COMP 421 /CMPET 401COMP 421 /CMPET 401

COMMUNICATIONS and NETWORKING

CLASS 5 (4B)

TRANSMISSION MEDIATRANSMISSION MEDIA

OverviewOverview

Guided - wireUnguided - wirelessCharacteristics and quality determined by

medium and signalFor guided, the medium is more importantFor unguided, the bandwidth produced by

the antenna is more importantKey concerns are data rate and distance

Design FactorsDesign Factors

Bandwidth– Higher bandwidth gives higher data rate

Transmission impairments– Attenuation

InterferenceNumber of receivers

– Major factor in guided media– More receivers (multi-point) introduce more

attenuation

Electromagnetic SpectrumElectromagnetic Spectrum

Guided Transmission MediaGuided Transmission Media

The transmission capacity depends on the distance and on whether the medium is point-to-point or multi-pointMedium Freq Typical Typical Repeater

Range Atten. Delay Spacing Twisted Pair 0 - 3.5KHz 0.2dB/km 50us/km 2km Twisted Pair 0 - 1.0MHz 3.0dB/km 5 us/km 2km Coaxial cable 0 - 500MHz 7.0dB/km 4 us/km 1-9km

Optical fiber– Multi-mode 180-370THz 0.5dB/km 5 us/km 2km

– Single Mode 180-370THz 0.2dB/km 5 us/km 40km

Twisted PairTwisted Pair Consists of two insulated copper wires arranged in a regular spiral pattern to

minimize the electromagnetic interference between adjacent pairs Often used at customer facilities and also over distances to carry voice as

well as data communications Low frequency transmission medium

Twisted Pair - ApplicationsTwisted Pair - Applications

Most common mediumTelephone network

– Between house and local exchange (subscriber loop)

Within buildings– To private branch exchange (PBX)

For local area networks (LAN)– 10Mbps or 100Mbps

Twisted Pair - Pros and ConsTwisted Pair - Pros and Cons

Cheap

Easy to work with

Low data rate

Short range

Twisted Pair - Transmission Twisted Pair - Transmission CharacteristicsCharacteristics Analog

– Amplifiers every 5km to 6km Digital

– Use either analog or digital signals

– repeater every 2km or 3km Limited distance Limited bandwidth (1MHz) Limited data rate (100MHz) using different modulation

& signaling techniques Susceptible to interference and noise

Unshielded and Shielded TPUnshielded and Shielded TP Unshielded Twisted Pair (UTP)

– Ordinary telephone wire– Cheapest– Easiest to install– Suffers from external electromagnetic interference (EM)

Shielded Twisted Pair (STP)

– the pair is wrapped with metallic foil or braid to insulate the pair from electromagnetic interference

– More expensive– Harder to handle (thick, heavy)

UTP CategoriesUTP Categories Cat 3

– up to 16MHz

– Voice grade found in most offices

– Twist length of 7.5 cm to 10 cm

Cat 4 (least common)

– up to 20 MHz

Cat 5

– up to 100MHz

– Commonly pre-installed in new office buildings

– Twist length 0.6 cm to 0.85 cm

Category 5E and 6Category 5E and 6

Today, cables and related components are available in more grade categories than the industry standards specify. You can choose from Cat 5, Cat 5e, Cat 5e+, Cat 6 and yes, even Cat 6+. While there is plenty of hype and confusion surrounding these implied categories

                                                                         

                      

CAT 6 FeaturesCAT 6 Features

Cat 6 more than doubles the bandwidth of Cat 5e, from 100 MHz to 250 MHz, supporting future emerging applications

Improved EMC performance to reject outside noise from TVs, wireless, and other adjacent applications.

Full backwards compatibility to support all legacy applications

Simpler and less costly installations, due to reduction in electronics needed for echo and NEXT (Near End Cross Talk) cancellation.

Equations for CAT 6 ParametersEquations for CAT 6 ParametersAttenuation (dB) = 1.991*sqrt(f) + 0.01785*f + 0.21/sqrt(f)

pr-pr NEXT (dB) = -20log( 10^( -0.05(74.3-15log(f)) ) + 2*10^( -0.05(94.0-20log(f)) ) )

PSNEXT (dB) = -20log( 10^( -0.05(72.3-15log(f)) ) + 2*10^( -0.05(90.0-20log(f)) ) )

pr-pr FEXT (dB) = -20log( 10^( -0.05(67.8-20log(f)) ) + 4*10^( -0.05(83.1-20log(f)) ) )

PSFEXT (dB) = -20log( 10^( -0.05(72.3-20log(f)) ) + 4*10^( -0.05(90.0-20log(f)) ) )

Return loss (dB) = 19 at 1-20 MHz; 19-10*log(f/20) at 20-250 MHz

Phase Delay (ns) = 546 + 34/sqrt(f)

Delay skew (ns) = 50

pr-pr PS pr-pr PS return phase delay

freq atten NEXT NEXT ELFEXT ELFEXT loss delay skew

(MHz) (dB) (dB) (dB) (dB) (dB) (dB) (ns) (ns)

100 21.7 39.9 37.1 23.2 20.2 12.0 549.4 50.0

250 36.0 33.1 30.2 17.2 14.2 8.0 548.2 50.0

The RJ 45 ConnectorThe RJ 45 Connector

To identify the RJ-45 cable type, hold the two ends of the cable next to each other so you can see the colored wires inside the ends

         Straight-through — the colored wires are in the same sequence at both ends of the cable.Crossover — the first (far left) colored wire at one end of the cable is the third colored wire at the other end of the cable

Understanding USOC & RJUnderstanding USOC & RJ

8-Wire Jack(10BaseT Data Connections)

8-Wire Jacks(USOC RJ31X Through RJ37X)

6-Wire Jack(USOC - RJ14W)

Understanding USOC & RJUnderstanding USOC & RJ

8-Wire Jack(IBM Token Ring Connections)

8-Wire Jacks(USOC RJ41 Through RJ48)

Also TIA 568B(TIA 568A Swaps Pairs 2 & 3)

6-Wire Jack Modified Jack(DEC MMJ)

Twisted Pair AdvantagesTwisted Pair Advantages

Inexpensive and readily available

Flexible and light weight

Easy to work with and install

Twisted Pair DisadvantagesTwisted Pair Disadvantages

Susceptibility to interference and noise

Attenuation problem– For analog, repeaters needed every 5-6km– For digital, repeaters needed every 2-3km

Relatively low bandwidth

LEVEL 5 CABLINGLEVEL 5 CABLING

PER Specification TSB-36 for UTP cable connections for LEVEL 5:

- A terminal jack can be 90M (295ft) from the wiring closet.

- A device can be 10M from a terminal jack at the users location.

- There can be up to 6M of cross-connect patch cords in the wire closet

- Termination of cables must obey the following:

- Twists of actual pairs must be maintained to half-inch of termination.

- Cable sheath should be stripped only as far as necessary to terminate.

- Cables bundles should not nopt tightly bound or cinched

- Cable bundles should not be placed under stress or tension

- Cable bend radii should not be less than 8 times the cable diameter 

Coaxial CableCoaxial Cable

Coaxial Cable ApplicationsCoaxial Cable Applications

Most versatile mediumTelevision distribution

– Aerial to TV– Cable TV

Long distance telephone transmission– Can carry 10,000 voice calls simultaneously– Being replaced by fiber optic

Short distance computer systems linksLocal area networks

Coaxial Cable - Transmission Coaxial Cable - Transmission CharacteristicsCharacteristicsAnalog

– Amplifiers every few km– Closer if higher frequency– Up to 500MHz

Digital– Repeater every 1km– Closer for higher data rates

CoaxCoax

The outer shield protects the inner conductor from outside electrical signals. The distance between the outer conductor (shield) and inner conductor plus the type of material used for insulating the inner conductor determine the cable properties or impedance. Typical impedances for coaxial cables are 75 ohms for Cable TV, 50 ohms for Ethernet Thinnet and Thicknet. The excellent control of the impedance characteristics of the cable allow higher data rates to be transferred than with twisted pair cable.

Coax AdvantagesCoax Advantages

Higher bandwidth– 400 to 600Mhz– up to 10,800 voice conversations

Can be tapped easily (pros and cons)

Much less susceptible to interference than twisted pair

Coax DisadvantagesCoax Disadvantages

High attenuation rate makes it expensive over long distance

Bulky

CABLE SUBSITUTION DATACABLE SUBSITUTION DATA

TYPECM Communication wires & cables CL2 Class 2 remote control, signaling, & power-limited cablesCL3 Class 3 remote control, signaling, & power-limited cablesFPL Power limited fire protective signaling cablesMP Multi-purpose cablesPLTC Power limited tray cable

 xxR Indicates a RISER cablexxP Indicates a PLENUM cable

 Plenum is highest grade. Order is : MPP -> CMP -> CL3P -> CL2P; FPLP -> CL3P & 2PRiser is next higher grade. Order is : MPR -> CMR -> CL3R -> CL2R; FPLR -> CL3R & CL2RGeneral Purpose is next. Order is : MP -> CM -> CL3 -> CL2 : FPL or PLTC -> CL3 & CL2Residential is lowest. The order is : CMX -> CL3X -> CL2X

THE CATEGORIES OF CABLE THE CATEGORIES OF CABLE

WIRE LEVEL 1 Level 1 cable is for basic comm & power limited circuits. VOICE GRADE ONLY.

2 Level 2 cable is similar to IBM Type 3 cable for 2 to 25 twisted pair cable. 1MHz max. 8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. DIGITAL DATA GRADE

3 Level 3 cable is Unshielded Twisted Pair (typical telephone wire). 16MHz max frequency. 7.8db/1000ft attenuation @ 1MHz; 4db/1000ft @ 256KHz. 10Mpbs ENET/ 4Mpbs

TR4 Level 4 cable is Low Loss Premises Telecommunication cable, shielded/unshielded, 20Mhz max

6.5db/1000ft attenuation @ 1MHz; 31db/1000ft @ 20MHz for 24AWG wire 4.5db/1000ft atten @ 1MHz; 24db/1000ft @ 20MHz for 22AWG wire. 16Mbps TR.

5 Level 5 cable is DATA GRADE up to 100Mbit

IBM CABLE TYPEIBM CABLE TYPE

1 Dual pair STP 22AWG solid, non-plenum data cable, used for long runs in walls of buildings 1P Dual pair STP 22AWG, plenum data cable2 Dual pair STP 22AWG data, 4 pair UTP 24AWG solid, telephone(voice) non-plenum

cable2P Dual pair STP 22AWG data, 4 pair 22AWG telephone plenum cable3 Multi-pair (usually 4) UTP 22 or 24 AWG solid data & voice cable for runs in walls5 Two 100/140 micrometer optical fiber in a single sheath6 Dual pair 26AWG non-plenum patch panel data cable, used for patch panels.

Attn=1.5xType18 One flat STP of 26AWG stranded wire for under carpet9 Dual pair STP 26AWG solid non-plenum data cable, Low grade dual pair.

Attn=1.5xType19P Dual pair STP 26AWG plenum data cable9R Dual pair STP 26AWG riser data cable

 Based on general description of cable per IBM definitions

Optical FiberOptical Fiber

Optical Fiber - BenefitsOptical Fiber - Benefits

Greater capacity– Data rates of hundreds of Gbps

Smaller size & weightLower attenuationElectromagnetic isolationGreater repeater spacing

– 10s of km at least

AttenuationAttenuation

Optical Fiber - ApplicationsOptical Fiber - Applications

Long-haul trunksMetropolitan trunksRural exchange trunksSubscriber loopsLANs

Optical Fiber - Transmission Optical Fiber - Transmission CharacteristicsCharacteristics Act as wave guide for 1014 to 1015 Hz

– Portions of infrared and visible spectrum Light Emitting Diode (LED)

– Cheaper– Wider operating temp range– Last longer

Injection Laser Diode (ILD)

– More efficient– Greater data rate

Wavelength Division Multiplexing

Fiber Optic TypesFiber Optic Types

Multimode step-index fiber– the reflective walls of the fiber move the light pulses

to the receiver

Multimode graded-index fiber– acts to refract the light toward the center of the fiber

by variations in the density

Single mode fiber– the light is guided down the center of an extremely

narrow core

Optical FiberOptical FiberOptical fiberOptical fiber consists of thin glass fibers that can carry information at frequencies in the visible light spectrum and beyond. The typical optical fiber consists of a very narrow strand of glass called the core. Around the core is a concentric layer of glass called the cladding. A typical core diameter is 62.5 microns (1 micron = 10-6 meters). Typically Cladding has a diameter of 125 microns. Coating the cladding is a

protective coating consisting of plastic, it is called the Jacket.

                                                                

Refraction in FiberRefraction in FiberAn important characteristic of fiber optics is refraction. Refraction is the characteristic of a material to either pass or reflect light. When light passes through a medium, it "bends" as it passes from one medium to the other. An example of this is when we look into a pond of water.

                                                   

Angle of IncidenceAngle of IncidenceIf the angle of incidence is small, the light rays are reflected and do not pass into the water. If the angle of incident is great, light passes through the media but is bent or refracted.

                                                                                       Optical fibers work on the principle that the core refracts the light and the cladding reflects the light. The core refracts the light and guides the light along its path. The cladding reflects any light back into the core and stops light from escaping through it - it bounds the medium!

Optical Fiber Transmission ModesOptical Fiber Transmission Modes

Step IndexStep Index

Step index has a large core, so the light rays tend to bounce around inside the core, reflecting off the cladding. This causes some rays to take a longer or shorter path through the core. Some take the direct path with hardly any reflections while others bounce back and forth taking a longer path. The result is that the light rays arrive at the receiver at different times. The signal becomes longer than the original signal. LED light

sources are used. Typical Core: 62.5 microns.

                                                                           

      

                                                   

Step Index Mode

Graded IndexGraded Index

Graded index has a gradual change in the core's refractive index. This causes the light rays to be gradually bent back into the core path. This is represented by a curved reflective path in the attached drawing. The result is a better receive signal than with step index. LED light sources are used. Typical Core: 62.5 microns.

                              

Graded Index Mode

Single ModeSingle ModeSingle mode has separate distinct refractive indexes for the cladding and core. The light ray passes through the core with relatively few reflections off the cladding. Single mode is used for a single source of light (one color) operation. It requires a laser and the core is very small: 9 microns.

                                                                                 

Single Mode

Comparison of Optical Fibers

                                                                                    

           

Loose Tube FiberLoose Tube Fiber

 

Non-armored Armored

FIBER OPTIC LINK SUMMARY

Radar to Control Center Link

OTHER LINKS

3.5km SH AR M

FIBER OPTIC LINK SUMMARY

12 S TR A N D S

12 S TR A N D S

Radar (6 - RS232)

Voice (2 phones)

LAN line

AIS Room

350m S H A R M

850nm 62.5 /125 -18dBm -38 dBm 5km

1300nm 9 /125 -18dBm -40 dBm 20km

1300nm 9 /125 -12dBm -40 dBm 50kmw laser

W avelenght F iber O utput Receive M ax Range

ST

ST

ST

Cable Type :F iber Type: S ingle# of F ibers: 12/cableW avelenght: 1300nmTem purature: -30 to 60CMax Attn: 1.5dB/kmApplication: D irect BurialJacket: A rm ored

2.5km LU X O R

4.0km H U R G H AD A

12 S TR A N D S

12 S TR A N D S

W ALLMT.

FIBERDIST.BOX

In terduct

2 DUPLEXJUM PERS

C O N TR O L C E N TE R /TO W E R

RadarMux

FIBERBOX

2 DUPLEXJUM PERS

Interduct

R A D A R

FIBERBOX

FIBERBOX

500m H U R G H A D A

FIBERBOX

FIBERBOX

ST ST

ST

FIBERBOX

3.0km LU X O R

FIBERBOX

ADOC

ST ST

ST

5 M

ST

ST

ST

20M

50m5 M

50m 5 M

5 M50m

EFIBSUM .vsd

ControlCenterMUX

RackMT.Dist.BOX

F iberJumpers

F iberJumpers

T3FIBERMUX

E1

LAN 1

LAN 2

T3FIBERMUX

E1

LAN 1

LAN 2

LAN 2

LAN 1

E1T3

FIBERMUX

LAN 2

LAN 1

E1T3

FIBERMUX

LAN 2

LAN 1

E1E1MUX T3

FIBERMUX

T3FIBERMUX

E1MUX

Voice

RS-232

E1

LAN 1

LAN 2

A Fiber ConnectorA Fiber Connector

Fiber ConnectorsFiber Connectors

Splicing Technologies

Splicing technologies may be

divided into two basic categories:

fusion and mechanical.

Mechanical methods may include

products that use mechanical

means to align two cleaved fibers

or products that require polishing

of the fiber ends.

Avg. Splice Loss (dB)Fusion Splicing 0.10 dBRotary Mechanical* 0.20 dBMechanical Splice 0.20 dB

Splicing

Return Loss

Return loss is the measure of the

level of signal reflected by the

splice back to the source. Return

loss of 40 dB or better is needed

to assure proper performance for

analog video transmission over

fiber.

DWDMDWDMDWDM works by combining and transmitting multiple signals simultaneously at different wavelengths on the same fiber. In effect, one fiber is transformed into multiple virtual fibers. So, if you were to multiplex eight OC -48 signals into one fiber, you would increase the carrying capacity of that fiber from 2.5 Gb/s to 20 Gb/s. Currently, because of DWDM, single fibers have been able to transmit data at speeds up to 400Gb/s. And, as vendors add more channels to each fiber, terabit capacity is on its way.

A key advantage to DWDM is that it's protocol and bit-rate independent. DWDM-based networks can transmit data in IP, SONET/SDH, Ethernet, and handle bit-rates between 100 Mb/s and 2.5 Gb/s. Therefore, DWDM-based networks can carry different types of traffic at different speeds over an optical channel.

Fiber Optic AdvantagesFiber Optic Advantages

Greater capacity (bandwidth of up to 2 Gbps)

Greater distance—can run fiber as far as several kilometers.

Smaller size and lighter weight

Lower attenuation - The light signals meet little resistance, so data can travel farther.

Immunity to environmental interference

Highly secure due to tap difficulty and lack of signal radiation

Fiber Optic DisadvantagesFiber Optic Disadvantages

Expensive over short distance

Requires highly skilled installers

Adding additional nodes is difficult

Fiber TestingFiber TestingTesting and certifying fiber optic cable.It's easy to certify fiber optic cable because of its immunity to electrical interference. You only need to check a few measurements:

Attenuation (or decibel loss)—Measured in dB/km, this is the decrease of signal strength as it travels through the fiber optic cable.

Return loss—This is the amount of light reflected from the far end of the cable back to the source. The lower the number, the better. For example, a reading of -60 dB is better than -20 dB.

Graded refractive index—Measures how much light is sent down the fiber. This is commonly measured at wavelengths of 850 and 1300 nm. Compared to other operating frequencies, these two ranges yield the lowest intrinsic power loss. (NOTE: This is valid for multimode fiber only.)

Propagation delay—This is the time it takes for a signal to travel from one point to another over a transmission channel.

Time-domain reflectometry (TDR)—Transmits high-frequency pulses so you can examine the reflections along the cable and isolate faults.

Fiber Design Considerations•Maximum 150 to 160 kilometers between repeaters

•Determined by loss budget

•Typical installation 60 to 80 kilometer between repeaters

•0.25 dB loss per kilometer for fiber

•Lasers

•Transmitters have output from 0 to +10 dBm

•Receivers have -30 dBm average receiver sensitivity

•Repeater amplifiers consume 100 watts per fiber

•Under 2.5 Gigabits/sec per fiber pair is no longer state of art

Wireless TransmissionWireless Transmission

Unguided mediaTransmission and reception via antennaTwo techniques are used:Directional

– Focused beam– Careful alignment required

Omnidirectional– Signal spreads in all directions– Can be received by many antennas

FrequenciesFrequencies 2GHz to 40GHz

– Microwave

– Highly directional

– Point to point

– Satellite 30MHz to 1GHz

– Omnidirectional

– Broadcast radio 3 x 1011 to 2 x 1014

– Infrared

– Local

Wireless ExamplesWireless Examples

Terrestrial microwave transmissionSatellite transmissionBroadcast radioInfrared

Troposcatter Antenna ConfigurationTroposcatter Antenna Configuration

Terrestrial MicrowaveTerrestrial Microwave

Uses the radio frequency spectrum, commonly from 2 to 40 Ghz

Transmitter is a parabolic dish, mounted as high as possible

Used by common carriers as well as by private networks

Requires unobstructed line of sight between source and receiver

Curvature of the earth requires stations (called repeaters) to be ~30 miles apart

Microwave Transmission Microwave Transmission ApplicationsApplications

Long-haul telecommunications service for both voice and television transmission

Short point-to-point links between buildings for closed-circuit TV or a data link between LANs

Microwave Transmission Microwave Transmission AdvantagesAdvantages

No cabling needed between sites

Wide bandwidth

Multi-channel transmissions

Microwave Transmission Microwave Transmission DisadvantagesDisadvantagesLine of sight requirement

Expensive towers and repeaters

Subject to interference such as passing airplanes and rain

LOS RadioLOS Radio

Fresnel ZonesFresnel Zones

So, in a nutshell, to visualize what happens to radio waves when they encounter an obstacle, we have to develop a picture of the wavefront after the obstacle as a function of the wavefront just before it (as opposed to simply tracing rays from the distant source). Now we're in a position to talk about Fresnel zones. A Fresnel zone is a simpler concept once you have some understanding of diffraction: it is the volume of space enclosed by an ellipsoid which has the two antennas at the ends of a radio link at its foci. The surface of the ellipsoid is defined by the path ACB, which exceeds the length of the direct path AB by some fixed amount. This amount is n  /2, where n is a positive integer. For the first Fresnel zone, n = 1 and the path length differs by  /2 (i.e., a 180 phase reversal with respect to the direct path). For most practical purposes, only the first Fresnel zone need be considered.

Fresnel ZoneFresnel ZoneThe two-dimensional representation of a Fresnel zone is

In order to quantify diffraction losses, they are usually expressed in terms of a

dimensionless parameter , given by:

             where d is the difference in lengths of the straight-line path between the

endpoints of the link and the path which just touches the tip of the diffracting object (see Fig. 7, where  d = d1 + d2 - d). By convention,   is positive when

the direct path is blocked (i.e., the obstacle has positive height), and negative

when the direct path has some clearance ("negative height").

DiffractionDiffraction

“Knife edge" diffraction means that the top of the obstacle is small in terms of wavelengths. This is sometimes a reasonable approximation of an object in the real world, but more often than not, the obstacle will be rounded (such as a hilltop) or have a large flat surface (like the top of a building), or otherwise depart from the knife edge assumption. In such cases, the path loss for the grazing case can be considerably more than 6 dB - in fact, 20 dB would be a better estimate in many cases. So, Fresnel zone clearance can be pretty important on real-world paths. And, again, keep in mind that the Fresnel zone is three-dimensional, so clearance must also be maintained from the sides of buildings, etc. if path loss is to be minimized. Another point to consider is the effect on Fresnel zone clearance of changes in atmospheric refraction, as discussed in the last section. We may have adequate clearance on a longer path under normal conditions (i.e., 4/3 earth radius)

Ground ReflectionsGround Reflections

One common source of reflections is the ground. It tends to be more of a factor on paths in rural areas; in urban settings, the ground reflection path will often be blocked by the clutter of buildings, trees, etc. In paths over relatively smooth ground or bodies of water, however, ground reflections can be a major determinant of path loss. For any radio link, it is worthwhile to look at the path profile and see if the ground reflection has the potential to be significant. It should also be kept in mind that the reflection point is not at the midpoint of the path unless the antennas are at the same height and the ground is not sloped in the reflection region - just the remember the old maxim from optics that the angle of incidence equals the angle of reflection

Other Sources of ReflectionsOther Sources of Reflections

On long links, reflections from objects near the line of the direct path will almost always cause increased path loss - in essence, you have a permanent "flat fade" over a very wide bandwidth. Reflections from objects which are well off to the side of the direct path are a different story, however. This is a frequent occurrence in urban areas, where the sides of buildings can cause strong reflections. In such cases, the angle of incidence may be much larger than zero, unlike the ground reflection case. This means that horizontal and vertical polarization may behave quite differently When the reflecting surface is vertical, like the side of a building, a signal which is transmitted with horizontal polarization effectively has vertical polarization as far as the reflection is concerned. Therefore, horizontal polarization will generally result in weaker

reflections and less multipath than vertical polarization in these cases.

Effects of Rain, Snow and FogEffects of Rain, Snow and Fog

The loss of LOS paths may sometimes be affected by weather conditions (other than the refraction effects which have already been mentioned). Rain and fog (clouds) become a significant source of attenuation only when we get well into the microwave region. Attenuation from fog only becomes noticeable (i.e., attenuation of the order of 1 dB or more) above about 30 GHz. Snow is in this category as well. Rain attenuation becomes significant at around 10 GHz, where a heavy rainfall may cause additional path loss of the order of 1 dB/km.

Attenuation from Trees and Attenuation from Trees and ForestsForests

Trees can be a significant source of path loss, and there are a number of variables involved, such as the specific type of tree, whether it is wet or dry, and in the case of deciduous trees, whether the leaves are present or not. Isolated trees are not usually a major problem, but a dense forest is another story. The attenuation depends on the distance the signal must penetrate through the forest, and it increases with frequency. According to a CCIR report [10], the attenuation is of the order of 0.05 dB/m at 200 MHz, 0.1 dB/m at 500 MHz, 0.2 dB/m at 1 GHz, 0.3 dB/m at 2 GHz and 0.4 dB/m at 3 GHz. At lower frequencies, the attenuation is somewhat lower for horizontal polarization than for vertical, but the difference disappears above about 1 GHz. This adds up to a lot of excess path loss if your signal must penetrate several hundred meters of forest! Fortunately, there is also significant propagation by diffraction over the treetops, especially if you can get your antennas up near treetop level or keep them a good distance from the edge of the forest, so all is not lost if you live near a forest

Link AnalysisLink Analysis

Some PDH to SDH Comparisons

PDH (Plesiochronous Digital Hierarchy)

Asynchronous

Bit Interleaving - Requires Complete Demux of Data Stream to Extract a Single ChannelRelatively Low Bandwidths1960’s TechnologyLimited Network Management

SDH•SDH (Synchronous Digital Hierarchy)

SynchronousByte Interleaving (Requires Much Demux to Extract a Single ChannelRelatively High Bandwidths1980’s - 1990’s TechnologyRobust Network Management

SDH Features

•Modern and Digital

•Equipment Availability for 15 Years Expected

•SDH Allows Drop and Insert Without Complete Demultiplexing

•SDH Allows Multiplexing of Tributaries That Have Different Bit Rates

•SDH Overhead Is Structured to Provide Access at Section, Line

and Path Layers Allows Enhanced Maintenance, Control,

Performance and Administration at Each Laye

•Digital Radio limits the dependence on Trans Atlas routing

SatellitesSatellites

Communications satellites are radio relaysin the sky. They receive signals transmittedfrom earth-based antennas, amplify thesignals, and return the signals to earth. Satellitesare extremely useful because they canhandle large amounts of different types of traffic,they offer almost worldwide coverage, andthey can be installed independently and relativelyquickly.

SatellitesSatellites

Satellite systems, which consist of special-case beyond-LOS equipment, consist ofthree parts: the space segment, which includesthe satellite; a ground segment comprisingsimple to complex communications terminalequipment; and a control segment that performssatellite station-keeping chores and directsallocation of satellite bandwidth between users.

SatellitesSatellitesSatellite systems use different frequenciesfor transmitting and receiving information.A ground terminal transmits the signal on theuplink frequency; the satellite retransmits thesignal on the downlink frequency to the groundreceiver terminal. A transponder device within a satellite receives the incoming signal, amplifiesit, changes the signal frequency, and retransmitsit to the receiving terminal. Satelliteuplink and downlink frequencies are usuallyreferred to in pairs, like 6/4 GHz with the firstnumber the uplink frequency and the secondnumber the downlink frequency.

SatellitesSatellitesMost commercial satellites have morethan one transponder, with bandwidth differingamong various designs. Contemporary C-bandcommercial satellites have as many as 34 transponderseach. Each transponder can relayone color television channel with program sound,1200 voice channels, or a data rate of up to 50Mbps. The number of channels a satellite canprovide is related to the available bandwidthand how it is used. This number may be increasedby improving the efficiency of the transponderor increasing its power. However, becausemore power requires more weight, thenumber of channels is related to the satellite’ssize and weight.

SatelliteSatellite

A microwave relay station in space

Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency

Geostationary satellites

– remain above the equator at a height of 22,300 miles (geosynchronous orbit)

– travel around the earth in exactly the time the earth takes to rotate

Satellite Transmission LinksSatellite Transmission Links

Earth stations communicate by sending signals to the satellite on an uplink

The satellite then repeats those signals on a downlink

The broadcast nature of the downlink makes it attractive for services such as the distribution of television programming

dish dish

uplink station downlink station

satellitetransponder

22,300 miles

Satellite Transmission ProcessSatellite Transmission Process

Signal Delayed 0.25ms each way

Satellite Transmission ApplicationsSatellite Transmission Applications

Television distribution– a network provides programming from a central

location using direct broadcast satellites (DBS)

Long-distance telephone transmission– high-usage international trunks

Private business networks

Principal Satellite Transmission BandsPrincipal Satellite Transmission Bands

C band: 4(downlink) - 6(uplink) GHz– the first to be designated–

Ku band: 12(downlink) -14(uplink) GHz– rain interference is the major problem

Ka band: 19(downlink) - 29(uplink) GHz– equipment needed to use the band is still very

expensive

Communications Satellite Frequency Bands

Satellite Lettered Bands

Classes of SatellitesClasses of SatellitesThe technical/operational performance characteristics that are to be used in

conjunction with the possible services are:

1. Standard T-2

Earth Stations having a nominal G/T of 37 dB/K and operating in the 11/14 GHz frequency bands via the EUTELSAT II satellite system for international public telephony and high quality television transmissions or international public telephony only. (Note: The T1 standard applied to TDMA transmissions on EUTELSAT-I has been replaced by the T2 standard)

2. Standard V-1

Earth Stations having a nominal G/T between 26 dB/K and 30.5 dB/K (depending upon location) and

operating in the 11/14 GHz frequency bands via the EUTELSAT II satellite system for international

high quality television transmissions only.

3. Standard S-1

Earth Stations having a nominal G/T of 30 dB/K and operating in the 12/14 GHz frequency bands via the EUTELSAT I/II satellite system for international SMS services (SMS Open Network).

SatellitesSatellitesGenerally, commercial systems operatewithin different parts of the UHF and SHF bandsthan do military systems. The accompanyingchart shows the relation of frequency bandswith letter frequency designators used in thetelecommunications industry. L-, C-, and Kubandsystems are currently available for lease;all can provide communications services to mostof the world. Wide geographic coverage by Cbandis more prevalent than that by Ku-bandbecause Ku-band satellites tend to use verynarrow beam antennas to support high populationdensity regional locations. L-band, which isassociated with small terminals and mobile applications,is used by INMARSAT and is availableworldwide.

Satellite Communication Access and Topology

•Multi-Channel Per Carrier

•Time Division Multiplex

•Demand Assigned Multiple Access (DAMA) Technology

•Provides Better Utilization of Bandwidth

•Adaptable to Traffic Needs of a Mission

•Topology Can Be a Star or Mesh Depending on Mission

Requirements

•Controlled From Command Center

•Secondary Sites Are Slaves to Command Center

Multiple Access Control Techniques for Satellite Communications

MultiplexingMultiplexing

FDMA (Frequency Division MultipleAccess): A static multiple access techniquewhere transponder bandwidth is subdivided intosmaller frequency bands, or sub-channels, in whicheach subchannel is assigned to a specific user.

TDMA (Time Division Multiple Access):A static multiple access technique wherethe transponder bandwidth is assigned to eachuser during a specific time slot in a cyclic timeframe.

ACCESS TECHNIQUESACCESS TECHNIQUESCDMA (Code Division Multiple Access):A dynamic multiple access technique,also known as spread spectrum, where totaltransponder bandwidth employs a separate and distinct code for each user to access a trafficchannel at any instant of time in sharing theoverall bandwidth with other users.

Polling (Roll Call and Round Robin):A dynamic multiple access technique wheretotal transponder bandwidth is made availableto a user for the duration of time the userrequires. Upon transmission completion, channelaccess is passed to the next user on thepolling list in a cyclic manner.

DAMA (Demand Assigned Multiple Access):A family of dynamic multiple accesstechniques where each user reserves channelspace based upon individual need.

CommunicationsCommunications Architecture Considerations Architecture Considerations Single Channel per Carrier (SCPC)

– Dedicated point to point communications

Demand Assign Multiple Access (DAMA) And Time Division Multiple Access (TDMA)

– Support multiple users on a as needed basis– Very bandwidth efficient

• Demand Assigned Multiple Access (DAMA)Technology

– Provides Better Utilization of Bandwidth

– Adaptable to Traffic Needs of a Mission

• Topology Can Be a Star or Mesh Depending onMission Requirements

– Controlled From Command Center

– Secondary Sites Are Slaves to Command Center

Satellite Communication Access & Topology

CONTENTIONCONTENTION

Contention: A family of dynamic multipleaccess techniques where users competewith each other for channel space by transmittingwhen required. If separate transmissionscollide, the corrupted transmissions are re-attemptedafter a random delay.

Each of the multiple access channelcontrol techniques has advantages and disadvantages.The selection of a multiple accesstechnique depends upon network application,traffic generation profiles for each network subscriber,and user tolerance to traffic throughputdelays.

Summary of TechniquesSummary of Techniques

Currently, FDMA and TDMA techniquesare static and do not adapt readily to changingtraffic loads. Polling techniques are not suitablefor networks with exceptionally large numbersof users due to the time needed to cycle throughthe polling list. CDMA has an inherent electroniccountermeasure resistance, but is expensiveto implement. DAMA is most efficientfor networks of users with varying traffic loads,but the automated reservation (control) systemtechnology is complex.

Antenna Diameter Vs. G/T

The signal level on any contour line isderived from the satellite’s EIRP at that location,with values of EIRP measured in decibelsreferenced to one watt of power or dBw. Thehigher the EIRP value, the better the signalquality. For example, the EIRP level of a satellitesignal could range from 18 dBw at beamedge to 21 dBw at beam center. The G/T gain-to-noise temperature ratio of the ground stationdetermines the quality of the received signal.

Satellite Terminal Parameters

Satellite CommunicationSatellite Communication

To achieve successful satellite communications,several technical considerations mustbe satisfied. Considerations include thegeolocation of the terminal with respect to thesatellite beam coverage or “footprint” on theearth’s surface, the frequency band, the signalbandwidth, the antenna transmit gain expressedas its Effective Isotropic Radiated Power (EIRP),the size of the antenna dish, and the antennareceive performance “figure of merit,” expressedas G/T (the ratio of antenna receive gain tosystem noise temperature in decibels per degreesKelvin, or dB/K).

Technical ConstraintsTechnical Constraints

Basic technical constraints affect systemperformance and dependability of satellitecommunications. Antenna size and polarizationinfluence system performance in terms ofradio receiver sensitivity G/T and transmitteroutput power EIRP. Besides these physicalcharacteristics, other factors such as atmospheric“noise” and temperature play significantroles.

EIRPEIRPThe EIRP of an earth terminal is a keyparameter in determining system performance.The EIRP required depends on the communicationstraffic that the earth terminal needs tosupport. The recently introduced micro earthterminals and very small aperture terminals(VSAT) with low ElRPs are not able to supportthe communications traffic volume that a largeearth terminal with a high EIRP can support.There is a trade-off in a communications link between the transmit EIRP and the receive G/Trequired to support a given data rate. There isalso a trade-off in available power versus bandwidthallocated by the satellite resource manager,as well as between transmitter power andantenna gain.

Satellites and NoiseSatellites and NoiseNoise is the principal enemy of asatellite receiver because it affects the receiver’sability to accurately separate the downlink radiosignal from ever-present random electrical energy.Noise can be natural cosmic backgroundstatic, can come from heat generated by theantenna’s own amplifier, or can originate fromother electronic parts of the receiver. Noise isalso caused by the sun’s RF energy falling onthe antenna. Fortunately, this phenomenon isrelatively short-lived, amounting to several minutesa day and occurring seasonally in the falland spring, when, during the solar equinoxes,the sun’s transit contributes to these disturbances.Sun spots and solar flares can alsoaffect receiver performance at any time.

VSAT TERMINALSVSAT TERMINALS

Examples of Satellite Terminals• 3.8-meter Trailerized Antenna

Current Area Beam Coverage - Arabsat II

C-Band Medium EIRP Coverage

Ku-Band EIRP Coverage

C-Band High EIRP Coverage

TYPICAL SATELLITE INTERFACETYPICAL SATELLITE INTERFACE

RADAR

Telephone VOICE

ASYNC. DATA

Resources Determine• Interfaces Type• Interface Quantity• Bit Rates

Satellite Interface• Combines lines• Compresses Data• Buffers Transmission

Terminal Equipment Physical Transmission & Reception of Combined Data

Link Budget Determines the dish size, output power, frequency, and other physical radio parameters

Electronics

PA

Modem

LNA

SYNC. DATA

SYNC. DATAModem

Modem

Modem

Link Budget & TimingLink Budget & Timing• The first step to a design/cost is a Link Budget

• The Link Budget will provide design requirements for:•Operating Band•Antenna size•Transmitter power•Satellite availability

•All these will help define the system Cost

• There is a 252 ms delay in the receipt of data over a satellite link

Satellite Data SheetSatellite Data Sheet FROM: DURRES TO: BELGIIUM REQUIREMENTS SATELLITE ---------------------------------- ---------------------------------- *Availability (%): 99.900 *Satellite INTELSAT 705*Required Eb/No (dB): 5.50 Satellite West Long : 18.0*Bit Error Rate : E-08 *Transponder SPOT-SPOT*Modulation Type : QPSK !Usable Trnspndr BW (MHz): 72.00*Info. Rate (Kbps): 256.00 !SFD @ 0 dB/K (dBW/M^2): -97.10*FEC Rate : 0.69 *Transponder Atten (dB): 12.0*Spread Spectrum Factor : 1.00*Modem Step Size (kHz): 1.00 TRANSMIT E/S RECEIVE E/S ---------------------------------- ---------------------------------- North Lat: 41.3 West Long: 39.0 North Lat: 51.0 West Long: 23.0 Frequency (GHz): 14.20 Frequency (GHz): 11.20*Satellite G/T (dB/K): 4.20 *Satellite EIRP (dBW): 42.10*Antenna Diameter (m): 2.4 *Antenna Diameter (m): 3.8 Antenna Gain (dBi): 49.40 Antenna Gain (dBi): 51.80 Antenna Elevation (Deg): 37.69 Antenna Elevation (Deg): 31.42 Carrier EIRP (dBW): 43.72 *LNA Noise Temp (K): 65.00*Power Control (dB): 0.00 *Loss betw.LNA & Ant.(dB): 0.06*Output Circuit Loss (dB): 0.00 System Noise Temp. (K): 107.94 Path Loss (dB): 207.11 Station G/T (dB/K): 31.47 Other Losses (dB): 0.70 Path Loss (dB): 205.16(other loss = atm,pol,ant point) Other Losses (dB): 0.60

Satellite Data SheetSatellite Data Sheet

C/Io Adj Sat U (dB-Hz): 71.92 #C/Io Intermod (dB-Hz): 75.41

C/Io Adj Sat D (dB-Hz): 78.52 C/No Thermal Up (dB-Hz): 68.71

C/Io Crosspol (dB-Hz): 80.28 C/No Thermal Dn (dB-Hz): 69.62

C/Io Adj Channel (dB-Hz): 79.42 C/Io Total (dB-Hz): 68.79

C/Io Adj Trans (dB-Hz): 83.67 C/No Therm Total (dB-Hz): 66.13

C/Io Microwave (dB-Hz): N/A C/No Total (dB-Hz): 64.25

RAIN ATTENUATION

----------------------------------------------------------------------------

Overall Link Margin (dB): 4.67 *Rain Model : CRANE

Uplink Availability (%): 99.912

Rain Margin (dB): 4.67 *Uplink Rain Zone : D2

Dnlink Availability (%): 99.988

Rain Margin (dB): 4.47 *Dnlink Rain Zone : C

G/T Degradation (dB): 4.36

TRANSPONDER H.P.A

---------------------------------- ----------------------------------

*Number of Carriers : MULTIPLE *Number of Carriers : 1.0

*Total OPBO (dB): 3.50 *Total HPA OPBO : 0.00

Total IPBO (dB): 7.00 HPA Power/Carrier (dBm): 24.32

Carrier OPBO (dB): 26.78 Required HPA Size (dBW): -5.68

Carrier IPBO (dB): 30.29 Required HPA Size (W): 0.27

FCC Req: 1) Uplink Flange Density (dBW/4kHz): -22.34 File: I705DBE

(@46.0) 2) Downlink EIRP Density (dBW/4kHz): 2.56

Transponder BW Used Per Carrier (x1.35) (%): 0.35 # = deltas used

Transponder Power Used Per Carrier (%): 0.47 ! = modif. default

Transponder Bandwidth Allocation (MHz): 0.251 * = user's input

INTERFERENCE

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Satellite as a Cost Effective Satellite as a Cost Effective SolutionSolution

Advances in Satellite Hardware has: •Lowered Hardware Cost•Decreased Large Hub Station Requirements•Systems Available in Transportable Configurations•Lease Minimal of Space Segment;

•Full Period •Occasional Use

Satellite AdvantagesSatellite Advantages

Can reach a large geographical area

High bandwidth

Cheaper over long distances

Satellite DisadvantagesSatellite Disadvantages

High initial cost

Susceptible to noise and interference

Propagation delay

UHF/VHF RadioUHF/VHF Radio

N

60N

MTMA

ENROUTE130NM

freq 128.1MHz

ENROUTE130NM

freq 128.8MHz

121.9GND CNTL

119.7TOWER TMA

CNTLTWR

CONTROLCENTER

118.1 TMA128.1 ENROUTE128.8 ENTOUTE121.5 TMA

RADIO COVERAGE REQUIREMENTS

NOTE: DISTANCE TO HORIZON IS1.228xHeight

RADIO HORIZON IS150NM AT 15,000ft213NM AT 30,000ft

BASED ON: Freq.= 126 MHz

RF FEED LOSS = 2.5dBANTENNA GAIN = 0dBd

TRANS. ERP = 14WRCVR SENSIT.= -90dBm

RADIO HORIZONAT 15,000'

Harris

Transmitter/Receiver

HarrisTransceiver

SunairTransmitter/Receiver

TransworldTransceiver

HF Radio SystemsHF Radio Systems

AntennasAntennas

Compact Rooftop RLPA Frequency range 2 to 30 MHz Radius of rotation 8.7 m Gain

– 7dBi @ 6.2 MHz

– 12dBi @ 30 MHz Range of rotation ± (n x 360°) Efficiency

– 6.2-30 90-98

– 5.4-6.2 50-90

– 4.4-5.4 25-50

– 2.0-4.4 5-25

HF Whip Antenna PatternsHF Whip Antenna Patterns

Radiation Pattern between SitesRadiation Pattern between Sites

A Complete HF SystemA Complete HF System

Broadcast RadioBroadcast Radio

OmnidirectionalFM radioUHF and VHF televisionRequires line of sightSuffers from multipath interference

– Reflections

InfraredInfrared

Achieved using transceivers that modulate noncoherent infrared light

Requires line of sight (or reflection)

Blocked by walls– e.g. TV remote control, Infrared port

Protocol LayersProtocol Layers

A Laser Infrared UnitA Laser Infrared Unit

System Block DiagramSystem Block Diagram

RangeRange

System Range

Beam Width

200m 100 x 100mm

500m 100 x 100mm

1000m 150 x 150mm

2000m 150 x 150mm

4000m 200 x 200mm

LensThis lens provides a beam divergence of 0.5 degrees, giving a large beam footprint. This is to avoid problems of loss of signal due to building movement, atmospheric distortions, ease of installation and long-term reliability. A coarse optical filter is placed in front of the lenses to reduce the effect of sunlight on the APD.

The size of the transmit aperture provides a wide area of emission to avoid safety and scintillation problems.

END ClassEND Class

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