radio propagation.ppt

8/18/2019 Radio Propagation.ppt

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Radio Propagation -

Large-Scale Path Loss


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Basics - Propagation

Radio waves are Easy to generate Can travel long distances Can penetrate bildings

!hey are both sed "or indoor and otdoor co##nication !hey are o#ni-directional$ can travel in all directions !hey can be narrowly "ocsed at high "re%encies &greater

than '00()*+ sing parabolic antennas &li,e satellite dishes+ Properties o" radio waves are "re%ency dependent

t low "re%encies. they pass throgh obstacles well. bt thepower "alls o"" sharply with distance "ro# sorce

t high "re%encies. they tend to travel in straight lines andbonce o" obstacles &they can also be absorbed by rain+

!hey are sb/ect to inter"erence "ro# other radio wave sorces


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Basics - Propagation t VLF, LF, and MF bands. radio

waves "ollow the grond ( radiobroadcasting ses (1 band

t HF bands. the grond

waves tend to be absorbed by the

earth !he waves that reach ionosphere

&'00-500,# above earth sr"ace+.are re"racted and sent bac, to

earth

absorption

re"lection

Ionosphere


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LS path

Re"lected 4ave

-Directional antennas are used-Waves follow more direct paths

- LOS Line-of-Si!ht "ommunication- #eflected wave interfere with the

ori!inal si!nal

VHF $ransmission


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4aves behave #ore li,e light at higher

"re%encies i""iclty in passing obstacles

(ore direct paths

!hey behave #ore li,e radio at lower

"re%encies Can pass obstacles


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Propagation (odels

4e are interested in propagation

characteristics and #odels "or waves with

"re%encyy in range$ "ew ()* to a "ew 7)*

(odeling radio channel is i#portant "or$ eter#ining the coverage area o" a trans#itter

eter#ine the trans#itter power re%ire#ent

eter#ine the battery li"eti#e

1inding #odlation and coding sche#es to i#prove the

channel %ality

eter#ine the #a8i## channel capacity


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Radio Propagation (odels

s the #obile #oves away "ro# the trans#itter overlarger distances. the local average received signalwill gradally decrease !his is called large-scalepath loss

!he #odels that predict the #ean signal strength "oran arbitrary-receiver trans#itter &!-R+ separationdistance are called large-scale propagation #odels

:se"l "or esti#ating the coverage area o" trans#itters


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S#all-Scale and Large-Scale 1ading

' '6 '; 20 22 2 26 2;

!-R Separation eters+

-90

-60

-50

-0

-30

Received Power &dB#+

!his "igre is /st an illstration

to show the concept


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4hat is ecibel &dB+

4hat is dB &decibel+$ logarith#ic nit that is sed to describe a ratio

Let say we have two vales P' and P2 !he di""erence &ratio+

between the# can be e8pressed in dB and is co#pted as

"ollows$ '0 log &P'>P2+ dB

E8a#ple$ trans#it power P' ? '004.

received power P2 ? ' 4

!he di""erence is '0log&'00>'+ ? 20dB


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dB

dB nit can describe very big ratios withn#bers o" #odest si*e

See so#e e8a#ples$

!8 power ? '004. Received power ? '4 !8 power is '00 ti#es o" received power i""erence is 20dB

!8 power ? '004. Received power ? '#4 !8 power is '00.000 ti#es o" received power

i""erence is 50dB !8 power ? '0004. Received power ? '#4

!8 power is #illion ti#es o" received power i""erence is 60dB


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dB#

1or power di""erences. dB# is sed to denote

a power level with respect to '#4 as the

re"erence power level Let say !8 power o" a syste# is '004 @estion$ 4hat is the !8 power in nit o" dB#A

nswer$ !8power&dB#+ ? '0log&'004>'#4+ ?

'0log&'004>000'4+ ? '0log&'00.0000+ ? 50dB#


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dB4

1or power di""erences. dB4 is sed to

denote a power level with respect to '4 as

the re"erence power level Let say !8 power o" a syste# is '004 @estion$ 4hat is the !8 power in nit o" dB4A

nswer$ !8power&dB4+ ? '0log&'004>'4+ ? '0log&'00+ ?

20dB4


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1ree-Space Propagation (odel

:sed to predict the received signal strengthwhen trans#itter and receiver have clear.nobstrcted LS path between the#

!he received power decays as a "nction o"!-R separation distance raised to so#epower

Path Loss$ Signal attenation as a positive%antity #easred in dB and de"ined as thedi""erence &in dB+ between the e""ectivetrans#itter power and received power


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1ree space power received by a receiver antennaseparated "ro# a radiating trans#itter antenna by adistance d is given by 1riis "ree space e%ation$

Pr &d+ ? &Pt7t7r λ2+ > &&π+2d2L+ E%ation 'D

Pt is trans#ited power Pr &d+ is the received power 7t is the tras#itter antenna gain &di#ensionless %antity+ 7r is the receiver antenna gain &di#ensionless %antity+ d is !-R separation distance in #eters L is syste# loss "actor not related to propagation &L ? '+

L ? ' indicates no loss in syste# hardware &"or or prposes wewill ta,e L ? '. so we will igonore it in or calclations+

λ is wavelength in #eters


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!he gain o" an antenna 7 is related to its a""ective

apertre e by$

7 ? π e > λ2 E%ation 2D

!he e""ective apertre o" e is related to the physical si*e o"the antenna.

λ is related to the carrier "re%ency by$

λ ? c>" ? 2πc > ωc E%ation 3D

" is carrier "re%ency in )ert*

ωc is carrier "re%ency in radians per second

c is speed o" light in #eters>sec


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Path loss. which represents signal attenationas positive %antity #easred in dB. is de"inedas the di""erence &in dB+ between the e""ective

trans#itted power and the received power

PL&dB+ ? '0 log &Pt>Pr + ? -'0log&7t7r λ2+>&π+2d2D E%ation D

&Fo can drive this "ro# e%ation '+


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';

1ree-Space Propagation (odel G

Re"erence istance d0


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'=


E8pressing the received power in dB# and dB4 Pr &d+ &dB#+ ? '0 log Pr &d0+>000'4D H 20log&d0>d+

where d ? d0 ? d" and Pr &d0+ is in nits o" watts

E%ation 9D

Pr &d+ &dB4+ ? '0 log Pr &d0+>'4D H 20log&d0>d+where d ? d0 ? d" and Pr &d0+ is in nits o" watts

E%ation ;D

Re"erence distance d0 "or practical syste#s$ 1or "re%ncies in the range '-2 7)*

' # in indoor environ#ents

'00#-',# in otdoor environ#ents


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E8a#ple @estion

trans#itter prodces 504 o" power + E8press the trans#it power in dB#

B+ E8press the trans#it power in dB4

C+


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2'

Soltion

+ Pt&4+ is 504

Pt&dB#+ ? '0logPt+>'#4+D

Pt&dB#+ ? '0log&508'000+Pt&dB#+ ? 9 dB#

B+

Pt&dB4+ ? '0logPt&4+>'4+DPt&dB4+ ? '0log&50+

Pt&dB4+ ? '9 dB4


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Soltion

Pr &d+ ? Pr &d0+&d0>d+2

Sbstitte the vales into the e%ation$ Pr &'0,#+ ? Pr &'00#+&'00#>'0,#+2

Pr &'0,#+ ? 00035#4&'0-+

Pr &'0,#+ ? 358'0-'04

Pr&'0,#+ dB#D ? '0log&358'0-'04>'#4+

? '0log&358'0-9

+ ? -65dB#


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!wo #ain channel design isses

Co##nication engineers are generally concernedwith two #ain radio channel isses$

Lin, Bdged esign Lin, bdget design deter#ines "nda#ental %antities sch as

trans#it power re%ire#ents. coverage areas. and battery li"e


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Lin, Bdged esign :sing Path Loss

(odels Radio propagation #odels can be derived

By se o" e#pirical #ethods$ collect#easre#ent. "it crves

By se o" analytical #ethods (odel the propagation #echanis#s #athe#atically and

derive e%ations "or path loss

Long distance path loss #odel

E#pirical and analytical #odels show thatreceived signal power decreases logarith#icallywith distance "or both indoor and otdoorchannels


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Long distance path loss #odel

!he average large-scalepath loss "or an arbitrary !-

R separation is e8pressed

as a "nction o" distance by

sing a path loss e8ponent

n$

!he vale o" n depends on

the propagation

environ#ent$ "or "ree space

it is 2I when obstrctionsare present it has a larger

vale

)log(10)()(

)()(

0

0

0

d

d nd PLdB PL

d

d d PL

n

+=

∝

dB)in(denotedddistanceaat

loss pathscale-largeaveragethedenotes)(d PL

E%ation ''


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Selection o" "ree space re"erence

distance


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Log-nor#al Shadowing

E%ation '' does not consider the "act thesrronding environ#ent #ay be vastlydi""erent at two locations having the sa#e !-R

separation !his leads to #easre#ents that are di""erent

than the predicted vales obtained sing theabove e%ation

(easre#ents show that "or any vale d. thepath loss PL&d+ in dB# at a particlar locationis rando# and distribted nor#ally


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X σ is a *ero-#ean 7assian &nor#al+ distribted rando# variable &in dB+

with standard deviation σ &also in dB+

Log-nor#al Shadowing- Path Loss

)(d PL

σ

σ

X d

d nd PLdBd PL

X d PLdBd PL

++=

+=

)log(10)(][)(

)(][)(

0

0

!hen adding this rando# "actor$

denotes the average large-scale path loss &in dB+ at a distance d

)( 0d PL is sally co#pted ass#ing "ree space propagation #odel between

trans#itter and d0 &or by #easre#ent+

E%ation '2 ta,es into accont the shadowing a""ects de to clttering on the

propagation path


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Log-nor#al Shadowing- Received

Power !he received power in log-nor#al shadowing

environ#ent is given by the "ollowing "or#la

&derivable "ro# E%ation '2+

!he antenna gains are inclded in PL&d +

++−=

−=

][)log(10])[(][])[(

])[(][])[(

0

0 dB X d

d ndBd PLdBm P dBmd P

dBd PLdBm P dBmd P

t r

t r

σ

E%ation '2


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Log-nor#al Shadowing. n and σ

!he log-nor#al shadowing #odel indicatesthe received power at a distance d isnor#ally distribted with a distance

dependent #ean and with a standarddeviation o" σ


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E8a#ple o" deter#ining n and σ

ss#e Pr &d0+ ? 0dB#

and d0 is '00#

ss#e the receiver

power Pr is #easredat distances '00#.

500#. '000#. and

3000#.

!he table gives the#easred vales o"

received power

Distance from$ransmitter

#eceived %ower

'00# 0dB#

500# -5dB#

'000# -''dB#

3000# -'6dB#


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4e ,now the #easred vales Lets co#pte the esti#ates "or received

power at di""erent distances sing long-

distance path loss #odel &E%ation ''+ Pr &d0+ is given as 0dB# and #easred vale

is also the sa#e #eanPr &d+ ? Pr &d0+ G #eanPL&"ro#d0 tod+

!hen #eanPr &d+ ? 0 G '0logn&d>d0+ :se this e%ation to co#pter power levels at

500#. '000#. and 3000#


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veragePr &500#+ ? 0 G '0logn&500>'00+ ? -6==n

veragePr &'000#+ ? 0 G '0logn&'000>'00+ ? -'0n

veragePr &3000#+ ? 0 G '0logn&3000>'00+ ? -'99n

Jow we ,now the esti#ates and also #easred

actal vales o" the received power at di""erent

distances


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Path Loss E8ponent and Standard eviation

(easred "or i""erent Bildings

&uildin! Fre'uenc( )MH*+ n )d&+

Retail Stores =' 22 ;9

7rocery Store =' '; 52

""ice. hard partition '500 30 90

""ice. so"t partition =00 2 =6

""ice. so"t partition '=00 26 ''

Factor( LOS

!e8tile>Che#ical '300 20 30

!e8tile>Che#ical 000 2' 90

Paper>Cereals '300 '; 60

(etalwor,ing '300 '6 5;

Sbrban )o#e

Che#ical 000 2' =9

(etalwor,ing '300 33 6;


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Partition Losses

!here are two ,ind o" partition at the sa#e

"loor$ )ard partions$ the walls o" the roo#s

So"t partitions$ #oveable partitions that does notspan to the ceiling

!he path loss depends on the type o" the

partitions


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Partition Losses

Material $(pe Loss )d&+ Fre'uenc( )MH*+

ll #etal 26 ;'5

l#ini# Siding 20 ;'5

Concerete Bloc, 4all 3= '300

Loss "ro# one 1loor 20-30 '300

!rning an ngle in a Corridor '0-'5 '300

Concrete 1loor '0 '300

ry Plywood &3>in+ G ' sheet ' =600

4et Plywood &3>in+ G ' sheet '= =600

l#in# &'>;in+ G ' sheet 9 =600

verage signal loss #easre#ents reported by varios researches

"or radio paths obscrcted by so#e co##on bilding #aterial


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Partition Losses between 1loors

!he losses between "loors o" a bilding are

deter#ined by E8ternal di#ensions and #aterials o" the bilding

!ype o" constrction sed to create "loors E8ternal srrondings

J#ber o" windows

Presence o" tinting on windows


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Partition Losses between 1loors

&uildin! FF )d&+ )d&+

Office &uildin!

!hrogh ' 1loor '2= 90

!hrogh 2 1loors ';9 2;

!hrogh 3 1loors 2 '9

!hrogh 1loors 290 '5

Office &uildin! .

!hrogh ' 1loor '62 2=

!hrogh 2 1loors 295 5!hrogh 3 1loors 3'6 92

verage 1loor ttenation 1actor in dB "or ne. !wo. !hree and1or 1loors in !wo ""ice Bildings


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Signal Penetration


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Signal Penetration

radio propagation.ppt

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