Multi-Carrier Constant Envelope Signal Generation for Power Amplifier Efficiency
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Solution Overview
Problem
Conventional multi-carrier waveforms, such as OFDM, do not produce constant envelope composite signals, leading to signal distortions and performance degradation due to non-linearities in power amplifiers, necessitating expensive, highly linear amplifiers and reduced power efficiency.
Innovation Solution
A technique that generates a constant-amplitude inphase and quadrature composite signal through majority voting of multiple signals, allowing these components to modulate a carrier signal and combine into a constant-envelope composite signal, using scale factors to equalize power and maintain a constant envelope, enabling the use of inexpensive, efficient amplifiers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional multi-carrier waveforms (OFDM) are used to achieve wide bandwidth and robustness to channel fades, then communication reliability is improved, but signal distortions and performance degradation occur due to non-linearities in power amplifiers
Solution Approach 1:
The patent transforms the multi-carrier signal into a constant envelope form by changing the amplitude parameter from variable (in OFDM) to constant. This is achieved through coordinate transformation where the in-phase and quadrature components are converted to magnitude and phase components, with the magnitude being constrained to a constant value. This parameter change allows the signal to be amplified using non-linear power amplifiers without generating signal distortions, while maintaining the multi-carrier structure's robustness to channel fades.
2Manufacturing precision
If expensive, highly linear amplifiers are used to minimize signal distortions, then signal quality is improved, but power efficiency deteriorates due to power backoff
Solution Approach 1:
The patent replaces expensive, highly linear power amplifiers with inexpensive, non-linear power amplifiers. By transforming the signal into constant envelope form, the system can use cheap non-linear amplifiers without sacrificing signal quality, as the constant envelope property immunizes the signal against non-linear distortions. This substitution dramatically improves power efficiency while maintaining signal quality.
3Reliability
If power is backed off to maintain operation in the linear range, then amplifier linearity is improved, but power efficiency deteriorates significantly
Solution Approach 1:
The patent converts the harmful effect of amplifier non-linearity into a beneficial property. By transforming the signal into constant envelope form, the non-linearity of the power amplifier no longer causes signal distortions but instead enables the amplifier to operate at maximum power output. The constant envelope ensures that the signal's amplitude information is preserved even when passed through a non-linear amplifier, effectively converting the amplifier's non-linearity from a source of distortion into an enabler of high-power efficient operation.
4Adaptability or versatility
If multiple carriers are combined to achieve wide effective bandwidth, then communication robustness is improved, but the composite signal envelope becomes non-constant
Solution Approach 1:
The patent applies coordinate transformation to change the representation of the multi-carrier signal from the conventional in-phase/quadrature amplitude representation to a magnitude/phase representation. In this transformed coordinate system, the magnitude (envelope) is constrained to be constant while the phase varies to carry the multi-carrier information. This parameter change allows the composite signal to maintain both wide bandwidth (through multiple carriers) and constant envelope (through the transformed representation), resolving the contradiction between bandwidth efficiency and envelope stability.
Data Source
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AI summary
A technique for combining a plurality of signals to form a multi-carrier constant- envelope composite signal includes generating a constant-amplitude inphase (I) composite signal based on a majority vote of a first set of signals and generating a constant-amplitude quadrature (Q) composite signal based on a separate majority vote of a second set of signals. The I and Q components of a earner signal are respectively modulated with the I and Q composite signals and combined to form the constant-envelope composite signal. In the case where a single offset carrier code is a constituent of the constant-envelope composite signal, a scale factor is applied to one of the I and Q composite signals to equalize the power of the I and Q components of the offset carrier code.