Crest Factor Optimization in Digital Repeater Systems
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Solution Overview
Problem
Repeater systems face inefficiencies due to the need for significant power amplifier backoff to prevent non-linear distortions, leading to increased error vector magnitude (EVM) in amplified signals, which can exceed permissible limits for different radio access technologies.
Innovation Solution
An optimization system that dynamically reduces the crest factor of carrier signals using crest factor reduction units, with meter units estimating error vector magnitude and adding inverse peaking signals to maintain EVM within permissible limits, thereby allowing for reduced power amplifier backoff and improved efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the power amplifier is operated closer to its saturation point to improve efficiency, then power efficiency is improved, but non-linear distortions increase leading to increased error vector magnitude
Solution Approach 1:
The invention applies preliminary action by reducing the crest factor of the modulated signal before it is fed to the power amplifier. This pre-processing of the signal removes peaks that would otherwise cause non-linear distortions when amplified, allowing the power amplifier to operate closer to saturation without exceeding the EVM limit. The crest factor reduction is performed in advance, enabling more efficient amplifier operation while maintaining signal quality.
2Loss of energy
If the power amplifier backoff is reduced to improve efficiency, then power efficiency is improved, but signal quality deteriorates due to non-linear distortions
Solution Approach 1:
The crest factor reduction is performed as a preliminary action before power amplification, removing signal peaks that would cause non-linear distortions. This allows the power amplifier to operate with minimal or zero backoff while maintaining signal quality within acceptable EVM limits, thereby reducing energy loss.
Solution Approach 2:
The invention introduces an intermediary processing stage (crest factor reduction unit) between the modulator and power amplifier. This intermediary removes harmful peaks from the signal, acting as a mediator that enables the power amplifier to operate efficiently without introducing non-linear distortions that would degrade signal quality.
3Use of energy by moving object
If the crest factor is reduced to improve power efficiency, then power amplifier efficiency is improved, but the error vector magnitude may exceed permissible limits
Solution Approach 1:
The invention implements feedback by continuously monitoring the error vector magnitude of the amplified signal and using this information to dynamically adjust the crest factor reduction amount. The EVM measurement feeds back to the crest factor reduction unit, which adapts its processing to ensure the EVM remains within permissible limits while maximizing power amplifier efficiency. This closed-loop control prevents EVM from exceeding limits while allowing optimal backoff settings.
Data Source
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Figure 5A
AI summary
An optimization system for use in a digital repeater system comprises at least one input port for receiving a carrier signal associated with a communication channel of a telecommunication network, at least one meter unit for obtaining an estimate of the error vector magnitude for the carrier signal, and at least one crest factor reduction unit for dynamically reducing, based on the estimate of the error vector magnitude, the crest factor of the carrier signal.