A method for realizing high-precision time-frequency synchronization by fusion in an Ethernet communication network

Abstract

The present invention discloses a method for integrating and implementing high-precision time-frequency synchronization in an Ethernet communication network. This method uses wavelength division multiplexing to incorporate high-precision time-frequency reference signals into Ethernet data; uses add-drop multiplexing to achieve the exchange and networking of Ethernet data and continuous time-frequency signals; and uses two-way feedback control to achieve precise synchronization of time-frequency signals between local nodes and terminal nodes. The present invention utilizes the advantages of networked data transmission of Ethernet to achieve high-precision time-frequency transmission and exchange while completing high-speed interconnection communication. The present invention further improves the time-frequency synchronization performance of Ethernet and better meets the requirements of distributed detection applications for high-speed data communication, high-precision time, frequency, and phase synchronization.

Description

Technical Field

[0001] The present invention relates to the field of synchronous Ethernet, and in particular to a method for integrating and implementing high-precision time-frequency synchronization in an Ethernet communication network. Background Art

[0002] The time synchronization protocol of Ethernet has evolved from NTP (Network Time Protocol) to PTP (Precise Time Protocol), and at the same time, its synchronization accuracy has been improved from the millisecond level to the nanosecond level. The recently developed White Rabbit protocol measures the master-slave clock delay through the digital dual-mixer time difference method, further improving the PTP accuracy to the order of dozens of picoseconds, which can meet the requirements of multi-node high-precision time synchronization in large scientific installations, such as the Large Hadron Collider in Europe and the Large High Altitude Air Shower Observatory in China.

[0003] As the current highest-precision time-frequency transmission method, high-precision fiber-optic time-frequency transfer has made many important progresses in applications independent of Ethernet. It also realizes the transmission of similar networks through methods such as multi-point downloading and uploading in linear and ring networks. Compared with Ethernet, the accuracy is very high but the degree of networking is limited.

[0004] Zhan Lu, Youzhen Gui, Jialiang Wang, Kang Ying, Yanguang Sun, Lei Liu, Nan Cheng, and Haiwen Cai, "Fiber-optic time-frequency transfer in gigabit Ethernet networks over urban fiber links," Opt. Express 29, 2021, 29(8): 11693-11701. proposed a new optical pulse amplitude modulation scheme based on the White Rabbit protocol. The essence of this scheme is to use the White Rabbit module based on gigabit Ethernet to achieve time transmission, use 100MHz radio frequency modulation and two-way compensation method to achieve frequency transmission, and fuse the radio frequency signal and WR (White Rabbit) signal together through optical pulse intensity modulation in the Mach-Zehnder interferometer modulator, completing the ultra-stable time-frequency signal and gigabit Ethernet data transmission under the same laser wavelength. While achieving time synchronization of dozens of picoseconds, the stable transmission of the frequency reference signal is also realized by modulating the transmission frequency reference signal. This meets the frequency synchronization requirements proposed by many current distributed detection systems on the basis of time synchronization.

[0005] However, since the time signal is a digital signal while the frequency signal is a continuous analog signal, the differences between the two must be considered in the large-scale networking and switching of Ethernet. The digital time signal can be exchanged in the form of IP packets together with communication data. If the frequency signal with continuous analog characteristics also adopts this method, the continuity of the frequency reference will be lost, and different switching methods must be used. Summary of the Invention

[0006] The object of the present invention is to meet the above application requirements and propose a method for fusing and implementing high-precision time-frequency synchronization in an Ethernet communication network. It uses wavelength-division multiplexing to fuse additional high-precision time-frequency signals into Ethernet data, and utilizes the advantages of networked data transmission of Ethernet to achieve high-speed interconnection communication while realizing high-precision time-frequency transmission and switching.

[0007] The object of the present invention is achieved through the following technical solutions:

[0008] A method for fusing and implementing high-precision time-frequency synchronization in an Ethernet communication network, which uses wavelength-division multiplexing to integrate high-precision time-frequency reference signals into Ethernet data; uses add-drop multiplexing to realize the switching and networking of Ethernet data and continuous time-frequency signals; and uses two-way feedback control to achieve precise synchronization of time-frequency signals between local nodes and terminal nodes. Specifically, it includes the following steps:

[0009] 1) The reference frequency signal and the reference time signal are modulated onto laser carriers of different wavelengths, and after wavelength-division multiplexing, they are fused into the data communication wavelength of Ethernet, so as to be transmitted in the same optical fiber as the Ethernet communication data. After the receiving end demultiplexes the wavelength division, the time signal, the frequency signal, and the communication data are demodulated.

[0010] 2) The communication data in step 1) completes route planning selection, network management, and upload and download of control signals at the switching node in the form of IP packets.

[0011] The time-frequency signal in step 1) enters the next node in a "light - electro - light" cascaded manner. That is, when the time-frequency signal reaches this node, it first completes demodulation through optoelectronic conversion and is sent back to the previous node to stabilize the link between the two nodes independently, so as to obtain high-quality time-frequency signals at this node. Then, it is converted into an optical signal through electro-optical conversion and transmitted to the next node determined by the route through an optical switch, thus realizing the continuous and precise exchange and cascade of time-frequency signals.

[0012] 3) The frequency signal in step 2) obtains the noise of the link through round-trip phase measurement, and then actively compensates for the phase fluctuation caused by the noise through a delay line device to achieve stable transmission and synchronization of the frequency signal.

[0013] In step 2), the time signal uses the spread-spectrum measurement method to achieve high-precision time delay measurement of the PPS time pulse signal, and then performs time delay calibration to achieve high-precision time synchronization. Through the time pulse sequence marking and real-time communication interaction, the absolute consistency of the time information is achieved.

[0014] Furthermore, the reference time signal and the reference frequency signal in step 1) are generated by a high-precision atomic clock.

[0015] Furthermore, the time signal and the frequency signal in step 1) are demodulated and restored by a photodetector, and the communication data is demodulated and restored by a fiber modem.

[0016] Furthermore, the delay line device is an optical fiber delay line driven by a circuit, which includes two parts: a fast-varying delay line and a slow-varying delay line.

[0017] Furthermore, the spread-spectrum measurement method is to spread the 1PPS time signal into an N PPS time signal, and take the average value of these N time delays as the final time delay value.

[0018] Furthermore, the principle of the time pulse sequence marking is as follows: after the system is started, second counting is performed according to the trigger of the rising edge of the divided-frequency 1PPS time pulse, and combined with the measured time delay value during the transmission process, the timing information from days to picoseconds is finally formed.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0020] Utilizing the advantages of networked data transmission of Ethernet and high-precision optical fiber time-frequency transmission, while completing high-speed interconnection communication, high-precision time-frequency transmission and exchange are also achieved, further improving the time-frequency synchronization performance of Ethernet. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of an embodiment of the present invention for realizing high-precision time-frequency synchronization in an Ethernet communication network.

[0022] Figure 2 It is a schematic diagram of the principle of time-frequency signal and communication data fusion, transmission, and exchange in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The present invention will be further described below in conjunction with the embodiments and the drawings, but the protection scope of the present invention should not be limited thereby.

[0024] Please first refer to Figure 1 , Figure 1 which is a schematic diagram of an embodiment of the present invention for realizing high-precision time-frequency synchronization in an Ethernet communication network. As shown in the figure, in this embodiment, the Ethernet network includes 1 local node, 3 switching nodes and 1 terminal node, and the communication rate used is 115.2 MHz.Figure 2 This is the schematic diagram of the fusion, transmission, and switching of time-frequency signals and communication data in the embodiments of the present invention. The reference time-frequency source is provided by a rubidium atomic clock. The reference time signal is the 1PPS signal output by the rubidium atomic clock, and the reference frequency signal is the 1GHz frequency signal generated by multiplying the 10MHz frequency output by the rubidium atomic clock by a frequency multiplier. The realization of high-precision time-frequency synchronization in an Ethernet communication network includes the following steps:

[0025] 1. The reference 1GHz frequency signal and the reference 1PPS time signal are modulated onto laser carriers of different wavelengths through a laser, and then fused onto the data communication wavelength of the Ethernet through a wavelength division multiplexer, so as to be transmitted in the same optical fiber as the Ethernet communication data. After the wavelength division multiplexing is demultiplexed at the receiving end, the 1PPS time signal, the 1GHz frequency signal, and the communication data are demodulated;

[0026] 2. The communication data described in step 1 completes routing planning selection, network management, and uploading and downloading of control signals at the switching node in the form of packets;

[0027] 3. The 1PPS time signal and the 1GHz frequency signal described in step 1 enter the next node in a "light - electro - light" cascaded manner, that is, after the 1PPS time signal and the 1GHz frequency signal reach this node, they are first demodulated through a photodetector and then sent back to the previous node to stabilize the link between the two nodes independently, so as to obtain high-quality 1PPS time signal and 1GHz frequency signal at this node. Then they are converted into optical signals through a laser and transmitted to the next node determined by the route through an optical switch, so as to realize the continuous and accurate switching cascade of time-frequency signals;

[0028] 4. The 1GHz frequency signal described in step 3 obtains the noise of the link through the round-trip phase measurement method, uses a phase discriminator to measure the phase difference between the 1 frequency signal of this node and the 1GHz frequency signal transmitted back from the next node, and then drives the fiber delay line to actively compensate for the phase fluctuation caused by the noise, so as to realize the stable transmission and synchronization of the 1GHz frequency signal. The short-term stability of the 1GHz frequency signal transmission between node 1 and node 4 is better than 5E - 15@1s, and the long-term stability is better than 5E - 19@10000s in a certain measurement;

[0029] 5. The 1PPS time signal described in step 3 is used to generate a 100PPS time signal by spreading spectrum. A time interval measuring instrument is used to measure the time delay between the 100PPS time signal of this node and the 100PPS time signal transmitted back by the next node. The average value of these 100 time delays is used as the time signal delay measurement value, and then time delay calibration is performed to achieve high-precision time synchronization. In a certain measurement, the synchronization accuracy of the 1PPS time signal between node 1 and node 4 is better than 70 ps; and through time pulse sequence marking and real-time communication interaction, absolute consistency of moment information is achieved. In a certain measurement, the synchronization error of the moment information between node 1 and node 4 is controlled within 60 ps.

Claims

1. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network, characterized in that, this method uses wavelength division multiplexing to integrate high-precision time-frequency reference signals into Ethernet data; uses add-drop multiplexing to realize the exchange and networking of Ethernet data and continuous time-frequency signals; uses two-way feedback control to achieve precise synchronization of time-frequency signals between local nodes and terminal nodes; specifically includes the following steps: 1) The reference frequency signal and reference time signal are modulated onto laser carriers of different wavelengths, and are integrated into the data communication link of the Ethernet through wavelength division multiplexing, so as to be transmitted in the same optical fiber as the Ethernet communication data. After the receiving end demultiplexes the wavelength division, the time signal, frequency signal, and communication data are demodulated; 2) The communication data obtained in step 1) is routed, planned, selected, network managed, and control signals uploaded and downloaded at the switching node in packet form; The time signal and frequency signal obtained in step 1) enter the next node in the form of "optical - electrical - optical" cascade to realize continuous and precise exchange and cascade of time-frequency signals; 3) The frequency signal described in step 2) obtains the noise of the link through round-trip phase measurement, and then actively compensates for the phase fluctuation caused by the noise through a delay line device to realize the transmission and synchronization of the frequency signal; The time signal described in step 2) uses the spread spectrum measurement method to achieve high-precision time delay measurement of the time pulse signal, and then performs time delay calibration to achieve high-precision time synchronization, and realizes absolute consistency of time information through time pulse sequence marking and real-time communication interaction.

2. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network according to claim 1, characterized in that, the reference time signal and reference frequency signal described in step 1) are generated by an atomic clock.

3. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network according to claim 1, characterized in that, the time signal and frequency signal described in step 1) are demodulated and restored through a photodetector, and the communication data is demodulated and restored through a cable modem.

4. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network according to claim 1, characterized in that, the delay line device described in step 2) is an optical fiber delay line driven by a circuit, and includes two parts: a fast-varying delay line and a slow-varying delay line.

5. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network according to claim 1, characterized in that, the spread spectrum measurement method is to spread the 1PPS (pulse per second) time signal into an N PPS time signal, and take the average value of these N time delays as the final time delay value.

6. A method for integrating and implementing high-precision time and frequency synchronization in an Ethernet communication network according to claim 1, characterized in that, the time pulse sequence marking is to perform second counting according to the trigger of the rising edge of the divided-frequency 1PPS time pulse after the system is started, and then combine the measured time delay value during the transmission process to finally form timing information from days to picoseconds.

Images