Power Amplifier Drive Prediction for DPD Over-Drive Control
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Solution Overview
Problem
In wireless communication systems, particularly 3GPP standards like WCDMA, maintaining an adequate adjacent channel leakage ratio (ACLR) is challenging due to high peak-to-average power ratios and unpredictable crest factors, which can lead to increased bit error rates and reduced system performance, as power amplifiers approach compression.
Innovation Solution
A method and apparatus for dynamic and adaptive selection of power amplifier drive levels using digital predistortion (DPD) to predict and manage over-drive conditions, involving the computation of expansion coefficients, look-up tables, and over-drive metrics to ensure linear operation and minimize spectral mask violations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the signal drive level is increased to improve signal-to-noise ratio, then radio link performance is improved, but the power amplifier approaches compression and generates more intermodulation products, increasing adjacent channel leakage ratio
Solution Approach 1:
The system performs preliminary detection of the power amplifier's compression point and predictively adjusts the drive level before the amplifier enters compression. By monitoring parameters like output power and intermodulation distortion in advance, the system proactively reduces the drive level to prevent excessive intermodulation product generation, rather than reacting after distortion occurs.
Solution Approach 2:
The system continuously monitors the power amplifier's output characteristics including output power, adjacent channel leakage ratio, and intermodulation distortion products. This feedback is used to dynamically adjust the drive level, creating a closed-loop control system that maintains optimal operation by balancing signal-to-noise ratio against intermodulation product generation.
2Object-generated harmful factors
If the drive level is reduced to minimize intermodulation products, then adjacent channel leakage ratio is improved, but signal-to-noise ratio decreases, compromising radio link performance
Solution Approach 1:
The system dynamically adjusts the drive level based on real-time conditions rather than using a fixed conservative setting. By continuously monitoring amplifier characteristics and signal conditions, the drive level is optimized moment-by-moment to achieve the highest possible signal-to-noise ratio while maintaining acceptable adjacent channel leakage ratio, avoiding the need for permanently reduced drive levels.
Solution Approach 2:
The system changes operational parameters including drive level, bandwidth, and detection thresholds based on measured conditions. When the amplifier is operating linearly, higher drive levels are permitted to maximize signal-to-noise ratio. When approaching compression, parameters are adjusted to reduce intermodulation products, creating an adaptive operating point that optimizes both contradictory requirements.
3Object-generated harmful factors
If digital predistortion is applied to linearize the power amplifier output, then spectral mask compliance is improved, but device complexity increases due to additional computation and processing
Solution Approach 1:
The system applies predistortion selectively rather than continuously, activating it only when measurements indicate the amplifier is approaching compression or when spectral violations are detected. This partial application reduces the computational burden compared to continuous predistortion while still preventing the majority of spectral mask violations, balancing performance improvement against processing complexity.
Data Source
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AI summary
A method and apparatus for efficient drive level selection for, e.g., power amplifiers (208) utilized within a wireless communication system, which utilizes digital predistortion (DPD) to adaptively and predictively select drive level. The DPD, e.g., increases the power amplifier's efficiency while maintaining spectral mask compliance within the designated frequency band of transmission. The method first determines a peak amplitude of an undistorted waveform that is to be transmitted (502), and then predicts the maximum power that is to be transmitted by the power amplifier (208) after the undistorted signal has been predistorted (508). An over-drive metric is then calculated based upon the predicted drive level of the power amplifier (208), which indicates whether or not the cascade of the predistorter (202) and the power amplifier (208) is predicted to operate linearly. The over-drive metric may then be used to ensure optimal power amplifier performance, thereby eliminating the need to use overly conservative power amplifier drive settings.