach uses non-linear filtering to suppress intermodulation products while allowing the power amplifier to operate in its highly non-linear high-efficiency region, thereby reducing distortion without increasing component bandwidth requirements
Solution Approach 2:
The patent changes the operating parameters of the system by allowing the power amplifier to operate at higher compression points (more non-linear operation) while compensating for the resulting distortion through post-distortion processing. This parameter change enables high efficiency operation while controlling intermodulation distortion through the non-linear filter's selective frequency response
2Object-generated harmful factors
If pre-distortion is applied to mitigate intermodulation distortion, then distortion is reduced, but power consumption increases
Solution Approach 1:
The patent inverts the conventional linearization approach by applying distortion compensation after the power amplifier rather than before. This allows the power amplifier to operate at maximum efficiency without the need for pre-distortion processing, thereby significantly reducing the power consumption associated with real-time pre-distortion calculation and application while still achieving distortion suppression through post-distortion filtering
3Productivity
If multi-carrier techniques are used to increase bandwidth, then data rate is improved, but intermodulation distortion spreads over a wider frequency range
Solution Approach 1:
The patent converts the harmful effect of multi-carrier operation by using the known structure of multi-carrier signals (such as OFDM subcarriers) to design the non-linear filter's frequency response. The filter is specifically configured to target and suppress intermodulation products generated by multi-carrier operation while preserving the desired multi-carrier signal, thereby enabling high data rates without the usual distortion spread problem
4Use of energy by moving object
If non-linear hardware components are used to achieve high power amplifier efficiency, then energy efficiency is improved, but intermodulation distortion is generated
Solution Approach 1:
The patent segments the transmitter into distinct functional sections: a non-linear power amplifier section that operates at high efficiency, and a separate non-linear filtering section that suppresses distortion. This segmentation allows each section to be optimized independently - the power amplifier for efficiency and the filter for distortion suppression - thereby resolving the contradiction between efficiency and distortion generation
Solution Approach 2:
The non-linear filter acts as an intermediary element between the power amplifier and the antenna. It selectively processes the power amplifier's output to suppress intermodulation products while passing the desired signal, thereby mediating between the high-efficiency non-linear operation of the power amplifier and the low-distortion requirement at the transmitter output
Data Source
AI summary
A method of a wireless transmitter is disclosed. The method is for mitigation of distortion caused by non-linear hardware components of the transmitter, wherein mitigation of distortion comprises mitigating at least one intermodulation component, wherein the transmitter is configured to process an input signal having an input signal spectrum, and wherein the transmitter comprises two or more signal branches, each signal branch comprising a respective non-linear hardware component. The method comprises modifying the input signal for a first one of the signal branches by applying a first phase shift to a first part of the input signal spectrum, wherein the first phase shift has a first sign and a first absolute value, and applying a second phase shift to a second part of the input signal spectrum. The second phase shift has a second sign which is opposite to the first sign, and a second absolute value which is equal to the first absolute value. The first and second parts are non-overlapping. The method also comprises modifying the input signal for a second one of the signal branches by applying the first phase shift to the second part of the input signal spectrum, and applying the second phase shift to the first part of the input signal spectrum. The method further comprises feeding the modified input signals to respective ones of the signal branches. Corresponding apparatus, wireless transmitter, communication device, and computer program product are also disclosed.