Download 2G Mobile Communication Systems

2G/3G Mobile Communication Systems
Winter 2012/13
Integrated Communication Systems Group
Ilmenau University of Technology
Outline



2G Review: GSM
 Services
 Architecture
 Protocols
 Call setup
 Mobility management
 Security
HSCSD
GPRS
 Architecture
 Protocols
 QoS

EDGE

UMTS
2G to 3G Evolution: GSM - GPRS - UMTS
Base station
Transmission
ATM based
Base station
Base station
controller
Base station
GSM
RAN
GSM
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
MSC
GSM Core
(Circuit
switched)
ISDN
GMSC
HLR
AuC
EIR
3
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



RSS (radio subsystem): covers all radio aspects
 MS (mobile station)
 BSS (base station subsystem) or RAN (radio access network)
 BTS (base transeiver station)
 BSC (base station controller)
NSS (network and switching subsystem): call forwarding, handover,
switching
 MSC (mobile services switching center)
 LR (location register): HLR and VLR
OSS (operation subsystem): management of the network
 OMC (operation and maintenance center)
 AuC (authentication center)
 EIR (equipment identity register)
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
4
GSM: cellular network
segmentation of the area into cells
possible radio coverage of the cell
cell





idealized shape of the cell
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
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
5
Cellular systems: Frequency planning I
Frequency reuse only with a certain distance between the base stations
Typical (hexagon) model:
f5
f4
f1
reuse-3 cluster:
f1
reuse-7 cluster:
f3
f3
f2
f1
f3
f2
f4
f6
f1
f3
f2
f7
f2
f5
f1
f6
f3
f5
f4
f7
f2
f6
f1
f3
f7
f2
Other regular pattern: reuse-19
 the frequency reuse pattern determines the experienced CIR
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 cells
Frequency 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
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
6
GSM: Air Interface
FDMA (Frequency Division Multiple Access) / FDD (Frequency Division Duplex)
Uplink
890 MHz
1
2
3
...
Downlink
935 MHz
915 MHz
123 124
1
2
3
...
960 MHz
123 124
200 kHz
frequency
TDMA (Time Division Multiple Access)
Downlink
1
2
3
4
5
6
7
8
Uplink
1
2
3
4
5
6
7
4,615 ms
= 1250 bit
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
8
time
7
GSM: Voice Coding
Channel
coding
Voice coding
Modulation
(GMSK)
Framing
114 bit/slot
114 + 42 bit
GSM TDMA frame
1
2
3
4
5
7
6
8
4.615 ms
GSM time-slot (normal burst)
guard
space
tail
3 bits
user data
S Training S
user data
57 bits
1 26 bits 1
57 bits
guard
tail space
3
546.5 µs
577 µs
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 equalizer
Tail: needed to enhance receiver performance
Flag S: indication for user data or control data
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
8
Mobile Terminated Call (MTC)
1: calling a GSM subscriber
2: forwarding call to GMSC
3: signal call setup to HLR
4, 5: request MSRN from VLR
6: forward responsible
MSC to GMSC
calling
station
7: forward call to
current MSC
8, 9: get current status of MS
10, 11: paging of MS
12, 13: MS answers
14, 15: security checks
16, 17: set up connection
4
HLR
5
3 6
8 9
14 15
7
PSTN
1
VLR
2
GMSC
MSC
10
10 13
16
10
BSS
BSS
BSS
11
11
11
11 12
17
MS
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
9
Location Management / Mobility Management
The issue: Compromise between
 minimizing the area where
to search for a mobile
 minimizing the number of
location updates
TOTAL
Signalling Cost
Solution 1:
Large paging area
Solution 2:
Small paging area
RA
RA
Location
RA
Update
RA
RA
Location
RA
Update
RA
RA
RA
=
Paging
 Signalling
Cost
Area Update
+ Paging
Signalling Cost
Location
Update
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
Location
Update
Location
Update
10
Handover
The problem:
Change the cell while
communicating
cell 2
cell 1
Link quality
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
cell 1
Handover margin
(avoid ping-pong
effect)
cell 2
Link to cell 1
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
Link to cell 2
time
11
Handover procedure (change of BSC)
„Make-before-break“ strategy
MS
BTSold
BSCold
measurement
measurement
report
result
MSC
BSCnew
BTSnew
HO decision
HO required
HO request
resource allocation
ch. activation
HO command
HO command
HO command
HO request ack
ch. activation ack
HO complete
HO complete
make
HO access
Link establishment
clear command
clear command
clear complete
clear complete
Mobile Communication Networks
break
Andreas Mitschele-Thiel, Florian Evers
12
GSM - authentication
Ki
AuC
RAND
128 bit
128 bit
A3
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
RAND
RAND
mobile network
Authentication Request (RAND)
Ki
128 bit
128 bit
A3
SRES
MSC
SIM
32 bit
Authentication Response (SRES 32 bit)
SRES
SRES* =? SRES
Ki: individual subscriber authentication key
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
SRES: signed response
13
GSM - key generation and encryption
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
Ki
AuC
RAND
RAND
128 bit
128 bit
MS with SIM
RAND
128 bit
A8
cipher
key
Kc
64 bit
BTS
Mobile Communication Networks
128 bit
SIM
A8
mobile network (BTS)
data
Ki
encrypted
data
A5
Kc
64 bit
SRES
data
MS
A5
Andreas Mitschele-Thiel, Florian Evers
14
GSM Evolution – Overview
adaptive
modulation
EDGE
space
Spectral
efficency
Intelligent antennas
diversity
time
interference
Frequency
hopping
adaptive
redundancy
Dynamic
channel
allocation
Mobile Communication Networks
Macro diversity
GPRS
Interference
cancelation
(multi-user
detection)
Andreas Mitschele-Thiel, Florian Evers
bursty
Equalizer
HSCSD
continuous
Data
traffic
15
HSCSD (High-Speed Circuit Switched Data)

continuous use of multiple time slots for a single user
(on a single carrier frequency)

asynchronous allocation of time slots between DL and UL

gain: net data rate up to 115,2 kbps (allocation of all 8 traffic channels)
Downlink
1
2
3
4
5
6
7
8
1
2
Uplink
1
2
3
4
5
6
7
8
1

mainly software update

additional HW needed if more than 3 slots are used
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
2
16
2G to 3G Evolution: GSM - GPRS - UMTS
Base station
Transmission
ATM based
Base station
Base station
controller
Base station
MSC
GSM Core
(Circuit
switched)
GSM
RAN
ISDN
GMSC
HLR
AuC
EIR
GSM+GPRS
SGSN
Internet
GPRS Core
(Packet
Switched)
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
GGSN
17
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
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
18
GPRS: Multiplexing and multislot allocation
Multiplexing
TS
0
1
2
3
4
5
6
7
5
6
7
carrier
Multislot capability
0
1
Mobile Communication Networks
2
3
4
Andreas Mitschele-Thiel, Florian Evers
19
GPRS protocol architecture
MS
BSS
Um
SGSN
Gb
Gn GGSN
Gi
appl.
IP/X.25
IP/X.25
SNDCP
SNDCP
LLC
LLC
RLC
MAC
RLC
MAC
BSSGP
FR
radio
GTP
UDP
GTP
UDP
BSSGP
IP
IP
FR
L1/L2
L1/L2
radio
BSSGP: Base Station Subsystem GPRS Protocol (control plane: routing & QoS)
SNDCP: Subnetwork-Dependent Convergence Protocol (mapping, segmentation,
header compression)
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
20
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
CS
CS
CS
1:
2:
3:
4:
9.05 Kbps/slot
13.4 Kbps/slot
15.6 Kbps/slot
21.4 Kbps/slot (no Forward Error Correction)
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
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
21
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)
Near-far problem
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!
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
UE 1
NodeB
UE 2
22
EDGE – Adaptive Modulation and Coding Schemes
Scheme
Modulation
M CS-9
M CS-8
M CS-7
M CS-6
M CS-5
M CS-4
M CS-3
M CS-2
M CS-1
8PSK
Mobile Communication Networks
GM SK
Maximum
rate [kb/s]
59.2
54.4
44.8
29.6 / 27.2
22.4
17.6
14.8 / 13.6
11.2
8.8
Andreas Mitschele-Thiel, Florian Evers
Code Rate
Family
1.0
0.92
0.76
0.49
0.37
1.0
0.80
0.66
0.53
A
A
B
A
B
C
A
B
C
23
2G to 3G Evolution: GSM - GPRS – UMTS R99/R3
Transmission
ATM based
Base station
Base station
Base station
controller
MSC
GSM Core
(Circuit
switched)
GSM
RAN
Base station
GSM+GPRS+UMTS R99
Base station
Base station
Base station
Radio network
controller
GMSC
HLR
AuC
EIR
SGSN
Internet
GPRS Core
(Packet
Switched)
UTRAN
Mobile Communication Networks
ISDN
Andreas Mitschele-Thiel, Florian Evers
GGSN
24
2G to 3G Evolution: GSM - GPRS - UMTS R5 - IMS
Base station
Base station
GERAN
GSM
RAN
Base station
Base station
Base station
Base station
Base station
controller
GERAN + UMTS R5 + IMS
Radio network
controller
SGSN
UTRAN
Mobile Communication Networks
Andreas Mitschele-Thiel, Florian Evers
Transmission
IP based
Internet
3G Core
GPRS
Core
(Packet
Switched)
GGSN
25