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ECE 5221 Personal Communication Systems
Prepared by:
Dr. Ivica Kostanic
Lecture 6: Link budgets and nominal cell
planning
Spring 2011
Florida Institute of technologies
Outline
Vehicle penetration losses
Building penetration losses
Aggregate fade margin
Link budget evaluation
Examples
Important note: Slides present summary of the results. Detailed
derivations are given in notes.
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Vehicle penetration losses
 Many calls are made inside vehicles
 Macroscopic propagation model predict “on
the street level”
 Vehicle introduces additional signal losses
 These losses depend on
o Type of vehicle
o Vehicle orientation
o Environment
 Vehicle losses are variable
 Typically modeled as normal variable in log
domain
 For nominal cell planning
o Mean vehicle loss; 6-8dB
o Standard deviation: 3dB
Histogram of vehicle losses
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Building penetration losses
 Many calls are placed inside buildings
 Buildings introduce additional losses
 Losses depend on type of building, frequency of
operation and environment
 Treated as a random variable following normal
distribution
Some building penetration data from some published sources*:
Example building penetration
measurements
Commonly assumed values
used in design of RF systems (800/1900 MHz)
----------------------------------------------------------------------Building type
Average(dB)
Std.(dB)
Urban Core
20
10
Urban
15
8
Suburban
10
6
Building
Frequency:
900MHz
1900MHz
--------------------------------------------------------------------------------------Ameritech
18.3
13.8
Continental
13.3
12.2
Jupiter
11.7
N/A
Zurich
11.9
10.8
Compri
6.7
7.9
Citibank
8.3
10.6
Woodfield Corp.
12.4
N/A
Marriott
13
15.7
NEC
8.1
6.1
600 Woodfield
3.9
3.6
---------------------------------------------------------------------------------------Average
Std.
10.8
5.8
10.2
5.6
* Garry C. Hess, Handbook of radio-mobile system coverage, Artech
House, Inc, 1998
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Link budget analysis
 Used to determine maximum allowable path loss
that balances two links
 Important: Cellular communication is 2-way – two
links need to balance
 Usually – mobile power smaller and the link budget
is determined by the uplink
o Typical process:
 Calculate uplink budget
 Adjust BS power to have balanced links
 In nominal cell planning link budget is used to
determine expected cell radius
 For nominal cell planning – three types of users
o On the street
Cellular system from link budget
point of view
o In vehicle
o In building
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Elements of link budget – Rx Sensitivity
 Rx sensitivity – minimum RSL required for an
RF connection of sufficient quality
 Calculated as:
RxSens
 10 log  kTB   F  S N
Where:
kT – PSD of thermal noise ~ 4e-18 mW/Hz
B – bandwidth of the system expressed in Hz
F – noise figure expressed in dB
S/N – required signal to noise ratio in dB
Components of RxSens
Example. Consider technology with bandwidth of 200KHz, Rx noise figure of 7dB
and min required S/N ratio of 12dB. Calculate the Rx sensitivity.
RxSens
 10 log 4  10
 18
 200  10
3
  7  12   102 dBm
Note: typically BS receivers have better sensitivity than the MS.
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Cable losses
 Cellular systems use coaxial cables
 There is a coaxial cable that connects
each o the antennas
 Losses expressed in xdB/100feet
Cables on
a cell tower
 For a typical tower heights losses of the
cables are on the order of 2-5dB
 Standard 50ohm impedance
 There may be other elements in Tx/Rx
path introducing signal loss (duplexers,
filters, jumper cables, splitters,…)
 In link budget analyses – all of the
“pluming” losses need to be taken into
account
Coaxial
cables
Note: on the RX link cable losses
are sometimes compensated
through tower mounted amplifiers
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Antennas
 Two configurations of antenna systems
o Omnidirectional
o Sectored (usually 3 sectors/site)
 Nominally – 3 antennas/cell
o Middle – transmit
o Edge – receive A,B
o Two receive antennas provide
diversity reception
 When there is space constraint on tower,
one of the antennas may duplex TX and
RX
 Antennas are characterized by
o Gain (6-15dB)
o Horizontal radiation pattern
o Vertical radiation pattern
Omni-directional
cell
Tri-sector cell
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Penetration and body losses
 Penetration losses
o Vehicular losses
o Building losses
 Specified by mean and std
 Mean added to the radio path losses
 Independence between the path loss
and penetration losses is assumed
 Penetration losses contribute to the
model uncertainty
 Total uncertainty-composite standard
deviation
T 
 PL  
2
Example. Consider system in an
environment with model uncertainty
of 8dB and path loss exponent of
3.84. Calculate fade margin for inbuilding coverage assuming standard
deviation of penetration losses of
6dB. The reliability requirement is
90%
Answers:
a) Composite standard deviation: 10dB
b) Z-score: 0.7436
c) Fade margin: 7.44dB
2
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Simple link budget example
 Environment
 Mobile
o Path loss exponent: 3.84
o Transmit power: 2W
o Model uncertainty: 8dB
o Antenna gain: 0dB
o Penetration losses
o Bandwidth: 200KHz

Mean: 15dB
o Noise figure: 8dB

Std: 6dB
o Required S/N: 12dB
o Reliability: 90%
 Base station
o Transmit power: 20W
o Cable losses: 3dB
o Antenna gain: 9dB
o Bandwidth: 200KHz
o Body losses: 3dB
1. Rx sensitivity at the base
RxSensBS
 10 log 4  10
 18
 200  10
3
  5  12   104 dBm
2. Rx sensitivity at the mobile
RxSensBS
 10 log 4  10
 18
 200  10
3
  8  12   101 dBm
o Noise figure: 5dB
o Required S/N: 12dB
o Diversity gain: 3dB
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Simple link budget example (cont.)
3. FM calculations
T 
8  6  10 dB
2
FM  7 . 4 dB
2
T
n
 10 / 3 . 84  2 . 6
Z  score  2 . 6 , 90 %   0 . 7436
4. Link budget spreadsheet
Note: Max allowable path loss is greater for forward link
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