Modified CPM Waveform Demodulation for Receiver Complexity Reduction
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Solution Overview
Problem
Current mobile wireless communications devices face challenges in achieving high spectral efficiency while maintaining a low peak-to-average ratio, leading to increased complexity, size, weight, and reduced battery life due to the need for complex demodulation techniques in continuous phase modulation (CPM) schemes.
Innovation Solution
A communications system that reduces complexity by generating a modified linear representation of the non-linear CPM waveform, allowing demodulation using a single symbol matched filter and a low-complexity MMSE-criterion equalizer, thereby trading a small increase in peak-to-average ratio for reduced receiver complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CPM modulation is used to achieve high spectral efficiency, then spectral efficiency is improved, but receiver complexity increases due to the need for MLSE-based demodulation
Solution Approach 1:
The patent modifies the CPM waveform parameters by using a reduced alphabet size (M=2 instead of M=4 or higher) and adjusting the modulation index h to specific rational values. This parameter change transforms the complex non-linear CPM signal into a form that can be demodulated with lower complexity while maintaining spectral efficiency above 1 bps/Hz
Solution Approach 2:
The patent segments the complex CPM demodulation problem into simpler components by using a reduced alphabet representation. This segmentation allows the receiver to process the signal in discrete, manageable steps rather than dealing with the full complexity of high-order CPM, enabling the use of simpler equalizers and decision feedback mechanisms
2Productivity
If QAM modulation is used to achieve high spectral efficiency, then spectral efficiency is improved, but peak-to-average ratio increases leading to higher power requirements
Solution Approach 1:
The patent changes the fundamental parameter of constellation size from QAM's typically 16-256 point constellations to a binary (M=2) CPM scheme. This parameter change inherently reduces the peak-to-average power ratio while maintaining spectral efficiency, as CPM with reduced alphabet produces more constant-envelope signals suitable for power-efficient transmission
3Power
If MSK or GMSK modulation is used to achieve low peak-to-average ratio, then power efficiency is improved, but spectral efficiency decreases to less than 1.25 bps/Hz
Solution Approach 1:
The patent adjusts the CPM modulation index h to specific rational values and uses reduced alphabet CPM with M=2, which modifies the spectral characteristics of the waveform. These parameter changes enable the system to achieve spectral efficiency greater than 1 bps/Hz while maintaining the low peak-to-average power ratio characteristic of MSK/GMSK, effectively bridging the performance gap between these two modulation types
Data Source
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AI summary
A communications system may include a first communications device that may include a transmitter and a modulator cooperating therewith to modulate a coded waveform using a constant phase modulation (CPM) to generate a non-linear CPM waveform, and generate a linear representation of the non-linear CPM waveform, the linear representation including a plurality of pulses. The transmitter and a modulator may further cooperate to remove at least some of the plurality of pulses to define a modified linear representation of the non-linear CPM waveform, and transmit the modified linear representation of the non-linear CPM waveform. The communications system may further include a second communications device that may include a receiver and a single pulse-matched filter linear demodulator cooperating therewith to demodulate the modified linear representation of the non-linear CPM waveform transmitted from the first communications device.