Coherent Receiver 3QAM Equalization Mechanism
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Solution Overview
Problem
Coherent optical receivers face issues processing three-quadrature amplitude modulation (3QAM) traffic due to false locks and catastrophic bit error rates when handling polarization multiplexed binary phase shift keying (PM-BPSK) and quadrature phase shift keying (PM-QPSK) traffic.
Innovation Solution
Implementing a method to receive and process four-bit symbols using a polarization multiplexed-quadrature phase shift keying (PM-QPSK) scheme, where a first pair of bits is equalized to restore their pre-transmission condition, and a second pair of bits is delayed and equalized separately to synchronize with the first pair, allowing identification and output of three-bit symbols corresponding to the 3QAM scheme.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If coherent optical receivers use standard PM-QPSK or PM-BPSK processing methods, then they can process those modulation schemes, but they cannot process 3QAM traffic without incurring false locks and catastrophic bit error rates
Solution Approach 1:
The patent segments the four-bit PM-QPSK symbols into two separate two-bit streams corresponding to different polarizations. By processing these streams separately through distinct equalization paths and then recombining them, the system can correctly decode 3QAM traffic while maintaining compatibility with standard PM-QPSK receivers. This segmentation allows the receiver to handle the unique characteristics of 3QAM modulation without false locks.
2Reliability
If the system margin is insufficient for PM-QPSK processing, then PM-QPSK cannot be processed reliably, but the system still needs to maintain service
Solution Approach 1:
The patent changes the processing parameters by applying separate equalization operations to the two polarization streams at different timing. The first equalization is performed on the first polarization stream, followed by a time delay, then the second equalization is performed on the second polarization stream. This parameter change in processing timing and method allows the system to maintain service reliability even when system margin is insufficient for standard PM-QPSK processing.
3Adaptability or versatility
If separate equalization is performed on first and second polarization streams with time delay, then 3QAM traffic can be processed correctly, but the processing complexity increases
Solution Approach 1:
The patent applies preliminary action by performing the first equalization on the first polarization stream before combining it with the second stream. This preliminary processing prepares the data in a form that simplifies subsequent operations. By pre-processing one stream and holding it in a buffer while processing the second stream, the overall complexity is managed more effectively than simultaneous processing of both streams.
Data Source
AI summary
A system receives four-bit symbols that correspond to traffic associated with a three-bit phase modulation scheme and are encoded based on a four-bit phase modulation scheme. The system determines values with which to perform equalization that enable the four-bit symbols to be restored to a condition that existed prior to being transmitted to the system. The system performs, using the values, equalization on a four-bit symbol that includes at least a first pair of bits associated with a first polarization, and performs, after completing the equalization, another equalization on another four-bit symbol that includes at least a second pair of bits associated with a second polarization. The system identifies a three-bit symbol, of a set of three-bit symbols associated with the three-bit phase modulation scheme, based on the equalized first pair of bits and the equalized second pair of bits, generates the three-bit symbol, and outputs the three-bit symbol.