Dr. Mohammad Mokhtari Director of National Center for Earthquake Prediction.
GSM Fundamentals by Dr. Hatem MOKHTARI
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Transcript of GSM Fundamentals by Dr. Hatem MOKHTARI
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GSM RF Design and Planning Fundamentals
Dr. Hatem MOKHTARICirta Consulting LLC
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During the 1980s, in Europe, Many Systems were used without anyRegulation, Standards, or Compatibilities. Most of them were Analog. As a result :
* No Roaming between Countries
* Major Capacity Problems and Congestions
* Limited Market for each Technology
* Very high subscriber equipment cost...Further growth difficult !
In The USA and Canada DAMPS (Digital Advanced Mobile Phone Service) : Cheaper handsets, roaming, easy subscribing, etc
A. Introduction to Wireless Telephony
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Modern Systems are :
* Digital : The signal is Digitized through A/D Converters, Modulated, and then sent via the Antenna
* High Capacity : They are able to simultaneously serve a large number of customers
* Encrypted : Due to the fact that they are digital, they have full protectionagainst fraud. Also, they are highly securised
* High Speech Quality : Due to Technology advance and electronicsimprovements
* Spectrum Efficient : They offer optimised frequency spectrum use
* Possibility to roam within the GSM Community Networks (provided a signedRoaming Agreement)
A. Introduction to Wireless Telephony
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Role of the RF Design Engineer :Design the Network ArchitectureSelect type of AntennasAnalyze the Links : Downlink and UplinkPropose Solutions to Enhance the Capacity of a Base StationConsider Marketing Inputs and Propose Design accordinglyPerform Drive Test to ensure Quality of the LinkUse Radio Planning rules to install Antennas in different sitesUse Radio Planning tools to assess the Coverage using SimulationPerform RF Propagation Model Tunning using measurementsSelects the RF Infrastructure to fullfil the Link Budget requirementsCalculates Propagation, Site Clearance, Link Quality using different Hardware and Software Tools
A. Introduction to Wireless Telephony
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A GSM subscriber (Mobile) Should be able to :Receive and Transmit within a given geographical areaRoam to other countries (If a Roaming Agreement exists)Have a continuous Quality of Service (QoS)
A Mobile Station should be able to :Change the Serving Base Station (BS) if the link is bad (or going to become bad) on the actual BS. This is the Handover (or Hand-off)Recognize which country, Network, or Base Station the user isattached toInform the actual Network about the Identity of the UserPrevent forthcoming Drop Calls, Quality Problems due to Interference, or Signal Level (shadowing by obstacles)
A. Introduction to Wireless Telephony
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Notation in dBm, dBW, dBi, dBd, dB
P (dBm) = 10Log10(P mW/1mW)Example : 100 mW power results in 10Log10(100)=20 dBm
P dBW = 10Log10(P W/1W)Example : 15 W power results in 10Log10(15)= 11.76 dBW
Relation between dBW and dBm :dBm = dBW + 30Example : 100 mW = 20 dBm = -10 dBW
B. RF Fundamentals
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If an internal resistor is to be considered:
•Voltage
•Power
•Voltage
•Power
E R
I
U
r
ER
I
U
B. RF Fundamentals : DC CIRCUITSRIU =
RUUIP
2
==
ErR
RU+
=
22)(E
RrRP
+=
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e
r
i
u R
•Voltage• If • Then
•Power
•RMS Notion = Root Mean Square
Riu =tEte ωcos)( =
tUtrR
REte m ωω coscos)( ≡+
=
tRUtitutp m ω2
2
cos)()()( ==
∫=T
dttuT
U0
2 )(1
B. RF Fundamentals : AC CIRCUITS
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Suppose we have a voltage :
With a period of
Compute the RMS Voltage for Um = 50 V
Is the RMS dependent of the frequency ?
B. RF Fundamentals : Exercise
tUtu m ωcos)( =
ωπ2
=T
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222
111
**
jyxzjyxz
+=+=
)()(1()(
)()(
2121212122
22
22
21
2
1
2121212121
212121
xyyxyyxxyxz
zzzz
xyyxjyyxxzzyyjxxzz
−+−×==
++−=×±+±=±
==Θ
==Θ
−
−
2
2122
1
1111
)arg(
)arg(*
xytgz
xytgzIf
212
1
2121
)arg(
)arg(
Θ−Θ=
Θ+Θ=
zzzz
Given
Compute
21
21
21
zzzzzz
−+
2
1
zz
2
1
ΘΘ
( )( )
( )214
2
13
22
11
arg
arg
argarg
zzzz
zz
=Θ
=Θ
=Θ=Θ
31
21
2
1
jz
jz
+−=
+=
Exercise
Complex numbers B.RF Fundamentals
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B.RF.Fundamentals
Exercise
Given
Given
Impedance
32
2
2
31
j
ej
−=Ζ
=Ζπ
( )
( )212121
2
1
2
1
2
1
212121
arg,)3
arg,)2
arg,)1
ΖΖΖΖΖΖ
ΖΖ
ΖΖ
ΖΖ
Ζ+ΖΖ+ΖΖ+Ζ
and
and
andCompute
Show thatΥ+Χ=Ζ j
ΧΥ
+Υ+Χ=Ζ −122loglog jtg
>~e U
( )12 −•=
=Ζ
•Ζ=
sradfjL
IU
πω
ωwhere
resistorpureaforR
inductoranforjL
capacitoraforCj
=Ζ
=Ζ
−=Ζ
ωω
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Y
XReal Part
Z
θρ jejYXZ =+=
θρ
θρθρ
sincos
==
YX
B. RF Fundamentals : Complex numbersImaginary Part
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ε
Zin
I
U Z
U=Z I U, Z and I are all Complex Numbers
B. RF Fundamentals : Impedance
Z : The Impedance of the Load and Zin internal to the Generator
ωjLZ =ωCjZ /−=
RZ = for a Resistorfor an Inductive Component
for a Capacitor
A
B
In Low Frequencies, all the power delivered to Z isabsorbed or dissipated into heat
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Vertical PolarizationRefers to thedirection of theElectric Field
Horizontal Polarization wouldbe to configure thedipole horizontally
Horizontal Polarization Refersto the direction of the Electric Field
Er
Hr Π
rDipole
Antenna
Πr
is the Poynting Vector (Power)
ηHErr
r ×=Π
B. RF Fundamentals
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ε
Zin
I
U Z
At RF domain, Energy flowsfrom the generator to the Load.It can be fully absorbed by Z, orPartly reflected and partly absorbed.
B. RF Fundamentals : High Frequency considerations
A
B
10011 2
×
+−
=VSWRVSWRρThe % of Reflected Energy is
VSWR : Voltage Standing Wave Ratio ( 1:1 is ideal )Acceptable VSWR = 1.5 : 1Impedance Match : Z* = Zin
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EIRP or Equivalent Isotropic Radiated Power :The Power to supply to an antenna to obtain the same power in all directions at a distance d :
We always consider the main lobe direction where no losses exist
dBi : Refers to an Isotropic antenna and dBd to the Dipole :
dBi = dBd + 2.15 dBEIRP = ERP + 2.15 dB
Example : G = 16 dBi, so G = 13.85 dBd and if P = 33 dBm (2 W)Then PE = 16 + 33 = 49 dBm in the main Lobe
B. RF Fundamentals
),(),( ϕθϕθ rE LGPP −+=
GPPE +=
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60
32.5
0
- 32,5
- 60dB
60
32.5
0
- 32,5
- 60dB
10 10
30 0
3
Horizontal Diagram Vertical Diagram
B. RF Fundamentals
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- 1 . 0 5
- 0 . 6 0
- 0 . 1 5
0 . 3 0
0 . 7 5
- 6 0 . 0 0
- 4 0 . 0 0
- 2 0 . 0 0
0 . 0 0
2 0 . 0 0
0 . 0 0 - 2 0 . 0 0
- 2 0 . 0 0 - 0 . 0 0
- 4 0 . 0 0 - - 2 0 . 0 0
- 6 0 . 0 0 - - 4 0 . 0 0
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B. RF Fundamentals
Directivity : Figure of Merit to quantify the ability of an antenna to concentrate the Energy in a particular Direction
Where Wmax is the Power Density at a distance d in the main lobe direction
Generally, we use the Gain instead :
Where PT is the supplied power to the antenna, commonly known as the output power (minus the cable and connector losses)
Given PT and G, we can compute the Power Density Wmax
densityMeanPowerDWD
@max=
2
max
4 dP
WGT
π
=
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B. RF FundamentalsRelation Between W and E (The Electric Field) :
Besides :
Maximum Useful Power :
377120
222 EEEW ===πη
dGP
EdGPE TTTT 30
4120 2
2
=⇒=ππ
12024.
120
2222R
RGEGEAEP
===
πλ
πλ
πη
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B. RF FundamentalsEffective Area of an Antenna (Reception) :
Received Power :W : Power Density (Per Unit Area)
Finally, the received power reads :
Free Space Loss Between Isotropic Antennas (GR=GT = 1) :
GAπ
λ4
2
=
WAP =
24 dGPW TT
π=
RTT
R GdGPP
πλ
π 44
2
2=
kmMHzT
R dLogfLogPPLogdBL 101010 202044.3210)( −−−==
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B. RF FundamentalsPropagation Over a Plane Reflecting Surface (Flat Earth Model) :
Assuming d >> Ht and Hr, the Path Loss (Iinear) :
HtHr
TxRx
δjkdd eEEE −−=
d
2
2
=dHHGG
PP rt
RTT
R
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B. RF FundamentalsReflection :
HtHr
TxRx
δjkdeEE −Γ=
d
Γ is the Complex Reflection CoefficientThe value of Γ depends upon frequency, Polarization and Electric Characteristicsof the reflecting surface
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A B C
A
CB
P
Shadow region
B. RF Fundamentals
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B. RF FundamentalsDiffraction :
HtHr
TxRx
δjkdeDEE −=
d
D is the Complex Diffraction CoefficientThe value of D depends upon frequency, Polarization, Geometry, and Angles of thestructure
h
D1D2
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The Diffraction Loss is shown to be :
Where v, the Fresnel Parameter is given by :
B. RF Fundamentals
( )
( ) 4.24.21
1008.0
/225.020))1.038.0(1184.04.0(20
))95.0exp(5.0(2062.05.020
)( 2
><<
<<<<−
−−−−
−
=
vvvv
vLogvLog
vLogvLog
vL
21)21(2
DDDDhv
λ+
=
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B. RF Fundamentals
Hb
Hp
Hm
Ho
A B
Compute L(v) for :Hb = 20 mHp = 5 mHo = 15 mHm = 1.5 mA = 1250 mB = 4.5 mFrequency = 900 MHz
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Bullington Model :“equivalent” Knife - edge
T R
0102
D1 D2
d1 d2 d3
h1 h2
H
Ht Hr
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Test : Bullington Diffraction Loss Model
Compute H, D1, D2, and then L(v) the DiffractionLoss given the following data :
Ht = 25 mHr = 1.5 md1=d2=d3=1000 mh1 = 30 m, h2 = 15 mFrequency = 1880 MHzCompare L(v) to the Free Space LossPlease Conclude
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d1 x d2 x d3 x d4
T R
The Epstein – Petersen diffraction construction
01
02
03
Propagation over irregular terrain
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d1 x d2 x d3 x d4
T R
The Deygout diffraction construction
01
02
03
Propagation over irregular terrain
Main edge
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B. RF Fundamentals : Receiver Theory
ReceiverDemodulation& Selective
Filtering
BS / MS
Receiver Input
Receiver Output
To operate properly the receiver has to receivea minimum power : Sensitivity
The Sensitivity depends on the technology involved
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Receiver Sensitivity :Is the minimum acceptable input signal level in dBm, at thereceiver‘s low noise amplifier, required by the system for reliablecommunication
Carrier to Noise Ratio CNR or C/N :For a given BER (Bit Error Rate) of about 10-3 for example, C/N isthe required minimum signal to noise ratio
Thermal/Environment Noise :Is a combination of
Antenna Noise (dBm)Receiver Noise Figure (NF) in dBTemperature and System Bandwidth
B. RF Fundamentals : Receiver Theory
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B. RF Fundamentals : Receiver Theory
(S/N)in (S/N)out
ReceiverNF
NFNSNS
NFNSNS
NFNS
NS
outinin
outinin
outin
+
+=
+
=−
+
=
Nin : Thermal Noise,
NF : Noise Figure
outin N
SNFBTkLogS
++= )..(10 10
RECEIVER SENSITIVITY :
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B. RF Fundamentals : Receiver Theory
outin N
SNFBTkLogS
++= )..(10 10
k : Boltzmann Constant ( 1.38 * 10-23 J/°K)T : System Operating Temperature (°K)B : System Bandwidth (Hz)
T : 290 °K typical value
Exercise : Compute Sin (dBm) for a GSM signal of 200 kHz Bandwidth, with a receiver NF=6 dB and C/N = 9 dB
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B. RF Fundamentals : Intermodulation
Non-LinearDevice
IM is a non-linear process that generates an output signalContaining frequency components not present in the inputsignal
...33
2210 ++++ xaxaxaax
Assuming x to be a two-carrier f1 and f2 sine wave :
)2cos()2cos()( 21 tfBtfAtx ππ +=
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B. RF Fundamentals : Intermodulation
3210)( yyxaaty +++=
( ) ( )( ) ( )( )[ ] ( )( ) ( )( )[ ]2121222
122222
2 2cos2cos22cos22cos22
ffffABafBfAaBAay −++++++= ππππ
Spectral Characteristics of y2 Usingf1 = 1800 MHz and f2 = 1830 MHz, A=B=1, and a2 = 1
f1 f2
0
DC f2-f1 2f1 2f2
1800 MHz 1830 MHz
3600 MHz 3660 MHz
3630 MHz
f2+f1
Cellular Band
30 MHz
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B. RF Fundamentals : Intermodulation
3210)( yyxaaty +++=
Spectral Characteristics of y3 Usingf1 = 1800 MHz and f2 = 1830 MHz, A=B=1, and a2 = 1
f1 f2
0
DC 2f2-f1
1800 MHz 1830 MHz
1860 MHz
Cellular Band
1770 MHz
2f1-f2
Six Different Frequencies are generated in IM3 :3f1, 3f2, 2f1-f2, 2f1+f2, 2f2-f1, 2f2+f1
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B. RF Fundamentals : Fade Margin
R
• Due to shadowing and terrain effects the signal level measured on a circlearound the BS shows radom behaviour around the predicted value given by thePropagation Model
• This Random Signal level through the cell boundary has a Log-Normaldistribution
• Log-Normal variable is in fact a Gaussian Process when expressed in dB
( )
−−= 2
2
2exp
21)(
σπσmxxp
x : is the received levelm: Mean value of xσ : Standard Deviation of x
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( )
−−= 2
2
2exp
21)(
σπσmxxp
B. RF Fundamentals
Theory shows that to ensure 90 % of Surface Reliability,One may push the received signal level requirement toHigher values than m (50%).
This leads to a notion called :
Fade Margin : the additional margin to fullfil y % of surfaceCovered.
PDF-Gaussian
0
0.01
0.02
0.03
0.04
0.05
0.06
-110
.00
-104
.00
-98.
00
-92.
00
-86.
00
-80.
00
-74.
00
-68.
00
-62.
00
-56.
00
-50.
00
PDF-Gaussian
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Fade Margin
50% is the median value. To achieve higher %, one may adda Fade Margin to fullfil X% > 50%
The Probability that a Field Strength Exceeds a Threshold E0 is :
−
−=
=≥= ∫∞
21
21
)()(
0
0
0
0
0
σEEerfp
dEEpEEpp
mE
EE
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Fade Margin
The Lognormal Margin is defined as :Mlog = Em – E0
Hata Model has a general form :
The Contour Probability can be written as :
)/(log10)( 100 RrErE m γ−=
+−=
Rrbaerfp E ln1
21
0
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Fade MarginThe parameters a and b are :
The Area Coverage Probability over a Circle of Radius R is :
The contour probability depends only upon the radius r, which simplifiesthe computation and leads to :
2log10
210
0
σ
σeb
EEa m
=
−=
∫∫= θθπ
rdrdrpR
P E ),(102cov
( )
+
−
+
−+=b
aberfbabaerfP 1112exp1
21
2cov
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Contour and Area Coverage Probability Versus the Fade Margin
0102030405060708090
100
0 1 2 3 4 5 6 7 8 9 10
Fade Margin (dB)
Prob
abili
ty (%
)
Cell Edge %Area %
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BasefadeBldgBodymmup
upFadeBldgbodymmBase
RXMLLGPAPl
PlMLLGPARX
−−−−+=
−−−−+=
CCCB
CCCB
LGLG
−+−+
Ms AntennaGain Loss
ERP
Body Loss
In-Building CarPenetration Loss
Fade margin
Path Loss
CombinerCable &
ConnectorLosses
RYCCCL
AG
Gains and losses in uplink
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PA
CombinerCable &
ConnectorLosses
PowerAmplifier
MBodyBldgDownFadeBCCCMobileB
MBodyBldgDownFadeBCCCBMobile
GLLPLMGLRXPA
GLLMMGLPARX
−++++−+=
+−−−−+−=
ERPFade margin
Path LossIn-Building CarPenetration Loss
Body Loss
MS AntennaGain Loss
CCCL
BG
RX
Gains and Losses in Down Link
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Maximum Allowable Path Loss
Starting with the reverse link UL•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 interferencefor 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
baseUp RXAllGainsAllLossesPLMAPL −+−=
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Balance Equation:
•Write the balance equation and see which termsget cancelled•Find the Base station and EIRP that resultsin balanced paths.•Changing which parameter jeopardizes the path balance?- Antenna Gain- Antenna Height- PA output
UpDown
MBodyBldgMobileFadeBCCCBDown
CCCDivBBaseFadeBldgBodyMmUp
PLPL
GLLRXMGLPAPL
LGGRXMLLGPAPL
=
+−−−−+−=
−++−−−−+=
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Cell Size / Count Estimation
• Objective- To determine the number of cells required to providecoverage for a given area
• Required Input:- Maximum Allowable Path Loss (MAPL)- Propagation Loss Model
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MAPL
Path Loss
Range or Cell Radius
Distance from TX
From MAPL to Cell SizePropagation Loss Model
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Cell Size Information With Hata Model
•Using Hata’s Empirical Formula
CFhaRhhfPL mbbc −−−+−+= )(log)log55.69.44(log82.13log16.2655.69 10101010
•Solve it backward to find cell radius estimate
b
mbc
hhahfCFMAPLR
10
101010 log55.69.44
)(log82.13log16.2655.69log−
++−−+=
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BS Installation Requirements :A certain isolation has to be present between Tx and Rx antennasRadiation Patterns must not be distorted by obstacles or reflectionsnearby the antennas
Isolation :Between 2 antennas : Attenuation from the connector of oneantenna to the connector of the other antenna when bothantennas are in their installation positions
To avoid unwanted signals into the receiver Rx, the followingisolation values are required :
40 dB Between a Tx Antenna and a Rx Antenna20 dB Between 2 Tx Antennas
H. Guidelines for interference Minimisation
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Isolation :
To obtain the Isolation values the antennas have to be placed at certain minimum distance from each other
The distance depends on : Antenna types, configuration
Omnidirectional antennas require greater horizontal distance thandirectional antennas
Vertical separation requires less distance than horizontal separation
H. Guidelines for interference Minimisation
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a
k
Pre-condition : a > 1 mTx-Tx : 0.2 m minimumTx-Rx : 0.5 m minimum
As a General Rule :
Isolation :
For GSM 900, λ = 0.33 m
With A = 35 dB, k = 0.5 m
dBkLogAV
+=
λ104028
dBkLogAV 104047 +=
H. Guidelines for interference Minimisation : Vertical Separation
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d
dBGGdLogAH )(2022 2110 +−
+=
λ
G1 : Gain of antenna 1 in dBdG2 : Gain of antenna 2 in dBd
dBGGdLogAH )(2031 2110 +−+=
General
@ 900 MHz
H. Guidelines for interference Minimisation : Horizontal Separation
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3.0 m28.0 m10
2.5 m22.0 m9
1.0 m11.0 m6
1.0 m *5.5 m3
1.0 m *3.0 m0
Tx-Rx distance(20 dB)
Tx-Rx distance(40 dB)
Omni AntennaGain (dBd)
Could be less for Tx-Tx but 1.0 m is a conservative option toavoid shadowing effects
H. Guidelines for interference Minimisation : Horizontal Separation
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d
k
α
H. Guidelines for interference Minimisation : Combined H/V Separation
( ) HHV AAAA +°°
−≈90
. α
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h
D
H. Guidelines for interference Minimisation
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5 10 15 20 25 30 35 40 45 distance(m)
4
3
2
1
Step function
First Fresnel zone
Antenna height
H. Guidelines for interference Minimisation
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Mast
a2 m is recommended
The mast is allowedto swing 1° at a windvelocity of 30 m/s
1±
H. Guidelines for interference Minimisation
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k
H. Guidelines for interference Minimisation
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d
H. Guidelines for interference Minimisation
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Forward direction
o90
oMax. 15
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d
k
α
H. Guidelines for interference Minimisation
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Ground level
H
Max
imum
div
ersi
ty
Axi
s
a
RxA RxB
H. Guidelines for interference Minimisation
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hD
H. Guidelines for interference Minimisation
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5 10 15 20 25 30 35 40 45 distance(m)
4
3
2
1
Step function
First Fresnel zone
Antenna height (m)
H. Guidelines for interference Minimisation
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Wall
Top viewForward direction
H. Guidelines for interference Minimisation
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Top view Forward direction
Maximum
Cell sector including safety margin °± 75
°15
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Top view Forward direction
More than
Cell sector including safety margin °± 75
°15
Wall
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Definition
Diversity is the statistical improvement of the received signal whenmore than one signal is used.
To improve the overall received signal level, due to multipathphenomenon, it is interesting to use more than one antenna and consider internally the best received signal.
Diversity in cellular is used only at the Base Station end, although it istheoretically possible for mobiles, it is quite cumbersome to have twoantennas moving with the subscriber !
H. Guidelines for interference Minimisation : Diversity
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H. Guidelines for interference Minimisation : Diversity
MobileStation (MS)
Base Station(BS)
Antenna #1
Antenna #2The Receiver uses different combining techniques. The mostpopular is the Maximum CombiningRatio Technique
d
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H. Guidelines for interference Minimisation : DiversityR
ecei
ved
sign
al
TimeSignal Level Received by Antenna 1 (RxA)Signal Level Received by Antenna 2 (RxB)Improvement due to Antenna Diversity
Typical Diversity Gains : 3.5 dB for Cross-Polarised antennas, 4.5 dB for SpaceDiversity. The maximum theoretical value is 6 dB.
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H. Guidelines for interference Minimisation : Correlation vs distanceC
orre
latio
nFu
nctio
n
Normalized Distance10λ
0.7
40λ
d
Antenna #1 Antenna #2).(2
0 dkJα
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Ground level
aRxA RxBa = distance betweenRx antennas
H = height of mastplus building(Effective antenna height)
H
H. Guidelines for interference Minimisation : Diversity Requirements
10Ha ≥
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°90
a
Maximum diversityRxA RxB
Minimum diversity
H. Guidelines for interference Minimisation
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Optimumdiversity
Coverage area RxB
RxA
H. Guidelines for interference Minimisation
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Urban
Suburban
Rural
Market Boundaries•Usually a midsize market covers heterogeneous areas,e.g.
- Downtown,Urban or dense urban areas- Suburban, Light residential areas- Rural, open areas, farmland…
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Radio Planning Methodology
Business Planning
Coverage Requirement & Demand Forecasts from
Marketing
Computer-BasedModelling
Design Nominal Cell Plan
Acquire Sites and Implement Cell Plan
Optimise Network
Define Design Rules and Parameters
Produce Frequency Plan
Set Long Term Plans and Performance Targets
Des
ign
Ite r
atio
n
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Market Boundaries
® Cirta Consulting LLC
( ) ( ) ( ) ( )[ ] ( )
( ) ( )[ ] ( )[ ]
( ) ( )[ ]
( )[ ]
( )[ ] ( )
( )[ ] ( ) 94,3533,1878,4
94,4033,1878,4
4,528/2
97,475,112,3
8,056,17,01,1
55,69,4482,1316,2655,69
2
2
2
2
−+−=
−+−=
−−=
−=
−−−=
−+−−+=
fLogfLogLL
fLogfLogLL
fLogLL
hhLogha
fLoghfLogha
dLoghLoghahLogfLogL
urqo
uro
usu
mmm
mm
bmbu
Hata RF Propagation Model for Urban Environments
For a Midium Size City
For a Big Size City and f > 400 MHz
For Suburban Environments
For Rural Environments
For Semi-Rural Environments
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Hata Model is valid under certain conditions :
Frequencies between 150 and 1000 MHzBase Station Antenna Height between 30 an 200 mMobile Station Antenna Height between 1 and 20 mBS-MS Distance between 1 and 20 km
As a Result, it is suitable for GSM900 only and NOT GSM1800 or PCS1900 !!!
Hata RF Propagation Model for Urban Environments
® Cirta Consulting LLC
[ ]
[ ] [ ]8,0)(56,17,0)(1,1)(
)()(55,69,44)()(82,13)(9,3333,46
−−−=
+−+−−+=
fLoghfLogha
CdLoghLoghahLogfLogL
mm
mbmbu
COST231-Hata RF Propagation Model for Urban Environments
dBCm 0=
dBCm 3=
For Medium Size Cities and Suburbs
For Big Metropolitan Centers
Validity : Frequencies between 1500 MHz and 2000 MHz
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Table of Penetration Losses
In Building penetration (dB) 15 - 25In Car penetration (dB) 3 - 10Body Loss (dB) 2 - 5
For all receiving environments a loss associated with the effectof users body on propagation has to be included.
This effect is in the form of a few dB loss in both uplink and downlink directions.
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Tower Mounted Amplifier : Effect on Coverage and Quality
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BTS BTS
TMA
3 dB cable loss
4 dB Gainin the UL
Static Sensitivity=-110 dBm Static Sensitivity=-110 dBm
S(without TMA) = -110 + 3 = -107 dBm* S(with TMA) = -110 + 3-4 = -111 dBm*
* Body Loss and Lognormal Fading have to be added
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Cell Range R computed using :MAPL=A+B*log(R)MAPL : Maximum Allowed Path LossMAPL = EIRP-Effective SensitivityExample :
Given EIRP=Pout+Gant-CableLosswith Pout=40 dBm; Gant=18 dBi; Cable Loss=3 dBEIRP=40+18-3=55 dBmMAPL =
• 55 - (-107+7+5) = 150 dB without TMA• 55 - (-111+7+5) = 154 dB with TMA
MAPL : The higher the bigger the cell radiuslog(R) = (MAPL-A)/B ⇒ R = 10^((MAPL-A)/B)
Overview on Linkbudget Impact (1/2)
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Numerical Example :Assume we use a Rural Propagation Model PL = 135 + 30*log(R)
Cell Radius R=10^( (150-135)/30 )= 3.2 km without TMA10^( (154-135)/30 )= 4.3 km with TMA !
Overview on Linkbudget Impact (2/2)
Path Loss (dB)
Distance (km)
135+30*lod(d)
MAPL=150 dB without TMA
MAPL=154 dB with TMA
3.2 km 4.3 km
4 dB due to TMA
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Uplink Coverage
Downlink Coverage
TMA Improves Uplink vs Downlink: To balance the Linkbudgetthe BTS output power has to be raised by 4 dB ! (the TMA gain)
DirectionalAntenna
Due to linkbudget imbalance
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Measurements and Propagation Model CalibrationThree Types of measurement equipment are commonly used :
1. Narrowband measurements (CW)a) Prior to starting the designb) For calibrating the prediction modelc) For verification of critical and borderline coverage areas
2. Test Mobile Measurementsa) Once the Network has been builtb) For analysis of System Parameters and Handover behaviorc) For Network Optimization
3. Reflection Measurements (channel sounder)a) As a research toolb) For analysis of Multipath Propagation and Delay Spreadc) Normally only necessary in mountainous regions
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Measurements and Propagation Model CalibrationMeasurement requirement for Tool Calibration
- To measure out to the cell radius, requires typically 145 dB (MAPL)- To measure out to the point where interference is significant, requires typically another 20 dB (i.e. a total of 165 dB dynamic range)- The measuring equipment should handle this range easily, i.e. should have a dynamic range of the order of 175 dB- To achieve this dynamic range, narrowband CW measurements are necessary
Wideband Receivers and Test Mobiles (Based on a modified subscriber handset – measuring GSM RXLEV) are unsuitable for model calibration but may be used later for confirmation of coverage
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Measurements and Propagation Model Calibration
Trigger Wheel
Antenna
Amplifier
Transmitter
Tx Antenna
Rx/Computer
Navigation
Rx Antenna
Storage
Trigger MSBTS
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Measurements and Propagation Model CalibrationFor CW measurements it is important to record an averaged value of
instantaneous measurements
1. Rayleigh Fading makes instantaneous measurement unrepresentative
a) Aim to eliminate the Rayleigh fading, but not the shadow fadingb) Average over an interval which is less than the magnitude of streets and
buildings. Some refereneces speak about a distance of 40λ
2. Averaging interval should be greater than the Rayleigh Fading interval, but shorter than the building interval
a) 13 m outdoorsb) 6.5 m indoors
3. Separation of instantaneous measurements should be :a) More than 36 per interval to reduce averaging variation to less than 1 dBb) Corresponds to 0.36 m (1.1λ at 900 MHz)
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Measurements and Propagation Model CalibrationSampling Rates
4.4492.00
3.40121.75
2.50161.50
1.74231.25
1.11361.00
0.63640.75
0.281440.50
ResultingSampling Interval(λ)
Number of averaged samplesin 13 m
RMS Error (dB)
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Measurements and Propagation Model CalibrationGuidelines for CW Measurements
1. The Survey Route should include various road directions and street widths in built up areas
2. Special features relevant to propagation such as tunnels, bridges, etc. should be clearly marked in the case of calibration measurements
3. If possible, measurement antennas should be the same as the planned antenna in type and installation
4. Measurements must be conducted and documented accurately, especially regarding antenna installation and transmitter height
5. Only measure within 3 dB beamwidth (antenna aperture)The pattern outside the main beam may not correspond to the stored antenna
pattern, due to local obstructions, such as the mast and other antennas
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Measurements and Propagation Model Calibration* To effectively calibrate a propagation model, many measurements
are needed :
1. About 10 different base stations in each city2. At least 75 km of survey route for each city3. At least 1000 km of route in total
* Measurements at each point are compared to the predictions at each point and the error statistics analyzed
Errors may be broken down by :
1. Clutter class2. LOS/NLOS3. Within a given range4. Outside a given range
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Measurements and Propagation Model Calibration• Error Analysis Statistics
• The Error is commonly defined as the difference between the predicted value (Propagation Model) and the measured value. At a given distance of index i, the error is noted εi
• Root Mean Square Error and Mean Error are given by :
N
NRMS
N
ii
N
ii
∑
∑
=
=
=
−=
1
2
1
)(
εε
εε
The target is to ensure a mean error=0 and an RMS < 9 dB (The Lower the Better)
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Non-uniform Propagation Types
• Each area has a different correction factor.• Also the coverage objectives are usually different for urban, suburban and rural areas.
• Therefore MAPL and the corresponding cell size has tobe calculated for each region and cell count is:• For each area: where R is the cell radius and A is the area of thecorresponding hexagon.
26.2 RA =
)()(
)()(
)()(
2
2
2
2
2
2
KmAKmRuralArea
KmAKmeaSuburbanAr
KmAKmUrbanAreaCellCount
RuralUrban Suburban
++=
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Introduction
•Definition of Outdoor signal level design threshold to be used in prediction tool.
•Insure good quality communications.
•Threshold important because it is the basis for the design, and cell size and no. of cells depend on this.
•Aim: understand the different elements in the determinationof the threshold.
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Introduction 2
• Receiver Sensitivity (from vendor or standard)
Use of Different Margins
• Outdoor coverage design threshold
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Receiver sensitivity margin (1)
•Sensitivities defined in GSM Rec. 05.05Portable: -104 dBmHandheld: -102 dBmDCS1800: -100 dBm
•Sensitivity : Min required signal level at receiver to meetperformance requirements
•Sensitivities defined for mobiles in an urban environmenttraveling at 50 km/h (TU 50)
•These sensitivities with a C/I of 9dB correspond to errorrate of 10% or RxQual =6
•These values include a margin for Rayleigh Fading
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Receiver sensitivity margin (2)
•Today many handsets used at walking pace or static
•At 50 km/h effect of fading is averaged but”static”mobiles will remain in fading “holes” longer.
•Measurements show that for a handheld moving at 3 km/h (TU3) then for an acceptable audio quality we need:- RxQual = 4 ( system without frequency hopping)- RxQual = 5 ( system with frequency hopping)
Quality margin must be introduced
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5 dB
3 Km/h
Receiver sensitivity margin (3)• Measurements campaign by CNET to link C/N, C/I and
Rxqual• With no interference, without frequency hopping a
Rxqual = 4 is obtained with C = -97 dBm• Quality margin = 5 dB• (FT 3 dB, Cellnet 4 dB)
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Prediction/Lognormal Margin (1)
• Propagation model predicts mean signal level
• Characteristics: Mean error (0) and standard deviation
• Shadow fading (obstacles) not taken into account
• Model this shadow fading by a probability following alognormal law
• Introduce Margin to guarantee a certain percentage of cell surface area is covered
( )σ
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Prediction/Lognormal Margin (2)
Standard Deviation ofPrediction model
Level of guaranteeRequired (probability)
Lognormal Margin
• To calculate the margin we use coverage probabilityat cell border which corresponds to the requiredcoverage probability over the surface of the cell.
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Prediction/Lognormal Margin (3)
•Typical values:- Urban environment (Typical distance exponent = 3.5 )- Standard Deviation of prediction model = 7 dB
Margin in dB Coverage probabilityon cell bordure %
CoverageProbabilityOver cell surface %
0 50 775 75 907 84 959 90 9712 95 99
- GSM Rec 3.30
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Head Effect
•The human body creates loss for handheld mobile.•Loss due to distortion of antenna diagram•Some suggested values :•Recommendations GSM 03.30 = 3 dB.•Dr. Lee proposes 5 dB in worst case ( mobile on belt)•Most operators use 6 dB.•Motorola proposes 9 dB head effect, 15 dB at belt.
•Telemate suggested value is 5 dB.
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Other Margins
• Hand – Over: Some Operators use a 2 dB margin to ensure a good HO to neighboring cell
• Material imperfections: we take a 1 dB margin to accountfor the tolerance in MS and BTS output power
• Interference Margin: Some vendors use an interferencemargin to overcome interference impairments
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Example Calculation of Outdoor coverage threshold for 2W GSM handheld
Sensitivity ( GSM Rec. 5.50 )
Sensitivity margin
Lognormal margin ( for 90% area coverage probability)
Head Effect Margin
Outdoor Coverage Threshold
- 102 dBm
5 dB
7 dB
5 dB
- 85 dBm
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Indoor Threshold (1)
• Different types of Indoor Threshold corresponding todifferent services
- Indoor Window: Near to window- Indoor: In room with windows- Indoor Deep : In corridor (loss through 2 walls)
• Penetration loss varies greatly. Depends on type ofmateriel, architecture (no. of windows…), floor withinbuilding etc.
• Mean penetration loss must be determined from extensive measurement campaigns
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Indoor Threshold (2)
•To determine an Indoor threshold from the penetrationloss there are two methods:
- Use the distribution function of the measurements to findthe loss corresponding to 90 % of the samples
- Use the mean penetration loss and increase thelognormal margin to take into account the standarddeviation of the indoor measurements.
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Use of margins
• Understand what goes into the determination of coveragethresholds.
• Make sure that all margins are included but only once!
• Translate the clients requirements for service quality intomargins
• Thresholds must be validated by the client.
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TEST : Link Budgets
Balanced link budgets show Maximum Allowable Path Losses for thecoverage objectives shown below. Drive tests have shown the following propagation equations are valid. Determine the cell radius for each coverage objective.
Coverage objectives: Rural on-street MAPL = 147 dBSuburban in-car MAPL = 135 dBUrban in-building MAPL = 125 dB
Propagation equations:Rural: path loss = 110 + 32 log dSurburban: path loss = 115 + 37 log dUrban: path loss = 120 + 48 log d
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The Cellular Concept
Urban Areas : High Interference AmountsC/(N+I)=C/I, The System is Interference-LimitedCoverage is not a problem (in General)Service Criterion : C > I
Rural Areas : Low Interference ProfileC/(N+I)=C/N, The System is Noise-LimitedInterference is not a problem (in General)Service Criteria : C > N
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Frequency Planning aims at :Optimising the Allocated SpectrumGuaranteeing a seamless coverageEnsuring minimum interference
Main Difficulty of Frequency Planning is :Limited Number of TRXs (Available Channels)
The concept of Frequency Re-Use overcomes theSpectrum Limitations. Caution has to be made concerningthe risk of generating co-channel and adjacent channelinterference
The Cellular Concept
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GSM SpectrumAllocated GSM1800 Band comprises two sub-bands :
1710 – 1785 MHz for Uplink (MS->BTS)1805 – 1880 MHz for Downlink (BTS->MS)Each Sub-band = 375 Channels of 200 kHz associated to a givencarrier95 MHz are necessary to ensure the isolation between Up and Down Links DuplexingEach Operator is allocated a DL/UL bandGSM uses TDMA (Time Division Multiple Access)
1 Physical Channel = 8 Logical Channels1 Logical Channel = TCH or Signalling Channel (SDCCH, FCCH, SCCH, AGCH, RACH, etc...)
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Interference
Definition of the Signal to Noise Ratio irrespective to the co-or adjacent channels
C/I = Puseful/Pharmfull
Co-Channel InterferenceInterference Due to a Signal using the same Frequency :
C is the useful Signal, I1 and I2 are co-channel interferersusing the same frequency as CC, I1 and I2 are linear units (i.e. Watts or mW)
02
01 IIC
IC
channelco +=
−
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InterferenceAdjacent Channel Interference are due to out-of-bandspurious transmissionGSM RF Mask is based upon the GMSK Modulation Scheme (GMSK = Gaussian Minimum Shift Keying)
NIIIC
IC
sulting ++++=
...210Re
GMSK RF Mask
0.5 dB
-30 dB
-60 dB
f f+200 kHz f+400 kHzf-200 kHzf-400 kHz
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InterferenceInterference = Impossible to identify and extract the wantedand interfering signal (noise included)GSM Specifications require C/I to be higher than 9 dB
580.0000125-493rd
Adjacent
500.0000794-412nd
Adjacent
180.125-91st Adjacent
07.949Co-Channel
ProtectionC/IC/I (dB)Protection
RecommendationGSM
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Traffic Theory : Erlang B
Poisson Input with mean of λ arrivals/sec.Mean Service Time = 1/µTraffic Intensity = A = λ. 1/µNumber of Serving Trunks (Channels) = SBlocked Calls Abandoned
∑=
== S
k
k
S
b
kASA
ASBP
0 !
!),(
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Traffic Theory : Erlang B
Etc.48.759842.152734.745628.337521.029414.92238.21422.371ErlangNb TCHNb Carriers
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Traffic Theory : Erlang CPoisson Input with mean of λ arrivals/sec.Negative Exponential Service Time with mean = 1/µTraffic Intensity = A = λ. 1/µNumber of Serving Trunks (Channels) = SBlocked Calls held until served
[ ]0),()(Pr >== DPASCDelayob τ
∑−
=
+−
−= 1
0 !.
!
.!),( s
i
iS
S
iA
ASS
SA
ASS
SA
ASC
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Traffic Theory : Erlang C
Probability of Delay Greater than t :
Average Delay :
tsAD eASCtP µτ )1(),()( −−=>
µτ
SAASCE D )1(
),(][−
=
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Traffic Theory : PoissonPoisson Input with mean of λ arrivals/sec.Negative Exponetial Service Time with Mean = 1/µTraffic Intensity = A = λ. 1/µNumber of Serving Trunks (Channels) = SBlocked Calls Held
∑∞
=
−==Sk
kA
b kAeASPP
!),(
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Capacity PlanningAims of Capacity Planning
To allocated Sufficient Channels to support the expected traffic loadTo ensure future sites are planned and implemented in time to meetsubscriber growth (Business Plan)To provide Traffic Loading Figures on which the fixed network can bebased
Traffic UnitTraffic is measured in Erlang : Etot = Esub*Nsubs
Etot is the total TrafficEsub is the average traffic per subscriberNsub Number of Subscribers
Example : Esub = 25 mE* and Nsub = 100, then Etot = 2.5 Erlangs*25 mE = 1.5 minutes of occupied TCH per Hour
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Capacity PlanningProcedure for Calculating Number of Required Channels
First Compute Busy Hour Traffic per Subscriber (Erlangs) :Average Daily Number of Call Attempts × Average Call LengthPlus Number times length of Incoming CallsTimes Proportion of Total Calls made in the Busy Hour
Then Calculate Total Traffic as Average Traffic Times Number of Subscribers
Finally Use Erlang B Tables to determine the number of Channelsrequired for a given Blocking Level
Example : For GSM, 2 % is the typical blocking rate used
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Capacity PlanningTEST ON DIMENSIONING USING CAPACITY DEMANDS
Given a Dense Urban Area of about 35 km2 and a penetration rate estimatedto 9 % over a total population of 500.000 inhabitants
Assuming 4 TRX 3-sector BTSs will be used,
Each sector (using 4 TRXs) has a cell radius of 0.45 km
Each Subscriber will require a 25 mE traffic
Compute the total required Traffic (Erlang) within this dense urban area, along with the required number of 3-sectorial BTSs
What would be these numbers if the unit traffic increase to 40 mE ?
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Tower Mounted Amplifier : Effect on Coverage and Quality
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BTS BTS
TMA
3 dB cable loss
4 dB Gainin the UL
Static Sensitivity=-110 dBm Static Sensitivity=-110 dBm
S(without TMA) = -110 + 3 = -107 dBm* S(with TMA) = -110 + 3-4 = -111 dBm*
* Body Loss and Lognormal Fading have to be added
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Cell Range R computed using :MAPL=A+B*log(R)MAPL : Maximum Allowed Path LossMAPL = EIRP-Effective SensitivityExample :
Given EIRP=Pout+Gant-CableLosswith Pout=40 dBm; Gant=18 dBi; Cable Loss=3 dBEIRP=40+18-3=55 dBmMAPL =
• 55 - (-107+7+5) = 150 dB without TMA• 55 - (-111+7+5) = 154 dB with TMA
MAPL : The higher the bigger the cell radiuslog(R) = (MAPL-A)/B ⇒ R = 10^((MAPL-A)/B)
Overview on Linkbudget Impact (1/2)
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Numerical Example :Assume we use a Rural Propagation Model PL = 135 + 30*log(R)
Cell Radius R=10^( (150-135)/30 )= 3.2 km without TMA10^( (154-135)/30 )= 4.3 km with TMA !
Overview on Linkbudget Impact (2/2)
Path Loss (dB)
Distance (km)
135+30*lod(d)
MAPL=150 dB without TMA
MAPL=154 dB with TMA
3.2 km 4.3 km
4 dB due to TMA
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Uplink Coverage
Downlink Coverage
TMA Improves Uplink vs Downlink: To balance the Linkbudgetthe BTS output power has to be raised by 4 dB ! (the TMA gain)
DirectionalAntenna
Due to linkbudget imbalance
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RF Repeater : Problem Statement (1/2)
No Coverage Tunnel
High Penetration Lossadded to propagation loss
Base Station
In Car Coverage Threshold not reached
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RF Repeater : Problem Statement (2/2)
Base StationMS
High Diffraction and Shadowing Loss : Hills, Blockings, etc.
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RF Repeater : Design IssuesRepeater = Bidirectional Amplifier used to
* Provide Coverage to “shadowed” rural areas* Provide Coverage to Tunnels* Provide Coverage to Indoor Areas where Capacity is not an issue
Repeater comprises :* A High Gain Amplifier* A Duplex-filter for Up and Downlink Service* A Donor Antenna : From the Repeater to the Donor Site* A Re-Radiating Antenna : From the Repeater to the Area to be covered
Repeater Features :* High Amplifier Gain* High Isolation Between the Repeater Ends to avoid oscillation* High Channel or Band Selectivity
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RF Repeater : Components
BPF
BPF
Donor Antenna (BTS)High Gain, Very Directional
Re-RadiatingAntenna (MS)Lower Gain, Wide Beamwidth
High Gain Amplifiersup to 85 dB
Band-Pass High Rejection Filters :Channel or Band Selective
To donor Cell
To poor area coverage
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RF Repeater : Typical Antennae Mounting
R
To a valleywide bandwidthantenna
To donorcell
R
To donorcell
To Tunnel
Uni- or Bidirectional High Gain Antenna
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RF Repeater : Design Tricks1. Donor Antenna should be :
a. Preferably in LOS with the Donor Cellb. High Gain and High Directionalc. Mounted in a location so that the RxLev > its static sensitivityd. Dip Fades have to be avoided : RF Measurements done prior to installation (Go or not Go)
2. To avoid interference between Donor and Re-Radiating antennas, an isolation is required : this should prevent the Repeater to oscillate.
3. Never have LOS between Re-Radiating antenna and Donor Cell
4. Depending on the application : Re-radiating antenna has to be chosen accordinglya. Tunnels : High gain (uni- or bidirectional)b. Valley or “shadow” : wide beamwidth and typical antenna gains
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RF Repeater : Antennae Location
R
To donorcell NOT RECOMMENDED
R
To a valleywide bandwidthantenna R
To a valleywide bandwidthantenna
To donorcell
RECOMMENDED
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RF Repeater : Powerbudget (1/3)
Allgon Indoor Repeater Technical Specs :Gain : 45 - 70 dBNoise Figure : 5 dBMaximum input power : +13 dBm
Assumptions :Donor BTS @ 4.5 km from the Repeater : Free Space and LOS assumed. BTS Donor Antenna EIRP : 48 dBmDonor Antenna to Repeater cable loss : 1.5 dBRe-radiating Antenna to Repeater cable loss : 0.5 dBDonor Antenna Gain : 18.5 dBiRe-radiating Antenna Gain : 14 dBi
Task : Balance the UL and DL, then compute the repeater cell radius
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Received Power at the donor antenna connector :Pr(donor)=EIRP(donor BTS)-PL = -56.6 dBm
PL = 32.44+20*log10(4.5*900) = 104.6 dB (free space loss)EIRP(donor BTS) = 48 dBm
Input Power at the Repeater (Downlink) :Pin = Pr(donor) - Cable Loss(DL) + G(donor)
Pin = -56.6 -1.5 + 18 = -40 dBm
Repeater Output power (downlink) :Pout(min) = Pin + Gmin(Repeater) = -40 + 45 = 15 dBmPout(min) = 15 dBm > 13 dBm (need a 2 attenuation)
EIRP(Re-Radiating) = Pout - Cable(to antenna) + G(Re-Radiating)EIRP(Re-Radiating) = 13 - 0.5 + 14 = 26.5 dBm
Without a repeater the penetration loss of 15 dB leads to :Rxlev (indoor) = -56.6 - 15 = -71.6 dBm !!! @ the vicinity of the lossy wall
RF Repeater : Powerbudget (2/3)
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Received Power at the Re-radiating antenna connector :Pr(Re-Rad.)=EIRP(MS)-PL = 33 - 106.5 = - 73.5 dBm
PL = 120 + 45*log(0.5) = 106.5 dB (e.g. Okumura-Hata Model)EIRP(MS) = 33 dBm (no Power control considered)
Input Power at the Repeater (Uplink) :Pin = Pr(Re-Rad) - Cable Loss(UL) + G(Re-rad)
Pin = -73.5 - 0.5 + 14 = -60 dBm
Repeater Output power (Uplink) :Pout(min) = Pin + Gmin(Repeater) = -60 + 45 = -15 dBmPout(min) = -15 dBm < 13 dBm (OK)
EIRP(Donor) = Pout - Cable(to antenna) + G(Re-Radiating)EIRP(Donor) = -15 - 1.5 + 18 = 1.5 dBmUplink Power Amp. Of repeater must be raised to maximum 75 dBEIRP (donor) = 1.5 + 30 = 31.5 dBm
RF Repeater : Powerbudget (3/3)
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Hybrid Combiners : Possible Usage
-3 dB
TX1 TX2
To Antenna
Matched Load
-3 dB -3 dB
-3 dB
TX1 TX2 TX3 TX4
To Antenna
50 Ω 50 Ω
50 Ω
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Hybrid Combiners : Features
Hybrid Combiners :4-Port Balanced Passive DevicesReciprocal : Tx/Rx
Disadvantage : High insertion loss : 3 to 3.3 dBNot suitable for large Number of Transmitters : High Losses
Advantage :Linear Device : Sufficient isolation between TransmittersCost-effective combining solution for small number of TransmittersBeing relatively Wide-band, permits Transmitter Frequency Hopping : Synthesized or Baseband
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Slow Frequency Hopping
Radio Propagation Channel :Dynamic : Mobility and Scattering problemsFast Fading : Frequency Selective (dispersive)
Some frequencies are more or less affected by Multipath fast fading (Reighley Fading)Fast Moving mobiles less sensitive to Multipath : GSM Standard define TU3 and TU50 and a Sensitivity margin of 4 dB is considered.Effective Receive Sensitivity improved for Fast Mobiles
Slow Frequency Hopping (SFH) :Allows an effective “Frequency Diversity”SFH statistically improves the overall signal receive powerSFH “diversity” gain : between 3 and 6 dB (ref. W.Y. Lee)
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Synthesized Frequency Hopping :The processor controlling the Tx retunes it to a new frequency on a per time-slot basis, according to a predetermined pattern or sequence
The Output from the Tx varies across a wide range of frequencies : Handled by the Hybrid combiner (wide-band device)
Baseband Frequency Hopping :The Digital baseband signal is applied to what is effectively a fast electronic switch, which is controlled by a processor in the Tx.The Switch is connected to a number of Txs, each being fixed-tuned to a different frequencyOn a per time-slot basis, baseband digital signal is switched between different transmittersCavity Filter Combiners or Hybrid Combiners can be used
Slow Frequency Hopping : Implementation
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Synthesized and Baseband Frequency Hopping : Comparison
Synthesized FH :Offers a versatile solution for multiple channelsCost-effective : No Cavity Filter Combiners requiredFew Transmitters can be used for more channels hopped
Baseband FH :Low losses when Cavity Filter Combiners are usedHopping can only occur over the same number of frequencies as there are Transmitters
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Slow Frequency Hopping : Implementation
Hybrid Combiner
TX1
TX2
TXProcessor
11001101110
0110110110
Tun
ning
Con
trol To Antenna
Varying Frequency
Varying FrequencyBaseband Data
Baseband Data
Synthesized Frequency Hopping
BasebandFrequency Hopping
TXProcessor
Baseband Data
11001101110
TX1
TX2
TX3
BPF
BPF
BPF
f1
f2
f3
To
An t
e nn a
ElectronicSwitch
Matching Stub
Cavity Filters
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Receiver Multicoupler
RECEIVER MULTICOUPLER
RX1 RX2
RxAntenna
A
RxAntenna
B
AC/DC POWERSUPPLY
RX A RX A RX BRX B
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DUPLEX FILTER
From TX To RX
Passes DLFrequencies only
Passes ULFrequencies only
DUPLEXFILTER
Common TX/RX Antenna
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Typical Antenna Connection : X-POL Diversity
DuplexFilter
ReceiverMulticoupler
Tx Rx
Tx Rx
HybridCombiner
Matched Load
Bandpass Filter
Tx/Rx A Rx B
Cross-PolarizedAntenna Assembly
Rx B
Rx A
Rx A
Rx B Rx A
Rx B
® Cirta Consulting LLC
Polarization Diversity SystemsUsing Separate Tx AntennaWithout Duplex Filter
d
RxARxBTx
BTS Equipment
Tx
2 Rx
2 Rx
2 Rx
Tx
Tx
Top View of 3-sector sitewith Vertical Polarization Diversity
® Cirta Consulting LLC
Polarization Diversity Systems
Duplexer
Tx Rx A Rx B
VerticalTx/Rx Antenna
HorizontalRx Antena
Tx/Rx
Tx/RxTx/Rx
® Cirta Consulting LLC
Polarization Diversity Systems
TxRx A Rx B
d1d2 d2
Horizontal separation d1 for diversity = 10λHorizontal Separation d2 for 30 dB Isolation = 2λ
Rx
Rx
Rx
Rx
Tx
Rx Tx
Tx