Coherent Optical Receiver Frequency Offset Compensation at Low Symbol Rates
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Solution Overview
Problem
Conventional frequency offset compensation systems in optical digital coherent reception systems face challenges when the symbol rate is low, requiring high frequency stability from the light source, leading to increased costs and limited frequency offset estimation range.
Innovation Solution
An optical reception device with a local oscillation light source and digital signal processing unit that estimates and compensates frequency offsets within a range of −Be to +Be, where Be > B/2, allowing compensation for frequency offsets up to ±B/2 or an integer multiple of the symbol rate B, even when the offset is outside the conventional range of −B/2 to +B/2.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the symbol rate B is reduced to enable low-speed transmission, then transmission speed requirement is met, but the frequency offset estimation range becomes limited to ±B/2, requiring higher frequency stability from light sources which increases cost
Solution Approach 1:
The patent applies dynamics by making the frequency offset compensation range adaptable to different symbol rates. The electric band Be is designed to be dynamically adjustable or sufficiently wide (Be > B/2) to accommodate varying symbol rates, allowing the system to maintain reliable frequency offset compensation even when the symbol rate B is reduced for low-speed transmission scenarios
Solution Approach 2:
The patent changes the parameter relationship by establishing that the electric band Be should be greater than B/2, which is a relaxation from the conventional equality condition. This parameter change allows the frequency offset estimation range to be determined by the electric band rather than being strictly limited by the symbol rate, enabling cost-effective operation at lower symbol rates
2Adaptability or versatility
If the electric band Be is increased beyond B/2 to expand frequency offset compensation range, then frequency offset compensation capability is improved, but device complexity and cost increase
Solution Approach 1:
The patent applies partial action by setting the electric band Be to be slightly greater than B/2 rather than significantly larger. This provides sufficient frequency offset compensation range for practical applications without excessively increasing the receiver bandwidth, thereby avoiding unnecessary device complexity and cost while still achieving the goal of expanded compensation 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
This approach relaxes the requirement for high frequency stability of the light source, enabling cost-effective frequency offset compensation and demodulation of signals with low symbol rates, while maintaining signal quality.
Implementation Method 1
generates beat components of the electric field components of the signal light and the electric field components of the local light by causing the received signal light to interfere with local oscillation light
Implementation Method 2
The optical reception device photoelectrically converts the generated beat components to generate four analog electric signals
Data Source
AI summary
A reception unit, in which a range of an electric band is in a range from −Be to +Be and Be >B/2 is satisfied, receives signal light of a symbol rate B generated by optically modulating transmission data, performs digital coherent reception by interfering the received signal light with the local oscillation light generated by the local oscillation light source, converts the signal light into an electric digital signal, and output the digital signal, and a frequency offset compensation unit provided in a digital signal processing unit estimates a frequency offset amount generated in the digital signal in a range of −B/2 or more and +B/2 or less in accordance with a frequency difference between the signal light and the local oscillation light, and perform frequency offset compensation for the digital signal on the basis of the estimated frequency offset amount to compensate the frequency offset amount in a range of −B/2 or more and +B/2 or less and compensate so as to remain the frequency offset amount of an integral multiple of the symbol rate B when the frequency offset amount is in a range of less than −B/2 and a range of more than +B/2.