gsm bianchi
TRANSCRIPT
1
Giuseppe Bianchi
wireless networkswireless networks
Giuseppe BianchiGiuseppe Bianchi
Giuseppe Bianchi
CourseCourse outlineoutline
Part 1: cellular planning concepts
Part 2: GSM
Part 3: Wi-Fi
GPRS, UMTS (extra classes - TIM)
Extra time?
2
Giuseppe Bianchi
Wireless communicationWireless communication
Early wireless communication: in the 400-900 TeraHertz Band!
150 BC smoke signals (Greece)1794, optical telegraph, Claude Chappe
What is wireless communication:Any form of communication that does not require the transmitter and receiver to be in physical contactElectromagnetic wave propagated through free-space
Radar, RF, Microwave, IR, Optical
Giuseppe Bianchi
types of communicationtypes of communication
Simplexone-way communication
radio, TV, etc
Half-duplex: two-way communication but not simultaneous
push-to-talk radios, etc
Full-duplex: two-way communication
cellular phones
Frequency-division duplex (FDD)Time-division duplex (TDD): simulated full-duplex
3
Giuseppe Bianchi
Why wireless communication?Why wireless communication?
User MobilityReduced Cost (cheap infrastructure)
Cabling very criticalDeveloping nations utilize cellular telephony rather than laying twisted-pair wires to each home
FlexibilityCan easily set-up temporary LANs
Disaster situationsOffice moves
Only use resources when sending or receiving a signal
Giuseppe Bianchi
Why wireless different than Why wireless different than wired?wired?
Noisy, time-varying channelBER varies by orders of magnitudeEnvironmental conditions affect transmission
Shared mediumOther users create interferenceMust develop ways to share the channel
Bandwidth is limitedspectrum allocated by state rulesISM band for unlicensed use
4
Giuseppe Bianchi
History of wireless History of wireless communicationcommunication
1896: Marconi first demonstration of wireless telegraphy tx of radio waves to a ship at sea 29 km away long wave transmission, high power req. (200 kW and +)
1901: MarconiTelegraph across the atlantic oceanClose to 3000 Km hop!
1907 Commercial transatlantic connectionshuge ground stations (30 by100m antennas)
1915: Wireless telephony established NY – S. FranciscoVirginia and Paris
1920 Marconi:Discovery of short waves (< 100m)reflection at the ionosphere(cheaper) smaller sender and receiver, possible due to the invention of the vacuum tube (1906, Lee DeForest and Robert von Lieben)
Giuseppe Bianchi
History of wireless History of wireless communicationcommunication
1920's: Radio broadcasting became popular1928: many TV broadcast trials1930's: TV broadcasting deployment1946: First public mobile telephone service in US
St. Louis, MissouriSingle cell system
1960's: Bell Labs developed cellular conceptbrought mobile telephony to masses
1960’s: Communications satellites launchedLate 1970's: technology advances enable affordable cellular telephony
entering the modern cellular era1974-1978: First field Trial for Cellular System
AMPS, Chicago
5
Giuseppe Bianchi
1st generation mobile 1st generation mobile systemssystemsFirst generation: 1980’sSeveral competing standards in different countries
NMT (Nordic Mobile Telephone)Scandinavian standard; adopted in mostof EuropeFirst european system (Sweden, 1981)
TACS (Total Access CommunicationSystems), starts in 1985
UK standard; A few of Europe, Asia, Japan
AMPS (Advanced Mobile PhoneService)
US standardC-Netz (Only in Germany)Radiocom 2000 (Only in France)
Analog transmissionFrequency modulation
Various bands:NMT:
450 MHz first900 MHz later
TACS900 MHz
AMPS800 MHz
Today still in use in low-technology countries
And not yet completelydismissed in high-tech countries
Giuseppe Bianchi
2nd generation mobile 2nd generation mobile systemssystems
4 systemsGlobal System for Mobile (GSM)Digital AMPS (D-AMPS), USCode Division Multiple Access (IS-95) – Qualcomm,USPersonal Digital Cellular(PDC),Japan
GSM by far the dominant one
Originally pan-europeanDeployed worldwide
(slow only in US)
Basic bands:900 MHz1800 MHz
(Digital Cellular System: DCS-1800)
1900 MHz(Personal CommunicationSystem:PCS-1900,US only)
Specifications forGSM-400 (large areas)GSM-800 (north america)
6
Giuseppe Bianchi
TimingTiming1982: Start of GSM-specification in Europe (1982-1990)1983: Start of American AMPS widespread deployment1984 CT-1 standard (Europe) for cordless telephones1991 Specification of DECT
Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications)
- ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication
1992: Start of GSM operation Europe-wide1994: DCS-1800
Giuseppe Bianchi
2 ½ generation mobile 2 ½ generation mobile systemssystemsGSM GSM incrementalincremental extensionextension
High speed circuit switched data (HSCSD)
Circuit switched data communicationUses up to 4 slots (1 slot = 9.6 or 14.4 Kbps)
General Packet Radio Service (GPRS)Packet data (use spectrum only when needed!)dial-up comparable speed
Enhanced Data-rates for Global Evolution (EDGE)
Higher data rate available on radio interface (3x)» Up to 384 Kbps (8 slots)» Thanks to new modulation scheme (8PSK)» May coexist with old GMSK
7
Giuseppe Bianchi
3rd generation mobile 3rd generation mobile systemssystems
UMTS (Universal Mobile TelecommunicationSystem)
ITU standard: IMT-2000 (International Mobile Telecommunication – 2000)UMTS forum created in 1996Later on 3GPP forum (bears most of standardization activities)
Wideband CDMA radio interfaceBut several other proposals accepted as“compatible”
Radio spectrum: 1885-2025 & 2110-2200 MHz
Giuseppe Bianchi
History of Wireless DataHistory of Wireless DataEarly Wireless LAN proprietary products
WaveLAN (AT&T) - the ancestor of 802.11HomeRF (Proxim)
45% of the home network in 2000; 30% in 2001, … ε% todayAbandoned by major chip makers (e.g. Intel: dismissed in april 2001)
IEEE 802.11 Committee formed in 1990Charter: specification of MAC and PHY for WLAN
First standard: june 19971 and 2 Mbps operation
Reference standard: september 1999Multiple Physical Layers
2.4GHz Industrial, Scientific & Medical shared unlicensed band » Legacy; 802.11b/g
5 GHz ISM (802.11a)1999: Wireless Ethernet Compatibility Alliance(WECA) certification
Later on named Wi-FiBoosted 802.11 deployment!!
8
Giuseppe Bianchi
WLAN speedsWLAN speeds
802.11a: PHY for 5 GHz
802.11b: higher rate PHY for 2.4 GHz
802.11g: OFDM for 2.4 GHz
802.11n: ??? (Higher data rate)Launched in september 2003Minimum goal: 108 Mbps (but higher numbers considered)
Giuseppe Bianchi
Why so much talking about of Why so much talking about of 802.11 today?802.11 today?
802.11: no more “just” a WLANHot-spots
Where the user goes, the network is available: home, school, office, hotel, university, airport, convention center…Freedom to roam with seamless connectivity in every domain, with single client device
May compete (complement) with 3G for Wireless Internet access
Which of these two is the proper (closer) picture
of Wireless Internet andMobile Computing?
Which technology is most suited?
9
Giuseppe Bianchi
WLAN Market WLAN Market -- HotSpotsHotSpots U.S. Commercial Hotspots
2001-2002: exceeded expectations by 14%
1.500
2.000
2.500
3.000
3.500
4.000
4.500
2001 2002
Forecasted Actual
0
10000
20000
30000
40000
50000
2002 2004 2006
U.S. Hotspots growth (2002-2006)
Unique U.S. Hotspots
2003: 125.000 regular hotspot US usersEnd 2006: 9 Million regular hotspot US usersEnd 2006: 1 Billion dollars revenue predicted from HotSpot operation
Giuseppe Bianchi
The global pictureThe global pictureWide Area
Local Area
Personal Area LAN:collection of secure
“hot spot” connections, providing broadband access to
the Internet
PAN:collection of secure
connections between devices in a
“very” local area
BT/802.11switching
WAN:everywhere outside of
the hotspots, where wireless Internet connection are
provided802.11/UMTSswitching
Bluetooth< 800 Kb/s 10 m
Mobile Broadband InternetIEEE 802.11 (b)
> 10 Mb/s 100 m
GPRS, 3G – UMTS< 400 Kb/s Kms
1
Giuseppe Bianchi
PART 1PART 1Propagation Characteristics of Propagation Characteristics of
Wireless Channels Wireless Channels
Lecture 1.1Basic concepts and
terminology
Giuseppe Bianchi
The Radio SpectrumThe Radio Spectrum
Radio waveWavelength λ = c/f Speed of light c=3x108 m/sFrequency: f
( )ϕπ += ftAts 2cos)(
λ
ff = 900 MHz λ = 33 cm
[V|U|S|E]HF = [Very|Ultra|Super|Extra] High Frequency
2
Giuseppe Bianchi
The radio spectrumThe radio spectrum
Optical communications400-900 THzLightLAN infrared, consumer electronics300 GHz – 400 THzIRExperimental, WLL30-300 GHzEHFSatellite, radar, terrestrial wireless links, WLL3-30 GHzSHFCellular, TV UHF, radar300 MHz - 3 GHzUHFTV VHF, FM radio, AM x aircraft commun.30-300 MHZVHFAmateur radio, military, long-distance aircraft/ships3-30 MHzHFAM radio, marine radio300 KHz –3 MHzMFLong-range, marine beacon30-300 KHzLFSubmarine, long-range3-30 KHzVLFRemote control, Voice, analog phone<3 KHzELF
Giuseppe Bianchi
Attenuation phenomena for Attenuation phenomena for millimeter waves (EHF)millimeter waves (EHF)
Impairments due to-Oxygen- water vapour
3
Giuseppe Bianchi
Spectrum AllocationSpectrum Allocation
Cellular systems400-2200 MHz range (VHF-UHF)Simple, small antenna (few cm)With less than 1W transmit power, can cover several floors within a building or several miles outside
SHF and higher for directed radio links, satellite communication
Large bandwidth availablewireless data systems
2.4, 5 GHz zones (ISN band)Main interference from microwave ovenslimitations due to absorption by water and oxygen - weather dependent fading, signal loss due to by heavy rainfall etc.
Giuseppe Bianchi
HigherHigher--lower Frequencieslower Frequencies
Higher frequencies: more bandwidth less crowded spectrumbut greater attenuation through walls
Lower frequenciesbandwidth limitedlonger antennas requiredgreater antenna separation requiredseveral sources of man-made noise
4
Giuseppe Bianchi
AntennasAntennas
Transmission and reception are achieved by means of an antennaAn antenna is an electrical conductor or system of conductors
Transmission - radiates electromagnetic energy into spaceReception - collects electromagnetic energy from space
In two-way communication, the same antenna can be used for transmission and reception
Giuseppe Bianchi
Antenna GainAntenna GainIsotropic antenna (idealized)
Radiates power equally in all directions (3D)Real antennas always have directive effects (vertically and/or horizontally)
Antenna gainPower output, in a particular direction, compared to that produced in any direction by a perfect omni-directional antenna (isotropic antenna)
Directional antennas “point” energy in a particular direction
Better received signal strengthLess interference to other receiversMore complex antennas
d distance aat density power mean radiation maximum ofdirection in the d distance aat density power Dy Directivit =
2T 4/P
radiation maximum ofdirection in the d distance aat density power G Gain dπ
=
5
Giuseppe Bianchi
Radiation PatternsRadiation Patterns
Graphical representation of radiation properties of an antennaDepicted as two-dimensional cross section
side view (xy-plane)
x
y
side view (yz-plane)
z
y
top view (xz-plane)
x
z
simpledipole
side view (xy-plane)
x
y
side view (yz-plane)
z
y
top view (xz-plane)
x
z
directedantenna
Giuseppe Bianchi
Base stations in cellular Base stations in cellular systemsystem
Often sectorized antennas used
top view, 3 sector
x
z
top view, 6 sector
x
z
sectorizedantenna
6
Giuseppe Bianchi
Three means of propagation Three means of propagation
Ground wave propagationsky wave propagation
IonosphericLine of Sight propagation
Giuseppe Bianchi
Ground Wave PropagationGround Wave Propagation
0-2 MHz (e.g. AM radio)follows contour of the earth (no need for LOS)
Bending by: current induced on earthBending by: atmospheric diffraction
Very long distancesBut signal dies off rapidly: need much power
reflection, refraction and scattering by objects on the ground
7
Giuseppe Bianchi
2-30 MHz (HF) Signal reflected from ionized layer of atmosphere back down to earth (actually, rifracted)Signal can travel a number of hops, back and forth between ionosphere and earth’s surface
By repeated reflection, communication can be established over 1000s of kmExamples: amateur radio, CB radio, International Broadcasting
IonosphericIonospheric or or Sky Wave Sky Wave PropagationPropagation
Giuseppe Bianchi
LineLine--ofof--Sight PropagationSight Propagation
Transmitting and receiving antennas must be within line of sight
Satellite communication – signal above 30 MHz not reflected by ionosphereGround communication – antennas within effective line of site (radio horizon) due to refraction (bending of wave in the lower atmosphere)
8
Giuseppe Bianchi
Radio horizonRadio horizon
Optical horizon Radio
horizon
][],[3/457.3:
57.3:
mhKmdKhKdhorizonradio
hdhorizonoptical
==≈⋅=
=
Giuseppe Bianchi
Antennas heightAntennas height reqsreqs(examples)(examples)
Antenna = 100m, K=4/3D = 41.2 Km (radio horizon)
Receiver antenna = 10m
D = 54.26
hr = 10m, d=41.2, ht=?ht = 46.75
( )rt hKhKd ⋅+⋅= 57.3
9
Giuseppe Bianchi
Propagation impairmentsPropagation impairments
Line of sight
Reflection
Shadowing
Giuseppe Bianchi
Propagation impairmentsPropagation impairments
DiffractionWhen the surface encountered has sharp edges
bending the wave
ScatteringWhen the wave encounters objects smaller than the wavelength (vegetation, clouds, street signs)
BS
MS
BS
10
Giuseppe Bianchi
Signal attenuationSignal attenuationSignal power
Distance BS MS
Giuseppe Bianchi
MultipathMultipath CharacteristicsCharacteristics(not just attenuation)(not just attenuation)
A signal may arrive at a receivermany different timesFrom many different directions
due to vector addition, signal mayReinforceCancel
signal strength differsfrom place to placefrom time to time!
(slow/fast fading)
11
Giuseppe Bianchi
Slow fading Slow fading –– fast fadingfast fadingSignal power
Distance BS MS (km)
Distance BS MS (m)
Giuseppe Bianchi
Radio Signal FadingRadio Signal Fading
T
Si g
nal s t
ren
gt h
(d
B)
Time
Long term fading
Short term fading
12
Giuseppe Bianchi
PART 1PART 1Propagation Characteristics of Propagation Characteristics of
Wireless Channels Wireless Channels
Lecture 1.2Attenuation models
Giuseppe Bianchi
Power units Power units -- decibeldecibel
Decibel (dB): logarithmic unit of intensity used to indicated power lost or gained between two signalsNamed after Alexander Graham Bell.
( )21 /log10 PPPA = 1 WattPB = 50 milliWatt
PA = 13 dB greater than PB
13
Giuseppe Bianchi
Decibels Decibels -- dBmdBmdBm = absolute value (reference= 1mW)
Power in dBm = 10 log(power/1mW)Power in dBW = 10 log(power/1W)
» Not much used by us 1dBW=30dBm
Examples10 mW = 10 log10(0.01/0.001) = 10 dBm10 µW = 10 log10(0.00001/0.001) = -20 dBm26 dBm = ___ 2W= ___ dBm?S/N ratio = -3dB S = ___ X N?
Properties & conversionsdBm = 10 log10(P (W) / 1 mW) = P (dB) + 30 dBmP1 * P2 (dBm) = P1 (dBm) + P2 (dB)P1 * P2 (dBm) = 10 log10(P1*P2 (W)/0.001) = 10log10(P1/0.001) + 10 log10P2 = P1 (dBm) + P2 (dB)
Giuseppe Bianchi
Computation with dBComputation with dB
Transmit powerMeasured in dBm
Es. 33 dBm
Receive PowerMeasured in dBm
Es. –10 dBm
Path LossReceive power / transmit powerMeasured in dBLoss (dB) = transmit (dBm) – receive (dBm)
Es. 43 dB = attenuation by factor 20.000
14
Giuseppe Bianchi
Attenuation model for LOSAttenuation model for LOS
Direct path between transmitter and receiver
unobstructed Line-Of-Sight (LOS)Radio signal behaves like light in free space (straight line)
Receive power:In absence of obstacles, received power follows inverse square law
(d = distance between sender and receiver)
2)( −∝ ddPr
Giuseppe Bianchi
free space model free space model –– ideal antennasideal antennas
Isotropic (omnidirectional)tx antenna in free space
Transmitted power: Pt
Power attenuation Pa at distance d:down with sphere superficies
Power received by isotropic rx antenna
Planar waveAe = Effective Area
24)(
dPdP t
a π=
πλ4
)()(2
=
=
e
ear
A
AdPdP
r
15
Giuseppe Bianchi
free space model free space model –– real antennasreal antennas
Non isotropic tx antennaAntenna gain Gt
Non isotropic rx antennaAntenna gain Gr
r
24)(
dPGdP tt
a π=
πλ
π 44)()(
2
2 rtt
erar GdGPAGdPdP ==
Giuseppe Bianchi
FriisFriis FreeFree--Space ModelSpace Modelsummarizing all previous considerationssummarizing all previous considerations
Pt = transmitter power (W or mW)
Gt = transmitter antenna gainGr = transmitter antenna gain
(dimensionless)λ = c/f = RF wavelength (m)
c = speed of light (3x108 m/s)f = RF frequency (Hz)
2
22
2
4)4()( ⎟⎟
⎠
⎞⎜⎜⎝
⎛==
fdc
LGGP
LdGGPdP rt
trtt
r ππλ
[ ] [ ]Ld
GGdBmPdBmdP rttr
10101010
1010
log10log20)4(log20log20log10log10)(
−−−+++=
πλ
0>d
Pt Gt = Equivalent Isotropic Radiated Power (EIRP)L = other system losses (hardware)
L >=1 (dimensionless) d = distance between transmitter and receiver (m)
16
Giuseppe Bianchi
ExampleExamplenormalized
frequency [MHz] 900 900000000speed of light [Km 300000 300000000lambda (m) 0,333333333gain Tx 1Gain Rx 1Loss 1Ptx [W] 5distance (Km) Prx W Prx dBm
200 8,80E-08 -40,56400 2,20E-08 -46,58600 9,77E-09 -50,10800 5,50E-09 -52,60
1000 3,52E-09 -54,541200 2,44E-09 -56,121400 1,79E-09 -57,461600 1,37E-09 -58,621800 1,09E-09 -59,642000 8,80E-10 -60,562200 7,27E-10 -61,392400 6,11E-10 -62,142600 5,20E-10 -62,842800 4,49E-10 -63,483000 3,91E-10 -64,083200 3,44E-10 -64,643400 3,04E-10 -65,173600 2,71E-10 -65,663800 2,44E-10 -66,134000 2,20E-10 -66,584200 1,99E-10 -67,004400 1,82E-10 -67,414600 1,66E-10 -67,794800 1,53E-10 -68,165000 1,41E-10 -68,52
-70,00
-60,00
-50,00
-40,00
-30,00
0 1000 2000 3000 4000 5000
distance (m)
rece
ived
pow
er (d
Bm)
Giuseppe Bianchi
Path Loss (propagation loss) Path Loss (propagation loss) positive value in dBpositive value in dB
[ ]
56.147log10log20log20
4log20log10log20log20
4log20log10log20
4log10log10)(
101010
10101010
101010
2
1010
−−+=
=−−+=
=−−=
=⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛==
LGGfd
cLGGfd
LGGd
dGGL
PPdPL
rt
rt
rt
rtr
tdB
π
πλ
λπ
17
Giuseppe Bianchi
Free space lossFree space losssame as path loss, but part due to attenuationsame as path loss, but part due to attenuation
in free space only (in dB)in free space only (in dB)
[ ]
56.147log20log204
/log204
log20)(
1010 −+=
⎥⎦⎤
⎢⎣⎡−=⎥⎦
⎤⎢⎣⎡−=
fddfc
ddL dBfree ππ
λ
2
4)(
−
⎟⎠⎞
⎜⎝⎛=
ddLfree π
λ
Giuseppe Bianchi
Reference distanceReference distance
If known received power at a reference distance dofrom tx
can calculate Pr(d) for any d
Must be smaller than typical distances encountered in wireless communication systems;Must fall in the far-field region of the antenna
So that losses beyond this point are purely distance-dependentTypical d0 selection: 100-1000m
2
)()( ⎟⎠⎞
⎜⎝⎛=
dddPdP o
orr
⎟⎠⎞
⎜⎝⎛+=⎟
⎠⎞
⎜⎝⎛+=
dddBmdP
dddPdBmdP o
oro
orr 101010 log20))((log20)(log10)()(
18
Giuseppe Bianchi
ExampleExample
d0 = 100m, for previous example
dBm
dLGGdBmPdBmdP rt
tr
5,341200
1log2005log1030
4log20log10)()()(
1010
10100
−=+++=
=++=
π
πλ
Pr(1000m)
dBmdBdBmdddPmP rr
5,54205,34
log20)()1000( 0100
−=−−=
=+=
Giuseppe Bianchi
Reference distance + frequencyReference distance + frequency
Similarly, one may evaluate received power at a reference distance do from tx and a reference frequency f0
( )
[ ] ( ) ( )dfdBmfdPfddf
LdfcGGP
LdGGPfdP
r
rttrttr
101000
200
20
2
20
22
2
log20log20),()4(
/)4(
),(
−−=
=⎟⎟⎠
⎞⎜⎜⎝
⎛⋅==
ππλ
[where f and d are measured in multiple of - f0 (typically 1 MHz)- d0 (typically 1 m or 1Km)
19
Giuseppe Bianchi
More realistic propagation More realistic propagation modelsmodels
Inverse square power lawWay too optimistic (ideal case)Real world: η-th power law
with η ranging up to as much as η=7If tough environment (e.g., lots of foliage),
typical values: η=2 for small distances (20 dB/decade)η=3 to η=4 (40 dB/decade) for mobile telephone distances
η higher in cities and urban areas; η lower in suburban or rural areas.
η−∝ ddPr )(
Giuseppe Bianchi
Extended formulaeExtended formulae
⎟⎠⎞
⎜⎝⎛+=
dddPdBdP o
orr 1010 log10)(log10)()( ηd_ref 1 KmP_ref -51,5266 dBm (Ptx=10W; 900 MHz; 1000m)
distance prx (eta=2)prx (eta=3,5) prx (eta=4)1 -51,5266 -51,5266206 -51,5266
1,2 -53,1102 -54,2979642 -54,69391,4 -54,4492 -56,6411018 -57,37171,6 -55,609 -58,67082 -59,69141,8 -56,6321 -60,4611582 -61,7375
2 -57,5472 -62,0626704 -63,56782,2 -58,3751 -63,5114144 -65,22352,4 -59,1308 -64,834014 -66,73512,6 -59,8261 -66,0506877 -68,12562,8 -60,4698 -67,1771517 -69,4129
3 -61,069 -68,2258645 -70,61153,2 -61,6296 -69,2068698 -71,73263,4 -62,1562 -70,1283827 -72,78583,6 -62,6527 -70,9972081 -73,77873,8 -63,1223 -71,8190464 -74,718
4 -63,5678 -72,5987203 -75,6094,2 -63,9916 -73,3403457 -76,45664,4 -64,3957 -74,0474642 -77,26474,6 -64,7818 -74,7231447 -78,03694,8 -65,1514 -75,3700639 -78,7763
5 -65,506 -75,9905707 -79,4854
-85-80-75-70-65-60-55-50
1 2 3 4 5distance (Km)
rece
ived
pow
er (d
Bm
)
η=2η=3,5η=4
20
Giuseppe Bianchi
Realistic scenariosRealistic scenariosobstructions between the transmitter and receiver
reflection, diffraction, scatteringPropagation strongly influenced by environment (building characteristics, vegetation density, terrain variation)Perfect conductors reflect waves; nonconductors absorb some energy
wave traverses multiple pathsRadio waves arrive at receiver from different directions and with different time delays
Resultant signal at receiving antenna is vector addition of incoming signals
signals can add constructively (resultant signal has large power) or destructively (resultant signal has small power) depending on relative phases
Software tools needed to analyze complex specific scenarios (ray-tracing)
Giuseppe Bianchi
Example scenarios: Example scenarios: LOS path non necessarily existing (and unique)LOS path non necessarily existing (and unique)
diffraction
reflection
Example: city with large buildings; No LINE OF SIGHT;Diffraction; reflection
21
Giuseppe Bianchi
Example scenariosExample scenariosLINE OF SIGHT +
Diffraction, reflection, scattering
LOS
Giuseppe Bianchi
TwoTwo--Ray Ground Ray Ground Propagation ModelPropagation Model
Theoretical foundation for η=4Two-ray model assumes one direct LOS path and one reflection path reach receiver with significant powerEasy to solve
ht
hr
Line-Of-Sight ray
reflected ray
Transmit and receive antennas at different height (in general)
22
Giuseppe Bianchi
TwoTwo--ray model ray model –– geometrygeometry
hr
ht
(θ θ)
ddirect
dreflect
rt hhd ,>>
( )
( )⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ +
+≈⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ +
+=++=
⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ −
+≈⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ −
+=−+=
22/1222
22/1222
2111
2111
dhhd
dhhdhhdd
dhhd
dhhdhhdd
rtrtrtreflect
rtrtrtdirect
Giuseppe Bianchi
Two ray model Two ray model –– path analysispath analysis
EM waves travel for different distanceSum up with different phase!
A = attenuation along direct pathB = attenuation along reflected path (reflection not ideal, in general)
dhh
dhhd
dhhddd rtrtrt
directreflect 2211
211
22
=⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ −
+−⎪⎭
⎪⎬⎫
⎪⎩
⎪⎨⎧
⎟⎠⎞
⎜⎝⎛ +
+≈−
⎥⎦
⎤⎢⎣
⎡⎟⎟⎠
⎞⎜⎜⎝
⎛−∝
⎥⎦
⎤⎢⎣
⎡⎟⎠⎞
⎜⎝⎛ −∝
cd
tfB
cdtfA
reflect
direct
π
π
2cosrayreflect
2cosraydirect
23
Giuseppe Bianchi
Two ray model Two ray model –– field strengthfield strengthPhase difference
Received field strength
Let Edirect be the field strength given by direct ray.Then
Assume ideal reflection (ρ=-1)
dhhd
cdf rt
λπ
λππϕ 422 =∆=
∆=∆
[ ]ϕρ ∆−+= jdirect eEE 1
[ ] [ ][ ]
2sin2
2cos12
sincos2cos1sincos11
2/122
ϕϕϕϕϕ
ϕϕϕ
∆=
∆−=
=∆+∆−∆+=
∆+∆−=−= ∆−
directdirect
direct
directj
direct
EE
EEjEeEE
Giuseppe Bianchi
Two ray model Two ray model –– power power computationcomputation
Received power
Proportional to |E|2
⎟⎠⎞
⎜⎝⎛⋅⎟
⎠⎞
⎜⎝⎛⋅=
dhh
dLGGPdP rtrtt
r λπ
πλ 2sin4
4)( 2
2
( )2/sin4 2 ϕ∆∝ directr EP
24
Giuseppe Bianchi
Two ray model Two ray model -- conclusionconclusion
Typical values:ht ~ few tens of mhr ~ couple of metersλ ~ few tens of cmd ~ hundred meters – few km
22 22sin2
⎟⎠⎞
⎜⎝⎛≈⎟
⎠⎞
⎜⎝⎛⇒≈
dhh
dhhsmall
dhh rtrtrt
λπ
λπ
λπ
4
2222 244
)(dhh
LGGP
dhh
dLGGPdP rtrttrtrtt
r ⋅=⎟⎠⎞
⎜⎝⎛⋅⎟
⎠⎞
⎜⎝⎛⋅≈
λπ
πλ
i.e. attenuation follows a 40 dB/decade rule! Versus 20 dB/decade of the free-space model
4)( −∝ ddPr
Giuseppe Bianchi
Design notesDesign notes
Typical assumptions for initial system developement
η=2 power law attenuation for small distancesFree space model
η=4 power law attenuation for large distancesLOS + reflected ray model
Cross-over distance when d >> ht+hr(e.g., d > 10(ht + hr))
25
Giuseppe Bianchi
Empirical modelsEmpirical models
Consider specific scenarios Urban area (large-medium-small city), rural areaModels generated by combining most likely ray traces (LOS, reflected, diffracted, scattered)Based on large amount of empirical measurements
Account for parametersFrequency; antenna heights; distance
Account for correction factors (diffraction due to mountains, lakes, road shapes, hills, etc)
First model: Okumura, 1968VERY complex due to many specific correction factors!
Giuseppe Bianchi
OkumuraOkumura--HataHata modelmodel
Hata (1980): very simple model to fit Okumura resultsProvide formulas to evaluate path loss versus distance for various scenarios
Large cities; Small and medium cities; Rural areasLimit: d>=1km
Parameters:
f = carrier frequency (MHz)d = distance BS MS (Km)hbs = (effective) heigh of base station antenna (m)hms = height of mobile antenna (m)
Effective BSAntenna height
26
Giuseppe Bianchi
OkumuraOkumura--HataHata: urban area: urban area
( )( )msbs
bs
path
hahdh
fdBL
−−+−+
++=
10
1010
10
log82.13loglog55.69.44
log16.2655.69)(
a(hms) = correction factor to differentiate large from medium-small cities; depends on MS antenna height
( ) ( )[ ]( ) [ ] [ ]8.0log56.17.0log1.1:cities med-small
40097.475.11log2.3:cities large
1010
210
−−−=≥−=
fhfhaMHzfhha
msms
msms
Very small correction difference between large and small cities (about 1 dB)
Giuseppe Bianchi
OkumuraOkumura--HataHata: suburban & : suburban & rural areasrural areas
Start from path loss Lp computed for small and medium cities
[ ] 94.40log33.18log78.4)(:rural
4.528
log2)(:suburban
102
10
2
10
−+−=
−⎥⎦⎤
⎢⎣⎡−=
ffLdBL
fLdBL
ppath
ppath
27
Giuseppe Bianchi
OkumuraOkumura--HataHata: : examplesexamples
80
90
100
110
120
130
140
150
0 1 2 3 4 5 6 7 8 9 10
distance (km)
path
loss
(dB
)
large citiessmall citiessuburbsrural area
F=900MHz, hbs=80m, hms=3m
Giuseppe Bianchi
OkumuraOkumura--HataHata and and ηη
Coefficient of Log(d) depends only on hbs
10η = attenuation (dB) in a decade (d=1 d=10)
The higher the BS, the lower the coefficient η
30
32
34
36
38
40
42
44
0 20 40 60 80 100 120 140
base station height (m)
10η
28
Giuseppe Bianchi
Other empirical modelsOther empirical modelsLee’s model
Use at 900MHZFor distances > 1kmBased on measurements taken in three cities (including Philadelpia)More complex than Okumura-Hata
Walfish-Ikegami modelFor frequency range 800-2000 MHzValid for microcellular distances (20m – 5 km)Adopted by European Cooperation in the field of Scientific and Technical (COST) research as reference model for 3G systems
Indoor propagation modelsInclude attenuation factors due to building penetrationAccount for number of walls, floors, reflection loss, etcBased on zones (large zone, middle zone, small zone, microzone)
Giuseppe Bianchi
PART 1PART 1Propagation Characteristics of Propagation Characteristics of
Wireless Channels Wireless Channels
Lecture 1.3fading models
29
Giuseppe Bianchi
Statistical Statistical nature of nature of received received powerpower
Si g
nal s t
ren
gt h
(d
B)
Time (or movement)
Long term fading
Short term fading
Mean value predictedby attenuation model (constant at given )
Giuseppe Bianchi
MultipathMultipath: short : short term term fadingfadingShort-term fading
Also: multipath fadingAlso: small-scale fadingAlso: fading
Generated by superposition of same signal travelling along many pathsReceived signal:
f0=carrier frequencyN=number of pathsak,φk=amplitude & phase of component k
BS
( )kN
k kr tfate φπ += ∑ = 012cos)(
Phase depends on path length Multipath fading consequencesSmall movements of tx or rx (order of ½λ)
change interference pattern drastic fluctuations in signal strength due to constructive/destructive interference
15-20 cm for 900 MHz
30
Giuseppe Bianchi
Multipath analysisMultipath analysis
( ) =+= ∑ = kN
k kr tfate φπ 012cos)(
( ) ( )( ) ( )tfYtfX
atfatf kN
k kkN
k k
00
1010
2sin2cos
sin2sincos2cos
ππ
φπφπ
−=
=−= ∑∑ ==
( )( ) ( ) ( ) ( )kk
k
tftftf
φπφπφπ
sin2sincos2cos2cos: thatrecall
00
0
−==+
In the assumptions:- N large (many paths)- φk uniformly distributed in (0,2π)- ak comparable (no privileged path such as LOS)
X,Y are gaussian, identically distributed random variables22 YX + Rayleigh distributionSignal envelope:
Giuseppe Bianchi
Rayleigh distributionRayleigh distribution
=)(xfa
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0 1 2 3 4 5
amplitude
prob
abili
ty d
istri
butio
n
sigma2=1sigma2=2sigma2=4
[ ] σπσσ
σ 253.120
22
22
==⋅= ∫∞
−xexxaE
[ ] 222
0
22
2 4292.02
22
22
σπσπσσ
σ =⎟⎠⎞
⎜⎝⎛ −=−⋅= ∫
∞−x
exxaVar
σ2 = variance of X and YGaussian r.v.
( ) =+<≤= dxxaxPr2
2
22
σ
σ
xex −
=
31
Giuseppe Bianchi
Signal Signal powerpower
Average power:2σ2 (average over time)
Instantaneous powerRandom variable, with:
probability density function:
Probability distribution function:
ondistributi lexponentia::powerondistributirayleigh ::amplitude
222
22
YXapYXa
+==
+=
( ) 2222
1 σ
σ
x
p exf−
=
( ) 221 σx
p exF−
−=
Giuseppe Bianchi
Outage probabilityOutage probability
Probability that received power is lower than a given threshold
Below which signal cannot be correctly received
Average received power P0 (= 2σ2)Minimum power threshold γ
( ) 01)Pr(:yprobabilit outage Pp eFp
γ
γγ−
−==≤
Example 1: average power=100 µW; lower threshold=15µW;
Outage probability= 1-exp(-15/100) = 13,9%
Example 2: average power= -13 dBm; lower threshold=-30 dBm;
Outage probability= 1-exp(-1/50) = 1,98%
32
Giuseppe Bianchi
LongLong--term term fadingfading
Signal multiply reflected and/or scattered before taking multiple paths to the receivermovements large enough change wave pathResult: long-term fading
= lognormal fading= shadowing
Giuseppe Bianchi
LongLong--term term fading fading statisticsstatisticslognormal distributionlognormal distribution
Y = 0 mean gaussian r.v. with standard deviation σdB dB Probability distribution (in dB):
YdddPdBdP o
orr +⎟⎠⎞
⎜⎝⎛+= 1010 log10)(log10)()( η
( )2
2
2
21)( dB
avdB Pp
dBdBY epf σ
σπ
−−
⋅=
33
Giuseppe Bianchi
LongLong--term term fading and fading and attenuation attenuation plotplot
attenuation: η=4 after 100m; η=2 before 100m
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
distance (m)
rece
ived
pow
er (d
Bm
)
no shadowingsigma=3 dBsigma=8 dB
Giuseppe Bianchi
Outage probability examplesOutage probability examplesaverage received power (dBm) -80lognormal stdandard deviation (dB) 6
outage threshold outage prob-86 15,87%-88 9,12%-90 4,78%-92 2,28%-94 0,98%-96 0,38%-98 0,13%
-100 0,04%
Excel computation:( )VEROstddev,med,thr,RMDISTRIB.NO=
General case computation:1) Convert to normal st. distr
0
02
>−=
<−
=
γσ
γ
g
Pthr
dB
av
2) Evaluate Prob[-g,g]==Erf(g)=-Erf(γ)
3) Outage = (1-Erf(g))/2 == Erfc(g)/2
Erf(g) (1-Erf(g))/2
34
Giuseppe Bianchi
-6 -4 -2 2 4 6
0.1
0.2
0.3
0.4
normal distributionnormal distribution
( )2
2
2
21)( σ
µ
σπ
−−
⋅=
x
X exf
σ=2
σ=3
µ=0
Standard:µ=0; σ=1
σ=1
Giuseppe Bianchi
-4 -2 2 4
0.2
0.4
0.6
0.8
1
Cumulative normal distributionCumulative normal distribution
µ=0; σ=1
( ) ∫∞−
−==
x t
X dtexFxQ 2
2
21)(π
35
Giuseppe Bianchi
erferf -- erfcerfc
( )
)(1)(
2
0
2
xerfxerfc
dtexerfx
t
−=
= ∫ −
π
( ) ( )( )∫∫∫
−
⋅−
−
−−
⋅===
x
x
tx
x
tx
t dtedtedtexerf2
2
22 2/12
0 2/12112
πππ
Normal distribution with µ=0, σ=1/sqrt(2)
Giuseppe Bianchi
-4 -2 2 4
0.2
0.4
0.6
0.8
1
Cumulative normal distribution andCumulative normal distribution and erfcerfc
22
⎟⎠⎞
⎜⎝⎛ xerfc
36
Giuseppe Bianchi
Normal distribution Normal distribution (standard)(standard)-4 0,003%
-3,9 0,005%-3,8 0,007%-3,7 0,011%-3,6 0,016%-3,5 0,023%-3,4 0,034%-3,3 0,048%-3,2 0,069%-3,1 0,097%
-3 0,135%-2,9 0,187%-2,8 0,256%-2,7 0,347%-2,6 0,466%-2,5 0,621%-2,4 0,820%-2,3 1,072%-2,2 1,390%-2,1 1,786%
-2 2,275%-1,9 2,872%-1,8 3,593%-1,7 4,457%-1,6 5,480%-1,5 6,681%-1,4 8,076%-1,3 9,680%-1,2 11,507%-1,1 13,567%
-1 15,866%
0,001%
0,010%
0,100%
1,000%
10,000%
100,000%
-4 -3 -2 -1 0
n x sigma
outa
ge p
rob
Giuseppe Bianchi
PART 1PART 1Propagation Characteristics of Propagation Characteristics of
Wireless Channels Wireless Channels
Lecture 1.4coverage area estimation
(cell sizing)
37
Giuseppe Bianchi
Cell radiusCell radiusOpen issue, until now:
How do we determine the cell radius?
Seems very simple: givenPt = transmitted power (dBm)Pth = threshold power (dBm)
Sensitivity of the receiver, i.e. minimum amount of received power for acceptable performance
Path loss computed asLp = Pt - Pth
Radius computed from Lp
Via η-law propagation formulaVia Okumura-Hata formula (or other refined model)
[ ] ⎟⎠⎞
⎜⎝⎛=⇒
ddddL o
op 10log10η
Giuseppe Bianchi
Example Example ((part part 1)1)
Received power at 10 mt: 0.1 WThreshold power: Pth = -50 dBmη = 3.7
[ ]
[ ] [ ]
mtR
RR
PRmtPRP
mtP
thdBmrdBmr
dBmr
7801010
3770
10log50
10log3720
10log10)10()(
20100log10)10(
3770
1010
10
10
=⋅=
=→−=−
=−=
==
η
Outage prob at cell border? 50%!!!
38
Giuseppe Bianchi
Fading Fading MarginMarginPrevious computation doesnot account for long-termfading
Need to keep it in count, as it does notreduce when the MS makes small movesIDEA: reduce cell radius to account for a “fading margin” M
Fading Margin definition:M = average received power at cell border (dB) – threshold power (dB)
M=0 means that the power received at cell border is equal to the threshold M=6 (dB) means that the power received at cell border is 4 x the power threshold
thtp PPL −=
MPPL thtp −−=
Powerat cellborder
Mean pathloss
1% - 2%
M
prob
Giuseppe Bianchi
Example Example ((part part 2)2)
Received power at 10 mt: 0.1 WThreshold power: Pth = -50 dBmη = 3.7Slow fading, with σdB=4 dBIf we use a fading margin M=6
[ ] [ ]
mtRR
MPRmtPRP thdBmrdBmr
537101065010
log3720
10log10)10()(
3764
10
10
=⋅=→+−=−
+=−= η
What is the experienced outage at cell border?
39
Giuseppe Bianchi
OutageOutage probabilityprobability (1)(1)Recall that slow fading has lognormal distribution. In dB:
( )( )( ) ( )( )
2
2,
2
21
dB
dBavdB rPrp
dBdBY erpf σ
σπ
−−
⋅=
pdB(r)= power (dBm) received at given distance rPav,dB(r)= mean power (dBm, from attenuation laws) at same distance
Outage occurs when received power < Pth As Pth is given in dB: ( ) ( )( ) ( )
( )⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅
−=
== ∫ ∞−
dB
thdBav
dB
P
dBYout
PrP
rpdrpfrP th
σ2erfc
21 ,
Giuseppe Bianchi
Outage probabilityOutage probability (2)(2)Let’s rewrite Pout(r) in terms of power received at cell border Rand in term of the loss parameter η. Recall that:
( ) ( ) ( )
( )⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅−
=
=⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅−−
=
dB
dB
thout
RrM
RrPRPrP
ση
ση
2/log10erfc
21
2/log10erfc
21 0
( ) ( ) ( ) ( )RrRPrP
rRRPrP dBavdBavdBavav log10,, η
η
−=⎯→⎯⎟⎠⎞
⎜⎝⎛⋅=
Hence, referring to Pav,dB(R)= P0(R)
Which represents the probability that an MS at generic distance r is subject to outage, given that the cell has a fading margin M.
From the definition of fading Margin M
40
Giuseppe Bianchi
Outage probabilityOutage probability (3)(3)If outage probability is specificaly computed for a terminal placedat cell border:
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅=
dBout
MbordercellPσ2
erfc21
Giuseppe Bianchi
Example Example ((part part 3)3)Received power at 10 mt: 0.1 WThreshold power: Pth = -50 dBmη = 3.7Slow fading, with σdB=4 dBfading margin M=6
Cell size =537mtPoutage= 6,68% 0%
5%
10%
15%
20%
25%
30%
400 450 500 550 600 650 700
terminal distance (mt)
outa
ge p
roba
bilit
y
( ) ( )⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅−
=dB
outrrPplot
σ210/log3770erfc
21:
41
Giuseppe Bianchi
Outage probability Outage probability area (1)area (1)To compute the outage probability in a circular area with radius R, we just need to integrate Pout(r) over the cell area:
( ) ( )
( )
( )
( )( )[ ]
[ ]⎪⎪⎩
⎪⎪⎨
⎧
==
=⎟⎠
⎞⎜⎝
⎛⋅
−⋅=
=⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅−
⋅=
=⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅−
⋅=
==
∫
∫
∫
∫
mWth
mWM
dB
dB
dB
outaout
PRPm
dxxmx
dxxMx
RdrRrM
Rr
drrrPR
RP
010
1
0
1
0
R
0
R
02
10
1010ln
where2
lnlnerfc
2log10erfc
2/log10erfc
21
σσ
ση
ση
ση
ππ
Substituting and simplifying
Changing variable
Converting from dBs
Giuseppe Bianchi
Outage probabilityOutage probability area (2)area (2)( ) then;2;
2lnlet 21 η
σσ
⋅=
⋅= QmQ
21
ln variablechangingQ
xQ −=θ( )
( ) ( )
( ) ( ) ( ) ( )
( ) ( ) ( )212
1
22
2
Q
22
1
02
1
erfc21erfc
21
erfc21erf
21
erfc
lnerfc
2221
1
12212
1
12
QQeQ
eQe
deQ
dxQ
xQxRP
QQQ
Q
QQQQQ
aout
+−=
=⎥⎦⎤
⎢⎣⎡ −+−=
=⋅=
=⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅=
+
∞−+
∞ −∫
∫
θθ
θθ
θ
θ
( )
( )[ ]
( ) ( ) 2
2
22
1erfcerfc
2erfc
212erfc0
x
x
xt
x
t
exxdxx
exD
dtedtex
−
−
−∞
−
−⋅=
−=
−==
∫
∫∫
π
π
ππ
42
Giuseppe Bianchi
1,E-05
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
0 5 10 15 20 25
fading margin M (dB)
outa
ge p
roba
bilit
y (a
rea)
sigma = 4 dBsigma = 6 dBsigma = 8 dB
( ) ( )xSTNORMDISTRIBxxxSTNORMDISTRIB 2..12
erfc2
erf121)(..
:availableerfc-erfnobut available, standard normal ofCDF if :NOTE
−=⇒⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠⎞
⎜⎝⎛+=
OutageOutage probabilityprobability area area versusversus MM
Represents the fractionof “not covered” area ina cell.
η=4 in the example
Application example:If σdB=6, and targetis 1% outage area,must set M~10
Giuseppe Bianchi
Outage probability Outage probability at at borderborderworstworst case case computationcomputation
1,E-05
1,E-04
1,E-03
1,E-02
1,E-01
1,E+00
0 5 10 15 20 25
fading margin M (dB)
outa
ge p
roba
bilit
y (c
ell b
orde
r)
sigma = 4 dBsigma = 6 dBsigma = 8 dB
Outage probability foruser at cell border
Greater than Paout(conservative)
Much simpler computation
η=4 in the example
example:If σdB=6, and targetis 1% outage at border,must set M~14
( ) ⎟⎟⎠
⎞⎜⎜⎝
⎛
⋅=
dBout
MRPσ2
erfc21
43
Giuseppe Bianchi
Cell radius computationCell radius computation
Step 1:From outage probability target (es. not greater than 2%)
On a per area basisOr on a border cell basis
Plus radio channel information (η, σdB)Compute M
Step 2:From Power threshold Pth, Plus transmitted power Pt
or equivalent information (es. received power at reference distance)
Compute radius
EXAMPLE
-Outage (border) = 5%−σdB = 6dB
From SW (or tables)M=1.65 σdB = 9.87 dB
-Acceptable performance: -90 dBm−η = 3.7-Received power = -65 dBm @ 3 Km
⎟⎟⎠
⎞⎜⎜⎝
⎛−−=+−
010log106590
ddm η
d~7.7 Km
Giuseppe Bianchi
Normal distributionNormal distribution (standard)(standard)-4 0,003%
-3,9 0,005%-3,8 0,007%-3,7 0,011%-3,6 0,016%-3,5 0,023%-3,4 0,034%-3,3 0,048%-3,2 0,069%-3,1 0,097%
-3 0,135%-2,9 0,187%-2,8 0,256%-2,7 0,347%-2,6 0,466%-2,5 0,621%-2,4 0,820%-2,3 1,072%-2,2 1,390%-2,1 1,786%
-2 2,275%-1,9 2,872%-1,8 3,593%-1,7 4,457%-1,6 5,480%-1,5 6,681%-1,4 8,076%-1,3 9,680%-1,2 11,507%-1,1 13,567%
-1 15,866%
0,001%
0,010%
0,100%
1,000%
10,000%
100,000%
-4 -3 -2 -1 0
n x sigma
outa
ge p
rob
44
Giuseppe Bianchi
Slow+Fast fading Slow+Fast fading marginsmarginspower
Transmitted power
Power threshold Pth = Pt - Ploss
d0 d1 d2
Long-term fading margin M1
Short-term fading margin M2
Pth + M1
Pth + M1 + M2
1% - 2%
1% - 2%
USAGE: - determine cell radius- determine Pt
Used also in the concept of LINK BUDGET:= Path Loss + M1 + M2
1
Giuseppe Bianchi
PART 2PART 2Cellular Coverage ConceptsCellular Coverage Concepts
Lecture 2.1why cells
Giuseppe Bianchi
Coverage for Coverage for a a terrestrial terrestrial zonezone
1 Base StationN=12 channels•(e.g. 1 channel = 1 frequency)
N=12 simultaneous calls
d
Signal OK if Prx > -X dBmPrx = c Ptx d-4
greater Ptx greater d
BS
2
Giuseppe Bianchi
Cellular coverageCellular coveragetarget: cover the target: cover the same same area area with with a a larger number larger number of of BSsBSs
19 Base Station12 frequencies 4 frequencies/cell
Worst case:4 calls (all users in same cell)Best case:76 calls (4 users per cell)Average case >> 12 Low transmit power
Key advantages:•Increased capacity (freq. reuse)•Decreased tx power
Giuseppe Bianchi
Cellular coverageCellular coverage ((microcellsmicrocells))
many BS
Very low power!!Unlimited capacity!!
Usage of same spectrum(12 frequencies)(4 freq/cell)
Disadvantage: mobility management
3
Giuseppe Bianchi
Cellular Cellular system system architecturearchitecture
f4
f5f6
f3
f1f2
f7
f4
f5f6
f3
f1f2
f7
f4
f5f6
f3
f1f2
f7
f4
f5f6
f3
f1f2
f7
MSC 1MSC 1 MSC 2MSC 2
Wired network1 BS per cellCell: Portion of territory covered by one radio stationOne or more carriers(frequencies; channels) per cell
Mobile users full-duplex connected with BS
1 MSC controls many BSs
MSC connected to PSTN
BS = Base StationMSC = Mobile Switching CentrePSTN = Public Switching Telephone Network
Giuseppe Bianchi
Cellular capacityCellular capacityIncreased via frequency reuse
Frequency reuse depends on interferenceneed to sufficiently separate cells
reuse pattern = cluster size (7 4 3): discussed later
Cellular system capacity: depends onoverall number of frequencies
Larger spectrum occupationfrequency reuse patternCell size
Smaller cell (cell microcell picocell) = greater capacitySmaller cell = lower transmission powerSmaller cell = increased handover management burden
4
Giuseppe Bianchi
AB
CD
AB
CD
hexagonal cellshexagonal cellsHexagon:
Good approximation for circle
Ideal coverage patternno “holes” no cell superposition
AB
CD
AB
CD
AB
CA
AB
CD
AC
D
B
DB
Example case:Reuse pattern = 4
Giuseppe Bianchi
Cells Cells in in real real worldworld
Shaped by terrain, shadowing, etcCell border: local threshold, beyond which neighboring BS signal
is received stronger than current one
5
Giuseppe Bianchi
PART 2PART 2Cellular Coverage ConceptsCellular Coverage Concepts
Lecture 2.2Clusters and CCI
Giuseppe Bianchi
Reuse patternsReuse patternsReuse distance:
Key conceptIn the real world depends on
Territorial patterns (hills, etc)Transmitted power
» and other propagation issues such as antenna directivity, height of transmission antenna, etc
Simplified hexagonal cells model:
reuse distance depends on reuse pattern (cluster size)Possible clusters:
3,4,7,9,12,13,16,19,…
13
4
5
6
7
21
3
4
5
6
7
2
D R
Cluster: K = 7
12
3
4
12
3
4
12
3
4
D
K = 4
12
3
4
6
Giuseppe Bianchi
Reuse distanceReuse distance
General formula
Valid for hexagonal geometry
D = reuse distance
R = cell radius
q = D/R =frequency reuse factor
3KRD =
K q=D/R3 3,004 3,467 4,589 5,2012 6,0013 6,24
Giuseppe Bianchi
ProofProofDistance between two cell centers:
(u1,v1) (u2,v2)
Simplifies to:
Distance of cell (i,j) from (0,0):
Cluster: easy to see that
hence:
[ ] [ ]212122
12 30sin)()(30cos)( oo uuvvuuD −+−+−=
30°
v
u
(1,1)
(3,2)
))(()()( 12122
122
12 vvuuvvuuD −−+−+−=
RijjiD 322 ++=
ijjiDK R ++== 222
KRD 3=
ijjiDR ++= 22
7
Giuseppe Bianchi K=7(i=2,j=1) K=4 (i=2,j=0)
K=12(i=3,j=1)
ClustersClustersClusters:• Number of BSs comprised in
a circle of diameter D• Number of BSs whose inter-
distance is lower than D
Giuseppe Bianchi
Possible clustersPossible clustersall integer all integer i,j i,j valuesvalues
i j K=ii+jj+ij q=D/R1 0 1 1,731 1 3 3,002 0 4 3,462 1 7 4,582 2 12 6,003 0 9 5,203 1 13 6,243 2 19 7,553 3 27 9,004 0 16 6,934 1 21 7,944 2 28 9,174 3 37 10,544 4 48 12,005 0 25 8,665 1 31 9,64
8
Giuseppe Bianchi
CoCo--Channel InterferenceChannel Interference
Frequency reuse implies thatremote cells interfere with tagged one
Co-Channel Interference (CCI)sum of interference from remote cellsC
BA
D
E
CB
AD
EF
G
C
AD
EF
AE
FG A
EF
G
CB
A
FG
CB
AD
small N as
(I)power signal ginterferin (S)power signal
(I)power signal ginterferin )(Npower noise(S)power signal
S
S
IS
NSISNS
≈
=
+=
Giuseppe Bianchi
CCI CCI Computation Computation --assumptionsassumptions
Assumptions
NI=6 interfering cells NI=6: first ring interferers onlywe neglect second-ring interferers
Negligible Noise NSS/N ~ S/I
d−η propagation lawη=4 (in general)
Same parameters for all BSsSame Ptx, antenna gains, etc
Key simplificationSignal for MS at distance RSignal from BS interferers at distance D
RR
DPower
Po
PowerPo
Dint
Dint ~ D
9
Giuseppe Bianchi
CCI CCI computationcomputation
ηηη
η
η
qNR
DND
RN
DR
IS
NS
III
N
kI
111
costcost
1
=⎟⎠⎞
⎜⎝⎛=⎟
⎠⎞
⎜⎝⎛=
=⋅
⋅=≈
−
=−
−
∑Results depend on ratio q=D/R
(q=frequency reuse factor)
KRD 3=
By using the assumptions of same cost and same D:
Alternative expression: recalling that
( ) ( )6
3313
1 22
ηη
η KKNKR
RNI
SNS
II
==⎟⎠
⎞⎜⎝
⎛=≈−
USAGE: Given an S/I target, cluster size K is obtained
NI=6,µ=4 ( ) 2
2
23
63 KK
IS
==
Giuseppe Bianchi
ExamplesExamples
target conditions: S/I=9 dBη=4
Solution:
target conditions: S= 18dBη=4.2
Solution:
( )
33.2
32
63
894.710
4
2
9.0
=⇒≥
⋅=⇒=
≈==
=
KK
ISKK
IS
IS
η
η
[ ] ( )
( )
763.53
10
23.121
78.7183log
6log103log5
23.1
=⇒=≥
=+
=
−=
KK
K
KdBIS η
10
Giuseppe Bianchi
S/I S/I computationcomputationassumingassuming 6 6 interferers onlyinterferers only (first ring)(first ring)
K q=D/R S/I S/I dB3 3,00 13,5 11,34 3,46 24,0 13,87 4,58 73,5 18,79 5,20 121,5 20,812 6,00 216,0 23,313 6,24 253,5 24,016 6,93 384,0 25,819 7,55 541,5 27,321 7,94 661,5 28,225 8,66 937,5 29,7
Giuseppe Bianchi
Additional interferersAdditional interferers
case K=4note that for each cluster there are always NI=6 first-ring interferers
AB
CD
AB
CD
AB
CD
AB
CD
AB
CD
AB
C
AB
C
AB
CD
B
CD
AB
CD
AB
CD
B
CD
AB
CD
AB
CD
BD
BD
B
AB
AB
In CCI computation, contribute of additional interferers is marginal
11
Giuseppe Bianchi
sectorizationsectorization
Directional antennas
Cell divided into sectors
Each sector uses different frequencies
To avoid interference at sector borders
PROS:CCI reduction
CONS:Increased handover rateLess effective “trunking” leads to performnce impairments
Sector 1Laa ff ,1, L
Sector 2LaLa ff 2,1, L+
Sector 3LaLa ff 3,12, L+
CELL a
Giuseppe Bianchi
CCI CCI reduction reduction via via sectorizationsectorizationthree sectors three sectors casecase
CB D
E
CB D
EF
G
CD
EF
EF
G AE
FG
CB
A
FG
CB
AD
FG
Inferference from 2 cells, only
Instead of 6 cells
A
A
A
A
77.4
32
120
120
+⎥⎦⎤
⎢⎣⎡=⎥⎦
⎤⎢⎣⎡
⎥⎦⎤
⎢⎣⎡⋅==⎥⎦
⎤⎢⎣⎡
−
−
dBISdB
IS
IS
DR
IS
omni
omni
o
oη
η
With usual approxs (specifically, Dint ~ D)
Conclusion: 3 sectors = 4.77 dB improvement
12
Giuseppe Bianchi
6 6 sectorssectors
60o Directional antennas
CCI reduction:1 interfereer only6 x S/I in the omni caseImprovement: 7.78 dB
Giuseppe Bianchi
PART 2PART 2Cellular Coverage ConceptsCellular Coverage Concepts
Lecture 2.3teletraffic considerations,
teletraffic planning
13
Giuseppe Bianchi
Traffic generated by Traffic generated by one one useruser((statistical notion statistical notion of of traffictraffic))
How to characterize this process?statistical distribution of the “BUSY” periodstatistical distribution of the “IDLE” periodstatistical characterization of the process “memory”
E.g. at a given time, does the probability that a user starts a call result different depending on what happened in the past?
1 user making phone calls
BUSY 1
IDLE 0timeTRAFFIC is a “stochastic process”
Traffic characterization suitable for traffic engineering
( ) ( )
valueprocessmean state BUSYin isuser t, timerandom aat y that,probabilit
duration call averagehourper calls of number averaget
tin busy time ofamount Aintensity traffic limi
===
=×=
=∆
∆=
∞→∆
τλt
All equivalent (if stationary process)
Giuseppe Bianchi
Traffic generated by Traffic generated by more more than than one one usersusers
TOT
U1
U2
U3
U4
ii
i AAA 44
1
==∑=
Traffic intensity (adimensional, measured in Erlangs):
[ ] ( )
[ ] AAE
AAk
P
i
ki
ki
=⋅=
−⎟⎟⎠
⎞⎜⎜⎝
⎛= −
4calls active
14
calls activek 4
14
Giuseppe Bianchi
exampleexample
5 usersEach user makes an average of 3 calls per hourEach call, in average, lasts for 4 minutes
[ ] [ ]
[ ] [ ]erlerlA
erlhourshourcallsAi
1515
51
6043
=×=
=×⎥⎦⎤
⎢⎣⎡=
Meaning: in average, there is 1 active call; but the actual number of active calls varies from 0 (no active user) to 5 (all users active),with given probability
number of active users probability0 0,3276801 0,4096002 0,2048003 0,0512004 0,0064005 0,000320
Giuseppe Bianchi
Second exampleSecond example30 usersEach user makes anaverage of 1 calls per hourEach call, in average, lasts for 4 minutes
Erlangs2604130 =⎟⎠⎞
⎜⎝⎛ ⋅×=A
SOME NOTES: -In average, 2 active calls (intensity A);-Frequently, we find up to 4 or 5 calls;-Prob(n.calls>8) = 0.01%-More than 11 calls only once over 1M
TRAFFIC ENGINEERING: how many channels to reserve for these users!
n. active users binom probab cumulat0 1 1,3E-01 0,1262131 30 2,7E-01 0,3966692 435 2,8E-01 0,6767843 4060 1,9E-01 0,8635274 27405 9,0E-02 0,9535645 142506 3,3E-02 0,9870066 593775 1,0E-02 0,9969607 2035800 2,4E-03 0,9993978 5852925 5,0E-04 0,9998989 14307150 8,7E-05 0,99998510 30045015 1,3E-05 0,99999811 54627300 1,7E-06 1,00000012 86493225 1,9E-07 1,00000013 119759850 1,9E-08 1,00000014 145422675 1,7E-09 1,00000015 155117520 1,3E-10 1,00000016 145422675 8,4E-12 1,00000017 119759850 5,0E-13 1,00000018 86493225 2,6E-14 1,00000019 54627300 1,2E-15 1,00000020 30045015 4,5E-17 1,00000021 14307150 1,5E-18 1,00000022 5852925 4,5E-20 1,00000023 2035800 1,1E-21 1,00000024 593775 2,3E-23 1,00000025 142506 4,0E-25 1,00000026 27405 5,5E-27 1,00000027 4060 5,8E-29 1,00000028 435 4,4E-31 1,00000029 30 2,2E-33 1,00000030 1 5,2E-36 1,000000
15
Giuseppe Bianchi
A note on A note on binomial coefficient computationbinomial coefficient computation
( ) ( ) ( )( )
( ) ( ) ( ) exp...)before !overflow! (no
)!problems!overflowbut
⎟⎠
⎞⎜⎝
⎛−−=
=−−=⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎟⎠
⎞⎜⎜⎝
⎛=⎟⎟
⎠
⎞⎜⎜⎝
⎛
+=
+==⎟⎟⎠
⎞⎜⎜⎝
⎛
∑∑∑===
48
1
12
1
60
1logloglogexp
!48log!12log!60logexp1260
logexp1260
(8132099.8!60
1239936.1!48!12
!601260
iiiiii
e
e
( )
( ) ( ) ( ) ( ) ( )
)never! !overflow! (no
⎟⎠
⎞⎜⎝
⎛−++−−=
=−⎟⎟⎠
⎞⎜⎜⎝
⎛
∑∑∑===
iiiii
ii
AAiii
AA
1log48log12logloglogexp
11260
48
1
12
1
60
1
4812
Giuseppe Bianchi
Infinite Infinite UsersUsers
[ ] ( ) ( ) k
M
kkM
iki
MA
MA
MA
kkMMAA
kM
P⎟⎠⎞
⎜⎝⎛ −
⎟⎠⎞
⎜⎝⎛ −
⎟⎠⎞
⎜⎝⎛
−=−⎟⎟
⎠
⎞⎜⎜⎝
⎛= −
1
1
!!!1users Mcalls, activek
Assume M users, generating an overall traffic intensity A (i.e. each user generates traffic at intensity Ai =A/M).We have just found that
Let M infinity, while maintaining the same overall traffic intensity A
[ ] ( )
( ) ( )!
1111lim!
11!
1!
!limusers calls, activek
kAe
MA
MA
MkMMM
kA
MA
MA
MA
kkMMP
kA
kA
AM
kM
k
kM
k
k
M
−−
−−
∞→
−
∞→
=⎟⎠⎞
⎜⎝⎛ −⋅
⎥⎥
⎦
⎤
⎢⎢
⎣
⎡⎟⎠⎞
⎜⎝⎛ −⋅
+−−⋅=
=⎟⎠⎞
⎜⎝⎛ −⋅⎟
⎠⎞
⎜⎝⎛ −⋅⋅⋅
−=∞
L
16
Giuseppe Bianchi
Poisson DistributionPoisson Distribution
( )!k
AeAPk
Ak
−=
0%
5%
10%
15%
20%
25%
30%
0 2 4 6 8 10 12 14 16 18 20 22
poissonbinomial (M=30)
A=2 erl
A=10 erl
Very good matching with Binomial(when M large with respect to A)
Much simpler to use than Binomial(no annoying queueing theory complications)
Giuseppe Bianchi
Limited number Limited number of of channelschannels
The number of channels C is less than the number of users M (eventually infinite)Some offered calls will be “blocked”What is the blocking probability?
We have an expression forP[k offered calls]
We must find an expression forP[k accepted calls]
As: TOT
U1
U2
U3
U4
THE most important problem in circuit switching
X
X
No. carried calls versus tNo. offered calls versus t[ ]calls accepted C]block[ PP =
17
Giuseppe Bianchi
Channel utilization probabilityChannel utilization probability
C channels availableAssumptions:
Poisson distribution (infin. users)Blocked calls cleared
It can be proven (from Queueing theory) that:
(very simple result!)
Hence:
[ ][ ]∑
=
=
=∈
C
iP
PP
0calls offered i
calls offeredk ]C)(0,k system,in the callsk [
offered traffic: 2 erl - C=3
0%
5%
10%
15%
20%
25%
30%
35%
0 1 2 3 4 5 6 7 8
offered callsaccepted calls
[ ][ ]∑
=
== C
i
P
PPP
0
calls offered i
calls offered C]calls accepted C[]full system[
Giuseppe Bianchi
Blocking probabilityBlocking probability: : ErlangErlang--BBFundamental formula for telephone networks planning
Ao=offered traffic in Erlangs
( )oCC
j
jo
Co
block AE
jA
CA
,1
0 !
! ==Π
∑=
( ) ( )( )oCo
oCooC AEAC
AEAAE
1,1
1,1,1
−
−
+=
0,01%
0,10%
1,00%
10,00%
100,00%
0 1 2 3 4 5offered load (erlangs)
bloc
king
pro
babi
lity
C=1,2,3,4,5,6,7
Efficient recursive computation available
18
Giuseppe Bianchi
NOTE: finite NOTE: finite usersusers
Erlang-B obtained for the infinite users caseIt is easy (from queueing theory) to obtain an explicit blocking formula for the finite users case:
ENGSET FORMULA:
MAA
iM
A
CM
A
oi
C
k
ki
Ci
block
=
⎟⎟⎠
⎞⎜⎜⎝
⎛ −
⎟⎟⎠
⎞⎜⎜⎝
⎛ −
=Π
∑=0
1
1
Erlang-B can be re-obtained as limit case
M infinityAi 0M·Ai Ao
Erlang-B is a very good approximation as long as:
A/M small (e.g. <0.2)
In any case, Erlang-B is a conservative formula
yields higher blocking probabilityGood feature for planning
Giuseppe Bianchi
Capacity Capacity planningplanning
Target: support users with a given GradeOf Service (GOS)
GOS expressed in terms of upper-bound for the blocking probability
GOS example: subscribers should find a line available in the 99% of the cases, i.e. they should be blocked in no more than 1% of the attempts
Given:C channelsOffered load Ao
Target GOS Btarget
C obtained from numerical inversion of ( )oC AEB ,1target =
19
Giuseppe Bianchi
Channel usage efficiencyChannel usage efficiency
oA C channels ( )BAA oc −= 1
Offered load (erl) Carried load (erl)
BAo
Blocked traffic
( )( )blocking small if
1:efficiency ,1
CA
CAEA
CA ooCoc ≈
−==η
Fundamental property: for same GOS, efficiency increases as C grows!!
Giuseppe Bianchi
exampleexample
0,1%
1,0%
10,0%
100,0%
0 20 40 60 80 100 120capacity C
bloc
king
pro
babi
lity
A = 40 erlA = 60 erlA = 80 erlA = 100 erl
GOS = 1% maximum blocking. Resulting system dimensioning
and efficiency:
40 erl C >= 5360 erl C >= 7580 erl C >= 96
100 erl C >= 117
η = 74.9%η = 79.3%η = 82.6%η = 84.6%
20
Giuseppe Bianchi
Erlang Erlang B B calculation calculation -- tablestables
Giuseppe Bianchi
Erlang Erlang B B calculation calculation -- softwaresoftware
Erlang-B formula very easy to implementEven if some tricks needed for numerical accuracy
Erlang-B inversion not so easySoftware tools
Online calculator:http://mmc.et.tudelft.nl/~frits/Erlang.htm
Given two parameter, calculates the thirdN = number of circuitsB = blocking probabilityA = offered load
21
Giuseppe Bianchi
Application to cellular networksApplication to cellular networksCell sizeCell size ((radiusradius R) R) may be determined may be determined on the on the basisbasis of of traffic considerationstraffic considerations
First step:Given num channels and GOS
C=50 available channels in a cellBlocking probability<=2%
Evaluate maximum cell (offered) loadFrom Erlang-B inversion(tables) A=40.25 erl
Second stepGiven traffic generated by each user
Each user: 4 calls/busy-hourEach call: 2 min in averageAi=4x2/60=0.1333 erl/user
Evaluate max num of users in cellM=301.87 ~ 302
Third step:Given density of users
δ=500 users/km2
Evaluate cell radius
R~438mπδπ
δ MRRM
=⇒= 2
Giuseppe Bianchi
Other exampleOther exampleThree service providers are planning to provide cellular service for an urban area. The target GOS is 2% blocking. Users make 3 calls/busy-hour, each lasting 3 minutes in average (Ai=3/20=0.15)
Question: how many users can support each provider?Provider A configuration: 20 cells, each with 40 channelsProvider B configuration: 30 cells, each with 30 channelsProvider C configuration: 40 cells, each with 20 channels
Provider A:40 channels/cellat 2%: Ao=30.99 erl/cell619.8 erl-totalM=4132 overall users
Provider C:20 channels/cellat 2%: Ao=13.18 erl/cell527.2 erl-totalM=3515 overall users
Provider B:30 channels/cellat 2%: Ao=21.93 erl/cell654.9 erl-totalM=4386 overall users
Compare case A with C! The reason is the lower efficiency of 20 channels versus 40
22
Giuseppe Bianchi
Sectorization Sectorization and and traffictraffic
Assume cluster K=7Omnidirectional antennas: CCI=18.7 dB120o sectors: CCI=23.4 dB60o sectors: CCI=26.4 dB
Sectorization yields to better CCIBUT: the price to pay is a much lower trunking efficiency!
With 60 channels/cell, GOS=1%, Omni: 60 channels Ao=1x46.95= 46.95 erl η=77.5%120o: 60/3=20 channels Ao=3x12.03= 36.09erl η=59.5%60o: 60/6=10 channels Ao=6x4.46= 26.76erl η=44.1%
Giuseppe Bianchi
conclusionconclusion
This module has given some hints regarding:Cell sizing via propagation considerationsFrequency reuse via propagation considerationsCell planning via teletraffic consideration
Very elementary modelsBut sufficient to understand what’s inside planning
No mobility!Teletraffic models need to be extended to manage handover rates!Blocking requirement for an handover call MUST be much lower than blocking for a new incoming call
severe math complicationsGuard channels for handoverOut of the scopes of this class!
1
Giuseppe Bianchi
PART 3PART 3Introduction to GSMIntroduction to GSM
Lecture 3.0History
Giuseppe Bianchi
History of wireless History of wireless communicationcommunication
1896: Marconi first demonstration of wireless telegraphy tx of radio waves to a ship at sea 29 km away long wave transmission, high power req. (200 kW and +)
1901: MarconiTelegraph across the atlantic oceanClose to 3000 Km hop!
1907 Commercial transatlantic connectionshuge ground stations (30 by100m antennas)
1915: Wireless telephony established NY – S. FranciscoVirginia and Paris
1920 Marconi:Discovery of short waves (< 100m)reflection at the ionosphere(cheaper) smaller sender and receiver, possible due to the invention of the vacuum tube (1906, Lee DeForest and Robert von Lieben)
2
Giuseppe Bianchi
History of wireless History of wireless communicationcommunication
1920's: Radio broadcasting became popular1928: many TV broadcast trials1930's: TV broadcasting deployment1946: First public mobile telephone service in US
St. Louis, MissouriSingle cell system
1960's: Bell Labs developed cellular conceptbrought mobile telephony to masses
1960’s: Communications satellites launchedLate 1970's: technology advances enable affordable cellular telephony
entering the modern cellular era1974-1978: First field Trial for Cellular System
AMPS, Chicago
Giuseppe Bianchi
1st generation mobile 1st generation mobile systemssystemsearly deploymentearly deployment
First system:NMT-450 (Nordic Mobile Telephone)
Scandinavian standard; adopted in most of Europe450 MHZ bandFirst european system (Sweden, october 1981)
Italian history:1966: first experiments (CSELT) at 160 MHZ
RTMI (Radio Telefono Mobile Italiano)Market: 1973
First italian cellular system: 1985RTMS (Radio Telefono Mobile di Seconda Generazione)450 MHZ
Evolution: 1990, TACSTotal Access Communication System900 MHZ
3
Giuseppe Bianchi
1st generation mobile 1st generation mobile systemssystemsFirst generation: 1980’sSeveral competing standards in different countries
NMT (Nordic Mobile Telephone)Scandinavian standard; adopted in mostof EuropeFirst european system (Sweden, 1981)
TACS (Total Access Communication Systems), starts in 1985
UK standard; A few of Europe, Asia, Japan
AMPS (Advanced Mobile Phone Service)
US standardC-Netz (Only in Germany)Radiocom 2000 (Only in France)
Analog transmissionFrequency modulation
Various bands:NMT:
450 MHz first900 MHz later
TACS900 MHz1230 bidirectional channels (25KHz)
AMPS800 MHz
Today still in use in low-technology countries
And not yet completely dismissed in high-tech countries
Giuseppe Bianchi
2nd generation mobile 2nd generation mobile systemssystems
4 systemsGlobal System for Mobile (GSM)Digital AMPS (D-AMPS), USCode Division Multiple Access (IS-95) – Qualcomm,USPersonal Digital Cellular (PDC),Japan
GSM by far the dominant one
Originally pan-europeanDeployed worldwide
(slow only in US)
Basic bands:900 MHz1800 MHz
(Digital Cellular System: DCS-1800)
1900 MHz (Personal CommunicationSystem:PCS-1900,US only)
Specifications forGSM-400 (large areas)GSM-800 (north america)
4
Giuseppe Bianchi
TimingTiming1982: Start of GSM-specification in Europe (1982-1990)1983: Start of American AMPS widespread deployment1984 CT-1 standard (Europe) for cordless telephones1991 Specification of DECT
Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications)
- ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication
1992: Start of GSM operation Europe-wide1994: DCS-1800
Giuseppe Bianchi
2 ½ generation mobile 2 ½ generation mobile systemssystemsGSM GSM incremental extensionincremental extension
High speed circuit switched data (HSCSD)
Circuit switched data communicationUses up to 4 slots (1 slot = 9.6 or 14.4 Kbps)
General Packet Radio Service (GPRS)Packet data (use spectrum only when needed!)Up to 115 Kbps (8 slots)
Enhanced Data-rates for Global Evolution (EDGE)
Higher data rate available on radio interface (3x)» Up to 384 Kbps (8 slots)» Thanks to new modulation scheme (8PSK)» May coexist with old GMSK
5
Giuseppe Bianchi
3rd generation mobile 3rd generation mobile systemssystems
UMTS (Universal Mobile TelecommunicationSystem)
ITU standard: IMT-2000 (International Mobile Telecommunication – 2000)UMTS forum created in 1996Later on 3GPP forum (bears most of standardization activities)
Wideband CDMA radio interfaceBut several other proposals accepted as “compatible”
Radio spectrum: 1885-2025 & 2110-2200 MHzAlready deployed in JapanTime to market in Italy: 2004?
Giuseppe Bianchi
Facts about wireless Facts about wireless communicationcommunication
Who has a cellular phone?USA: Over 50% of US householdsItaly: from 2001, more wireless lines than wiredWorld: from march 2002, 1 billion wireless cellular users
Much faster than projections!August 2000: 372 GSM networks, 362M customers
Revenues:global revenue from wireless portals predicted to grow from $700M to $42 billion by 2005WLAN revenues predicted at $785M by 2004Forecasting a 59 percent growth rate for wireless usage in rural areas between 2000 and 2003
6
Giuseppe Bianchi
PART 3PART 3Introduction to GSMIntroduction to GSM
Lecture 3.1Architecture and components
Giuseppe Bianchi
GSM NetworkGSM Networkhighhigh--level viewlevel view
Base Station
MSC
PSTNPublic switched
telephone network
PSTNPublic switched
telephone network
Base Station
MSC
PLMNPublic Land
Mobile Network
MSC = Mobile Switching Center= administrative region
MSC role: telephone switching central with special mobility management capabilities
7
Giuseppe Bianchi
GSM system hierarchyGSM system hierarchy
BTS
BSCLOCATION AREA
MSC MSC region
Hierarchy: MSC region n x Location Areas m x BSC k x BTS
MSC: Mobile Switching CenterLA: Location AreaBSC: Base Station ControllerBTS: Base Transceiver Station
Giuseppe Bianchi
GSM essential componentsGSM essential components
BTS
BTSBTS
BTS
BTSBSC
BSC
MSCVLRHLRAUCEIRGMSC
To fixed network (PSTN, ISDN, PDN)
OMC
MS Mobile StationBTS Base Transceiver StationBSC Base Station ControllerMSC Mobile Switching Center GMSC Gateway MSCOMC Operation and Maintenance CenterEIR Equipment Identity RegisterAUC Authentication CenterHLR Home Location RegisterVLR Visitor Location Register
MS
8
Giuseppe Bianchi
GSM SubGSM Sub--SystemsSystems
NSS
External Networks
OSS
BSS MS Users
operator
A Interface Radio Interface (Um)
Two components:Fixed installed infrastructure
The network in the proper senseMobile subscribers
MS: Mobile StationFixed infrastructure divided into three sub-systems
BSS: Base Station subsystemManages transmission path from MS to NSS
NSS: Network Switching SubsystemCommunication and interconnection with other nets
OSS: Operational SubsystemGSM network administration tools
Giuseppe Bianchi
PART 3PART 3Introduction to GSMIntroduction to GSM
Lecture 3.2Mobile Station and addresses
9
Giuseppe Bianchi
Mobile Station (MS)Mobile Station (MS)GSM separates user mobility from equipment mobility,
by defining two distinct components
Mobile EquipmentThe cellular telephone itself (or the vehicular telephone)
Address / identifier: IMEI (International Mobile Equipment Identity)
Subscriber Identity Module (SIM)Fixed installed chip (plug-in SIM) or exchangeable card (SIM card)
Addresses / identifiers:IMSI (International Mobile Subscriber Identity)MSISDN (Mobile Subscriber ISDN number)
» the telephone number!
Giuseppe Bianchi
Mobile Equipment structureMobile Equipment structure
TerminalEquipmentTerminal
EquipmentMobile
TerminationMobile
Termination MobileTermination
TerminalAdaptor
TerminalEquipment
Mobile Termination functionstRadio interface (tx, rx, signalling)
Terminal Equipment functionsUser interface (microphone, keyboard, speakers, etc);Functions specific of services (telephony, fax, messaging, etc), independent of GSM
Terminal Adaptor functionsInterfaces MT with different types of terminals (PCs, Fax, etc.)
TE1 MT
TE2 TA MT
UmS
R
Mobile Equipment
10
Giuseppe Bianchi
portable0.8V
portable2IV
portable5III
vehicular8II
vehicular20I
Type of terminal
max power (watt)
CLASS
Normally used
Mobile Equipment Max PowerMobile Equipment Max Power5 power classes5 power classes
This was for 900 MHz – for 1800 MHz only two classes: 1W, and 0.25 W
Giuseppe Bianchi
IMEIIMEIInternational Mobile Equipment IdentityInternational Mobile Equipment Identity
Uniquely identifies the mobile equipment15 digits hierarchical address assigned to ME during manifacturing and “type approval” testing
Type approval procedure: guarantees that the MS meets a minimum standard, regardless of the manifacturer
IMEI structure:
TAC – 6 digits(Type Approval Code)
FAC – 2 digits(Final Assembly Code)
SNR – 6 digits(Serial Number)
SP – 1 digit(Spare Digit)
centrally assigned upon type approval
assigned by manufacturer
Identifies place where ME was assembled ormanufactured
assigned by manufacturer
Unique for given TAC+FAC
combination
Additionaldigit
available
11
Giuseppe Bianchi
IMEI managementIMEI managementProtection against stolen and malfunctioning terminalsEquipment Identity Register (EIR): 1 DataBase for each operator; keeps:
WHITE LIST:valid IMEIsCorresponding MEs may be used in the GSM network
BLACK LIST:IMEIs of all MEs that must be barred from using the GSM networkException: emergency calls (to a set of emergency numbers) Black list periodically exchanged among different operators
GRAY LIST:IMEIs that correspond to MEs that can be used, but that, for some reason (malfunctioning, obsolete SW, evaluation terminals, etc), need to be tracked by the operatorA call from a “gray” IMEI is reported to the operator personnel
Giuseppe Bianchi
SIM cardSIM cardSubscriber Identity ModuleSubscriber Identity Module
Uniquely associated to a userNot to an equipment, as in first generation cellular networks
Stores user addressesIMSIMSISDNTemporary addresses for location, roaming, etc
authentication and encryption featuresAll security features of GSM are stored in the SIM for maximum protection
subscriber’s secret authentication key (Ki)Authentication algorithm (“secret” algorithm - A3 – not unique)Cipher key generation algorithm (A8)
PersonalizationSIM stores user profile (subscribed services)RAM available for SMS, short numbers, user’s directory, etcProtection codes
PIN (Personal Identification Number, 4-8 digits)PUK (PIN Unblocking Key, 8 digits)
12
Giuseppe Bianchi
IMSIIMSIInternational Mobile Subscriber IdentityInternational Mobile Subscriber Identity
Uniquely identifies the user (SIM card)GSM-specific address
unlike MSISDN - normal phone number15 digits hierarchical address assigned by operator to SIM card upon subscriptionIMSI structure:
MCC – 3 digits(Mobile Country Code)
MNC – 2 digits(Mobile Network Code)
MSIN – max 10 digits(Mobile Subscriber Identification Number)
Internationally standardized;identifies operator country
Identifies operatornetwork (PLMN) within country
Uniquely identifies subscriber in the operator network
Italy: 222 TIM=01 OMNI=10WIND=88 BLU=98
Giuseppe Bianchi
MSISDNMSISDNMobile Subscriber ISDN NumberMobile Subscriber ISDN Number
MSISDN: the “usual” telephone numberFollows international ISDN numbering plan (ITU-T E.164 recommendations)Structure:
CC – up to 3 digits(Country Code)
NDC – 3 digits (for PLMN)(National Destination Code)
SN – max 10 digits(Subscriber Number)
GSM is the first network to distinguishThe user identity (i.e. IMSI)From the number to dial (i.e. MSISDN)
Separation IMSI-MSISDN protects confidentialityIMSI is the real user address: never public!Faking false identity: need signal IMSI to the network; but IMSI hard to obtain!
Separation IMSI-MSISDN allowsEasy modification of numbering and routing plans
single IMSI may be associated to several MSISDN numbersE.g. different services (fax, voice, data, etc) may be associated with different MSISDN numbers
13
Giuseppe Bianchi
Temporary addressesTemporary addresses
TMSI - Temporary Mobile Subscriber Identity
32 bitsassigned by VLR within an administrative area
has significance only in this areatransmitted on the radio interface instead of IMSI
reduces problem of “eavesdropping”
MSRN - Mobile Station Roaming Number
An MSISDN numberCC, NDC of the visited networkSN assigned by VLR
Used to route calls to a roaming MSSubscriber Number (SN) assigned to provide routing information towards actually responsible MSC
Giuseppe Bianchi
PART 3PART 3Introduction to GSMIntroduction to GSM
Lecture 3.3Fixed Infrastructure
14
Giuseppe Bianchi
Components Components and and interfacesinterfaces
OMC
VLR
OtherVLR
OtherMSC
EIR
MS
BTS
BSC
MSC
HLR
AUC
BSS
OtherNetworks
Um
Abis
A
BC
F
D
E
G
MS Mobile StationBTS Base Transceiver StationBSC Base Station ControllerMSC Mobile Switching Center OMC Operation and Maintenance CenterEIR Equipment Identity RegisterAUC Authentication CenterHLR Home Location RegisterVLR Visitor Location Register
Components
Um Radio InterfaceAbis BTS-BSCA BSS-MSCB MSC-VLRC MSC-VLRD HLR-VLRE MSC-MSCF MSC-EIRG VLR-VLR
Interfaces
Giuseppe Bianchi
Base Station SubBase Station Sub--SystemSystem
BTS
BTS
BTS
BSC
A-bisInterface
Um - RadioInterface
BSS
AInterface
OSS
Base Transceiver Station (BTS)Transmitter and receiver devices, voice coding & decoding, rate adaptation for dataProvides signaling channels on the radio interfaceLimited signal and protocol processing (error protection coding, link layer LAPDm)
Base Station Controller (BSC)performs most important radio interface management functions:Radio channels allocation and deallocation; handover management; …
15
Giuseppe Bianchi
Base Base TransceiverTransceiver Station Station -- BTSBTS
Outputfilter
InputFilter
HFTransmitter
HFReceiver
Slow
freq
.H
oppi
ng TRXDigital Signal
Processing
Tran
smis
sion
Syst
em
Operation and Maintenance Functionality/clock distribution
Abi
sIn
terfa
ce (t
o B
SC
)
Um Interface(to MS)
TRX radio interface functions:- GMSK modulation-demodulation- channel coding- encryption/decryption- burst formatting, interleaving- signal strength measurements- interference measurements
In essence, BTS is a complex modem!
Giuseppe Bianchi
BTS BTS –– maximum maximum powerpower
GSM 900320 W160 W80 W40 W20 W10 W5 W2.5 W0.25 W (micro-BTS)0.08 W (micro-BTS)0.03 W (micro-BTS)
DCS 180020 W10 W5 W2.5 W1.6 W (micro-BTS)0.5 W (micro-BTS)0.16 W (micro-BTS)
16
Giuseppe Bianchi
Base Station Controller Base Station Controller -- BSCBSC
FUNCTIONS:switch calls from MSC to correct BTS
and converselyProtocol and coding conversion
for traffic (voice) & signaling (GSM-specific to ISDN-specific)
Manage MS mobilityEnforce power control
Xswitchmatrix
BTS-1BTS-2
BTS-K
1 BSC may controlup to 40 BTS
DB
From/to MSC
DB contains - state information for all BSS- BTS software
Giuseppe Bianchi
Transcoding Transcoding and Rate and Rate AdaptationAdaptation
BTS: -collects speech traffic-Deciphers and removes error protection-Result:
-13 kbps air-interface GSM speech-coded signalMSC:-A modified ISDN switch-Needs to receive ISDN-coded speech
-64 kbps PCM format (A-law)
Transcoding andRate Adaptation Unit (TRAU)needed!
Rationale: re-use existing ISDN switches & protocols
17
Giuseppe Bianchi
TRAU TRAU possible placementspossible placements
BTS TRAU BSC MSC
64 kbit/s64 kbit/sOn BTS
13 kbit/s
BTS BSC
64 kbit/s16 kbit/s13 kbit/sOn BSCTRAU MSC
BTS BSC
64 kbit/s(4x16 sub-mux)
16 kbit/s13 kbit/sOn MSCTRAU MSC
Why 16 kbps instead of 13? Inband signalling needed for BTS control of TRAU(TRAU needs to receive synchro & decoding information from BTS)
Giuseppe Bianchi
Network Switching SubNetwork Switching Sub--SystemSystem
Elements:Mobile Switching Center (MSC) / Gateway MSC (GMSC)Home Location Register (HLR ) / Authentication Center (AuC)Visitor Location Register (VLR)Equipment Identity Register (EIR)
Functions:Call controlUser management
Inter-component communicationVia SS7 signalling networkWith suitable extensions (e.g. MAP – Mobile Application Part)
18
Giuseppe Bianchi
Mobile Mobile Switching Switching Center Center -- MSCMSC
An ISDN switch (64 kbps channels)Performs all the switching and routing functionsof a fixed network switching nodePLUS specific mobility-related functions:
Allocation and administration of radio resourcesManagement of mobile users
registration, authenticationhandover execution and controlpaging
A PLMN (operator network) has, in general, many MSC
Each MSC is responsible of a set of BSS (note: a BSS refers to just 1 MSC, not many)
Giuseppe Bianchi
Home Location Home Location Register Register -- HLRHLR1 database per operator (PLMN)
In principle; in practice may beN-plicated for reliability reasonsIn large operator networks, there may be 2+ HLR with distinct information, although MSISDN-HLR association needs to be introduced (e.g. first two digits of the Subscriber Number)
HLR entries:Every user / MSISDN that has subscribed to the operator
Stores:Permanent information associated to the user
IMSI, MSISDNServices subscribedService restrictions (e.g. roaming restrictions)Parameters for additional servicesinfo about user equipment (IMEI)Authentication data
Temporary information associated to the user
Link to current location of the user:Current VLR address (if avail)Current MSC address (if avail)MSRN (if user outside PLMN)
19
Giuseppe Bianchi
Authentication Authentication Center Center -- AUCAUC
Associated to HLREventually integrated with HLR
Search key: IMSIResponsible of storing security-relevant subscriber data
Subscriber’s secret key Ki (for authentication)Encryption key user on the radio channel (Kc)Algorithms to compute volatile keys used during authentication process
Giuseppe Bianchi
Gateway Gateway MSC MSC –– GMSCGMSC
X XX
XX
MSC
PLMNPublic Land
Mobile Network
MSCMSC
GMSC
Needed, as fixed networkswitches are not mobilecapable!!
GMSC task: query HLR forcurrent MS location
(if fixed network switcheswere able to query HLR,direct connection with local MSC would be available)
HLR
20
Giuseppe Bianchi
Visitor Location Visitor Location Register Register -- VLRVLRAt most 1 database per MSC
Generally, joint MSC-VLR implementation No need to carry heavy MSC-VRL signalling load on network links
but 1 VLR may serve many MSCsVLR entries:
Every user / MSISDN actually staying in the administrative area of the associated MSC
Entry created when an MS enters the MSC area (registration)NOTE: may store data for roaming users (subscribed to different operators)
Stores:
Subscriber and subscription dataIMSI, MSISDNParameters for additional servicesinfo about user equipment (IMEI)Authentication data
Tracking and routing informationMobile Station Roaming Number (MSRN)Temporary Mobile Station Identity (TMSI)Location Area Identity (LAI) where MS has registered
Used for paging and call setup
Giuseppe Bianchi
Operation & Maintenance Operation & Maintenance SubSub--system (OSS)system (OSS)
Network measurement and control functionsMonitored and initiated from the OMC (Operation and Maintenance Center)Basic functions
Network Administrationconfiguration, operation, performance management, statistics collection and analysis, network maintenance
Commercial operation & chargingAccounting & billing
Security Management E.g. Equipment Identity Register (EIR) management
O&M functions based on ITU-T TMN standards (Telecommunication Network Management) – complex topic out of the scopes of this course
1
Giuseppe Bianchi
PART 4PART 4GSM GSM –– Radio InterfaceRadio Interface
Lecture 4.1Physical channels
Giuseppe Bianchi
GSM Radio SpectrumGSM Radio Spectrum
2 x 25 Mhz bandDuplex spacing: 45 MHz
124 carriers x band200 KHz channelsSuggested use: only 122
Use top & bottom as additional guard8 TDMA slots x carrier
full rate calls – 13 KbpsIf half-rate used, 16 calls at 6.5 kbps
Frequency [MHz]
890
915
935
960
UPLINKMS BS
DOWNLINKBS MS
890.2
890.4
“guard band”
1 2 3 4 5 6 7 8
( ) ( )[ ]( ) ( )[ ]MHz12.02.935
MHz12.02.890
−+=
−+=
nnF
nnF
dwlink
uplink
2
Giuseppe Bianchi
Adjacent channelsAdjacent channels(due (due toto GMSK)GMSK)
35dB60dB
Specification: 9dBIn practice, due to power control and shadowing, adjacent channelsCannot be used within the same cell…
Giuseppe Bianchi
Physical channel Physical channel
200 KHz bandwidth + GMSK modulation1625/6 kbps gross channel rate (270.8333 kbps)
1 time slot = 625/4 bits156.25 bits15/26 ms = 576.9 µs
timetimeslot0
577 µs
timeslot7
1 frame = 60/13 ms = 4.615 ms26 frames = 120 ms (this is the key number)
3
Giuseppe Bianchi
Hybrid FDMAHybrid FDMA--TDMATDMAphysical channel = (time slot, frequency)physical channel = (time slot, frequency)
time577us 577us 577us 577us 577us 577us 577us 577us
frequency
200 KHz
200 KHz200 KHz
200 KHz
200 KHz
200 KHz
200 KHz
200 KHz
200 KHzslot
Total n. of channels: 992
Giuseppe Bianchi
DCS 1800 radio spectrumDCS 1800 radio spectrum
Greater bandwidth availableEUROPE: 75 MHz band
1710-1785 MHz uplink; 1805-1880 MHz downlinkITALY: 45 MHz band from 2005
1740-1785 MHz uplink; 1835-1880 MHz downlinkSame GSM specification
200 KHz carriersA total of 374 carriers (versus124 in GSM)
DCS 1800 operatorsCommon rule in most of the countries:
First and second operators @ 900 MHz; Third etc @1800 MHzDCS 1800 deployment (1996+):
» 15 MHz (=75 carriers) to Wind; 7.5 (=37 carriers) to first and second operator (plus existing 27 GSM 900 carriers)
4
Giuseppe Bianchi
Other Other GSM GSM bandsbands
Extended GSM (E-GSM) bandUplink: 880-915 MHzDownlink: 925-960 MHz
Other bands:450 MHz (450.4-457.6 up; 460.4-467.6 down)480 MHz (478.8-486 up; 488.8-496 down)1900 MHz (1850-1910 up; 1930-1990 MHz)
Giuseppe Bianchi
DuplexingDuplexing
0 1 2 3 4 5 6 7UPLINK
0 1 2 3 4 5 6 7 DOWNLINK
- MS uses SAME slot number on uplink and downlink
- Uplink and downlink carriers always have a 45 MHz separation-I.e. if uplink carrier is 894.2 downlink is 919.2
-3 slot delay shift!!
MS: no need to transmit and receive in the same time on two different frequencies!
5
Giuseppe Bianchi
Slow Frequency hoppingSlow Frequency hopping(optional procedure within (optional procedure within individualindividual cell)cell)
f1f2f3f4f5f6f7
Hopping sequence (example):… f1 f2 f5 f6 f3 f7 f4 f1…
Slow = on a per-frame basis- 1 hop per frame (4.615 ms) = 217 hops/second
Physical motivation:- combat frequency-selective fading- combat Co-Channel Interference
next slot may not interferere with adjacent cell slot (different hopping sequence)- improvements: acceptable quality with 9 dB SNR versus 11 dB
Giuseppe Bianchi
GP8.25
Structure of a TDMA slotStructure of a TDMA slot
Symmetric structureDATA: 2 x 57 data bits
114 data bits per burst“gross” bits (error-protected; channel coded)“gross” rate: 24 traffic burst every 26 frames (120 ms)
22.8 kbps gross rate13 kbps net rate!
S: 2 x 1 stealing bit Also called stealing flags, toggle bitsNeeded to grab slot for FACCH (other signalling possible)
TB3
DATA57
S1
S1
Trainingsequence
26
Data57
TB3
148 bit burst156.25 bit (15/26 ms = 0.577 ms)
Normal burst
6
Giuseppe Bianchi
Tail & training bitsTail & training bits
2 x TB = 3 tail bits set to 000At start and end of frameLeave time available for transmission power ramp-up/downAssures that Viterbi decoding starts and ends at known state
26 bit training sequenceKnown bit pattern (8 Training Sequence Code available)for channel estimation and synchronizationWhy in the middle?
Because channel estimate reliable ONLY when the radio channel “sounding” is taken!Multipath fading rapidly changes the channel impulse response…
Giuseppe Bianchi
Training sequencesTraining sequences
Different codes used in adjacent cells! Avoids training sequence Disruption because of co-channel interference.
7
Giuseppe Bianchi
Power mask for Normal BurstPower mask for Normal Burst
7.6 bits 4.9 bits
156.75 bits; 162.2 bits
Giuseppe Bianchi
Guard Period rationaleGuard Period rationale
Assume the followingsynchro mechanism:
BTS transmits at time 0MS receives at time d/cMS transmits at time 3+d/cBTS receives at time 3+ 2d/c
Offset depending on d!
BTSd
1 2 3 4BTS downlink tx
MS downlink rx 1 2 3 4
1
1
MS uplink rx
BTS uplink rx1
Expected RX time!
8
Giuseppe Bianchi
Guard period sizingGuard period sizing
BTS timeMS time
dwlink slot 1 dwlink slot 4…
dwlink slot 1 dwlink slot 4…
uplink slot 1
uplink slot 1
…
…
Maximum cell radius:
KmCGTcd
cd
CGT
rate
bits
rate
bits 5.42708332
25.83000002
2≈
⋅⋅
≈⋅
=→=
Is there something wrong? (GSM says that cells go up to 35 km)
Giuseppe Bianchi
Frame synchronizationFrame synchronization
Timing Advance (TA)Parameter periodically transmitted by BTS during MS activity6 bits = 0-63Meaning: anticipate transmission of TA bitsTA=0: no advance
I.e. transmit after 468.75 bitsafter downlink slot
TA=63: Transmit after 405.75 bits time
BTSTA (transmitted in the SACCH)
dwlink slot 4
uplink slot 1MS timeTA
dwlink slot 4
uplink slot 1uplink slot 1
BTS time
TA avoids collision!
9
Giuseppe Bianchi
Timing Advance analysisTiming Advance analysis
Downlink propagation delay:d/c
Uplink propagation delay:d/c
Uplink delay with TA:d/c-TA
Perfect resynchronization occurs whenTA = 2d/c
Maximum cell size for perfect resync:
[ ][ ] [ ] [ ]kmskm
sbitsbitscTAd 89.34/300000
/2708335.31
2=⋅=⋅=
8.25 bits Guard time additionally available for imperfect sync (+/- error)
Giuseppe Bianchi
And when the user is not connected?And when the user is not connected?But wants to connect…But wants to connect…
TB8
Trainingsequence
41
Data36
TB3
88 bit burst156.25 bit (0.577 ms)
Access burst
Solution: USE A DIFFERENT BURST FORMATAccess Burst: much longer Guard Period availabledrawback: much less space for useful information
GP68.25
No collision with subsequent slot for distances up to 37.8 km
10
Giuseppe Bianchi
Other burst formats in GSMOther burst formats in GSM
5 different bursts available
Normal BurstAccess Burst
Frequency Correction BurstSynchronization BurstDummy Burst
Giuseppe Bianchi
Frequency Correction BurstFrequency Correction Burst
All 0s burst (TB=0, too)After GMSK modulation:
Sine wave at freference+1625/24 kHz (67.7083 kHz)Acts as a “beacon”
When an MS is searching to detect the presence of a carrierAllows an MS to keep in sync with reference frequency
GP8.25
TB3
Fixed bit pattern (all 0s)142
TB3
Frequency Correction Burst
11
Giuseppe Bianchi
Dummy BurstDummy Burst
Used to fill inactive bursts on the BCCHGuarantees more power on BCCH than that on other channels
Important, when MS needs to find BCCH
GP8.25
TB3
TB3
Dummy BurstTraining
sequence26
Fixed bit pattern58
Fixed bit pattern58
Giuseppe Bianchi
Synchronization BurstSynchronization Burst
Longer training sequenceIt is the first burst an MS needs to demodulate!1 single training sequence
Data field:Contains all the information to synchronize the frame
i.e. synchronize frame counter Contains the BSIC (Base Station Identity Code, 6 bits)
3 bits network code (operator)» Important at international boundary, where same frequencies
can be shared by different operators3 bits color codeTo avoid listening a signal from another cell, thinking it comes from the actual one!
GP8.25
TB3
TB3
Synchronization BurstTraining
sequence64
Sync data39
Sync data39
12
Giuseppe Bianchi
PART 4PART 4GSM GSM –– Radio InterfaceRadio Interface
Lecture 4.2logical channels
Giuseppe Bianchi
LogicalLogical vsvs Physical channelsPhysical channels
Physical channelsTime slots @ given frequenciesIssues: modulation, slot synchronization, multiple access techniques,duplexing, frequency hopping, etc
Logical channelsBuilt on top of phy channelsIssue: which information is exchanged between MS and BSS
Physical channels(FDMA/TDMA)
Logical channels(traffic channels, signalling (=control) channels)
13
Giuseppe Bianchi
Logical Logical –– physical mappingphysical mapping
frequency
Physical Channel: data rate r, time slot i
frequency
Logical Channel Mapping: Different channels may share a same physical channel
Logical channel A: data rate r/3, time slot i, frame 3kLogical channel B: data rate 2r/3, time slot i, frame 3k+1, 3k+2
Frame 8 Frame 9 Frame 10 Frame 11 Frame 12
Giuseppe Bianchi
GSM logical channelsGSM logical channels
MS BSSFast associated controlFACCH(dedicated to a specific MS)
MS BSSSlow associated controlSACCH(point-to-point signalling channels)
MS BSSStand-alone Dedicated controlSDCCHDedicated Control channel (DCCH)
BSS MSPagingPCH(used for access management)
BSS MSAccess GrantAGCH(point to multipoint channels)
MS BSSRandom AccessRACHCommon Control channel (CCCH)
BSS MSSynchronizationSCH
BSS MSFrequency CorrectionFCCH(same information to all MS in a cell)
BSS MSBroadcast controlBCCHBroadcast channel
MS BSSTCH half RateTCH/H
MS BSSTCH full rateTCH/FTraffic channel (TCH)
Additional logical channels available for special purposes(SMS, group calls, …)
14
Giuseppe Bianchi
An example procedure involvingAn example procedure involving signallingsignalling
Setup for an incoming call (call arriving from fixed network part -MS responds to a call)
Steps:- paging for MS- MS responds on RACH- MS granted an SDCCH- authentication & ciphering on SDCCH- MS granted a TS (TCH/FACCH)- connection completed on FACCH- Data transmitted on TCH
Giuseppe Bianchi
PART 4PART 4GSM GSM –– Radio InterfaceRadio Interface
Lecture 4.3Traffic channels and
associated signalling channels
15
Giuseppe Bianchi
Traffic channels (TCH/F)Traffic channels (TCH/F)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
Periodic pattern of 26 frames (120 ms = 15/26 ms/TS * 8 TS/frame* 26 frame)
24 TCH frames over 26
20 1 3 4 5 6 7 20 1 3 4 5 6 7 20 1 3 4 5 6 7 20 1 3 4 5 6 7Same TS in every frame
GP8.25
TB3
DATA57
S1
S1
TrainingSeq. (26)
Data57
TB3
148 bit burst156.25 bit (0.577 ms)
Theoretical rate: 1/8 channel rate: r=33.85 kbps
2 signalling frames: r 31.25 kbps
Burst overhead (114 bits over 156.25): r 22.8 kbps
Giuseppe Bianchi
Speech codingSpeech coding
Analog voice
A/D conversion8000 samples/s13 bit/sample
Digital voice104 kbps
160 voice samples (20 ms)
(2080 bits)
Speech CODER(8:1 compression)
260 bits block13 kbps
16
Giuseppe Bianchi
Discontinuous transmissionDiscontinuous transmission
Speech coder implements Voice Activity Detection (VAD)Voice activity: idle for about 40% of the timeTo avoid clipping: hangover period (80ms)
When IDLE, do not transmitSave battery consumptionReduces interference
Receiver side: silence is disturbing!Missing received frames replaced with “comfort noise”Comfort noise spectral density evaluated by TX decoderAnd periodically (480ms) transmitted in special frame (SID= Silence Descriptor)
time
talking talkinglistening
Giuseppe Bianchi
Channel CodingChannel Coding
182 bits 78 bits
260 bits260 bits block divided into-Class I: important bits (182)
-Class Ia: Most important 50-Class Ib: Less important 132
-Class II: low importance bits (78)
50 bits 3 132 bits 4
Parity bitsTail bits(0000)
First step: block coding for error detection in class Ia (error discard frame)Second step: convolutional coding for error correction
378 bits
Convolutional coding, r=1/2
78 bits
456 bits
Coding: needed to move from 10-1 to 10-3 radio channel native BERdown to acceptable range (10-5 to 10-6) BER
17
Giuseppe Bianchi
Block interleavingBlock interleaving
0 1 2 3 4 5 6 7
8 9 10 11 12 13 14 15
16 17 18 19 20 21 22 23
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..
.. .. .. .. .. .. .. ..448 449 450 451 452 453 454 455
8
57
B1 B2 B3 B4 B5 B6 B7 B8
8 blocks, each with 57 bits
Giuseppe Bianchi
Diagonal InterleavingDiagonal Interleaving
B1 B3B2 B4 B5 B7 B8B6 B1 B3B2 B4 B5 B7 B8B6 B1 B3B2 B4 B5 B7 B8B6
Block n-1 Block n Block n+1
nn BB 11
5 /− nn BB 41
8 /− 115 / +nn BB… … … … 1
48 / +nn BB
InterInter--burst Interleavingburst Interleaving
GP8.25
TB3
S1
S1
Trainingsequence
26
TB3
1−= nxB n
xB 4−=
PRICE TO PAY: delay!! (block spreaded over 8 bursts 37 ms)
18
Giuseppe Bianchi
Bad Frame IndicatorBad Frame Indicator
When errors cannot be corrected:Frame must be discarded
In substitution, transmit speech frame
predictively calculated No more than 16 consecutive BFI
If this happens, receiver muted
Giuseppe Bianchi
Slow Associated Control ChannelSlow Associated Control Channel
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
TCH/F(0…7) TCH/F(0…7)
SACCH(0…7) IDLE frame
SACCH-0 SACCH-1 SACCH-2 SACCH-3 SACCH-4 SACCH-5 SACCH-6 SACCH-7
1 SACCH burst (per TCH) every 26 frames (120 ms)
Always associated to instaurated call on TCH (TCH + SACCH = TACH)On the same Time Slot
Periodic (order of ½ second) time-scale information for radio link control
19
Giuseppe Bianchi
SACCH blockSACCH block
184 signalling bitsBlock coding adds 40 bits (=224)4 tail (zero) bits (=228)1/2 Convolutional encoding (=456 bits)
Interleaving:8 blocks of 57 bits;spreaded into four consecutive bursts
4 bursts = 1 and only 1 SACCH block!SACCH rate:
184 bits/480 ms = 383.3 bit/s
B1 B3B2 B4 B5 B7 B8B6
Odd/eveninterleaving
104 frames = 480 ms
Giuseppe Bianchi
SACCH contentsSACCH contents
184 bits = 23 bytes
Power levelTiming advanceMeasurement reports for link qualityMeasurement reports for handover management
When available space: SMS
When call in progress!
free
free
(21 bytes – datalink layer)Includes measurement reports
0 41 52 63 7
Power level
Timing advance
20
Giuseppe Bianchi
Power controlPower control
MS has ability to reduce/increase power
Up to its power class maximumMaximum one 2 dB step every 60 msuplink power measures taken by BTSnotified back to MS via SACCH
Power level values: 0-150 = 43 dBm (20 W)15 = 13 dBm (20 mW)
algorithm: manifacturer specificruns on BSC
power control applied also on downlink
Maximum power (defined by class)
Minimum power(13 dBm for GSM)
(0 dBm for DCS 1800)
2 dB steps;
Giuseppe Bianchi
Measurement valuesMeasurement valuesRXLEV
Power level Present channel + neighbohr cell)
RXQUALBit Error Rate (raw)
--48RXLEV_63
-48-49RXLEV_62
………
………
-107-108RXLEV_3
-108-109RXLEV_2
-109-110RXLEV_1
-110-RXLEV_0
To (dBm)
From (dBm)
RX signal level
-12.8RXQUAL_7
12.86.4RXQUAL_6
6.43.2RXQUAL_5
3.21.6RXQUAL_4
1.60.8RXQUAL_3
0.80.4RXQUAL_2
0.40.2RXQUAL_1
0.2-RXQUAL_0
To (%)
From (%)
Bit error Ratio
Averaged over 1 SACCH block (480ms = 104 frames)
21
Giuseppe Bianchi
Fast Associated Control ChannelFast Associated Control Channel
FACCH: urgent signallingUsed when several signalling information needs to be transmitted
Call setupHandover
FACCH block = 184456 after coding
Interleaved as voice blockSpreaded on 8 bursts
Replaces a voice block (20 ms) on the TCHVia stealing bitsVoice block(s) discarded
Maximum FACCH bit rate184*6/120 [bits/ms] = 9.2 kbps (vs 383 bps of SACCH!)
Giuseppe Bianchi
FACCH insertion in TCHFACCH insertion in TCH
Via Stealing bits- upper bit = odd bits stolen- lower bit = even bits stolen- both bits = all burst stolen
time
Figure: shows example of 2 FACCH blocks stealing a TCH (note begin and end behavior due to interleaving)
22
Giuseppe Bianchi
HalfHalf--rate traffic channels (TCH/H)rate traffic channels (TCH/H)Support for 5.6 kbps voice codecsSpecification in 1995228 bits block
112 bits of compressed 20ms voice 95 bits class I
» + 3 parity + 6 tail + convolutional coding 104/21117 bits class 2
Interleaving: Same as voice (block + diagonal + odd/even)But on 4 bursts
Framing:
5 63 41 2 11 129 107 8
TCH/H 0…7 [subchannel 0]
TCH/H 8…15[subchannel 1] SACCH 0…7 SACCH 8…15
Giuseppe Bianchi
Other traffic channelsOther traffic channels
TCH dataBasic speed: 9.6 kbps (data,fax)Other speeds: <2.4; 4.8; 9.6; 14.4;
Different coding detailsSee text(s)
Major difference with voice:Interleaving with depth = 19 (!!!)complete fading of a burst is recoverable (unlike voice)
23
Giuseppe Bianchi
PART 4PART 4GSM GSM –– Radio InterfaceRadio Interface
Lecture 4.4Broadcast Carrier and
Channels
Giuseppe Bianchi
SF BB BB PP PP SF PP PPPP PP SF PP PPPP PP SF PP PPPP PP SF PP PPPP PP
Broadcast Channel (usual) Broadcast Channel (usual) organizationorganization
51 frame structure vs 26235.38 ms period (vs 120 ms)
Sub-blocks with 10 framesStarting with Frequency Correction Channel (FCCH)Immediately followed by Synchronization Channel (SCH)
Other frames (numbered from #0 to #50):#50 idle#2,3,4,5 BCCHRemaining: Paging (PCH) / Access Grant (AGCH) [=PAGCH]
51 frame structure - downlink
10 frame sub-block
24
Giuseppe Bianchi
BCCH carrier placementBCCH carrier placementOn Downlink
Corresponding uplink dedicated to Random Access Channel
RR RR RR RR RR R
51 frame structure - uplink
On one frequency per cell (beacon)MUST BE on Time Slot #0Other Time slots may be used by TCHProvided that:• All empty slots are filled with DUMMY bursts• Downlink power control must be disabled
RR RR RR RR RR RR RR RR RR RR RR RR RR RR RRRR RR RR RR RR
Giuseppe Bianchi
MS powering upMS powering up
First operation when MS turned ON: spectrum analysis(either on list of up to 32 Radio Frequency Channel Numbers of current network)(or on whole 124 carriers spectrum)
25
Giuseppe Bianchi
tuningtuning
MS listens on strongest beacon for a pure sine wave (FCCH)
Coarse bit synchronizationFine tuning of oscillator
Immediately follows SCH burstFine tuning of synchronization (64 bits training sequence)Read burst content for synchronization data
25 bits (+ 10 parity + 4 tail + ½ convolutional coding = 78 bits)6 bits: BSIC19 bits: Frame Number (reduced)
Finally, MS can read BCCH
Giuseppe Bianchi
MultiMulti--framing structureframing structure
0 1 2 3 4 5 6 7
8 TS, 4.615 ms
SF BBBB PP P P SF PP P PPP P P SF PP P PPP P P SF PP P PPP P P SF PP P PPP P PT T T T T T T T T T T T T T T T T T T T T T T TS
1 multiframe = 26 TDMA frames (120 ms) 1 multiframe = 51 TDMA frames (235.38 ms)
Multiframe 0 Multiframe 1 Multiframe 49 Multiframe 50Multiframe 2
Multiframe 0 Multiframe 1 Multiframe 25
…………
1 superframe = 51 x 26-multiframe or 26 x 51-multiframe (1326 TDMA frames, 6.12 s)
superframe 0 superframe 1 superframe 2046 superframe 2047superframe 2
1 hyperframe = 2048 superframe (2715648 TDMA frames, 3h28m53s.76)
26
Giuseppe Bianchi
Why frame number?Why frame number?
Frame #Distinguishes logical channels in the same physical channel
Multiframe #Determines how BCCH is constructed
I.e. which specific information transmitted on BCCH during a given multiframe
Superframe #Used as input parameter by encyphering algorithm
Superframe # Multiframe # frame #FN =
Giuseppe Bianchi
BCCH contentsBCCH contents184 bits
Coded in 456 bits and interleafed in 4 burstssame coding and interleaving as SACCHBCCH capacity
184 bits / (51*8*15/26 ms) ~ 782 bpsInformation provided
Details of the control channel configurationParameters to be used in the cell
Random access backoff values Maximum power an MS may access (MS_TXPWR_MAX_CCCH)Minimum received power at MS (RXLEV_ACCESS_MIN)Is cell allowed? (CELL_BAR_ACCESS)Etc.
List of carriers used in the cellNeeded if frequency hopping is applied
List of BCCH carriers and BSIC of neighboring cells
27
Giuseppe Bianchi
control channel alternative control channel alternative organizationorganization
SF BB BB PP PP SF PP PPPP PP SF D SF SF
51 frame structure – small capacity cell
RR RR RR RR RR RR RR RR RR R RRR RR RR R
DOWN
UP
D D D D D D D D D D D D D D D D D D D D D DD
D D DD D D DDD D DD D D DDD D DD D D DD
BB BB PP PP PP PPPP PPDOWN
51 frame structure – large capacity cell
PP PPPP PP PP PPPP PP PP PPPP PP
RR RR RR RR RR RRR RR RR RR RR RR RR RR RR RR RR RR RR RR RRRR RR RR RR RR
Used in TS 2 (and, eventually, 4 and 6) of beacon carrierProvides additional paging and RACH channels
Integrates SDCCH in same channel as other control informationLeaves additional TS all available for TCH
UP
Giuseppe Bianchi
Why 26 and 51?Why 26 and 51?Last frame (idle) in TCH multiframe (Frame #25) used as “search frame”!
T T T T T T T T T T T T T T T T T T T T T T T TS
- An active call transmits/receive in 25 frames, except the last one.- in this last frame, it can monitor the BCCH of this (and neighbor) cell- this particular numbering allows to scan all BCCH slots during a superframe
- important slots while call is active: frequency correction FCCH and sync SCH!- needed for handover
-Worst case: at most every 11 TCH multiframes (1.32 s), there will bea frequency correction burst of a neighboring cell
28
Giuseppe Bianchi
PART 4PART 4GSM GSM –– Radio InterfaceRadio Interface
Lecture 4.5Paging, Random Access,
dedicated signaling
Giuseppe Bianchi
Why pagingWhy pagingChannel assignment:
only upon explicit request from MSPaging
needed to “wake-up” MS from IDLE state when incoming call arrives to MS
MS accesses on RACH to ask for a channel Generally SDCCH (but immediate TCH assignment is possible)
BSS/MSCMS
1) paging
3) Channel assignment
2) Random access
Paging channel: PCHAccess Grant Channel: AGCHRandom Access Channel: RACH
PAGCH CCCHCommon ControlCHannel
29
Giuseppe Bianchi
PagingPaging
Paging message generated by MSCWhich receives incoming call
Transferred to subset of BSCPaging limited to user’s location areaPaging message contains:
List of cells where paging should be performedIdentity of paged user (IMSI or TMSI)
Paging message coded in 4 consecutive bursts over the air interface
Same coding/interleaving structure of SACCH (184 456 bits)Paging for more MSs may be joined in one unique paging message
Giuseppe Bianchi
Discontinuous Reception (DRX)Discontinuous Reception (DRX)
MS in idle mode should listen to paging channelTo save battery, PCH divided into sub-channels
Subdivision based on last 3 digits of IMSIUser listens only to relevant sub-channel
Switches off otherwisePCH sub-channels pattern communicated on BCCH
Up to 9 sub-channels
SF BB BB PP PP SF PP PPPP PP SF PP PPPP PP SF PP PPPP PP SF PP PPPP PP
51 frame BCCH structure - downlink
30
Giuseppe Bianchi
Access procedureAccess procedureAlways activated by MS
In response to paging (incoming call)When location update needs to be performedWhen new call is generated by MS
Based on access burst sent on RACHAccess burst coding: 8 payload bits (channel_req) 36 coded bits
+6 parity; + 4 tail; + ½ convolutional coding
TB8
TrainingSeq. (41)
Data36
TB3
Access burstGP
68.25
Establishment Cause (3 bits)
Random discriminator(5 bits)
100: response to radio call101: emergency call110: new establishment of call111: supplementary service (SMS, etc)…000: other case
Random discriminator: (0…31) value randomly generated by MS
Channel_req message
Giuseppe Bianchi
RACH operationRACH operation
A,B C,B C A,B A B
MS-A MS-B
MS-C
Multiple Access Technique for simultaneous accessCollision resolution based on
- random retrial period- “permission” probability
(SLOTTED ALOHA protocol)Same thing..!
31
Giuseppe Bianchi
RACH performanceRACH performance
N stationsEach transmits with probability p
Retries, in average, every 1/p slotsrelevant probabilities:
( )( )
( )∑=
−
−
−⎟⎟⎠
⎞⎜⎜⎝
⎛
−
−
N
k
kNk
N
N
ppkN
pNp
p
2
1
1:collision
1:success
1:idle
Maximum efficiency: when p=1/N
Giuseppe Bianchi
RACH performance controlRACH performance control
BCCH broadcastsBackoff time
uniform distribution; max value: 3 to 50Maximum number of retransmission attempts
Never greater than 7May also specify:
time interval for a retry after failure (default=5s)RACH group access control
MSs divided into 10 groups, depending on SIM-related informationBTS may block selected groupsAllows to reduce RACH load down to as low as 10%
» Emergency calls bypass this rule…
32
Giuseppe Bianchi
Access Access signaling signaling -- 11MS BTS BSC MSC
Channel_requestrnd number Channel_required
rnd&frame number,Delay (TA estimate)
Channel_activation
Ch_activation_ack
rnd&frame number, channel description,Initial TA, initial max power
Immediate_assignment
Giuseppe Bianchi
Immediate Assignment messageImmediate Assignment messageon paging channel
I.e. AGCH is a dynamically mapped channel– name PAGCH is perhaps better…
Sent “as soon as possible”MS continues accessing the RACHMessage scheduling is an implementation dependent issue
I.e. which message to send in case of many messages, and on which paging slot (4 bursts)
MS must disable DRXTo monitor PAGCH for Immediate Assignment message detection
Immediate assignment reject possible
33
Giuseppe Bianchi
If same random discriminator?If same random discriminator?two MSs may have same random discriminator
Likely in heavy load, with only 5 bitsAnd transmit in the same frameOnly one wins (the other is faded)contention resolved via explicit MS identification
On SDCCH MS1ID1
MS2
ID2
BTS
ID1leave
continues
Giuseppe Bianchi
Access Access signalingsignaling -- 22MS BTS BSC MSC
Immediate_assignment… … … …
Initial_message
MS ID (IMSI or TMSI), MS capabilities (=classmark), establishment cause
Initial_message_ack (UA)
Copy of Initial message (including MS ID)
Establishment_indication
Further signaling: MSC to MS
34
Giuseppe Bianchi
StandStand--alone alone Dedicated Dedicated Control Control Channel Channel -- SDCCHSDCCH
Dedicated bidirectional channel to MSbut used to exchange signalling
Has an associated SACCHCoding: as SACCH
184 456 bits on 4 consecutive burstsTypical framing (SDCCH/8)
8 SDCCH (+8 SACCH) on 1 channel (carrier,TS)1 SDCCH message per 51-multiframe
184 bits / (51*8*15/26 ms) = 598/765 kbps ~ 782 bit/s1 SACCH every 2 multiframe
D0
D0
D0
D0
D1
D1
D1
D1
D2
D2
D2
D2
D3
D3
D3
D3
D4
D4
D4
D4
D5
D5
D5
D5
D6
D6
D6
D6
D7
D7
D7
D7
A0
A1
A2
A3
A0
A1
A2
A3
A0
A1
A2
A3
A0
A1
A2
A3
D0
D0
D0
D0
D1
D1
D1
D1
D2
D2
D2
D2
D3
D3
D3
D3
D4
D4
D4
D4
D5
D5
D5
D5
D6
D6
D6
D6
D7
D7
D7
D7
A4
A5
A6
A7
A4
A5
A6
A7
A4
A5
A6
A7
A4
A5
A6
A7
SDCCH/4 for smallcells – SDCCH shares
BCCH+PAGCH channel- see before -
1
Giuseppe Bianchi
PART 5PART 5GSM GSM –– Switching & MobilitySwitching & Mobility
Lecture 5.1Protocol architecture overview
Giuseppe Bianchi
The GSM network layerThe GSM network layer
Divided in three sub-layersRadio Resource Management (RR)
Provides a communication link between MS and MSC;
Mobility Management (MM)Manages DB for MS location
Communication Management (CM)Controls user connection
Underlying base:Transmission level
Transmission
RR
MM
CM
2
Giuseppe Bianchi
RRRR
Manages administration of frequencies and channelsMostly deals with air interface
Several RR functions considered in previous partGuarantees stable link upon handover
Surprise! handover is part of RR, not MM!Function summary:
Monitoring BCCH, PCHRACH administrationRequest/assignment of channelsMS power control & synchronizationHandover
Where is RR:MS, BTS, BSC, MSC
Giuseppe Bianchi
MMMM
Manages user location and tasks resulting from mobilityFunction summary:
TMSI assignmentMS localizationLocation updatingMS authenticationMS identification, attach/detach
Where is MM:MS, MSC
3
Giuseppe Bianchi
CMCM
Controls calls, supplementary services, and SMSFunction summary:
Call establishment (from MS, to MS)Emergency call managementCall terminationDTMF signaling (Dual Tone MultiFrequency)In-call modification
Where is CM:MS, MSC, GMSC
Giuseppe Bianchi
Protocol placementProtocol placement
CM
MM
RR
Trans.
MS BTS BSC MSC(VLR)
HLR
GMSC
4
Giuseppe Bianchi
Protocol outlineProtocol outlineMS BTS BSC
RelayMSC
AnchorMSC HLR
CM
MM
RR
RIL3-CC
RIL3-MM
RSM MAP/E
MAP/D
LAPDm LAPD MTP MTP MTPSCCP SCCP SCCP
TCAP
BSSMAPRIL3-RR
RIL3: Radio Interface Layer 3RSM: Radio Subsystem ManagementBSSMAP: BSS Management Application PartMAP: Mobile Application Part
TCAP: Transaction Capabilities Application PartSCCP: Signaling Connection Control PartMTP: Message Transfer PartLAPD: Link access Protocol on D channelLAPDm: Link access Protocol on Dm channel
Giuseppe Bianchi
PART 5PART 5GSM GSM –– Switching & MobilitySwitching & Mobility
Lecture 5.2handover (physical mobility)
5
Giuseppe Bianchi
Neighbor cellsNeighbor cells
A station must:monitor beacon power level of neighbor cells Keep detailed track of best 6 neighbor cellsDECODE their BCCH (i.e. read FCCH, SCH) to get parameters
At least once every 5 minutesBSIC (from SCH) refreshed every at most 30s
BTS1
BTS2
BTSn
Giuseppe Bianchi
Camping cell selection Camping cell selection path loss criterion C1path loss criterion C1
When cell parameters are the same, simply select cell with higher RXLEV!
( )[ ]PAX_CCHMS_TXPWR_M,0max SS_MINRXLEV_ACCE
RXLEV(n)C1(n)
−−−−
−=
RXLEV(n): received power from BTS(n)RXLEV_ACCESS_MIN: minimum received power level required for registration in the cell
(parameter transmitted on BCCH; typically –98 to –106 dB)MS_TXPWR_MAX_CCH: maximum allowed transmitted power on RACH
(parameter transmitted on BCCH; typically 31-39 dBm)P: maximum MS power (from MT class)
Select cell with greatest c1(n)>0:
6
Giuseppe Bianchi
Cell reselection criterion (C2)Cell reselection criterion (C2)
⎩⎨⎧
≥<
=
−×−−+=
0x10x0
H(x) where
T)TIMEH(PENALTY_ OFFSETTEMPORARY_ECT_OFFSETCELL_RESELC1(n)C2(n)
T: amount of consecutive time since considered cell became with C1>0PENALTY_TIME, CELL_RESELECT_OFFSET, TEMPORARY_OFFSET: BCCH parametersIf all parameters = 0, reselect cell with better path loss performance (no time hysteresis included)
Reselect cell with greatest C2>0:
Giuseppe Bianchi
Consequences of cell reselectionConsequences of cell reselection
None, when MS idle!No need to inform BTS at all!
Exception:When cell reselection implies a Location Area Update
Need to inform the network!Additional restriction:
C2>CELL_RESELECT_HYSTERESIS
BTS BTS
7
Giuseppe Bianchi
handoverhandoverProcedure in which an MS releases a connection with a BTS, and establishes a connection with a new BTS, while ensuring that the ongoing call is maintained
The MS remains in dedicated state (unlike cell reselection, where MS is in idle state)
Handoff: synonymous of handoverNeeds two mechanisms
Handover preparation: detection of cell-border crossingBased on radio link quality measurements
Handover execution: setup of a new channel in a cell, and tear-down of a previous channel
Improved handover mechanisms:Seamless handover: when active call performance is not impaired
Not possible in GSM: for about 100-200ms, communication is interruptedSoft Handover: when two channels are simultaneously set-up (old and new)
Not possible in GSM; possible in UMTS
Giuseppe Bianchi
Hard, Seamless, Soft handoverHard, Seamless, Soft handover
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf1
MSC
BSS 1 BSS 2
MSf2
MSC
BSS 1 BSS 2
MS
MSC
BSS 1 BSS 2
MS
f2
f1
f2
f1f1
before during after
Hardhandover
(GSM)
Seamless(DECT)
Softhandover(UMTS)
8
Giuseppe Bianchi
Handover classificationHandover classification
Rescue handover (mandatory handover)
Driven by radio channel quality degradation
Confinement handover (network-directed handover)
Target: minimize radio interferenceAssign new channel when old channel results critical for total interference
Traffic handover (network-directed handover)
Driven by traffic congestion conditionsAlso called load-balancing
Internal handoverIntra-BTS
New radio channel in the same cellNot termed as “handover” but as“subsequent assignment”
Inter-BTS (Intra-BSC)Under control of same BSC
External handoverInter-BSC (Intra-MSC)
Change reference BSC; may imply a location area update
Inter-MSCMost complex: need to change MSC
Classification by motivation Classification by typology
Giuseppe Bianchi
Types of handoverTypes of handover
A-MSC
BSC
BTS BTS BTS BTS
BSC BSC
R-MSC
A
A-bis
radiointerface
Anchor MSC: the MSC that first
managed the current call
Relay MSC: the MSC that currently
manages the call
Switchingpoint forinternal
handover
Switchingpoint for
all inter-MSChandover
Switchingpoint for
inter-BSChandover
9
Giuseppe Bianchi
Handover taxonomyHandover taxonomyBCHO: Base station Controlled Handover
Handover detection: BSHandover Execution: BS
MCHO: Mobile Controlled HandoverHandover detection: MSHandover Execution: MS
MAHO: Mobile Assisted HandoverHandover detection: MSHandover Execution: BS
GSM: somehow a BCHO with a flavor of MAHOHandover decision always taken by BSCBased on measures taken at both BTS and MSNew channel selection decision taken at BSC or R-MSC or A-MSC (depending on handover type) based on traffic consideration
Giuseppe Bianchi
Handover preparationHandover preparationMeasurements performed at BTS
Up-link signal level received from MS lower than thresholdRXLEV_UL < L_RXLEV_UL_H
Up-link signal quality (BER) received from MSRXQUAL_UL < L_RXQUAL_UL_H
Distance between MS and BTS adaptive timing advance parameter > MAX_MS_RANGE
Interference level in unallocated time slots.Measurements performed at MS.
Down-link signal level received from serving cellRXLEV_DL < L_RXLEV_DL_H
Down-link signal quality (BER) received from serving cellRXQUAL_DL < L_RXQUAL_DL_H
Down-link signal level received from n-th neighbor cell RXLEV_NCELL(n) > RXLEV_MIN(n)
--48RXLEV_63
-48-49RXLEV_62
………
………
-107-108RXLEV_3
-108-109RXLEV_2
-109-110RXLEV_1
-110-RXLEV_0
To (dBm)
From (dBm)
RX signal level
-12.8RXQUAL_7
12.86.4RXQUAL_6
6.43.2RXQUAL_5
3.21.6RXQUAL_4
1.60.8RXQUAL_3
0.80.4RXQUAL_2
0.40.2RXQUAL_1
0.2-RXQUAL_0
To (%)
From (%)
Bit error Ratio
10
Giuseppe Bianchi
A note on MS distanceA note on MS distance
Distance can be measured based on TATA = advance bits
Ideally, TA should be set as
Hence, the TA resolution, in mt, is:
INSUFFICIENT for microcells! Sufficient only to understand we are going out of the cell
[ ] bitbit tcTAdcdtbitsTA ⋅⋅=⇒=⋅
22
( ) mtTAmsmsmt
TAtcTATAd bit 5542
][833.270
1]/[300000
2⋅≈
⋅=
⋅=
Giuseppe Bianchi
Handover preparation Handover preparation ––additional metricsadditional metrics
Transmission powerMaximum MS transmission powerMaximum serving BTS transmission powerMaximum neighboring BTSs transmission power
congestion statusof serving BTSof neighboring BTSs
provided they can support the MS.Handover Margin
To avoid ping-pong handover effect5-10 dB in normal operation; up to 30dB in urban operation (to fight shadowing)
RXLEV(cell A)
RXLEV(cell B)Handover
RXLEV(cell A)
RXLEV(cell B)Handover
hysteresis
HANDOVER ALGORITHM: operator-dependent!GSM standard SUGGESTS a simple referencealgorithm, but implementation left to operator
11
Giuseppe Bianchi
handover procedure skeletonhandover procedure skeleton
2) Switching point prepares new path on fixed net
2
1) Handover request goes up to switching point
1
MSC
BTSBTS
BSCBSC
3) Switching point sends HO command to MS
3
4) MS accesses new channel
4
5) Old channel/path torn down
5
Giuseppe Bianchi
Signaling for intraSignaling for intra--MSC handoverMSC handover(simplified)(simplified)
MS BTS-A MSC BSC-B MSBTS-BBSC-A
Measurement info handover required(destination cell)
handover requestChannel allocationChannel activation
ACKhandover req. ack(contains handovercommand messageprepared by BSC-Bwith info on BCCH,
channel assigned, etc)
handover commandhandover command
handover access(an access burst on new TCH!!!)physical info
(new TA, power)handover complete
handover complete
handover detectionhandover detection
clear command
clear complete Measurementinfo
12
Giuseppe Bianchi
InterInter--MSC handoverMSC handoverMore complex, as an ISDN circuit must be set between MSCs
We’ll not enter into details (just the basic ideas)Two cases
MSC-A MSC-R1
First MSC change (basic handover)
MSC-A MSC-R1
Second MSC change (subsequent handover)
MSC-R2
X
X
X Note the role of theAnchor MSC!
Giuseppe Bianchi
PART 5PART 5GSM GSM –– Switching & MobilitySwitching & Mobility
Lecture 5.3location registration/updateAuthentication & Ciphering
13
Giuseppe Bianchi
Location AreaLocation Areavs vs
MSC service areaMSC service area
LA-4 … LA-n
LA-1 LA-2 LA-3
MSC VLR
Giuseppe Bianchi
RegistrationRegistration vsvs updateupdateVery similar procedures, with goals:
Determine where the user isAuthenticate user
Differences:Location Registration
User first access to PLMN» Needs to send IMSI and receive TMSI
Location UpdateSubsequent accesses to PLMN (either in old or new MSC/VLS)
» Also after MS shut-down!» TMSI-based identification
Registered user:The PLMN knows the LA where the user is (or is supposed to be)
14
Giuseppe Bianchi
Procedure startProcedure start--upup
MS switches onDetects BCCH carrier
Tune and synchronizeListens to BCCHObtains Location Area Identifier
LAI: [CC,MNC,LAC]Country Code (CC): 3 digitsMobile Network Code: 2 digitsLocation Area Code: max 5 digits
Giuseppe Bianchi
LR/LU (very) basic ideaLR/LU (very) basic idea
MSC VLR
BTS
BTSBTS
BSC
MS
HLR
1
1) Obtain LAI from BCCH2
2) Register MS ID into local VLR
3
3) Update pointer at HLR
15
Giuseppe Bianchi
Location RegistrationLocation RegistrationMS VLR HLR AUCBSS/MSC
Loc. Upd. RequestIMSI, LAI
Update Loc. AreaIMSI, LAI
Auth. Param. Req.IMSI
Auth. Info. Req.IMSI
Auth. Info(Auth. Parameters)
Auth. Info(Auth. Parameters)
authentication
Activateciphering
Update LocationIMSI, MSRN
Insert Subscrib. Data IMSI, additional data
Insert Subscrib. DataACK
Locat. Upd. AcceptIMSI
Start CipheringKc
Locat. Upd. Accept
Forward new TMSI TMSI
TMSI Realloc Cmd
Locat. Upd. Accept
TMSI Realloc ACKTMSI ACK
Giuseppe Bianchi
AuthenticationAuthentication(managed by VLR)(managed by VLR)
Authentication RequestChallenge: 128 bit RAND
A3
RANDKi
SRES Authentication ResponseSigned RESult: 32 bit SRES
Equal?
SRES
VLRMS
HLR /AUC
IMSI, RAND
SRES, Kc
A8
RANDKi
Kc
16
Giuseppe Bianchi
Authentication (details)Authentication (details)Side effect of authentication:
Generate encryption key Kc via A8 algorithmSecret A3, A8 algorithms (one-way hash functions)
Stored into the SIM Along with secret key Ki
Note that roaming operator DOES NOT need to know them!Since A3,A8 run ONLY in the AUC at the home HLRKi is NEVER transmitted away from AUC or MS!
Generally implemented together[SRES,Kc] = A38[Ki,RAND]
To reduce signaling, real implementation slightly different:
VLR sends IMSIReceives back several tuples of (RAND, SRES, Kc) to be used for the considered MS also in subsequent accesses
Giuseppe Bianchi
cipheringcipheringA5 algorithm is known (to allow roaming)Generates two ciphering sequences
one for uplink, one for downlinkSequence periodic with period 26x51x2048=2,715,648
221=2,097,152 < 2,715,648 < 222=4,194,304114 bits per frame, depending on frame numberXOR-ed with burst data field
A5MS A5 BTS
Frame numberFN, 22 bits
Kc64 bits
Frame numberFN, 22 bits
Kc64 bits
XOR XOR
XOR XOR
S2 S2S1S1
In-clear uplink In-clear uplinkenciphered uplink
In-clear downlinkenciphered downlinkIn-clear downlink
17
Giuseppe Bianchi
Location Update in same VLRLocation Update in same VLR(same as location registration, but with TMSI)(same as location registration, but with TMSI)
MS VLR HLR AUCBSS/MSCLoc. Upd. Request
TMSI, LAIUpdate Loc. Area
TMSI, LAI
Auth. Param. Req.IMSI
Auth. Info. Req.IMSI
Auth. InfoN x (Kc,RAND,SRES)
Auth. InfoN x (Kc,RAND,SRES)
authentication
Activateciphering
Update LocationIMSI, MSRN
Insert Subscrib. Data IMSI, additional data Ins. subs. data ACK
Locat. Upd. AcceptIMSI
Start CipheringKc
Locat. Upd. Accept
Forward new TMSI
TMSI Realloc Cmd
Locat. Upd. Accept
TMSI Realloc ACK TMSI ACK
GenerateNew TMSI
Giuseppe Bianchi
Changing Changing MSC/VLRMSC/VLR
Base Station
MSC Public switched telephone network
PSTN
Public switched telephone network
PSTN
Base Station
MSC
VLR
VLR
HLR
An MS always has a dedicated entry in the HLR Plus one entry in JUST 1 VLR
(related to the MSC the user is connected to)
18
Giuseppe Bianchi
TMSITMSITMSI = Temporary Mobile Subscriber Identity
4 octets (32 bits)Renewed periodically; at every LU / IMSI_attach
Via TMSI_Reallocation_Command/TMSI_Reallocation_CompleteRATIONALE: renew TMSI when transmitted in clear!(TMSI reallocation occurs in ciphering mode)
Meaningful only in a given VLRSpecifically, only for a given Location Area!!
Some author (Mouly-Pautet) uses the term» TIC (Temporary Identity Code) = 4 bytes» TMSI = TIC+LAI = unambiguous user identification
While entering a new Location Area:user must identify itself with TMSI+LAI pair.
Operator may set a 6min up to 24hrs periodicity
for LU (value transmitted on BCCH)
IMSI_attach = a special LU in a same Location Area;
IMSI_attach followsan IMSI_detach
(power-down of MS)
Giuseppe Bianchi
Location Update: different VLRLocation Update: different VLRMS VLR-new HLR VLR-oldBSS/MSC
Loc. Upd. RequestTMSI(+ old LAI), LAI
Update Loc. AreaTMSI(+ old LAI), LAI
authentication
Activateciphering
Update LocationIMSI, MSRN
Insert Subscrib. Data IMSI, additional data Ins. subs. data ACK
Locat. Upd. AcceptIMSI
Start CipheringKc
… …
Forward new TMSI
GenerateNew TMSI
Send parameters (TMSI, old LAI)
IMSI response (IMSI,RAND,SRES,Kc)
Cancel LocationIMSI
Cancel Locat. ACK
determineVLR-old
From old LAI
19
Giuseppe Bianchi
Special Special casescases
1. New VLR not capable of determining old VLR from old LAI
2. Old VLR does not recognize TMSI
Identification procedureIMSI transmitted in clear
MS MSC
Identity ResponseIMSI
Identity Request
PAGING: - Normally based on TMSI- But when no valid TMSI information available (e.g. after a DB restore
after crash), based on IMSI
Giuseppe Bianchi
PART 5PART 5GSM GSM –– Switching & MobilitySwitching & Mobility
Lecture 5.4Call Management & routing
20
Giuseppe Bianchi
NotationNotation
A call involves two “Parties”Calling Party (caller)
user generating the callCalled Party (callee)
user receiving the callMobile Originating Call (MOC)
Call originated by an MSMobile Terminating Call (MTC)
Call directed to an MS
Giuseppe Bianchi
Call Call establishment establishment basicsbasics
MS MSCFixedparty
setup
MS MSCFixedparty
setup
setup
Call confirmed
alertingalerting
connectconnect
DATA
setup
Mobile Terminated Call Mobile Originated Call
Call proceedingalerting
alerting
ConnectConnect
Connect Ack
DATA
In ISDN ISUP: - setup = IAM (Initial Address Message); - Alerting = ACM (Address Complete Message); - Connect = ANS (Answer)
21
Giuseppe Bianchi
CallCall establishment establishment stepssteps
Channel requestPaging request
Paging ResponseImmediate Assignment
Authentication ResponseAuthentication Request
Ciphering Mode CompleteCiphering mode command
Call ConfirmedSetup
Assignment CompleteAssignment Command
AlertingConnect
Connect Acknowledge
MobileTerminated CallMS network
Channel request
Service RequestImmediate Assignment
Authentication ResponseAuthentication Request
Ciphering Mode CompleteCiphering mode command
Call proceedingSetup
AlertingConnect
Connect Acknowledge
MobileOriginated CallMS network
Assignment CompleteAssignment Command
Giuseppe Bianchi
Radio Radio Resource allocationResource allocationthree standardized solutionsthree standardized solutions
Non-Off Air Call Set-Up (Non-OACSU)Normally used (previous description)
Off Air Call Set-Up (OACSU)TCH assigned only when the called party actually responds!
Best utilization of radio resource (avoids allocation if callee not available)Call drop if no TCH is available at this point
Very Early Assignment (VEA)Immediate assignment of TCH
Fastest signalling processWaste of resources
RACHRACHRACH
VEA TCH (FACCH)TCH (FACCH)Non-OACSU
OACSUSDCCH
TCH (DATA)
SDCCHTCH (DATA)TCH (DATA)
Connection established Callee responds
22
Giuseppe Bianchi
DTMF DTMF signalingsignalingDual-Tone Multi-Frequency
Digital tones associated to terminal keys ‘0’…’9’…’#’…
Inband signalling transmitted in the traffic channels!Not in the signalling network
MS MSCStart DTMF (w. key code)
Start DTMF ACK On FACCH)KeyPressed
Stop DTMF
On air interface: Signal trasmitted on FACCH as signalling data (code of pressed key)Otherwise coded compression would distort DTMF tonesTone generated at MSC when STOP DMTF message received
Giuseppe Bianchi
MSCAHLR
MSCC
MSCB
PLMN
ISDN
GMSC
VLRB
Routing an Routing an MTCMTC
1: M
SISDN
4: M
SRN2: M
SISDN3: M
SRN5: MSRN
6: TMSI 7: paging
23
Giuseppe Bianchi
Routing anRouting an MTC (alternative)MTC (alternative)reduces signalling load during reduces signalling load during LULU
MSCAHLR
MSCC
MSCB
PLMN
ISDN
GMSC
VLRB
During an LU within a same VLR, MSRN is NOT signaled!
MSRN retrieved on a per-call basis!(choice of solution depends on trade-offs)
1: M
SISDN
2: MSISDN
6: M
SRN 5: MSRN
7: MSRN
8: TMSI 9: paging 3: IMSI4: MSRN
Giuseppe Bianchi
PLMN 1(ITA)
MSCGMSC 1
HLR
PLMN 2(UK)
MSC
ISDN(ita)
TransitExchange
LocalExchange
InternationalSwitching
Center
MSISDN+39.335.1234567
335.1234567
InternationalSwitching
Center
ISDN(UK)
MSRN+44.NDC.8877665
Routing calls to Roaming Routing calls to Roaming MSMS
24
Giuseppe Bianchi
““tromboningtromboning””
PLMN 1(ITA)
MSCGMSC 1
HLR
PLMN 2(UK)
MSCISC(UK)
MSISDN+39.335.1234567
MSRN+44.NDC.9876543
Call to MSISDN+39.335.1234567
ISC(ITA)
Is the PRICE (!) to pay for
simple routing and billing
Call to MSISDN+39.335.3043125
Giuseppe Bianchi
Tromboning technical solutionsTromboning technical solutions
First alternative: national-wiseAdd a new database - Roamer Location Cache (RLC)
Consulted by ISCs (which MUST support GSM-MAP!)
Second alternative: PLMN specificRLC within the PLMN + associated switchCaller must dial special NDC number (the switch!)
I.e. must know the MS is roaming in the PLMN…
Additional devices and protocol modifications required» Extensions toVLR or to GMSC» Details in “Lin-Chlamtac”
25
Giuseppe Bianchi
RLC at ISC RLC at ISC -- Location Location Registration Registration and and call call managementmanagement
HLR
PLMN 2(UK)MSCVLRISC
(UK)
ISC(ITA)
PLMN 1(ITA)
RLC
1
2
3
3 bis
4
Giuseppe Bianchi
Short Short Message ServiceMessage ServiceSMS:
messages up to 160 bytesMessage concatenation allowed
Transmitted on air interface over:SACCH (when user in conversation)SDCCH (when user in idle state)
Two transmission modes in a cell:Point-to-pointcell broadcast
Connectionless servicemessage switching (store&forward)Implemented through the Short Message Service Center
26
Giuseppe Bianchi
SMS SMS routing routing managementmanagement
MSC
IWMSC
Short Message Service Center
PLMNInternet, PSDN
SMS-GMSC
MSCPLMN
HLR
Get routing info for terminating MS
Giuseppe Bianchi
Protocol hierarchyProtocol hierarchy
Short MessageRelay Entity
(SMR)
Short MessageControl Entity
(SMC)
Short MessageApplication Layer
(SM-AL)
Short MessageTransfer Layer
(SM-TL)
Short MessageRelay Layer
(SM-RL)
ConnectionManagement
Sublayer (CM-sub)
MS
MSC IW-MSC
SM-SC
Short MessageRelay Entity
(SMR)
Short MessageControl Entity
(SMC)
Short MessageRelay Protocol
(SM-RP)
Short MessageControl Protocol
(SM-CP)
Short Message Transfer Protocol (SM-TP)
Quite complex signalling involved (see specific texts)
27
Giuseppe Bianchi
Number portabilityNumber portability
Subscriber may switch operator without changing his numberFirst implemented in fixed network
Recently (may 2002) extended to mobile networksEssential for fair competition among network operators
UK survey: 42% of corporate subscribers were willing to change mobile operator; but 96% were, if number could be ported
Resistence from leading operatorsNumber portability helps newer operators to compete with traditional ones
Giuseppe Bianchi
NotationNotation
Donor switchThe switch corresponding to a “ported” telephone number
Recipient switchThe switch to which the ported number is attached
28
Giuseppe Bianchi
Technical solutionsTechnical solutionsa)a) call forwardingcall forwarding
switch switch
switch
Originating network Donor network
Recipient networkOriginating switch sets-up trunk to donor switchDonor switch sets-up trunk to recipient switchSimplest solution, as call forwarding is a feature available in virtually all switches
But extremely inefficient routing and trunking resource consumption!
Giuseppe Bianchi
Technical solutionsTechnical solutionsb) b) query query on on releaserelease
switch switch
switch
Originating network Donor network
Recipient network
Donor switch “blocks” incoming call with a release message (REL)REL carries a QoR cause value, stating that called party number is ported Originating switch then queries Number Portability database
SS7 ISUP IAM
SS7 ISUP REL
NumberPortabilityDataBase
29
Giuseppe Bianchi
Technical solutionsTechnical solutionsc) c) allall--call querycall query
switch switch
switch
Originating network Donor network
Recipient network
Originating switch queries Number Portability database for every call!!- best solution if majority of numbers are ported (no interaction with donor)- but very high DB load, as EVERY number must be looked-up!
NumberPortabilityDataBase
Giuseppe Bianchi
Mobile Mobile Number PortabilityNumber PortabilitySame ideas as fixed number portability
The donor switch is the GMSC of the donor networkDonor GMSC Call forwarding (if more efficient fixed number portability not supported)
While porting number, may also get MSRN!
GMSC
Incoming call
Donor network
HLRSignaling relayfunction
GMSC
Recipient network
HLRMSC Note: If path must cross GMSC:Use Intermediate Routing Number
MSRN(or IRN)
MSRN IRN
Clearly, still suffers of tromboning!
30
Giuseppe Bianchi
Return IRN
Mobile Mobile Number PortabilityNumber Portability((with all call query approachwith all call query approach))
switch
Incoming call
GMSC
Recipient network
HLRMSC
IRN
NumberPortabilityDataBase
Query IRN
Return MSRNQuery MSRN
Giuseppe Bianchi
MobileMobile Number PortabilityNumber Portabilityimprovedimproved –– ((with all call query approachwith all call query approach))
Return MSRNswitch
Incoming call
GMSC
Recipient network
HLRMSC
MSRN
NumberPortabilityDataBase
Query MSRN
Signaling relayfunction