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GSM Prepared by : Eng. Mahmoud Yousry
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  • GSMPrepared by :

    Eng. Mahmoud Yousry

  • Contents

    Introduction

    Basic GSM Network Architecture

    Air interface

    Traffic cases

    Planning

  • Introduction

    History of GSM system.

    Wireless transmission

    Multiple Access Techniques

    Wireless Challenges

  • What is the GSM?

    GSM is the Global System for Mobile telecommunications.

    It is the European standard for the Mobile telecommunications and it is considered as one of the most popular standard worldwide.

    It is known as the second generation mobile telecommunications system 2G system.

    It is used in Egypt by the three existing operators; Mobinil and Vodafone; Etisalat.

  • Evolution of GSM

    1982, CEPT conference is held to specify a common European mobile telecommunications in the band of 900 MHz.

    1987, GSM specs drafted TDMA+FDMA, Time multiplexing of order 8 with slow frequency hopping.

    1992, first GSM network was commercial in Finland .

    Global System for Mobile (GSM) is a second-generation digital cellular telephone system.

  • Evolution of GSM

    1996, first GSM operator in Egypt owned by the government.

    1998, Egypt privatizes its GSM operator.

    1998, Click GSM commercial launch.

    GSM became the world's leading and fastest growing mobile standard, spanning over 174 countries, serving more than one in ten of the world's population.

    2000, First GPRS roll out.

  • What is the GPRS?

    GPRS is the General Packet Radio Service.

    GPRS is defined by 3GPP (Third Generation Partnership Project) and is employed to connect mobile cellular users to PDN (Public Data Network).

    Within the GSM network it shares the network databases and radio access network.

    It is known as the 2.5 generation mobiletelecommunications system 2G system.

  • GSM to GPRS development

    GSM offers circuit-switched with good voice quality, but it is providing data rates of 9.6 kbps which is too slow.

    In 1999 General Packet Radio Service (GPRS) reuses the existing GSM infrastructure to provide higher data rate

    It was lunched to increase the data rate to 115 kbps by using the packet-switched in data transmission and defining new coding scheme.

    In 2001 Evolved Data rate for GSM Evolution (EDGE) offers data rate of 384 kbps by using new modulation scheme.

    Now, EDGE is used in Mobinil the first operator in Egypt.

  • 3G Systems

    In 2000 the ITU-T was responsible for the IMT-2000 specification, which is meant to be a guideline for every 3G standard

    Universal Mobile Telecommunication Service (UMTS) is the marketing name for the 3G has two standardization bodies:

    1- 3GPP which uses the W-CDMA technology.

    2- 3GPP2 which uses the CDMA2000 technology.

  • WCDMA as a 3G Approach

    The 3G solution for GSM is called WCDMA (Wideband CDMA).

    WCDMA requires a new radio spectrum as it operates in ultra wide 5-MHz radio channels.

    WCDMA meets the IMT-2000 requirements of 384 kbps outdoors and 2 Mbps indoors.

  • Evolution Vs. Time

    Functionality

    & capabilities

    Speech

    Circuit

    data

    9.6 kbps

    UMTS capable systems

    EDGE

    384

    kbps

    WCDMA2 Mbps

    1998 1999 2000 2001 20021997 Time

    HSCSD

    57.6

    kbpsCircuit Switched

    GPRS

    115 kbpsPacket

    Switched

    Fig 9-1 GSM Data Rates Evolution

  • Introduction

    History of GSM system.

    Wireless transmission

    Multiple Access Techniques

    Wireless Challenges

  • Wireless transmission

    source DestinationTransmission medium

  • Wireless transmission

    The kinds of transmission medium :

    1- Twisted-pair: It has very low bandwidth and it is easily tapped either physically or by monitoring its electromagnetic radiation

    2- Coaxial cable:

    It has greater bandwidth than twisted-pair but it is very expensive.

    3- optical fibers: It is very high bandwidth , very high bit rate and inherently transmission medium.

  • Wireless transmission

    4- Radio (wireless):

    It is greatly depending on the particular frequency of the electromagnetic wave

    Some of their advantages :

    a- They are very flexible and suitable for all terrain.

    b- Portable system can be installed very quickly

    c- There are often the most cost-effective solution

  • Wireless transmission

    As a summary, the radio transmission is used in case of mobile telecommunications. Also, the using of Radio transmission is combined with many problems that may cause the degradation of the service quality.

  • Introduction

    History of GSM system.

    Wireless transmission

    Multiple Access Techniques

    Wireless Challenges

  • Multiple Access Techniques

    What is the Multiple Access Technique?

    It is the use of the same transmission media by more than one user.

    It is used because the limitation of transmission resources comparing with

    the number of users

  • Multiple Access Techniques

  • Multiple Access Techniques

    Three types of Multiple Access Technique are available:

    Frequency Division Multiple Access (FDMA)

    Time Division Multiple Access (TDMA)

    Code Division Multiple Access (CDMA)

  • Multiple Access Techniques

    Frequency Division Multiple Access (FDMA), divide the available bandwidth into smaller bandwidths and allocated to the users.

    Strength

    f1 f2 f3

  • Multiple Access Techniques

    Time Division Multiple Access (TDMA), allocate the whole available bandwidth to one subscriber for a certain period of time

    Strength

    User 1, time=0User 2, time=t0

  • Multiple Access Techniques

    Time Division Multiple Access (TDMA) and Frequency Division Multiple Access.

    Strength

    User 7User 2

    User 1

  • Multiple Access Techniques

    Code Division Multiple Access (CDMA).

    Frequency

    Strength

  • Introduction

    History of GSM system.

    Wireless transmission

    Multiple Access Techniques

    Wireless Challenges

  • Wireless Challenges

    Radio Communication applied to mobile telephony has the following limitations :

    Powerful transmitters & huge equipment are required.

    Capacity is limited to the frequency band allocated.

    So, in order to get rid of these shortages the cellular system is being used in the mobile communications.

  • Wireless Challenges

    The Area to be covered is

    divided into small cells.

    So,

    Low Transmission power.

    Smaller equipment size.

    Capacity of the system can be increased by reuse the frequency.

  • Cell Geometry

    The simplest shape is the circular shape

    So, why not using this shape???????

    Dead Spots

  • Cell Geometry

    So, what are the possible shape and what is the used shape???

    RRR

  • Types of Antennas

    Two types of antennas are being commonly used; the Omni-directional antenna and the directional antenna.

    A site is the place where the transmission equipment is placed; this maybe on the top of the buildings or on the top of the advertising.

    In case of directional type antenna; one site is corresponding to 3 cells and in case of Omni-directional antenna one site is corresponding to one cell and one antenna.

    Sectorial CellsOmni-Directional Cell

  • Frequency Reuse

    As the frequency resources that are given to an operator Vodafone or Mobinil are limited; the frequency used in a cell should be reused again in a cell that is away from this cell in order to increase the capacity of the system. Moreover, for a certain frequency 8 time slots are used for more capacity of the system.

    So, the access technique that is used is FDMA+TDMA with frequency reused.

  • Cellular System Concepts

    Reuse Pattern(Cluster):

    Cells are grouped into Clusters

    Available Band is distributed among the cells of the cluster

    N is the number of cells in a cluster .

    Each frequency is reused after the same distance D

    Reuse Plan = (D/R)= 3N

    Where R is the cell radius

    5

    2

    3

    4

    7

    1

    6

    5

    N=7 Cell ClusterN=7 Cell Cluster

    7 Cell Reuse Plan7 Cell Reuse Plan

    2

    3

    4

    7

    1

    6

    5

    2

    3

    4

    7

    1

    6

    5

    2

    3

    4

    7

    1

    6

    5

    2

    3

    4

    7

    1

    6

    5

    D

  • Contents

    Introduction

    Basic GSM Network Architecture

    Air interface

    Traffic cases

    Planning

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • Basic GSM Network Structure

    BSC

    BSC

    MSC

    MS

    MS

    MS BTS

    BTS

    BTS

    GMSC

    EIR

    AUC

    HLR

    VLR

    PSTNISDNPDN

    EIR

    AUC

    HLR

    VLR

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • Mobile Station (MS)

    The Mobile Station (MS) is the interface between the user and the network. The MS consists of two independent parts:

    Subscriber Identity Module (SIM) card

    Mobile Equipment (ME)

    +

    The Mobile Equipment is said to be a Mobile Station if the Subscriber Identity Module ( SIM Card ) is added to it.

  • Mobile Station (MS)

    MS features are defined as mandatory or optional

    Mandatory features are:

    Display of called number: Check the dialed number before call setup.

    Support of A5/1 and A5/2: Provisions are made for support of up to seven algorithms as well as the support of no encryption. It is mandatory for A5/1 and A5/2 and non-encrypted mode to be implemented, but other algorithms are optional.

    Short message indication and acknowledgment: This feature allows the reception of the delivery report of short messages to a MS from a service center.

    Emergency call capabilities: It must be possible to make an emergency call even without a valid SIM.

  • Mobile Equipment (ME)

    The MS sends these features to the network when it is powered on.

    Optional features are:

    On/Off switch: The MS can be equipped with the means of switching its power supply on and off.

    Short Message Service Cell Broadcast (SMSCB) screening

  • Subscriber Identity Module (SIM) card

    A SIM card is an electronic smart card, which stores information about the subscription.

    Thus it contains a microprocessor and a memory

    The SIM stores three types of subscriber related information:

    Fixed data stored before the subscription: e.g. IMSI, authentication key and security algorithms.

    Temporary network data: e.g. the location area of the subscriber and other data of the subscriber.

    Service data

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • Base Station Subsystem (BSS)

    MS

    BTS BSC

    The Base Station Sub-system (BSS) is responsible for all the radio-related functions in the system.

    BSS

  • Base Transceiver Station (BTS)

    A BTS acts as the interface between MSs and the network, by providing radio access to the network subscribers.

    Converts the GSM radio signals into a format that can be recognized by the BSC.

    Ciphering using the ciphering key.

    Channel coding and interleaving.

    Records and passes to the BSC the Signal strength measurements.

  • Base Station Controller (BSC)

    The BSC is the central node within a BSS and co-ordinates the actions of Base Stations. The BSC controls a major part of the radio network.

    Its main functions can be divided into two types:

    During Call Set Up:

    Finding the called mobile station by paging.

    Allocate the frequency for setting the call.

    During Call Progress:

    Monitoring the call quality.

    Controlling the transmitted power to the MS depending on the location of the MS.

    Control the handover for the MS after receiving the power measurements from the MS and from the BTS.

  • Base Station Controller (BSC)

    TRC Handling

    The TRC provides the BSS with rate adaptation capabilities. This is necessary because the rate used over the air interface and that used by MSC/VLRs are different -33.8 Kbit/s and 64 Kbit/s respectively. A device, which performs rate adaptation is called a transcoder.

  • LAI and CGI

    LAI: Location Area Identification.

    A location area is determined by the operator and it consists of one or more BSC coverage area. It is used to control the subscribers within a coverage area larger than the cell area and smaller than the MSC coverage area.

    LAI consists of MCC (Mobile Country Code) + MNC (Mobile Network Code) + LAC (Location Area Code 4 hex digit); for example for Vodafone, Egypt one LAI can be as following: 602 02 8f65

  • LAI and CGI

    CGI: Cell Global Identification.

    It is an identifier for the cell of GSM system.

    CGI consists of LAI+CI (Cell Identity, 4 hex digit)

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • Network Switching Subsystem (NSS)

    MSC/VLR

    HLR

    AUC

    BSC

    NSS

    BTS

    BTS

  • Mobile Switching Center (MSC)

    The primary node in a GSM network is the MSC. It is the node which controls calls establishment. The primary functions of an MSC include the following:

    Switching and call routing to or from MS.

    Charging.

    Service provisioning.

    Control of connected BSCs.

    Access to PSTN.

    Provides the gateway functionality to other networks.

    One MSC controls more than one BSC.

  • Types of the MSC

    VMSC: Visited MSC

    There are three types of the MSC, the difference just in the function.

    GMSC: Gateway MSC

    TMSC: Transit MSC

  • Visited Mobile Switching Center

    Its function is to switch in the level of BSCs and it is combined with a VLR.

    MSC/VLR

    BSC BSC

  • Transit Mobile Switching Center

    Its function is to switch between the different VMSC. It is not combined with a VLR.

    TMSC

    VMSC VMSC

  • Gateway Mobile Switching Center (GMSC)

    Its function is to connect the PLMN to the PSTN or to the other PLMN existing in the country.

    TMSC

    VMSCVMSC

    TMSC

    VMSCVMSC

    Mobinil GMSC

    PSTNVodafone

  • Home Location Register (HLR)

    The HLR is a centralized network database that stores and manages all mobile subscriptions belonging to a specific operator.

    It acts as a permanent store for a persons subscription information until that subscription is cancelled.

    The primary functions of the HLR include: Stores for each mobile subscriber:

    Basic subscriber categories. Supplementary services. Current location. Allowed/barred services. Authentication data.

    Subscription database management Controls the routing of mobile terminated calls and SMS.

  • Visitor Location Register (VLR)

    The role of a VLR in a GSM network is to act as a temporary storage location for subscription information for MSs, which are within a particular MSC service area.

    Thus, there is one VLR for each MSC service area. This means that the MSC does not have to contact the HLR (which may be located in another country) every time the subscriber uses a service or changes its status.

    The VLR is always integrated with the MSC.

  • Visitor Location Register (VLR)

    For the duration when the MS is within one MSC service area, then the VLR contains a complete copy of the necessary subscription details, including the following information:

    Identity numbers for the subscriber

    Supplementary service information (e.g. Does the subscriber has call waiting activated or not)

    Activity of MS (e.g. idle or busy)

    Current Location Area of MS

  • Authentication Center (AUC)

    To protect GSM systems, the following security functions have been defined:Subscriber authentication: by performing authentication,

    the network ensures that no unauthorized users can access the network, including those that are attempting to impersonate others.

    Radio information ciphering: the information sent between the network and an MS is ciphered. An MS can only decipher information intended for it.

  • Authentication Center (AUC)

    The information provided by the AUC to ensure authentication processing is called a triplet and consists of:

    A non predictable random number (RAND)

    A Signed Response (SRES)

    A ciphering Key (Kc)

  • Triplets

    Authentication Center

    Triplet

    RAND SRES Kc

    Home Location Register

    Triplet

    RAND SRES Kc

    Visitor Location Register

    RAND SRES Kc

  • The Ciphering Procedure

    Base Transceiver StationDecryption

    Algorithm A5

    Encryption

    Algorithm A5

    From the BSCTo the BSC

    Mobile Station

    TDMA

    Frame Number

    DATA

    En

    cry

    pte

    d

    DA

    TA

    DATA

    En

    cry

    pte

    d

    DA

    TA

    Encryption

    Algorithm A5

    Decryption

    Algorithm A5

    Kc

    TDMA

    Frame Number

    DATA DATA

    Kc

    Air Interface

  • The Authentication Procedure

    Visitor Location RegisterRand SRES AUC Kc

    SRES AUC SRES MS

    Barred

    Base Station Subsystem

    SIM Card

    A8

    SRES MS

    = Access

    Kc

    SRES MSRand

    Rand

    A3 KiRand

    VLR

  • Equipment Identification Register(EIR)

    In order to block the stolen mobiles equipments; the EIR equipment is used; also in case of the Mobile operator wants to block a certain type of Mobile phones.

    Example, In Turkey all the mobile phones bought from outside Turkey are blocked and can not be used before paying fees.

    The Mobile equipment is identified by a number called International Mobile Equipment Identity (IMEI). This number is uniquely identifies the MS worldwide.

  • Equipment Identification Register(EIR)

    Because the subscriber and equipment are separate in GSM, it is necessary to have a separate authentication process for the MS equipment.

    The equipment identification procedure uses the identity of the equipment itself (IMEI) to ensure that the MS terminal equipment is valid.

    EIR

    1. IMEI Request

    2. IMEI 3. IMEI Check

    4. Access/ Barring Data

    MSC / VLR

  • Equipment Identification Register(EIR)

    International Mobile Equipment Identity (IMEI)

    IMEI

    6 Digits

    TAC

    2 Digits

    FAC

    6 Digits

    SN

    TAC: Type Approval Code,

    The first two digits are the

    code for the country

    approval

    FAC: Final Assembly Code

    SN: Serial Number

  • Short Message Center (SMC)

    An SMC is added to a GSM network to provide one or more of the following messaging services:

    Short Message Service (SMS) text messages.

    Any service that combined with SMS; like the missed call notification SMS and the voice mail notification SMS.

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • OSS

    The operation and Maintenance center (OMC) is connected to all equipment (the GMSC, MSC, HLR, VLR, AUC, EIR and the BSC).

    It can be viewed as a computerized monitoring center were staff can monitor and control the network remotely.

    MSC

    SMCBSC

    HLROMC LAN

  • OSS

    In the GSM network, the implementation of the OMC is called the operation and support sub-system (OSS).

    OSS is the functional entity from which the network operator can monitor and control the entire mobile network.

    Other functions provided by the OSS include provision of network maintenance support as well as customer support.

  • Basic GSM Network Structure

    Mobil station and SIM card

    BSS part

    NSS part

    OSS

    GSM subscriber identifications

  • Subscribers Identities in GSM

    In order to identify the subscribers of the GSM system; the standard defined identities to be assigned to the subscribers uniquely worldwide.

    MSISDN: Mobile Subscriber Integrated Service Digital Number

    IMSI: International Mobile Subscriber Identity

    MSRN: Mobile Subscriber Roaming number

    TMSI: Temporary Mobile Subscriber Identity

  • GSM Identities

    CC : Country Code

    NDC : National Destination Code

    SN : Subscriber Number

    Vodafone Egypt MSISDN

    20

    CC

    10

    NDC

    1100477

    SN

    Mobile Station ISDN Number (MSISDN)

    Vodafone UK MSISDN

    44

    CC

    385

    NDC

    196099

    SN

  • GSM Identities

    International Mobile Subscriber Identity (IMSI)

    MCC : Mobile Country Code

    MNC : Mobile Network Code

    MSIN : Mobile Station Identification Number

    Vodafone UK IMSI

    234

    MCC

    15

    MNC

    1234567890

    MSIN

    Vodafone Egypt IMSI

    602

    MCC

    02

    MNC

    1234567890

    MSIN

  • GSM Identities

    Temporary Mobile Subscriber Identity Number (TMSI)

    The TMSI is allocated to the mobile subscriber in order to be used instead of his IMSI during all radio communications. The purpose is to keep subscriber information confidential on the air interface. So that this make the call is so difficult to be traced.

    The VLR is the device responsible for the allocation of the TMSI for the mobile subscriber.

    This TMSI is changed at certain events or after a certain time.

    The TMSI consists of 4 bytes and determined by the telecom operator.

  • GSM Identities

    Mobile Station Roaming Number (MSRN)

    When a mobile terminating call is to be set-up, the HLR of the called subscriber requests the MSC/VLR to allocate an MSRN to the called subscriber.

    This MSRN is returned via the HLR to the MSC where the calling subscriber exists.

    The routing is done using the MSRN. When the routing is completed, the MSRN is released so it can be used in the routing of another call.

    The MSRN is in the same format like that of the MSISDN.

  • GSM Identities

    On the SIM card the following data is included:

    IMSI

    TMSI

    KI

    KC

    A3 Algorithm

    A8 Algorithm

  • Contents

    Introduction

    Basic GSM Network Architecture

    Air interface

    Traffic cases

    Planning

  • Communication Channels types

    ApplicationsPropertiesChannel Type

    FM radio, televisionOne-way onlySimplex

    Police radio, push-to-talkTwo-way, only one at a timeHalf duplex

    PSTN, Mobile systemsTwo-way, both at the same

    timeFull duplex

    A duplex channel, such as that used during a mobile call, uses two frequencies: one to the MS and one from the MS. The direction from the

    MS to the network is referred to as uplink. The direction from the network to the MS is referred to as downlink.

    Because it requires less power to transmit at lower frequency over a given distance, uplink frequencies in mobile systems are always the lower

    band of frequencies this saves valuable battery power of the Mobile station.

  • Frequency Allocation

    GSM 1900GSM 1800GSM 900

    1850-1910 MHz1710-1785 MHz890 -915 MHzUplinkFrequency

    1930-1990MHz1805-1880 MHz935-960MHzDownlink

    60 MHz75 MHz25 MHzBandwidth

    80 MHz95 MHz45MHzDuplex Distance

    200KHz200 KHz200 KHzCarrier Separation

    299374124Radio Channels

  • FDMA in GSM

    Separation between carriers Frequency gap must be sufficient to eliminate interference between adjacent channels.

    Where The more the separation the less the co-channel interference but the less the available channels suited in the bandwidth.

    It is found that a 200 kHz channel separation is suitable for all systems.

  • Spectrum Allocation (GSM 900)

    GSM 900 Frequency Allocation

    F (MHz)915890

    Uplink1 2 3 4 121 122 123 124

    F (MHz)

    Downlink

    960935

    1 2 3 4 121 122 123 124

    890.2

    890.4

    890.6

    935.2

    935.4

    935.6

    200 KHz

    1

    1

    121

    121

    Downlink 935 960 MHz

    Uplink 890 915 MHz

  • TDMA in GSM

    With TDMA, one carrier is used to carry a number of calls, each call using that carrier at designated periods in time .

    These periods of time are referred to as time slots .

    Each MS on a call is assigned one time slot on the uplink frequency and one on the downlink frequency, and both the same.

    It is found that a 8 Time Slots per carrier, called physical channels is suitable for all systems.

    Information sent during one time slot is called a burst, and depending on information sent we named what called logical Channels

  • Physical Channels

    GSM band is divided into 124 RF channels, and each channel is divided into 8 time slots using TDMA.

    These time slots are called physical channels.

    CH 1 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

    CH 2 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

    CH 3 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7

    CH 124 0 1 2 3 4 5 6 7 0 1 2 3 4 5

  • Logical Channels-Traffic Channels

    TCH

    Traffic Channels

    Speech

    TCH/FS

    Data

    TCH/HSTCH/9.6 TCH/2.4

    TCH/4.8

    Normal Burst

    TCH Traffic Channel

    TCH/FS Full rate Speech Channel

    TCH/HS Half rate Speech Channel

    TCH/9.6 Data Channel 9.6kb/s

    TCH/4.8 Data Channel 4.8kb/s

    TCH/2.4 Data Channel 2.4Kb/s

  • Traffic Channels

    Carries either encoded speech or user data up and down link between a single mobile and a single BTS.

    Types of traffic channel:

    Full rate (TCH)

    Transmits full rate speech (13 Kbits/s). A full rate TCH occupies one physical channel.

    Half rate (TCH/2)

    Transmits half rate speech (6.5 Kbits/s).

    Two half rate TCHs can share one physical channel, thus doubling the capacity of a cell.

  • Logical Channels-Control Channels

    FCCHSCH

    CCH Control Channels

    DCCH

    SDCCH

    BCH

    BCCH Synch. CH.ACCH

    SACCHFACCH CCCH

    RACH

    CBCH

    PCH/AGCH

  • Control Channels

    These are used to carry signaling or synchronization data. They are divided into three types:-

    Broadcast CHannels (BCH)

    Common Control CHannels (CCCH)

    Dedicated Control CHannels (DCCH)

  • Broadcast Channels

    From Single BTS to all the mobiles in the area

    Frequency Correction Control CHannel (FCCH) Carries information for frequency correction of the mobile

    Synchronization CHannel (SCH) Carries 2 important pieces of information

    TDMA frame number (max = 2715684 ) Base station identity Code (BSIC)

    Broadcast Control CHannel (BCCH) Broadcasts some general cell information such as:

    Location Area Identity (LAI), maximum output power allowed in the cell and the identity of BCCH carriers for neighboring cells.

  • Common Control Channels

    To or from a certain BTS to a single mobile

    Paging Channel (PCH)

    BTS Transmits a paging message to indicate an incoming call or short message. The paging message contains the identity number of the mobile subscriber that the network wishes to contact.

    Random Access Channel (RACH)

    MS Answers paging message on the RACH by requesting a signaling channel of SDCCH.

    Access Grant Channel (AGCH)

    Assigns a signaling channel (SDCCH) to the MS.

  • Dedicated Control Channels

    Stand alone Dedicated Control Channel (SDCCH) The BTS switches to the assigned SDCCH. The call set-up procedure is performed in

    idle mode. The BSC assigns a TCH (carrier and time slot) and the MS switches to the assigned SDCCH.

    SDCCH is also used to Registration & Authentication

    Slow Associated Control Channel (SACCH) BTS Instructs the MS the transmitting power to use and gives instructions on

    timing advance (TA).

    MS Sends averaged measurements on its own BTS (signal strength and quality) and neighboring BTSs (signal strength). The MS continues to use SACCH for this purpose during a call.

    Fast Associated Control Channel (FACCH) Transmits handover information.

    Transmits necessary handover information

  • Burst Structure Types

    Normal Burst Structure

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    The tail bits help the equalizer to determine the start and stop points of the

    transmitted bits. They are three bits at the beginning and at the end of the burst

    and they are always zeros

  • Burst Structure Types

    Normal Burst Structure

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    The subscriber speech or data is encrypted into 57 bit blocks. Each burst will

    contain two 57 bits blocks from two different speech segments(20m Sec).

  • Burst Structure Types

    Normal Burst Structure

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    One bit stealing flag will be added to each block to indicate whether the burst is stolen for the FACCH

    signaling or used as a normal traffic channel

  • Burst Structure Types

    Normal Burst Structure

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    The guard period of 8.25 bits length, which is equivalent to about 30 s,

    is left at the end of each burst, to prevent overlapping between

    consecutive bursts and to facilitate burst synchronization

  • Burst Structure Types

    Normal Burst Structure

    It carries information of all logical channels except RACH, SCH and FCCH

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

  • Burst Structure Types

    Tail Bits Fixed Bits

    Tail Bits

    Guard Period

    3 142 3 8.25

    This is the one used by the channel (FCH) for frequency correction of the mobile.

    It consists of a long sequence of bits called the fixed bits which are all equal to

    zeros, leading to a constant frequency output from the GMSK modulator

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    Frequency Correction Burst Structure

  • Burst Structure Types

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    Tail Bits

    Encrypted Bits

    Synchronization Sequence

    Encrypted Bits

    Tail Bits

    Guard Period

    3 39 64 39 3 8.25

    The SCH burst consists of a long synchronization sequence along with the important

    information being encrypted and divided into two blocks. The TDMA frame number is

    sent on the SCH channel, which carries also the Base station Identity code (BSIC).

    The TDMA frame number is used by the mobile to determine which control channels

    will be transmitted on that frame.

    Synchronization Burst Structure

  • Burst Structure Types

    Tail Bits

    Synchronization Sequence

    Encrypted Bits

    Tail Bits Guard Period

    8 41 36 3 68.25

    The Access Burst is used by the RACH channel. The mobile sends this burst when

    it does not know the distance to its serving BTS, which is the case when the

    mobile is switched on or after it makes a handover to a new cell. So this burst

    must be shorter in order to prevent it from overlapping with the burst on the next

    time slot.

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    Access Burst Structure

  • Burst Structure Types

    0 1 2 3 4 5 6 7

    TDMA Frame

    156.25 bits in 577 u Sec

    Tail Bits

    Encrypted Bits

    Training Sequenc

    e

    Encrypted Bits

    Tail Bits

    Guard Period

    3 58 26 58 3 8.25

    The dummy burst is sent from the BTS when there is nothing else to be sent. It

    carries no information and it has the same structure of a normal burst with the

    encrypted bits replaced by a known bit pattern to the mobile.

    Dummy Burst Structure

  • 3 57 1 26 1 57 3 8.25

    0 1 2 3 4 5 6 7

    156.25 bits in 577 m Sec

    Normal burst

    1 2 e.g. TCH 26 1 2 e.g. BCCH 51

    1 e.g. BCCH 26

    1 2 e.g. TCH 51

    1 Hyper frame = 2048 Super frames = 2,715,648 TDMA Frames = 3hrs 28 min and 53.76 s

    Hyper Frame

    12

    1

    2

    2

    1 Super frame = 51 TCH Multi frames

    1 Super frame = 26 BCCH Multi frames

    1 BCCH Multi frame = 51 TDMA Frames1 TCH Multi frame = 26 TDMA Frames

  • Power Measurements in Active Mode

    1. To enable the mobile from making power measurements during a call, the uplink time slot will be delayed by an offset of three time slots from the down link time slot. (The mobile will try to measure the signal strength of these carriers one by one during the time between transmission and reception of the allocated traffic channel)

    2. The mobile is informed on the SACCH channel which BCCH frequencies to be measured.

    3. To make sure that the measured carriers do not belong to co-channel cells, the mobile will have to check the identity of the adjacent cells by reading the BSIC value sent on the SCH of each cell. This will take place during the idle frame number 26.

    (Note) The signal strength of the serving cell is measured during reception of the allocated traffic channel.

    4. The mobile will make a list of the strongest six carriers and their BSIC values along with the signal strength of its cell, and reports this list to the BSC via the uplink SACCH channel which is repeated once every 26 frame.

  • Radio Transmission problems

    As it was stated before that the mobile telecommunications will use radio transmission as the transmission technique; the radio transmission is suffering

    from many problems which causing unacceptable degradation of the service

    quality.

    We will discuss these problems in details during our course.

  • Radio Transmission problems

    1. Path Loss

    2. Shadowing (Normal Fading)

    3. Multipath Fading

    a. Rayleigh Fading

    b. Time Dispersion

    4. Time Alignment

  • Radio Transmission problems

    1. Path Loss

    Cause

    Due to Increasing distance between MS, and BTS.

    Solution

    Handover

  • Radio Transmission problems

    2. Shadowing (Normal Fading)

    Cause

    Due to Obstacles between MS, and BTS.

    Solution

    increase the fading margin for the receiver in the mobile

    station and at the Transceiver station of the mobile network; so that how

    weak the signal received is the receiver will still can receive and regenerate

    this signal.

  • Radio Transmission problems

    3. Multipath Fading

    a. Rayleigh Fading

    Cause

    Due to different paths of signals between MS, and BTS.

    Which cause fading dips as a result of different in phase and amplitude

    Solution

    Diversity

    a. Space Diversity

    b. Polarization Diversity

    c. Frequency Diversity ( Frequency Hopping)

  • Radio Transmission problems

    3. Multipath Fading

    b. Time Dispersion

    Cause

    Due to different paths of signals between MS, and BTS.

    Which cause Intersymbol Interference (ISI)

    Solution

    Adaptive Equalizer, by using training sequence in bursts

  • Radio Transmission problems

    4. Time Alignment

    Cause

    Due to different distance of different MSs from BTS (Near-Far)

    Solution

    Time Advance

  • Contents

    Introduction

    Basic GSM Network Architecture

    Air interface

    Traffic cases

    Planning

  • Traffic cases

    Location update

    Handover

    Mobile originating a call

    Mobile terminating a call

    SMS

  • Location Update

    Why do we need to update our location data ?

    Actually, the location update process is done in aim to exactly identify the location of the subscribers within the network so that any incoming call goes directly to the called subscriber.

    To fulfill this aim, one can say that we may update the system with the cell ID each time the subscriber changes his serving cell. The MSC/VLR will now know the exact cell you are roaming in. This will result in a huge amount of location update messages.

    An extreme is never to make a location update and to be paged in all the network. This will cause huge amount of paging messages.

  • Location Update

  • Types of Location Update

    1. Normal Location update within same MSC/VLR service area

    2. Normal Location update between 2 different MSC/VLR service areas

    3. IMSI attach/detach

    4. Periodic Location Update

  • Normal Location within the same MSC/VLR Service area

    BSC

    1. The Mobile sends an SDCCH allocation

    request message to the BTS on RACCH

    2. The BTS responds with the SDCCH

    allocation message on AGCH .

    3. The mobile sends a location update

    request message with its IMSI to the

    MSC/VLR on SDCCH

    4

    4. The MSC/VLR updates the location

    information and sends a Location Update

    confirmation message on SDCCH

    MSC/VLR

    Updates

    LA Record

    5. SDCCH is released

  • Normal Location Update between 2 different MSC/VLR service areas

    Old MSC/VLR New MSC/VLR

    NEW BSCOld BSC

    LA 1

    LA 2

    1. The mobile sends a location

    update request to the MSC.

    2. The new MSC/VLR receives the IMSI

    and conclude the its HLR address.

    IMSI to MGT

    translation

    3. The MSC/VLR sends a subscriber

    information request with the IMSI

    to the proper HLR

    4. The HLR stores the address of

    the new MSC/VLR

    VLR Address

    =

    Old MSC

    VLR Address

    =

    New VLR

    5. The HLR sends the data to the

    new MSC/VLR and it is kept there

    6. The HLR sends a location

    cancellation message to the old

    MSC/VLR to remove the data

    HLR

    7. The new MSC/VLR sends a location

    updating confirmation message to

    the mobile

  • IMSI Detach

    1. At power off, the MS asks for a signaling SDCCH channel.

    2. The MS uses this signaling channel to send the IMSI detach message to the

    MSC/VLR.

    3. In the VLR, an IMSI detach flag is set for the subscriber. This is used to reject

    incoming calls to the MS.

    4. The subscribers record is kept in the VLR for a certain time; i.e. 24 hour then it is removed if the subscriber doesnt switch on his mobile.

  • IMSI Attach

    IMSI attach is a complement to the IMSI detach procedure. It is used by the

    mobile subscriber to inform the network that it has re-entered an active state

    and is still in the same location area. If the MS changes location area while

    being switched off, a normal location update takes place.

    1. The MS requests a signaling SDCCH channel.

    2. The MSC/VLR receives the IMSI attach message from the MS.

    3. The MSC/VLR sets the IMSI attach in the VLR. The mobile is now ready

    for normal call handling.

    4. The VLR returns an acknowledgment to the MS.

  • IMSI Attach

    MSC/VLRBSC

    1

    2 3

    4

  • Periodic Location Update

    Periodic location update is a routine task performed by the network if the MS doesnt make any network action (sets a call, sends SMS, location

    update, receives a call,. etc)

    If the MS doesnt respond to this periodic location update, it will be marked as implicitly detached. ( Temporarily out of service )

  • Traffic cases

    Location update

    Handover

    Mobile originating a call

    Mobile terminating a call

    SMS

  • Handover

    Handover is to keep continuity of the call when the subscriber is roaming along the network moving from one cell to another and moving between different nodes in the network.

    During call, the MS is continuously measuring transmission quality of neighboring cells and reports this results to the BSC through the BTS.

    The BSC, being responsible on supervising the cells, is responsible of handover initiation.

    Good neighbor relations between cells is an important factor in keeping the network performance in the accepted level.

  • Types of Handover

    1. Intra BSC Handover:

    When the cell to which the call will be handed over belongs to the same BSC of the serving cell.

    2. Inter BSC / Intra MSC Handover:

    When the cell to which the call will be handed over belongs to the different BSCs but to the same serving MSC.

    3. Inter MSC

    When the cell to which the call will be handed over belongs to the different BSC and different MSC.

  • BSC

    New Cell

    1. The BSC decides from the power measurement

    reports that the call must be handed over to

    another cell

    2

    2. The BSC checks for an vacant traffic TCH in the new cell and orders this cell to activate the TCH

    3

    3. The BSC orders the serving cell to send a message to the MS on FACCH telling the

    information

    of new TCH

    4. The MS tunes to the new frequency and Sends handover access burst

    45. The new cell detects the handover burstand sends information about the suitable

    timing advance to the MS

    5 6. The MS sends a HO complete message to the new cell

    6

    7. The new cell sends a message to the BSC that the handover is successful

    7

    8. The BSC orders the old Cell to release the TCH

    8

  • Old BSC New BSC

    MSC/VLR

  • Old MSC

    Old BSC

    New MSC

    New BSC

  • Traffic cases

    Location update

    Handover

    Mobile originating a call

    Mobile terminating a call

    SMS

  • 1. The MS uses RACH to ask for a signaling channel.

    2. The BSC/TRC allocates a signaling channel, using

    AGCH.

    3. The MS sends a call set-up request via SDCCH to the

    MSC/VLR. Over SDCCH all signaling preceding a

    call takes place. This includes:

    Marking the MS as active in the VLR The authentication procedure Start ciphering Equipment identification Sending the B-subscribers number to the network Checking if the subscriber has the service Barring

    of outgoing calls activated4. The MSC/VLR instructs the BSC/TRC to allocate an

    idle TCH. The BTS and MS are told to tune to the

    TCH.

    5. The MSC/VLR forwards the Bnumber to an exchange in the PSTN, which establishes a connection to the

    subscriber.

    6. If the B-subscriber answers, the connection is

    established.

    BSC

    MSC

  • Traffic cases

    Location update

    Handover

    Mobile originating a call

    Mobile terminating a call

    SMS

  • 1. Calling a GSM subscribers

    2. Forwarding call to GMSC

    3. Signal 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

  • Traffic cases

    Location update

    Handover

    Mobile originating a call

    Mobile terminating a call

    SMS

  • Short Messages

    The Short Message Service (SMS) allows a mobile subscriber to send and receive text messages composed of 160 characters at most.

    These messages can be read on the phones LCD panel and they are delivered using the signaling channel SACCH; so short messages can be received while a call is in progress.

    The short messages sent or received are handled by the Short Message Service Center (SMSC), which consists of three parts:

    Service Center SC

    Short Message Service GMSC SMS-GMSC

    Short Message Service Inter-working MSC SMS-IWMSC

  • Short Message Delivery

    Process

    1

    MSC1

    HLR

    3

    SMS-GMSC

    SC

    SMS-IWMSC

    4

    2

    MSC25

    6

    7

    8

    MTMOMT

  • Unsuccessful delivery

    HLR

    SMS-GMSC

    SC

    SMS-IWMSC

    MSC2

    1

    2

    5

    6

    MT

    43

    Retry method

    Usage of Alert Service Center in the HLR

  • Contents

    Introduction

    Basic GSM Network Architecture

    Air interface

    Traffic cases

    Planning

  • GSM Coverage Plan

    To provide coverage for a large service area of a mobile network we have two Options:

    (A) Install one transceiver with high radio power at the center of the service area

    Drawbacks: The mobile equipments used in this network should have

    high output power in order to be able to transmit signals across the coverage area.

    The usage of the radio resources would be limited.

  • GSM Coverage Plan

    (B) Divide the service area into smaller areas (cells) Advantages:

    Each cell as well as the mobile handsets will have relatively small power transceivers.

    The frequency spectrum might be reused in two far separated cells. This yields:

    1- Unlimited capacity of the system.

    2- Good interference characteristics

  • Cell Geometry

    Problem of omni directional antennas

    Dead Spots

  • Cell Geometrical Shape

    Differentiation between these three shapes will be in order to optimize the number of cells required to cover a given service area against the cell transceiver power. By some calculations, you will find that using hexagonal shaped cells achieves the optimum.

    RR

    R

  • Cell Geometrical Shape

    Umbrella Cell

    Normal Cell Normal Cell

  • Cell Geometrical Shape

    Umbrella cell

    Macro cell

    Slow moving subscribers

    Fast moving subscribers

    Pico

    cellIn buildingcoverage

  • Clusters

    Cluster is a set of cells where the frequency is not being reused within this cluster.

    Cluster can be 3, 4, 7 and 9 cells.

  • Sectorization

    sectroized CellsOmni-Directional Cell

  • 3/9 Cluster

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

  • 4/12 Cluster

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

    A3

    A2

    A1

    B3

    B2

    B1

    C3

    C2

    C1

    D3

    D2

    D1

  • 7/21 Cluster

    A3

    A2

    A1

    C3

    C2

    C1

    D3

    D2

    D1

    B3

    B2

    B1

    E3

    E2

    E1

    F3

    F2

    F1

    G3

    G2

    G1

    A3

    A2

    A1

    C3

    C2

    C1

    D3

    D2

    D1

    B3

    B2

    B1

    E3

    E2

    E1

    F3

    F2

    F1

    G3

    G2

    G1

    A3

    A2

    A1

    C3

    C2

    C1

    D3

    D2

    D1

    B3

    B2

    B1

    E3

    E2

    E1

    F3

    F2

    F1

    G3

    G2

    G1

    A3

    A2

    A1

    C3

    C2

    C1

    D3

    D2

    D1

    B3

    B2

    B1

    E3

    E2

    E1

    F3

    F2

    F1

    G3

    G2

    G1

    A3

    A2

    A1

    C3

    C2

    C1

    D3

    D2

    D1

    B3

    B2

    B1

    E3

    E2

    E1

    F3

    F2

    F1

    G3

    G2

    G1

  • Frequency Reuse

    If the GSM900 system has 124 Absolute Radio Frequency Traffic Channels, and if we are using only in our network 60 of them, then we can only serve 8 x 60 = 480 Calls if we only use the frequency once.

    However, a cellular network overcome this constraint and maximizes the number of subscribers that it can serve by using frequency re-use.

    The frequency reuse is performed by dividing the whole available frequencies between a group of neighboring cells which is called frequency reuse pattern or a Cluster, and then repeat this cluster over the whole network

  • Co- Channel Interference

    Co-channel interference is caused by short distance between the cell and other cell that use the same frequency.

    To overcome this type of interference. Each frequency is reused after the same distance D

    Reuse Plan = (D/R)2 = 3N. Where N is the number of cells per cluster

  • Adjacent Channel Interference

    Adjacent frequencies, that are frequencies shifted 200kHz from the carrier frequency, must be avoided in the same cell and preferably in neighboring cells also .

    To overcome this type we must make good planning for the frequencies in the cluster

  • Frequency Planning

    A3A2

    A1

    B3B2

    B1C3

    C2C1

    A3A2

    A1

    B3B2

    B1C3

    C2C1

    B3

    B2B1

    C3C2

    C1

    A3A2

    A1

    B3B2

    B1C3

    C2C1

    A3A2

    A1

    C3B3A3C2B2A2C1B1A1Frequency

    group

    727170696867666564

    Channels 818079787776757473

    878685848382

  • Frequency Planning

    In a real network the allocation of channels to cells will not be as uniform as in table, as some cells will require more channels and some will require less.

    In this case, a channel may be taken from a cell with low traffic load and moved to one with a higher traffic load.

    However, if doing so, it is important to ensure that interference is still minimized.

  • Which Cluster Size to use?

    Carrier to interference ratio

    Its the difference in power level between the carrier in a given cell and the same carrier received from the nearest cell that reuses the same frequency.

    Number of frequencies per site

    Traffic Channels

    C/I Ratio

    3/9 High High Low

    4/12 Medium Medium Medium

    7/21 Low Low High

  • END