Optical Transmitter Adaptive Bitrate via QAM Symbol State Selection
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Solution Overview
Problem
Current bitrate adaptation methods in optical networks, such as changing symbol rates or using different modulation formats, face challenges in achieving fine granularity and ease of implementation, particularly due to the impact of physical impairments on signal transmission.
Innovation Solution
The method introduces a correlation between coded states in quadrature amplitude modulation (QAM) and polarization division multiplexing (PDM) to adapt bitrate without changing the modulation format, selecting a reduced number of symbol states to increase Euclidean distance and enhance transmission robustness, allowing for adaptive bitrate capabilities with fine granularity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high order modulation formats (QAM, QPSK) are used to increase data throughput, then data rate is improved, but transmission reach is reduced due to increased sensitivity to physical impairments
Solution Approach 1:
The patent implements dynamic bitrate adaptation by enabling the optical transmitter to adjust the number of bits per symbol in real-time based on transmission conditions. The system dynamically selects between different bit rates (e.g., 4 bits/symbol for PDM-16QAM, 2 bits/symbol for PDM-QPSK) to optimize the trade-off between data throughput and transmission reach, allowing the modulation format to adapt to varying channel quality without changing the fundamental modulation scheme.
Solution Approach 2:
The patent changes the parameter of bits per symbol while maintaining the same modulation format (PDM-QAM). By adjusting this parameter, the system can achieve different data rates with the same physical layer infrastructure, effectively resolving the contradiction between high throughput and long reach by selecting appropriate bit rates based on transmission distance and channel conditions.
2Adaptability or versatility
If symbol rate is changed to adapt bitrate, then adaptive bitrate capability is achieved, but device complexity increases due to multiple clock frequencies required
Solution Approach 1:
Instead of changing the symbol rate, the patent changes the number of bits per symbol while keeping the symbol rate constant. This approach achieves adaptive bitrate capability without requiring multiple clock frequencies, thereby avoiding the complexity of synchronizing and managing multiple clock sources in the transmitter and receiver.
Solution Approach 2:
The patent extracts the bitrate adaptation function from the symbol rate control mechanism and implements it through modulation format selection (changing bits per symbol). This separation allows the clock frequency to remain fixed while still achieving flexible bitrate adaptation, removing the complexity associated with dynamic clock frequency changes.
3Adaptability or versatility
If different modulation formats (PDM-BPSK, PDM-QPSK) are used to adapt bitrate, then adaptive bitrate capability is achieved, but granularity is limited to two bits per symbol
Solution Approach 1:
The patent implements a dynamic modulation format selection mechanism that can adaptively choose between PDM-16QAM (4 bits/symbol), PDM-QPSK (2 bits/symbol), and potentially other formats. This dynamic selection provides fine granularity in bitrate adaptation, allowing the system to precisely match the required data rate to the transmission needs without being constrained to fixed two-bit increments.
Solution Approach 2:
The patent creates a universal PDM-QAM modulation framework that can accommodate multiple bit rates (4 bits, 2 bits, and potentially 1 bit per symbol) within a single modulation scheme family. This multi-functional approach allows the same physical layer to support various bitrate requirements, achieving fine granularity adaptation while maintaining system simplicity and interoperability.
Data Source
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AI summary
The present invention refers to a method for adapting a bitrate of a modulated signal in an optical network using a quadrature amplitude modulation with a given power of two, 2N with N being an natural number larger than one, number of states combined with at least one other coded modulation comprising at least two coded states wherein for a given quadrature amplitude modulation symbol state of a given coded state, only a predetermined number of associated quadrature amplitude modulation symbol states of the other at least one coded state are selected as possible transmitted quadrature amplitude modulation symbol states, said predetermined number being a predetermined power of two, 2M, smaller than the given power of two, 2N, with M being a natural number smaller than N.