User Guide

PMP 450 Planning Guide
GPS synchronization
The Navigation Satellite Timing and Ranging (NAVSTAR) Global Positioning System (GPS) use 24 satellites
to relay information for precise derivation of position and time.
The cluster management module (CMM) contains a Cambium GPS Receiver. The CMM is a critical element in
the operation of the system. At one AP cluster site or throughout an entire wireless system, the CMM provides
a GPS timing pulse to each module, synchronizing the network transmission cycles.
The Oncore GPS Receiver tracks eight or more NAVSTAR satellites. The CMM uses the signal from at least
four of these satellites to generate a one-second interval clock that has a rise time of 100 nsec. This clock
directly synchronizes APs and which, in turn, synchronize the SMs in the network.
The Oncore GPS Receiver also provides
• the latitude and longitude of the GPS antenna (collocated with the CMM)
• the number of satellites that are being tracked
• the number of satellites that are available
• the date
• the time in Universal Coordinated Time (UCT)
• the altitude of the GPS antenna
• other information that can be used to diagnose network problems.
Alternative to GPS synchronization
A link can operate without GPS sync, but cannot operate without sync. The alternative to GPS sync is to
configure the AP in the link to generate a sync pulse to pass to the SM. Depending on the RF environment in
which the link operates, this latter alternative may or may not be plausible.
For example, in Figure 28, AP4
• is not synchronized with any of the other APs.
• is transmitting nearby the other APs while they are expecting to receive SM transmissions from a
maximum distance.
pmp-0047 (March 2014)
1-117