Mobile Communication-Session 1

Cellular Mobile Course 1

Mobile Communication

By Azim Fard


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


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


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


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


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


Cell Classification

• Umbrella cell

Megacell

MacrocellMicrocell

Picocell


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


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


Diffraction

• Diffracting edge classification• Evaluation of diffraction loss

– Should be added to free space loss– Different models are available


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


Propagation over Flat Terrain

d

ggPP RTTR

1

4

2

d

h 1

h2

Reflected wave

2

221

d

hhggPP RTTR

)(52)( nattenuatiostrongspacefree

Sever Multipath

4.33: TerrainIrregularFor


• 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)


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

0 0.2 0.4 st

r(t)

0.01

0.1

1

10

100VMean

Threshold

Fad

e m

arg

in

r1(t)r2(t)

r(t)

A

Selection Diversity

Signal Envelope of the Received Voltage


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

}{,)(22

2

2 rrEer

rpr

functionbesselisIrr

Ier

rp os

o

rr s

),()(2

22

2

22

2 40 8 106

0.1

0.2

0.3

0.4

0.5

0.6

rP

(r)

0

1

2 4 6

Parameter rs

1

Rayleigh Distribution

Rician Fading Signal

In phase

Quadrature-phase

Dominant Component


Channel Condition: Dispersion

• Delay Spread– Different path length– RMS delay spread:

• Frequency (Doppler) Spread– Doppler Effect

cosv

f

t

ChannelImpulse Response

Speed v

2

1

2

1

1

)( d

n

iii

n

iirms PP

n

iii

n

iid PP

1

1

1

i : ith path delay, n: incoming paths

Pi: received level of path,


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)


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

Gonçalves 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


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,


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


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:


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


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


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)


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 ×

Gonçalves Model × ×De Jong’s Model ×E-Plus ray-tracing model for dense urban areas × × ×Indoor coverage extension to E-Plus ray-tracing model × × ×


Comparison of Different ModelsB

erg

’s r

ecu

rsiv

e st

reet

mic

ro c

ell

mo

del

(V

PM

, T

PM

)

Wiart’s m

od

el(V

PM

, TP

M)

Jako

by’

s m

od

el(V

PM

, T

PM

)G

on

çalves Mo

del

(VP

M, T

PM

)


Comparison of Different Sub-models

VPM MPM

TPM BPM


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


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


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


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


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

76

5

34

21

76

5

34

21

76

5

34

21

76

5

34

21

76

5

34

21

76

5

34

21

76

5

34

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

5

32

1

78

9

10

1112

4

6

52

31

23

1

23

12

31

23

1

23

1

23

1

32

2

33RAh

R


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

D

)10~5(,,1

FFKNNII v

K

kk

I

6,6

1

66

1

I

kk

KqD

R

D

R

I

C

1

6I

C

R

Dq

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

24.04


C/I for Sectorized Cell Configuration

• Three sector configuration

• 2 to 3 interferer sectors rather than 6

R

D

D

R

q

D

R

D

R

I

C

kk

3

1

33

1

1

3I

C

R

Dq Two

interferers

Three interferers


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

55

5

5

10

2020

20

15

10

15

15

15

15 15

2

2

15105

3

33

3

3

3

2

2

Cell size and user density dependences


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


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


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)


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


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 /


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


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


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


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

4 5 5 6 o o o o o o Go

-Bac

k-N

AC

KN

AK

Transmit window

Receive window

Sen

d-a

nd

-wai

t

NA

K

5 5 6 o o o o o o

5 5 6 o o o o o o

AC

K

Transmit window

Receive window

4 5 6 7 8 9 5 6 7 8 9 o o o o o o

4 5 6 7 8 9 5 1011 o o o o o o

Sel

ecti

ve-r

eje

ct

NA

K

Transmit window

Receive window


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

0216031190

Azim Fard

0216031190

Azim Fard

0216031190

Azim Fard

0216031190

Azim Fard

0216031190

tPure ALOHA

t

collisionSlotted ALOHA

Time-Slots


End of Session 1End of Session 1

Documents

Mobile Communication-Session 1