Adaptive Peak Reduction Filtering for OFDM Signal Control
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Solution Overview
Problem
Current wireless communication systems face challenges in reducing peak power requirements, particularly with the adoption of multi-channel signaling and orthogonal frequency-division multiplexing (OFDM) waveforms, which lead to increased peak magnitudes and spectral regrowth, violating regulatory spectral masks and incurring high costs due to the need for expensive amplifiers.
Innovation Solution
A signal processing system that generates an excursion signal by identifying peaks exceeding a threshold, dynamically scales and filters these signals to remove unwanted frequency components, and subtracts the filtered excursion from the original signal to reduce peak power, while adapting to varying channel power levels and error vector magnitude constraints.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If clipping is used to reduce peak power requirements, then amplifier cost is reduced, but spectral regrowth occurs violating regulatory spectral masks
Solution Approach 1:
The signal processing is segmented into multiple stages: excursion signal generation, filtering to remove unwanted frequency components, scaling to adjust amplitude, and subtraction from the original signal. This segmented approach reduces peak power while controlling spectral regrowth, avoiding the need for expensive amplifiers without violating spectral masks.
Solution Approach 2:
The harmful peak portions (excursion signals) are extracted from the original signal, processed separately through filtering and scaling, then subtracted back. This extraction approach removes the problematic spectral regrowth components while preserving the essential signal information, resolving the contradiction between cost reduction and spectral compliance.
2Object-generated harmful factors
If expensive high peak-power amplifiers are used to accommodate peak signals, then spectral mask compliance is maintained, but system cost increases exponentially
Solution Approach 1:
The patent applies preliminary signal processing actions (excursion generation, filtering, scaling, and subtraction) before the signal reaches the amplifier. By pre-reducing the peak power requirements through these preliminary operations, the system can use less expensive amplifiers while still maintaining spectral mask compliance, avoiding exponential cost increases.
Solution Approach 2:
The excursion signal processing chain acts as an intermediary between the original signal and the amplifier. This intermediary processing stage controls spectral regrowth and reduces peak power before amplification, enabling the use of cost-effective amplifiers without sacrificing spectral mask compliance.
3Power
If the magnitude threshold is lowered to reduce peaks more aggressively, then peak power reduction is enhanced, but signal-to-noise ratio deteriorates
Solution Approach 1:
The magnitude threshold is made dynamic rather than fixed, allowing the system to adapt the threshold level based on signal conditions. This dynamic adjustment enables optimal peak power reduction while maintaining adequate signal-to-noise ratio, resolving the contradiction between aggressive peak reduction and signal quality preservation.
Solution Approach 2:
The system monitors signal conditions and adjusts the magnitude threshold accordingly through feedback mechanisms. This feedback control ensures that peak power reduction is optimized without excessively degrading the signal-to-noise ratio, balancing both competing requirements.
Data Source
AI summary
A signal processing system according to various aspects of the present invention includes an excursion signal generator, a scaling system and a filter system. The excursion signal generator identifies a peak portion of a signal that exceeds a threshold and generates a corresponding excursion signal. The scaling system applies a real scale factor to contiguous sets of excursion samples in order to optimize peak-reduction performance. The filter system filters the excursion signal to remove unwanted frequency components from the excursion signal. The filtered excursion signal may then be subtracted from a delayed version of the original signal to reduce the peak. The signal processing system may also control power consumption by adjusting the threshold. The signal processing system may additionally adjust the scale of the excursion signal and/or individual channel signals, such as to meet constraints on channel noise and output spectrum, or to optimize peak reduction. The magnitude threshold, excursion signal and/or individual channel signals may also be adaptively adjusted based on, for example, a channel signal quality such as a noise level specification.