Ubiquiti AF5 Design Guide

DESIGN GUIDE: airFiber AF‑5/AF‑5U

Best Practices for Installation of the airFiber AF‑5/AF‑5U

Ideal Mounting Location: High in Elevation with
ClearLine of Sight

Custom Frequency and Transmit Power
Conguration to Fit Your Application

Selection of Installation Site

The airFiber® AF‑5/AF‑5U, referred to as the AF‑5 in this Design
Guide, features unique functionality that requires you to be
cognizant of the installation environment.

For best performance, you must install the AF‑5 as high up
as possible, with a line of sight free from obstructions. This is
especially true in FDD (Frequency Division Duplexing) mode,
as there is a requirement to maximize channel/spectrum reuse.
Any objects in front of or near the front of the AF‑5 can have a
signicant impact on overall performance. The AF‑5 should be
installed 1 m (3.3 ft) below the highest point of the structure
to reduce the risk of a lightning strike. When the AF‑5 must be
installed above a metallic surface like a corrugated at roof or
water tower, you should ensure that the AF‑5 is located more
than 3 m (10 feet) above the metal/reective surface.

1 m (3.3 ft)

Good Location

Throughout Optimization with Maximum
Frequency Reuse and Link Symmetry

What is generally true for cellular installations is true for
the AF‑5. You should mount the AF‑5 where it can see no
reections in the near eld, so we recommend the following
types of mountingsites:

§ Perimeter mounting on a water tower/structure (best)

§ Mounting near the edge of the top of a structure

§ Mounting on an elevated mast or tower

Radios that are mounted anywhere near the surface of a
roof or the top of a water tower can be signicantly aected
by reections. FDD is more susceptible to the elements
of a deployment environment than TDD (Time Division
Duplexing)is.

Bad Location:

Reection o Rooftop

and Lip of Building

Best Location

3 m (10 ft)

Close-up of Installation on Top of Water Tower

Close-up of Installation on Rooftop of Building

Good and bad examples of deployments are depicted in this
section, “Typical Deployment Scenarios” on page 2.

Typical Deployment Scenarios

1 m (3.3 ft)

Good Location

Reective Surface

Reective Surface

Bad Location

Bad Location

3 m (10 ft)

Good Location

Minimal Reective

Surface

Best Location:

No Reective

Surface

Best Location

Deployment on Water Tower

Good Location

Bad Location:

Too close to rooftop and

obstruction in line of sight

Deployment on Rooftop of Building

Bad Location:

Too close to rooftop

and lip of building

Best Location

Frequency Conguration

FDD will be most useful in situations that have plenty of
spectrum available and will show the greatest benet on
shorter‑range links. For optimal performance, you should plan
out channel pairs that have maximum frequency separation.
Since the AF‑5 uses sophisticated data processing algorithms
and a special antenna structure to eliminate the need for a
pre‑congured duplexing lter, you should space the two
duplex channels at either end of the spectrum near the band
edges for maximum‑range applications.

Generally speaking, you can congure shorter‑range links

for less channel separation between uplink and downlink.
You should also use the narrowest channel bandwidth that
supports the intended link capacity. This conserves valuable

frequency resources and also maximizes link budgets.

The airFiber5Conguration Interface includes the Link
Calculator* conguration tool that will guide you on how to

best minimize bandwidth and power/interference based on
the specic requirements of your installation.

Examples of airFiber5 Link Calculator

* If you do not see the airFiber5 Link Calculator, download the latest airFiber5 rmware at: downloads.ubnt.com/airber

Transmit Power Conguration

Power Balance Optimization for FDD

The AF‑5 allows for a very high degree of exibility in
conguring transmit power, supported constellations, channel
bandwidths, and duplexing modes. Because of the number of
conguration options, refer to this guideline as you customize
your AF‑5 conguration:

Depending on the country or region, the AF‑5 may be
congured to support maximum transmit power as high
as +50 dBm EIRP. Power levels in excess of approximately

+43dBm will start to aect the maximum supported

constellation.

TX Power (dBm EIRP) Supported Constellation

43 256QAM

45 64QAM

47 16QAM

50 QPSK

For example, if you have a relatively short‑range link and you
need to support a maximum constellation of 256QAM, then
congure the AF‑5 for less than +43 dBm EIRP.

To minimize interference, you should use the lowest practical
power setting that supports the intended target constellation
for a given distance. Looking at the sensitivity values for the
given channel bandwidth, you should target a receive signal
value approximately 3 to 6 dB higher than the sensitivity
threshold.

10 MHz 20 MHz 30 MHz 40 MHz 50 MHz

10x ‑63 dBm ‑60 dBm ‑59 dBm ‑58 dBm ‑57 dBm

8x ‑70 dBm ‑67 dBm ‑66 dBm ‑65 dBm ‑64 dBm

6x ‑77 dBm ‑74 dBm ‑73 dBm ‑72 dBm ‑71 dBm

4x ‑84 dBm ‑81 dBm ‑80 dBm ‑79 dBm ‑78 dBm

2x ‑90 dBm ‑87 dBm ‑86 dBm ‑85 dBm ‑84 dBm

1x ‑93 dBm ‑90 dBm ‑89 dBm ‑88 dBm ‑87 dBm

In the default state, the AF‑5 has this conguration:

§ TX power: +40 dBm (EIRP)

§ Channel bandwidth: 10MHz

§ Duplexing mode: TDD

To optimize throughput with maximum frequency reuse:

1. Aim the AF‑5 using the factory default settings andTDD.

2. Allow the AF‑5 to automatically rate‑adapt.

3. Congure the AF‑5 for FDD operation.

4. Check the modulation rate and capacity indicators for
asymmetry.

5. You may notice signicant asymmetry. If you do, then this
could be due to a poorly aimed AF‑5 or an AF‑5 that is
operating in some sort of reective Fresnel environment.

Ensure that the AF‑5 is correctly aimed and free of any
potential reections before proceeding to the next
procedure.

To optimize both ends of the link for the best symmetry:

1. Test for a local desense condition (possibly due to a
reection or other disturbance). Begin with the AF‑5 that is
receiving the lowest RX capacity reading, and decrease the

TX power on that AF‑5 by 1 dB.

a. Check if there is any increase in the RX capacity at the AF‑5.

b. Watch for decreases in the TX capacity of the AF‑5.

2. Perform step 1 iteratively to nd out if there is any RX
capacity sensitivity to the local TX power level.

3. If this condition persists, try the following:

a. Run the lowest transmit power that still allows for the best

balance of performance on both ends of the link.

b. Increase the FDD frequency separation and repeat the

optimization process. (In general you should run the
lowest power possible to meet the data rate requirements
for the link.)

This link symmetry procedure should be repeated on the
opposite end of the link to test for desense on the other side.

Ultimate ‑95 dBm ‑93 dBm ‑93 dBm ‑92 dBm ‑91 dBm

To obtain the greatest range performance, you may
want to explore power settings above +43 dBm since
the longest‑range links will be limited to the lower‑order
constellations. The best possible range will be achieved with
a combination of maximum power level, narrowest channel
bandwidth, lowest‑order constellation, and TDD.

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If desense is not an issue, then try this method to mitigate
the asymmetry: Slightly increase the transmit power on the
opposite end of the link. (Note: This should be tried only after
you rule out local desenserst.)

For the best possible FDD performance, use as much

frequency separation as possible to minimize external
coupling of energy.

Online Resources

Support: support.ubnt.com

Community: community.ubnt.com/airber
Downloads: downloads.ubnt.com/airber