Afar AR-24010E, Руководство оператора

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pulsAR radio Operator's Manual
The traditional approaches to reduce this self-interference include:

Separate the antennas of the two radios further apart.

Use different antenna polarization.

Lower the transmit power of the interfering radio.
These approaches are limited and, at most, may allow you to co-locate three of four radios. The Afar
SPAN technology implements a synchronization scheme that completely eliminates this self-
interference allowing you to co-locate a much larger number of radios. This is explained in the
following sections.
2.4.3 SPAN Network synchronization
The pulsAR can be operated in a fixed TDD mode, where the complete cycle is divided into fixed
length outbound and inbound phases. You can specify this cycle split to be 50/50 or asymmetric.
When you co-locate multiple devices you must choose a fixed split and it must be the same for all the
co-located radios. The radios will then synchronize their cycle periods so that all co-located radios
transmit at the same time and then receive at the same time. This avoids the situation depicted in
Figure 2.4 altogether. With a synchronized site you can then deploy upwards of 24 radios at the same
location.
The key to the synchronized SPAN network is the generation and distribution of the synchronization
information or
heartbeat. At any site where there is more than one co-located radio, the various
radios detect each other, and automatically negotiate which should become the source of the
heartbeat. If that device later is turned off or fails, another device will take its place without user
intervention.
Once a heartbeat source is selected, that device multicasts into the LAN one short heartbeat packet in
every cycle. All the other co-located devices periodically measure the Ethernet transit time to the
source in order to cancel out any Ethernet delays through intervening switches. This process allows
all the co-located radios to synchronize their cycles in a very precise fashion.
Figure 2.5 shows an example of a mixed network with multiple topologies. When the whole network
is synchronized each radio runs its TDD in one of two timings, A or B, as shown in the figure. All
radios at a single site run on the same cycle.
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