Frequency Offset Detection in Digital Coherent Optical Receivers
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Solution Overview
Problem
Current frequency offset detection methods in digital coherent optical receivers are limited by high computational complexity and can only detect frequency offsets up to half of the required range, making them impractical for high-speed optical communication systems.
Innovation Solution
A frequency offset detecting apparatus and method that eliminates multiplication operations of complex numbers, using an argument difference obtaining unit, subtracters, a quantizer, and an averager to achieve stable and precise detection, with optional 2π/M quantization and low-speed implementations to reduce complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional frequency offset detection methods using multiplication operations of complex numbers are used, then detection precision can be maintained, but computational complexity becomes excessively high making it impractical for high-speed optical communication systems
Solution Approach 1:
The patent extracts only the argument (phase) information from the complex baseband signal, ignoring the magnitude information. By using only the argument difference between adjacent symbols, the method eliminates the need for complex multiplication operations while maintaining frequency offset detection capability. This extraction principle reduces computational complexity from O(1) complex multiplications to simple argument calculation and subtraction operations.
Solution Approach 2:
The patent replaces the mechanical computation of complex multiplication with a simpler mathematical approach using argument differences. Instead of performing complex arithmetic operations (multiplication and addition), the method substitutes these with argument extraction, subtraction, and averaging operations, which are computationally less intensive and can be implemented more efficiently in hardware for high-speed systems.
2Adaptability or versatility
If conventional frequency offset detection methods are used, then detection can be performed, but the detection range is limited to half of the required range
Solution Approach 1:
The patent employs a quantizer that can be configured with different quantization intervals (e.g., 2π/M) to adapt to different frequency offset ranges. By adjusting the quantization parameter, the same detection apparatus can handle various detection range requirements while maintaining reliable detection through the feedback control mechanism that uses the quantized argument difference to correct frequency offsets.
3Productivity
If high symbol rate processing is required, then communication speed increases, but the computational complexity of frequency offset detection becomes prohibitive
Solution Approach 1:
The patent replaces complex multiplication operations with simpler argument difference calculations and averaging operations. This substitution enables the system to process high symbol rates (e.g., 10 Gsymbol/s or higher) because the simplified operations can be executed faster and with less computational resources, directly supporting higher productivity in optical communication systems.
Data Source
AI summary
The present invention discloses a frequency offset detecting apparatus and method for use in a digital coherent optical receiver. The digital coherent optical receiver comprises: a front-end processing section for generating a digital baseband electric signal; an equalizer for performing equalized filtering on the digital baseband electric signal; and the frequency offset detecting apparatus for detecting frequency offset contained in the digital baseband electric signal or frequency offset contained in a signal outputted by the equalizer; wherein the frequency offset detecting apparatus comprises an argument difference obtaining unit, a first subtracter, a second subtracter, a quantizer and an averager, of which the argument difference obtaining unit obtains an argument difference of adjacent symbols in a signal inputted therein; the first subtracter subtracts an output of the averager from the argument difference obtained by the argument difference obtaining unit; the quantizer performs uniform quantization with predetermined intervals on an output of the first subtracter; the second subtracter subtracts an output of the quantizer from the argument difference obtained by the argument difference obtaining unit; and the averager averages an output of the second subtracter.