gsm adapted from acoe 422. history of gsm during the 80s, analog cellular systems experienced...
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GSM
Adapted from www.mobinet.gr
Acoe 422
History of GSM During the 80s, analog cellular systems
experienced rapid growth in Europe, yet they were incompatible with each other
In 1982 the Groupe special mobile (GSM) was formed to study and develop a pan-European public land mobile system
Commercial service started in 1991 Although standardized in Europe, GSM is
not only a European standard
GSM Growth 1992-2002 By 1993
there were 36 GSM networks in 22 countries
Today, over 200 GSM networks are operational in 110 countries
24 Billion SMS messages are sent per month In the UK, the market for handset ring-tones is currently
worth over €87 million annually, while young adults spent €71 million on downloadable logos
GSM accounts for 72.0% of the World's digital market and 70.0% of the World's wireless market
GSM Coverage
GSM Systems Worldwide GSM was designed to be used in the
900MHz band Later on, the frequency band of 1800MHz
was allocated to facilitate a second system, similar to GSM. This system, originally called DCS1800, evolved to be essentially the same as GSM
The American-Japanese GSM version uses the 1900MHz, used to be called PCS1900
There are now 3 GSM systems: GSM 900, GSM 1800 and GSM 1900
Dual Band Network Overview DCS 1800 cells are generally coverage
limited GSM 900 cells tend to be capacity limited Implying a need for more DCS 1800 cells to
provide similar coverage to a comparable GSM 900
Uplink Band
Downink Band
Channel Spacing
Total Number of Channels
Duplex Spacing
No of Timeslots per Channel
890 - 915 MHz
935 - 960 MHz
200 kHz
124
45 MHz
GSM 900
8
1710 - 1785 MHz
1805 - 1880 MHz
200 kHz
374
95 MHz
DCS 1800
8
GSM Characteristics Benefits
Support for international roaming Distinction between user and device
identification Excellent speech quality Wide range of services Interworking (e.g. with ISDN, DECT) Extensive security features
Services Offered by GSM Services
Telephony Asynchronous & synchronous data
services (2.4/4.8/9.6 kbps) Access to packet data network (X.25) Telematic services (SMS, fax, videotext,
etc.) Many value-added features (call
forwarding, caller ID, conferencing with up to 7 participants, voice mailbox)
GSM Radio Interface
124
FDMA FDMA
TDMAFRAME n
TDMAFRAME
n+1
200 kHz 200 kHz
2 12331
25 MHz
DownlinkMS Tx
935MHz
960MHz
UplinkMS Tx
915MHz
890MHz
25 MHz
1 2 124123 Channel Channel
124 Channels x 8 Time Slots = 992 Duplex Channels
4.615 ms
TN 7
TN 6
TN 5
TN 1
TN 4
TN 3
TN 2
3
TN 0
GSM FDMA/TDMA
Channel Structure The fundamental
unit of time in the TDMA scheme is called a burst period
Eight burst periods are grouped into a TDMA frame
Traffic Channels (TCH) are defined using a 26-frame multiframe of 120ms length
Signaling Channels (SCH)
TCH/CCH Traffic Channel
A TCH is used to carry speech and data traffic In addition to the full-rate TCHs, there are also
half-rate TCHs defined to double the capacity of the system
Control Channel To help the MS find the control channels To provide information about
voice and control channel repetition cycle. parameters in the cell surrounding cells paging
To allow random access attempts by the MS
Burst The information contained in one time slot
is a burst Five types of burst are defined
Normal Burst (NB) To carry information on traffic and control
channels Frequency Correction Burst (FB)
To synchronize the frequency of the mobile Synchronization Burst (SB)
To synchronize the frames of the mobile Access Burst (AB)
For random and handover access Dummy Burst
For padding the frame
GSM Network Architecture (1/5)
BTS Base transceiver stationBSC Base station controllerBSS Base station subsystem (BTS+BSQ)MSC Mobile switching centerGMSC Gateway MSC
MS Mobile stationHLR Home location registerVLR Visited location registerEIR Equipment identity registerAUC Authentication center
BTS
BTS
BTS
MS
BSC
BSC
MS
MS
MSC
EIRAUC
HLRVLR
GMSC
PSTNISDNPDN
GSM Network Architecture (2/5) Mobile Station
Mobile Equipment Identified by the International Mobile
Equipment Identity (IMEI) Subscriber Identity Module (SIM)
Contains a unique identification number called IMSI
It is removable, thus irrespective of a specific terminal
GSM Network Architecture (3/5) Base Station Subsystem (BSS)
Base Transceiver Station (BTS) A BTS is comprised of radio transceivers,
antennas, the interface to the PCM facility BTS is the entity that connects the mobiles to
a cellular network Base Station Controller (BSC)
Its primary function is call maintenance, by deciding when to initiate a handover, changing the BTS transmitter power, etc.
A BSC is connected to a group of BTSs and manages the radio resources for them
GSM Network Architecture (4/5) Network Subsystem
Mobile Switching Center (MSC) MSC provides functions such as registration,
authentication, location updating, handovers and call routing to a roaming subscriber
Home Location Register (HLR) The HLR contains all the administrative information and
current location of each subscriber registered in the corresponding GSM network
Visitor Location Register (VLR) Contains subscription information needed for call
control, for all mobiles in the area of the associated MSC Equipment Identity Register (EIR)
EIR is a database that contains a list of all valid mobile equipment on the network
Authentication Center (AUC) Stores the secret key held in each user’s SIM card
GSM Network Architecture (5/5) Application Service Centers are responsible
for GSM network add-on services Operation and Maintenance Center (OMC)
Monitoring and control the network Usually connect with MSC, BSC, HLR, and other
service centers Short Message Service Center (SMSC)
provide short message services usually connect to MSC
Unstructured Supplementary Service Data Center (USSDC)
provide USSD service in the form of *ID*ID*info#
usually connect to HLR
Mobility Management
Location Registration Call delivery Handoff Management
Handoff is caused by: signal strength deterioration user mobility
There are two kinds of handoff: soft handoff hard handoff
There are three ways to handoff: network-controlled handoff mobile-assisted handoff mobile-controlled handoff
MS MS
Handoffmargin
BTS old BTS new
BTS old BTS new
Evolution of GSM Platform
Development o
f Radio Tech
nology
1997Basic GSM data at 9.6 kbps
1998Landline-like circuit services (HSCSD)
1999Internet-like IP packet services (GPRS)
2000More capacity when neede (GSM 384)
2001-2002New multimedia servicesMass market cost of service (IMT-2000)
Introduction of 3rd generation radio
Evolution of GSM Platform