Motorola PTP 300 - Manual (Page 30)

PTP SOLUTIONS GUIDE 30
The Motorola Fixed Point-To-Point (PTP) 600 Series Wireless Ethernet Link consists of a pair of radios
deployed one at each end of the link and operates on a single frequency channel in each direction using
Time Division Duplex (TDD). In situations where a number of radios are installed on the same mast or where
a large number of links are installed in a sizeable, dense network, it is possible that the performance or
throughput of some of the links can be reduced. In some cases, a number of the links may not work at all.
This is due to interference between the units, and the levels of interference can worsen when the links are
operating on the same or adjacent channels.
Memorylink UltraSync™ GpS-100M
Synchronization Unit
The effect of this cross interference between units can be reduced by ensuring that the radios are in
synchronism, meaning that transmit and receive frames of the units are synchronized so they do not interfere
with each other. TDD Synchronization introduces a fixed TDD framing mode and allows frame timing in a
PTP 600 link to be synchronized with an external reference – a Global Positioning System (GPS) unit.
The result is that TDD synchronization minimizes the interference between links and promotes optimal spectral
re-use while greatly enhancing link performance. By timing and synchronizing transmit and receive signals,
network operators can collocate multiple radios on a rooftop or tower with greatly reduced interference.
Simple example of cross-
interference when three links of
different lengths are mounted
on a mast and operating on the
same or adjacent channels
Link 1
Link 3
Interference Link 3 to Link 2
Interference Link 1 to Link 3
Interference Link 3 to Link 1 Interference Link 2 to Link 1
Interference Link 1 to Link 2
Interference Link 2 to Link 3
Link 2
Time
Transmit Receive
Link 1
Link 3
Time
Link 2
Transmit Receive
Before TDD Synchronization
After TDD Synchronization