Uncorrelated Phase Rotation Polarity in CPM Signals
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Solution Overview
Problem
Conventional continuous phase modulation (CPM) methods, such as MSK and GMSK, suffer from phase transition polarity ambiguity, leading to net frequency shifts, spreading of PN symbol information, and degradation of time acquisition performance in receivers, particularly for navigational signals, due to fixed or alternating phase rotation polarities.
Innovation Solution
The technique involves generating a phase modulated, constant envelope transmit signal with continuous phase transitions where the phase rotation polarity is controlled to be uncorrelated with the sequence of symbol states, maintaining deep autocorrelation nulls and spectral efficiency by patterning the phase rotation polarity over a sequence of symbols.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a fixed phase rotation polarity is used for all phase transitions in CPM, then the phase transitions are continuous and the envelope is constant, but a net frequency shift occurs which skews the frequency spectrum and degrades time acquisition performance
Solution Approach 1:
The patent applies dynamics by making the phase rotation polarity variable rather than fixed. The polarity is dynamically adjusted based on the current symbol state and the desired next symbol state, transitioning between positive and negative phase rotation directions as needed. This dynamic adjustment eliminates the net frequency shift while maintaining continuous phase transitions and constant envelope, thereby resolving the contradiction between envelope stability and time acquisition performance.
2Ease of manufacture
If a fixed phase rotation polarity is used for all phase transitions, then the modulation is simple to implement, but the autocorrelation function is degraded with filled-in side nulls
Solution Approach 1:
The patent makes the phase rotation polarity dynamic, switching between positive and negative based on the symbol transitions required. This dynamic polarity adjustment preserves the deep nulls in the autocorrelation function by ensuring that phase transitions do not systematically bias the correlation structure, while still maintaining the simplicity of CPM implementation through straightforward polarity switching logic.
3Shape
If alternating phase rotation polarity is used for each transition, then the frequency spectrum is symmetric, but the Q component has fixed polarity which generates unwanted clock spurs
Solution Approach 1:
The patent applies dynamics by making the phase rotation polarity variable, transitioning between positive and negative based on the specific symbol state changes required. This dynamic approach allows the system to achieve frequency spectrum symmetry when needed while avoiding fixed polarity patterns that would generate clock spurs, thus resolving the contradiction between spectral symmetry and harmful signal components.
Data Source
AI summary
A technique for generating a phase modulated, constant envelope transmit signal having continuous phase transitions between adjacent symbols involves generating a stream of symbols having a sequence of symbol states and identifying antipodal phase transitions between adjacent symbols representing different states. The phase rotation polarity of the continuous phase transitions between adjacent symbols having antipodal phase transitions is controlled such that a phase rotation polarity pattern of the antipodal phase transitions in the stream of symbols is uncorrelated with the sequence of symbol states. The constant envelope transmit signal is then generated from the stream of symbols. The spectral profile of the constant envelope signal can be tailored by selection of the phase trajectory shape and the portion of the symbol over which the continuous phase transition occurs.