Cellular Mobile Course 2
Session 1
• Concept and history• Cell types and diversity techniques• Propagation phenomenon• Statistics of propagation channel• Propagation models• Adaptive model implementation• Cell planning• Error performance• Random access of network
Introduction to Cellular Mobile System
Cellular Mobile Course 3
Concept of Cellular Mobile System
• Subscriber access to the network and vice versa anywhere anytime
• Removing of wire limitation in access network• Increment of frequency spectrum reuse• Automatic roaming among home and foreign
PLMN, PSTN, ISDN and PDN networks• Providing wide speech and data services• Compatibility with the wireline networks
Cellular Mobile Course 4
Types of Cellular Mobile Systems
• Paging Systems– (Almost) unidirectional transmission of
alphanumeric messages to subscriber with unknown location
• Trunk Systems– Non-public bidirectional land mobile radio
network
• Cellular Mobile Systems– Public bidirectional land mobile system
2- LINE POCSAGALPHANUMERIC PAGER
Cellular Mobile Course 5
Worldwide Standard for Mobile
IMT2000 (3G)UMTS
GSM D AMPS CDMA PDCERMESDECTPHP
DSC1800
RMTS RC2000 C450 NMT900
D AMPS2
CT3CT2+
CT1+
CT1
City RUF
EURO SIGNAL NMT450i
E TACS
TACS
A
NAMTS
CT2
PCS 1900 PCSPHS1900
ARTS
B
NMT450
IMTS
AMPS
US Japan
GBDSWENORFIN
DFITA
Paging Europe
CT0
PLMN EuropeEuropeUS
CND
Analoge
Digital
PLMN PLMNCordless Telephony
1958
1974
1972
1981
1989
1984
1989
1991 1997
1994
1991
2002
1984
1986
1984
1991 1991
Cellular Mobile Course 6
Diversification Techniques
• FDMA/CDMA + FDMA/TDMA
• (FDMA/CDMA + FDMA/TDMA)/SDMA
Duplex separation
f0
f
FDMA
TS0 TS1 TSnt
Time slots in f0
o o o
TDMA
TS0
t
TS1
TSn
f0
f
TDMA/FDMA
Code 0
Code 1
Code n
f
CDMA
Code 0
Code 1
Code n
f1f2
f
FDMA/CDMA
Cellular Mobile Course 8
Propagation Phenomenon
• Regular free space and atmospheric gases loss• Fading
– Long term (shadowing): 12-60 m (1.2-6 s in 36km/h)– Short term: (8-15 cm)
• Multipath fading
• Dispersive fading– Delay spread
– Doppler spread
• Diffraction• Refraction• Reflection
*
2
1HEP
r
P
Point Source Radiation
Cellular Mobile Course 9
Free Space and Atmospheric Losses
102
10
10– 1
10– 2
1
2
5
5
2
5
2
5
2
5
Specific attenuation (dB/km)Specific attenuation (dB/km)
3.552 52 2102101Frequency, (GHz)
Pressure: 1 013 hPaTemperature: 15° C
Water vapour: 7.5 g/m3
Source: ITU-R P.676 Source: ITU-R P.676
H2O Dry Air
H2O Dry Air
• Major part of propagation loss
• AG loss is significant above 3GHz
• Dust and precipitation loss
24
d
L
Cellular Mobile Course 10
Diffraction
• Diffracting edge classification• Evaluation of diffraction loss
– Should be added to free space loss– Different models are available
Cellular Mobile Course 11
Refraction
• Beam bending along troposphere
• Non-homogenous propagation constant
• Modification of Earth radios to: kae
ae=3672 km
Actual path(k < 0)
Expected pathTransmitter
Earth Bulge
Actual path(k > 0)
Expected pathReceiver
ModifiedEarth Radios
Actual path
Cellular Mobile Course 12
Propagation over Flat Terrain
d
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Reflected wave
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)(52)( nattenuatiostrongspacefree
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4.33: TerrainIrregularFor
Cellular Mobile Course 13
• Different paths difference in nth Fresnel zone is equal to n×
• nth Fresnel zone radios:• Clearance criteria for LOS: C > 0.7
Fresnel Zone
)/( 2121 ddddnFn
F1
H
d1d2
Path ProfilePath Profile
Line of Sight1F
HC , (Signed)
Cellular Mobile Course 14
Propagation Channel
• Time Characteristics of Signal Envelope:
• Diversity receiver is necessary in sever condition (20 to 40 dB fading)
• Reflectors movement changes statistical conditions
• Distribution Density Function– No Line of Sight: Rayleigh Distribution
– Existing Line of Sight: Rice Distribution
)()()( trtmtr o
Short term characteristics
long term (lognormal distribution) characteristics
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arg
in
r1(t)r2(t)
r(t)
A
Selection Diversity
Signal Envelope of the Received Voltage
Cellular Mobile Course 15
Statistical Distributions
• Rayleigh Distribution, no LOS path
• Rice Distribution– rs
2 represents the power of direct wave
– rs=0 is Rayleigh Distribution
– rs is Gussian Distribution
655.0,2
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functionbesselisIrr
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0.2
0.3
0.4
0.5
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rP
(r)
0
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Parameter rs
1
Rayleigh Distribution
Rician Fading Signal
In phase
Quadrature-phase
Dominant Component
Cellular Mobile Course 16
Channel Condition: Dispersion
• Delay Spread– Different path length– RMS delay spread:
• Frequency (Doppler) Spread– Doppler Effect
cosv
f
t
ChannelImpulse Response
Speed v
2
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n
iii
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Pi: received level of path,
Cellular Mobile Course 17
Different Propagation Models
• Macro cell modelusing low-resolutiondata (M1)
• Small macro cellusing high-resolution data (M2)
• Micro cell modelsusing high-resolution data (M3)
• Outdoor-to-indoor models using high-resolution data (M4)• Indoor models using high-resolution data and their
extension to the indoor-to-outdoor scenario (M5)
Cellular Mobile Course 18
Applicable Propagation ModelModel GenericDescription
COST231-Hata M1
Hata M1
Walfisch-Bertoni M1, M2
COST231-Walfisch-Ikegami M1, M2, (M3)
Vehicular Test Environment M1, M2
GENERAL model (MOMENTUM model) M1
Basile’s Model M1, M2
Berg’s recursive street micro cell model M3
Wiart’s model M3
Jakoby’s model M3
Pedestrian Test Environment M3
Gonc¸alves Model M3
De Jong’s Model M5, M4
Mottley-Keynan-Model M5
Gahleithner-Bonek-Model M5
COST231-Berg Model M4
E-Plus hybrid prediction model for macro cells M1
E-Plus ray-tracing model for dense urban areas M2
Indoor coverage extension to E-Plus ray-tracing model M4
Cellular Mobile Course 19
Implementation of Models
• Several propagation models are necessary simultaneously
• Adaptive Model: The planning tool should switch between models automatically
• Accordingly, different DTM resolution should be applied,
Cellular Mobile Course 20
Adaptive Propagation Model
• Different models should be implemented in a single engineering tool
(simplified)
BS Location
BS in A2outdoor
BS in A2indoor
BS in A1outdoor
MS location and distance
Indoor to outdoor model
Macro-cell model
Outdoor to indoor model
Increment o decrement of model precision due to accessible map accuracy
Superposition of VPM/MPM/TPM predictions
Cellular Mobile Course 21
Indoor Statistical Model
• Taking into account attenuation and multipath with the complex elements of all paths
L: overall attenuation in dB, n: number of incoming paths
di: length of ith path, : wavelength
Rj: jth reflection factor of ith route, r: number of reflections on jth path,
Tk: kth transmission factor of ith route, t: number of reflections on kth path
n
i
d
i
ii
ed
L0
2
4log20
r
j
t
kkji TR
0 0
Attenuation:
Reflection and transmission effects:
Cellular Mobile Course 22
Indoor/Microcell Exact Model
• No approximation in radiated electromagnetic field• Ray tracing:
– Snell’s law,– Free space loss and Edge diffraction,– Reflection and transmission coefficient– Multiple reflection until signal vanish
Radiating station
Measured
direction
Simulation ComparisonFree Space Model
Measurement Ray Tracing Model
f = 900MHzf = 900MHz
Cellular Mobile Course 23
Okumura/Hata Model
• An empirical model based on long-term statistics (1962/63,65 Okumura and 1968 Hata)
• Measurement carried out in city area• Frequency Range: 500-2000 MHz• Transmitter height less than 200 m and
distance less than 20 km• Can be used for macro-cell planning if
combined with diffraction loss • Nowadays is more suitable for broadcasting
Cellular Mobile Course 24
Basic Sub-models
• Vertical PropagationPlane Model (VPM)
• Transversal PropagationPlane Model (TPM)
• Multi PathPropagationModel (MPM)
• Building PenetrationModel (BPM)
Vertical Plane Model (VPM)
Multipath Model (MPM)
BS
MS
Transversal Plane Model (TPM)
Cellular Mobile Course 25
Propagation Model Classification
Model VPM MPM TPMWalfisch-Bertoni ×COST231-Walfisch-Ikegami ×Vehicular Test Environment ×GENERAL model (MOMENTUM model) ×Basile’s Model ×Berg’s recursive street micro cell model × ×Wiart’s model × ×Jakoby’s model × ×Pedestrian Test Environment ×
Gonc¸alves Model × ×De Jong’s Model ×E-Plus ray-tracing model for dense urban areas × × ×Indoor coverage extension to E-Plus ray-tracing model × × ×
Cellular Mobile Course 26
Comparison of Different ModelsB
erg
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ecu
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reet
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ro c
ell
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, T
PM
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Wiart’s m
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od
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PM
, T
PM
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on
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del
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M, T
PM
)
Cellular Mobile Course 28
Outdoor to Indoor Propagation
• High resolution outdoor map is necessary,
• Distinguishing building locations digitally,
• No information for building interior structures is available,
• In case of low resolution map (worse than 5 m), penetration loss is enough
Calculate path loss at floor level
Calculate path loss at floor level
Is LOS pathIs LOS path
Calculate path loss at higher
levels empirically
Calculate path loss at higher
levels empirically
Calculate path loss at floor level using
penetration loss
Calculate path loss at floor level using
penetration loss
Is not LOS pathIs not LOS path
Calculate path loss at higher levels
empirically
Calculate path loss at higher levels
empirically
average
Example of Outdoor to Indoor Propagation
Cellular Mobile Course 29
Penetration loss
• Standard Deviation (SD) of signal level within a building is larger than outside (LOS, NLOS),
• For 1900 MHz:– in building 12 dB, SD = 10
dB– in car 7 dB, SD = 8 dB
• 1.5~2dB loss decrement for each level increment
• In human body 2~3 dB
Head Exposure against handset
Adult Child
Cellular Mobile Course 30
Indoor to Outdoor Propagation
• TX power is low,
• A simple method is enough,
• Total loss:
nwall×LWall + Loutdoor
– nwall: number of walls
– Lwall: loss of single wall
– Loutdoor: outdoor loss
Cellular Mobile Course 31
Scope of Radio Network Planning
• Investigation for feasible sites
• Selection of suitable BTS site
• Selection of suitable sectorization in a given site
• Determination of antenna type for each sector
• Calculation of antenna height and its tilt
• Allocation of enough power for pilot signal
Cellular Mobile Course 32
Cluster Size in Hexagonal Sys.
• Cluster size: N=i2 + ij + j2
• i and j are step size along orthogonal direction toward a co-channel cell
21
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Cellular Mobile Course 33
C/I & Interference Reduction Factor
• Minimum Co-channel Cells Distance:
• Unwanted signal:
• A trade off between channel number and cluster size
• Additional security distance is necessary
RND 3
R
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FFKNNII v
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Cluster size 3 4 7 9 12 13
D/R
C/I [dB]
3
11.3
3.464
13.8
4.58
18.66
5.20
20.85
6
23.34
6.24
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Cellular Mobile Course 34
C/I for Sectorized Cell Configuration
• Three sector configuration
• 2 to 3 interferer sectors rather than 6
R
D
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R
q
D
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D
R
I
C
kk
3
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interferers
Three interferers
Cellular Mobile Course 35
Cell Size Adaptation to Traffic
• There is trade off among cost, bandwidth and user density
• Population density with penetration rate produce user density
2015
10
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5
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2020
20
15
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Cell size and user density dependences
Cellular Mobile Course 36
Cell Coverage Overlap
• Adjacent cells overlap is necessary for supporting handover
• Hystersis level
• Site distances = 2d1+d2
BTS
BTSBTS
BTS
BTS
BTS
BTS
Site Select Level
Site Search Level
RF Signal Quality
Coverage Distance
Signal Strength Variation
Hysteresis Level
d2d1 d3
Cellular Mobile Course 37
Playing Variables in Cellular Traffic
• Call duration statistics,• Call rate, maximum number of calls per hour,• Handover statistics due to roaming,• Handover statistics due to fading,• Fresh call statistics,• Redial statistics for lost connections,• Channels number in cell/sectors,• Guard channels number,• Cell type and capacity assignment hierarchy
(reassignment),• Repetition of rejected handover requests
ch 1
…
ch n
ch 2
ch 1
…
ch m
ch 2
ch 3
Guard channels
Fresh calls
channels
Cellular Mobile Course 38
Blockage Probability: without roaming
• Without roaming:– Suitable for WLL system– Blockage probability of Fresh Calls: PBF
Total Blockage probability = PBF
– Traffical model obeys Erlang B, which is tabulated in technical documents
A: handled traffic in Erlang, n: number of channels
n
i
i
n
BF
iA
nAP
0
!/
!/
Mr. A.K. Erlang (1878-1929)
Cellular Mobile Course 39
Subscriber Traffic
• C: call rate per hour
• D: call duration in seconds
• Nominal values:– 30 ~ 70 mE in rural area– More than 100 mE in other locations
ErlangDC
ASub 3600
Cellular Mobile Course 40
Blockage Probability: with roaming
• As a basic model for cellular mobile
• N1 is number of channels for fresh calls
• N2 is number of additional cannels supporting roaming
• The capacity of cell in Erlang is:
• The number of accepted subscribers:
• Many accurate numerical models were provided
)],(),(),([5.0 2121 GOSNAGOSNNAGOSNAAcell
SubcellSub AAN /
Cellular Mobile Course 41
An Example
• Assumptions:– Traffic model: Erlang B– Grade Of Service: 0.02 (2%)– Call duration (average): 300 s– Call rate (peak): 2 in hour– Subscriber traffic:
300*2/3600 = 166.7 mE
45 ch.s
A=35.6 E,Users = 214
60 ch.s
A=49.6Users = 298
A = 7* 38.1 = 266.7 EUsers: 1600
6* 35.6 + 49.6 = 263.2 E Users: 1579
45 + 15 ch.s
A=38.1 E,Users = 228
Shared with neighbor cells
Cellular Mobile Course 42
Error Protection
• Necessity for error protection methods– Reduce of eliminate interference defects– Residual BER 10-2 for speech is tolerable– RBER for data should be lower than 10-7
• Methods of error protection– Error detection, (using checksum of cyclic codes
(CRC))– Error correction,
• Using FEC: Forward Error Correction,• Using ARQ: Automatic Repeat Request
– Error handling
Cellular Mobile Course 43
Forward Error Correction
• Addition of redundancy to a data word for correction of a certain number of errors
• Reverse channel is not necessary• Types of FEC:
– Linear block codes (systematic codes)– Convolutional codes (non-systematic codes)
• Puncturing
Data block
Code generator
Coded Data word
Data block
SystematicCode generator
Code Data block
Cellular Mobile Course 44
Automated Repeat Request
• Requesting for updating of corrupted codes
• Reverse ch. is needed for acknowledgement– Positive
acknowledgement ACK[NS]– Negative
acknowledgement NAK[NS]
• Transmitter should maintain a copy packet sent
4 5 6 7 8 9 5 6 7 8 9 o o o o o o
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Transmit window
Receive window
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4 5 6 7 8 9 5 1011 o o o o o o
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ecti
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ct
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Transmit window
Receive window
Cellular Mobile Course 45
Slotted-ALOHA Access Method
• Basic idea: in pure ALOHA usersare allowed to send data anytime
• The channel efficiency in pure ALOHA is 18%
• In slotted ALOHA users are permitted to send at beginning of time-slots (efficiency 36%)
Azim Fard
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t
collisionSlotted ALOHA
Time-Slots