2G Mobile Communication Systems - Startseite TU Ilmenau
Transcript of 2G Mobile Communication Systems - Startseite TU Ilmenau
Integrated Communication Systems Group Ilmenau University of Technology
2G/3G Mobile Communication Systems
Winter 2012/13
Outline
2G Review: GSM
Services
Architecture
Protocols
Call setup
Mobility management
Security
HSCSD
GPRS
Architecture
Protocols
QoS
EDGE
UMTS
Mobile Communication Networks 3 Andreas Mitschele-Thiel, Florian Evers
2G to 3G Evolution: GSM - GPRS - UMTS
GSM
RAN
Base station
Base station controller
Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLR AuC EIR
GMSC
TransmissionATM based
GSM
Mobile Communication Networks 4 Andreas Mitschele-Thiel, Florian Evers
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 5 Andreas Mitschele-Thiel, Florian Evers
possible radio coverage of the cell
idealized shape of the cell cell
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
Mobile Communication Networks 6 Andreas Mitschele-Thiel, Florian Evers
Cellular systems: Frequency planning I
Frequency 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 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
f4 f5
f1 f3
f2
f6
f7
f4 f5
f1 f3
f2
f6
f7
f4 f5
f1 f3
f2
f6
f7 f2
f1 f3
f2
f1 f3
f2
f1 f3
Mobile Communication Networks 7 Andreas Mitschele-Thiel, Florian Evers
GSM: Air Interface
FDMA (Frequency Division Multiple Access) / FDD (Frequency Division Duplex)
1 2 3 123 124 . . .
890 MHz 915 MHz
1 2 3 123 124 . . .
935 MHz 960 MHz
200 kHz
Uplink Downlink
frequency
TDMA (Time Division Multiple Access)
time
Downlink
8 7 6 5 4 3 2 1
4,615 ms
= 1250 bit
Uplink
8 7 6 5 4 3 2 1
Mobile Communication Networks 8 Andreas Mitschele-Thiel, Florian Evers
Framing Modulation
(GMSK)
GSM: Voice Coding
Voice coding Channel coding
Framing Modulation
(GMSK)
114 bit/slot 114 + 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 equalizer
Tail: needed to enhance receiver performance
Flag 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 µs 577 µs
tail user data Training S guard
space S user data tail guard
space
3 bits 57 bits 26 bits 57 bits 1 1 3
Mobile Communication Networks 9 Andreas Mitschele-Thiel, Florian Evers
Mobile Terminated Call (MTC)
PSTN calling
station GMSC
HLR VLR
BSS BSS BSS
MSC
MS
1 2
3
4
5
6
7
8 9
10
11 12
13
16 10 10
11 11 11
14 15
17
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
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
Mobile Communication Networks 10 Andreas Mitschele-Thiel, Florian Evers
RA
RA
RA RA
RA
RA RA
RA
RA
Location Update
Location Update
Location Update
Location Update
Location Update
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
Paging
Signalling Cost
Paging Area Update
Signalling Cost
TOTAL
Signalling Cost
+
=
Mobile Communication Networks 11 Andreas Mitschele-Thiel, Florian Evers
Handover
The problem:
Change the cell while communicating
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
Lin
k q
ualit
y
Link to cell 1 Link to cell 2 time
cell 1
cell 2
Handover margin (avoid ping-pong effect)
cell 1 cell 2
Mobile Communication Networks 12 Andreas Mitschele-Thiel, Florian Evers
Handover procedure (change of BSC)
HO access
BTSold BSCnew
measurement
result
BSCold
Link establishment
MSC MS
measurement
report
HO decision
HO required
BTSnew
HO request
resource allocation
ch. activation
ch. activation ack HO request ack
HO command HO command
HO command
HO complete HO complete
clear command clear command
clear complete clear complete
„Make-before-break“ strategy
make
break
Mobile Communication Networks 13 Andreas Mitschele-Thiel, Florian Evers
GSM - authentication
A3
RAND Ki
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
Mobile Communication Networks 14 Andreas Mitschele-Thiel, Florian Evers
GSM - key generation and encryption
A8
RAND Ki
128 bit 128 bit
Kc
64 bit
A8
RAND Ki
128 bit 128 bit
SRES
RAND
encrypted
data
mobile network (BTS)
MS with SIM
AuC
BTS
SIM
A5
Kc
64 bit
A5
MS
data data
cipher
key
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
Mobile Communication Networks 15 Andreas Mitschele-Thiel, Florian Evers
GSM Evolution – Overview
Spectral
efficency
Data
traffic
adaptive
modulation EDGE
diversity
space
time
Macro diversity
Intelligent antennas
Equalizer
adaptive redundancy interference
Frequency hopping
Dynamic channel
allocation
GPRS
bursty
HSCSD
continuous
Interference cancelation (multi-user detection)
Mobile Communication Networks 16 Andreas Mitschele-Thiel, Florian Evers
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)
mainly software update
additional HW needed if more than 3 slots are used
Uplink
Downlink
7 1 2 3 8 4 5 6 1 2
7 1 2 3 8 4 5 6 1 2
Mobile Communication Networks 17 Andreas Mitschele-Thiel, Florian Evers
2G to 3G Evolution: GSM - GPRS - UMTS
GPRS Core (Packet Switched)
SGSN
GGSN
Inter-net
GSM
RAN
Base station
Base station controller
Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLR AuC EIR
GMSC
TransmissionATM based
GSM+GPRS
Mobile Communication Networks 18 Andreas Mitschele-Thiel, Florian Evers
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 19 Andreas Mitschele-Thiel, Florian Evers
carrier TS
0 1 2 3 4 5 6 7
0 1 2 3 4 5 6 7
Multiplexing
Multislot capability
GPRS: Multiplexing and multislot allocation
Mobile Communication Networks 20 Andreas Mitschele-Thiel, Florian Evers
GPRS protocol architecture
appl.
IP/X.25
LLC
GTP
MAC
radio
MAC
radio FR
RLC BSSGP
IP/X.25
FR
Um Gb Gn
L1/L2 L1/L2
MS BSS SGSN GGSN
UDP
Gi
SNDCP
RLC BSSGP IP IP
LLC UDP
SNDCP GTP
BSSGP: Base Station Subsystem GPRS Protocol (control plane: routing & QoS)
SNDCP: Subnetwork-Dependent Convergence Protocol (mapping, segmentation,
header compression)
Mobile Communication Networks 21 Andreas Mitschele-Thiel, Florian Evers
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 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 22 Andreas Mitschele-Thiel, Florian Evers
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
Mobile Communication Networks 23 Andreas Mitschele-Thiel, Florian Evers
EDGE – Adaptive Modulation and Coding Schemes Scheme Modulation Maximum
rate [kb/s]
Code Rate Family
MCS-9 59.2 1.0 A
MCS-8 54.4 0.92 A
MCS-7 44.8 0.76 B
MCS-6 29.6 / 27.2 0.49 A
MCS-5
8PSK
22.4 0.37 B
MCS-4 17.6 1.0 C
MCS-3 14.8 / 13.6 0.80 A
MCS-2 11.2 0.66 B
MCS-1
GMSK
8.8 0.53 C
Mobile Communication Networks 24 Andreas Mitschele-Thiel, Florian Evers
2G to 3G Evolution: GSM - GPRS – UMTS R99/R3
GPRS Core (Packet Switched)
SGSN
GGSN
Inter-net
GSM
RAN
Base station
Base station controller
Base station
Base station
UTRAN
Radio network controller
Base station Base station
Base station
MSC
ISDN
GSM Core (Circuit switched)
HLR AuC EIR
GMSC
TransmissionATM based
GSM+GPRS+UMTS R99
Mobile Communication Networks 25 Andreas Mitschele-Thiel, Florian Evers
2G to 3G Evolution: GSM - GPRS - UMTS R5 - IMS
GPRS Core (Packet Switched)
SGSN
GGSN
Inter-net
GSM
RAN
Base station
Base station controller
Base station
Base station
UTRAN
Radio network controller
Base station Base station
Base station
TransmissionIP based
3G Core
GERAN GERAN + UMTS R5 + IMS