FT Pre-coding for OFDM PAPR Reduction
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Solution Overview
Problem
Conventional power amplifiers for OFDM and OFDMA systems face inefficiencies due to high peak-to-average power ratio (PAPR), leading to increased costs, heat dissipation, and performance degradation, as they often operate in back-off mode to accommodate large signal peaks, resulting in excessive heat and higher power ratings.
Innovation Solution
Implementing Fourier Transform (FT) pre-coding in subscriber and base stations to generate time-domain signals with a lower PAPR, using Fast Fourier Transform (FFT) or Discrete Fourier Transform (DFT) blocks to preprocess data and control signals before transmission, thereby reducing the PAPR of multi-carrier signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power amplifiers operate in back-off mode to accommodate large signal peaks, then PAPR distortion is reduced, but device cost and heat dissipation increase
Solution Approach 1:
The patent applies preliminary action by performing FFT pre-coding on the input signal before it reaches the power amplifier. This preprocessing transforms the signal in the frequency domain to reduce the peak amplitude of the time-domain signal, thereby lowering PAPR before amplification. The pre-coding operation modifies the signal characteristics in advance, enabling the power amplifier to operate more efficiently without requiring excessive back-off, thus reducing heat dissipation while maintaining signal quality.
2Reliability
If power amplifiers use higher power ratings to accommodate signal peaks, then PAPR distortion is avoided, but device cost increases
Solution Approach 1:
The patent applies parameter changes by transforming the signal representation from time-domain to frequency-domain using FFT pre-coding. This parameter transformation allows the signal to be processed in a different domain where peak reduction can be achieved. By changing the domain of signal representation and applying appropriate filtering or shaping in the frequency domain, the time-domain signal exhibits reduced PAPR characteristics, enabling the use of lower-rated, more cost-effective power amplifiers.
3Device complexity
If conventional power amplifiers handle high PAPR signals, then system simplicity is maintained, but power efficiency and heat dissipation worsen
Solution Approach 1:
The patent introduces an intermediary component - the FFT pre-coding block - that acts as a mediator between the data source and the power amplifier. This intermediary performs frequency-domain processing to reshape the signal characteristics, specifically reducing PAPR, before the signal is amplified. The FFT pre-coder serves as a buffer that prepares the signal in a form more suitable for efficient amplification, improving power amplifier efficiency without requiring major system redesign.
Data Source
AI summary
A subscriber station for use in a wireless network capable of communicating according to a multi-carrier protocol, such as OFDM or OFDMA. The subscriber station comprises a size M Fourier Transform (FFT or DFT) block for receiving input symbols and generating M FT pre-coded outputs and a size N inverse Fourier Transform (IFFT or IDFT) block capable of receiving N inputs, where the N inputs include the M FT pre-coded outputs from the size M FT block. The size N IFT block generates N outputs to be transmitted to a base station of the wireless network. The input symbols comprise user data traffic to be transmitted to the base station. The size N IFT block also receives signaling and control information on at least some of N-M inputs. The FT pre-coding generates a time-domain signal that has a relatively lower peak-to-average power ratio (PAPR).