Search

EP-4741786-A1 - METHOD, DEVICE AND SYSTEM FOR MONITORING TEMPERATURE IN FIBER OPTIC NETWORKS

EP4741786A1EP 4741786 A1EP4741786 A1EP 4741786A1EP-4741786-A1

Abstract

Method, system and device for monitoring temperature in a fiber optic network, including an OLT(110) and customer devices (121,122) connected through a link (100), using existing protocols and without additional hardware, as the OLT (110) performs: measuring the round-trip delay (RTD) between each customer device (121) requiring synchronization with the customer devices (122) previously set in service and connected to the link (100) at scheduled intervals, and estimating variations in RTD to determine temperature changes (ΔT) in the link (100). Additionally, the method allows generating temperature maps by calculating the variation in average temperature along the link by dividing it into segments and calculating the average temperature variation iteratively, starting from the initial segment between the OLT (110) and the closest customer device and progressing through subsequent segments. This calculation provides points of temperature along the fiber tree and the information of several trees can be represented together to build a 2D map.

Inventors

  • VIDAL RODRIGUEZ, BORJA
  • MONTALVO GARCÍA, Julio
  • CORTES OLMEDA, Daniel

Assignees

  • Telefonica, S.A.
  • UNIVERSIDAD POLITECNICA DE VALENCIA

Dates

Publication Date
20260513
Application Date
20241108

Claims (15)

  1. A method for monitoring temperature in a fiber optic network comprising a plurality of first customer devices (121) and second customer devices (122), both first and second customer device (121, 122) configured to be connected to an optical fiber link (100) to communicate with an optical line termination (110), wherein the first customer devices (121) require synchronization with the second customer devices (122) previously set in service and connected to the optical fiber link (100), wherein the method comprises the following steps, performed by the optical line termination (110): - measuring a round-trip delay (RTD) between each first customer device (121) and the optical line termination (110) during time intervals scheduled by the optical line termination (110), - estimating variations in the measured round-trip delay (RTD) for each customer device (121, 122) to determine temperature variations (ΔT) of the optical fiber link (100).
  2. The method according to claim 1, wherein determining temperature variations (ΔT) from the variations in the measured round-trip delay (RTD) is performed by computing: Δ T i = Δ RTD i ⋅ c / L i ⋅ n up + n down ⋅ dn dT i where Δ RTD i is a variation in the round-trip delay, RTD i , estimated for an i-th customer device (121, 122) of the fiber optic network which is a passive optical network, L i is a fiber distance between the optical line termination (110) and the i-th customer device (121, 122), c is the speed of light in vacuum, n up is an effective propagation index in an optical signal transmitted from the i-th customer device (121, 122) to the optical line termination (110), n down an effective propagation index in an optical signal transmitted from the optical line termination (110) to the i-th customer device (121, 122), dn dT i is an average linear thermo-optic coefficient of an optical fiber path between the optical line termination (110) and the i-th customer device (121, 122).
  3. The method according to claim 2, wherein the round-trip delay for the i-th customer device (121, 122), RTD i , is estimated by the optical line termination (110) using the equation: RTD i = Z EqD i − EqD i − RD i where: Z EqD i is a zero-distance equalization delay between the optical line termination (110) and the i-th customer device (121, 122), EqD i is an equalization delay for the i-th customer device (121, 122) RD i is a random delay used by the i-th customer device (121, 122) during ranging.
  4. The method according to any of the preceding claims, wherein measuring the round-trip delay (RTD) is performed when the first customer device (121) is connected to the optical fiber link (100) or electrically rebooted, and during the time intervals scheduled by the optical line termination (110).
  5. The method according to any of the preceding claims, wherein the synchronization of the first customer devices (121) with the second customer devices (122) in service in the fiber optic network comprises suppressing transmission from the second customer devices (122) during the time intervals scheduled by the optical line termination (110) for measuring the round-trip delay (RTD), transmitting from the first customer devices (121) initial synchronization messages and synchronizing the first customer devices (121) with upstream frames before transmitting to the optical line termination (110) by adjusting the transmission time of the first customer devices (121) using the estimated variations in the measured round-trip delay (RTD).
  6. The method, according to any of the preceding claims, further comprising a step of retrieving a variation of average temperature along a monitored optical link (200), wherein the step of retrieving the variation of average temperature comprising: - dividing the monitored optical link (200) into a plurality of segments (S 01 , S 12 , S 23,... ) whose lengths are determined by the points (P 0 , P 1, P 2, P 3,,... ) at which a group of customer devices (221, 222, 223) of selected customers of the fiber optic network are connected, - calculating the variation of average temperature for each segment (S 01 , S 12 , S 23,... ) iteratively, starting from an initial segment (S 01 ) defined between the OLT (110) and an initial customer device (221), and progressing through subsequent segments (S 12 , S 23,... ) defined between subsequent customer devices (222, 223) along the monitored optical link (200), wherein - the variation of average temperature of the initial segment (S 01 ) is given by: Δ T 0 → 1 = 1 L 0 → 1 ∫ 0 L 0 → 1 T z dz where T ( z ) is a spatial evolution of environmental temperature along the monitored link (200) and Δ T 0→1 is the variation of the average temperature of the initial segment (S 01 ); and - the variation of average temperature of the subsequent segments (S 12 , S 23,... ) is calculated based on the variation of average temperature calculated for a previous segment.
  7. The method, according to claim 6, wherein the variation of average temperature of the subsequent segments (S 12 , S 23,... ) is calculated by computing 1 0 ⋯ 0 L 0 → 1 L 0 → 1 + L 1 → 2 L 1 → 2 L 0 → 1 + L 1 → 2 ⋯ 0 ⋮ ⋮ ⋮ ⋮ L 0 → 1 ∑ L k − 1 → k L 1 → 2 ∑ L k − 1 → k ⋯ L n − 1 → n ∑ L k − 1 → k ΔT 0 → 1 ΔT 1 → 2 ⋮ ΔT n − 1 → n = ΔT 0 → 1 ΔT 1 → 20 ⋮ ΔT 0 → n where 〈ΔT i→j 〉 denotes a variation of average temperature of a segment S ij between points Pi and Pj of the monitored optical link (200).
  8. An optical line termination (110) device comprising an optical digital signal processor configured to perform the method according to any of claims 1-7.
  9. A system for monitoring temperature in a fiber optic network comprising: an optical line termination (110), a plurality of first customer devices (121) and second customer devices (122), both first and second customer device (121, 122) configured to be connected to the optical line termination (110) through an optical fiber link (100), wherein the first customer devices (121) require synchronization with the second customer devices (122) previously set in service and connected to the optical fiber link (100), wherein the optical line termination (110) is configured to: - measure a round-trip delay (RTD) between each first customer device (121) and the optical line termination (110) during time intervals scheduled by the optical line termination (110), - estimate variations in the measured round-trip delay (RTD) for each customer device (121, 122) to determine temperature variations (ΔT) of the optical fiber link (100).
  10. The system according to claim 9, wherein the optical line termination (110) or a remote computing equipment communicated with the optical line termination (110) is configured to determine temperature variations (ΔT) from the variations in the measured round-trip delay (RTD) by computing: Δ T i = Δ RTD i ⋅ c / L i ⋅ n up + n down ⋅ dn dT i where Δ RTD i is a variation in the round-trip delay, RTD_i, estimated for an i-th customer device (121, 122) of the fiber optic network which is a passive optical network, L i is a fiber distance between the optical line termination (110) and the i-th customer device (121, 122), c is the speed of light in vacuum, n up is an effective propagation index in an optical signal transmitted from the i-th customer device (121, 122) to the optical line termination (110), n down an effective propagation index in an optical signal transmitted from the optical line termination (110) to the i-th customer device (121, 122), dn dT i is an average linear thermo-optic coefficient of an optical fiber path between the optical line termination (110) and the i-th customer device (121, 122).
  11. The system according to claim 10, wherein the optical line termination (110) or the remote computing equipment communicated with the optical line termination (110) is configured to estimate the round-trip delay, RTD i , by computing: RTD i = Z EqD i − EqD i − RD i where: Z EqD i is a zero-distance equalization delay between the optical line termination (110) and the i-th customer device (121, 122), EqD i is an equalization delay for the i-th customer device (121, 122) RD i is a random delay used by the i-th customer device (121, 122) during ranging.
  12. The system according to any of claims 10-11, wherein the optical line termination (110) is configured to measure the round-trip delay (RTD) when the first customer device (121) is connected to the optical fiber link (100) or electrically rebooted, and during the time intervals scheduled by the optical line termination (110).
  13. The system according to any of claims 10-12, wherein the fiber optic network is a passive optical network, PON.
  14. The system according to any of claims 10-12, wherein the fiber optic network is point-to-point, PtP.
  15. A computer program comprising computer executable instructions for implementing the method according to any of claims 1-7, when executed on a computer, a microprocessor, a microcontroller or any other form of programmable hardware.

Description

TECHNICAL FIELD The present invention is applied to the technical sector of fiber optic telecommunications and, in particular, shows a technical solution for monitoring the environmental temperature in any passive optical network (PON). BACKGROUND OF THE INVENTION FTTx (Fiber to the x) networks are known for their high bandwidth capabilities, reliability, and ability to support a wide range of digital services, including internet, television, and telephony. The "x" in FTTx denotes the specific endpoint where the fiber optic cable terminates. For example, FTTH (Fiber to the Home) means the fiber runs directly to individual homes, providing high-speed internet directly to residential customers. FTTB (Fiber to the Building) refers to fiber terminating at a multi-dwelling unit or business building, with the final connection to individual units or offices typically being made via copper or wireless technology. The three main parts of a FTTx-PON system are: Optical Line Termination (OLT): This is equipment installed in the network operator premises.Optical Network Unit (ONU). This is the customer premises equipment (CPE) which performs as an optical modem, transforming the optical signals received from the PON into electrical signals towards the customer premises, typically Ethernet and Wi-Fi signals.PON infrastructure: This is the passive optical infrastructure consisting of different optical fiber cables and fiber splitters connecting OLTs and ONUs. Each OLT optical interface is connected to several ONUs through the PON infrastructure, with typically uses optical splitters in cascade, forming a tree physical topology. Existing solutions to monitor temperature on optical fibers use dedicated measurement equipment (such as OTDR - Optical Time Domain Reflectometer-, or OFDR - Optical Frequency Domain Reflectometry-) with dedicated optical signals for monitoring purposes, and can only measure at a single fiber at a time, requiring optical switching if a big amount of measurement fibers are in scope, thus increasing the total cost of the solution and increasing the measurement time. The solutions are generally based on Raman or Rayleigh backscattering effects in optical fiber. For example, US8858069B2 discloses a fiber optic temperature distribution measurement device that measures the temperature distribution along an optical fiber using backward Raman scattering light generated in the optical fiber. Another example is disclosed in US11644369B2, which describes a technique for monitoring fiber optics by distributed temperature sensing (DTS) coupled to an OLT, the DTS employing Raman-based optical time domain reflectometry (OTDR) to determine installation problems/errors and/or optical fiber differences occurring over the length of the optical fiber cable and the determination. These solutions introduce optical losses when used in fibers also transmitting data signals. For PON networks, in the state of the art it is found a technique that rely only on the "Equalization delay" parameter of the Physical Layer Operation Administration and Maintenance (PLOAM) layer; see "Towards Costless Temperature Monitoring through PLOAM Information in TDMA PON Networks" by Cristian Salgado-Cazorla and Borja Vidal, Optical Fiber Communications Conference and Exhibition (OFC) 2023, 5-9 March 2023. Nevertheless, the measurement method does not take into account all the delays involved in the PON protocol (ex: random delays, pre-assigned delays...), thus the "equalization delay" parameter is not generalizable to measure temperature variations in the environment around an optical fiber in all the operational cases, such as a device reboot or upgrade, thus the calculations of the temperature variations in the fiber environment may be incorrect. Therefore, an objective technical problem addressed by the invention is how to accurately and cost-effectively estimate the variations of the average environment temperature around the optical fiber infrastructure in a PON system, specifically for FTTx applications, without introducing additional hardware and overcoming the limitations of existing temperature monitoring solutions that rely on dedicated measurement equipment, which increase costs and measurement time, and can only measure temperature on a single fiber at a time. SUMMARY OF THE INVENTION The present invention is useful for solving the problems mentioned above, by means of a method and system for monitoring the environmental temperature in the coverage of fiber networks, without the need to use additional measurement hardware and using existing protocols, reducing the cost and the time required for measurement and to obtain temperature monitoring information from a big amount of fiber paths over other existing approaches. The present invention applies to Fiber to the Home (FTTH) technology, more specifically, to Passive Optical Network (PON) architecture. As the PON infrastructure is built on a tree physical topology of each OLT conne