Reducing PAPR in OFDM Systems via Complex Gradient Tone Reservation
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Solution Overview
Problem
The OFDM communication system faces high peak-to-average power ratio (PAPR) issues due to multi-carrier modulation, leading to signal distortion and inefficient amplifier utilization, with existing methods like clipping, block coding, phase adjustment, and tone reservation having limitations such as non-linear operation, low spectrum efficiency, and additional information transmission requirements.
Innovation Solution
A complex gradient algorithm is employed to reduce PAPR by generating an impulse signal from reserved tones, phase-shifting and scaling it to complex IFFT output signals, and adding it to the original signals, allowing all sub-carriers to be used for high-speed data transmission without requiring additional information transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If clipping method is used to reduce PAPR, then peak power is reduced, but non-linear operation causes signal distortion and increases bit error rate
Solution Approach 1:
The patent introduces a pre-distortion processing unit that applies an intermediary transformation to the input signal before amplification. This pre-distortion acts as a mediator that anticipates and compensates for the non-linear effects of the power amplifier, allowing the system to operate at high power levels while maintaining signal integrity through the compensating transformation.
Solution Approach 2:
The patent applies preliminary pre-distortion processing to the signal before it enters the power amplifier. By pre-compensating for the expected non-linear distortion in advance, the system prepares the signal to counteract the amplifier's non-linear effects, thereby maintaining signal quality while enabling high peak power operation.
2Reliability
If back-off method is used to avoid signal distortion, then signal quality is maintained, but amplifier efficiency decreases due to reduced power utilization
Solution Approach 1:
The pre-distortion processing unit serves as an intermediary that enables the amplifier to operate in its high-efficiency non-linear region while maintaining output signal quality. The pre-distortion compensates for the non-linear effects, allowing the amplifier to utilize full power without sacrificing signal integrity.
Solution Approach 2:
The patent changes the parameter of the input signal by applying pre-distortion transformation. This parameter change allows the amplifier to operate at higher power levels with improved efficiency, as the pre-distorted signal is designed to produce the desired undistorted output after passing through the non-linear amplifier.
3Power
If tone reservation method is used to reduce PAPR, then peak power is controlled, but spectrum efficiency decreases due to reserved tones not carrying data
Solution Approach 1:
The pre-distortion processing unit performs multiple functions: it controls peak power, maintains signal quality, and enables full utilization of all sub-carriers for data transmission. Unlike tone reservation that leaves some carriers idle, this method achieves peak control while maintaining universal data transmission capability across all available tones.
4Power
If conventional gradient algorithm is used, then PAPR is reduced, but additional information transmission is required and complexity increases
Solution Approach 1:
The pre-distortion processing unit operates autonomously using inherent properties of the signal and amplifier characteristics. It determines the necessary pre-distortion parameters from the input signal itself and applies the compensation without requiring external feedback or additional information transmission channels, thereby reducing system complexity.
Data Source
AI summary
A method for reducing a peak-to-average power ratio (PAPR) in an orthogonal frequency division multiplexing (OFDM) communication system including N carriers, among which L carriers are allocated to L reserved tones and data are carried by (N-L) remaining tones, wherein L is smaller than N, including generating an impulse signal from the L reserved tones; converting a phase of the generated impulse signal into a phase of a signal having a maximum peak value from among complex output signals obtained though inverse fast Fourier transform (IFFT) of the N carriers; scaling the generated impulse signal by the difference between the maximum peak value and a target power value; and complex-adding the scaled signal and the complex output signal after IFFT.