Crest Factor Reduction Processor for Wireless Base Stations
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Solution Overview
Problem
Conventional peak reduction techniques in spread spectrum communications systems, such as those used in WCDMA and CDMA2000, are ineffective in reducing peaks in multi-carrier signals, often causing peak regrowth and introducing distortion, and are not suitable for real-time adjustments in wireless base stations.
Innovation Solution
A peak compression circuit function is implemented in the transmit path of wireless base stations, which applies multiple peak compression operations sequentially after digital upconversion, using peak detection and cancellation circuits to identify and reduce peak amplitudes with minimal impact on neighboring amplitudes, and includes user-definable cancellation thresholds and pulse amplitudes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional peak reduction techniques are used in spread spectrum communications, then peak amplitudes are reduced, but peak regrowth and distortion occur, making the techniques ineffective for multi-carrier signals
Solution Approach 1:
The peak reduction process is divided into multiple sequential stages, with each stage operating on different aspects of the signal. The first stage performs initial peak detection and reduction, while subsequent stages refine the process by detecting remaining peaks and applying targeted compression. This segmentation allows each stage to focus on specific peak characteristics, preventing regrowth and distortion that occur in single-stage conventional approaches.
Solution Approach 2:
The system performs preliminary peak detection and characterization before applying compression. By analyzing the signal structure and identifying peak candidates in advance, the system can apply targeted compression only where needed, rather than applying blanket reduction that causes distortion. This preliminary action enables more precise peak management while preserving signal quality.
2Reliability
If peak compression is applied to reduce peak-to-average power ratio, then communication quality improves, but device complexity increases due to multiple sequential operations
Solution Approach 1:
The peak compression function is segmented into multiple independent stages that can be implemented sequentially in time or in parallel using multiple processors. Each stage performs a specific function (peak detection, peak characterization, compression application), allowing the system to achieve high compression ratios while managing complexity through modular design. The segmented approach enables real-time processing by distributing computational tasks across multiple operational phases.
3Productivity
If conventional peak reduction is used in real-time wireless base stations, then processing speed is maintained, but the techniques cannot effectively handle multi-carrier signals
Solution Approach 1:
The peak compression system is designed to be dynamic and adaptable to different signal conditions. The multiple stages can be configured with different detection thresholds and compression parameters depending on the specific multi-carrier signal characteristics. This dynamic configuration allows the system to maintain real-time processing capability while adapting to various signal scenarios, making it versatile enough to handle different multi-carrier communication modes without requiring separate dedicated processing paths.
Data Source
AI summary
A wireless base station (15) for transmitting spread spectrum signals is disclosed. The base station (15) includes a peak compression unit (16), which is comprised of a sequence of peak detection and cancellation circuits (32). Each peak detection and cancellation circuit (32) detects and compresses identified peaks. The further stages of peak detection and cancellation circuits (32) serve to reduce peaks that, as a result of “peak regrowth”, are caused at sample points near to a reduced peak point. According to one disclosed embodiment, a peak sample point is not qualified for compression unless a number of sample points subsequent to the peak all have lower magnitude than that of the peak. The cancellation pulses applied by the peak detection and cancellation circuits (32) may be generated by a finite impulse response (FIR) filter pulse, or alternatively by a minimum phase infinite impulse response (IIR) pulse. The peak compression unit (16) identifies and compresses statistical peaks in the digital symbol amplitude, so that the dynamic range requirements of the power amplifier (24) in the base station (15) may be relaxed.