Digital Coherent Receiver Frequency Offset Compensation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing digital coherent receivers face challenges in accurately compensating large frequency offsets between signal light and local oscillator light, leading to deteriorated reception quality due to limitations in frequency offset estimation and compensation, which can further degrade the Optical Signal Noise Ratio (OSNR).
Innovation Solution
A digital coherent receiver that calculates the spectrum gravity center of the digital signal and uses this information to estimate and reduce frequency offsets, thereby improving reception quality without relying on differential decoding, which can otherwise deteriorate OSNR properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency offset estimation is performed using conventional methods, then frequency offset compensation can be achieved, but the pull-in range is limited and large frequency offsets cannot be accurately estimated
Solution Approach 1:
The patent transforms the frequency offset estimation problem from the time domain to the frequency domain by calculating the spectrum gravity center of the digital signal. This dimensional transformation enables accurate estimation of large frequency offsets that were previously beyond the pull-in range of conventional time-domain methods.
Solution Approach 2:
The patent introduces the spectrum gravity center as an intermediary parameter to bridge the gap between the received signal and the frequency offset. By calculating the spectrum gravity center from the digital signal and using it to estimate the frequency offset, the system achieves accurate compensation for large frequency offsets without requiring the offset to be within a limited pull-in range.
2Adaptability or versatility
If differential decoding is used to expand pull-in range, then large frequency offsets can be compensated, but OSNR property is deteriorated
Solution Approach 1:
The patent replaces the mechanical/differential decoding approach with a spectral analysis approach. Instead of using differential decoding to expand pull-in range, the system calculates the spectrum gravity center of the digital signal to estimate frequency offset, thereby achieving the same pull-in range expansion without the OSNR deterioration caused by differential decoding.
3Speed
If frequency offset is large, then the constellation rotates during observation time, but signal identification becomes difficult
Solution Approach 1:
The patent moves the signal analysis from the time domain to the frequency domain by computing the spectrum gravity center. This allows the system to detect and measure frequency offsets of any magnitude, including large offsets that cause rapid constellation rotation in the time domain, thereby maintaining signal identification capability.
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
The proposed solution accurately compensates frequency offsets, expanding the pull-in range and enhancing reception quality while minimizing OSNR deterioration, allowing for more precise frequency offset estimation and improved signal identification.
Implementation Method 1
The front end converts a light signal into an electric signal by using a signal light and a local oscillator light
Data Source
AI summary
A digital coherent receiver includes a front end, an A/D convertor, and a processor. The front end converts a light signal into an electric signal by using a signal light and a local oscillator light. The A/D convertor converts the electric signal of the front end into a digital signal. The processor calculates a spectrum gravity center of the digital signal converted by the A/D convertor, estimates a frequency offset of the digital signal based on the calculated spectrum gravity center, and reduces the frequency offset of the digital signal based on the estimated frequency offset.