Optical Signal Reception Frequency Error Estimation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In optical signal reception systems, the feedback loop for frequency error estimation does not converge for high-order modulation signals like 16-QAM, 32-QAM, or 64-QAM, especially when the frequency pull-in range is small, making it difficult to estimate frequency errors without a training signal.
Innovation Solution
An optical signal reception apparatus is designed with an optical front end for interference between optical and local light beams, a signal conversion unit for generating digital signals, a frequency difference compensation unit for carrier recovery, and symbol determination units that temporarily and regularly generate compensation signals using reduced multi-value modulation arrangements, allowing the feedback loop to converge even without a training signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a decision feedback type frequency error estimation system is used for high-order modulation signals (16-QAM, 32-QAM, 64-QAM), then the system can handle multi-value modulation, but the feedback loop does not converge when frequency error is great due to small frequency pull-in range
Solution Approach 1:
The patent applies preliminary action by using a training signal before normal data transmission to initialize the feedback loop. The training signal allows the system to establish initial synchronization and reduce frequency error to within the pull-in range before switching to decision feedback mode, ensuring subsequent convergence during normal operation.
Solution Approach 2:
The patent introduces a training signal as an intermediary element that mediates between the transmitter and receiver during the initialization phase. This training signal serves as a known reference that enables the feedback loop to converge initially, after which normal data transmission can proceed with decision feedback.
2Reliability
If a training signal is used to cause feedback loop convergence, then frequency error estimation becomes possible for high-order modulation, but the system complexity and processing overhead increase
Solution Approach 1:
The patent segments the communication process into distinct phases: a training signal phase for initial feedback loop convergence, followed by a normal data transmission phase using decision feedback. This segmentation allows the complex training process to occur only once during initialization, while subsequent operation uses the simpler decision feedback mechanism.
Solution Approach 2:
The patent implements periodic action by using the training signal only during initial system setup or when needed for re-synchronization, rather than continuously. After the initial convergence is achieved, the system transitions to continuous decision feedback operation, reducing overall processing complexity while maintaining reliability.
3Measurement precision
If the frequency pull-in range is small for high-order modulation signals, then more precise frequency control is achieved, but the feedback loop cannot converge when frequency error exceeds the narrow pull-in range
Solution Approach 1:
The patent uses preliminary action by providing a training signal that enables the feedback loop to converge initially, reducing the frequency error to within the narrow pull-in range. Once converged, the system can maintain precise frequency estimation during normal operation without requiring continuous training signals.
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 solution enables the feedback loop to converge and estimate frequency errors effectively for high-order modulation signals, improving the frequency error estimation process in optical communication systems.
Implementation Method 1
an optical front end that generates a plurality of output light beams by causing an optical signal on which polarization multiplexing and multi-value modulation are performed and a local light beam to interfere with each other
Implementation Method 2
a signal conversion unit that generates a plurality of digital signals by photoelectrically converting and further analog-digital converting each of the plurality of output light beams
Data Source
AI summary
A frequency difference compensation unit (510) generates a carrier recovery signal by compensating for a frequency difference between a local light beam and an optical signal in a plurality of digital signals. A first symbol determination unit (521) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with the signal arrangement of multi-value modulation. A second symbol determination unit (522) determines the symbol position of the carrier recovery signal in which a frequency difference is compensated for, in accordance with a signal arrangement in which the number of multi-values of the multi-value modulation is reduced. A loop filter unit (540) and a compensation signal generation unit (550) temporarily generates a compensation signal using a determination result of the second symbol determination unit (522), and then regularly generates the compensation signal using a determination result of the first symbol determination unit (521).