Constant Envelope Waveform for Power Amplifier Efficiency
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Solution Overview
Problem
Wireless communication systems face challenges with high Doppler spread, phase noise, frequency mismatch, and low power efficiency, particularly at high frequencies, due to the sensitivity of OFDM to these impairments and its large peak-to-average power ratio (PAPR), which affects power amplifier efficiency and receiver design complexity.
Innovation Solution
A new waveform with constant amplitude in the discrete-time complex baseband representation is generated, using a summation of instantaneous frequency signals with a cyclic prefix and a Constant Amplitude Zero Autocorrelation (CAZAC) signal for multipath estimation, allowing robustness against Doppler, phase noise, and carrier frequency offsets by discarding impairments below a cutoff subcarrier index.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OFDM is used for efficient user and data multiplexing, then spectral efficiency is improved, but power amplifier efficiency deteriorates due to large PAPR
Solution Approach 1:
The patent changes the fundamental parameter of the waveform by using constant envelope modulation instead of conventional OFDM. The transmitted signal is designed to have constant amplitude (envelope), which allows power amplifiers to operate in their non-linear high-efficiency region without requiring large back-off values, thereby resolving the contradiction between spectral efficiency and power amplifier efficiency
Solution Approach 2:
The patent applies local quality by maintaining constant envelope property specifically at the transmitted signal level while still enabling efficient data transmission. The constant envelope constraint is applied locally to the amplitude characteristic, allowing the signal to achieve both good spectral efficiency through proper modulation design and high power amplifier efficiency through envelope constancy
2Reliability
If subcarrier width is increased to deal with large phase noise and Doppler spreads, then robustness to phase noise and Doppler is improved, but receiver design complexity increases due to non-flat channels requiring intra-subcarrier equalization
Solution Approach 1:
The patent changes the approach by using constant envelope modulation with carefully designed phase progression that inherently provides robustness to phase noise and Doppler effects. The constant envelope property combined with specific phase coding allows the system to achieve reliability without requiring large subcarrier widths, thereby avoiding the complexity of intra-subcarrier equalization
3Loss of energy
If constant envelope modulation is used to improve power efficiency, then power amplifier efficiency is improved, but sensitivity to frequency misalignments and Doppler spread increases
Solution Approach 1:
The patent applies local quality by designing the constant envelope signal with specific local phase properties that are robust to frequency misalignments and Doppler. The phase progression is carefully designed at local segments to maintain correlation properties even under frequency offsets, allowing the system to achieve both power efficiency and robustness to frequency-related impairments
4Loss of energy
If OFDM-PM is used to achieve constant envelope and high power efficiency, then power amplifier efficiency is improved, but performance loss occurs in AWGN channels compared to conventional OFDM
Solution Approach 1:
The patent changes the modulation parameters by using a specific constant envelope modulation scheme with optimized phase progression and pulse shaping. The design adjusts the phase transitions and timing parameters to minimize susceptibility to AWGN while maintaining constant envelope, thereby achieving both high power amplifier efficiency and acceptable bit error performance in AWGN channels
Data Source
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AI summary
The method comprises the generation of a waveform for application in the wireless communication system characterized by significant phase noise, Doppler spread, multipath, frequency instability, and/or low power efficiency by at the transmitter side: creating a discrete-time instantaneous frequency signal f̃[n]; appending a cyclic prefix with length LCP to the beginning of the discrete-time instantaneous frequency signal f̃[n] ; constructing a discrete-time unwrapped instantaneous phase φ[n]; constructing a discrete-time complex baseband signal, and appending at the beginning a Constant Amplitude Zero Autocorrelation, CAZAC, signal of length LCP for multipath detection; and passing the constructed discrete-time complex baseband signal through a digital-to-analog, DAC, converter to yield the continuous-time radio frequency signal s(t) after conversion to the carrier frequency.