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Introduction
The Motorola wi4 Fixed Point-To-Point (PTP) 600 Series Wireless Ethernet Link, which consists of a pair of
radios deployed one at each end of the link, 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.
Simple example of cross-
interference when three links of
different lengths are mounted
on a mast and operating on the
same or adjacent channels
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.
Before TDD Synchronization
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 co-locate multiple radios on a rooftop or tower without interference.
3
Link 1
Link 2
Link 3
Time
Transmit
Receive
Interference Link 2 to Link 1
Interference Link 1 to Link 2
Interference Link 2 to Link 3
GPS SynchronizaTion UniT GUiDE
After TDD Synchronization
Link 1
Link 2
Link 3
Time
Interference Link 3 to Link 2
Interference Link 1 to Link 3
Interference Link 3 to Link 1
Transmit
Receive
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