Modification Pulses for OFDM Signal Power Profile Control
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Solution Overview
Problem
Conventional wireless systems, such as OFDM systems, face challenges with high peak-to-average power ratio (PAPR) leading to high error vector magnitude (EVM) and interference, which existing clipping and filtering methods fail to adequately address.
Innovation Solution
The proposed solution involves modifying the power profile of transmitted signals by selectively lowering power using modification pulses. These pulses are designed to raise PAPR while minimizing spectral splatter and EVM, and can be generated based on the output signal characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional clipping and filtering methods are used to address high PAPR, then peak power reduction is achieved, but error vector magnitude increases and signal quality deteriorates
Solution Approach 1:
The patent introduces an intermediary signal processing stage between the OFDM modulator and power amplifier that uses complex signal manipulation (involving multiple signal paths with different delays and phase shifts) to reduce PAPR before amplification, thereby avoiding the need for aggressive clipping that would increase EVM. This intermediary processing allows the power amplifier to operate in a more linear region without requiring excessive peak power reduction.
Solution Approach 2:
The patent transforms the signal representation by changing parameters in the complex signal domain, using mathematical operations to modify the amplitude and phase characteristics of the OFDM signal. By operating on the complex baseband signal rather than directly clipping the real-valued waveform, the system can reshape the power profile while maintaining signal integrity and minimizing EVM degradation.
2Reliability
If high-resolution DAC and wide linear region PA are used, then signal quality is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies preliminary signal processing to pre-distort or pre-condition the OFDM signal before it reaches the DAC and power amplifier. By proactively shaping the signal's power profile and compensating for potential nonlinearities in advance, the system enables the use of lower-resolution DACs and power amplifiers with smaller linear regions while still achieving acceptable signal quality at the output.
3Power
If peak values are clipped, then PAPR is reduced, but spectral splatter and out of band interference increase
Solution Approach 1:
The patent replaces direct temporal clipping (a mechanical-like operation in the time domain) with complex signal processing operations in the frequency and complex baseband domains. Instead of abruptly truncating peak values, the system uses mathematical transformations that smoothly reshape the signal envelope, thereby reducing PAPR while maintaining spectral containment and minimizing out-of-band emissions.
Data Source
AI summary
A method can include receiving a plurality of digital data symbols; encoding each data symbol into frequency domain values, the frequency domain values for each data symbol transmitted over a different frequency range; combining samples of multiple frequency domain values into a sequence of initial output values in time; generating a sequence of modification values that form a modification pulse, the modification pulse having a non-linear slope that decreases as it approaches a modification pulse maximum and increases as it departs from the modification pulse maximum; decreasing the initial output values according to the modification values to generate modified output values; and transmitting a wireless signal compatible with at least one IEEE wireless standard according to the modified output values. Corresponding devices and systems are also disclosed.