Integrated Communication Systems Group
Ilmenau University of Technology
Mobile Network Evolution – Part 1
GSM and UMTS GSM
Cell layout Architecture Call setup Mobility management Security
GPRS Architecture Protocols QoS
EDGE
UMTS
Architecture
2
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
2G to 3G Evolution: GSM - GPRS - UMTS
GSMRAN
Base station
Base stationcontroller
Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLRAuCEIR
GMSC
TransmissionATM based
GSM
3
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Architecture of the GSM system
GSM is a PLMN (Public Land Mobile Network) several providers setup mobile networks following the GSM standard
within each country
GSM system comprises 3 subsystems
Radio Access Network: covers all radio aspectsMS (mobile station) BSS (base station subsystem) or RAN (radio access network)
BTS (base transeiver station) BSC (base station controller)
Core Network: call forwarding, handover, switchingMSC (mobile services switching center) LR (location register): HLR and VLROMC (operation and maintenance centre) AuC (authentication centre) EIR (equipment identity register)
4
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
possible radio coverage of the cell
idealized shape of the cellcell
segmentation of the area into cells
GSM: cellular network
use of several carrier frequencies not the same frequency in neighboring cells cell radius varies from some 100 m up to 35 km depending on
user density, geography, transceiver power etc. hexagonal shape of cells is idealized (cells overlap, shapes depend
on geography) if a mobile user changes cells
-> handover of the connection to the neighbor cell
5
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Cellular systems: Frequency planning IFrequency reuse only with a certain distance between the base stations
Typical (hexagon) model:
reuse-3 cluster: reuse-7 cluster:
Other regular pattern: reuse-19 the frequency reuse pattern determines the experienced SIR Fixed frequency assignment:
certain frequencies are assigned to a certain cell problem: different traffic load in different cells
Dynamic frequency assignment: base station chooses frequencies depending on the frequencies already used in
neighbor cellsFrequency Hopping (fixed or random sequence of frequencies)
Improves quality for slow moving or stationary users (frequency diversity) Reduces impact of intercell interference by statistical averaging
f4f5
f1f3
f2
f6
f7
f4f5
f1f3
f2
f6
f7
f4f5
f1f3
f2
f6
f7f2
f1f3
f2
f1f3
f2
f1f3
6
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
GSM: Air Interface
FDMA (Frequency Division Multiple Access) / FDD (Frequency Division Duplex)
1 2 3 123124. . .
890 MHz 915 MHz
1 2 3 123124. . .
935 MHz 960 MHz
200 kHz
Uplink Downlink
frequency
TDMA (Time Division Multiple Access)
time
Downlink
87654321
4,615 ms = 1250 bit
Uplink
87654321
7
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Framing Modulation(GMSK)
GSM: Voice Coding
Voice coding Channelcoding
Framing Modulation(GMSK)
114 bit/slot114 + 42 bit
Guard (8.25 bits): avoid overlap with other time slots (different time offset of neighboring slot)Training sequence: select the best radio path in the receiver and train equalizerTail: needed to enhance receiver performanceFlag S: indication for user data or control data
1 2 3 4 5 6 7 8
GSM TDMA frame
GSM time-slot (normal burst)
4.615 ms
546.5 µs577 µs
tail user data TrainingSguardspace S user data tail
guardspace
3 bits 57 bits 26 bits 57 bits1 1 3
8
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Mobile Terminated Call (MTC)
PSTNcallingstation GMSC
HLR VLR
BSSBSSBSS
MSC
MS
1 2
3
4
5
6
7
8 9
10
11 12
1316
10 10
11 11 11
14 15
17
1: calling a GSM subscriber2: forwarding call to GMSC3: signal call setup to HLR4, 5: request MSRN from VLR6: forward responsible
MSC to GMSC7: forward call to
current MSC8, 9: get current status of MS10, 11: paging of MS12, 13: MS answers14, 15: security checks16, 17: set up connection
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Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
RA
RA
RA RA
RA
RA RA
RA
RA
LocationUpdate
LocationUpdate
LocationUpdate
LocationUpdate
LocationUpdate
Location Management / Mobility Management
The issue: Compromise between minimizing the area where
to search for a mobile minimizing the number of
location updates
Solution 1:Large paging area
Solution 2:Small paging area
PagingSignalling Cost
Paging Area UpdateSignalling Cost
TOTALSignalling Cost
+
=
10
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Handover
The problem:Change the cell whilecommunicating
Reasons for handover: Quality of radio link
deteriorates Communication in other cell
requires less radio resources Supported radius is
exceeded (e.g. Timing advance in GSM)
Overload in current cell Maintenance
Link
qua
lity
Link to cell 1 Link to cell 2 time
cell 1
cell 2
Handover margin (avoid ping-pong effect)
cell 1 cell 2
11
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Handover procedure (change of BSC)
HO access
BTSold BSCnew
measurementresult
BSCold
Link establishment
MSCMSmeasurementreport
HO decisionHO required
BTSnew
HO request
resource allocationch. activation
ch. activation ackHO request ackHO commandHO commandHO command
HO completeHO completeclear commandclear command
clear complete clear complete
„Make-before-break“ strategy
make
break
12
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
GSM - authentication
A3
RANDKi
128 bit 128 bit
RAND
SRES* =? SRES
A3
RAND Ki
128 bit 128 bit
SRES 32 bit
SRES
Authentication Request (RAND)
Authentication Response (SRES 32 bit)
mobile network
AuC
MSC
SIM
Ki: individual subscriber authentication key SRES: signed response
SRES* 32 bit
Challenge-Response:• Authentication center provides RAND to Mobile• AuC generates SRES using Ki of subscriber and
RAND via A3• Mobile (SIM) generates SRES using Ki and RAND• Mobile transmits SRES to network (MSC)• network (MSC) compares received SRES with one
generated by AuC
13
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
GSM - key generation and encryption
A8
RANDKi
128 bit 128 bit
Kc64 bit
A8
RAND Ki
128 bit 128 bit
SRES
RAND
encrypteddata
mobile network (BTS)
MS with SIM
AuC
BTS
SIM
A5
Kc64 bit
A5MS
data data
cipherkey
Ciphering:• Data sent on air interface ciphered for security• A8 algorithm used to generate cipher key• A5 algorithm used to cipher/decipher data• Ciphering Key is never transmitted on air
14
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
2G to 3G Evolution: GSM - GPRS - UMTS
GPRS Core (PacketSwitched)
SGSN
GGSN
Inter-net
GSMRAN
Base station
Base stationcontroller
Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLRAuCEIR
GMSC
TransmissionATM based
GSM+GPRS
15
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
GPRS (General Packet Radio Service)
Introducing packet switching in the network Using shared radio channels for packet transmission over the air:
multiplexing multiple MS on one time slot flexible (also multiple) allocation of timeslots to MS
(scheduling by PCU Packet Control Unit in BSC or BTS) using free slots only if data packets are ready to send
(e.g., 115 kbit/s using 8 slots temporarily) standardization 1998, introduction 2001 advantage: first step towards UMTS, flexible data services
GPRS network elements GSN (GPRS Support Nodes): GGSN and SGSN GGSN (Gateway GSN)
interworking unit between GPRS and PDN (Packet Data Network) SGSN (Serving GSN)
supports the MS (location, billing, security) HLR (GPRS Register – GR)
maintains location and security information
16
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
carrierTS0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
Multiplexing
Multislot capability
GPRS: Multiplexing and multislot allocation
17
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
GPRS services
End-to-end packet switched traffic (peak channel rates) 28 kbps (full use of 3 time slots, CS-1: FEC) 171.2 kbps (full use of 8 time slots, CS-4: no FEC)
Average aggregate throughput of a cell (Source: H. Menkes, WirelessWeb, Aug.
2002) 95 kbps (for both up and downlink)Assumptions: 4/12 reuse, realistic RF conditions, random traffic Worse figures for individual TCP traffic
Adaptive Coding Schemes (adaptive Forward Error Control – FEC) CS 1: 9.05 Kbps/slot CS 2: 13.4 Kbps/slot CS 3: 15.6 Kbps/slot CS 4: 21.4 Kbps/slot (no FEC)
Problems and limits IP-based network => high latency, no guarantees Limited data rate: 28 kbps (3 slot/CS-1) - 64.2 kbps (3 slot/CS-4) Latency/flow control problems with TCP
18
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
EDGE (Enhanced Data Rates for GSM Evolution)Enhanced spectral efficiency depends on: Size of frequency band Duration of usage Level of interference with others (power)
EDGE Technology: EDGE can carry data speeds up to 236.8 kbit/s for 4
timeslots (theoretical maximum is 473.6 kbit/s for 8 timeslots)
Adaptation of modulation depending on quality of radio path GMSK (GSM standard – 1 bit per symbol) 8-PSK (3 bits per symbol)
Adaptation of coding scheme depending on quality of radio path (9 coding schemes)
Gain: data rate (gross) up to 69,2kbps (compare to 22.8kbps for GSM)
complex extension of GSM!
NodeB
UE 1
UE 2
Near-far problem
19
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
EDGE – Adaptive Modulation and Coding SchemesS c h e m e M o d u la t i o n M a x i m u m
ra te [k b /s ]C o d e R a te F a m i l y
M C S -9 5 9 .2 1 .0 AM C S -8 5 4 .4 0 .9 2 AM C S -7 4 4 .8 0 .7 6 BM C S -6 2 9 .6 / 2 7 .2 0 .4 9 AM C S -5
8 P S K
2 2 .4 0 .3 7 BM C S -4 1 7 .6 1 .0 CM C S -3 1 4 .8 / 1 3 .6 0 .8 0 AM C S -2 1 1 .2 0 .6 6 BM C S -1
G M S K
8 .8 0 .5 3 C
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Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
Payload for GPRS and EDGE
21
Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
2G to 3G Evolution: GSM - GPRS – UMTS R99/R3
GPRS Core (PacketSwitched)
SGSN
GGSN
Inter-net
GSMRAN
Base station
Base stationcontroller
Base station
Base station
UTRAN
Radio networkcontroller
Base station Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLRAuCEIR
GMSC
ATM based
GSM+GPRS+UMTS R99
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Integrated Communication Systems Group
Mobile Communication Networks (RCSE)
2G to 3G Evolution: GSM - GPRS - UMTS R5 - IMS
GPRS Core (PacketSwitched)
SGSN
GGSN
Inter-net
GSMRAN
Base station
Base stationcontroller
Base station
Base station
UTRAN
Radio networkcontroller
Base station Base station
Base station
IP based
3G Core
GERANGERAN + UMTS R5 + IMS