1

The Free Space Wireless Link(Text Section 8-5 )

EELE445Lecture 39

Isotropic Radiator

• Power is radiated equally in alldirections

• F= flux density in Watts/m2

• Also use Field strength, Fs= Volts/m

Pt

224 mWatts

RPF tp

=

2

Flux Density and Field Strength

224 mWatts

RPF tp

=

W==== 377120pem

em

o

ooZ

meterVolts

RP

RPZF ttosF 22

304

120==·=

pp

Real Antenna – Not IsotropicPolar Plot of Normalized F

0dB

3

Polar Antenna Beam Pattern

Some common antenna gains

4

Some common antenna gains

5

6

Free Space Path Loss (Friss loss):

metersinh wavelengttheiswhere

:thatshownbecanIt

metersinantennasreceiveandtransmittbetweendistancesquaredmetersinareaantennareceiveeffective

t watts/watingainantenna wattsinpowertransmitt

:Combining

llp

p

2

2

4

4

e

e

t

t

ettr

AG

RAGP

wattsRAGPP

=

====

=

Think of this as the number of wavelengthsthe area of the antenna intersects

7

2

2

2

2

2

4

4

444

÷øö

çèæº

÷øö

çèæ

==

=

lp

lp

pl

ppl

R

RGGPP

RGGPPGA

rttr

rttr

re

p

e

L

:islosspath(Friss)spacefree

gaintheknow wef,andAgiven

Free Space Path Loss (Friss loss):

Free Space Path Loss (Friss loss):

8

Free Space Path Loss (Friss loss):

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–25 Galaxy I (134° W longitude) antenna patternEIRP footprint contours given in dBw units).

[Courtesy of Hughes Communications, Inc., a wholly owned subsidiary of Hughes Aircraft Company.]

9

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–25 Galaxy I (134° W longitude) antenna patternEIRP footprint contours given in dBw units).

[Courtesy of Hughes Communications, Inc., a wholly owned subsidiary of Hughes Aircraft Company.]

10

C band 4 to 8 GHz

X band 8 to 12 GHz

Ku band 12 to 18 GHz

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Figure 8–8 Communications satellite in geosynchronous orbit.

gtu=55 dBi

gru=20 dBi

grd=51 dBi

gtd=16 dBi36,000 km

5000km

Lu

Ld

gamp

11

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–9 Simplified block diagram of a communicationssatellite transponder.

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–10 64-GHz satellite transponder frequency plan for the downlinkchannels. (For the uplink frequency plan, add 2225 MHz to the numbers given

above.)

12

Link Budgetand

Wireless Link Example

EELE445Lecture 40

Satellite RelayThe “Bent Pipe”

13

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–8 Communications satellite in geosynchronous orbit.

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 8–8 Communications satellite in geosynchronous orbit.

gtu=55 dBi

gru=20 dBi

grd=51 dBi

gtd=16 dBi36,000 km

5000km

Lu

Ld

gamp

14

Earth BulgeEarth BulgeWhen planning for paths longer than seven miles, the curvature of the earthmight become a factor in path planning and require that the antenna belocated higher off the ground. The additional antenna height needed can becalculated using the following formula:

8

2DH =whereH = Height of earth bulge (in feet)D = Distance between antennas (in miles)

= =1,201,250 feet !

15

A full Link Budget will also include a noise analysis

16

Additional Link Path Loss Factors:Fading and Atmospheric Absorption

Additional Link Path Loss Factors:Fading and Atmospheric Absorption

17

Additional Link Path Loss Factors:Antenna Pointing Error

Additional Link Path Loss Factors: Rainfall

18

Additional Link Path Loss Factor: Elevation Angle

Plane Earth Loss-

EELE445-13

•Free space path loss only applies when the wavedoes not interact with the ground.•Examples: mountain top links and satellite links•The loss is higher with ground interaction or whenthe wave passes through a material.

19

Plane Earth Loss- LOS

• When the wave interacts with the ground or some other obstruction weno longer have free space propagation

Plane Earth Loss with line of site-LOS

20

Fresnel Diffraction ( non LOS)

• Non-LOS communication involves an additional loss due to Diffraction

Earth Bulge with Fresnel Diffractionhttp://www.cisco.com/univercd/cc/td/doc/product/wireless/bbfw/ptop/p2pspg02/spg02ch2.htm#xtocid19

Minimum Antenna HeightThe minimum antenna height at each end of the link for paths longer thanseven miles (for smooth terrain without obstructions) is the height of the FirstFresnel Zone plus the additional height required to clear the earth bulge. Theformula would be:

843.43

2DF

DH +=

whereH = Height of the antenna (in feet)D = Distance between antennas (in miles)F = Frequency in GHz

21

Tower HeightLine of Sight

Distance BetweenAntenna Towers

Height of Tower toAvoid Flat Earth

Curvature

Tower Height Required Over TallestObstacle In Line-of-Sight to Provide 60%

Fresnel Zone Clearance2.4GHz 802.11b/g

(Fresnel Zone Radius =39 Feet)

5.8 GHz 802.11a(Fresnel Zone Radius =

25 Feet)

8 Miles 10 feet 33 25

10 Miles 15 feet 38 30

12 Miles 20 feet 43 35

14 Miles 25 feet 48 40

16 Miles 30 feet 53 45

18 Miles 40 feet 63 55

20 Miles 50 feet 73 65

22 Miles 60 feet 83 75

24 Miles 70 feet 93 85

26 Miles 80 feet 103 95

28 Miles 100 feet 123 115

32 Miles 125 feet 148 140

Path Loss: Free Space vs Ground effects

22

Plane Earth Loss

multiple signalsarrive at the receive antenna

Plane Earth Loss

23

Plane Earth Loss

Plane Earth Loss

24

Plane Earth Loss - PELPlane earth loss includes ground reflections

bmpeldB

bmbmpel

t

r

hhrL

krhh

rhhk

rL

PP

log20log20log40

224 4

22

--=

=»÷øö

çèæ»=

:dBloss,earthPlain

lp

pl

Plane Earth Loss: Example

25

Empirical Path Loss

21 )1()( nb

n

ddddg -- +=

See text eq 8-47

Mobile SignalThe received power of a mobile wireless signal is not constant

26

Lecture 39BER- Bit Error Rate

EELE445

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 7–2 Error probability for binary signaling.

27

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 7–4 Receiver for baseband binary signaling.

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 7–4 Receiver for baseband binary signaling.

28

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 6–17 Integrate-and-dump realization of a matched filter.

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 6–17 Integrate-and-dump realization of a matched filter.

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The best we can do:

( )( )

( )0

0

/

!/2

NEQP

docanweBestTheNEQP

be

be

=

=

:FSKcoherentOOK,baseband,unipolarfor

:QPSKBPSK,baseband,PolarforRateErrorBit

HzwattsN

dttvATEbT

bb

/

)(

0

2

densitynoisetheis

bitperenergytheò==

Couch, Digital and Analog Communication Systems, Seventh Edition ©2007 Pearson Education, Inc. All rights reserved. 0-13-142492-0

Figure 7–5 Pe for matched-filter reception of several binary signaling schemes.

30

Figure B–7 The function Q(z) and an overbound,

:numbersBERpracticalfor

2/2

21)( ze

zzQ -»

p

Q, ERF, and ERFC functions

31

Q, ERF, and ERFC functions

Q, ERF, and ERFC functions

32

Q, ERF, and ERFC functions

Q, ERF, and ERFC functions

33

Figure 7–13 Matched-filter detection of QPSK.