Test of 1588 V2 time synchronization scheme of TD base station
With the actual commercial deployment of the domestic PTN network in 2009, the actual commercial test of using 1588 to achieve time synchronization of base stations through PTN in a commercial TD network has also met the conditions. The commercial test of 1588 time synchronization has provided technical and experience reserves for the truly comprehensive GPS replacement practice of the later TD base station, which has important practical significance.
As one of the key technologies of PTN, 1588 V2 breaks the history that packetized networks cannot transmit accurate clock signals. The new generation mobile bearer network supporting 1588 V2 only needs a high-precision clock source input to accurately transmit clock signals to various Base stations to achieve accurate synchronization of base stations across the network. The core idea of ​​1588 is to use the master-slave clock mode to encode time information, and use the network symmetry and delay measurement technology to achieve master-slave time synchronization. 1588 can achieve frequency synchronization and time synchronization at the same time, and the accuracy of time transfer depends mainly on two conditions: the counter frequency is accurate and the symmetry of the link. The key to 1588 implementation is delay measurement.
As a leader in PTN technology and industry, ZTE attaches great importance to the research and development and investment of PTN, and its technologies and solutions in the field of PTN time synchronization have always led the development of the industry.
◠In the test of China Mobile's PTN laboratory in August 2008, ZTE became the only manufacturer that could complete the PTN GPS replacement test. Since then, ZTE ’s PTN time synchronization solution has passed the stress test of 35 nodes on China Mobile ’s existing network, and its performance is stable under high network load, and it can communicate with the TD-SCDMA system.
â— From April to June 2009, in the pilot city live network test organized by China Mobile, ZTE became the only manufacturer that could provide end-to-end 1588 V2 time synchronization test, with excellent test results and compliance with relevant specifications.
â— From September to December 2009, in the 1588 V2 time synchronization interface interoperability test organized by China Mobile (the PTN and TD-SCDMA base stations of different manufacturers conducted 1588 V2 interworking), ZTE took the lead in completing the docking with TD-SCDMA base stations of multiple manufacturers Tests, including the 1588 in-band / out-of-band mode connection with Datang, Huawei, and Xinyoutong base stations, time synchronization indicators are in line with China Mobile requirements. Among them, ZTE uses patented technology to achieve the unique "time accuracy is completely independent of traffic" feature, that is, when the link load is 100%, it does not affect the time synchronization accuracy.
◠In March 2010, in order to further expand the feasibility study of the GPS time synchronization alternative technology in the commercial network environment, Guangdong Mobile selected Yangjiang Mobile as a pilot for the 1588 time synchronization in the case of "ZTE TD + PTN" commercial networking The function, performance and TD base station time synchronization were switched from GPS to 1588 after TD service performance was tested by commercial tests. The test results are far better than the requirements of China Mobile ’s relevant specifications, which provides a useful reference for China Mobile ’s 1588 V2 large-scale commercial use And illustration.
Guangdong Yangjiang Mobile ’s PTN network is built using ZTE ’s ZXCTN series of PTN products, using access, aggregation, and a two-layer networking model. The services carried are mainly TD-SCDMA base station services, including some 2G and major customer group user services The network topology diagram is shown in Figure 1.
Figure 1 Guangdong Yangjiang Mobile PTN network (ZTE PTN equipment)
Guangdong Yangjiang Mobile's 1588 commercial test selected 2 of the 5 convergence rings of the Yangjiang Mobile PTN live network for testing. The test sites are the sites covered by "Yangxi Ring" and "Hailing Ring", a total of 27 PTN Node, as shown in Figure 2.
Figure 2 1588 V2 commercial test network (Guangdong Yangjiang Mobile)
The test is conducted with reference to the 1588 test specification of China Mobile Group Corporation. Based on the 1588 functional characteristics and verification requirements of the existing network applications, Yangjiang Mobile's 1588 test is divided into three stages: one, time source calibration stage; two, link asymmetry compensation Engineering stage; three, according to the standard testing stage.
In this test, the key test contents such as the long-term synchronization accuracy performance of the base station, the time source switching, the time performance under service switching, the GPS to ground synchronization switching, and the service quality between the 1588 networks across the city have all achieved more than standard standards Requires much better results. The test results of key test items are shown in Table 1.
Table 1 Key indicators of 1588 commercial test (Guangdong Yangjiang Mobile)
Guangdong Yangjiang Mobile's 1588 commercial test project was successfully completed. The test results showed that all indicators were excellent. The PTN network link asymmetry compensation value was within 100 ns. The TD base station side performed well in clock maintenance and time source switching, which was fully satisfactory TD base station 1.5μs (1500ns) clock synchronization requirements.
The large-scale commercial use of IEEE 1588V2 function in Yangjiang Mobile, through long-term online verification, further clarified the possibility of using PTN to replace the large-scale commercial implementation of GPS through 1588V2, which provides reliable reliability for Guangdong Mobile and even the 1588V2 commercial scale in other provinces and cities nationwide Commercial examples and reference.
At the same time, it also once again demonstrated ZTE's strength as a leader in PTN technology and industry. ZTE Corporation will maintain a high priority for the research and development and investment of PTN, and will fully promote the maturity and development of the PTN industry.
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