Crest Factor Reduction for Multi-Carrier RF Signals
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Solution Overview
Problem
In multi-carrier RF systems, 'superpeak' situations occur due to closely spaced signals, leading to peak re-growth even after cancellation algorithms are applied, resulting in peaks larger than the original peak, which complicates achieving the required adjacent channel leakage ratio (ACLR) and error vector magnitude (EVM) standards.
Innovation Solution
A system comprising a crest factor reduction (CFR) unit with a peak detector, cancellation pulse calculator, and output logic that calculates and applies a cancellation pulse to reduce the peak-to-average ratio (PAR) of the wideband signal, using a combination of peak detection, gain calculation, contribution approximation, and coefficient calculation to generate a cancellation pulse that matches the peak's envelope and phase information, thereby reducing peak re-growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a cancellation pulse algorithm is used to reduce peak-to-average ratio, then the adjacent channel leakage ratio requirement is improved, but peak re-growth occurs causing new peaks larger than the original peak
Solution Approach 1:
The cancellation pulse algorithm segments the peak cancellation task by identifying individual carrier contributions to the peak and processing them separately. The system calculates the contribution of each carrier to the peak and generates carrier-specific cancellation pulses, then combines them to form the total cancellation pulse. This segmentation allows precise control over which carriers are cancelled and prevents unintended peak re-growth from residual interference.
Solution Approach 2:
The system dynamically adjusts the cancellation pulse parameters including the pulse width, amplitude, and timing based on the detected peak characteristics and carrier contributions. By changing these parameters adaptively, the system optimizes the cancellation effect while minimizing the creation of new peaks. The pulse width is adjusted to match the carrier spacing, and the amplitude is scaled to achieve the required ACLR without causing excessive peak reduction.
2Loss of energy
If simple clipping is used to reduce peak-to-average ratio, then the power amplifier efficiency is improved, but a noise floor across the frequency is generated
Solution Approach 1:
The system converts the harmful effect of peak clipping into a beneficial cancellation mechanism. Instead of simply clipping peaks and accepting the resulting noise floor, the system detects the clipped peaks and generates cancellation pulses that target the specific carrier contributions causing the peaks. This transforms the clipping artifact into a controlled cancellation process that reduces peaks without generating broadband noise.
Solution Approach 2:
The cancellation pulse algorithm acts as an intermediary between the clipped signal and the final output. It processes the clipped signal by identifying the peak locations and generating intermediate cancellation pulses that compensate for the clipping effects. This intermediary processing step removes the harmful noise floor while preserving the peak reduction benefits, effectively mediating between simple clipping and the final clean output.
3Productivity
If closely spaced multi-carrier signals are transmitted, then the spectral efficiency is improved, but superpeak situations occur leading to peak re-growth
Solution Approach 1:
The system performs preliminary peak detection and carrier contribution calculation before the actual signal transmission. By analyzing the multi-carrier signal in advance, the system identifies potential peak locations and calculates the contribution of each carrier to those peaks. This preliminary action allows the cancellation pulses to be pre-configured to prevent superpeak formation during transmission, enabling closely spaced carriers without reliability issues.
Solution Approach 2:
The system implements feedback by continuously monitoring the signal spectrum and adjusting the cancellation pulse parameters based on detected peak locations and carrier contributions. The feedback loop detects when peaks occur, calculates the relevant carrier contributions, and adjusts the cancellation pulses accordingly. This feedback mechanism allows the system to maintain spectral efficiency while dynamically preventing superpeak and peak re-growth conditions.
Data Source
AI summary
An apparatus and system are provided for crest factor reduction (CFR). Preferably, a peak from the wideband signal is detected. A gain from the magnitude of the peak and a threshold can then be calculated. Based on this information, each carrier's contribution to the peak can be approximated, and a cancellation pulse coefficient for each carrier from its contribution to the peak can be calculated. A base cancellation pulse can be calculated from the cancellation pulse coefficients for each carrier, and a cancellation pulse can be calculated from the base cancellation pulse and the gain, which can then be applied to the wideband signal.