This document discusses link budget calculations and decibel (dB) measurements used in wireless communications. It provides examples of converting between milliwatts and dBm and how gains and losses in dB are additive. It also defines key terms like intentional radiator, which refers to the RF device and cabling before the antenna, and EIRP, which is the equivalent isotropically radiated power from the antenna and accounts for antenna gain. Regulations from the FCC restricting maximum EIRP are discussed for different types of wireless links.

1. Link Budget
Calculation
Marco Zennaro
mzennaro@ictp.it
Carlo Fonda
cfonda@ictp.it

2. Link Planning
How long can a wireless link be?
How much power can we use?
What kind of antennas should be use?
Do the connection cables effect the link?
What is the effect of trees?

3. dB math
decibels are a relative measurement unit
unlike the absolute measurement of milliwatts
on the logarithmic scale, the reference cannot be
zero because the log of zero does not exist!
log(0) is undefined!

4. dB math
the reference point that relates the logarithmic dB scale to
the linear watt scale is:
1 mW = 0 dBm
the m in dBm refers to the fact that the reference is 1 mW
and therefore a dBm measurement is a measurement of
absolute power

5. dB math
to convert mW to dBm:
P(dBm)= 10 log P(mW)
to convert dBm to mW:
P(mW)= log
-1
(P(dBm)/10)
the advantage of using dB is that gains and losses are
ADDITIVE

6. dB math
gain or loss in an RF system may be referred to by absolute
power measurement (10W of power) or by a relative power
measurement (half of its power)
-3dB = half the power in mW
+3dB = double the power in mW
-10dB = one tenth the power in mW
+10dB = ten times the power in mW

7. dB math
for example:
10 mW + 3 dB = 20 mW
100 mW - 3dB = 50 mW
10 mW + 10 dB = 100 mW
300 mW - 10 dB = 30 mW

8. dB math
"#$%&'(&)*+!,-.!/0!12))!/&3'&4(&!56&!1455!%4)7&!5#!#$&!5&$56!#8!5645!%4)7&9!
!
3:55!06!;!45/8!!!:5!069!
!
:6&(&!'7)&(!12))!4))#1!4!;723<!34)37)452#$!#8!=2))21455!>#1&'!)&%&)(!16&$!?2%&$!>#1&'!
)&%&)(+!?42$(+!4$/!)#((&(!2$!/0=!4$/!/0@!!A2?7'&!B@-C!(6#1(!5645!56&!'&8&'&$3&!>#2$5!2(!
4)14*(!56&!(4=&+!D75!>#1&'!)&%&)(!34$!=#%&!2$!&256&'!/2'&352#$!8'#=!56&!'&8&'&$3&!>#2$5!
/&>&$/2$?!#$!16&56&'!56&*!'&>'&(&$5!4!>#1&'!?42$!#'!)#((@!
!
#$%&'(")*+," <=>'(!1'?'1!@#$(&"
!
!
;A5
/80
;:5
/80
;)5
/80
;45
/80
5
/80
745
/80
7)5
/80
7:5
/80
7A5
/80
455
.6
4
-6
45
-6
455
-6
4
06
45
06
455
06
4B555
06
45B555
06
;4)
/80
;C
/80
;D
/80
;:
/80
;5
/80
7:
/80
7D
/80
7C
/80
74)
/80
D)EF
-6
4)F
-6
)F5
-6
F55
-6
4
06
)
06
A
06
G
06
4D
06 !
!
E$!56&!5#>!364'5!#8!A2?7'&!B@-C+!?42$(!4$/!)#((&(!#8!-.!/0!4'&!(6#1$!45!&436!2$3'&=&$5@!!
F#523&!5645!4!?42$!#8!G-.!/0!8'#=!56&!'&8&'&$3&!>#2$5!#8!-!=H!=#%&(!56&!>#1&'!5#!G-.!
/0=!I-.!=HJ@!!"#$%&'(&)*+!$#523&!5645!4!)#((!#8!,-.!/0!=#%&(!56&!>#1&'!5#!,-.!/0=!
I-..!=23'#1455(J@!!K$!56&!D#55#=!364'5+!56&!(4=&!>'2$32>4)!4>>)2&(@!!:6&(&!364'5(!D#56!

9. dB math
for example:
+43 dBm
43dB = 10dB + 10dB + 10dB + 10dB + 3dB
1 mW x 10 = 10 mW
10 mW x 10 = 100 mW
100 mW x 10 = 1000 mW
1000 mW x 10 = 10000 mW
10000 mW x 2 = 20000 mW = 20 W

10. dB math
exercise:
express -26 dBm in Watts
-26dB = - 10dB - 10dB - 3dB - 3dB
1 mW / 10 = 100 μW
100 μW / 10 = 10 μW
10 μW / 2 = 5 μW
5 μW / 2 = 2.5 μW

11. dB math
when quantifying the gain of an antenna, the decibel units are
usually represented by dBi
the i stands for isotropic, which means that the change in
power is referenced against an isotropic radiator
an isotropic radiator is a theoretical ideal transmitter
that produces an e.m. field in all directions with equal
intensity at a 100% efficiency
other decibels units are also used, as for example the dBd
which is a measure of the gain of an antenna system relative
to a dipole antenna

12. antenna gain
an antenna element is a passive device
the antenna can create the effect of amplification by virtue
of its physical shape
by intentional radiator we mean the RF device and all
cabling and connectors up to, but not including, the antenna

13. intentional radiator
,-1+?-#%$'!$#3!6&1%+5$'!;&$(*+3%,2!%-!($@+(+?&!3+2%$#5&!-0!%,&!/1-/$9$%&3!*$6&!$%!'-*!
/-*&17!
!
+%&'%&*,%(-#.(/*(&,0#
!
"2!3&0+#&3!;4!%,&!=&3&1$'!K-((.#+5$%+-#!K-((+22+-#!G=KKH:!$#!+#%&#%+-#$'!1$3+$%-1!+2!
$#!<=!3&6+5&!%,$%!+2!2/&5+0+5$''4!3&2+9#&3!%-!9&#&1$%&!$#3!1$3+$%&!<=!2+9#$'27!!L#!%&1(2!-0!
,$13*$1&:!$#!+#%&#%+-#$'!1$3+$%-1!*+''!+#5'.3&!%,&!<=!3&6+5&!$#3!$''!5$;'+#9!$#3!
5-##&5%-12!./!%-:!;.%!#-%!+#5'.3+#9:!%,&!$#%&##$:!$2!+''.2%1$%&3!+#!=+9.1&!M7NM!;&'-*7!!!
!
1+)2.3#!45!### 3.%&.%45.#1(+#/4#%5'(
(
6#71&
6#71&
65..&6%5'
65..&6%5'
65..&6%5'
#.%&..#
!50$5.&.%2
4.61-/&/(4.(%"&
3.%&.%45.#1(+#/4#%5'
8'4/9&
(
#
!
"#4!1&0&1&#5&!%-!O/-*&1!-.%/.%!-0!%,&!L#%&#%+-#$'!<$3+$%-1O!1&0&12!%-!%,&!/-*&1!-.%/.%!$%!

14. intentional radiator
any reference to “power output of the Intentional
Radiator” refers to the power output at the end of the
last cable or connector before the antenna
for example:
if a 30 mW transmitter loses 15 mW of power in the
cables and another 5 mW in the connectors, the power of
the intentional radiator is 10 mW

15. intentional radiator! ! "#$%&'(!)!*!+,!,-./$0'.&$12!!!!"#
$%&'()#*+,"# 3$0%1'!45('1'22!678!9:.;5<-($&5:.#
!
9$=1'
9$=1'
9:..'9&:(
9:..'9&:(
9:..'9&:(
$.&'..$
799'22!%:5.&
>:5.&!7 >:5.&!?
>:5.&!" >:5.&!@
!
!
!
! ! ! -../00#12345## 12345#-###12345#6###12345#7###12345#8#
ABB!0C! ! DE!/?! !!!!!DE!/?!!!!!!!DE!/?! FA)!/?5!
G! ABB!0C! ! !)! !!!!!!)! !!!!!!!!!!)! HI)!I)!I)!I)J!
G! ABB!0C! ! !)!!!!!!!!!!!!!!)! !!!!!!!!!!)! IAK!
G! LB!0C!! ! ! !!!!!!)! !!!!!!!!!!)! IAK!
G! )L!0C!! ! ! ! !!!!!!!!!!)! IAK!
G! A)ML!0C! ! ! ! ! ! IAK!
G! )BB!0C!
!!!!!!!
-..9:;5/#</;09:/=/450#
!
"#$%&'(%!$%)*)!$)+%,-.')*!/0)!%)#12'#!/,3!)41)3-),$!-,!*&5)!*-$'/$-&,*6!$%)0)!/0)!$-5)*!

16. EIRP
the EIRP is the Equivalent Isotropically Radiated
Power
EIRP is the power actually radiated by the antenna element
and is important because
it is regulated by the FCC or other regulatory agency
it is used in calculating whether or not a wireless link is
viable

17. EIRP
the EIRP takes into account the gain of the antenna
!"#$%&!$#'()*+&(,&-*($*(),*'#&.'/)'(,!%&'*/&(0$)!&1,2$!&,"(1"(3&&4*/$!%('*/)*+&0,2&1,2$!&
,"(1"(&)%&5$'%"!$/6&0,2&5"70&1,2$!&)%&'##,2$/6&'*/&0,2&(,&7'#7"#'($&(0$%$&8'#"$%&'!$&'##&
7,8$!$/&)*&(0)%&9,,:3&&;<<&!$+"#'(),*%&7,*7$!*)*+&,"(1"(&1,2$!&'(&(0$&-*($*(),*'#&
.'/)'(,!&'*/&=-.>&'!$&?,"*/&)*&>'!(&@A&<;.6&<0'1($!&B6&C$7(),*&BD3E@A&/'($/&F7(,9$!&B6&
EGGG3&
&
$%&'()*+,-#./0-102'3)**4#5)6')-+6#708+1#9$.57:#
&
=-.>&)%&(0$&1,2$!&'7("'##H&!'/)'($/&9H&(0$&'*($**'&$#$5$*(6&'%&%0,2*&)*&;)+"!$&E3BI3&&
J0)%&7,*7$1(&)%&)51,!('*(&9$7'"%$&)(&)%&!$+"#'($/&9H&(0$&;<<&'*/&9$7'"%$&)(&)%&"%$/&)*&
7'#7"#'()*+&20$(0$!&,!&*,(&'&2)!$#$%%&#)*:&)%&8)'9#$3&&=-.>&(':$%&)*(,&'77,"*(&(0$&+')*&,?&
(0$&'*($**'3&&&
&
;.<=5$#!>?@### 34+5#
&
6$71'
6$71'
68..'6&8(
68..'6&8(
68..'6&8(
$.&'..$
9(:/;'
34+5
<8-&%-&!%8='(>
+,!9'$0
&
&
C"11,%$&'&(!'*%5)(()*+&%('(),*&"%$%&'&BGK/L)&'*($**'&M20)70&'51#)?)$%&(0$&%)+*'#&BGK?,#/N&
'*/&)%&?$/&9H&BGG&5)##)2'((%&?!,5&(0$&)*($*(),*'#&!'/)'(,!3&&J0$&=-.>&)%&BGGG&5O6&,!&B&
O'((3&&J0$&;<<&0'%&!"#$%&/$?)*)*+&9,(0&(0$&1,2$!&,"(1"(&'(&(0$&)*($*(),*'#&!'/)'(,!&'*/&

18. EIRP
suppose a transmitting station uses a 10 dBi antenna (which
amplifies the signal 10 times) and is fed by 100 mW from the
intentional radiator
the EIRP is 1000 mW or 1 W
the FCC has rules defining both the power output at the
intentional radiator and the antenna element

19. EIRP
the FCC enforces certain rules regarding the power
radiated by the antenna element, depending on whether the
implementation is point-to-multipoint (PtMP) or point-to-
point (PtP)
PtMP links are typically configured in a star topology
when an omnidirectional antenna is used, the FCC
automatically considers the link a PtMP link

20. PtMP
in the setup of a point-to-multipoint link, the FCC limits the
EIRP to 4 Watts
the power limit set for the intentional radiator is 1 Watt
is the transmitting LAN devices are adjustable with respect
to their output power, then the system can customized to
the needs of the user

21. PtMP
for example:
a radio transmitting at 1 Watt(+30 dBm) is connected
directly to a 12 dBi omnidirectional antenna
the total output power at the antenna is about 16 Watts,
which is well above the 4 Watts limit
the FCC stipulates that for each 3dBi above the antenna’s
initial 6dBi of gain, the power of the intentional radiator
must be reduced by 3dB below the initial +30dBm

22. PtMP
for our example, since the antenna gain is 12dBi, the power
of the intentional radiator must be reduced by 6dB
this reduction will result in an intentional radiator power of
24 dBm, or 36 dM of EIRP which is 4 Watts
the end result is that the power at the intentional radiator
must never be more than 1 Watt, and the EIRP must never
be above 4 Watts for a PtMP connection

23. PtMP
87*<+</.A5<8*);$)*5.**)3$$P6.$585);$8,5-,5$-8:./$)5$56.$)*5.**)$<=$)(8,5$EQ$F)55=9$:6<A6$
<=$:.;;$)(8@.$56.$R$F)55$;<7<53$$P6.$4SS$=5<-,;)5.=$56)5$!"#$%&'($)$*+,$&-".%$/(%$
&0/%00&12$,0,/,&3$4$*+,$"!$5&,06$/(%$7"8%#$&/$/(%$,0/%0/,"0&3$#&*,&/"#$9:2/$-%$#%*:'%*$-;$)$
*+$-%3"8$/(%$,0,/,&3$<)=$*+93$$48/$8,/$.T)7-;.9$=<*A.$56.$)*5.**)$B)<*$<=$EO$+N<9$56.$
-8:./$)5$56.$<*5.*5<8*);$/)+<)58/$7,=5$(.$/.+,A.+$(J$Q$+N3$$P6<=$/.+,A5<8*$:<;;$/.=,;5$<*$
)*$<*5.*5<8*);$/)+<)58/$-8:./$8>$KOR$+N7$?LM$+N7$U$Q$+ND9$8/$O0M$7F$)*+$)*$V%CW$8>$
LQ$+N7$?OR$+N7$K$EO$+N<D9$8/$R$F)55=3$$S;.)/;J$56<=$/,;.$A)*$(.A87.$A8*>,=<*B9$(,5$56.$
.*+$/.=,;5$7,=5$(.$56)5$56.$-8:./$)5$56.$<*5.*5<8*);$/)+<)58/$7,=5$*.@./$(.$78/.$56)*$E$
F)55$?=..$4<B,/.$Q3OD9$)*+$56.$V%CW$7,=5$*.@./$(.$)(8@.$R$F)55=$>8/$)$W5'W$A8**.A5<8*3$
$
-$ 96,4%:%6:;<-%,$6,4%(96=&'(/,>,%(?#@-&$
./012$34$5641663$
789:;$
5641663$'3<6$
789<;$
*&).$
789:;$
*&).$
70344=;$
AB( )( A)( C(
DE( F( A)( C(
DC( GD( A)( C(
DG( GH( A)( C(
GI( GI( A)( C(
GH( DG( A)( C(
GD( DC( A)( C(
?"&(.$&J,K,J(,4K6'>#%,64(J64%#,4&7(,4(L,3<'&()MD(,.(46%(J6N&'&7(64(%"&(!+10(&O#>M((
?"&(,4K6'>#%,64(,.($'6N,7&7(#.(#('&.6<'J&(K6'(P6<'(#7>,4,.%'#%,N&(%#.Q.M(

24. PtP
point-to-point links include a single directional transmitting
antenna and a single directional receiving antenna
the FCC mandates that for every 3 dBi above the initial 6
dBi of antenna gain, the power at the intentional radiator
must be reduced by 1 dB from the initial +30 dBm
consider the previous example: 1W (+30 dBm) at the
intentional radiator and a 12 dBi antenna (directional
antenna in this case)

25. PtP
the total output power is still 16 Watts
since the antenna gain is 12 dBi, the power at the intentional
radiator must be reduced by 2 dB
this reduction will result in an intentional radiator power of
28 dBm (30-2), and an EIRP of 40 dBm or 10Watts
in the case of PtP links, the power of the intentional radiator
is still limited to 1 Watt, but the limit of the EIRP increases
with the gain of the antenna

26. PtP
"#$%!$&!'(!)*$+!,-.!/01.2!#,!,-.!$%,.%,$0%#3!2#)$#,02!45&,!6.!2.)57.)!68!(!)*+!#&!0//0&.)!
,0!#!9!)*!2.)57,$0%!$%!,-.!/2.:$05&!.;#4/3.<!!=-$&!2.)57,$0%!1$33!2.&53,!$%!#%!$%,.%,$0%#3!
2#)$#,02!/01.2!0>!(?!)*4!@AB!)*4!C!(!)*D+!02!#605,!9AB!4E!#%)!#%!FGHI!0>!JB!)*4!
@(?!)*4!K!'(!)*$D+!02!'B!E#,,&<!!G%!,-.!7#&.!0>!I,I!3$%L&+!,-.!/01.2!#,!,-.!$%,.%,$0%#3!
2#)$#,02!$&!&,$33!3$4$,.)!,0!'!E#,,+!65,!,-.!3$4$,!0>!,-.!FGHI!!"#$%&'%'!1$,-!,-.!"#$%!0>!,-.!
#%,.%%#!@M$"52.!9<AD<!!G,!$&!:.28!$4/02,#%,!,0!73.#238!)$&,$%"5$&-!6.,1..%!,-.!253.&!,-#,!
"0:.2%!I,I!#%)!I,NI!1$2.3.&&!3$%L&<!
!
'()*+,-! 96,4&:&6:96,4&!96;'(!/,<,&!=$>-'!
!
./012*34*5641663*
789:;*
<3=*5641663*&3>6*
789>;*
)%(.*
789:;*
)%(.*
70344?;*
?@! )! ?)! A!
BC! C! ?D! )E?!
BD! FB! A@! F@!
BG! FH! AB! F)!
B)! FD! AA! BH!
BH! BF! A)! ?CED!
BA! BA! AD! )?!
B?! BG! H@! F@@!
BB! ?@! HB! FHD!
!
!
=#'!.%'I,J,I!,4J6(<$&,64!I64&$,4'7!,4!K,3L('!)E?!,.!46&!I6M'('7!64!&#'!"+10!'N$<E!!
=#'!,4J6(<$&,64!,.!%(6M,7'7!$.!$!('.6L(I'!J6(!O6L(!$7<,4,.&($&,M'!&$.P.E!
!
=-.!MOO!-#&!#!)$>>.2.%,!253.!>02!I,I!3$%L&!$%!,-.!5//.2!PQGG!6#%)<!!M$;.)!/0$%,R,0R/0$%,!

27. Fresnel zone
the Fresnel Zone occupies a series of concentric
ellipsoid-shaped areas around the Line-of-Sight path
RF LOS is different that visual LOS
visual LOS is present when one can stand next one
antenna and use binoculars to view the other antenna
RF LOS requires not only a visual sight line between the
antennas but it also requires that a football shaped area
between the two antennas be free of obstructions

28. Fresnel zone
the fresnel zone is an area that is larger in diameter at the
center and smaller in diameter at either end. Also, the
greater the distance between the antennas, the larger the
diameter of the fresnel zone in the center.
the Fresnel Zone is important to the integrity of the RF link
because it defines an area around the LOS that can
introduce RF signal interference if blocked
objects in the Fresnel Zone as trees, hilltops and buildings
can diffract or reflect the main signal away from the receiver

29. Fresnel zone
! "#$%&'(!)!*!+,!,-./$0'.&$12!!!!"#
*++# ,('2.'1!34.'#
!
,('2.'1!34.'
!
!
!
"#$!%&'()*!+,!-#$!.%$*/$0!1+/$!&-!(-*!2('$*-!3+(/-!4&/!5$!4&04)0&-$'!56!-#$!,+00+2(/7!
,+%8)0&9!

30. Fresnel zone
the radius of the Fresnel Zone at its widest point can be
calculated as
r=43.3 x sqrt(d/4f)
where d is the link distance in miles, f is the frequency in
GHz and the answer r is in feet
r=17.3 x sqrt(d/4f)
where d is the link distance in kilometers, f is the
frequency in GHz and the answer r is in meters
at 2.4 GHz, for a distance of 10 km, the Fresnel Zone has a
radius of 17.6 meters

31. Fresnel zone
considering the importance of the Fresnel Zone, it is
important to quantify the degree to which it can be blocked
typically, 20% to 40% Fresnel Zone blockage introduces little
to no interference into the link
it is better to err to the conservative side, allowing no more
than 20% blockage of the Fresnel Zone
http://gbppr.dyndns.org:8080/fresnel.main.cgi

32. Propagation Basics
signal power is diminished by geometric spreading of the
wavefront, commonly known as Free Space Loss
signal power is attenuated as the wave passes through
solid objects as trees, walls, windows and floors of buildings
the signal is scattered and can interfere if there are
objects in the beam of the transmit antenna even if these
objects are not in the direct path between the transmitter
and the receiver

33. Free Space Loss
geometric spreading happens because the wavefront
radiated signal’s energy expands as a function of the distance
from the transmitter
using decibels to express the loss and using 2.45 GHz as the
signal frequency, the equation for the Free Space Loss is
L
fsl
= 40 + 20*log(r)
where L
fsl
is expressed in dB and r in meters

34. Attenuation
when the RF signal passes through solid objects, some of the
signal power is absorbed
the most convenient way to express this is by adding an
“allowed loss” to the Free Space
attenuation can vary greatly depending upon the structure
of the object the signal is passing through
metal in the barrier greatly increases the attenuation

35. Attenuation
trees account to 10 to 20 dB of loss per tree in the direct
path. Loss depends upon the size and the type of tree
walls account to 10 to 15 dB depending upon the
construction
floors of buildings account 12 to 27 dB of loss. Floors with
concrete and steel are a the high end and wood floors at the
low end
mirrored walls have very high loss because the reflective
coating is conductive

36. Scattering
RF signals can reflect off of many things and the direct signal
combines with signals that have reflected off of objects that
are not in the direct path
this effect is usually described as multipath, fading or
signal dispersion
9-/%1$#%"(
%
@:%;*"%-),,%'.2&,,%:'*4%E0&5$.'%F6%=>%>"+(&4.+$&,#6%$0.'.%&'.%$-*%$;5.#%*:%,)+.%*:%#)30$%
G7HIJ?%%>)'#$6%$0.'.%)#%!"#$%&%7HI6%-0)20%)#%-0&$%$0.%0"4&+%.;.%#..#?%%K)#"&,%7HI%)#%;*"'%
:)'#$%&+(%4*#$%<&#)2%7HI%$.#$?%%@:%;*"%2&+%#..%$0.%=>%'.2.)1.'%:'*4%$0.%)+#$&,,&$)*+%5*)+$%
*:%$0.%=>%$'&+#4)$$.'6%$0.+%;*"%0&1.%!"#$%&%,)+.%*:%#)30$?%%I.2*+(6%&+(%()::.'.+$%:'*4%
1)#"&,%7HI6%)#%=>%,)+.%*:%#)30$?%%=>%7HI%)#%-0&$%;*"'%=>%(.1)2.%2&+%C#..D?%
%
A0.%3.+.'&,%<.0&1)*'%*:%&+%=>%#)3+&,%)#%$*%3'*-%-)(.'%&#%)$%)#%$'&+#4)$$.(%:&'$0.'?%%
L.2&"#.%*:%$0)#%$;5.%*:%<.0&1)*'6%$0.%=>%#)3+&,%-),,%.+2*"+$.'%*<M.2$#%)+%)$#%5&$0%$0&$%-),,%
'.:,.2$6%()::'&2$6%*'%*$0.'-)#.%)+$.':.'.%-)$0%$0.%#)3+&,?%%N0.+%&+%=>%-&1.%)#%'.:,.2$.(%*::%
&+%*<M.2$%G-&$.'6%$)+%'**:6%*$0.'%4.$&,%*<M.2$6%.$2?J%-0),.%4*1)+3%$*-&'(#%)$#%'.2.)1.'6%
4",$)5,.%-&1.%:'*+$#%&'.%2'.&$.(%G*+.%:*'%.&20%'.:,.2$)*+%5*)+$J?%%A0.'.%&'.%+*-%-&1.#%
4*1)+3%)+%4&+;%()'.2$)*+#6%&+(%4&+;%*:%$0.#.%'.:,.2$.(%-&1.#%&'.%#$),,%0.&(.(%$*-&'(%$0.%
'.2.)1.'?%%A0)#%<.0&1)*'%)#%-0.'.%-.%3.$%$0.%$.'4%'$&(")%(*+%&#%#0*-+%)+%>)3"'.%O?P?%%
Q",$)5&$0%)#%(.:)+.(%&#%$0.%2*45*#)$)*+%*:%&%5')4&';%#)3+&,%5,"#%("5,)2&$.%*'%.20*.(%
-&1.%:'*+$#%2&"#.(%<;%'.:,.2$)*+#%*:%-&1.#%*::%*<M.2$#%<.$-..+%$0.%$'&+#4)$$.'%&+(%
'.2.)1.'?%%A0.%(.,&;%<.$-..+%$0.%)+#$&+$%$0&$%$0.%4&)+%#)3+&,%&'')1.#%&+(%$0.%)+#$&+$%$0&$%
$0.%,&#$%'.:,.2$.(%#)3+&,%&'')1.#%)#%/+*-+%&#%,-&%./#)0-%,?%
%
%&'()*$+,-$ 9-/%1$#%"(
%
512&(,:(;13"%
<&:/&=%&>(?#%"
<1@&'
%
%
%

37. Scattering
the distortion degrades the ability of the receiver to recover
the signal in a manner much like signal loss
multipath can cause several different conditions, all of which
can affect the transmission of the RF signal differently

38. Decreased Signal
Amplitude
!
3&'4&1)&5*6/781.*9:0./(-5&*
!
E)-+!(+!67!4(.-!(//&.-,!(%!%)-!/-*-&.-/3!5(+9!/-1$-*%-0!4(.-,!5(9!(//&.-!(%!%)-!,(5-!
%&5-!1/25!0&11-/-+%!0&/-*%&2+,:!!;)-!*25F&+(%&2+!21!%)-,-!4(.-,G!(5'$&%#0-,!&,!(00&%&.-!%2!
%)-!5(&+!67!4(.-:!!6-1$-*%-0!4(.-,3!&1!2#%H21H')(,-!4&%)!%)-!5(&+!4(.-3!*(+!*(#,-!
0-*/-(,-0!,&8+($!(5'$&%#0-!(%!%)-!/-*-&.-/3!(,!&$$#,%/(%-0!&+!7&8#/-!I:J:!!;)&,!2**#//-+*-!&,!
*2552+$9!/-1-//-0!%2!(,!!"#$%&!'!(+0!,)2#$0!F-!%(K-+!&+%2!*2+,&0-/(%&2+!4)-+!
*2+0#*%&+8!(!,&8)%!,#/.-9!(+0!,-$-*%&+8!(''/2'/&(%-!(+%-++(,:!
!
;<=>?$*@A!* 9,:2;$<'!
!
6=%/1&-<'!<'>('$0'
<-'!&,!?$&#!5,00
@-&A,;A%#$0'!(';/'>&'<
0132$/!10!$<<'<!&,!&#'
=$12!0132$/
+,:'(!:1&#
$2!$2&'22$
!
!
!
B+44-0(/+8*
B2//#'%-0!,&8+($,!@4(.-,A!0#-!%2!5#$%&'(%)!*(+!2**#/!(,!(!/-,#$%!21!%)-!,(5-!')-+25-+(!
%)(%!*(#,-!0-*/-(,-0!(5'$&%#0-3!F#%!%2!(!8/-(%-/!0-8/--:!!E)-+!/-1$-*%-0!4(.-,!(//&.-!(%!

39. Corruption!"#$$$!"#$%&'()(*+',-./&0",,%123(41'&/&00(567(820%#//#%1,20((
%&'()*$+,"$ 9:(;132#/(!,''-$%1,2(
!
9&0-/%#2%('&<&1=&>
0132#/(10(<,''-$%&>(.?
'&@/&<%&>(0132#/0
9&@/&<%1=&(0-'@#<&
9&@/&<%1=&(0-'@#<& !
!
"#!$%&'!&($)$*!+')!$,-#(.!+/!#/,$)!0(+,/!12345!,$!-)#)0(..6!7)06!./8*!8')0)!+')!$,-#(.!,+$).9!
,$!7)06!&./$)!+/!+')!#/,$)!9.//0:!!;')!0)&),7)0!,$!%#(<.)!+/!&.)(0.6!=)&,>')0!<)+8))#!+')!
,#9/0?(+,/#!$,-#(.!(#=!#/,$)*!&(%$,#-!+')!=(+(!+'(+!,$!0)&),7)=!+/!<)!/#.6!>(0+!1,9!(#65!/9!

40. Nulling! ! "#$%&'(!)!*+(,-./'0#,,&123!41('/'00!567!820&$//$&1,20!!!!"#!
$%&'()*#+,* 9:!;132$/!7-//123!
!
9'</'=&'>!0132$/0!$>>'>!&,!&#'
?$12!0132$/!=$2='/!$//!0132$/
$?%/1&->'!('0-/&123!12!2,
0132$/!$&!$//@
9'</'=&1A'!0-(<$='
9'</'=&1A'!0-(<$=' !
!
"#$%!%&''(%)!*++&,-.!,$/,0%-1(--(*%!*2!/#$!30/0!4(''!%*/!-*'5$!/#$!6,*7'$18!!9#$!
/,0%-1(//$,.!,$+$(5$,.!*,!,$2'$+/(5$!*7:$+/-!1&-/!7$!1*5$38!!;*1$/(1$-!1*,$!/#0%!*%$!*2!
/#$-$!1&-/!7$!,$'*+0/$3!/*!+*16$%-0/$!2*,!/#$!%&''(%)!$22$+/-!*%!/#$!<=!405$8!!!

41. Increased Signal
Amplitude
!"#$$$!"#$%&'()(*+',-./&0",,%123(41'&/&00(567(820%#//#%1,20((
%&'()*$+,-$ 9$:#;&((
!
6<$/1%-;&(;&='&#0&
;-&(%,(>#%"(5,00
82?$"#0&('&:/&=%&;
0132#/(10(#;;&;(%,
%"&(<#12(0132#/
+,@&'(@1%"
#2(#2%&22#
!
!
"#!$%!$&'()#*+#!#(!,+-.)%#*+-!#/*#!*!).0.$1.-!23!%$4+*5!0*+!+.1.)!6.!*%!5*)4.!*%!#/.!%$4+*5!
#/*#!7*%!#)*+%&$##.-!-,.!#(!#/.!%$4+$8$0*+0.!(8!8)..!%'*0.!'*#/!5(%%!9,%,*55:!0*55.-!!"#$%
&'((;<!!=*#/!5(%%!$%!#/.!.88.0#!(8!*!%$4+*5!5(%$+4!*&'5$#,-.!-,.!#(!.>'*+%$(+!*%!#/.!%$4+*5!
#)*1.5%!#/)(,4/!('.+!%'*0.<!
!

42. Scattering
antenna diversity was devised for the purpose of
compensating the multipath
antenna diversity means using multiple antennas in order to
compensate the conditions that cause multipath
antenna switching diversity: multiple antennas on multiple
inputs, with a single receiver.The signal is received through
only one antenna at a time
transmission diversity: transmits out of the antenna last used
for reception. Can alternate antennas for retries

43. Scattering
a simple way of applying the effects of scattering is to
change the exponent on the distance factor of the Free
Space Loss formula like this:
L(dB) = 40 + 10 * n * log(r)
the exponent tends to increase with the range in an
environment with a lot of scattering
calculating a range can often require some iteration of the
exponent to be used

44. Total Loss
when Free Space Loss,Attenuator and Scattering are
combined, the loss is
L(dB) = 40 +10*n*log(r) + L
allowed

45. Link Margin
the performance of any communication link depends on the
quality of the equipment being used
the link margin is a way of quantifying equipment
performance
an 802.11 link has an available link margin that is determined
by four factors

46. Link Margin
Transmit Power
Transmit Antenna Gain
Receive Antenna Gain
Cable Losses, Connector Losses and Lightning Arrestor
Losses
Minimum Received Signal Strength or Level
the link margin is then
TX(power)+TX(ant gain)+RX(ant gain)-RSL

47. Link Margin
the link factors are usually listed in the manufacturer’s data
sheets for the equipment being used
note that the minimum RSL is dependent upon rate
and the 1 Mbps rate is used for maximum range
TX power can also be rate dependent but manufacturers
rarely indicate this

48. Maximum Range
the maximum range is achieved when the signal
loss is less than the link margin
we must know the equipment parameters and must
estimate the allowed loss and the scattering exponent to
complete the calculation
the equipment parameters can be found on the data
sheets
http://www.qsl.net/n9zia/

49. Maximum Range
! Min RSL = -89 dBm
! Link margin = 110.5 dB
Note that the Min RSL is dependent upon rate and the 1 Mbps rate is used for
maximum range. TX power can also be rate dependent but manufacturers rarely
indicate this.
Maximum range. The maximum range is achieved when the signal loss expressed in
Equation 4 is less than the link margin expressed in Equation 5. The system operator
needs to know the equipment parameters and must estimate the allowed loss and the
scattering exponent to complete the calculation. Example parameters are shown in
Tables 1 and 2.
Table 1. Application Dependent Environment Parameters
Application
Allowed Loss
(dB)
Scattering
Exponent Example
Outdoor free space 0 2
Outdoor, no barriers 0
2.5 at 200m
3 at 400m
3.5 > 500m Marina
Outdoor with trees 10 to 20 3 to 4 Park
Outdoor buildings 0 4 Urban café
Indoor - no barriers 0 2.5 Conference room
Indoor partitions 0 3.5 Office cubicles
Indoor walls & floors
12 to 27 (floors)
10 to 15 (walls) 4 to 5
Condo,
apartment

50. Link Margin
!"#$"%& '()*+,-).,/( &0
!"#$% "&$% '()*+,-$
!" !#
$% &%
'"
'#
(#))*+,-.)*/011
2"
2#
345
65

51. Example
suppose a university wants to setup a point-to-multipoint
link

52. Example
Access Point:
TX Power: 13 dBm
TX Antenna Gain: 8.5 dBi
PC Cards:
RX Antenna Gain: 0 dBi
RX Sensitivity: -89 dBm

53. Example
the link margin is
TX(power)+TX(ant gain)+RX(ant gain)-RSL
13+8.5+0-(-89)= 110.5 dB

54. Example
we can estimate the allowed loss to be 10 dB if the park had
a modest number of trees mixed with open spaces and use a
scattering exponent of 3
to get the maximum range we solve
110.5=40+10*3*log(rmax)+10
and we find
rmax=102 meters

55. Example
using the same equation to calculate the range assuming free
space loss only (exponent=2, and allowed loss=0)
110.5=40+10*2*log(rmax)+0
rmax=3264 meters
this example shows that environmental factors can
play a significant role in diminishing the signal
strength

56. Thank you for your attention!
Contact info:
Marco Zennaro
mzennaro@ictp.it
http://wireless.ictp.it
Link Budget Calculation