PMP Synchronization Solutions User Guide
Neutralizing interference
PMP-0297 007v001 (January, 2017)
1-6
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
, 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.
Figure 2 One unsynchronized AP in cluster resulting in self-interference
The result is self-interference. In this scenario, the self-interference can be avoided only by
synchronizing the TDD transmit cycles of all APs that operate in the same frequency band.
An AP that is isolated by at least 5 miles (8 km) from any other equipment can generate
and pass sync pulse without GPS timing and not risk that interference will result from the
generated sync. In any other type of link, sync should be derived from GPS timing.
Although the embedded timing generation capability of the AP keeps a precise clock
(configuration parameter Sync Source set to Generate Sync Signal), no trigger exists to
start the clock at the same moment in each AP of a cluster. So, the individual AP can
synchronize communications between itself and registered SMs, but cannot synchronize
itself with other modules, except by GPS timing.
Time
