Differential Latency Measurement in Optical Transport Networks
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Solution Overview
Problem
Current methods fail to accurately measure and manage differential latency between upstream and downstream transmissions in optical transport networks, particularly in applications like CPRI, which require low latency and zero jitter.
Innovation Solution
An apparatus that measures round trip delays of optical signals at different wavelengths, calculates differential latency, and compensates for it using a processing unit and add/drop filters, allowing non-intrusive measurement and dynamic compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single measurement wavelength is used to measure differential latency, then the measurement process is simple, but the measurement accuracy is insufficient for applications requiring near-zero jitter
Solution Approach 1:
The measurement process is segmented into multiple wavelength components. Instead of using a single wavelength, the patent measures round-trip delays at multiple distinct wavelengths (e.g., λ1, λ2, λ3) and combines these measurements to achieve high-precision differential latency calculation. This segmentation of the measurement into spectral components resolves the contradiction by trading controlled complexity (multiple wavelength measurements) for significantly improved measurement precision.
Solution Approach 2:
The patent changes the measurement parameter from a single wavelength to multiple wavelengths. By measuring round-trip delays at different wavelengths and using the dispersion characteristics of the optical fiber, the system derives both upstream and downstream delays with high precision. This parameter change (from single to multi-wavelength) directly addresses the need for near-zero jitter measurement accuracy while maintaining a manageable measurement apparatus.
2Measurement precision
If intrusive measurement methods are used, then measurement can be performed, but transmission quality is degraded
Solution Approach 1:
The patent introduces measurement wavelengths as intermediary signals that do not interfere with the payload wavelengths. By using distinct measurement wavelengths separate from the data-carrying wavelengths, the system can perform differential latency measurements without degrading transmission quality. The measurement wavelengths act as mediators that enable precise measurement while remaining transparent to the actual data transmission.
Solution Approach 2:
The measurement function is extracted from the data transmission function. The patent separates measurement wavelengths from payload wavelengths, allowing differential latency measurement to be performed independently without affecting the quality of data transmission. This extraction of the measurement function into a separate wavelength domain resolves the contradiction between measurement capability and transmission quality.
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
Enables accurate measurement and compensation of differential latency, ensuring low latency and zero jitter in optical transport networks, thereby meeting the stringent requirements of applications like CPRI.
Implementation Method 1
measuring round trip delays of at least two optical measurement signals having different measurement wavelengths
Implementation Method 2
The at least two generated optical measurement signals are inserted at a near end of the optical transportation link by means of an add/drop filter
Implementation Method 3
The at least two inserted optical measurement signals are transported through the optical transportation link to a far end of the optical transportation link and at least partially reflected by a signal reflector
Data Source
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AI summary
An apparatus and method for providing a differential latency, DL, between an upstream, US, transmission and a downstream, DS, transmission via an optical transmission link (OTL), said apparatus comprising a measurement unit (2) configured to measure the round trip delays, RTD, of at least two measure-ment signals having different measurement wavelengths; and a processing unit (3) configured to derive an upstream, US, delay of at least one optical signal at an upstream wavelength from the at least two measured round trip delays, RTD, and to derive a downstream, DS, delay of at least one optical signal at a downstream wavelength from the at least two measured round trip delays, RTD, wherein the differential latency, DL, is calculated on the basis of the derived delays, RTD.