QAM OFDM Signal Peak-to-Average Power Ratio Reduction
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Solution Overview
Problem
Existing techniques fail to effectively reduce the peak-to-average power ratio (PAR) in quadrature amplitude modulated (QAM) orthogonal frequency division multiplexed (OFDM) radio frequency signals, leading to inefficiencies in high power amplifier operation and increased out-of-band emissions.
Innovation Solution
A method that involves quadrature amplitude modulation, limiting the magnitude of the modulated symbol vector, demodulating and constraining QAM constellations to specific thresholds, and remodulating the signal to produce a modified OFDM symbol, which reduces PAR while controlling out-of-band emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM modulation is used to transmit digital signal over multiple subcarriers, then spectral efficiency and resistance to multipath distortion are improved, but peak-to-average power ratio increases causing amplifier inefficiency and out-of-band emissions
Solution Approach 1:
The patent applies preliminary action by performing magnitude limiting on the OFDM symbol vector before transmission. This pre-processing step constrains the signal peaks in advance, preventing the high PAR from causing amplifier distortion and out-of-band emissions while preserving the spectral efficiency benefits of OFDM modulation
Solution Approach 2:
The patent changes the signal parameter by applying magnitude limiting to constrain the OFDM symbol vector within a predetermined range. This parameter modification reduces the peak-to-average power ratio by controlling the signal envelope, allowing the High Power Amplifier to operate more efficiently without generating excessive out-of-band emissions
2Use of energy by moving object
If High Power Amplifier operates at high power to maintain efficiency, then power efficiency is improved, but peak distortion increases causing subcarrier modulation distortion and out-of-band emissions
Solution Approach 1:
The patent performs preliminary magnitude limiting on the OFDM symbol vector to remove or reduce peaks before amplification. This pre-processing ensures that when the High Power Amplifier operates at high power for efficiency, the signal peaks are already constrained, preventing distortion and maintaining signal quality
Solution Approach 2:
The patent converts the potentially harmful effect of high PAR into a benefit by using the magnitude limiting process to shape the signal envelope. The constrained peaks become advantageous by enabling high-power amplifier operation without distortion, thus improving both efficiency and signal quality
Data Source
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AI summary
A peak-to-average power reduction method includes: (a) quadrature amplitude modulating a signal including a set of subcarriers with a set of data to produce an OFDM modulated symbol vector; (b) limiting the magnitude of the modulated symbol vector to produce a first limited OFDM modulated symbol; (c) demodulating the first limited OFDM modulated symbol to recover distorted QAM constellations; (d) constraining points in the distorted QAM constellations recovered from the first limited OFDM modulated symbol to produce constrained QAM constellations; (e) modulating an OFDM symbol vector with the constrained QAM constellations to produce a modified modulated OFDM symbol; and (f) output the modified modulated OFDM symbol. A transmitter that implements the method is also provided.