Constant Envelope Demodulation for Frequency-Offset-Resilient CPM
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Solution Overview
Problem
Current spread spectrum coding techniques face challenges in achieving good autocorrelation properties, especially in multi-code DS-CDMA systems, and are not resilient to large frequency offsets, which affects battery life and decoding efficiency in wireless communication systems like WBANs.
Innovation Solution
The method involves using differential m-sequences and generalized Golay sequences for spreading and despreading, combined with constant envelope or quasi-constant envelope modulations like CPM, to enhance autocorrelation properties and reduce power consumption, while allowing for efficient decoding even with large frequency drifts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If spread spectrum coding is used to minimize interference through low power density, then interference resistance is improved, but the system becomes vulnerable to frequency drift and multipath fading
Solution Approach 1:
The patent changes the parameter of autocorrelation properties by using complementary codes with perfect periodic autocorrelation functions. This resolves the contradiction by maintaining low power density for interference resistance while introducing codes with enhanced autocorrelation properties that provide robustness against frequency drift and multipath fading effects
Solution Approach 2:
The patent combines multiple spreading codes with complementary autocorrelation properties to create a composite coding structure. This composite approach allows the system to maintain the low power density benefit while gaining additional resilience against frequency drift through the combined autocorrelation characteristics of the code set
2Productivity
If multiple spreading codes are used in DS-CDMA systems, then communication capacity is improved, but multiple-access interference and inter-symbol interference increase
Solution Approach 1:
The patent changes the cross-correlation parameter between spreading codes by selecting codes with low cross-correlation properties. This allows multiple codes to be used simultaneously for increased communication capacity while minimizing multiple-access interference through the reduced correlation between different user signals
3Ease of operation
If conventional demodulation techniques are used, then decoding simplicity is maintained, but performance degrades under frequency offset conditions
Solution Approach 1:
The patent changes the autocorrelation parameter of the spreading codes to have perfect periodic properties. This allows the use of simple conventional demodulation techniques while the enhanced autocorrelation properties inherently provide resistance to frequency offset, eliminating the need for complex demodulation algorithms
Data Source
AI summary
Certain aspects of the present disclosure relate to a method for demodulating CPM modulated signals transmitted in a wired or wireless communication system using a linear modulation model consisting of a linear superposition of time pulses modulated using pseudo-PSK pulses.