SC-FDMA Peak Window Clipping for Lower Power Amplifier Drain
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Solution Overview
Problem
LTE SC-FDMA uplink systems face increased peak-to-average power ratio due to pulse shaping filters, leading to reduced power amplifier efficiency and faster power supply drainage, which is undesirable in mobile communication devices.
Innovation Solution
The method employs window clipping to suppress peak-to-average power ratio by sampling input signals, predicting peak samples, and adjusting window length based on peak width or subcarrier number, with optional interpolation and dynamic threshold adjustment to optimize power amplifier performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If pulse shaping filters are used in LTE transmitters, then out-of-band emission is reduced, but peak-to-average power ratio increases
Solution Approach 1:
The pulse shaping filter is segmented into multiple filter banks, each handling different frequency subcarriers independently. This segmentation allows selective optimization where filters can be designed to minimize out-of-band emission in critical frequency regions while using shorter filter lengths in other regions, thereby reducing the overall peak-to-average power ratio without completely sacrificing spectral containment.
Solution Approach 2:
Different filter characteristics are applied to different parts of the frequency spectrum. Specifically, filters with longer impulse responses are used where out-of-band emission control is most critical, while shorter filters are used in regions where spectral containment is less stringent. This local optimization balances the trade-off between out-of-band emission reduction and peak-to-average power ratio control.
2Reliability
If peak-to-average power ratio increases, then power amplifier efficiency decreases, but power supply drainage increases
Solution Approach 1:
The filter bank structure enables dynamic adjustment of filter characteristics based on transmission conditions. The system can adaptively select filter lengths and characteristics for different subcarriers and time slots, optimizing the balance between power amplifier efficiency and power consumption. This dynamic adaptation allows the system to maintain acceptable out-of-band emission while minimizing peak-to-average power ratio under varying operational conditions.
Solution Approach 2:
The invention changes the parameters of the pulse shaping filter, specifically the filter length and characteristics, to optimize system performance. By using a bank of filters with different parameters rather than a single fixed filter, the system can adjust filter parameters to achieve better power efficiency while maintaining spectral containment requirements.
Data Source
AI summary
A method for controlling peak-to-average power ratio prior to amplification by a power amplifier is provided. The peak sample of a signal is predicted, window length is adjusted based on the peak width around the peak sample or subcarriers used to transmit the signal, and the window is subsequently used to clip the samples. A peak suppression window may be applied prior to predicting the peak sample when a set number of samples exceed a predetermined threshold. Window clipping may be deactivated if interference and throughput of the power amplifier is detrimentally affected. A pulse shaping filter may be optimized based on the window clipping to control transmitted signal characteristics. Various thresholds used in the prediction may be initially based on system design and power amplifier linearity and then dynamically adjusted based on an estimation of active subcarriers or of interferers present in the communication system.