User guide

Design Guide
How airSync
™
works
airSync reduces problems when co-locating multiple radios
near each other. When airSync is enabled, all APs transmit
at the same time, and receive at the same time, reducing
co-location interference. airSync synchronizes airMAX APs
with a satellite reference timing signal. When enabled,
airSync eliminates receive (RX) errors due to co-location
transmission interference. To use airSync, all Stations must
have Ubiquiti products with GPS functionality running airOS
version 5.4.5 or above.
GPS Performance Expectations
• All APs will transmit at the same time, and receive at the
same time.
• Reduces co-location interference.
• Latency may be slightly higher (8-16 ms latency), but it
should be constant as network scales.
• Throughputisxed(xedtimeslots/directions),sothe
throughput in one direction may be as much as half of
what it is with airSync disabled, but it remains constant
as the network scales. Lower timing values will provide
better TCP performance (especially single stream) but the
throughputwillbelowerwhensendingbulktrafcwith
lotsofTCPstreamsmultiplexed.Highertimingvalueswill
provide better multi-stream TCP and UDP performance,
but at the cost of latency. Overall throughput linearly
increases based on the number of APs.
Recommended Guidelines
• Adjacent sectors should use different frequencies.
• Back-to-back sectors can use the same frequency.
• Do not use the same frequency on ALL of your co-located
APs. Some of your co-located APs may be able to use
the same frequency, depending on the scenario. See the
Design Examples: Four APs and TwoAPs.
• The number of frequencies you should use depends on
the number of APs you have on a single tower because a
client can get confused if it receives signals on the same
frequency from two different APs.
• If using more than one frequency, ensure that you have
20MHzseparationbetweenthefrequencybandedges.
Forexample:iffrequencyrangeAendsat5815MHz,then
frequencyrangeBshouldstartat5835MHzorhigher.
Requirements
To sync multiple APs, these are the requirements:
• ThemasterAPhasIPconnectivity(specicallyUDP)tothe
slave APs.
• All APs have an active GPS signal.
• Transmitandreceivedurationshavebeenconguredon
the master AP.
Design Examples
Four APs
Use two different frequencies. Set the same frequency on
eachback-to-backpairofAPs.Forexample,aclientislocated
equidistant from two APs (one set to frequency A and one set
to frequency B). The client will only receive signals from the
AP that shares its frequency. Be sure that A and B have at least
aminimumof20MHzchannelseparation.
ABAB Channel Design
Three APs
SetadifferentfrequencyoneachAP.Forexample,aclientis
located equidistant from two APs (one set to frequency A and
one set to frequency B). The client will only receive signals
from the AP that shares its frequency. A different client is
located equidistant from a different pair of APs (one set to
frequency B and one set to frequency C). This client will only
receive signals from the AP that shares its frequency.
ABC Channel Design
Two APs
Set the same frequency on both APs located back to back.
AA Channel Design
Design Guide