Trio JR240, Руководство пользователя

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Page 16
J-Series Data Radio – User Manual
Issue 09-10
Multi-Access Point
Synchronization
When more than one J-Series network shares the same physical
site (i.e: antennas for each network are in close proximity)
the Access Point radios can interfere with each other. This
interference may occur when one AP is transmitting while the
other AP is receiving. The problem is caused by receiver blocking
and desensitization.
To avoid this problem, all collocated Access Point radios can
be synchronised to transmit and receive at the same time using
a special multiple “Access Point” synchronisation feature. This
feature is enabled by configuring one Access Point radio as the
“multi-Access Point primary” Access Point and all other Access
Point radios as the “multi-Access Point secondary” Access Point.
A cable is installed between all APs which connects Pin 9 on
the Port A/Port B data port of all APs. Configuration jumpers
on the “primary” Access Point set it’s Pin 9 as an output. This
allows the “primary” AP to generate a synchronization pulse for
all “secondary” Access Points, dictating to them when they can
transmit and when they must return to receive mode. In this mode
of operation, the transmit/receive duty cycle is 50%.
When operating in this mode, all Access Point radios must have
the same hopping interval and have the appropriate configuration
for the General Purpose Pin 9 on Port B (See Port B - Advanced).
Multi-Access Point synchronisation divides each hop interval into
half - the first half is a dedicated Access Point transmit time slot
and the second half is a dedicated receive timeslot. Because the
Access Points each have the same hop interval and each hop
interval begins at the same time (as synchronised by the primary
Access Point), no Access Point will transmit when the others are in
receive mode.
As such, there is no opportunity for desensitization and
interference is limited to a very low statistical probability of two
radios transmitting on the same frequency at the same time
Multi-Access Point synchronisation can also be used in a PTMP
system by itself (i.e.: even if there is only one Access Point) for the
purpose equally sharing the bandwidth in each direction (Access
Point to Remotes and Remotes to Access Point).
In some applications it is not possible to mount separate antennas
for each Access Point. This may be due to physical (ie: tower is
already loaded to capacity) or economic reasons (ie: too expensive
to mount multiple omnidirectional antennas) or for antenna
radiation pattern reasons (ie: best location for omni antennas being
at top of tower). In the above scenarios, it is desirable for multiple
Access Points to share one common antenna.
This can also be achieved by using a 3dB combiner/splitter as
shown in the diagram below. The 3dB combiner/splitter (Mini-
Circuits ZAPD-1 or similar) much provide >25dB of isolation
between ports and be capable of handling 1W (+30dBm EIRP) RF
input powers.