TPSK Modulator Phase Shifter for Reduced Out-of-Band Emissions
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Solution Overview
Problem
Tone Phase Shift Keying (TPSK) signals exhibit phase discontinuity between symbols, leading to infinite bandwidth and uncontrolled out-of-band emissions due to lack of linearity when operating at saturation, which is problematic for practical transmitters and IoT devices requiring efficient power amplifiers.
Innovation Solution
A modulator with a phase shifter is used to apply a predetermined phase shift to the TPSK-modulated signal, reducing phase jumps and minimizing out-of-band spectral leakage, while maintaining constant amplitude and user orthogonality, by configuring the phase shifter to minimize or set phase shifts based on maximum phase jumps or average phase jumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If TPSK modulation is used to achieve constant amplitude for efficient power amplification, then power amplifier efficiency is improved, but phase discontinuity causes uncontrolled out-of-band emissions
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal phase shift values in lookup tables before transmission. The phase shifter retrieves and applies the appropriate phase shift value for each symbol based on the current and previous symbols, preventing phase discontinuity before it occurs. This proactive approach maintains constant amplitude while controlling spectral emissions.
Solution Approach 2:
The patent changes the phase parameter of the TPSK-modulated signal by applying a predetermined phase shift to reduce phase jumps between consecutive symbols. This parameter modification transforms the signal from having uncontrolled phase discontinuities to having controlled phase transitions, thereby reducing out-of-band emissions while maintaining the benefits of constant amplitude modulation.
2Object-generated harmful factors
If phase shift is applied to reduce phase jumps, then out-of-band emissions are reduced, but signal processing complexity increases
Solution Approach 1:
The patent performs preliminary action by pre-calculating all possible phase shift values and storing them in lookup tables during system initialization. During actual transmission, the phase shifter simply retrieves the appropriate value from the lookup table based on current and previous symbols, avoiding complex real-time calculations. This approach reduces runtime processing complexity while maintaining emission control.
Solution Approach 2:
The patent uses copying by creating lookup tables that store pre-computed phase shift values for all possible symbol transitions. Instead of performing complex phase optimization calculations in real-time, the system copies the appropriate pre-computed value from the lookup table, significantly simplifying the processing required during actual signal transmission.
3Use of energy by moving object
If constant amplitude modulation is used for saturation operation, then power efficiency is improved, but linearity is lost causing spectral leakage
Solution Approach 1:
The patent changes the phase parameter of the modulated signal while maintaining constant amplitude. By applying a predetermined phase shift that reduces phase jumps between consecutive symbols, the system preserves the constant amplitude property needed for saturation operation and power efficiency, while simultaneously improving signal linearity and reducing spectral leakage through controlled phase transitions.
Data Source
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Figure 4B
AI summary
The present invention relates to a modulator for generating a modulated signal with a reduced transmit spectrum, comprising a tone-phase shift keying unit configured to generate a TPSK-modulated signal, and a phase shifter configured to apply a predetermined phase shift to the TPSK-modulated signal to obtain a phase-shifted TPSK-modulated signal with reduced phase jumps.