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Posted by: aviatnetworks | May 4, 2011 The World’s Longest All-IP Microwave Link
Successfully Implementing a 193-km Microwave Link over Water to Deliver 99.9995 Percent
Availability
Introduction
For most designers of microwave transmission paths, engineering a reliable link over water can be a
daunting task. Reflections off the water surface can play havoc with the received signal, leading to
high levels of interference resulting in fading and ultimately a high level of errors and signal
interruptions. For these types of paths, performance calculations using commercially available
software planning tools will be insufficient to ensure superior path performance. In these cases,
experience and understanding of the key parameters that influence microwave performance are
critical.
Recently, Aviat Networks and our agent, Telecomunicaciones y Sistemas S.A. (TELSSA), deployed
an Eclipse microwave link for Central American Corporation for Air Navigation Services (COCESNA)
in Honduras that crosses over 193 km, most of which is over water. With careful design and
installation, this link is now operating successfully.
COCESNA is responsible for the air traffic control over Central America territory and oceanic areas,
therefore, availability of service is a critical issue.
Key Design Considerations
A key design criteria for designers to keep in mind is the prevalent propagation conditions to meet or
exceed the expected Error Performance Objective (EPO), particularly for the design of very long
terrestrial microwave systems traversing large and warm bodies of water, like the ones prevailing in
Central America. To meet the specified EPO for any path, designers must have a thorough
understanding of the following key aspects:
a) The effect of antenna diameter
b) Precise alignment
c) Accurate diversity spacing to counter reflections
d) Deterministic prediction of the variations of atmospheric conditions
e) Multi-path propagation delay
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With these parameters in mind, achieving a microwave path that delivers fiber-optic level error
performance over water is possible. The mathematical models to predict the link’s EPO don’t have a
meaning if the design variables above are not fully grasped, respected and implemented.
Understanding Local Propagation Conditions
Understanding the behavior of the atmospheric conditions determines the type of design needed to
accommodate how the link will perform over time in any region, regardless of the temporal, seasonal
and climatic variations along the path. In Central America, with its warm days and nights, standard
propagation is prevalent, because the troposphere in this region is “assumed” to be
thermodynamically unstable and in a state of constant turbulent mixing—ducting (a key propagation
impairment over long paths) has not been observed.
Under these conditions and based on Aviat Networks’ experience, long (exceeding 80 km), over-
water, semi-horizontal and windy paths exhibit excellent performance, even with relatively low
ground elevations above mean sea level at both sites.
The Design
For the 6GHz, QPSK, 40 Mbps, 193-km path in Honduras, which was more than double the length
of a typical long microwave path, experience, propagation considerations and exact installation were
crucial in the design. Even though the path inclination was relatively small, Aviat Networks’
prediction of the propagation conditions’ “soft” fluctuations along the path determined that the link
was viable. To span such an enormous path, sufficient site elevation is a must to prevent diffraction
or blockage. In this design, Site A, “Las Cruces,” is at 1600 meters above mean sea level and Site
B, “Dixon Hill,” at 250 meters on Roatan Island. The reflections and delay were optimally neutralized
with precise antenna spacing and up-tilt.
Figure 1. Microwave Path Profile showing antenna elevations and path clearance over effective
earth curvature.
To make the design even more unusual and challenging, the short radar tower facility at Site B
Dixon Hill lacked space to mount a second space diversity antenna. As a result, Aviat
Networks/TELSSA installed the second antenna on a separate structure, located 15 meters in front
of the main antenna. Consequently, the design had to take into account and negate any additional
signal delay arising from the horizontal antenna offset.
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Figure 2. Diversity antenna installation showing 15 meter horizontal separation
at the radar site Dixon Hill.
The resulting link was designed to provide an overall availability of 99.9995 percent availability,
equating to just 32 seconds of accumulated outage every year.
Installation
Once the design was done, the challenge was not over. Ensuring superior link performance took
careful and exact installation, with precise alignment of the antennas by an experienced crew to
achieve a stable received signal level. A few days after the initial alignment, the crew revisited the
1600-meter site to adjust the antenna installation to counter very strong wind shears that threatened
to cause instantaneous twisting of both antennas that could degrade performance.
Figure 3. The view looking out from Site A, Las Cruces, (elevation 1600
meters) across the water.
The Result
With the design and installation complete, further adjustments were made for local weather
conditions. The microwave link was then monitored over several days to measure actual
performance to verify that it met or exceeded the design requirements.
The measured unfaded link RBER (Residual Bit Error Rate) performance test showed a result of
1×10-13, or just one bit error for every trillion bits received. This level of error performance is
equivalent to what you would expect if you connected two Eclipse terminals on a bench, directly
connected by a cable! The link is also exceeding the 6-9’s availability target.
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Posted in Aviat Products & Features, Customer Stories, From the Field, Technology, Tips & Tricks,
Transmission Engineering | Tags: Central America, Honduras, Ivan Zambrano, Space Diversity, World
Longest Link
“This IP link was a challenge for us from the moment of the project’s inception, but we have always
relied on link engineering support from Aviat Networks to complement installations carried out by our
engineers and technicians—who have great experience in complex hops—which has led to
excellent results,” says Jose Raul Gomez, CEO TELSSA.
At 193 km, this Eclipse link is probably the longest all-packet microwave link in the world and
demonstrates that making challenging paths work well takes experience, superior product
performance and quality, careful design and precise installation, with results that can—and did, in
this case—exceed customer expectations.
Ivan Zambrano
Senior Network Engineer, Aviat Networks
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Refarming UHF Spectrum: Wireless Opportunities & Challenges for 4G »Like
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RESPONSES
Great achievement. Well done. Proud to be an
Aviat Employee.
By: Sunil Kumar on May 4,
2011
at 3:10 PM
Reply
Great job. I’d like to see the pathloss
calculations.
Thanks,
Tony
By: Tony Maietta on May
5, 2011
at 1:33 PM
Reply
Hi, Tony,
Thanks for your comment. It was a very
challenging but rewarding project.
Unfortunately, the pathloss calculations
are based on proprietary data, and we cannot release
them online. You might get a rough idea of what they are
by using a wireless engineering tool such as Starlink,
though there was additional tweaking of the numbers by
hand. But if you would like a closer discussion regarding
the calculations offline, we would be happy to give your
request more consideration. Let us know.
Best,
Aviat Networks
By: aviatnetworks on
May 10, 2011
at 9:56 AM
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Great achievement. Good Job. Proud to be
an Aviat Employee.
By: Mirza Baig on May 5,
2011
at 1:48 PM
Reply
Obviously a great achievement! Wish I was
working with that installation team!
I was always dreaming to do this kind of precise
installation job.
Excellent!!! Feeling very proud to be an Aviat
employee!
By: Shibly Sadik Al Zaidy
on May 4, 2011
at 10:17 PM
Reply
Dear Ivan,
Your “news” is abolutely great. I love it!
Congratulations.
By: William Leclerc on
May 5, 2011
at 12:35 AM
Reply
Fantastic technological achievement, fascinated
and intrigued when reading this blog, by Aviat’s
true genius.
By: Peter A Coward on
May 5, 2011
at 4:21 AM
Reply
Great achievement. Congrats!! What is the dish
size used for main and standby??
By: Umar Khan on May 5,
2011
at 2:11 PM
Reply
Thanks, Umar,
For this wireless installation, we used four 3-
meter antennas for main and standby.
Regards,
Aviat Networks
By: aviatnetworks on
May 10, 2011
at 10:12 AM
Reply
Loved reading your report.
I have engineered a number of links to offshore
platforms.
The maximum path length was/is 73 km (high –
low path) and using hybrid space / frequency
diversity. And carefully modeling path geometry
over range of k = +.5 to k = -.5 also achieved great results – at
times the diversity combiner switch has to cope with very high
transitions from A – B path but modeling showed that by carefully
By: John Churchill on May
5, 2011
at 8:30 PM
Reply
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choosing frequency and antenna spacing, the reflection fading on
one path does not correlate with fading on the other path, hence
– providing the diversity combiner switch is functioning – traffic is
unaffected.
Your 193 km link definitely sets the record.
Great job,
I am proud to work with these professionals who
made these links.
Regards
Pavel Kamburov
By: Pavel Kamburov on
May 5, 2011
at 10:09 PM
Reply
Appreciable achievement! This breaks our record
in india 162 Kms link in 7Ghz.
By: ashmar on May 6,
2011
at 12:01 AM
Reply
My 2006 Tutor has done it. Well done Ivan and
co. Reflection analysis is one of the 2 most
important considerations for a path like this. I
learned that from you.
By: Rasheed Amuda on
May 6, 2011
at 2:15 AM
Reply
A very impressive achievement given the
99.9995 availability and over water tx.
By: Joro Joe Sallau on
May 6, 2011
at 4:41 AM
Reply
Congratulations!!!! I’m interested in knowing what
was the diameter size of the antennas employed
due to the long distance of the link? Also, was a
QPSK signal used as well due to the distance or
was it 16 or 128 QAM?
Again congratulations!
By: Gerard Casey on May
6, 2011
at 7:08 AM
Reply
Hello Gerard,
For this long distance installation over water,
we employed QPSK for more robustness and
used four 3-meter diameter antennas.
Let us know if you’d like anymore information.
By: aviatnetworks on
May 10, 2011
at 10:19 AM
Reply
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Regards,
Aviat Networks
Ivan presented this feat to us in person during his
last visit to MTN-SA. Congratulations!
It would be very interesting to get an update on
recorded link reliability (i.t.o. SES & Availability) a
year after it has been put into operation.
By: Freddie (MTN-SA) on
May 6, 2011
at 7:55 AM
Reply
Stunning job…great work done. I wish I was part
of that planning team, being a microwave
planner….
By: Masood Yousfani on
May 10, 2011
at 10:08 PM
Reply
Great Achievement.
Can anyone share the Link Budget?
By: Deep on May 11, 2011
at 1:11 AM
Reply
Thanks, Deep,
We checked with the customer and they wish
to keep the link budget confidential.
Sorry!
Aviat Networks
By: aviatnetworks on
May 12, 2011
at 7:52 AM
Reply
WOW, Great job man. Hats off to you! Can you
please provide some more details like polarity,
TX power and antenna spacing? It’s only SD?
Have you de-correlated the specular reflections?
15 M diversity antenna offset? How did you de-
correlate that?
Thanks,
BR
Hasnat Babar
By: hasnat babar on May
11, 2011
at 1:57 PM
Reply
Hi Hasnat,
Over water paths should be assigned vertical
polarization to reduce the reflective fade
depth; for this reason, vertical polarization
was used here. The antenna spacing was less than 10-m at
each end; with this, the reflections were totally de-correlated.
Transmit power was around 1-W; however, this is by no
By: aviatnetworks on
June 24, 2011
at 4:03 PM
Reply
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means “relevant” in path design in the majority of cases.
What’s important is solid path engineering and all its
implications to span microwave radios over any type of geo-
climatic conditions and meeting the Error Performance
Objective. The horizontal offset was due to the fact that the
radar tower was too short to accommodate both dishes.
Regards,
Aviat Networks
Good job!
I am interested in knowing radio & antenna
system parameters used in this link.
By: Hassan on May 13,
2011
at 3:55 AM
Reply
Thanks, Hassan,
The only additional information we are able
to reveal is that the antenna diameters were
3 meters and a QPSK modulation was used
in the link. If you would like any additional details, perhaps
we can talk offline. Let us know.
Regards,
Aviat Networks
By: aviatnetworks on
May 13, 2011
at 8:46 AM
Reply
Really a great achievement…a new benchmark
set in the field of MW.
Ahsan Ghumman…TXN Microwave Engineer,
Pakistan.
By: Ahsn Ghumman on
May 13, 2011
at 5:46 AM
Reply
Hi all,
I am fortunate enough to know part of the team
behind this great achievement and for them all I
leave my congratulations.
All the best!
Paulo
By: Paulo Nunes on May
16, 2011
at 2:58 PM
Reply
Hi Paulo,
Thanks! Ivan and team are really glad this
got your attention! We hope to have
something further on this at a later date.
Stay tuned!
Regards,
Aviat Networks
By: aviatnetworks on
May 16, 2011
at 3:39 PM
Reply
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Great…!! Just a Buff..!!
I’m working with NSN and learned lot from my
team and projects I undertook…but anytime, if
given a chance, to be a part of these activities is
a dream of mine.
Congratzzz Team…!!
Many Thanks..!
Ashish Jain
By:
ashish.9.jain@nsn.com
on May 19, 2011
at 1:05 AM
Reply
Great Achievement! To implement an MW link
over water for 193 km and with 99.9995%
availability is stunning. Congratulations to all the
members of that team.
We would like to know, the antenna gain and the channel
bandwidth used for this link.
Thanks and regards
Sayan Asanar
By: Sayan Asanar on May
19, 2011
at 1:12 AM
Reply
Hello Sayan,
Thanks for your positive comments. To
answer your questions succinctly, the
antenna gain is 43.3-dB and the RF channel
bandwidth is 28 MHz.
Regards,
Aviat Networks
By: aviatnetworks on
May 24, 2011
at 5:23 PM
Reply
I am a transmission maintenance engineer. I
need to know that the link will have the same
performance all the time or not? I’m interested in
knowing the diameter of the antennas employed
due to the long distance of the link. Maybe 3.2
meters or more. Also, was QPSK used as well
due to the distance or was it 16 or 128 QAM? Why not more
capacity?
Congratulations to the team to design such a link!!!
By: Amit on May 20, 2011
at 1:17 AM
Reply
Hello Amit,
A microwave communications link’s
performance is standardized by American
and ITU Error Performance Objectives that
By: aviatnetworks on
May 24, 2011
at 5:07 PM
Reply
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predict the time the link will be “off the air” due to standard
atmospheric multi-path conditions. Consequently, we expect
that this link will meet or exceed the customer’s objective.
For the antennas, 3-meter units were used. Due to the geo-
climatic conditions and capacity requirements, QPSK was
implemented. Why not more capacity, you ask? There’s a
possibility that more capacity can be supported, but the
customer did not specify this objective at this time.
Regards,
Aviat Networks
Dear, Ivan,
Thank you for this interesting information, and
could you please indicate what K-factor value
was used in the design for the Earth bulge
clearance. As well, could we have some more explanation on
why the diversity antenna was installed away horizontally and not
vertically, as usual, with the main antenna.
Regards,
Jean
By: Jean on May 21, 2011
at 4:37 PM
Reply
K=4/3. The horizontal offset was fortuitous
because the radar tower was too short.
By: aviatnetworks on
June 24, 2011
at 4:08 PM
Reply
Ivan & Team,
This is a great feat keeping in mind that the path
is over water and the link’s throughput is 40Mbps!
There is a lot for us to learn here; please share
with us the link’s performance stats.
Best Regards,
Joseph
By: Joseph Mwangi on
May 22, 2011
at 10:25 PM
Reply
Joseph,
“Wireless fiber optics performance” is
possible with microwave when many
experience-rich factors converge. This type
of behavior is due to a good assessment of the propagation
conditions, solid path design and optimum antenna
separation and alignment. These three parameters are of
paramount importance to span any geo-climatic conditions
and still meet the expected Error Performance Objective
according to Vigants or ITU.
By: aviatnetworks on
June 24, 2011
at 4:12 PM
Reply
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Regards,
Aviat Networks
Fascinating achievement! 20 years ago Richard
U. Laine and Ross Lunan from Harris MCD wrote
several top value articles on the design
techniques for difficult links. How far was this
knowledge applied to this link design and which
new knowledge—if any—was used? It is worth it
to supplement these classic articles with a new part describing
this record link design.
Regards,
M.J.
By: M. Jüngst on May 27,
2011
at 2:30 PM
Reply
Dear M.J.,
Definitely, the technical descriptions
contained in the papers written by the “old”
masters are necessary to predict the
performance of difficult Ethernet paths. What’s important
here, as in any link design, is the knowledge of the
propagation conditions to assess how they vary over time to
adapt the antenna system to the geo-climatic conditions. The
papers written by Dick Laine are of great relevance in the
design of these types of challenging links.
Regards,
Aviat Networks
By: aviatnetworks on
June 24, 2011
at 4:19 PM
Reply
What equipment was used? Was it an IDU GE
with 20x or an INU-based system and what type
of ODU was used.
By: Gautam on June 14,
2011
at 10:05 AM
Reply
ODU 300hp, INU with DAC ES. This is a
native Ethernet link, 40 Mbps.
By: aviatnetworks on
June 24, 2011
at 4:23 PM
Reply
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