User guide

Canopy System User Guide Understanding Synchronization
pmp-0229 (Mar 2013)
95
Alternative to GPS Sync
A link can operate without GPS sync, but cannot operate without sync. The alternative to GPS
sync is to configure the AP or BHM in the link to generate a sync pulse to pass to the SM or BHS,
respectively. Depending on the RF environment in which the link operates, this latter alternative
may or may not be plausible.
For example, in Figure 27, 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.
Time
Figure 27: One unsynchronized AP in cluster
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, or a BHM in an
isolated standalone BH link 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.
NOTE:
The OFDM Series BHMs generate their own sync. For more information about
these modules, see the user guides that support them. Titles are listed under
Products Not Covered by This User Guide on Page 24.