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Introduction
ÄÄ Definitions and Objectives Definitions and Objectives
ÄÄ Review of Decibel (Optional) Review of Decibel (Optional)
ÄÄ Inputs Inputs
ÄÄOutputsOutputs
ÄÄ Process Process
ÄÄ Examples Examples
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RF Path
BSSensitivity
MSSensitivity
Path Loss
Down Link
Path Loss
Up Link
PBS
PMS
End to End Channel •Noise
•Fading,
•Interference,
•Hardware Losses
• .......
End to End Channel •Noise
•Fading,
•Interference,
•Hardware Losses
• .......
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Objectives and Definitions
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Inputs
n Base and Mobile Receiver Sensitivity Parameters
– Minimum Acceptable Signal to Noise Ratio
– Environmental/Thermal Noise Assumption
– Receiver Noise Figure
n Antenna Gain at Base and Mobile Station
n Hardware Losses (Cable, Connectors, Combiner,....)
n Target Coverage Reliability
n Propagation Characteristics of the Channel
n Receiving Environment
L B AL B A
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Outputs
n Coverage Threshold
– In-Building
– In-Car
– On-Street
n Base Station ERP
n Maximum Allowable Path Loss
n Cell Size Estimate
n Cell Count Estimate
L B AL B A
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Path Balancing
Uplink Limited: BS Can Reach MS but
MS Cannot Reach BS
Uplink Limited: BS Can Reach MS but
MS Cannot Reach BS
Downlink Limited: MS Can Reach BS but
BS Cannot Reach MS
Downlink Limited: MS Can Reach BS but
BS Cannot Reach MS
Communication is possible only when both both links are available.
UNDESIREDUNDESIRED
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Need dB Review?
How About ReviewingHow About Reviewing
Decibel Units, e.g.Decibel Units, e.g.
dB,dB, dBmdBm,, dBwdBw,, dBudBu
dBidBi,, dBddBd
Go to
Appendix
A1Continue
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List of Gains and Losses
Gainsn Base Station Antenna
Gain
n Mobile Antenna Gainn Diversity Gains
Lossesn Hardware
– Combiner
– Cables– Connectors
– Duplexer
n Air Interface
– Fade Margin
– Penetration Losses
» In-car
» In-Building
» Body Loss
+ _
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Antenna Gains
Portable antennas
typically have no
gain
Omni
Directional
Directional
Antenna
0-9 dBd 9-14 dBd
Base Station Antennas Mobile Station Antennas
Portable
Phones
Vehicle Mounted
Phones
-1 to 0 dBd 1-3dBd
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Antenna Gain Units: dBi and dBd
n dBi
– is a unit to measure antenna gain in reference to an isotropicantenna.
– So: an isotropic antenna has a power gain of unity; i.e., 0 dBi.
n dBd – is a unit to measure antenna gain in reference to a lossless Half-
Wave Dipole antenna.
– So, a lossless half-wave dipole antenna has a power gain of 0 dBd
or 2.15 dBi.
G dBi = GdBd + 2.15 dB
2 wire
Balanced feed
λ/4λ/4
λ/4λ/4
Half-Wave Dipole Half-Wave Dipole
Converting
dBd to dBi
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Diversity Gain
n If we use multiple receiving antennas with
certain spatial separation at the BS along with
adaptive combining techniques we will have a
diversity gain.
n Diversity gain should be considered in LBAwhenever it is used.
n It is usually used at the base station.
n Sometimes it is used only for the receiving
antennas.
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Effective Radiated Power (ERP)
Power
Amplifier
HardWare
Losses
PA
LCCC
Gantenna
ERP
ERP=PA - Lccc + GAntenna
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ERP vs. EIRP
n ERP (Effective Radiated Power):
– is the transmitted power with respect to a dipole antenna within a
given geographic area.
n EIRP (Effective Isotropic Radiated Power):
– is the transmitted power with respect to a dipole antenna within agiven geographic area.
Converting
ERP to EIRPEIRP(dBw) = ERP (dBw) + 2.15 (dB)
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RF Components in a Typical Base Station
LNA
TX/RX2RX1
Lightning
Arrestor
PA RX1 RX2
Duplexer
Combiner
Top Jumper Cables
Main Cable
Connector Receiver Multicoupler
High Power Amplifier
Receiver
Bottom Jumper Cables
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Cable Loss Jumper Cable
Main Cable
Cable Size Recommended Use Loss (per 100 ft.at 900 MHz)
Loss (per 100ft at 1800
MHz)
LDF4-50 1/2 inch Heliax Foam Jumper Cables 2.160 dB
LDF5-50 7/8 inch Heliax Foam Main Cable < 55 m 1.210 dB 1.97 dB
LDF6-50 1 1/4 inch Heliax Foam Main Cable < 75 m 0.907 dB 1.45 dB
LDF7-50 1 5/8 inch Heliax Foam Main Cable < 90 m 0.750 dB 1.25 dB
HJ12-50 2 1/4 inch Air Dielectric Main Cable > 90 m 0.535 dB
HJ8-50B 3 inch Air Dielectric Main Cable > 90 m 0.510 dB
HJ9-50 5 inch Air Dielectric Main Cable > 90 m 0.750 dB
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Connector Losses
oConnectors, used to connect RF components, typically
each have a loss of 0.1 dB .
o In US, a typical 50W connector is the “ N-type” coaxial connector. whereas in Europe, it is the “ 7/16
DIN ” connector.
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Combiner
Characteristic Cavity Hybrid
Frequency Range (MHz) 806-960 806-1000
Continuous Input Power (W) 150 150
Insertion Loss (dB) 2 to 4.8 3.8 to 7.4
Maximum VSWR 1.5:1 1.5:1
Freq.1
Freq.2
Freq.3
A combiner is a device
that enables several
transmitters of different
frequencies to transmit
from the same antenna.
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Duplexer
Duplexer Characteristic Value Isolation (accross all 3 ports, with unused ports terminated
at 50 Ω)
> 60 dB
Insertion Loss (across all ports) 0.5 dB
Power handling 500 W
Input VSWR 1.5:1 (max)
n A Duplexter enables us to simultaneously transmit and receive
signals on the same antenna.
n It provides an isolation between the transmitted and received
signals.
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Coverage Environments
In-CarIn-Building
On-Street
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Table of Penetration Losses
In Building Penetration (dB) 15-25
In Car Penetration (dB) 3-10
Body Loss (dB) 2-5
n For all receiving environments
a loss associated with the effect
of users body on propagationhas to be included.
n This effect is in the form of a
few dB loss in both uplink and
downlink directions
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Contour Coverage Reliability
n Due to various shadowing and terrain effects the signal level measured
on a circle around the base station shows some random fluctuations
around the estimated value given by the propagation model.n This random signal level along the cell boundary has lognormal
variations.
Normal Distribution
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LogNormal Distribution
0 0.001031 1.50.2 0.001594 2
0.4 0.002420.6 0.00361
0.8 0.005291
1 0.0076171.2 0.010774
1.4 0.0149691.6 0.020432
1.8 0.027397
2 0.0360892.2 0.046702
2.4 0.0593692.6 0.074143
2.8 0.090962
3 0.109633.2 0.129801
3.4 0.1509743.6 0.172508
3.8 0.193644 0.21353
4.2 0.231314
4.4 0.246164
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0 .
6
1 .
2
1 .
8
2 .
4 3
3 .
6
4 .
2
4 .
8
5 .
4 6
6 .
6
7 .
2
7 .
8
8 .
4 9
9 .
6
n A lognormal random process when expressed in dB’s has a normal
i.e. Gaussian distribution.
n According to this distribution 50% of time the signal level is below its
mean value.
n Therefore by setting the coverage threshold at any level L we can only
ensure about 50% of coverage reliability.
-(x - x)2_
p(x) = exp[ ]σ(2π)σ(2π)1/21/2 2σ2σ22
11
%50%50
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Lognormal Fade Margin
0 0.001031 1.50.2 0.001594 2
0.4 0.002420.6 0.00361
0.8 0.005291
1 0.0076171.2 0.010774
1.4 0.0149691.6 0.020432
1.8 0.027397
2 0.0360892.2 0.046702
2.4 0.0593692.6 0.074143
2.8 0.090962
3 0.109633.2 0.129801
3.4 0.1509743.6 0.172508
3.8 0.193644 0.21353
4.2 0.231314
4.4 0.246164
0
0.05
0.1
0.15
0.2
0.25
0.3
0
0 .
6
1 .
2
1 .
8
2 .
4 3
3 .
6
4 .
2
4 .
8
5 .
4 6
6 .
6
7 .
2
7 .
8
8 .
4 9
9 .
6
n Therefore by setting the coverage threshold at any level L we can only
ensure about 50% of coverage reliability.
n Usually contour coverage reliability of 70-80% is needed..
n Therefore to assure e.g. %80 contour coverage reliability one has to
shift the distribution toward higher signal levels so that the dashed
area reduces to %20.
n This requires providing additional signal power called fade margin or
lognormal margin.
%20 %80
Fade Margin
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Area Coverage Reliability
n Coverage design objectives are usually defined in terms of
Area Reliability.
n Area Reliability is the percentage of area where the
received signal is above the threshold.
n It can be thought of as the average of contour reliability's
for all circles of radii r, 0 < r < R.
99%
97%
94%
90%95%
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From Area to Contour Reliability
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
0.9
0.95
1
σσ/n
A r e a R e l i a b i l i t y
0 1 2 3 4 5 6 7 8
P X 0(R) = 0.95
0.9
0.850.8
0.75
0.7
0.65
0.6
0.55
0.5
Area Reliability
σσ /nContour Reliability
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Fade Margin vs Contour Reliability
0
2
46
8
10
12
14
1618
20
0.5 0.55 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95
Location Probability at Cell Edge
F a d e M a r g i n i n d B
σσ =12 dB
1110
9
8
7
6
Standard
Deviation
Contour Reliability
Contour Reliability
Standard Deviation of FadeFade Margin
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Summary of Fade margin Calculation
n For a given
– standard deviation for the local mean σ,
– the propagation loss factor, n:
Compute σ/n.
n For the required area reliability and computed σ/n– Estimate coverage contour reliability from plot_I
n Use the contour reliability and the standard deviation σ and
plot-II to estimate the fade margin Mfade.
n Enter the Mfade (fade margin) into the LBA work sheet toestimate the maximum path loss & coverage threshold.
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Case Study I
nExample: Check with Plots (I,II)– Let signal attenuation law be 40 dB per decade, i.e. n=2.5
– Standard deviation of lognormal fading is estimated as 10
dB.– Clients ask for 90% area reliability
– From Plot _I and σ /n=4 and 90% area reliability, contour
reliability is 80%.
– From Plot_II with σ=10 and 80% contour reliability the
fade margin is about 8.5 dB.
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Case Study II
nExample: Check with Plots (I,II)– Let signal attenuation law be 40 dB per decade, i.e. n=2.5
– Standard deviation of lognormal fading is estimated as 10
dB.– Clients ask for 90% area reliability
– From Plot _I and σ /n=4 and 90% area reliability, contour
reliability is 80%.
– From Plot_II with σ=10 and 80% contour reliability the
fade margin is about 8.5 dB.
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Sample Fade/Log-normal Margin
Terrain Standard
deviation σdB
Pro o a-
tion Law
Cell
Boundar
P n for 90%
Covera e
Fade
Mar in
dB
Urban 6 3.5-3.75 70 % 4 to 6Suburban 8 3.0-3.5 76 % 6
Rural 12 2.5-3.0 82 % 10Fade Margin and Cell Coverage
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Receiver Sensitivity
n Receiver sensitivity
– is the minimum acceptable input signal level in
dBm, at the input of the receiver’s low noise
amplifer, required by the system for reliable
communication.
n Carrier to Noise Ratio (CNR)
– For a given FER, e.g. of about 1%, the each type
of modulation and coding requires a minimum
signal to noise ratio which at the bit level is
stated as Eb / N0.
n Thermal/Environmental Noise:– is a combination of
» Antenna Noise (dBm)
» Receiver Noise Figure(NF) in dB
» Temprature and System Bandwidth
RX
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Receiver Sensitivity Calculation
Receiver
NF
k T B (S/N) out
(S/N)in
Thermal Noise Noise Figure
Absolute SensitivityRX Sensitivity
( ) ( )
( )
( )
log( ) ( )
S N S N NF
S N S N NF
S N S N NF
S k T B NF S N
in out
in in out
in in out
in out
== ++
−− == ++
== ++ ++
== ⋅⋅ ⋅⋅ ++ ++10
All values areAll values arein dB’sin dB’s
or Eb/No
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Overview of Up-Link Budget Analysis
Starting with the reverse link
n Find the Maximum Allowable Path Loss (MAPL)
– Start from MS maximum power
– Subtract all the losses in due to, RF components
– Subtract all the margins due to fading and interference for a given
target loading
– Add all the gains in the path e.g. antenna and diversity gains
– Subtract the receiver sensitivity of the base station for a given FER
– The result is MAPL.
MAPL=PLUp = PA m - All Losses + All Gains - RX Base MAPL=PLUp = PA m - All Losses + All Gains - RX Base
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Overview of LBA Forward Link
In the forward link:
n For each channel
– Compute the MS sensitivity for a given Eb/No requirement
– Add the reverse link path loss and add a path imbalance if needed
– Add/subtract all losses/gains not considered in the reverse link calculations
– The result is ERP of base station
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Gains and Losses in UpLink
LCCC
RX
Combiner,
Cable &
Connector
Losses
GA
Path Loss
Fade Margin
ERP
In-Building/Car
Penetration Loss
Body Loss
MS AntennaGain/Loss
PA
RX Base = PA m + G M - L Body - L Bldg - M Fade- PLUp + G B - LCCC
PLUp = PA m + G M - L Body - L Bldg - M Fade- RX Base + G B - LCCC
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Gains and Losses in Down Link
Power
Amplifier
Combiner,
Cable &
Connector
Losses
PA
LCCC
G B Path Loss
Fade Margin
ERP
In-Building/Car
Penetration Loss
Body Loss
MS Antenna
Gain/Loss
RX
RX Mobile = PA B - LCCC + G B - M Fade- PL Down - L Bldg - L Body + G M
PA B = RX Mobile + LCCC - G B + M Fade+ PL Down + L Bldg + L Body - G M
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Cell Size/Count Estimation
n Objective:
– To determine the number of cells required to provide coverage for
a given area.
n Required Input:
– Maximum Allowable Path Loss (MAPL)– Propagation Loss Model
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n Using Hata’s Empirical Formula
Cell Size Estimatation
o Solve it backward to Cell radius estimate based on Hata’s
formula:
PL f h
h R a h
c b
b m
= + − +
− −
69 55 26 16 13 82
44 9 6 55
10 10
10 10
. . log . log
( . . log ) log ( )
log. . log . log ( )
. . log10
10 10
10
69 55 2616 13 82
44 9 6 55 R
MAPL f h a h
h
c b m
b
==−− −− ++ ++
−−
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Cell Count Estimation
1
2
3
4
5
7
6
9
8
10
12
11
Link Budget Analysis
Max Allowable Path Loss)
Estimate Cell Radius
Estimate Cell Count
Market Boundary
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Outline
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dB Unit for Gains and Losses
n Decibell (dB) is a logarithmic unit for
representing power gains and losses.
n Gain Glinear=Pout /Pin is equivalent to GdB
where
Examples:– A gain of 100 is equivalent to 20dB gain
– A 10 times attenuation in power = -10 dB loss
SubsystemPin
Pout
P out
Pin
G dB= 10 Log ( G Linear ) =10 Log ( )
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dB Units for Signal Power
nBy fixing P0 as a reference power,
e.g.... to 1 Watt or 1Miliwatt, one can
define similar units for power.
nExamples:– (P) dBw = 10 log P/(1Watt)
– (P) dBm = 10 log P/(1mW)
P0 Name of unit Example Interpretation
W dBw 10dBw 10:1 over 1W
or 10W
mW dBm 20dBm 100:1 over 1mW
or 100 mW
Decibel in reference to a power unit
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dB Units for Signal Level (Voltage)
n dB is also a logarithmic unit for voltage gains and losses.
n Gain G=V/V0 = g dB where g=20 log (P/P0)
n Since power is proportional to voltage squared the two
definitions are consistent.
n Similarly by fixing V0 as a reference voltage, e.g.... to 1volt or 1microvolt, one can define similar units for
voltage.
n Examples:
– (V) dBV = 10 log V/(1Volt)
– (V) dBu = 10 log V/(1µW)
V0 Name of the unit Example Interpretation
V dBv 20dBv 10:1 over 1V
or 10V
µV dBu 20dBu 10:1 over 1µµV
or 10 µµV
Decibel in reference to a voltage unit
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Relation between dBv and dBw
n Converting a voltage in dBµV to its received power
in dBm with 50Ω terminal impedance is given by:
0dBu =20log(V/V0) where V0 = 1 µV
0dBu = 10 log[(10-6)2 (1000)/50]dBm
= -107 dBm
where P(mW) = V2 /R * 1000 mW for R = 50Ω
n Converting a field strength in dBµV/m to its
received power in dBm with a 50Ω optimum terminal
impedance and effective length of a half dipole: λ/π.
0dBu = 10 log[(10-6)2 (1000)(λ/π)2/(4∗50)] dBmAt 850MHz: 0dBu (=) -132 dBm
39dBu (=) -93 dBm
32dBu (=) -100dBm
50ΩΩ
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Common Mistakes Regarding dB Units
n Remember the difference between dB as a unitless measure
of gain or loss and dBm as a unit of power or voltage.
n Also note that addition in the logarithmic scale e.g.... in dBdomain is like multiplication in the linear scale.
n Therefore the following are meaningless and not correct:– Adding two signal levels in dBm domain.
– Multiplication of gains or losses expressed in dB’s
– Looking at the ratio between two signal in dB domain.
dBm+dBm
dB*dB
dBm/dBm
dBm+dB=dBm
dBm-dB=dBm
dB+dB=dB
Incorrect
Correct
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n Let’s consider two signals– S1 with power P1 Watts or Q1 dBm
– S2 with power P2 Watts or Q2 dBm
n From Watts to dBm
– (Q1)dBm =10 log (P1 W/1mW)=10 log(103 P1)=30 + 10 log P1
n From dBm to Watts
– (P1)mW= 10(Q1/10) and (P1)W=10-3 x 10(Q1/10)
n Adding two signals has to be in the linear domain:
– S1+S2 = P1 + P2 = 10Q1/10
+ 10Q2/10
Q1 +Q2
n The ratio between two signals or signal to noise ratio has to be
calculated in the linear domain
– S1/S2= P1 / P2 = (Q1-Q2) dBm Q1/Q2
dB to linear conversion & vice versa