summary of path loss in propagation
DESCRIPTION
Summary of Path Loss in Propagation. Narayan Mandayam. Understanding RF Propagation. Goals Estimate radio coverage area Estimate link performance Estimate network design parameters Transmitters and their location Transmit power Antenna type. Interesting Scenarios. - PowerPoint PPT PresentationTRANSCRIPT
Summary of Path Loss in Propagation
Narayan Mandayam
Understanding RF Propagation
Goals1. Estimate radio coverage area2. Estimate link performance3. Estimate network design parameters
1. Transmitters and their location2. Transmit power3. Antenna type
Interesting Scenarios
At which locations will correct reception take place?
Antenna Basics
Isotropic Dipole High gain directional
isotropic
ldirectiona
P
PG
0 dBi 2.2 dBi 14 dBi
Free Space Propagation Model
PT
PR
d
2/24
mWd
PP TDi
Isotropic powerdensity
24 d
GPP TTD
Power density alongthe direction ofmaximum radiation
effTT
R Ad
GPP
24
4
2
G
Aeff
2
d
GGPP RTTR
Power received byAntennaeffDR APP
Predict received signalstrength when the transmitterand receiver have a clearline-of-sight path between them Also known
as Friis freespace formula
Path Loss (relative measure)
Pt
PR
2
d
GGP
PRT
T
R
)log20log205.32()()( 1010 fdGGP
PdBRdBT
dBT
R
2
3
)(
10*57.0
dfGG
P
PRT
T
R
f is in MHzd is in Km
Path Loss represents signal attenuation(measured on dB) between the effective transmitted power and the receive power(excluding antenna gains)
Path Loss (Example)
Pt
PR
50 W= 47 dBm
Assume that antennas are isotropic.Calculate receive power (in dBm) at free space distance of 100m from the antenna. What is PR at 10Km?
dBP
P
dBT
R 5.71
)log20log205.32()()( 1010 fdGGP
PdBRdBT
dBT
R
dBP
P
dBT
R 5.111
)900log201.0log205.32(00 1010
dBT
R
P
P
-20 (for d = 0.1)
59
20 (for d = 10)
dBmP dBmR 5.245.7147)( dBmP dBmR 5.645.11147)(
Path Loss (another example)
Path Loss Vs. Distance
0
20
40
60
80
100
120
140
160
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Distance (Km)
Path
Lo
ss (
dB
)
2.4 GHz 5 GHz
Path Loss (another example)
Path Loss Vs. Distance
60
70
80
90
100
110
120
130
140
150
0.01 0.1 1 10 100
Distance (Km) Log Scale
Pat
h L
oss
(d
B)
2.4 GHz 5 GHz
Radio propagation: path loss
Pt
Pr
Pr
near field
path loss = 10 log (4r2/) r 8m
= 58.3 + 10 log (r3.3 /8) r > 8m
r
path loss in 2.4 Ghz band
near field far field
r2
r 8m r > 8m
r3.3
Signal Strength
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
1 61 121 181 241 301 361 421
Time
RS
SI
Channel 3 Channel 4 Channel 5 Channel 10
Indoor Signal Measurement
Signal Strength
-95
-93
-91
-89
-87
-85
-83
-81
1 51 101 151 201 251
Packet number
dB
m
Outdoor P2P Link Signal Measurement