longest ip link

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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of 12The World’s Longest All-IP Microwave Link « AVIAT NETWORKS: Official Wireless ...

03-08-2011http://blog.aviatnetworks.com/2011/05/04/the-worlds-longest-all-ip-microwave-link/

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

« Synchronization Over Microwave Mobile Backhaul Networks

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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



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


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



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.


May 10, 2011

at 10:19 AM

Reply



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


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


June 24, 2011

at 4:03 PM

Reply



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


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


May 16, 2011

at 3:39 PM

Reply



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:

[email protected]

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


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


May 24, 2011

at 5:07 PM

Reply



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.


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.


June 24, 2011

at 4:12 PM

Reply

of 12The World’s Longest All-IP Microwave Link « AVIAT NETWORKS: Official Wirele...


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


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.


June 24, 2011

at 4:23 PM

Reply

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