Transmission fundamentals

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TRANSMISSION :
A PROCESS WHERE TRAFFIC (VOICE,DATA,VIDEO) IS DESPATCHED OVER A MEDIUM BETWEEN THE SOURCE AND THE DESTINATION

TYPES OF TRANSMISSION MEDIA :
WIRED TRANSMISSION MEDIA
1.COPPER CABLE
2.OPTICAL FIBER

WIRELESS TRANSMISSION MEDIA
1.VSAT NETWORKS
2.MICROWAVE RADIO

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Transmission fundamentals

  1. 1. Telecom TutorialsMonday, June 03, 2013www.tempustelcosys.comTRANSMISSION FUNDAMENTALS……….
  2. 2. Monday, June 03, 2013www.tempustelcosys.comTRANSMISSION :A PROCESS WHERE TRAFFIC (VOICE,DATA,VIDEO) IS DESPATCHED OVERA MEDIUM BETWEEN THE SOURCE AND THE DESTINATIONTYPES OF TRANSMISSION MEDIA :WIRED TRANSMISSION MEDIA1.COPPER CABLE2.OPTICAL FIBERWIRELESS TRANSMISSION MEDIA1.VSAT NETWORKS2.MICROWAVE RADIO
  3. 3. Monday, June 03, 2013www.tempustelcosys.comCOPPER CABLE : -OLDEST KNOWN TRANSMISSION MEDIAADVANTAGES1. CHEAP2. EASILY AVAILABLEDISADVANTAGES1. PRONE TO LOSSES
  4. 4. Monday, June 03, 2013www.tempustelcosys.comVSAT NETWORKS : -VSAT NETWORKS ARE A POPULAR TRANSMISSIOM MEDIA WHEREFIBER OR MW CONNECTIVITY IS NOT POSSIBLENETWORK ELEMENTS IN A VSAT NETWORK1.UPLINK ANTENNA (TRANSPONDER)2.GEOSTATIONARY SATELLITE3.DOWNLINK ANTENNA (RECIEVER)
  5. 5. Monday, June 03, 2013www.tempustelcosys.comFIBER OPTICS COMMUNICATIONSFiber-optic lines are strands of optically pure glass as thin as a human hair thatcarry digital information over long distancesA FIBER Cable is essentially made up ofCORECLADDINGBUFFER COATING
  6. 6. Core - Thin glass center of the fiber where the light travelsCladding - Outer optical material surrounding the core thatreflects the light back into the coreBuffer coating - Plastic coating that protects the fiber from damage andmoistureThousands of optical fibers are arranged in bundles to form an optical cable.Optical cables are covered with protective jacketsTYPES OF OPTICAL FIBERSSINGLE MODE FIBER :Single-mode fibers have small cores (about 3.5 x 10-4 inches or 9 micronsin diameter) and transmit infrared laser light (wavelength = 1,300 to1,550 nanometers).MULTI MODE FIBER :Multi-mode fibers have larger cores (about 2.5 x 10-3 inches or 62.5microns in diameter) and transmit infrared light (wavelength = 850 to1,300 nm)Monday, June 03, 2013www.tempustelcosys.com
  7. 7. Monday, June 03, 2013www.tempustelcosys.com
  8. 8. When light passes from a medium with one index of refraction (m1)to another medium with a lower index of refraction (m2), it bends orrefracts away from an imaginary line perpendicular to the surface(normal line).As the angle of the beam through m1 becomes greater with respectto the normal line, the refracted light through m2 bends furtheraway from the lineAt one particular angle (critical angle), the refracted light will not gointo m2, but instead will travel along the surface between the twomedia (sine [critical angle] = n2/n1 where n1 and n2 are the indicesof refraction [n1 is greater than n2]).If the beam through m1 is greater than the critical angle, then therefracted beam will be reflected entirely back into m1 (total internalreflection), even though m2 may be transparentCRITICAL ANGLE = COS -1 ( N2 / N1)Monday, June 03, 2013www.tempustelcosys.com
  9. 9. Monday, June 03, 2013www.tempustelcosys.comTRANSMISSION OF LIGHT SIGNAL IN A FIBER OPTICThe light in a fiber-optic cable travels through the core (hallway) byconstantly bouncing from the cladding (mirror-lined walls), a principlecalled total internal reflection
  10. 10. Because the cladding does not absorb any light from thecore, the light wave can travel great distancesSome of the light signal degrades within the fiber, mostlydue to impurities in the glassThe extent that the signal degrades depends on the purity ofthe glass and the wavelength of the transmitted light (For eg :850 nm = 60 to 75 percent/km;1,300 nm = 50 to 60 percent/km; 1,550 nm is greater than 50percent/km).Some premium optical fibers show much less signaldegradation -- less than 10 percent/km at 1,550 nm.Fiber-Optic Relay SystemMonday, June 03, 2013www.tempustelcosys.comTRANSMITTEROPTICALRECEIVEROPTICALREGENERATOROPTICAL FIBER OPTICAL FIBER
  11. 11. Transmitter - Produces andencodes the light signalsOptical fiber - Conducts thelight signals over a distanceOptical regenerator - May benecessary to boost the lightsignal (for long distances)Optical receiver - Receivesand decodes the light signalsMonday, June 03, 2013www.tempustelcosys.com
  12. 12. ADVANTAGES :1. RELIABLITY2. HIGH DATA CARRYING CAPACITY3. LOW SIGNAL LOSSES4. NO INTERFERENCE DUE TO USE OF LIGHTSIGNALS5. FLEXIBLE AND LIGHTWEIGHTDISADVANTAGES :1. COSTLIER THAN MICROWAVE,COPPER CABLE2. MORE REPAIR TIME3. TRENCHING AND DUCTING INVOLVED HENCEMORE DEPLOYMENT TIMEMonday, June 03, 2013www.tempustelcosys.com
  13. 13. Monday, June 03, 2013www.tempustelcosys.comMIRCOWAVE TRANSMISSION : -MICROWAVE MEDIA CAN BE USED FOR POINT–TO-POINTAND POINT-MULTIPOINT TRANSMISSIONWHY MICROWAVE :-1. Supports hop length from less than 50 meters to 60 k ms2. Easy and fast deployment compared to any other media3. Flexibility ,upgradeability ,capacity increase ,redeployment4. High reliability and low maintenance cost5. High MTBF and Low MTTR6. Can reach farther remote inaccessible areas over water , forests andmountains
  14. 14.  MICROWAVE PROPOGATION PRINCIPLES Microwave transmission occurs in the atmospheresurrounding earth called troposphere which extends to anaverage of 10 km from earth’s surface. Microwave is essentially a LINE OF SIGHT communication. Microwave travels at speed of light (3 x 10 power 8 m/s) Microwave transmission can occur between 2 Ghz to 30 Ghz Microwave frequency bands are 2,4,6,7,8,13,15,18,23 Ghz Microwave signal propogates through free space and suffers losses while travelling called FREE SPACE LOSS FSL =92.4 + 20 log10 (D x f) Where D=distance (kms) and f=frequency (Ghz) Total Loss suffered by a MW sig is given by Total Loss = FSL + Atmospheric Absorption Loss + Field Margin Net Path Loss suffered by a MW sig is given by =Total Loss – Gain of both antennaMonday, June 03, 2013www.tempustelcosys.com
  15. 15.  Components of a MW link A MW link consists of a. Radios (IDU) – 2nos b. ODU – 2nos c. Antennas – 2nos d. Inter-facility cables between IDU and ODU Function of componentsa. Radio (IDU) : Coding and decoding digital data and converting digital data to IFfrequencyb. Inter-facility cable : Carries the IF frequency signal to ODU c. ODU : Converts IF signal to RF signal for propogation through medium d. Antenna : Transmitting and receiving RF signalsMonday, June 03, 2013www.tempustelcosys.com
  16. 16.  MW RADIO : Which MW radios to be used a. Should meet ITU standards b. High Transmit Power c. High System Gain d. ATPC , XPIC e. High tolerance for co-channel and adjacent channel interference f. High dispersive fade margin to combat signal distortion g. Variable modulation schemes h. Rate independenti. Should sustain severe climate f. Should have max traffic carrying capacityMonday, June 03, 2013www.tempustelcosys.com
  17. 17.  Types of MW Radios a. Plesiochronous Digital Heirarchy (PDH)b. Synchronous Digital Heirarchy (SDH) Radio Configurations :a. Space Diversity (SD)b. Frequency Diversity (FD)c. 1 + 0d. 1 + 1e. XPICf. MHSB INTER-FACILITY CABLE : Acts as a medium for transfer of signal to ODU Is a hollow waveguide covered by protecting sheath. Losses incurred are generally 0.5 dB for 100 mtrs cableMonday, June 03, 2013www.tempustelcosys.com
  18. 18.  Outdoor Unit (ODU) : Types of ODUa. Antenna mountb. Pole Mount MW Antenna : Can be omni-directional as well as directional Consists of following parts a. Reflector – Reflects MW energy towards the MW beam b. Antenna Mount – Mount for installing on pole c. Feed – Matches ODU and free space impedence and facilitates polarisation adjustment from H to V and vice versa d. Shield – Attached to reflector to improve radiation pattern of the antenna e. Radome –Protective cover from ice, rain and windMonday, June 03, 2013www.tempustelcosys.com
  19. 19.  TYPES OF MW ANTENNA SPACE DIVERSITY HIGH GAIN HIGHLY DIRECTIONAL MW ANTENNA PARAMETERS1. Antenna Gain : Gain is the figure of merit of its directivity and indicates how well it focuses MWenergy Antenna Gain = 17.8 + 20 log10 (d x f ) where d= antenna diameter( mtrs) and f =frequency (Ghz) Also gain can be given as Antenna Gain = ( 4 x ∏ /λ ^ 2) x Aeff where Aeff = 0.65 x (∏ x D ^ 2)/4 2. Beam Width : Width of the beam having 50 % of focused MW energy Beam Width = 70 x λ / D where λ = wavelength and D = Antenna Diameter(mtrs)Monday, June 03, 2013www.tempustelcosys.com
  20. 20.  Requirements for a MW link LOS – If a MW link has to be installed successfully there should be a proper line ofsight. In order to predict whether a MW link can be installed between two points aLOS survey is required. LOS can be deduced by Toposheet study and LOS survey Toposheet study involves plotting the points on SOI maps and noting the AMSLcontours in the LOS path . The contour readings can be used to calculate the MWantenna height required at both points. How to conduct a LOS Survey A surveyor needs to have the following equipments to successfully carry out a LOS surveya. Two Altimetersb. Compassc. GPS ( min 12 channel)d. Binoculars Monday, June 03, 2013www.tempustelcosys.com
  21. 21. Procedure :1 .Calibrate the two altimeters by taking the AMSL at a railway station or at a previouslycalibrated point.2. Proceed to the far end by taking AMSL readings at regular intervals and also at placeswhere the AMSL changes drastically3. Take the height of man made and natural obstructions ( bldgs, trees ,mountains) inthe LOS path4. Calculate the MW antenna height required by using the formulaAntenna Height = Max obstruction height – First Obstruction height and Last ObstructionheightObstruction height is sum of actual obstruction height , Earth Bulge ,Fresnel ZoneClearancePoints to remember while planning a MW linkThe link should clear the first and second Fresnel Zones (min 60 % for first Fresnel Zoneand 30 % for second Fresnel zone)Monday, June 03, 2013www.tempustelcosys.com
  22. 22. Monday, June 03, 2013www.tempustelcosys.comD1 D2Optical horizon
  23. 23. Optical Horizon is the straight line distance from the reciever and transmitterantennaOptical Horizon = 3.57 x √ (Ht + Hr)Radio Horizon is due to the bending of the MW ray towards the earth.Radio Horizon is 15 % bigger that the optical horizonRadio Horizon = 4.12 x √ (Ht + Hr)Monday, June 03, 2013www.tempustelcosys.com
  24. 24. Fresenel Zones and LOSAs said earlier for a MW link to work successfully the first and second Fresnelzones need to be cleared by minimum 60 % and 30 % resp.Fresnel zones are ellipsoids around the MW link caused because of the differences in therefractive indices of different mediumMonday, June 03, 2013www.tempustelcosys.comFor calculating the Fresnel zone radius at any point P in the middle of the linkis the following:Fn = √n λ d1 d2 / d1 + d2where,Fn = The nth Fresnel Zone radius in metresd1 = The distance of P from one end in metresd2 = The distance of P from the other end in metresλ = The wavelength of the transmitted signal in metres
  25. 25.  If we take n =1 then the First Fresnel Zone can be given as F1 = 17.32 x √d1 d2 / f x d where d1 = The distance of P from one end in metres d2 = The distance of P from the other end in metres f = Frequency in Ghz d = Total path length ( d1 + d2) Earth Bulge and K Factor Earth’s curvature and microwave beam refraction combined to form fictitious earth curvatureor Earth Bulge Earth Bulge is given as EARTH BULGE at a dist d1 km = d1 * d2 / (12.75 * K) mtrs Where d2 = (d – d1) Km K = K Factor K Factor is given by r / ro Where r = true earth radius r0 = effective earth radiusMonday, June 03, 2013www.tempustelcosys.com
  26. 26.  Losses due to obstacles MW signal is degenerated due to losses during propogation dueto two types of obstacles 1.Knife Edge Obstacle : - Knife Edge Loss is given by A obst = 6.4 – 20 log ( V √ 2 + √ 1 + 2 V power 2 ) V = hlos / rMonday, June 03, 2013www.tempustelcosys.com
  27. 27. Smooth surface losses are generally higher than knife edge lossesand can go high as 40 db.Monday, June 03, 2013www.tempustelcosys.com
  28. 28. 1.Reflection :There might be a free space loss calculated while designing a link and the actualfree space loss encountered by the link. This is because of multi-path propogations.Multipath is caused because of smooth ground, water bodies,man made structuresetcThe signal received at the Rx antenna is a combination of the direct signal and themultipath reflections.These reflected waves might cause losses if the reflectedsignal is out of phase from the desired signal.These losses are called as down fade.How to reduce multipath:a.The Tx and Rx antennas should be adjusted in such a way that they are not at thesame height so that the angle of incidence is not same as the angle of reflection/b.Use space diversity keeping a separation of atleast 200 λ between two antennasMonday, June 03, 2013www.tempustelcosys.com
  29. 29. 2. Refraction :The MW rays experience refractions due to the change in the refractiveindices of the propogating medium .These are due to variousatmospheric anomallies.Temperature Inversion : Typicallly warm air in found near the earths surfaceand the as the altitude increases the air becomes cooler. Sometimes the heat isradiated from the ground and the air at the earths surface becomes coolerwhereas the upper layer of the atmosphere is cooler. This is known as aatmospheric duct and the condition is called as temperature inversion.When the MW signal passes through such a duct the refraction occurs in such away that the ray bends more than the normal and the radio horizon increases andthe ray travels beyond the LOS. This is called as the Super Refraction.When the atmospheric density increases with height instead of decreasing itcauses a fog with warm air over cool air. When the MW link encounters thisatmospheric effect it causes the MW ray to bend less than the normal and the rayfalls short than the LOS. This leads to less Fresnel Zone clearance andobstructions. This is called as the Sub RefractionMonday, June 03, 2013www.tempustelcosys.com
  30. 30. 3. Diffraction :Diffraction is seen due to the knife edge and smooth edge obstructions.Typically good clearance of Fresnel zones nullifies the diffraction effectFading and their types:Fading is generally of two typesa. Flat Fade : Flat fades are seen because of rain attenuation, ducting and beam bending.Rain Fading : MW signal faces attenuation due to fading if the MW frequencies used are above10 Ghz. Below 10 Ghz rain has no effect on a MW link.Rain drops act as poor di-electric absorbingMW energy.While designing a link the PL (50 or 90 ) factor and the rain file should be used as per the rainfallrate in that particular region.Also in regions where there is heavy rainfall links should be designed with vertical polarisation asrain attenuation is considerably reduced as opposed to a horizontally polarised link.This is due tothe fact that as rain drops approach the earths surface because of the gravitational pull the dropsacquire a shape which is wider at its axis.b. Frequency selective Fade : Frequency selective fade avries with frequency.It is seen in caseswhere the reflected signal is received out of phase from the desired signal.Monday, June 03, 2013www.tempustelcosys.com
  31. 31. Monday, June 03, 2013www.tempustelcosys.comParameter PDH SDHFrequency Bands (GHz) 2,4,6,7,8,13,15,18,23 6,7,8,15,18,23Traffic Capacity Max 32 E1 Max 63 E1Modulation QPSK 128 QAMBand Width Occupied 28 MHz 28 MhzSystem Gain 110 to 100 dB 90 dBGood comb for 10 kms 1.2 m 1.8 mMW cost with 1.2 mantenna4 lacs 6 lacs
  32. 32. Other parameters required to design a MW link1. Received Signal (RSL) : The link is generally designed to get a receive signal ofaround 30-36 dBRSL = Tx power – Net Path Loss= Pt – Lctx + Gatx –Lcrx + Garx – FSLwhere Pt – Transmitted power in dBmLctx – Cable loss between Tx and its antennaGatx – Gain of transmitting antennaLcrx – Cable loss between Rx and its antennaGarx – Gain of receiving antennaFSL – Free Space LossReceiver threshold value is directly proportional to data rate or capacitySDH ( 63 E1 ) threshold - -68 dBmPDH ( 16 E1 ) threshold - -83 dBmReceiver threshold is inversely proportional to BER( Bit error rate)BER 10 -6 - Rx threshold -68 dBmBer 10 -3 - Rx threshold -69 dBm Monday, June 03, 2013www.tempustelcosys.com
  33. 33. Max Rx signal is equiment related generally - 20 dBm .If the received signal is morethat the equipment max Rx signal the equipment goes into saturation ( los of link).2. Effective Isotropic Radiated Power ( EIRP ) :EIRP = Tx Power (dBm) + Gain of single antenna (dBm)3. Fade Margin :1. Thermal Fade Margin :Thermal Fade Margin = Rx s/g level – Rx threshold level2. Dispersive Fade Margin : Due to inband distortions3. Adjacent channel interference fade margin : Due to energy spill over in the adjacentchannel receivers4. External interference fade margin : Due to inter system co-channel interference5. Composite of Effective Fade Margin :EFM = -10 log10 ( 10 – TFM /10 + 10 – DFM /10 + 10 – EIFM /10 )4 . Path Inclination is given asPI = Elevantion Diff / Path LengthMonday, June 03, 2013www.tempustelcosys.com
  34. 34. 5. Fade Occurrence Factor Po is given asPo = C x (f/4) x d 3 x 10 – 5 dBmWhere C – speed of light ( 3 x 10 8 m/s)f – Frequency in Ghzd – Path distance6. Fade Probability is given asP = K x d 3.6 x f 0.89 x ( 1 + £p) -1.4 x 10 –F /10Where K – Geo-climatic factor for worst month fadingd – path length in kmsf - Frequency in Ghz£p – Path inclination in milli radiansF – Effect Fade MarginMonday, June 03, 2013www.tempustelcosys.com

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