CPM Demodulator Using Parallel Linear Filters
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Solution Overview
Problem
Current CPM demodulator designs face high complexity, especially for longer pulse lengths, which limits their implementation on digital hardware platforms and reduces spectral efficiency, particularly for coherent demodulation of constant or quasi-constant envelope CPM signals.
Innovation Solution
A low complexity demodulator design using K parallel linear discrete filters after a bank of matched filters to reduce intersymbol interference, combined with a memoryless ML or MAP detector, and optional soft decision feedback for improved accuracy, allowing for efficient signal processing across various CPM configurations and pulse lengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If optimal CPM demodulator is used, then demodulation performance is improved, but device complexity increases exponentially with pulse length
Solution Approach 1:
The patent segments the complex optimal demodulator into multiple parallel linear discrete filters, each processing a specific pulse length. This segmentation allows the system to handle different pulse lengths independently, reducing the overall computational complexity from exponential to linear growth with pulse length, while maintaining near-optimal demodulation performance through parallel processing.
2Productivity
If phase smoothing pulses with longer length are used, then spectral efficiency is improved, but intersymbol interference increases
Solution Approach 1:
The patent introduces parallel linear discrete filters as intermediary components between the received signal and the detector. These filters act as mediators that selectively process signals with different pulse lengths, allowing the system to maintain long pulse lengths for spectral efficiency while canceling out the harmful intersymbol interference through the filtering operation before detection.
3Device complexity
If CPM decomposition techniques are applied, then device complexity is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The patent replaces the complex mechanical/trellis-based demodulation system with a streamlined system using parallel linear discrete filters. This substitution reduces computational complexity by eliminating the need for complex trellis structures and state machine operations, while the filter-based approach requires precise implementation of filter coefficients and timing, shifting the precision requirements to the filter design and signal synchronization aspects.
Data Source
AI summary
To reflect advantages of continuous phase modulation (CPM), the invention provides a low complexity transmitter and receiver to transmit and receive CPM signals and addresses a significant reduction in the CPM demodulator complexity, and is especially well-suited for large values of L, e.g., L≥3. The invention utilizes a linear filter front end as an integral part of the CPM demodulation process to reduce the ISI inherent in CPM transmit signal, and minimizes the influence of L in the reception process. To that end, the invention renders the complexity of a CPM demodulator non-exponentially dependent on L, and L only has a weak impact on the number of coefficients of the linear front end filters. Moreover, the invention provides a simple way of forming CPM signals for a digital communication transmitter using parallel Time Invariant Phase Encoders, which simplifies the production of CPM waveforms on software or hardware.