QAM Differential Decoding Using MSB Coordinate Rotation
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Solution Overview
Problem
Existing multilevel differential decoding devices for QAM modulation communication systems face challenges in maintaining phase noise tolerance and circuit operating speed, especially during high-speed transmission, as increasing multilevel degree decreases phase noise tolerance and requires complex circuit configurations to combine differential encoding/decoding with error correction.
Innovation Solution
A multilevel differential decoding device that includes a synchronous detection part, MSB coordinate rotating parts, MSB symbol likelihood generating part, LSB symbol likelihood generating part, and soft decision error correction decoding part, which performs differential decoding processing after coordinate rotation based on the first two most significant bits, reducing the circuit complexity and maintaining phase noise tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multilevel modulation degree is increased to improve frequency utilization efficiency and transmission capacity, then transmission capacity is improved, but phase noise tolerance deteriorates
Solution Approach 1:
The 16-QAM signal is segmented into two independent QPSK signals through coordinate rotation and differential decoding. By separating the signal processing into multiple stages (coordinate rotation based on MSB, then differential decoding), the system achieves high transmission capacity while maintaining phase noise tolerance comparable to QPSK.
2Reliability
If differential encoding is applied to deal with phase slipping, then phase noise tolerance is improved, but circuit complexity increases when combining with error correction
Solution Approach 1:
Coordinate rotation is performed as a preliminary action before differential decoding. By pre-rotating the coordinate system based on the most significant bits, the subsequent differential decoding becomes simpler and can be combined more easily with error correction codes, reducing overall circuit complexity while maintaining phase noise tolerance.
Solution Approach 2:
The decoding process is segmented into coordinate rotation (based on MSB) and differential decoding (for LSB). This segmentation allows each stage to be optimized independently, making the integration with error correction more manageable and reducing overall circuit complexity.
3Reliability
If pilot signal insertion is used to guarantee transmission performance, then phase noise tolerance is improved, but signal operating speed increases leading to difficulty in high-speed transmission
Solution Approach 1:
The system uses self-service differential encoding where each symbol carries information about phase transitions relative to previous symbols. This eliminates the need for external pilot signals while maintaining phase noise tolerance, allowing high-speed transmission without the overhead and speed limitations associated with pilot insertion.
Data Source
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AI summary
Differential decoding processing applied to multilevel modulation is accomplished with the circuit scale kept small by including: an MSB coordinate rotating part for performing coordinate rotation based on information of the first two most significant bits of a signal received via a synchronous detection part; an MSB symbol likelihood generating part for generating likelihood with respect to the first two most significant bits after differential decoding, with the use of two sets of bit strings at different points in time for which coordinate rotation has been performed; an LSB symbol likelihood generating part for generating likelihood with respect to less significant bits; and a soft decision error correction decoding part for generating a decoded signal with the use of the likelihood of the first two most significant bits and the likelihood of the less significant bits.