Training on microwave communication


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Possible media for communication
Introduction to Communication Media
Introduction to Microwave communication
Manufacturers of Microwave
Why Microwave?
Characteristics of microwave
Types of Microwave communication
Types of Microwave Links
Requirements for the microwave communication
What is LOS?
Wave Propagation in the atmosphere
Multi path Propagation
LOS Purpose & requirements
Limitations of Line of Sight Systems
Design of Line of Sight Microwave Links
K- factor
Variations of the ray curvature as a function of k
Fresnel zone
Obstacles & Loses
Knife Edge Obstacles
Smooth Spherical Earth Obstacles
Path Loss
Other losses
Why vertical polarization favorable at high freq
Antenna type & Gain
Fading Margin

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Training on microwave communication

  1. 1. Telecom TutorialsMonday, June 03, 2013www.tempustelcosys.comTraining on Microwave Communication
  2. 2. Possible media for communicationIntroduction to Communication MediaIntroduction to Microwave communicationManufacturers of MicrowaveWhy Microwave?Characteristics of microwaveTypes of Microwave communicationTypes of Microwave LinksRequirements for the microwave communicationWhat is LOS?Wave Propagation in the atmosphereMulti path PropagationLOS Purpose & requirementsLimitations of Line of Sight SystemsDesign of Line of Sight Microwave LinksK- factorVariations of the ray curvature as a function of k Monday, June 03,
  3. 3. Monday, June 03, 2013www.tempustelcosys.comObstacles & LosesKnife Edge ObstaclesSmooth Spherical Earth ObstaclesPath LossOther lossesWhy vertical polarization favorable at high freqAntenna type & GainRECEIVER SENSITIVITY, FADE MARGIN AND SIGNAL TO NOISE RATIOFading MarginReliability
  4. 4. Monday, June 03, 2013www.tempustelcosys.comCopper mediaMicrowave mediaOptical fiber MediaSatellite Media
  5. 5. Microwave communication system is used to transfer data from one node to the other node usingthe frequency ranging from 2GHz to 60GHz.Small capacity systems generally employ the frequencies less than 3 GHz while medium andlarge capacity systems utilize frequencies ranging from 3 to 15 GHz. Frequencies > 15 GHz areessentially used for short-haul transmission.Monday, June 03,
  6. 6. Few well known Radio ManufacturersNokiaNeraNECSiemensDigital Microwave CorporationFujitsuEricssonAlcatelHarissMonday, June 03,
  7. 7. Monday, June 03, 2013www.tempustelcosys.comFast DeploymentFlexibilityLow implementation CostLink across Mountains and Rivers are economical & feasibleQuick maintenance of the systemGHz band has very low noiseLOW MTTRDrawback of MicrowaveNeeds frequency licenseEnvironment dependant link quality (e.g. rainfall)LOS not always available
  8. 8.  Microwave are used for point to point and point to multipoint communication Microwaves are the electromagnetic waves comprises of electrical and magnetic field atangle of 90 degree to each other. Normally communication on microwave is done between 3GHz to 30 GHz frequencyMonday, June 03,
  9. 9. Monday, June 03, 2013www.tempustelcosys.comPoint to point communicationPoint to multi pointcommunication
  10. 10.  Long Haul Radios: ~ 30 - 80 km2 GHz, 7 GHz Medium Haul Radios: ~ 25 - 45 km10 GHz, 13 GHz, 15 GHz Short Haul Radios: ~ 5 - 30 km18 GHz, 23 GHz, 26 GHz, 38 GHz, Nokia Metro hopper: < 1 km57 GHz(uses oxygen absorption in air to limit range)Monday, June 03,
  11. 11.  Microwave communication requires a clear line of sight between two nodes A Fresnel ellipsoids and their clearance criteria concept is used to calculate the radio Lineof sight Antenna height Calculation for clear LOS Parameters design like Power ,Frequency , Rx level and many moreMonday, June 03,
  12. 12.  Radio signals, like all electromagnetic radiation, usually travel in straight lines. However, at lowfrequencies (below approximately 2 MHz or so) diffraction effects cause significant ray bending,allowing ray bundles to partially follow the Earths curvature, thus enabling AM radio signals in low-noise environments to be recieved well after the transmitting antenna has dropped below thehorizon. Additionally, frequencies between approximately 1 and 30 MHz, can be reflected by theionosphere, thus giving radio transmissions in this range a potentially global reach (see shortwaveradio). However, at higher frequencies, neither of these effects apply, and so any obstruction between thetransmitting and receiving antenna will block the signal, just like the light that the eye senses.Therefore, as the ability to visually sight a transmitting antenna (with regards to the limitations of theeyes resolution) roughly corresponds with the ability to receive a signal from it, the propagationcharacteristic of high-frequency radio is called "line-of-sight" as per radiowave propagation is calledas "radio horizon".Monday, June 03,
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  14. 14.  When rays reaches to the receiver from different paths then two possibilities are thereA) If they reaches in the same phase then the signal strength increases.B) If they reaches in opposite phase then its cause fading called multipath fadingMonday, June 03,
  15. 15. 1. PurposeFor the establishment of short / long haul LOS linksFeasibility studiesSubmission of tendersUp gradation of existing links2. Requirements of LOS links• site locations• planned antenna height• direction to the other end of link• restrictions to cherry-picker, etc.Output• LOS/NLOS• minimum antenna height• exact antenna location (rooftop)• panorama picture withlandmarks and their directions• extra observations(forests,building sites etc.)Monday, June 03,
  16. 16. How far we can go: The range of LOS microwave systems is limited by:-Curvature of earth-ActualTechnical radio characteristics (K-factor)-Modified Earth CurvatureActual Obstructions en-route in each hopRF effect of fresnel zonePath lossTransmitter powerAntenna gainsTransmission line loosesFrequency of operationReceived powerReceiver thresholdSignal to noise ratioFade margin requiredDesired reliability of linkMonday, June 03,
  17. 17. Link Design: The design of microwave links, involves three sets of calculations.1. Working out antenna heights for the link.K-factor is major dominant variable.Earth bulge.Fresnel zone radius.Actual obstructions on the routePath LossOperating frequency.Path profile: it indicates the distance from one of the transmitter site where obstructions to the lineof sight radio link may occur.The object of this calculation is to arrange tower heights along the entire route of the link, so thatan obstruction in the path does not enter into the fresnel zone by a specified amount for aspecified K-factor used.Monday, June 03,
  18. 18. Earth bulge and K-factor:The propagation of radio beam is affected by atmospheric conditions and the obstructions on the way. Itcan be subjected to:DiffractionReflectionRefractionMost important is refraction, which is caused by changes in the density of atmospheric layersconfronted by the radio beam front.The curvature of earth and slight bending of waves as it is refracted downwards by the earth’s atmosphereare two factors, that, must be considered while making path profiles.The earth’s curvature and microwave beam refraction are combined to form fictitious earth curvature orearth bulge.EARTH CURVATURE (M) = 0.078 x d1 x d2 / KWHERE K = EFFECTIVE EARTH RADIUS/TRUE EARTH RADIUSEARTH BULGE = d1 x d2 / 12.75 x KEARTH BULGE FOR K=4/3 = d1 x d2 / 17EARTH BULGE FOR K=2/3 = d1 x d2 / 8.5Monday, June 03,
  19. 19. Different K valuesMonday, June 03, 2013www.tempustelcosys.comTrue Earth’s curvature= 6,371 KmK=1K=0.5K=0.33
  20. 20. Fresnel zone:The radio beam energy travels in an ellipsoidal wave front, the different components of whichmaintains different path lengths.The distance from microwave beam’s center is commonly measured in fresnel zones to take intoaccount both frequency and distance.The first fresnel zone (FFZ) is the surface of the point along which the distance to the ends of thepath is exactly ½ wave length larger than the direct end to end path.FFZ radius in meters=17.32√d1*d2/fDWhere d1 & d2 are in km’s, f is the frequency in GHz and D is the hop distance in Km’s.In order to achieve a free space propagation condition for a radio beam at least 60 % of FFZshould be cleared under the standard atmospheric condition of K=4/3.Monday, June 03,
  21. 21. Keep 1st Fresnel zone clear of obstaclesnth Fresnel zone: Ellipse around direct path, where path difference to direct line is n* /2.Monday, June 03, 2013www.tempustelcosys.comdb1st Fresnel zone2nd3rdRadius for n-th zone = b * sqrt(n)bd kmf MHzm274[ ][ ][ ]
  22. 22. 1. If f=2.5 GHz and D=30 Km, then FFZ=32.99 M2. If f=4.5 GHz and D=30 Km, then FFZ=24.03 M3. If f=6.5 GHz and D=30 Km, then FFZ=19.75 MConclusion :FFZ radius decreases with increase in frequency.1. If f=2.5 GHz and D=30 Km, then FFZ=32.99 M2. If f=2.5 GHz and D=34 Km, then FFZ=35.33 M3. If f=2.5 GHz and D=36 Km, then FFZ=36.46 MConclusion: FFZ radius increases with increase in distanceMonday, June 03,
  23. 23. With 100% fresenal zoneMonday, June 03, 2013www.tempustelcosys.comNATURAL EARTH FEATURESEARTH BULGE“A” “B”TBUILDINGd1 d2Df
  24. 24. Types of LossMonday, June 03, 2013www.tempustelcosys.comObstacle lossKnife edgeobstacle lossSmooth sphericalearth obstacle loss
  25. 25. Knife Edge ObstaclesMonday, June 03,
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  30. 30. Free Space LossFree space loss: consider a signal is traveling between transmitter at “A” to a receiver at “B”.There is for a given frequency and distance, a characteristic loss. This loss increases withboth distance and frequency. It is known as free space loss.Free space loss LdB=92.44+20 log10 F+20 log10 DWhere F is in GHz and D is in kms.If D is 40 Km and F is 6 GHz, then free space in dBLdB=92.44+20 log 40+20 log 6=92.44+20*1.6021+20*0.7782=92.44+32.042+15.564=140.046 dBMonday, June 03,
  31. 31. Example:- Free space loss if F=2.5 GHz and D=30 KmFSL (dB) = 92.44 + 20 log 2.5 + 20 log 30=92.44 + 20*0.398 + 20*1.478=92.44 + 7.96 + 29.56 = 129.96 dBNow, if F=7.5 GHz (changed) and D=30 Km (unchanged)FSL (dB) = 92.44 + 20 log 7.5 + 20 log 30=92.44 + 20*0.875 + 20*1.478=92.44 + 17.5 + 29.56 = 139.5 dBNow, if F=2.5 GHz (unchanged) and D=40 Km (changed)FSL (dB) = 92.44 + 20 log 2.5 + 20 log 40=92.44 + 20*0.398 + 20*1.602=92.44 + 7.96 + 32.04 = 132.44 dBIt can be seen, that, free space loss increases both with distance and frequencyMonday, June 03,
  32. 32. PrecipitationTransmission of microwave signal above 10 GHz is vulnerable to precipitation The energyis attenuated due to radiation (scattering) and absorption (heating) ScatteringRadio waves are a time varying electromagnetic field, the incident field willinduce a dipole moment in the raindrop. The rain drop will also have the same time Variationas the radio waves and will act as an antenna and reradiate the energy. As rain drop-antennahave low directivity it will radiate energy arbitrary direction and add to loss.AbsorptionWhen the wavelength becomes small (High freq. < 18GHz) relative to the raindrop size moreenergy is absorbed by heating of the raindrop.Monday, June 03,
  33. 33. As the rain-drop increases in size they depart spherical shape and extended in thethe horizontal direction.For freq. Higher than 18 GHz the wavelength is generallyin mm. So these rain-drops attenuate horizontally polarized waves than the verticalPolarized.Raindrop shapesMonday, June 03, 2013www.tempustelcosys.com1mm 1.5mm 2mm 2.5mm
  34. 34. Transmit power : Transmit power is the power in dB that is required for the signal to travel fromone node to other.The max and minimum transmission power for the equipment is vendor specific and changeswith the capacity of the E1 carried by the radio.Monday, June 03,
  35. 35. Digital Modem : To interface with customer equipment and to convert customer traffic to amodulated signalRF Unit : To Up and Down Convert signal in RF RangePassive Parabolic Antenna : For Transmitting and Receiving RF SignalMonday, June 03,
  36. 36. Antenna type : There are different types of antenna used for the Microwave communication.Mostly parabolic antennas are used.Antenna can be put in vertical or horizontal mode. Also cross polarized antennas are availablethat can carry both horizontal and vertical beams with a very low interference.Gain of Antenna: Gain of the antenna is calculated by the approximate formulaGain = 17.8 + 20 log (D.f) dBiWhereD = Antenna diameter [m]F = Frequency in GHzMonday, June 03,
  37. 37. Receiver Sensitivity: Sensitivity or Threshold Power of receiver is the level of signal which wouldproduce a 30 dB signal to noise ratio out of the base band of an analogue receiver, or a bit errorratio (BER)=10-4 out of the base band of a digital receiver. Typically it is -70 to -90 dB.Fading: Received Signal vary with time due to multipath fading and rain etc. Refractive index ofatmosphere varies with Temp. humidity and pressure which in turn cause the electromagneticwaves to change direction. Another cause for Multipath fading is ground reflection. So a fademargin is built in Link Designing.Fade Margin: The fade margin is the power level, that, the unfaded received signal can fall tountil it reaches the receiver threshold. This margin will vary depending on geographic and climaticconditions of different geographic areas and desired reliability of the system. Typically it is 20-40dB.Fade Margin dB=Prx-PthreshSignal to Noise Ratio: It’s the minimum power difference between the wanted received signaland received noise.Signal/Noise Ratio (dB)=10 log10 (Signal Power/Noise Power)Typically it is > 50 dB, logically it should be more than the Fade Margin, so that it isalways below the threshold level.Monday, June 03,
  38. 38.  Fading margin:“Safety” margin. Should belarge enough to guaranteethat quality and availabilityobjectives are met duringfading conditions.Typical value ~ 40 dBMonday, June 03, 2013www.tempustelcosys.comReceived PowerFading MarginReceiverthreshold
  39. 39. Reliability of the link: Outage time for each hop and for the complete link is to be worked out,which in turn will give the over all reliability of the link in terms of percentage.Single hop reliability (%) Fade Margin99.9 28 dB99.99 38 dB99.999 48 dBCCIR defines its availability objective for radio relay systems over a hypotheticalreference circuit as 99.7 %. Resulting unavailability 0.3 % is of three components.Outage due to power failureOutage due to equipment failureOutage due to propagationIt is reasonable to allot 50 % of the outage time to power and equipment failures and 50% for propagation. Considering propagation alone, system should have an availability (reliability)of 99.85 % apportioned across the 2500 Km route. This provide guide to establish a per hoppropagation reliability for a particular system.Planner rather first set the limit for the reliability and for wide band links it is better than99.99 %.Monday, June 03,