As IP increasingly becomes the preferred networking technology, MOBATIME looked to design a scalable and efficient way to serve these customers on IP. The radio Network used by the customer was based on TDM (Time Division Multiplex) technology. The system was discontinued and has to be replaced by a new system as such IP technology was chosen as the new transmission standard. The entire TDM network has to be converted to IP technology inorder to achieve higher accuracy and stability. Besides a higher data rate and better voice quality, there should also be a wide area network. Different participants (e.g. fire brigade, police, army) should be able to communicate with each other.
In order to achieve higher data rates and better voice quality via IP technology, all base stations must be synchronized with high accuracy. A maximum time deviation of 5 µs was specified. For the conversion to IP, a large part of the old infrastructure will be retained. Some of the base stations will be equipped with new hardware to become IP-compatible.
The MOBATIME solution
The highly accurate time synchronization for the base station is achieved by using the Precision Time Protocol (PTP, IEEE Standard 1588-2008). The PTPv2 protocol with the ITU G.8275.1 profile was selected. Therefore, a PTPv2 capable network is required, every hardware component must support PTP with this ITU G.8275.1 profile (Boundary Clock or Transparent Clock).
However, since the base stations themselves are not PTPv2 compatible, a PTP slave (DTS 4020.timebridge) has to be used. The PTP slave (DTS 4020.timebridge) is converting the PTP signal to ToD (Time of Day + 1pps) compatible with the base stations.
In the central station a redundant Grandmaster (DTS 4160.grandmaster) is installed. The Grandmaster (DTS 4160.grandmaster) are GPS synchronized and are equipped with an atomic Rubidium oscillator in order to provide an excellent holdover time. The PTP slaves (DTS 4020.timebridge) are synchronized with PTPv2 protocol.
The DTS 4020.timebridge transmits the 1PPS / 10MHz and ToD signal in the required CCSA (China Mobile) format to the base station and achieves an accuracy of < +/- 100ns in the laboratory. (Tested with a radio link)