Constant-Envelope Trellis Modulation for Power-Efficient QAM
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Solution Overview
Problem
Current communication systems using spectrally dense modulation schemes face inefficiencies due to non-constant envelope transmissions requiring high-linearity amplifiers, which are power inefficient, and are sensitive to power amplifier performance variability, necessitating complex monitoring systems and pre-distortion algorithms.
Innovation Solution
A method and system for transmitting spectrally dense, covertly modulated data using a power-efficient transmit chain by generating a transmit signal with a constant envelope and variable phase through combining a base symbol signal and a perturbation signal, allowing for non-constant envelope responses at the receiver without requiring high-power, linear amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If spectrally dense modulation schemes (QAM) are used, then spectral efficiency is improved, but power efficiency deteriorates due to requirement of high-linearity amplifiers
Solution Approach 1:
The modulation scheme is segmented into two independent components: a constant-envelope carrier signal and a perturbation signal. This segmentation allows the power amplifier to operate efficiently in saturation mode on the carrier while the perturbation signal carries the spectral information, resolving the contradiction between spectral efficiency and power efficiency
Solution Approach 2:
A perturbation signal acts as an intermediary between the constant-envelope carrier and the desired spectrally dense modulation. The perturbation signal modulates the carrier phase without requiring the power amplifier to operate in linear mode, enabling both spectral density and power efficiency
2Reliability
If complex pre-distortion algorithms are used to improve power efficiency, then power amplifier linearity is improved, but system complexity increases
Solution Approach 1:
The need for complex pre-distortion algorithms is extracted and eliminated by using constant-envelope modulation. The perturbation signal approach inherently compensates for power amplifier non-linearities without requiring additional complexity in the transmitter signal processing chain
Solution Approach 2:
The constant-envelope modulation scheme is self-compensating for power amplifier non-linearities. The perturbation signal's phase modulation automatically accounts for amplifier characteristics, eliminating the need for external pre-distortion complexity
3Use of energy by moving object
If constant envelope waveforms are used to improve power efficiency, then power efficiency is improved, but spectral efficiency deteriorates
Solution Approach 1:
The information transmission is moved from the amplitude dimension to the phase dimension. By modulating the phase of the constant-envelope carrier with the perturbation signal, spectral efficiency is achieved without compromising power efficiency, as the envelope remains constant
4Manufacturing precision
If high-linearity amplifiers are used to support spectrally dense modulation, then modulation accuracy is improved, but heat generation increases
Solution Approach 1:
The modulation function is segmented between the constant-envelope carrier (handled by efficient saturated amplifier) and the perturbation signal (carrying spectral information). This allows modulation accuracy to be maintained through precise perturbation signal design while the amplifier operates in the efficient saturated region, minimizing heat generation
Data Source
AI summary
A method of generating a transmit signal by a transmitter for transmission to a receiver includes receiving input data, generating a base symbol signal, the base symbol signal, generating a perturbation signal based on the input data, and combining the base symbol signal and the perturbation signal to generate the transmit signal.