NCR (Network Clock Reference) is a procedure to provide the master clock (i.e. time information) of the satellite to all its user terminals. Typically, NCR packets are provided periodically over a continuous DVB-S2 or DVB-S2X link. The receiving user terminal uses the knowledge of the master clock in the system to determine when it is allowed to transmit data in a time-division multiple access (TDMA) system, such as DVB-RCS or DVB-RCS2.
In these TDMA systems, the same frequency band is shared among many terminals, making it mandatory to apply a strict transmission schedule for all terminals. The NCR Processor IP core has two main functionalities:
* NCR tracker
* NCR local clock
The NCR tracker provides a local NCR clock which is frequency- and phase-latched to an incoming DVB-S2/DVB-S2X stream containing NCR information. The absolute phase difference between the NCR tracker and the clock source, e.g., satellite, depends upon the distance to the clock source. The NCR local clock provides a precisely settable NCR source clock provided a local and stable 27 MHz clock and a precise 1 PPS (Pulse Per Second) source are available.