Coherent Receiver Phase Rotation Compensation
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Solution Overview
Problem
In optical transmission systems using MIMO diversity technology, achieving high transmission capacity while maintaining low signal correlation between signals passing through different paths or wavelengths is challenging, leading to reduced overall system capacity.
Innovation Solution
The system employs multiple coherent receivers with controlled local oscillators to perform coherent detection and digital signal processing, including phase rotation compensation and adaptive equalization, to stabilize demodulation and improve reception characteristics without reducing transmission capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple coherent receivers with different local oscillator frequencies are used to perform MIMO diversity reception, then reception characteristics are improved through low-correlation signal synthesis, but the frequency differences cause phase rotation that deteriorates demodulation stability
Solution Approach 1:
The patent changes the frequency parameter of the local oscillators to create controlled frequency differences between multiple receivers. This enables MIMO diversity reception with low-correlation signals while introducing manageable phase rotation that can be compensated through digital signal processing, thus improving reception characteristics without sacrificing demodulation stability
Solution Approach 2:
The patent implements phase rotation compensation mechanisms that measure and correct the phase differences introduced by frequency offsets between local oscillators and signal light. This feedback approach maintains demodulation stability while allowing the system to benefit from MIMO diversity reception with improved reception characteristics
2Reliability
If multiple signal lights with different wavelengths are used to achieve low signal correlation for MIMO diversity, then reception characteristics improve, but the transmission capacity of the entire system decreases
Solution Approach 1:
The patent makes the coherent receivers universal by enabling them to process multiple wavelength signals through wavelength division multiplexing. The same receiver infrastructure can handle different wavelengths simultaneously, achieving MIMO diversity with low-correlation signals while maintaining high transmission capacity through efficient resource utilization
Solution Approach 2:
The patent transitions from using only spatial diversity to incorporating wavelength diversity as an additional dimension. By utilizing multiple wavelengths in conjunction with multiple receivers, the system achieves low signal correlation for improved reception characteristics while the wavelength multiplexing maintains high overall transmission capacity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for stable demodulation and enhanced reception characteristics by compensating phase rotations caused by frequency differences, thereby improving signal quality without compromising transmission capacity.
Implementation Method 1
two coherent receivers that perform coherent detection of the signal light using two pieces of local oscillator of optical frequencies f11 and f12 close to the optical frequency f1
Data Source
Figure 1(1)~1(4)
Figure 2
Figure 3
AI summary
A receiver is configured to have two coherent receivers using two pieces of local oscillator of optical frequencies f11 and f12 close to optical frequency f1 of signal light, the two pieces of local oscillator being controlled to have a predetermined optical frequency spacing ΔF, and a digital signal processor demodulating transmission data signal sequences based on outputs from the coherent receivers. When the frequency difference Δf1 of one of the two pieces of local oscillator from a virtual reference frequency f1' close to the optical frequency f1 of the signal light is set, the digital signal processor obtains the frequency difference Δf2 of the other of the two pieces of local oscillator by calculating Δf1 - ΔF, inputs electric signals output from the two coherent receivers, and compensates the phase rotation caused in the electric signals by frequency differences Δf1 and Δf2.