GPS-free time synchronization in SFN networks


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Time Transfer is a value added software option for the Nimbra 360 and 680 platforms. Typically it can be used to distribute real time with high accuracy over a Nimbra network in order to enable Single Frequency Network (SFN) capabilities for Digital Terrestrial TV and Mobile TV services. Networked time transfer can also be very useful in mobile telephony networks and defense applications.

In a single frequency network the transmitter stations must be synchronized to send their signals at exactly the same time to avoid interference at the receiving antennas. Today this is achieved by installing Global Positioning System (GPS) receivers at all transmitter sites. However, GPS receivers may easily be jammed and represent an additional cost in the network. The GPS is also military controlled, which could be a concern to some countries. Previously there was no alternative solution that could deliver real time in a large public network with the accuracy needed for these applications.

Key features of Net Insight's Time Transfer solution include:

  • Standard timing interfaces 1 PPS and 10 MHz
  • Integrated distribution of time and traffic for higher reliability and reduced OPEX
  • Eliminates the need for costly and potentially insecure GPS receivers
  • Automatic optimization and restoration of timing distribution paths
  • High accuracy with maximum 1.5 microseconds timing error after 10 hops
  • Works on any topology and over SDH, PDH, wavelength, dark fiber, and microwave links

The Time Transfer option uses an augmented two-way time transfer mechanism between nodes of the network in order to compensate for link delays and diurnal wander. The links and nodes in a Time Transfer enabled network may also be calibrated for even higher time accuracy and to support asymmetric delays.

The time transfer capabilities include time interface support e.g. for headend and transmitter sites (Nimbra 360) as well as time transit support (Nimbra 360/680) for intermediate nodes. The Nimbra 360 chassis is equipped with dual pairs of time transfer interfaces (1PPS and 10MHz). The time transfer ports are configurable to support either input or output signals. The built-in synchronization protocol also supports standby reference clocks at geographically separated locations.



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