Summary of Path Loss in Propagation by jackl17

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									Summary of Path Loss
in Propagation


     Narayan Mandayam
Understanding RF Propagation



                 Goals
                 1. Estimate radio coverage area
                 2. Estimate link performance
                 3. Estimate network design parameters
                    1. Transmitters and their location
                    2. Transmit power
                    3. Antenna type
Interesting Scenarios
                        At which locations will
                        correct reception take
                        place?
Antenna Basics
              Pdirectiona
      G                    l

               Pisotropic




  Isotropic                     Dipole    High gain
                                          directional

   0 dBi                        2.2 dBi   14 dBi
   Free Space Propagation Model
                                                                         Isotropic power
                                  PR             PT                  2
                                       PDi                   W /m       density
                                               4 d
                                                          2
                        d
           PT
                                               PT G T            Power density along
                                       PD                       the direction of
                                               4 d
                                                      2
                                                                 maximum radiation

                                                                 Power received by
                                       PR  PD A eff             Antenna

                                                                                    
                                                                                        2
                                               PT G T                    Aeff
                                                                                
                                       PR                    Aeff        G         4
                                               4 d
Predict received signal                               2
strength when the transmitter
and receiver have a clear
                                                                          2     Also known
line-of-sight path between them
                                                                             as Friis free
                                       PR  PT G T G R                        space formula
                                                         d 
Path Loss (relative measure)
                                                2
           PR           PR            
                            GT G R       
                        PT            d 
Pt
                                                        3   f is in MHz
                        PR              0 . 57 * 10
                              GT G R               2        d is in Km
                        PT                 ( df )

      PR 
         
      P   ( G T ) dB  ( G R ) dB  ( 32 . 5  20 log     10
                                                                  d  20 log   10
                                                                                    f)
      T  dB


                                   Path Loss represents signal attenuation
                                   (measured on dB) between the effective
                                   transmitted power and the receive power
                                   (excluding antenna gains)
   Path Loss (Example)
                                Assume that antennas are isotropic.
                     PR         Calculate receive power (in dBm) at free
                                space distance of 100m from the antenna.
    Pt                          What is PR at 10Km?

50 W           PR 
                  
= 47 dBm       P   ( G T ) dB  ( G R ) dB  ( 32 . 5  20 log   10
                                                                         d  20 log    10
                                                                                            f)
               T  dB

               PR                                                                         59
                  
               P   0  0  ( 32 . 5  20 log     10
                                                         0 . 1  20 log   10
                                                                               900 )
               T  dB

               -20 (for d = 0.1)                              20 (for d = 10)
               PR                                         PR 
                                                               
                  
               P    71 . 5 dB                           P    111 . 5 dB
               T  dB                                      T  dB

      ( PR ) dBm  47  71 . 5   24 . 5 dBm     ( PR ) dBm  47  111 . 5   64 . 5 dBm
                         Path Loss (another example)
                                                               P a th L o s s V s . D is ta n c e

                                                                           2 .4 G H z     5 GHz


                        160



                        140



                        120



                        100
P a th L o s s (d B )




                         80



                         60



                         40



                         20



                          0
                              0   5   10   15   20   25   30   35    40    45       50       55    60   65   70   75   80   85   90   95   100

                                                                            D is ta n c e (K m )
                      Path Loss (another example)
                                      P a th L o s s V s . D is ta n c e

                                                    2.4 G H z    5 G Hz


                      150



                      140



                      130



                      120
P ath L o ss (d B )




                      110



                      100



                       90



                       80



                       70



                       60
                        0.01    0.1                          1                   10   100

                                              D ista n ce (K m ) L o g S ca le
Radio propagation: path loss


   near field                          path loss in 2.4 Ghz band
                Pr
                                      r  8m              r > 8m
         Pt
                                       near field         far field
                     r                   r2               r3.3
                         Pr




                 path loss = 10 log (4r2/)                  r  8m

                              = 58.3 + 10 log (r3.3 /8)       r > 8m
       Indoor Signal Measurement

                           Signal Strength

               Channel 3     Channel 4         Channel 5   Channel 10

        0
       -10 1   61    121      181        241       301     361   421

       -20
       -30
       -40
RSSI




       -50
       -60
       -70
       -80
       -90
                                    Time
 Outdoor P2P Link Signal Measurement

                     Signal Strength


      -81
      -83
      -85
dBm




      -87
      -89
      -91
      -93
      -95
            1   51   101        151        201   251
                           Packet number

								
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