ConnecTechAsia Show Daily - Day 1, 2019 - 40

40

Incorporating:

Show Daily | Tuesday 18 June 2019

MARINA BAY SANDS & SUNTEC SINGAPORE

CWDM vs DWDM:
What's the difference?
Dense	Wavelength	Division	Multiplexing	(DWDM),	with	its	routes	in	the	
IP domain has suddenly become a hot topic for the satellite industry,
says Steve Fendley of ETL Systems...

G

enerally speaking, there is now a much
bigger distance between the satellite
dish and operating center. When sending
signals over 400km distances and in certain
circumstances, DWDM is the only reliable way
to do that without affecting signal quality.

RF over Fiber
When you send RF signals from a satellite
dish over fiber to the control center, how
you do it depends on a number of factors.
These include the distance it needs to travel,
the number of fibers you have, whether you
own that fiber or have to rent it, how many
channels there are, for example. The simplest
way to do it is to have a separate fiber for
each feed. In 90% of cases we are talking just
a few feeds coming off the antenna and going
across a short unimpeded distance. In these
cases, simple works absolutely fine.
However, the demand from SatComs
operators requesting to carry signals
from dishes over hundreds of kilometers
distances has surged. And the rising use
of High Throughput Satellite (HTS) and KA
Band is one of the biggest drivers for DWDM
technology. Many operators are deploying
diverse sites to combat potential rain fade,
which can cause severe loss of signal in
extreme weather conditions. But the distance
of diverse sites away from the main site
depends on the location. In some places,
weather is so localized that 40 kilometers may
be enough. But in most scenarios, between
70 - 100 kilometers is required to be in a
different weather pattern. The signals need to
get to both the main and backup antennas in
the same condition and DWDM is currently
the only way to ensure that.

What is the difference
between DWDM and CWDM?
There is often confusion between Coarse
Wavelength Division Multiplexing (CWDM)
and DWDM. Both technologies are able to
send multiple optical signals over single
fibers.
CWDM combines up to eight optical
signals on a single fiber by using different
wavelengths (at 20 nanometers apart) for
each signal. Wavelengths are combined in a
CWDM multiplexer and separated at the other
end in a CWDM demultiplexer.

Steve Fendley is International Sales Manager
at ETL Systems. Steve has over 25 years'
experience in sales, as well as technical
expertise in RF and microwave components
and systems and fiber optic system design

CWDM combines up to eight
optical signals on a single fiber

DWDM combines multiple optical signals
on a single fiber, again by using different
wavelengths. These are combined and
separated using DWDM multiplexers
and demultiplexers, in the same way as
CWDM. However, DWDM transmitters use
a different laser technology, each creating a
narrower spectrum of light allowing a higher
number of wavelengths to be combined in
a narrow optical bandwidth, allowing them
to be combined at spacings of less than 1
nanometer.
The problem arises when you want to go
over a longer distance. This naturally causes
more optical loss in the fiber, resulting in
the use of an optical amplifier to boost
signal. This is most commonly done using
an Erbium-Doped Fiber Amplifier (EDFA).
The distance at which the EDFA becomes
necessary depends on the quality of the
equipment and the fiber itself. Generally, if you
operate above 70 kilometers, you are likely to
need an EDFA but sometimes you may need
that at a shorter distance.
As soon as you use an EDFA, CWDM
becomes unfeasible. Because EDFAs are
inherently narrow band so in order to amplify
multiple wavelengths you now need that
much finer optical signal only achieved with
DWDM.

The Challenges

The Opportunity of DWDM

DWDM is becoming increasingly important
in the satellite industry. However, it is not
without its challenges. The biggest of which
is that of dark fiber, i.e. fiber that is rented,
usually from a telecoms operator.
Most long fiber transmission paths use dark
fiber. Which makes sense, as even though the
cost of rental is extremely high wherever you
are in the world, the cost and effort of laying
your own fiber is even higher and totally
impractical.
Making cost another driver for DWDM.
Nobody wants to rent more fibers than
necessary, therefore being able to send
multiple signals on a single fiber is very
attractive.
However, dark fiber isn't without
disadvantages. Not knowing the condition of
the cable you are using and lack of specialist
knowledge from providers can be a drawback.
Many telecom operators do not understand
the requirements for RF signal transmission.
Consequently, making it clear that RF
signals need a dedicated and specific type
of fiber cable, not shared with other data
communications is quite challenging. If that
is not adhered to, it can be detrimental to the
signal, the very thing we are trying to protect.

Despite that challenge, DWDM mostly
represents an excellent opportunity for
those long-distance signals. Dark fiber can
have its challenges, but predominantly it
doesn't cause a problem, with many telecom
operators perfectly able to adhere to stringent
RF requirements.
Ultimately, DWDM means that RF signals
can be sent over hundreds of kilometers
without massive signal losses, therefore
maintaining that all important quality of the
feed.
Of course, if your antenna and control
center are 50 kilometers away and only have
a couple of feeds, use a normal RF over
fiber link. If you are crossing long distances
but you have a perfectly functioning satellite
network in each location, use satellite.
However, if you need something that works
when satellite is not available or could be
disturbed by extremes in weather, DWDM is
an extremely valuable, even vital, technology.
See ETL at Stand 1V3-03 MBS.
www.etlsystems.com
ETL Systems designs and manufactures
RF satellite signal handling equipment and is
one of the largest of its kind in the UK.

Rain fade: HTS and KA Band drives demand for DWDM technology


http://www.etlsystems.com

ConnecTechAsia Show Daily - Day 1, 2019

Table of Contents for the Digital Edition of ConnecTechAsia Show Daily - Day 1, 2019

ConnecTechAsia Show Daily - Day 1, 2019 - Intro
ConnecTechAsia Show Daily - Day 1, 2019 - Cover1
ConnecTechAsia Show Daily - Day 1, 2019 - Cover2
ConnecTechAsia Show Daily - Day 1, 2019 - 3
ConnecTechAsia Show Daily - Day 1, 2019 - 4
ConnecTechAsia Show Daily - Day 1, 2019 - 5
ConnecTechAsia Show Daily - Day 1, 2019 - 6
ConnecTechAsia Show Daily - Day 1, 2019 - 7
ConnecTechAsia Show Daily - Day 1, 2019 - 8
ConnecTechAsia Show Daily - Day 1, 2019 - 9
ConnecTechAsia Show Daily - Day 1, 2019 - 10
ConnecTechAsia Show Daily - Day 1, 2019 - 11
ConnecTechAsia Show Daily - Day 1, 2019 - 12
ConnecTechAsia Show Daily - Day 1, 2019 - 13
ConnecTechAsia Show Daily - Day 1, 2019 - 14
ConnecTechAsia Show Daily - Day 1, 2019 - 15
ConnecTechAsia Show Daily - Day 1, 2019 - 16
ConnecTechAsia Show Daily - Day 1, 2019 - 17
ConnecTechAsia Show Daily - Day 1, 2019 - 18
ConnecTechAsia Show Daily - Day 1, 2019 - 19
ConnecTechAsia Show Daily - Day 1, 2019 - 20
ConnecTechAsia Show Daily - Day 1, 2019 - 21
ConnecTechAsia Show Daily - Day 1, 2019 - 22
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ConnecTechAsia Show Daily - Day 1, 2019 - 26
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ConnecTechAsia Show Daily - Day 1, 2019 - 28
ConnecTechAsia Show Daily - Day 1, 2019 - 29
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ConnecTechAsia Show Daily - Day 1, 2019 - 31
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ConnecTechAsia Show Daily - Day 1, 2019 - 40
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ConnecTechAsia Show Daily - Day 1, 2019 - Cover3
ConnecTechAsia Show Daily - Day 1, 2019 - Cover4
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