Transmitter Peak-Null Clipping for Power De-rating Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
COFDM systems face inefficiencies due to high peak-to-average power ratio (PAR) and cubic metric (CM), leading to power amplifier inefficiency and spectral regrowth, while existing solutions like power backoff and signal clipping cause interference and efficiency losses.
Innovation Solution
A transmitter structure is implemented within a single carrier-frequency division multiple access (SC-FDMA) system that includes a peak-null clipping block to adjust symbol amplitudes, reducing PAR and CM through sub-carrier mapping and inverse discrete Fourier transform (IDFT) processing, followed by cyclic prefix addition and power amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If power amplifier operates at large output power backoff to reduce non-linearity, then spectral regrowth is reduced, but power efficiency deteriorates
Solution Approach 1:
The patent applies preliminary action by pre-processing the signal before power amplification. Specifically, the signal undergoes clipping in the frequency domain (after FFT) to reduce peak-to-average power ratio before being converted to time domain and amplified. This preliminary signal processing reduces the dynamic range requirements and allows the power amplifier to operate more efficiently without excessive spectral regrowth.
Solution Approach 2:
The patent changes the signal parameters by transforming the time-domain signal to frequency domain using FFT, applying clipping in the frequency domain, and then transforming back using IFFT. This parameter transformation allows clipping to be applied more effectively, reducing the peak-to-average power ratio and enabling better power amplifier operation with reduced spectral regrowth.
2Power
If signal clipping is applied directly to reduce PAR, then peak-to-average power ratio is reduced, but spectral regrowth and inter-carrier interference increase
Solution Approach 1:
The patent applies preliminary action by performing FFT on the signal before clipping. This transforms the signal to the frequency domain where clipping can be applied more selectively and effectively. The clipping is performed on the frequency-domain components, and then the inverse FFT reconstructs the time-domain signal with reduced peak-to-average power ratio and minimized harmful effects.
Solution Approach 2:
The patent changes the domain in which clipping is applied by using FFT to transform the signal from time domain to frequency domain. This parameter change allows clipping to be applied to frequency components rather than time-domain samples, resulting in better control over the peak-to-average power ratio and reduced spectral regrowth and inter-carrier interference.
3Power
If DFT-SOFDM is used to reduce PAR and CM, then power de-rating is reduced, but implementation complexity increases
Solution Approach 1:
The patent applies universality by using a single DFT-SOFDM transmitter structure that performs multiple functions: it implements the modulation scheme, performs the FFT/IFFT transformations, applies clipping in the frequency domain, and handles the cyclic prefix addition. This unified approach reduces the overall system complexity compared to separate implementations of each function, while achieving reduced PAR and CM.
Data Source
AI summary
A wireless transmitter is configured to map N first samples of a first discrete Fourier transform (DFT) of a group of coded symbols to M sub-carriers according to a first sub-carrier mapping rule. In this case, M is greater than N. The wireless transmitter is also configure to perform a first inverse DFT (IDFT) on the M sub-carriers to provide M second samples and clip the M second samples according to a clipping rule to provide M third samples. The wireless transmitter is further configured to perform a second DFT on the M third samples, de-map the M third samples to N fourth samples, and map the N fourth samples to O subcarriers according to a predetermined second subcarrier mapping rule. In this case, O is greater than or equal to M.