Power Amplifier Signal Limiting with Predictor Filters for Low PAR
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Solution Overview
Problem
Current power amplifiers in wireless cellular networks face challenges in reducing peak-to-average power ratio (PAR) without degrading error vector magnitude (EVM) and increasing adjacent channel leakage ratio (ACLR), especially for uplink signals, due to high computational complexity in existing pre-processing schemes.
Innovation Solution
A method involving predictor filters with different sets of coefficients to approximate the pulse-shape filter, determining the amplitude indicator, and using a modifier to limit the signal before applying the pulse-shape filter, reducing computational complexity while maintaining acceptable EVM and ACLR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If existing pre-processing schemes are used to reduce peak-to-average power ratio, then PAR reduction is achieved, but computational complexity increases significantly
Solution Approach 1:
The patent uses predictor filters that approximate the pulse-shape filter to create simplified copies of the filtering operation. Instead of directly applying the complex pulse-shape filter to predict signal peaks, the invention uses multiple simpler predictor filters with different coefficient sets that mimic the pulse-shape filter's behavior. This copying approach reduces computational complexity while maintaining acceptable accuracy in PAR prediction and reduction.
2Loss of energy
If signal limiting is applied to reduce PAR, then peak power is reduced, but error vector magnitude degrades
Solution Approach 1:
The patent applies preliminary action by predicting future signal peaks using predictor filters before the actual pulse-shape filtering occurs. The limiting operation is performed in advance based on these predictions, allowing the system to prepare appropriate scaling factors that will prevent excessive peak power while minimizing distortion to the signal. This timing of the limiting action before pulse-shaping helps maintain signal quality.
Solution Approach 2:
The invention dynamically adjusts the limiting operation by selecting different predictor filters from a set of filters with different coefficient sets. The system adapts to varying signal conditions by choosing the most appropriate predictor filter for the current signal characteristics, allowing flexible control over the trade-off between PAR reduction and EVM maintenance based on real-time signal conditions.
3Loss of energy
If signal limiting is applied to reduce PAR, then peak power is reduced, but adjacent channel leakage ratio increases
Solution Approach 1:
The patent incorporates feedback by using the output of predictor filters to inform the limiting operation. The predictor filters provide information about upcoming signal peaks, and this feedback is used to adjust the limiting scaling factors accordingly. This feedback mechanism allows the system to make informed limiting decisions that reduce PAR while being aware of the impact on signal spectrum and adjacent channel emissions, thereby controlling ACLR degradation.
Data Source
AI summary
A method for limiting peak-to-average power of a signal transmitted from a power amplifier. The method comprises: applying a pulse-shape filter to a first signal, thereby generating a second signal being a filtered version of the first signal; and outputting the second signal for transmission from a power amplifier. The method further comprises: applying each of a plurality of predictor filters to a respective instance of the first signal, each predictor filter approximating the application of the pulse-shape filter to the first signal based on a different respective set of filter coefficients, and each thereby generating a respective third signal. The method also further comprises determining an indicator of amplitude of each of the third signals, selecting the indicator corresponding to the largest of those amplitudes, generating a modifier based on the selected indicator, and using the modifier to limit the first signal prior to applying the pulse-shape filter.