Phase Reference Tracking for Digital Phase Modulated Signals
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Solution Overview
Problem
Current digital communication systems face challenges in accurately tracking phase references for digital phase modulated signals, particularly due to frequency offset and phase variations, leading to performance degradation and errors in decoding, especially for differential phase-shift keying (DPSK) signals.
Innovation Solution
A method and apparatus for phase reference tracking using a phase-domain based gradient algorithm that converts received complex signals to phase, employing a phase reference tracking unit to estimate transmit phases and correct frequency offsets, enabling robust phase tracking for BPSK, MPSK, and DPSK modulation systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a first-order IIR filter in phase-domain is used for phase tracking, then device complexity is reduced, but phase tracking accuracy deteriorates due to insufficient handling of heavy phase variations
Solution Approach 1:
The patent employs a second-order IIR filter in the phase domain to dynamically track phase variations. The filter coefficients are adaptively adjusted based on the detected signal characteristics, allowing the system to respond to heavy phase variations while maintaining computational simplicity. This dynamic adjustment resolves the contradiction by enhancing tracking accuracy without significantly increasing device complexity.
Solution Approach 2:
The patent changes the filter order parameter from first-order to second-order IIR filter, which fundamentally alters the phase tracking capability. This parameter change enables the system to handle heavy phase variations (up to 400 Hz/μs) while keeping the implementation relatively simple in the phase domain, thus resolving the contradiction between complexity and accuracy.
2Measurement precision
If multiple symbol detection based on maximum likelihood sequence detection is used for phase reference tracking, then phase reference accuracy is improved, but device complexity increases exponentially
Solution Approach 1:
The patent substitutes the complex multiple symbol detection approach with a simpler phase-domain IIR filter method. Instead of performing computationally intensive maximum likelihood sequence detection across multiple symbols, the system uses a second-order IIR filter that operates in the phase domain, achieving comparable or superior phase reference accuracy with exponentially reduced complexity.
Solution Approach 2:
The patent changes the fundamental approach from time-domain multiple symbol detection to phase-domain filtering. This parameter change in the processing domain transforms the complexity characteristics, reducing exponential complexity growth while maintaining high phase reference accuracy through the adaptive IIR filter.
3Ease of operation
If differential decoding is used for DPSK signals, then ease of operation is improved, but reliability deteriorates due to unavoidable double errors from noisy references
Solution Approach 1:
The patent introduces feedback mechanisms through the second-order IIR filter that continuously tracks and corrects phase reference errors. The filter uses feedback from the received signal to adaptively adjust phase estimates, preventing the propagation of errors during differential decoding. This feedback loop maintains reliability while preserving the simplicity of differential decoding operations.
Solution Approach 2:
The patent applies beforehand cushioning by using the second-order IIR filter to pre-correct phase reference errors before they propagate into decoding errors. The filter anticipates and compensates for noisy references in advance, cushioning against the potential for double errors during differential decoding while maintaining operational simplicity.
Data Source
AI summary
The present invention discloses a method and apparatus to provide, effectively and robustly, a phase reference in phase-domain for digital phase-modulated signals. Not only the first-order but also higher order PLLs are delineated for robust and fast tracking of frequency errors and time-varying frequency errors between the transmitter and the receiver. This invention can be applied to any phase-modulated signal such as PSK, DPSK, π/4-DPSK, and CPM. The decoders with this invention can achieve close to the performance of coherent detection.Reference[1] D. Divsalar and M. K. Simon, “Multiple-symbols differential detection of MPSK,”IEEE Trans. Commun., vol. 38, pp. 300-308, March 1990.[2] Specification of the Bluetooth System, 2.0+EDR, 4 Nov. 2004.