Towards Broadband Global Optical and Wireless Networking

8/9/2019 Towards Broadband Global Optical and Wireless Networking

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Towards Broadband GlobalTowards Broadband Global

Optical and Wireless NetworkingOptical and Wireless Networking

Marian Marciniak

National Institute of Telecommunications

Warsaw, Poland


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Acknowledgements toAcknowledgements to COST 266Advanced Infrastructure for Photonic Networks

COST 270Reliability of Optical Components and Devices in

Communications Systems and Networks

COST 273 Towards Broadband Mobile Multimedia Networks

URSI Commission DElectronics and Photonics

ITU Study Group 15 Optical and Other Transport Networks

IEC Technical Committee 86Fibre Optics andNEXWAY Network of Excellence


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MOTIVATION

Radio-over-fibre transmision can be realised in the core

networks even at large distances, with potential of amplification/switching in the optical domain - COST

Action 273 Towards Broadband Mobile Multimedia

Networks

Radio-over-fibre arrangements can be applied in theaccess part of the Mobile Broadband Systems (MBS) in

60 GHz band.

The 60 GHz millimeter-wave band is a goal frequency

band for mobile broadband services allocation.

attenuation 10dB/km@60GHz! light in fibres


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OUTLINEOUTLINE

y Introduction

Voice vs. IP specifics

y Transparent photonic transport network

y All - optical solutions

y Hybrid network concept

y Conclusions


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INTRODUCTIONINTRODUCTIONy Dramatic growth of Internet traffic.

y almost stable voice traffic .

y Actual networks are based on classical circuit

switching principle.y Internet and data traffic exhibit inherent packet

switched features.

Transparent terabit optical network infrastructure

provides an excellent realization of circuit switched

network.

But it is not capable to realise packed switched services

in an efficient way.


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Voice traffic

Circuit switched

Deterministic

Real time, i.e. without noticeable delays no retransmission if some bits are lost

inherent Quality of Service guarantees

Well developed SDH/ATM technology


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Packet traffic Statistic (bursts!)

Packet switched, connectionless

best effort, no QoS guarantees

Latency (time delay)

lost packets, can be retransmitted

efficient optical buffering wanted!


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Transparency story

- - - - - optics

________ electronics


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EDFAEDFA The introduction ofErbium-Doped Fibre Amplifiers(EDFA) which have replaced electronic regenerators in

fibre based transmission links in early 90s resulted in

optical transparency of the links.

This was in contrary with electronic regenerator based

links. In those a combination of electronic logic circuit

along with electro-optical and opto-electrical

conversions of the digital signal transmitted has beenused in order to cope with signal distortion.


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THENOTIONOFTHENOTIONOFTRANSPARENCYTRANSPARENCY

OFATRANSMISSIONLINK:OFATRANSMISSIONLINK:y the output signal is proportional to the signal at the

input.

This provides a potential to modulate and detect theoptical wave power with microwave or milimetre

wave envelope

The transparency is rather an analogue feature of a link

what is in contrary to digital transmission schemes.

Transparency in optical domain has its common sense:

a medium is transparent if the light goes through it.


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Idealcase:Idealcase: signal at the output exactly the same as in the input,

obviously with acceptation of time delay caused by

finite value of light velocity,

and eventually of attenuation of the signal power.

But without degradation of its other characteristics!

Unfortunately that ideal situation is not realisable in an

optical network.

Even an ideal glass fibre exhibits attenuation,chromatic dispersion, andoptical nonlinearities.

Real fibres PMD!


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Vacuum is the onlymedium

ideallytransparent:y no attenuation,

y no dispersion,

y and no nonlinear interactions.

Even in free-space optical beams are subjects of diffraction!

y diffraction is overcome in fibre based 1-D telecommunication links.

y It is compensated with the guiding core focusing properties,

Fibre modes are special beams having unique property of perfectlyvanished total effect of diffraction and focusing interplay.


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Transparent photonicTransparent photonic

networknetworky insures the scalability, i.e. possibility of future upgrades

y Almost unlimited capacity is available

New demands, especially in optical signal digital processing

y full 3R (4R?) regeneration (4th in spectral domain, Thyln, ICTON'99)

y Wavelength - new degree of freedom (wavelength-switched and routed

networks)y wavelength converters (PC)


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Transparencyof the network inTransparencyof the network in

practicalpoint of viewpracticalpoint of view::

The networks provides a telecommunication cloud

Clients send and receive properly their information

regardless of:

y Wavelength

y Transmission speed

y Format used (analogue, digital)

Data need no special adaptation procedure to be

transmitted through the network.

Possibility to modulate optical wave with microwave

signal


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Transparencyof:Transparencyof:

The fibre itself (attenuation spectrum)

The optical amplifier (gain spectrum)

Other system components.


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(lack of) Transparencyconstraints(lack of) Transparencyconstraints Ideal glass fibre

y attenuation

y chromatic dispersion

y nonlinear interactions

Real fibre: Polarization Mode Dispersion, PMD, results from randomlocal lack of circular symmetry of the fibre due to :

y technology imperfections

y local stresses caused by cable layout.

Those analogue features of a fibre result in:

y distortion,crosstalk

y and noise of the transmitted optical signal.


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The term "PMD" is usedThe term "PMD" is usedy in the general sense of two polarization modes having

different group velocities,

y and in the specific sense of the expected value of

differential group delay between two orthogonally

polarized modes.

y PMD causes the spreading of a pulse in the time domain

y It is actually the main transmission distance-limiting

factor in 40 Gbit/s systems and above

y as such it became recently a subject of intense research

both for fibre optimisation and characterization


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TransparencyconstraintsIITransparencyconstraintsII

Very high wavelength precision and stability of optical sources is

a fundamental requirement of a Dense WDM network

This increases the cost of the devices.

Goal: not to loose that precious wavelength !

Solution: keeping the signal in the optical domain while it

traverses as large part of the network as possible.

This is why transparency is a so important issue.


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Some questions:

WDMorOTDM?WDMorOTDM?WDMorOTDM?

WDM channel spacing 100 GHz = 0.8 nm? 10 Gbit/s TDM ?

50 GHz ? 40 Gbit/s ETDM?

25 GHz ? 160 Gbit/s OTDM?

Requires 200 GHz WDM

12.5 GHz ? (y.2002 standard)

in future: 6.25 GHz? or 5 GHz?

400 Gbit/s OTDM?

What about 20 nm? Coarse WDM

Bandwidth limitations DWDM vs. OTDM trade-off


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The opticalsignalis characterisedbyThe opticalsignalis characterisedby

y temporal characteristics: shape absolute and relative(instantaneous power), and

y spectral characteristics.

So what we do in order the output signal resembles the input one as

much as possible, or at least it is detectable properly?

y To compensate for attenuation, optical amplifiers and especially

Erbium-Doped Fibre Amplifiers are already a well-developed

solution.

y To compensate for chromatic dispersion, dispersion-

compensating modules are developed with dispersioncompensating fibres and fibre gratings as typical examples.

y Unfortunately, it is especially difficult to compensate for

nonlinear distortion and interactions.


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Network behavesNetwork behaves

transparent way:transparent way:y we allow attenuation and / oramplification,

y and eventually wavelength conversion.

Transparent wavelength conversion assumes the

conservation of temporal signal shape, which is

superimposed to a different wavelength.

This works with wirelessmobile signal modulation of

the optical wave as well.


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Back to theAnalogueAgeBack to theAnalogueAge Transparent components of the optical network treat the passing

signals in an analogue way.

Broadband wireless is transmitted as an optical wave properly

modulated in an analogue way.

y The transparent length is a distance over which the signal

can be transmitted successfully.

y Transmission over longer lengths requires some form of

regeneration.

y The transparent length can increase in the future, when thetechnology is sufficiently developed.


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Opticalswitching in adynamicOpticalswitching in adynamic

WDMnetworkenvironmentWDMnetworkenvironment

Instantaneous network parameters are

y bit-rate

y WDM channel powery Aggregate optical power

y Number of WDM channels

y Wavelengths

y Transmitter and amplifier output power and

y nonlinear interaction resulting from

y attenuation, chromatic dispersion and PMD


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The "history" of thesignalThe "history" of thesignal

i.e. How much it has suffered from analogue distortion,

noise, cross-talk etc.

History may be differentfor different WDM channels

History may vary

in a dynamic wavelength allocation environment


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Degrees of freedom

of an optical network

space3- space

time ( DM )

avelengt (WDM)

v2 polarisatio s!


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Optical switching & routingOptical switching & routing

Degrees of freedom of an optical network:

y 3-D space co-ordinates,

y time (and resulting possibility of Optical Time Domain

Multiplexing, OTDM),

y wavelength (WDM),y polarisation

Opportunities for optical switching:

y in space, temporal, wavelength, and polarisation domains.

In addition to that,

logical on/offswitching is performed in optical logic elements.


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Optical routingOptical routing

can be realised as wavelength routing in a transparent

way.

y an analogue and passive solution,

y or an analogue and active one if wavelength

conversion is applied.

All-optical packet routing

y involves some intelligence of the router

y and some decision based on the information included

in the packet.

not realisable transparent way !


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BASICFACTS

Two electrons interact via electromagnetics

While two photons do not at all!

This is Main cause of the great success of optical

transmission

but

Means great difficulities forall-optical switching/signal processing !


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AllAll--Optical OpacityOptical Opacity

Even though all-optical routing element involves

optical logics, optical memory, etc.,

it is not optically transparent and it exploits optically

opaque elements.

The signal remains in optical domain, but digital

operations result in that the fundamental transparency

condition of proportionality of output and input signals

is not satisfied.


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HYBRIDNETWORKCONCEPT

oice and broadband wireless signals transmitted via

circuit-switched subnetworkwith digital (voice) or

analogue (wireless) coding,

while IP is transmitted as packet-switchedconnectionless traffic.

Voice/wireless is carried on dynamically allocated

wavelengths, according to instantaneous demand for

real-time services.

The two kinds of traffic are separated and interleaved

in frequency (wavelength) domain, not in time

domain.


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Voice + IPhybrid network table

Characteristics Voice, real-time

incl. Mobile wireless signal

Internet, data

Basic principle Circuit-switched /ATM Packet-switched

Packet length Constant length cells Variable

Lost data No retransmission Retransmitted

Quality of Service Guaranteed by overprovisioning Best-effort

Traffic Deterministic Statistic

Other Instantaneous bandwidth (# of s)

controlled logically in IP routers

Intelligence

Transparent Includes all-optical opacity

Bandwidth Dedicated on demand As wide as available

Access Conventional twisted-pair access to

public exchange offices for voice,

or wireless access

Broadband access to servers,

e.g. via cable-TV


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CONCLUSIONSCONCLUSIONSHybrid network saves voice technology with transparent transmission.

Real-time traffic including mobile wireless realised via dynamicallyallocated wavelengths as circuit-switched traffic.

The number of wavelengths allocated by IP layer for instantaneous

demand for real-time traffic.

Broadband wireless signal modulates the optical wavelength power.

All remaining wavelengths are for the IP traffic.

IP free of real-time restrictions, with potential of:

variable-packet length,

no idle bits,

best-effort scheme.Whole available bandwidth can be fully exploited.

Quality of Service can be differentiated for IP.

.


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Towards Broadband Global Optical and Wireless Networking