Transcript Global System for Mobile (GSM)

Global System for Mobile communications
(GPRS, EDGE, UMTS, LTE
and…)
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GSM History
Year
Events
1982
CEPT establishes a GSM group in order to develop the standards for a pan-European
cellular mobile system
1985
Adoption of a list of recommendations to be generated by the group
1986
Field tests were performed in order to test the different radio techniques proposed for the
air interface
1987
TDMA is chosen as access method (in fact, it will be used with FDMA) Initial
Memorandum of Understanding (MoU) signed by telecommunication operators
(representing 12 countries)
1988
Validation of the GSM system
1989
The responsibility of the GSM specifications is passed to the ETSI
1990
Appearance of the phase 1 of the GSM specifications
1991
Commercial launch of the GSM service
1992
Enlargement of the countries that signed the GSM- MoU> Coverage of larger
cities/airports
1993
Coverage of main roads GSM services start outside Europe
1995
Phase 2 of the GSM specifications Coverage of rural areas
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GSM world coverage map
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Differences Between First and Second
Generation Systems
• Digital traffic channels – first-generation systems are
almost purely analog; second-generation systems are
digital
• Encryption – all second generation systems provide
encryption to prevent eavesdropping
• Error detection and correction – second-generation digital
traffic allows for detection and correction, giving clear
voice reception
• Channel access – second-generation systems allow
channels to be dynamically shared by a number of users
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GSM network
The GSM network can be divided into four subsystems:
• The Mobile Station (MS).
• The Base Station Subsystem (BSS).
• The Network and Switching Subsystem (NSS).
• The Operation and Support Subsystem (OSS).
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GSM Network Architecture
Mobile Station
• Mobile station communicates across Um interface (air
interface) with base station transceiver in same cell as
mobile unit
• Mobile equipment (ME) – physical terminal, such as a
telephone or PCS
– ME includes radio transceiver, digital signal
processors and subscriber identity module (SIM)
• GSM subscriber units are generic until SIM is inserted
– SIMs roam, not necessarily the subscriber devices
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Base Station Subsystem (BSS)
• BSS consists of base station controller and one or more base
transceiver stations (BTS)
• Each BTS defines a single cell
– Includes radio antenna, radio transceiver and a link to a base
station controller (BSC)
• BSC reserves radio frequencies, manages handoff of mobile unit
from one cell to another within BSS, and controls paging
• The BSC (Base Station Controller) controls a group of BTS and
manages their radio ressources. A BSC is principally in charge of
handovers, frequency hopping, exchange functions and control of
the radio frequency power levels of the BTSs.
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Network Subsystem (NS)
• NS provides link between cellular network and public
switched telecommunications networks
– Controls handoffs between cells in different BSSs
– Authenticates users and validates accounts
– Enables worldwide roaming of mobile users
• Central element of NS is the mobile switching center
(MSC)
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Mobile Switching Center (MSC)
Databases
• Home location register (HLR) database – stores
information about each subscriber that belongs to it
• Visitor location register (VLR) database – maintains
information about subscribers currently physically in the
region
• Authentication center database (AuC) – used for
authentication activities, holds encryption keys
• Equipment identity register database (EIR) – keeps track of
the type of equipment that exists at the mobile station
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The Operation and Support Subsystem (OSS)
• The OSS is connected to the different components of the
NSS and to the BSC, in order to control and monitor the
GSM system. It is also in charge of controlling the traffic
load of the BSS.
• However, the increasing number of base stations, due to
the development of cellular radio networks, has provoked
that some of the maintenance tasks are transferred to the
BTS. This transfer decreases considerably the costs of the
maintenance of the system.
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GSM Channel Types
• Traffic channels (TCHs)
carry digitally encoded user speech or user data and have
identical functions and formats on both the forward and
reverse link.
• Control channels (CCHs)
carry signaling and synchronizing commands between
the base station and the mobile station. Certain types of
control channels are defined for just the forward or
reverse link.
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How a Cellular Telephone Call is Made
• All base stations continuously send out identification
signals (ID) of equal, fixed strength. When a mobile unit
is picked up and goes off-hook, it senses these
identification signals and identifies the strongest. This
tells the phone which cell it is in and should he associated
with. The phone then signals to that cell's base station
with its ID code, and the base station passes this to the
MSC, which keeps track of this phone and its present cell
in its database. The phone is told what channel to use for
talking, is given a dial tone, and the call activity proceeds
just like a regular call. All the nontalking activity is done
on a setup channel with digital codes.
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• Mobile unit
initialisation
• Mobile-originated
call
• Paging
• Call accepted
• Ongoing call
• Handoff
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GSM Radio interface
• Frequency allocation
• Two frequency bands, of 25 Mhz each one, have been
allocated for the GSM system:
• The band 890-915 Mhz has been allocated for the uplink
direction (transmitting from the mobile station to the base
station).
• The band 935-960 Mhz has been allocated for the
downlink direction (transmitting from the base station to
the mobile station).
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Multiple access scheme
• In GSM, a 25 MHz frequency band is divided, using a
FDMA, into 124 carrier frequencies spaced one from
each other by a 200 kHz frequency band.
• Each carrier frequency is then divided in time using a
TDMA. This scheme splits the radio channel into 8
bursts.
• A burst is the unit of time in a TDMA system, and it lasts
approximately 0.577 ms.
• A TDMA frame is formed with 8 bursts and lasts,
consequently, 4.615 ms.
• Each of the eight bursts, that form a TDMA frame, are
then assigned to a single user.
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GSM bands
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Maximum number of
simultaneous calls =
[(124) × 8] / N = 330
(if N=3)
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Multiframe components
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GSM frame format
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TDMS format
Trail bits: synchronisation between mobile and BS.
Encrypted bits: data is encrypted in blocks, Two 57-bit fields
Stealing bit: indicate data or stolen for urgent control signaling
Training sequence: a known sequence that differs for different
adjacent cells. It indicates the received signal is from the correct
transmitter and not a strong interfering transmitter. It is also used for
multipath equalisation. 26 bits.
Guide bits: avoid overlapping, 8.25 bits
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Data rate
• channel data rate in GSM
(1/120 ms) × 26 × 8 × 156.26 = 270.8 33Kbps
• User data rate
Each user channel receives one slot per frame
114 bits/slot  24 slots/mult iframe
 22.8kbps
120 ms/multifr am
With error control
65data bits/slot  24 slots/mult iframe
 13kbps
120 ms/multifr am
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Traffic Channels
full rate channels offer a data rate of 22.8 kBit/s:
• speech data: used as 13 kBit/s voice data plus FEC data
• packet data: used as 12, 6, or 3.6 kBit/s plus FEC data
half rate channels offer 11.4 kBit/s:
• speech data: improved codecs have rates of 6.5 kBit/s,
plus FEC
• packet data: can be transmitted at 3 or 6 kBit/s
Two half rate channels can share one physical channel
Consequence: to achieve higher packet data rates, multiple
logical channels have to be allocated =) this is what GPRS
does
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Speech coding
There are 260 bits coming out of a voice coder every 20 ms.
260 bits/20ms = 13 kbps
These 260 bits are divided into three classes:
• Class Ia having 50 bits and are most sensitive to errors
3-bit CRC error detection code 53, then protected by a
Convolutional (2,1,5) error correcting code.
• Class Ib contains 132 bits which are reasonably sensitive
to bit errors--protected by a Convolutional (2,1,5) error
correcting code.
• Class II contains 78 bits which are slightly affected by bit
errors– unprotected
• After channel coding: 260 bits
456bits
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Channel coding: block coding Then Convolutional coding
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Signal Processing in GSM
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Global Wireless Frequency Bands
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Evalution to 2.5G mobile Radio Networks
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• Newer versions of the standard were backward-compatible with
the original GSM phones.
• Release ‘97 of the standard added packet data capabilities, by
means of General Packet Radio Service (GPRS). GPRS provides
data transfer rates from 56 up to 114 kbit/s.
• Release ‘99 introduced higher speed data transmission using
Enhanced Data Rates for GSM Evolution (EDGE), Enhanced
GPRS (EGPRS), IMT Single Carrier (IMT-SC), four times as
much traffic as standard GPRS. accepted by the ITU as part of the
IMT-2000 family of 3G standards
• Evolved EDGE standard providing reduced latency and more than
doubled performance e.g. to complement High-Speed Packet
Access (HSPA). Peak bit-rates of up to 1Mbit/s and typical bitrates of 400kbit/s can be expected.
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GSM-GPRS
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• the Base Station Subsystem (the base stations and their
controllers).
• the Network and Switching Subsystem (the part of the
network most similar to a fixed network). This is
sometimes also just called the core network.
• the GPRS Core Network (the optional part which allows
packet based Internet connections).
all of the elements in the system combine to produce
many GSM services such as voice calls and SMS.
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ITU’s View of Third-Generation Capabilities
• Voice quality comparable to the public switched telephone
network
• High data rate. 144 kbps data rate available to users in highspeed motor vehicles over large areas; 384 kbps available to
pedestrians standing or moving slowly over small areas; Support
for 2.048 Mbps for office use
• Symmetrical / asymmetrical data transmission rates
• Support for both packet switched and circuit switched data
services
• An adaptive interface to the Internet to reflect efficiently the
common asymmetry between inbound and outbound traffic
• More efficient use of the available spectrum in general
• Support for a wide variety of mobile equipment
• Flexibility to allow the introduction of new services and
technologies
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Third Generation Systems (3G)
The dream of 3G is to unify the world's mobile computing
devices through a single, worldwide radio transmission
standard. However,
3 main air interface standards:
W-CDMA(UMTS) for Europe
CDMA2000 for North America
TD-SCDMA for China (the biggest market)
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UMTS (Universal Mobile Telecommunications
System ) Services
UMTS offers teleservices (like speech or SMS) and bearer services,
which provide the capability for information transfer between access
points. It is possible to negotiate and renegotiate the characteristics of
a bearer service at session or connection establishment and during
ongoing session or connection. Both connection oriented and
connectionless services are offered for Point-to-Point and Point-toMultipoint communication.
Bearer services have different QoS parameters for maximum transfer
delay, delay variation and bit error rate. Offered data rate targets are:
144 kbits/s satellite and rural outdoor
384 kbits/s urban outdoor
2048 kbits/s indoor and low range outdoor
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UMTS Architecture
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Core Network
The Core Network is divided in circuit switched and packet
switched domains. Some of the circuit switched elements are
Mobile services Switching Centre (MSC), Visitor location
register (VLR) and Gateway MSC. Packet switched elements
are Serving GPRS Support Node (SGSN) and Gateway GPRS
Support Node (GGSN). Some network elements, like EIR,
HLR, VLR and AUC are shared by both domains.
The Asynchronous Transfer Mode (ATM) is defined for
UMTS core transmission. ATM Adaptation Layer type 2
(AAL2) handles circuit switched connection and packet
connection protocol AAL5 is designed for data delivery.
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Summary of UMTS frequencies:
Universal Mobile Telephone System (UMTS)
• 1920-1980 and 2110-2170 MHz Frequency Division
Duplex (FDD, W-CDMA) Paired uplink and downlink,
channel spacing is 5 MHz and raster is 200 kHz. An
Operator needs 3 - 4 channels (2x15 MHz or 2x20 MHz)
to be able to build a high-speed, high-capacity network.
1900-1920 and 2010-2025 MHz Time Division Duplex
(TDD, TD/CDMA) Unpaired, channel spacing is 5 MHz
and raster is 200 kHz. Tx and Rx are not separated in
frequency.
1980-2010 and 2170-2200 MHz Satellite uplink and
downlink.
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W-CDMA Parameters
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Base station finder: http://www.sitefinder.ofcom.org.uk/
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Frequency Spectrum in UK(Sep 2007)
900MHz
Vodafone
O2
Restricted to 2G
services only
1800MHz
Vodafone
O2
2100MHz ( 3G )
Vodafone
O2
T-Mobile
T-Mobile
Orange
Orange
Three
Restricted to 3G
services only
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GSM frequency allocations
Mobile phone
transmit frequency MHz
Base station transmit
frequency MHz
Vodafone GSM 900
O2 (BT) GMS 900
Vodafone GSM 900
890 - 894.6
894.8 - 902
902 - 910
935 - 939.6
939.8 - 947
947 - 955
O2 (BT) GMS 900
910 - 915
955 - 960
Vodafone GSM 1800
& O2 GSM 1800:
T Mobile GSM 1800
Orange GSM 1800:
1710 - 1721.5
1805 - 1816.5
1721.5 - 1751.5
1751.5 - 1781.5
1816.5 - 1846.5
1846.5 - 1876.5
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The UMTS/3G frequency allocations
Frequency (MHz)
1900 - 1900.3
1900.3 - 1905.2
1905.2 - 1910.1
1910.1 - 1915.0
1915.0 - 1919.9
1919.9 - 1920.3
1920.3 - 1934.9
1934.9 - 1944.9
1944.9 - 1959.7
1959.7 - 1969.7
1969.7 - 1979.7
2110 - 2110.3
2110.3 - 2124.9
2124.9 - 2134.9
2134.9 - 2149.7
2149.7 - 2159.7
2159.7 - 2169
2169.7 - 2170
Bandwidth (MHz) licence
4.9
4.9
4.9
4.9
licence D
licence E
licence C
licence A
14.6
10
14.8
10
10
licence A
licence C
licence B
licence D
licence E
14.6
10
14.8
10
10
licence A
licence C
licence B
licence D
licence E
holder
Guard band
T-Mobile
Orange
O2
3
Guard band
3
O2
Vodafone
T-Mobile
Orange
Guard band
3
O2
Vodafone
T-Mobile
Orange
Guard band
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Signal level measured at T701
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MVNO
A mobile virtual network operator (MVNO) is a
mobile phone operator that provides services
directly to their own customers but does not own
key network assets such as a licensed frequency
allocation of radio spectrum and the cell tower
infrastructure.
The UK mobile market has 5 main mobile
network operators and has a total of more than 60
MVNOs.
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Market share per mobile provider
Everything Everywhere (T-mobile+
Orange, inc Virgin Mobile) 38%
O2 (inc Tesco) 30%,
Vodafone (inc ASDA, 25%,
3UK 7% (end 2010)
(from Ofcom | The Communications Market Report: United
Kingdom 2011)
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LTE (Long Term Evolution)
• Initiated in 2004
• focused on enhancing the Universal Terrestrial Radio
Access (UTRA)
• Downlink (100Mbps), OFDM, support data modulation
schemes QPSK, 16QAM, and 64QAM
• Uplink (50Mbps) Single Carrier-Frequency Division
Multiple Access (SC-FDMA), support BPSK, QPSK,
8PSK and 16QAM
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• 4 x Increased Spectral Efficiency, 10 x Users Per Cell
• Multiple Input / Multiple Output (MIMO) antenna
• both paired (FDD) and unpaired (TDD) band operation is
supported
• LTE can co-exist with earlier 3GPP radio technologies
• 3GPP’s core network has been undergoing System
Architecture Evolution (SAE), optimizing it for packet
mode and in particular for the IP-Multimedia Subsystem
(IMS) which supports all access technologies – even
wire-line
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International Mobile Telecommunications
(IMT) Advanced
Key features of ´IMT-Advanced´
• a high degree of commonality of functionality worldwide while
retaining the flexibility to support a wide range of services and
applications in a cost efficient manner;
• compatibility of services within IMT and with fixed networks;
• capability of interworking with other radio access systems;
•
•
•
•
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high quality mobile services;
user equipment suitable for worldwide use;
user-friendly applications, services and equipment;
worldwide roaming capability; and,
enhanced peak data rates to support advanced services and
applications (100 Mbit/s for high and 1 Gbit/s for low mobility
were established as targets for research)*.
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The Forth Generation
• 4G is mainly a marketing buzzword at the moment. Some
basic 4G research is being done, but no frequencies have
been allocated.
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Smart antennas
Multiple-Input-Multiple-Output Systems
Space-Time Coding
Dynamic Packet Assignment
Wideband OFDM
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OFDM for 4G Wireless
OFDM is being increasingly used in high -speed
information transmission systems:
• European HDTV
• Digital Audio Broadcast (DAB)
• Digital Subscriber Loop (DSL)
• IEEE 802.11 Wireless LAN
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Key Features of 4G W-OFDM
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IP packet data centric
Support for streaming, simulcasting & generic data
Peak downlink rates of 5 to 10 Mbps
Full macro-cellular/metropolitan coverage
Asymmetric with 3G uplinks (EDGE)
Variable bandwidth - 1 to 5 MHz
Adaptive modulation/coding
Smart/adaptive antennas supported
MIMO/BLAST/space-time coding modes
Frame synchronized base stations using GPS
Network assisted dynamic packet assignment
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