PRESENTATIONPRESENTATION

CONTEMPORARY CONTEMPORARY STUDENTSSTUDENTS

NAME:NAME: AZIZ ZOAIB AZIZ ZOAIB

ID:ID: FA06-BS-0013 FA06-BS-0013

COURSE:COURSE: SWITCHING THEORY SWITCHING THEORY

TOPIC:TOPIC: GSM ARCHITECTUREGSM ARCHITECTURE

What is TelecommunicationWhat is Telecommunication

Telecommunications means to change information Telecommunications means to change information into electric signals for remote transmission.into electric signals for remote transmission.

Getting Wireless---What's the Advantage?Getting Wireless---What's the Advantage?• Saving Transmission Cost.Saving Transmission Cost.• Fast Deployment.Fast Deployment.• Easy and Fast AccessEasy and Fast Access

Challenges Challenges • InterferenceInterference• Multipath Fading Multipath Fading • LOS and NLOS (RAN and Backhaul)LOS and NLOS (RAN and Backhaul)• Changing Terrain and Air Interface Changing Terrain and Air Interface Characteristics(weather)Characteristics(weather)

History of Cellular Mobile Radioand GSM(Global Systems for

Mobile)Early 1980s there was analog technologies:

Advanced Mobile Phone Services(AMPS)in

North America. Total Access Communications

System(TACS)in the UK. Nordic Mobile Telephone(NMT) in Nordic

countries.

ContdContd

Each country developed its own system, whichcaused problems:

System worked only within theboundaries of each country. Mobile equipment manufacturersMarkets were limited by the operatingsystem.Solution was GSM, which is digitaltechnology and was developed byCEPT(Conference of European Posts andTelecommunications)

The Goals of GSM

Improved spectrum efficiency International roaming Low-cost mobile sets and base stations High-quality speech Compatibility with ISDN and othertelephone company services. Support for new services QoS

Gsm facts(2003)Gsm facts(2003)

Used in over 170 countries

Over 400 GSM network operators

Over 550 million people were subscribers to GSM

FDMA, CDMAFDMA, CDMA

FDMA (FREQUENCY DIVISON MULTIPLEXING)1) Each user on a different frequency.2) A channel is a frequency.

CDMA (CODE DIVISION MULTIPLEXING)1) Each user uses the same frequency all the time, but mixed with different distinguishing code patterns.2) A channel is a unique set of code patterns.

Gsm uses TDMAGsm uses TDMAShort for Time Division Multiple Access, atechnology for delivering digital wireless serviceusing time-division multiplexing (TDM). TDMAworks by dividing a radio frequency into time slotsand then allocating slots to multiple calls. In thisway, a single frequency can support multiple,simultaneous data channels.TDMA is used by theGSM digital cellular system.

Time

Frequency

0 1 2 3 4 5 6 7

Time Slot

CONTDCONTD

Time Division Multiple Access• Each carrier frequency subdivided in time domain into

8 time slots • Each mobile transmits data in a frequency, in its

particular time slot - Burst period = 0.577 milli secs.• 8 time slots called a TDMA frame. Period is .577 * 8 =

4.616 milli secs

0 1 2 3 4 5 6 7

4.616 ms

0.577 ms

FDD/ TDDFDD/ TDD

UP / Down-LinkUP / Down-Link Down-link: the transmission Down-link: the transmission

path frompath from

Base Station to Mobile StationBase Station to Mobile Station Up-link: the transmission path Up-link: the transmission path

from Mobilefrom Mobile

Station to Base StationStation to Base Station

GSM Cell Structure

The power level of a

transmitter within a

single cell must be

limited to reduce the

interference with the

neighboring cells.

ContdContd

Neighboring cells cannot share the

same channels Different size of patterns:

4,7,12 or 21cells in one cluster

Types of Cells

Macrocells(3 to 35 km) Microcells(0.1 to 1 km)

1) Picocells(0.01 to 1km)

2) Nanocells(1m to 10m)

GSM ArchitectureGSM Architecture

Mobile Station (MS)Mobile Station (MS) Used by the subscriber to access the GSM network via Used by the subscriber to access the GSM network via

the air interfacethe air interface Contains the hardware and software specific to the radio Contains the hardware and software specific to the radio

interfaceinterface Need a Subscriber Identity Module (SIM) which contains the Need a Subscriber Identity Module (SIM) which contains the

subscriber-specific data to access GSM network, subscriber-specific data to access GSM network,

except emergency callexcept emergency call SIM cards are embedded with a microprocessor Stores SIM cards are embedded with a microprocessor Stores

customer identity information and is made to fit inside the customer identity information and is made to fit inside the

cellular phonecellular phone Memory capacity Memory capacity 1K, 3K, 8K, 16K1K, 3K, 8K, 16K

Base Transceiver Station(BTS)

serves a single cell usually placed in the center of

a cell. multiplexing modulating synchronizing

Base Station Controller(BSC) Frequency hopping Time and frequency synchronization Power management Time delay measurements

The Transcoder and adaptation

unit(TRAU)• (13Kbps speech or data

+ 3Kbps additional

synchronizing data)*4

=64Kbps (TRAU

Standard rate)

Base Station Subsystem(BSS)

= BTS + BSC

Mobile Switching Center(MSC) The central component of the NetworkSubsystem (30 + 2)* 64Kbps = 2,048Mbps(E1) or better tothe other network interfaces(PSDN,ISDN) Billing Location registration Gateway to SMS Synchronizing BSS Handover management

GSM Architectures 3 broadparts

Subscribers carries MOBILE STATION BSS controls the radio link with the

mobile station NETWORK SUBSYSTEM (NSS), which

main part is MSC

The Registers Completing theNSS

Home Location Register (HLR) contains all information of each subscriber registered in the corresponding GSM network Visitor location Register (VLR) contains selectedinformation from the HLR, which is necessary forcall control and provision of the subscribedservices, for each mobile currently located in thegeographical area controlled by the VLR NSS = HLR + VLR + MSC

Equipment Identity Register (EIR) contains a list of all valid mobile equipment on the network Authentication Center (AUC) stores a copy of the secret key stored in each subscribers SIM card EIR and AUC are used for security and authentication purposes EIR has three databases.,EIR has three databases.,

• White list - For all known, good IMEI’sWhite list - For all known, good IMEI’s• Black list - For all bad or stolen handsetsBlack list - For all bad or stolen handsets• Grey list - For handsets/IMEI’s that are Grey list - For handsets/IMEI’s that are

on observation on observation

GSM IS A HALF DUPLEX

Trunking theory and EARLANGTrunking theory and EARLANG

Trunking theory:Trunking theory: Cellular radio systems rely on Cellular radio systems rely on trunking theory to accommodate a large number trunking theory to accommodate a large number of users in a limited radio spectrum.of users in a limited radio spectrum.

The fundamentals of trunking theory was The fundamentals of trunking theory was developed by Earlang, a Danish mathematician in developed by Earlang, a Danish mathematician in the late 1990s.the late 1990s.

EARLANG: EARLANG: Earlang represents the amount of Earlang represents the amount of traffic intensity carried by a channel that is traffic intensity carried by a channel that is completely occupied.completely occupied.

CONTDCONTD

EARLANG B: (EARLANG B: (Also called Block calls Cleared) that is for Also called Block calls Cleared) that is for every user who requests service it is assumed that user every user who requests service it is assumed that user is given a immediate access to a channel if one is is given a immediate access to a channel if one is available. If no channel is available the user is blocked available. If no channel is available the user is blocked without access and is free to try again later. without access and is free to try again later.

EARLANG B: EARLANG B: (Also called Block calls Delayed) is one in (Also called Block calls Delayed) is one in which a que is provided to hold calls which are blocked. which a que is provided to hold calls which are blocked. If a channel is not available immediately the call request If a channel is not available immediately the call request may be delayed until a channel becomes available.may be delayed until a channel becomes available.

Channel conceptChannel concept

Physical channel: One timeslot of a TDMA-frame on one carrier is referred

to as a physical channel. There are 8 physical channels per carrier in GSM,channel 0-7(timeslot 0-7).

Logical channel: A great variety of information must be transmitted

between BTS and the MS,for e.g. user data and control signaling. Depending on the kind of information transmitted we refer to different logical channels. These logical channels are mapped on physical channel.

GSM CHANNELSGSM CHANNELS

CONTDCONTD

Control channels are intended to carry signaling or synchronization data. Three are defined: Broadcast Channels (BCHs), Common Control Channels (CCCHs), Dedicated Control Channels (DCCHs).

Broadcast channels are point to multipoint unidirectional (downlink) control channels from the the fixed subsystem to the mobile telephone.

First, BCHs include a Frequency Control Channel (FCCH) that allows an MS to accurately tune to a Base Transceiver Station (BTS).

Then BCHs contain the Synchronization Channel (SCH), which provide TDMA frame oriented synchronization data to a MS.

Last, BCHs include the Broadcast Control Channel (BCCH) intended to broadcast a variety of information to MSs, including cues necessary for the MS to register in the network.

CONTDCONTD

Common Control Channels (CCCHs) are point to multipoint channels that is primarily intended to carry signaling information for access handling functions. The CCCHs include:

Paging Channel (PCH), which is down channel used to page (call terminating) MSs.

Access Grant Channel (AGCH) that is a downlink channel used to assign a MS to a specific Dedicated Control Channel (DCCH).

Cell Broadcast Channel (CBCH), which is down channel used to broadcast miscellaneous short messages to the MSs.

Random Access Control Channel (RACH) is an uplink channel which allows MS to initiate a call.

CONTDCONTD

Stand Alone control channelStand Alone control channel (SDCCH) it is used to (SDCCH) it is used to send sms.send sms.

Slow Associated control channelSlow Associated control channel (SACCH) It is used (SACCH) It is used to gather the information of surrounding area and to gather the information of surrounding area and updates the network.updates the network.

Fast Associated control channelFast Associated control channel (FACCH) It has the (FACCH) It has the authority to discard speech channel while executing the authority to discard speech channel while executing the handoff.handoff.

Types of handoffsTypes of handoffs

Intra cell handover: The MS in handed over to Intra cell handover: The MS in handed over to another channel on the same cell, under the same another channel on the same cell, under the same BTS.BTS.

Intra BSC handover: The MS is handed over to the Intra BSC handover: The MS is handed over to the another channel on a d/f cell, under the control of another channel on a d/f cell, under the control of the d/f BTS of the same BSC.the d/f BTS of the same BSC.

Inter BSC Handover: the MS is handed over to the Inter BSC Handover: the MS is handed over to the another channel on a d/f cell, under the control of a another channel on a d/f cell, under the control of a d/f BSC of the same MSC.d/f BSC of the same MSC.

Inter MSC Handover: The MS is handed over to Inter MSC Handover: The MS is handed over to another MSC. another MSC.

THANKS Q/A.?THANKS Q/A.?