Ron Milione Ph.D.Ron Milione Ph.D.W2TAPW2TAP
Information Modulator AmplifierAntFeedlineTransmitterInformation Demodulator Pre-AmplifierAntFeedlineReceiverFilterFilterR...
 As the wave propagates, thesurface area increases The power flux densitydecreases proportional to1/d2• At great enough ...
 Most real antennas do notradiate spherically The wavefront will beonly a portion of a sphere• The surface area of the w...
 Radiated power often referenced to power radiatedby an ideal antennattGPEIRP =Pt= power of transmitterGt= gain of transm...
λ22Dd f =• Large-scale (Far Field) propagation model• Gives power where random environmental effectshave been averaged tog...
2222)4()4()(cfddPPlinlossFreert πλπ===For Free Space (no buildings, trees, etc.)dBdfcfddBlossFree 56.147log20log204log10)(...
A transmission system transmits a signal at 960MHz with a power of 100mW usinga 16cm dipole antenna system with a gain of ...
A transmission system transmits a signal at 960MHz with a power of 100mWusing a 16cm dipole antenna system with a gain of ...
 A Link Budget analysis determines if there isenough power at the receiver to recover theinformationInformation Modulator...
 Begin with the power output of the transmit amplifier Subtract (in dB) losses due to passive components in the transmit...
dBi12Antenna gaindB(1.5)150 ft. at 1dB/100 footFeedline lossdB(1)Jumper lossdB(0.3)Filter lossdBm4425 WattsPower Amplifier...
 The Receiver has several gains/losses Specific losses due to known environment around the receiver Vehicle/building pe...
 Sensitivity describes the weakest signal power levelthat the receiver is able to detect and decode Sensitivity is depen...
 Thermal noise N = kTB (Watts) k=1.3803 x 10-23J/K T = temperature in Kelvin B=receiver bandwidth Thermal noise is u...
 The smaller the sensitivity, the better the receiver Sensitivity (W) =kTB * NF(linear) * minimum SNR required (linear)...
 Example parameters Signal with 200KHz bandwidth at 290K NF for amplifier is 1.2dB or 1.318 (linear) Modulation scheme...
 Transmit/propagate chain produces a receivedsignal has some RSS (Received Signal Strength) EIRP minus path loss For ex...
Information Modulator AmplifierAntFeedlineTransmitterInformation Demodulator Pre-AmplifierAntFeedlineReceiverFilterFilterR...
 A Link Budget determines what maximum path loss a system cantolerate Includes all factors for EIRP, path loss, fade mar...
 Forward (Base to Mobile) Amplifier power 45dBm Filter loss (2dB) Feedline loss (3dB) TX Antenna gain 10dBi Path los...
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Rf propagation in a nutshell

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Fundamental Communication Engineering

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Rf propagation in a nutshell

  1. 1. Ron Milione Ph.D.Ron Milione Ph.D.W2TAPW2TAP
  2. 2. Information Modulator AmplifierAntFeedlineTransmitterInformation Demodulator Pre-AmplifierAntFeedlineReceiverFilterFilterRF PropagationThis presentation concentrateson the propagation portion
  3. 3.  As the wave propagates, thesurface area increases The power flux densitydecreases proportional to1/d2• At great enough distancesfrom the source, a portion ofthe surface appears as aplane• The wave may be modeledas a plane wave• The classic picture of an EMwave is a single ray out ofthe spherical wave
  4. 4.  Most real antennas do notradiate spherically The wavefront will beonly a portion of a sphere• The surface area of the waveis reduced• Power density is increased!• The increase in powerdensity is expressed asAntenna Gain• dB increase in power along“best” axis• dBi = gain over isotropicantenna• dBd = gain over dipoleantennaGain inthis area
  5. 5.  Radiated power often referenced to power radiatedby an ideal antennattGPEIRP =Pt= power of transmitterGt= gain of transmitting antenna system• The isotropic radiator radiates power uniformly in alldirections• Effective Isotropic Radiated Power calculated by:Gt = 0dB = 1 for isotropic antennaThis formula assumes power and gain is expressed linearly. Alternatively,you can express power and gain in decibels and add them: EIRP = P(dB) + G(dB)The exact same formulas andprinciples apply on thereceiving side too!
  6. 6. λ22Dd f =• Large-scale (Far Field) propagation model• Gives power where random environmental effectshave been averaged together• Waves appear to be plane waves• Far field applies at distances greater than theFraunhofer distance:D = largest physical dimension of antennaλ = wavelength• Small-scale (Near Field) model applies for shorterdistances• Power changes rapidly from one area/time to the next
  7. 7. 2222)4()4()(cfddPPlinlossFreert πλπ===For Free Space (no buildings, trees, etc.)dBdfcfddBlossFree 56.147log20log204log10)( 1010210 −+==πf = frequencyd = distance (m)λ= wavelength (m)c = speed of lighthb= base station antenna height (m)hm= mobile antenna height (m)a(hm) is an adjustment factor for the type of environment and theheight of the mobile.a(hm) = 0 for urban environments with a mobile height of 1.5m.Note: Hata valid only with d in range 1000-20000, hb in range 30-200m)3)(loglog55.60.44()(log82.13)6(log16.2655.69)(10101010−−+−−−+=dhhahfdBlossHatabmbFor Urban environments, use the Hata model
  8. 8. A transmission system transmits a signal at 960MHz with a power of 100mW usinga 16cm dipole antenna system with a gain of 2.15dB over an isotropic antenna.At what distance can far-field metrics be used?λ = 3.0*108m/s / 960MHz = 0.3125 metersFraunhofer distance = 2 D2/ λ = 2(0.16m)2/0.3125 = 0.16mWhat is the EIRP?Method 1: Convert power to dBm and add gainPower(dBm) = 10 log10 (100mW / 1mW) = 20dBmEIRP = 20dBm + 2.15dB = 22.15dBmMethod 2: Convert gain to linear scale and multiplyGain(linear) = 102.15dB/10= 1.64EIRP = 100mW x 1.64 = 164mWChecking work: 10 log10 (164mW/1mW) = 22.15dBm
  9. 9. A transmission system transmits a signal at 960MHz with a power of 100mWusing a 16cm dipole antenna system with a gain of 2.15dB over an isotropicantenna.What is the power received at a distance of 2km (assuming free-spacetransmission and an isotropic antenna at the receiver)?Loss(dB) = 20 log10(960MHz) + 20 log10(2000m) – 147.56dB= 179.6dB + 66.0dB – 147.56dB = 98.0dBReceived power(dBm) = EIRP(dB) – loss= 22.15dBm – 98.0dB = -75.85dBmReceived power(W) = EIRP(W)/loss(linear)= 164mW / 1098.0dB/10= 2.6 x 10-8mW = 2.6 x 10-11WChecking work: 10 -75.85dBm/10= 2.6x 10-8mWWhat is the power received at a distance of 2km (use Hata model with baseheight 30 m, mobile height 1.5 m, urban env.)?Loss(dB) = 69.55+26.16(log(f)-6) – 13.82(log(hb)) – a(hm)+ 44.9-6.55(log(hb))(log(d)-3)=69.55 + 78.01 – 27.79 – 0 + (35.22)(0.30)= 130.34 dB  Received power = 22.15dBm – 130.34dB = -108.19dBm
  10. 10.  A Link Budget analysis determines if there isenough power at the receiver to recover theinformationInformation Modulator AmplifierAntFeedlineTransmitterInformation Demodulator Pre-AmplifierAntFeedlineReceiverFilterFilterRF PropagationGainGainLoss
  11. 11.  Begin with the power output of the transmit amplifier Subtract (in dB) losses due to passive components in the transmitchain after the amplifier Filter loss Feedline loss Jumpers loss Etc. Add antenna gain dBi Result is EIRPInformation Modulator AmplifierAntFeedlineTransmitterFilterRF Propagation
  12. 12. dBi12Antenna gaindB(1.5)150 ft. at 1dB/100 footFeedline lossdB(1)Jumper lossdB(0.3)Filter lossdBm4425 WattsPower AmplifierScaleValueComponentdBm53TotalAll values are example values
  13. 13.  The Receiver has several gains/losses Specific losses due to known environment around the receiver Vehicle/building penetration loss Receiver antenna gain Feedline loss Filter loss These gains/losses are added to the received signal strength The result must be greater than the receiver’s sensitivityInformationDemodulatorPre-AmplifierAntFeedlineReceiverFilter
  14. 14.  Sensitivity describes the weakest signal power levelthat the receiver is able to detect and decode Sensitivity is dependent on the lowest signal-to-noise ratioat which the signal can be recovered Different modulation and coding schemes have differentminimum SNRs Range: <0 dB to 60 dB Sensitivity is determined by adding the requiredSNR to the noise present at the receiver Noise Sources Thermal noise Noise introduced by the receiver’s pre-amplifier
  15. 15.  Thermal noise N = kTB (Watts) k=1.3803 x 10-23J/K T = temperature in Kelvin B=receiver bandwidth Thermal noise is usually very small for reasonablebandwidths Noise introduced by the receiver pre-amplifier Noise Factor = SNRin/SNRout (positive becauseamplifiers always generate noise) May be expressed linearly or in dB
  16. 16.  The smaller the sensitivity, the better the receiver Sensitivity (W) =kTB * NF(linear) * minimum SNR required (linear) Sensitivity (dBm) =10log10(kTB*1000) + NF(dB) + minimum SNRrequired (dB)
  17. 17.  Example parameters Signal with 200KHz bandwidth at 290K NF for amplifier is 1.2dB or 1.318 (linear) Modulation scheme requires SNR of 15dB or 31.62 (linear) Sensitivity = Thermal Noise + NF + Required SNR Thermal Noise = kTB =(1.3803 x 10-23J/K) (290K)(200KHz)= 8.006 x 10-16W = -151dBW or -121dBm Sensitivity (W) = (8.006 x 10-16W )(1.318)(31.62) = 3.33 x 10-14W Sensitivity (dBm) = -121dBm + 1.2dB + 15dB = -104.8dBm Sensitivity decreases when: Bandwidth increases Temperature increases Amplifier introduces more noise
  18. 18.  Transmit/propagate chain produces a receivedsignal has some RSS (Received Signal Strength) EIRP minus path loss For example 50dBm EIRP – 130 dBm = -80dBm Receiver chain adds/subtracts to this For example, +5dBi antenna gain, 3dB feedline/filterloss  -78dBm signal into receiver’s amplifier This must be greater than the sensitivity of thereceiver If the receiver has sensitivity of -78dBm or lower, thesignal is successfully received.
  19. 19. Information Modulator AmplifierAntFeedlineTransmitterInformation Demodulator Pre-AmplifierAntFeedlineReceiverFilterFilterRF PropagationEIRPProp LossRSSSensitivity
  20. 20.  A Link Budget determines what maximum path loss a system cantolerate Includes all factors for EIRP, path loss, fade margin, andreceiver sensitivity For two-way radio systems, there are two link budgets Base to mobile (Forward) Mobile to base (Reverse) The system link budget is limited by the smaller of these two(usually reverse) Otherwise, mobiles on the margin would have only one-waycapability The power of the more powerful direction (usually forward) isreduced so there is no surplus Saves power and reduces interference with neighbors
  21. 21.  Forward (Base to Mobile) Amplifier power 45dBm Filter loss (2dB) Feedline loss (3dB) TX Antenna gain 10dBi Path loss X Fade Margin (5dB) Vehicle Penetration(12dB) RX Antenna gain 3dBi Feedline loss (3dB) Signal into mobile’s LNA hasstrength 33dBm – path loss If Mobile Sensitivity is -100dBm Maximum Path loss = 133dB• Reverse (Mobile to Base)• Amplifier power 28dBm• Filter loss (1dB)• Feedline loss (3dB)• TX Antenna gain 3dBi• Fade Margin (5dB)• Vehicle Penetration (12dB)• Path Loss X• RX Antenna gain 10dBi• Feedline loss (3dB)• Signal into base’s LNA hasstrength 17dBm – path loss• If Base Sensitivity is -105dBm• Maximum Path loss = 122dBUnbalanced – Forward path can tolerate 11dB more loss (distance) than reverse

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