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        Anurag Malik                Shivanshu Rastogi
        Associate Professor         Assistant Professor

                 CE & IT Dept. M.I.T Moradabad
                    B.Tech VIII CS / IT

                          UNIT I
                    Recommended Books:

   1.     J. Schiller, Mobile Communications, Addison
   2.     A. Mehrotra, GSM System Engineering
   3.     Asok    K.   Talukder,  Mobile    Computing-
          Technology, Applications & Service Creation,
   4.     Raj Kamal,Mobile Computing, Oxford University
Mobile Computer
• A computer which you can take with you all around.
 You can do all the things which can be done with a desktop
 You should be able to use same software, which you use on a
   desktop computer.

Mobile computer - How?
 One possibility is to have a standalone computer capable of storing
  large amount of software and data files,
 processing power to support the required applications.

 Modern day laptop computer are something like this.

 Whenever you are static, connect to internet through an access
  point and you can do the file transfer, telnet, web browsing etc..
 While on the move, connectivity is desired for using software which
  require cooperation of at least two machines.
Mobile Computing
   Mobile computing is a generic term describing one's ability to use
    technology while moving, as opposed to portable computers, which are
    only practical for use while deployed in a stationary configuration.
   Using a computing device while in transit. Mobile computing implies
    wireless transmission, but wireless transmission does not necessarily imply
    mobile computing. Fixed wireless applications use satellites, radio systems
    and lasers to transmit between permanent objects such as buildings and

Mobile computing device
 Acts as a terminal
 Have wireless connectivity to the network
 Whatever command or application you run is executed on a remote server.
 Mobile computing device acts as remote terminal.

Issues in mobile computing networks
 Nature of medium
 Mobility
 Portability
Wireless characteristics

   Variant Connectivity
       Low bandwidth and reliability
   Frequent disconnections
    •   predictable or sudden
   Asymmetric Communication
       Broadcast medium
   Monetarily expensive
       Charges per connection or per
   Connectivity is weak, intermittent and expensive
What is Mobility
   Mobility means different things to different people. Some people are
    quite happy being able to get around town. Others view the world in
    terms of time distance-Obviously, range of motion is an important
    aspect of mobility.

   Another factor in mobility is ease of access. What might be
    considered mobile in one context is quite immobile in another.

   A more pertinent example of mobility is the ever decreasing size of
    cellular telephones. What was once considered a "mobile phone"
    had to be transported in a vehicle. This continuing decrease in size
    and weight of handsets has greatly increased the mobility of cellular

   We define mobility as the ability to send and receive
    communications anytime anywhere. Mobility means that both source
    and destination devices, applications and people are free of the
    constraints imposed by physical location.
Mobility Characteristics

    Location changes
     • location management - cost to locate is
       added to communication
    Heterogeneity in services
      bandwidth restrictions and variability

    Dynamic replication of data
     • data and services follow users

    Querying data - location-based responses
    Security and authentication
    System configuration is no longer static
   Two aspects of Mobility
       User Mobility : a user communicates, anytime, anywhere using
        any access technology
       Device Portability : A device can connect to the network anytime
        and anywhere.
          Wireless      Mobile    Example

              X           X       Stationary computer
              X            √      Notebook in ahotel
              √           X       Wireless LAN in buildings
              √            √      Cellular Phone
   The demand for mobile communication creates the need for
    integration of wireless networks into existing fixed networks:
       In the local range: standardization of IEEE 802.11 (Wireless LAN,
        WLAN considering existing wired standards like Ethernet)
       In Wide area range: e.g. Internetworking of GSM and ISDN
       IN the Internet protocols: Mobile IP as enhancement of normal IP

Portability Characteristics
   Resource constraints
     Mobile computers are resource poor

     Reduce program size – interpret script languages (Mobile

     Computation and communication load cannot be distributed

   Small screen sizes
   Asymmetry between static and mobile computers
   Battery power restrictions
     transmit/receive,     disk spinning, display, CPUs, memory
      consume power
   Battery lifetime will see very small increase
     need energy efficient hardware (CPUs, memory) and system
     planned disconnections - doze mode

   Power consumption vs. resource utilization                   8
Mobile Computing Functions
   User Mobility: User should be able to move from one physical
    location to another location and use the same service. E.g. user
    moves from London to New Delhi and uses Internet to access the
    corporate application the same way the user uses in home office.

   Network Mobility: User should be able to move from one Network
    to another network and use the same service. E.g. user moves from
    London to New Delhi and uses the same GSM phone to access the
    corporate application through WAP. In home Network he uses this
    services over GPRS whereas in Delhi he access it over the GSM

   Bearer Mobility: User should be able to move from one bearer to
    another and use the same service. E.g. user was using a service
    though WAP bearer in his home N/W in Bangalore. He moves to
    Coimbatore, where WAP is not supported, he switch over to voice or
    SMS bearer to access the same application. (switching from BSNL
    to Vodafone on roaming)

Mobile Computing Functions
   Device mobility: User should be able to move from one device to another
    and use the same service. E.g. could be sales representatives using their
    desktop computer in home office. During the day while they are on the street
    they would like to use their Palmtop to access the application.

   Session Mobility: A user session should be able to move from one user-
    agent environment to another. E..g. could be a user was using his service
    through a CDMA iX network. The user entered into the basement to park the
    car and got disconnected from the CDMA n/w. User goes to home office and
    starts using the desktop. The unfinished session in the CDMA moves from
    the mobile device to the desktop computer.

   Service Mobility: User should be able to move from one service to another.
    E.g. a user is writing a mail. To complete the mail user needs to refer to
    some other information. In a desktop PC, user simply opens another service
    (browser) and moves between them using the task bar. User should be able
    to switch amongst services in small footprint wireless devices like in the
    desktop. (In a browser we use HTTP to open yahoo. COM page and POP3
    or SMTP to send & receive mail )

   Host Mobility: The user device can be either a client or server. When it is a
    server or host, some of the complexities change. In case of host mobility the
    mobility of IP needs to be taken care of.

• Advantages
    Spatial flexibility in radio reception range
    Ad hoc networks without former planning
    No problems with wiring (e.g. historical buildings, fire
    protection, esthetics)
    Robust against disasters like earthquake, fire – and careless
    users which remove connectors!
• Disadvantages
   Generally very low transmission rates for higher numbers of
   Often proprietary, more powerful approaches, standards are
    often restricted
   Consideration of lots of national regulations, global regulations
    are evolving slowly
   Restricted frequency range, interferences of frequencies

Types of Wireless Networks
Cellular Networks
• Base stations distributed over the area to be covered
• Each base station covers a cell
• Need of an infrastructure network connecting all base stations
• Used for mobile phone networks and data networks like Wireless LAN

Mobile Ad-Hoc Networks (MANETs)
• Self-configuring network of mobile nodes
• Each node serves as client and router
• No infrastructure (base stations) necessary, direct connections between
   any pair of nodes
• E.g. Bluetooth

Mesh Networks
• Enhancement of above concepts: “Ad-hoc network with infrastructure”
• Allow a whole mesh of connections between wireless nodes• Increased
   fault tolerance
• E.g. used in WiMAX                                                  12
Classification of Wireless Network

Wireless Personal Area Network (WPAN)

Wireless Local Area Network (WLAN)

Wireless Metropolitan Area Network

Wireless Wide Area Network (WWAN)

Frequencies For Communication

Limitations of Mobile Environments
   Limitations of the Wireless Network
      heterogeneity of fragmented networks
      frequent disconnections
      limited communication bandwidth

   Limitations Imposed by Mobility
      lack of mobility awareness by system/applications
      route breakages

   Limitations of the Mobile Computer
      short battery lifetime
      limited capacities

Mobile       Applications
   Vehicles
     transmission of news, road condition etc

     ad-hoc network with near vehicles to prevent accidents

   Emergencies
     early transmission of patient data to the hospital

     ad-hoc network in case of earthquakes, cyclones

     military ...

   Traveling salesmen
     direct access to central customer files

     consistent databases for all agents

     mobile office

Mobile        Applications
   Web access
     outdoor Internet access

     intelligent travel guide with up-to-date
       location dependent information
   Location aware services
     find services in the local environment, e.g. printer

   Information services
     push: e.g., stock quotes

     pull: e.g., nearest cash ATM

   Disconnected operations
     mobile agents, e.g., shopping

   Entertainment
     ad-hoc networks for multi user games

Mobile Computing Architecture

              Presentation Tier
                                                                    Application Tier                           Data Tier

Internet            iPlanet Web   Java Server
                                                       IBM WebSphere
Explorer               Server       Pages                                                                       XML
            SOAP                                RMI    BEA WebLogic
                                                                                  Servlets                   Data Stores
Netscape              Jigsaw         XSLT                 JBOSS
                                                IIOP                                               SQL         Database
            IIOP                                          iPlanet                 Enterprise
                                                                                 Java Beans
                      Apache         HTML
 Opera                                                    Jakarta                                   XML

                                                SOAP                                                           Applications &
LIB WWW                             WML /                                                                      Web Services
                                    HDML                                          CGI (C. Perl,
                                                                                    Python)                  Aggregation Service

Java URL
                                                                                                    XML          Data Feeds
  Class                                         RPC
                                                             ZEND                      PHP
                                                                                                             Lotus Domino mail
                                                                                                              and Documents
  Lynx                            Javascript
            HTTPS                                            Roxen                     Pike

 WAP                                                                                                             Equipment

                                                                                  MS Transaction   Adapter
                                                         MS Exchange
                      Internet                  COM                                   Server                 Legacy Applications
J2ME                Information       ASP
                                                        MS Commerce Server             COM

Mobile Computing Architecture
   To design a system for mobile computing, we need to keep in mind that the system
    will be used through any network, any bearer, any agent and any device.
   The three tier architecture is better suited for an effective networked client/server
   It provides increased performance, flexibility, maintainability, reusability and
    scalability while hiding the complexity of distributed processing from the user.
   Centralized process logic makes administration and change management easier by
    localizing changes in central place and using it throughout the systems.
   The network-centric mobile computing architecture uses a three-tier architecture.
        User Interface or Presentation Tier :This layer deals with user facing device
         handling and rendering. This tier includes a user system interface where user
         services (such as session, text input, dialog and display management) reside.
            This is the layer of agent applications and systems. These applications run on
             the client device and offer all the user interfaces. This tier is responsible for
             presenting the information to the end user.
            Humans generally use visual and audio means to receive the information from
             machines (laptop, cell phones, paltops, tablet PC, touch screen.)
            The visual presentation will relate to rendering on a screen which includes
             Web browsers like Mozila, lynx, Internet Explorer and Netscape Navigator,
             WAP browsers.

Mobile Computing Architecture
 Process Management or Application Tier : This layer is for application
  programs or process management where business logic and rules are
  executed. This layer is capable of accommodating hundreds of users. In
  addition to ensure reliable completion tier controls transactions and
  asynchrono, queuing to ensure reliable completion of transactions.
    It performs the business logic of processing user input, obtaining data,
     and making it’s presentation decisions. In certain cases, this layer will
     do the transcoding of data for appropriate rendering in this layer.
    It includes technology like CGI’s, Java, JSP, .NET services, PHP or
     ColdFusion, deployed in products like Apache, WebSphere, WebLogic,
     iPlanet , Pramati, JBOSS or ZEND and database-independent.
    A few additional management functions (decisions on rendering,
     network management, security, datastore access etc.) need to be
     performed which are implemented using different middleware software.
     A middleware framework is defined as a layer of software, which sits in
     the middle between the OS and the user facing software.
    The different types of middleware are:
      1. Message-Oriented Middleware              2. Database Middleware
      3. Transaction Processing Middleware        4. Transcoding Middleware
      5. Communication Middleware 6. Distributed Object & components

Mobile Computing Architecture
     Database Management or Data Tier : This layer is for database access and
        It is used to store data needed by the application and acts as a repository for both
         temporary and permanent data. The data could be stored in any form of datastore
         or database (relational, legacy, text).
        The data can also be stored in XML format for interoperability with other system
         and data sources.
     JBoss :- A popular open source Java application server that supports the J2EE 1.3
      specifications. Runs under any J2SE 1.3 or later Java virtual machine. Based on an
      JMX core where other pieces of the system are plugged in. Supports JNDI, Servlet/JSP
      (Tomcat or Jetty), EJB, JTS/JTA, JCA, JMS. Also supports Clustering (JavaGroups),
      Web Services (Axis), and IIOP integration (JacORB).

     iPlanet was a product brand that was used jointly by Sun Microsystems and Netscape
      Communications Corporation when delivering software and services as part of a non-
      exclusive cross marketing deal. iPlanet Directory Server ,iPlanet Web Server ,iPlanet
      Web Proxy Server, iPlanet Portal Server , iPlanet Portal Search,iPlanet Application
      Server ,iPlanet Messaging Server , iPlanet Calendar Server, iPlanet Meta Directory,
      iPlanet Instant Messaging Server .
     The Apache HTTP Server, commonly referred to simply as Apache a web server
      notable for playing a key role in the initial growth of the World Wide Web. Apache was
      the first viable alternative to the Netscape Communications Corporation web server
      (currently known as Sun Java System Web Server), and has since evolved to rival
      other Unix-based web servers in terms of functionality and performance. The majority
      of all web servers using Apache are Linux web servers.

Mobile Computing Architecture
     Zope is a free and open-source, object-oriented web application server written in the Python
      programming language. Zope stands for "Z Object Publishing Environment." It can be almost
      fully managed with a web-based user interface. Zope publishes on the web Python objects
      that are typically persisted in an object database, ZODB. Basic object types, such as
      documents, images, and page templates, are available for the user to create and manage
      through the web. Specialized object types, such as wikis, blogs, and photo galleries, are
      available as third-party add-ons (called products), and there is a thriving community of small
      businesses creating custom web applications as Zope products.
     Zend Framework is a simple, straightforward, open-source software framework for PHP 5
      designed to eliminate the tedious details of coding and let you focus on the big picture. Its
      strength is in its highly-modular MVC design, making your code more reusable and easier to

     The Roxen WebServer, from the Swedish company Roxen Internet Software, is a viable
      alternative for those who find Apache inappropriate for their needs. Although Apache
      dominates the internet web server market, it has some weak points: it lacks a built-in SQL
      database backend, flexible administration tools and easy SSL certificate management. All of
      these features can be found, however, in the Roxen WebServer. In fact, Roxen includes so
      many additional features that it seems more like an application server than an ordinary web
     PHP is a scripting language originally designed for producing dynamic web pages. It has
      evolved to include a command line interface capability and can be used in standalone
      graphical applications.
     Jakarta Struts is incredibly useful in helping you create excellent Web applications. When
      you use Jakarta Struts, your applications should work more effectively and have fewer bugs.
      Just as important (because your time is important), Struts should save you hours and hours of
      programming and debugging.

Mobile Computing Architecture
    WebLogic server is based on Java 2 Platform, Enterprise Edition
     (J2EE), the standard platform used to create Java-based multi-tier
     enterprise applications. J2EE platform technologies were developed
     through the efforts of BEA Systems and other vendors in collaboration
     with the main developer, Sun Microsystems. Because J2EE applications
     are standardized modules, WebLogic can automate many system-level
     tasks that would otherwise have demanded programming time.
    Pike is an outliner that's been custom-fitted to plug into Manila sites. You
     can create and edit stories with Pike. You can use it to edit your home
     page. And you can also use it to edit the myriad of templates that define
     how a Manila site is rendered. It's both a writing and design tool. Pike is
     as easy to use as a web browser but has the common features that web
     writers and designers need.
    WebSphere is a set of Java-based tools from IBM that allows customers
     to create and manage sophisticated business Web sites. The central
     WebSphere tool is the WebSphere Application Server (WAS), an
     application server that a customer can use to connect Web site users
     with Java applications or servlets. Servlets are Java programs that run on
     the server rather than on the user's computer as Java applets do.
     Servlets can be developed to replace traditional common gateway
     interface (CGI) scripts.

Mobile Computing Architecture
   HTTPS (HTTP over SSL or HTTP Secure) is the use of Secure Socket Layer (SSL) or Transport
    Layer Security (TLS) as a sublayer under regular HTTP application layering. HTTPS encrypts and
    decrypts user page requests as well as the pages that are returned by the Web server. The use of
    HTTPS protects against eavesdropping and man-in-the-middle attacks. HTTPS was developed by
    Netscape. HTTPS and SSL support the use of X.509 digital certificates from the server so that, if
    necessary, a user can authenticate the sender. Unless a different port is specified, HTTPS uses
    port 443 instead of HTTP port 80 in its interactions with the lower layer, TCP/IP. HTTPS encrypts
    and decrypts the page requests and page information between the client browser and the web
    server using a secure Socket Layer (SSL).
   IIOP (Internet Inter-ORB Protocol) is a protocol that makes it possible for distributed programs
    written in different programming languages to communicate over the Internet.
   SOAP (Simple Object Access Protocol) is a way for a program running in one kind of operating
    system (such as Windows 2000) to communicate with a progam in the same or another kind of an
    operating system (such as Linux) by using the World Wide Web's Hypertext Transfer Protocol
    (HTTP) and its Extensible Markup Language (XML) as the mechanisms for information exchange.
    Since Web protocols are installed and available for use by all major operating system platforms,
    HTTP and XML provide an already at-hand solution to the problem of how programs running
    under different operating systems in a network can communicate with each other. SOAP specifies
    exactly how to encode an HTTP header and an XML file so that a program in one computer can
    call a program in another computer and pass it information. It also specifies how the called
    program can return a response.
   The Extensible Markup Language (XML) is a general-purpose specification for creating custom
    markup languages. It is classified as an extensible language, because it allows the user to define
    the mark-up elements. XML's purpose is to aid information systems in sharing structured data,
    especially via the Internet ,to encode documents, and to serialize data; in the last context, it
    compares with text-based serialization languages such as JSON and YAML
   HTTP, short for HyperText Transfer Protocol, is the protocol for transferring hypertext
    documents that makes the World Wide Web possible.

Mobile Computing Architecture
   Remote Method Invocation (RMI) is the process of activating a method on a remotely
    running object. RMI offers location transparency in the sense that it gives the feel a method
    is executed on a locally running object. Java RMI (Remote Mathod Invocation) provides a
    mechanism for supporting distributed computing.
   remote procedure call, a type of protocol that allows a program on one computer to
    execute a program on a server computer. Using RPC, a system developer need not
    develop specific procedures for the server. The client program sends a message to the
    server with appropriate arguments and the server returns a message containing the results
    of the program executed.
   Microsoft COM (Component Object Model) technology in the Microsoft Windows-family of
    Operating Systems enables software components to communicate. COM is used by
    developers to create re-usable software components, link components together to build
    applications, and take advantage of Windows services. The family of COM technologies
    includes COM+, Distributed COM (DCOM) and ActiveX® Controls.
   Java database connectivity (JDBC) is the JavaSoft specification of a standard application
    programming interface (API) that allows Java programs to access database management
    systems. The JDBC API consists of a set of interfaces and classes written in the Java
    programming language. Using these standard interfaces and classes, programmers can
    write applications that connect to databases, send queries written in structured query
    language (SQL), and process the results.
   SQL (Structured Query Language) is a database computer language designed for the
    retrieval and management of data in relational database management systems (RDBMS),
    database schema creation and modification, and database object access control
    management. SQL is a programming language for querying and modifying data and
    managing databases. SQL was standardized first by the ANSI and (later) by the ISO

Typical Application : Road traffic

World Wide Web and Mobility
   HTTP/ HTML have not been designed for mobile applications/devices
   HTTP Characteristics
       stateless, connection oriented overheads
       big protocol headers, uncompressed content transfer
   HTML Characteristics
       designed for computers with ―high‖ performance, color high-resolution display,
        mouse, hard disk
       typically, web pages optimized for design, not for communication; ignore end-
        system characteristics
   Adaptations for Mobile WWW
       Enhanced browsers and/or servers
       Client proxy: pre-fetching, caching, off-line use
       Network proxy: adaptive content transformation for connections
       Client and network proxy
       New protocols/languages: WAP/WML

Early Wireless Communication

History Of Wireless Communication
• 1896 - Guglielmo Marconi
   First demonstration of wireless telegraphy (digital!)
   Long wave transmission, high transmission power necessary (>200kw)

• 1907 - Commercial transatlantic connections
   Huge base stations (30 100m high antennas)

• 1915 - Wireless voice transmission New York - San Francisco

• 1920 - Discovery of short waves by Marconi
    Reflection at the ionosphere
    Smaller sender and receiver, possible due to the invention of the vacuum tube
    (1906, Lee DeForest and Robert von Lieben)

• 1926 - Train-phone on the line Hamburg - Berlin
   Wires parallel to the railroad track

History Of Wireless Communication
• 1928 - Many TV broadcast trials (across Atlantic, color TV, TV news)

• 1933 - Frequency modulation (E. H. Armstrong)

• 1958 - A-Netz in Germany
   Analogue, 160MHz, connection setup only from the mobile station, no Handover, 80%
    coverage, 1971 11000 customers

• 1972 - B-Netz in Germany
   Analogue, 160MHz, connection setup from the fixed network too (but location of the mobile
    station has to be known)
   available also in Austria, Netherlands and Luxembourg, 1979 13000 customers in

• 1979 - NMT at 450MHz (Scandinavian countries)

• 1982 - Start of GSM-specification
    Goal: pan-European digital mobile phone system with roaming

• 1983 - Start of the American AMPS (Advanced Mobile Phone System, analog)

• 1984 - CT-1 standard (Europe) for cordless telephones

History Of Wireless Communication
• 1986 - C-Netz in Germany
   Analog voice transmission, 450MHz, hand-over possible, digital signaling,
    automatic location of mobile device
   Was in use until 2000, services: FAX, modem, X.25, e-mail, 98% coverage

• 1991 - Specification of DECT
   Digital European Cordless Telephone (today: Digital Enhanced Cordless
   1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data
    transmission, voice encryption, authentication, up to several 10000 user/km2,
    used in more than 50 countries

• 1992 - Start of GSM
   In Germany as D1 and D2, fully digital, 900MHz, 124 channels
   Automatic location, hand-over, cellular
   Roaming in Europe - now worldwide in more than 170 countries
   Services: data with 9.6kbit/s, FAX, voice, ...

History Of Wireless Communication
• 1994 - E-Netz in Germany
   GSM with 1800MHz, smaller cells
   As E-plus in Germany (1997 98% coverage of the population)

• 1996 - HiperLAN (High Performance Radio Local Area Network)
   ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s
   Recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz)
   as wireless ATM-networks (up to 155Mbit/s)

• 1997 - Wireless LAN – IEEE 802.11
   IEEE standard, 2.4GHz and infrared, 2Mbit/s
   Already many (proprietary) products available in the beginning

• 1998 - Specification of GSM successors
   UMTS (Universal Mobile Telecommunication System) as
   European proposals for IMT-2000
   Iridium: 66 satellites (+6 spare), 1.6GHz to the mobile phone
History Of Wireless Communication
1999 - Standardization of additional wireless LANs
  IEEE standard 802.11b, 2.4-2.5GHz, 11Mbit/s
  Bluetooth for piconets, 2.4Ghz, <1Mbit/s
  Decision about IMT-2000
  Several ―members‖ of a ―family‖: UMTS, cdma2000, DECT, …
  Start of WAP (Wireless Application Protocol) and i-mode
  Access to many (Internet) services via the mobile phone

• 2000 - GSM with higher data rates
   HSCSD offers up to 57,6kbit/s
   First GPRS trials with up to 50 kbit/s (packet oriented!)
   UMTS auctions/beauty contests
   Hype followed by disillusionment (approx. 50 B$ payed in Germany for 6
   UMTS licenses!)

• 2001 - Start of 3G systems
   Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan

• since 2002 – Standardization of high-capacity wireless networks
    IEEE 802.16 as WMAN, IEEE 802.20 (WWAN), IEEE 802.22 (WRAN)

Cellular Concept
The    use of radio channels on the same carrier frequency to cover different areas
which are separated from one another by sufficient distance so that co-channel
interference is not objectionable.
Consider a cellular system which has a total of S channels available and each cell is
allocated a group of k channels ( k <S ). S = k N
The N cells which collectively use the complete set of available frequencies is called a
Cellular systems offer location-independent voice communications:
Users can move freely while talking
They can place calls at any time and any place
They can be called everywhere
          The cellular concept was a major breakthrough in solving the problem of spectral
congestion and user capacity.
It offered very high capacity in a limited spectrum allocation without any major technological
 Assuming that the cell size is kept constant and fixed spectrum per cluster:
– More cells per cluster mean:
» Fewer channels per cell
» Less system capacity
» Less co-channel interference (co-channel cells farther apart)
– Less cells per cluster mean:
» More channels per cell
» More system capacity
» More co-channel interference (co-channel cells closer together)
• Choose reuse factor N is maximize capacity per area subject to interference limitations

Fundamentals of Cellular
                         Of Cellular Systems
   A BS constitutes a cell by its transmission radius
   A mobile equipment (e.g. a cellphone) always communicate with the closest
    base station (BS)
       100 m in cities to 35 km on the country side (GSM)
       even less for higher frequencies
       Umbrella cell: large cell that includes several smaller cells
       Avoid frequent handoffs for fast moving traffic
       Hexagonal cell shape is useful for theoretical analysis
       Practical footprint (radio coverage area) is amorphous
   The BS's are spreaded over the area to provide full coverage
   Multiple BS are aggregated in a mobile switching center (MSC)
   The MSC's are interconnected by a backbone
   The overall cellular system is granted some part of the spectrum, which is
    subdivided into channels
   Each BS is assigned a (sub-)set of channels to serve mobiles
   Neighboring BS's are assigned different sets of channels to avoid interference
   The same channel could be re-used by another base station having sufficient
    distance to avoid interference ( => frequency reuse)
    Moving mobiles will occasionally leave the transmission range of one BS to
    enter the range of another => handover

Fundamentals Of Cellular Systems
   Total number of frequency channels in the system :
   Note that each channel could accommodate more
    than 1 user• e.g. In GSM, each traffic channel can
    have 8 users (TDMA)•
   Each cell is assigned a fixed number of frequency
   No. of channels per group: k= F/N•
   Note: k must be integer!
   Reuse same channel group in cells that are far
   Co-channel cells: cells that use the same set of
    frequency channels
   Co-channel interference: interference caused by
    signals from co-channel cells

Fundamentals Of Cellular Systems

Fundamentals Of Cellular Systems

During a call a BS assigns a fixed portion of a slot to a mobile:
 Reducing cell size / transmission power while increasing the
  number of BS:
  increases the system capacity
  increases the number of handovers

  Goal for Channel Assignment Schemes
-Minimize co-channel interference : Interference from users/BS in
   co-channel cells transmitting at the same frequency
-Minimize adjacent channel interference
        •Interference from users transmitting at adjacent channel
        caused by power leakage in the modulation scheme
–Avoid cell congestion
•Calls may be blocked if all channels are occupied, even though
   the channels in other cells are available
Channel Assignment Schemes

   Fixed channel assignment : A fixed frequency channel pattern is
    assigned according to the reuse pattern
       To minimize the co-channel interference
       Adjacent frequency channels are not assigned in the same cell
           To minimize the adjacent channel interference
   •If the cluster size is large enough, the adjacent frequency channels
    are also not assigned to neighbouring cells but to those farther away
   Channel Borrowing
       To avoid cell congestion
       A fully occupied cell is allowed to borrow free channels from neighboring
       Involve MSC (mobile switching center) to supervise the borrowing

Channel Assignment Schemes

   Dynamic channel assignment: Channels are allocated to cells on
       MSC assign channels based on the co-channel & adjacent channel
       Maintain the minimum required SIR (Signal to Interference Ratio)
   Advantages
       Increase system capacity
       Reduce probability of blocking and drop call
   Disadvantages
       Extensive computation in MSC
       Keep track of real time data on channel occupancy, traffic
        distribution & radio signal strength indications (RSSI)
       Real time channel assignment computations

    Cellular System Architecture
 Each cell is served by a base station (BS)
 Each BS is connected to a mobile switching center
  (MSC) through fixed links
 Each MSC is connected to other MSCs and PSTN

               MSC                   MSC

               HLR                   HLR
                          To other
                 VLR      MSCs         VLR

               PSTN                  PSTN             52
Cellular System Architecture
   Each MSC is a local switching exchange that handles
     Switching of mobile user from one base station to another
     Locating the current cell of a mobile user

          Home Location Register (HLR): database recording the current
           location of each mobile that belongs to the MSC
          Visitor Location Register (VLR): database recording the cell of
           ―visiting‖ mobiles
     Interfacing with other MSCs
     Interfacing with PSTN (traditional telephone network)

    Standard ―Common Air Interface specifies 4 Channels (2 for Traffic and
    2 for Control channels) ‖ One channel in each cell is set aside for signaling
    information between BS and mobiles
   Voice Transmission Channels: Channels used for sending and receiving
    data transmission.
   Control Transmission channels: Beacons for controlling signals b/w BS
    and user and vice versa.
     Mobile-to-BS (Reverse voice Channel): location, call setup for outgoing,
        response to incoming
     BS-to-Mobile (Forward Voice channel): cell identity, call setup for
        incoming, location updating

Call Setup
   Outgoing call setup:
       User keys in the number and presses send (no dial tone)
       Mobile transmits access request on uplink signaling channel
       If network can process the call, BS sends a channel allocation message
       Network proceeds to setup the connection
   Network activity:
       MSC determines current location of target mobile using HLR, VLR and by
        communicating with other MSCs
       Source MSC initiates a call setup message to MSC covering target area
   Incoming call setup:
       Target MSC (covering current location of mobile) initiates a paging msg
       BSs forward the paging message on downlink channel in coverage area
       If mobile is on (monitoring the signaling channel), it responds to BS
       BS sends a channel allocation message and informs MSC
   Network activity:
       Network completes the two halves of the connection
What is a Home Location Register (HLR)?
 A HLR is a database of user (subscriber) information, i.e.,
  customer profiles, used in mobile (cellular) networks. It is a key
  component of mobile networks such as GSM, TDMA, and CDMA
  networks. A HLR contains user information such as account
  information, account status, user preferences, features
  subscribed to by the user, user‘s current location, etc. The data
  stored in HLRs for the different types of networks is similar but
  does differ in some details.
 HLRs are used by the Mobile Switching Centers (MSCs) to
  originate and deliver arriving mobile calls.

What is a Visiting Location Register (VLR)?
 A VLR is a database, similar to a HLR, which is used by the
  mobile network to temporarily hold profiles of roaming users
  (users outside their home area). This VLR data is based on the
  user information retrieved from a HLR. MSCs use a VLR to
  handle roaming users.

How are the HLR and VLR used?
Each mobile network has its own HLRs and VLRs. When a MSC detects a
  mobile user‘s presence in the area covered by its network, it first
  checks a database to determine if the user is in his/her home area or is
  roaming, i.e., the user is a visitor.
 User in Home Area: HLR has the necessary information for initiating,
  terminating, or receiving a call.
 User is Roaming: VLR contacts the user‘s HLR to get the necessary
  information to set up a temporary user profile.
  The user‘s location is recorded in the HLR, and in case the user
  roaming, it is also recorded in the VLR.
 Suppose that the user wants to make a call:
User in Home Area: MSC contacts the HLR prior to setting up the call.
 User is Roaming: MSC contacts the VLR prior to setting up the call.
Suppose that there is a call for the user (call goes to the home MSC):
 User in Home Area: Home MSC delivers the call immediately.
 User is Roaming: Home MSC contacts the VLR to determine the
  appropriate switch in the roaming area to handle the arriving call and
  then transfers the call to the roaming area MSC.
 In cellular telecommunications, the term handoff refers to the
process of transferring an ongoing call or data session from one
channel connected to the core network to another. In satellite
communications it is the process of transferring satellite control
responsibility from one earth station to another without loss or
interruption of service. The British English term for transferring a
cellular call is handover, which is the terminology standardised by
3GPP within such European originated technologies as GSM and
 In telecommunications there may be different reasons why a handoff
(handover) might be conducted:
 when the phone is moving away from the area covered by one cell
and entering the area covered by another cell the call is transferred to
the second cell in order to avoid call termination when the phone gets
outside the range of the first cell;
 when the capacity for connecting new calls of a given cell is used up
and an existing or new call from a phone, which is located in an area
overlapped by another cell, is transferred to that cell in order to free-up
some capacity in the first cell for other users, who can only be
connected to that cell.


   In non-CDMA networks when the channel used by the phone becomes
    interfered by another phone using the same channel in a different cell,
    the call is transferred to a different channel in the same cell or to a
    different channel in another cell in order to avoid the interference.

   In non-CDMA networks when the user behavior changes, e.g. when a
    fast-traveling user, connected to a large, umbrella-type of cell, stops
    then the call may be transferred to a smaller macro cell or even to a
    micro cell in order to free capacity on the umbrella cell for other fast-
    traveling users and to reduce the potential interference to other cells or
    users (this works in reverse too, when a user is detected to be moving
    faster than a certain threshold, the call can be transferred to a larger
    umbrella-type of cell in order to minimize the frequency of the handoffs
    due to this movement)

   in CDMA networks a soft handoff may be induced in order to reduce the
    interference to a smaller neighboring cell due to the "near-far" effect
    even when the phone still has an excellent connection to its current cell

       Handoff Management Phases:
         The initiation phase may employ a decision making strategy based on
          the measured received signal level, with and without hysteresis.
            Without hysteresis, a handoff is initiated as soon as the average signal
             level from the new BS exceeds that from the current BS.
            With hysteresis, handoff is initiated when the average signal level from the
             new SB exceeds that from the current BS by threshold amount.
         The execution phase will include the allocation of new radio resource
          and the exchange of control messages
       Handoff Strategies
         Depending on the information used and the action taken to initiate the
          handoff, the methods for handoff can be
         ���� Mobile controlled handoff(MCHO): is a desirable method
          because it reduces the burden on the network. However, this will
          increase the complexity of the mobile terminal. DECT
         ���� Network controlled handoff(NCHO): the BS monitors the signal
          quality from the mobile and reports the measurements to the MSC.The
          MSC is responsible for choosing the candidate BS. eg. AMPS, CT-2
         ���� Mobile assisted handoff(MAHO) is a variant of NCHO and is
          employed by GSM. In MAHO, the mobile measures the signal levels
          from the various BSs. The mobile collects set of powers levels from
          different BSs and feeds it back to the MSC. e.g. GSM, IS-95 CDMA
Handoff Features

    The Effective handoff scheme should have the following
1.   Fast & Lossless
2.   Minimal no. of Control signal exchanges
3.   Scalable with network size
4.   Capable of recovering from link features , such as abrupt loss
     of radio link.

The design goals of an effective Handoff scheme include
1.   Less Handoff delay
2.   Low cell loss
3.   Small buffer required
4.   Efficient use of resources.

Types of Handoff
   The most basic form of handoff (handover) is when a phone call
    in progress is redirected from its current cell (called source) and
    its used channel in that cell to a new cell (called target) and a
    new channel. In terrestrial networks the source and the target
    cells may be served from two different cell sites or from one and
    the same cell site (in the latter case the two cells are usually
    referred to as two sectors on that cell site). Such a handoff, in
    which the source and the target are different cells (even if they
    are on the same cell site) is called inter-cell handoff. The
    purpose of inter-cell handoff is to maintain the call as the
    subscriber is moving out of the area covered by the source cell
    and entering the area of the target cell.
   A special case is possible, in which the source and the target are
    one and the same cell and only the used channel is changed
    during the handoff. Such a handoff, in which the cell is not
    changed, is called intra-cell handoff. The purpose of intra-cell
    handoff is to change one channel, which may be interfered or
    fading with a new clearer or less fading channel.

Types of Handoff
   A hard handoff is one in which the channel in the source cell is released and
    only then the channel in the target cell is engaged. Thus the connection to the
    source is broken before the connection to the target is made -- for this reason
    such handoffs are also known as break-before-make. Hard handoffs are
    intended to be instantaneous in order to minimise the disruption to the call. A
    hard handoff is perceived by network engineers as an event during the call.
   A soft handoff is one in which the channel in the source cell is retained and
    used for a while in parallel with the channel in the target cell. In this case the
    connection to the target is established before the connection to the source is
    broken, hence this handoff is called make-before-break. The interval, during
    which the two connections are used in parallel, may be brief or substantial. For
    this reason the soft handoff is perceived by network engineers as a state of the
    call, rather than a brief event. A soft handoff may involve using connections to
    more than two cells, e.g. connections to three, four or more cells can be
    maintained by one phone at the same time. When a call is in a state of soft
    handoff the signal of the best of all used channels can be utilised for the call at a
    given moment or all the signals can be combined to produce a clearer copy of
    the signal. The latter is more advantageous, and when such combining is
    performed both in the downlink (forward link) and the uplink (reverse link) the
    handoff is termed as softer. Softer handoffs are possible when the cells
    involved in the handoff have a single cell site.

Hand-off necessary when mobile moves from area of one BS into another
  BS initiated:
      BS monitors the signal level of the mobile
      Handoff occurs if signal level falls below threshold
      Increases load on BS
           Monitor signal level of each mobile
           Determine target BS for handoff
   Mobile assisted:
      Each BS periodically transmits beacon
      Mobile, on hearing stronger beacon from a new BS, sends it a greeting
           changes routing tables to make new BS its default gateway
           sends new BS identity of the old BS
      New BS acknowledges the greeting and begins to route mobile‘s call
  Intersystem:
      Mobile moves across areas controlled by different MSC‘s
      Handled similar to mobile assisted case with additional HLR / VLR effort
      Local call may become long-distance
How to cope with handovers?
  Treat a handover as a new call => blocking =) connection drop=> angry users
  A guard channel concept: set aside some channels for handover calls=> wasted capacity
  Queuing off handovers: between initiation of handover and the actual event some time
   passes (in GSM: 1-2 seconds), this time can be used to wait for ending / leaving calls, the
   waiting call is then treated next
  Umbrella cells for highly mobile users
Cellular Cellular Systems with small cells
Advantages of
     higher capacity, higher number of users
     less transmission power needed
     more robust, decentralized
     base station deals with interference, transmission area etc. locally
      Infrastructure Needed
      Handover Needed
      Frequency Planning
     fixed network needed for the base stations
     handover (changing from one cell to another) necessary
     interference with other cells: co-channel, adjacent-channel
Important Issues:
     Cell sizing
     Frequency reuse planning
     Channel allocation strategies

   GSM is a cellular network, which means that mobile phones connect to it by
    searching for cells in the immediate vicinity. GSM networks operate in four
    different frequency ranges. Most GSM networks operate in the 900 MHz or 1800
    MHz bands. Some countries in the Americas (including Canada and the United
    States) use the 850 MHz and 1900 MHz bands because the 900 and 1800 MHz
    frequency bands were already allocated.

   In the 900 MHz band the uplink frequency band is 890–915 MHz, and the
    downlink frequency band is 935–960 MHz. This 25 MHz bandwidth is
    subdivided into 124 carrier frequency channels, each spaced 200 kHz apart.

   Time division multiplexing is used to allow eight full-rate or sixteen half-rate
    speech channels per radio frequency channel.
   There are eight radio timeslots (giving eight burst periods) grouped into what is
    called a TDMA frame. Half rate channels use alternate frames in the same
    timeslot. The channel data rate is 270.833 kbit/s, and the frame duration is
    4.615 ms.
   The transmission power in the handset is limited to a maximum of 2 watts in
    GSM850/900 and 1 watt in GSM1800/1900.


   There are four different cell sizes in a GSM
    network—macro, micro, pico and umbrella cells.
    The coverage area of each cell varies according to
    the implementation environment. Macro cells can be
    regarded as cells where the base station antenna is
    installed on a mast or a building above average roof
    top level. Micro cells are cells whose antenna height
    is under average roof top level; they are typically
    used in urban areas. Picocells are small cells whose
    coverage diameter is a few dozen meters; they are
    mainly used indoors. Umbrella cells are used to
    cover shadowed regions of smaller cells and fill in
    gaps in coverage between those cells.
      Functional Architecture of a GSM System

                                                                         •RSS- Radio Subsystem
                                   Cell              BSS                 •MS- Mobile Station
                              MS          MS                             •BSS- Base Station Subsystem
                                                                         •BTS- Base Transceiver Station
                                                Cell                     •BSC- Base Station Controller
RSS                            BTS
                                                       MS                •NSS- Network & Switching Subsystem
                                                                         •MSC- Mobile services Switching Centre
                                                                         •VLR- Visitor Location Register
         Abis                                    BTS                     •HLR- Home Location Register
                 BSC               BSC                                   •GMSC- Gateway MSC
                                                                         •OSS- Operation Subsystem
         A                                                               •EIR- Equipment Identity Register
                                                                         •AUC- Authentication Centre
                         MSC                               MSC           •OMC- Operation & Maintenance centre
                                                            Signalling   •IWF- Inter-Working Function
 NSS            VLR
                                                                 ISDN, PSTN

  OSS     EIR     AUC               OMC

   It is the most successful digital mobile telecommunication system in
   To avoid the situation for numerous co-existing analog mobile phone
    system running on slightly diff. carrier frequency in 2G fully digital
    system, the Groupe Speciale Mobile(GSM) was founded in 1982
    which renamed later as global system for mobile communications
   GSM initially introduced for Rail Road as GSM Rail( 19 channels,
    emergency call with ack, voice group call service, voice broadcast
    service, priority calls, control of trains, switches, gates, signals).
   GSM has defined 3 different categories of services:
     Bearer     services( Transparent, Non-transparent, synchronous,
        asynchronous data)
     Tele-services (encrypted voice transmission message services,
        emergency no. SMS, EMS, MMS, group 3 FAX.
     Supplementary          Services: user identification, call redirection
        forwarding, closed user groups multiparty.
   Various versions of GSM
     GSM at 900MHZ                890-915MHZ -(U)          935-960MHZ -(D)
     GSM at 1800MHZ (DCS) 1710-1785MHZ-(U) 1805-1880MHZ(D)

     GSM at 1900MHZ(PCS) 1850-1910MHZ-(U) 1930-1990MHZ-(D)

   Four possible Handover scenarios in GSM:
    1. Intra cell HO: Within a cell a narrow-band
    interference could make transmission at certain
    frequency impossible.
    2. Inter-cell, Intra-BSC HO: Between cells but stays
    within control of the same BSC.
    3. Inter-BSC, Intra-MSC HO: Ho controlled by MSC
    maintaining different BSC.
    4. Inter MSC HO: Ho controlled by different MSCs.
   Primary goal was to provide a mobile phone system
    that allows users to roam throughout Europe &
    compatible to ISDN and PSTN systems.

                        Intra _ MSC Handover
MS                 BTS old                    BSC old                    MSC                    BSC new           BTS new

        report                 Measurement
                                             HO Required      Required
                                                                                  HO Request

                                                                                  Resource Allocation
                                                                                                          Ch. Activation

                                                                                                    Ch. Activation Ack
                                                                               HO Request Ack
                                                        HO Command
                              HO Command
 HO Command
                                                            HO access

                                                        Link Establishment

                                                                                                      HO Complete
                                                                                HO Complete
                                                        Clear Command
                             Clear Command
                              Clear Complete
                               Clear Complete
                                Clear Complete
                                Clear Complete          Clear Complete
GSM Security
   GSM offers several security services using confidential information
    stored in the AuC and in the individual SIM. The security services
    offered by GSM are as follows:-
   Access control and Authentication: the first step includes the
    authentication of a valid user for the SIM. The user needs a secret PIN
    to access the SIM. The nest step is the subscriber authentication.
   Confidentiality: All user–related data is encrypted. After
    authentication, BTS and MS apply encryption to voice, data and
    signaling. This confidentiality exists only between MS and BTS, but
    doesn‘t exist end-to-end or within the whole fixed GSM/ telephone
   Anonymity: To provide user anonymity, all data is encrypted before
    transmission and user identifiers are not used over the air. Instead
    GSM transmit a temporary identifier (TMSI) which is newly assigned by
    the VLR after each location update.
    Algorithm A3 for authentication, A5 for encryption, A8 for generation
    for cipher key.

The GSM Network
   GSM                    provides
    recommendations,             not
    requirements.     The      GSM
    specifications    define     the
    functions     and      interface
    requirements in detail but do
    not address the hardware.
    The reason for this is to limit
    the designers as little as
    possible but still to make it
    possible for the operators to
    buy equipment from different
    suppliers. The GSM network
    is divided into three major
    systems: the switching
    system (SS), the base
    station system (BSS), and
    the operation and support
    system (OSS). The basic
    GSM network elements are
    shown in Picture

The GSM Network
   The Switching System The switching system (SS) is responsible for performing call processing and
    subscriber-related functions. The switching system includes the following functional units.

    Home Location Register (HLR) - The HLR is a database used for storage and management of
    subscriptions. The HLR is considered the most important database, as it stores permanent data about
    subscribers, including a subscriber's service profile, location information, and activity status. When an
    individual buys a subscription from one of the PCS operators, he or she is registered in the HLR of that

   Mobile Services Switching Center (MSC) - The MSC performs the telephony switching functions of the
    system. It controls calls to and from other telephone and data systems. It also performs such functions as
    toll ticketing, network interfacing, common channel signaling, and others.

    Visitor Location Register (VLR) - The VLR is a database that contains temporary information about
    subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always
    integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that
    MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call,
    the VLR will have the information needed for call setup without having to interrogate the HLR each time.

   Authentication Center (AUC) - A unit called the AUC provides authentication and encryption
    parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects
    network operators from different types of fraud found in today's cellular world.

   Equipment Identity Register (EIR) - The EIR is a database that contains information about the identity
    of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC
    and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node.

The GSM Network Structure
   The Base Station System (BSS)All radio-related functions are performed in the
    BSS, which consists of base station controllers (BSCs) and the base transceiver
    stations (BTSs).

   BSC - The BSC provides all the control functions and physical links between the
    MSC and BTS. It is a high-capacity switch that provides functions such as
    handover, cell configuration data, and control of radio frequency (RF) power
    levels in base transceiver stations. A number of BSCs are served by an MSC.

    BTS - The BTS handles the radio interface to the mobile station. The BTS is the
    radio equipment (transceivers and antennas) needed to service each cell in the
    network. A group of BTSs are controlled by a BSC.

   The Operation and Support System :The operations and maintenance center
    (OMC) is connected to all equipment in the switching system and to the BSC.
    The implementation of OMC is called the operation and support system (OSS).
    The OSS is the functional entity from which the network operator monitors and
    controls the system. The purpose of OSS is to offer the customer cost-effective
    support for centralized, regional, and local operational and maintenance
    activities that are required for a GSM network. An important function of OSS is
    to provide a network overview and support the maintenance activities of different
    operation and maintenance organizations.

The GSM Network Structure
Additional Functional Elements

   Message center (MXE) - The MXE is a node that provides integrated voice, fax,
    and data messaging. Specifically, the MXE handles short message service, cell
    broadcast, voice mail, fax mail, e-mail, and notification.

   Mobile Service Node (MSN) - The MSN is the node that handles the mobile
    intelligent network (IN) services.

   Gateway Mobile Services Switching Center (GMSC) - A gateway is a node
    used to interconnect two networks. The gateway is often implemented in an
    MSC. The MSC is then referred to as the GMSC.

   GSM Interworking Unit (GIWU) - The GIWU consists of both hardware and
    software that provides an interface to various networks for data
    communications. Through the GIWU, users can alternate between speech and
    data during the same call. The GIWU hardware equipment is physically located
    at the MSC/VL.

GSM Channel Structure
  Depending on the kind of information transmitted (user data and control
   signaling), we refer to different logical channels which are mapped
   under physical channels (slots). Digital speech is sent on a logical
   channel named TCH, which during the transmission can be a allocated
   to a certain physical channel. In a GSM system no RF channel and no
   slot is dedicated to a priori to the exclusive use of anything (any RF
   channel can be used for number of different uses).
 Logical channels are divided into two categories :
        i) Traffic Channels (TCHs)          ii)Control Channels .
 1. Traffic Channels (TCHs) : A traffic channel (TCH) is used to carry
   speech and data traffic. Traffic channels are defined using a 26-frame
   multiframe, or group of 26 TDMA frames. The length of a 26-frame
   multiframe is 120 ms, which is how the length of a burst period is
   defined (120 ms divided by 26 frames divided by 8 burst periods per
   frame). Out of the 26 frames, 24 are used for traffic, 1 is used for the
   Slow Associated Control Channel (SACCH) and 1 is currently unused .
   TCHs for the uplink and downlink are separated in time by 3 burst
   periods, so that the mobile station does not have to transmit and
   receive simultaneously, thus simplifying the electronics
           TCHs carry either encoded speech or user data in both up and
   down directions in a point to point communication.

GSM Channel Structure
        There are two types of TCHs that are differentiated by their traffic
         They are:
        Full Rate TCH (TCH/F) -It carries information at a gross rate of
         22.82 Kbps.
        Half Rate TCH (TCH/H) -It carries information with half of full rate
2.       Control Channels (CCH) : Used to control medium access,
         allocation of traffic channels or mobility management. These are
         of three types
        Broadcast Control Channel (BCCH): BTs uses this channel to
         signal information (freq availability) to all MSs within cell about
         cell identifier, options available within cell (freq hopping),
         Frequency available inside & neighboring cell.
           Frequency Correction Channel (FCCH) – For Frequency
           Synchronization Channel (SCH) – For synchronization

GSM Channel Structure
   Common Control Channel (CCCH): All info. Regarding connection
    setup between MS and BTS is exchanged via the CCCH.
    Comprised of three control channels used during call origination and
    call paging.
     Paging Channel (PCH) – BTS use for calls towards MS. Used
       to alert the mobile station of incoming    call.
     Random Access Channel (RACH): A slotted Aloha channel to
       request access to the network i.e MS use it to send data to BTS
       to setup call.
     Access Grant Channel (AGCH): BTS uses to signal an MS to
       use TCH for further setup.
   Dedicated control channel (DCCH) : It is a bidirectional channel
    used by MS before connection for control signals to BTS.
     Stand alone Dedicated Control Channel (SDCCH) with low
       data rate (782 bits/s) for signaling (authentication , registration,
       setting up TCH)
     Slow Associated Dedicated Control Channel (SACCH) – used
       to exchange system information such as channel quality & signal
       power level.
     Fast Associated Dedicated Control Channel (FACCH) – used
       during HO when BTS and MS have to exchange larger amounts         78
       of data in less time.
GSM Channel Structure

GSM: Performance Characteristics
   Support for voice and data services
   Total mobility
    International access, chip-card enables use of access points of
    different providers
   Worldwide connectivity
   One number, the network handles localization
   High capacity
   Better frequency efficiency, smaller cells, more customers per
   High transmission quality
   High audio quality and reliability for wireless, uninterrupted
   phone calls at higher speeds (e.g., from cars, trains)

Advantages of GSM

   GSM is mature; this maturity means a more stable
    network with robust features
   Less signal deterioration inside buildings.
   Ability to use repeaters.
   Talktime is generally higher in GSM phones due to
    the pulse nature of transmission.
   The availability of SIM allows users to switch
    networks and handsets at will, aside from a subsidy
   GSM covers virtually all parts of the world so
    international roaming is not a problem.

Disadvantages of GSM
   There is no perfect system!!
   No end-to-end encryption of user data
   No full ISDN bandwidth of 64 kbit/s to the user,
   No transparent B channel
   Security and Privacy issues
   Abuse of private data possible
   Roaming profiles accessible
   High complexity of the system
   Several incompatibilities within the GSM standards
   Safety issues
   Reduced concentration while driving
   Electromagnetic radiation

Location/Mobility Management
   Mobility Management is one of the major functions of a GSM or a UMTS network that
    allows mobile phones to work. The aim of mobility management is to track where the
    subscribers are, so that calls, SMS and other mobile phone services can be delivered to
   A GSM or UMTS network, like all cellular networks, is a radio network of
    individual cells, known as base stations. Each base station covers a small
    geographical area which is part of a uniquely identified location area. By
    integrating the coverage of each of these base stations, a cellular network
    provides a radio coverage over a very much wider area. A group of base
    stations is called a location area, or a routing area.
   The location update procedure allows a mobile device to inform the cellular
    network, whenever it moves from one location area to the next. Mobiles are
    responsible for detecting location area codes. When a mobile finds that the
    location area code is different from its last update, it performs another update by
    sending to the network, a location update request, together with its previous
    location, and its Temporary Mobile Subscriber Identity (TMSI).
   There are several reasons why a mobile may provide updated location
    information to the network. Whenever a mobile is switched on or off, the network
    may require it to perform an IMSI attach or IMSI detach location update
    procedure. Also, each mobile is required to regularly report its location at a set
    time interval using a periodic location update procedure. Whenever a mobile
    moves from one location area to the next while not on a call, a random location
    update is required. This is also required of a stationary mobile that reselects
    coverage from a cell in a different location area, because of signal fade. Thus a
    subscriber has reliable access to the network and may be reached with a call,
    while enjoying the freedom of mobility within the whole coverage area.
Location / Mobility Management
 When a subscriber is paged in an attempt to deliver a call or SMS and
  the subscriber does not reply to that page then the subscriber is marked
  as absent in both the MSC/VLR and the HLR (Mobile not reachable flag
  MNRF is set). The next time the mobile performs a location update the
  HLR is updated and the mobile not reachable flag is cleared.
The "Temporary Mobile Subscriber Identity" (TMSI) is the identity that is
  most commonly sent between the mobile and the network. It is a
  randomly allocated number that is given to the mobile, the moment it is
  switched on. The number is local to a location area, and so it has to be
  updated, each time the mobile moves to a new geographical area.
 Roaming
Roaming is one of the fundamental mobility management procedures of all
  cellular networks. Roaming is defined as the ability for a cellular
  customer to automatically make and receive voice calls, send and
  receive data, or access other services, including home data services,
  when travelling outside the geographical coverage area of the home
  network, by means of using a visited network. This can be done by
  using a communication terminal or else just by using the subscriber
  identity in the visited network. Roaming is technically supported by
  mobility management, authentication, authorization and billing
Location / Mobility Management
 Location Area
A "location area" is a set of base stations that are grouped
  together to optimise signalling. Typically, 10s or even 100s
  of base stations share a single Base Station Controller
  (BSC), the intelligence behind the base stations. The BSC
  handles     allocation   of    radio    channels,    receives
  measurements from the mobile phones, controls handovers
  from base station to base station.
 Routing Area
A "routing area" is a subdivision of a "location area". Routing
  areas are used by mobiles which are GPRS-attached.
  GPRS ("General Packet Radio Services"), GSM‘s new data
  transmission technology, is optimized for "bursty" data
  communication services, such as wireless internet/intranet,
  and multimedia services. It is also known as GSM-IP
  ("Internet Protocol") because it will connect users directly to
  Internet Service Providers (ISP).

GSM Services
   GSM Subscriber ServicesThere are two basic types of services offered through
    GSM: telephony (also referred to as teleservices) and data (also referred to as bearer
    services). Telephony services are mainly voice services that provide subscribers with
    the complete capability (including necessary terminal equipment) to communicate
    with other subscribers. Data services provide the capacity necessary to transmit
    appropriate data signals between two access points creating an interface to the
   Dual-tone multifrequency (DTMF)—DTMF is a tone signaling scheme often used
    for various control purposes via the telephone network, such as remote control of an
    answering machine. GSM supports full-originating DTMF.
   facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax
    machines are designed to be connected to a telephone using analog signals, a
    special fax converter connected to the exchange is used in the GSM system. This
    enables a GSM–connected fax to communicate with any analog fax in the network.
   short message services—A convenient facility of the GSM network is the short
    message service. A message consisting of a maximum of 160 alphanumeric
    characters can be sent to or from a mobile station.. If the subscriber's mobile unit is
    powered off or has left the coverage area, the message is stored and offered back to
    the subscriber when the mobile is powered on or has reentered the coverage area of
    the network. This function ensures that the message will be received.

GSM Services
   cell broadcast—A variation of the short message service is the cell
    broadcast facility. A message of a maximum of 93 characters can be
    broadcast to all mobile subscribers in a certain geographic area. Typical
    applications include traffic congestion warnings and reports on accidents.
   voice mail—This service is actually an answering machine within the
    network, which is controlled by the subscriber. Calls can be forwarded to the
    subscriber's voice-mail box and the subscriber checks for messages via a
    personal security code.
   fax mail—With this service, the subscriber can receive fax messages at any
    fax machine. The messages are stored in a service center from which they
    can be retrieved by the subscriber via a personal security code to the
    desired fax number.
   call forwarding—This service gives the subscriber the ability to forward
    incoming calls to another number if the called mobile unit is not reachable, if it is
    busy, if there is no reply, or if call forwarding is allowed unconditionally.
   barring of outgoing calls—This service makes it possible for a mobile
    subscriber to prevent all outgoing calls.
   barring of incoming calls—This function allows the subscriber to prevent
    incoming calls. The following two conditions for incoming call barring exist:
    baring of all incoming calls and barring of incoming calls when roaming outside
    the home PLMN.

GSM Services
   advice of charge (AoC)—The AoC service provides the mobile subscriber with
    an estimate of the call charges. There are two types of AoC information: one
    that provides the subscriber with an estimate of the bill and one that can be
    used for immediate charging purposes. AoC for data calls is provided on the
    basis of time measurements.
   call hold—This service enables the subscriber to interrupt an ongoing call and
    then subsequently reestablish the call. The call hold service is only applicable to
    normal telephony.
   call waiting—This service enables the mobile subscriber to be notified of an
    incoming call during a conversation. The subscriber can answer, reject, or
    ignore the incoming call. Call waiting is applicable to all GSM
    telecommunications services using a circuit-switched connection.
   multiparty service—The multiparty service enables a mobile subscriber to
    establish a multiparty conversation—that is, a simultaneous conversation
    between three and six subscribers. This service is only applicable to normal
   calling line identification presentation/restriction—These services supply
    the called party with the integrated services digital network (ISDN) number of
    the calling party. The restriction service enables the calling party to restrict the
    presentation. The restriction overrides the presentation.
   closed user groups (CUGs)—CUGs are generally comparable to a PBX. They
    are a group of subscribers who are capable of only calling themselves and
    certain numbers.

What is Multiple Access
   Multiple users want to communicate in a common geographic area
   Cellular Example: Many people want to talk on their cell phones. Each
    phone must communicate with a base station.
   Imagine if only one person could talk on their cell phone at a time!
   Problem: How should we share our resources so that as many users as
    possible can communicate simultaneously
   The concept behind multiple access is to permit a number of users to
    share a common channel. The two traditional ways of multiple access
    are Frequency Division Multiple Access (FDMA) and Time Division
    Multiple Access (TDMA).

Access Scheme
  In Frequency Division Multiple Access, the frequency band is divided in slots. Each user
   gets one frequency slot assigned that is used at will. It could be compared to AM or FM
   broadcasting radio where each station has a frequency assigned. FDMA demands good
   In Time Division Multiple Access, the frequency band is not partitioned but users are
   allowed to use it only in predefined intervals of time, one at a time. Thus, TDMA demands
   synchronization among the users

Access Scheme (CDMA)
 CDMA, for Code Division Multiple Access, is different than those traditional
  ways in that it does not allocate frequency or time in user slots but gives the
  right to use both to all users simultaneously. To do this, it uses a technique
  known as Spread Spectrum. In effect, each user is assigned a code which
  spreads its signal bandwidth in such a way that only the same code can
  recover it at the receiver end. This method has the property that the unwanted
  signals with different codes get spread even more by the process, making them
  like noise to the receiver.
 CDMA (Code-Division Multiple Access) refers to any of several protocols used
  in so-called second-generation (2G) and third-generation (3G) wireless
  communications. As the term implies, CDMA is a form of multiplexing, which
  allows numerous signals to occupy a single transmission channel, optimizing
  the use of available bandwidth. The technology is used in ultra-high-frequency
  (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.
 CDMA employs analog-to-digital conversion (ADC) in combination with spread
  spectrum technology. There are trillions of possible frequency-sequencing
  codes, which enhances privacy and makes cloning difficult.

Access Scheme (CDMA)
   The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a
    scheme called soft handoff, which minimizes signal breakup as a handset
    passes from one cell to another. The combination of digital and spread-
    spectrum modes supports several times as many signals per unit bandwidth
    as analog modes. CDMA is compatible with other cellular technologies; this
    allows for nationwide roaming.
   The original CDMA standard, also known as CDMA One and still common
    in cellular telephones in the U.S., offers a transmission speed of only up to
    14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel
    form. CDMA2000 and wideband CDMA deliver data many times faster.
   Uses
       One of the early applications for code division multiplexing—predating, and
        distinct from cdmaOne—is in GPS.
       The Qualcomm standard IS-95, marketed as cdmaOne.
       The Qualcomm standard IS-2000, known as CDMA2000. This standard is used
        by several mobile phone companies, including the Globalstar satellite phone
       CDMA has been used in the OmniTRACS satellite system for transportation

Idea of Communication with Coding Technique
            d1                                                    d2

      1                                                       2
            d1.c1                                   D2.c2

                    d1.C1 + d2.c2 + d3.c3 + d4.c4
                      Communication Channel

          D3.c3                                       D4.c4
     3                                                        4

          d3                                                       d4

                      Data Representation in CDMA
           Data Bit 0 → -1      Data Bit 1 → +1 Silent -> 0

Idea of Communication with Coding Technique
                                    C1                  C2                   C3                    C4
   Chip Sequence          [+1, +1, +1 , +1]      [+1, -1, +1 , -1]     [+1, +1, -1 , -1]   [+1, -1, -1 , +1]

              Bit 0                                                                        Bit 0

        1            -1                                                               2        -1
               [ -1, -1, -1 , -1]                              [-1, +1, -1 , +1]

                                     [ -1 , -1, -3 , +1 ]
                                  Communication Channel
               [0 , 0 , 0 , 0 ]                                 [+1 , -1 , -1 , +1]

       3             0                                                                 4        +1

            Silent                                                                          Bit 1

                       Data Representation in CDMA
            Data Bit 0 → -1      Data Bit 1 → +1 Silent -> 0

CDMA Coding scheme
   Each user is associated with a different code, say v. If the data to be
    transmitted is a digital zero, then the actual bits transmitted will be –v,
    and if the data to be transmitted is a digital one, then the actual bits
    transmitted will be v. For example, if v=(1,–1), and the data that the
    user wishes to transmit is (1, 0, 1, 1) this would correspond to (v, –v, v,
    v) which is then constructed in binary as ((1,–1),(–1,1),(1,–1),(1,–1)).
    For the purposes of this article, we call this constructed vector the
    transmitted vector.
   Each sender has a different, unique vector v chosen from that set, but
    the construction method of the transmitted vector is identical.
   Now, due to physical properties of interference, if two signals at a point
    are in phase, they add to give twice the amplitude of each signal, but if
    they are out of phase, they "subtract" and give a signal that is the
    difference of the amplitudes. Digitally, this behavior can be modeled by
    the addition of the transmission vectors, component by component.

CDMA Coding scheme
   If sender0 has code (1,–1) and data (1,0,1,1), and sender1 has code (1,1) and
    data (0,0,1,1), and both senders transmit simultaneously, then this table
    describes the coding steps:
   Step Encode sender0                                  Encode sender1
0 vector0=(1,-1),data0=(1,0,1,1)=(1,-1,1,1) vector1=(1,1),data1=(0,0,1,1)=(-1,-1,1,1)
1   encode0=vector0.data0                       encode1=vector1.data1
2   encode0=(1,-1).(1,-1,1,1)                   encode1=(1,1).(-1,-1,1,1)
3   encode0=((1,-1),(-1,1),(1,-1),(1,-1))       encode1=((-1,-1),(-1,-1),(1,1),(1,1))
4   signal0=(1,-1,-1,1,1,-1,1,-1)               signal1=(-1,-1,-1,-1,1,1,1,1)

   Because signal0 and signal1 are transmitted at the same time into the air,
    they add to produce the raw signal: (1,-1,-1,1,1,-1,1,-1) + (-1,-1,-1,-1,1,1,1,1)
    = (0,-2,-2,0,2,0,2,0)

CDMA Coding scheme
   This raw signal((0,-2,-2,0,2,0,2,0)) is called an interference pattern. The
    receiver then extracts an intelligible signal for any known sender by
    combining the sender's code with the interference pattern, the receiver
    combines it with the codes of the senders. The following table explains how
    this works and shows that the signals do not interfere with one another:

   Step        Decode sender0                                Decode sender1
0   vector0=(1,-1), pattern=(0,-2,-2,0,2,0,2,0) vector1=(1,1), pattern=(0,-2,-2,0,2,0,2,0)
1   decode0=pattern.vector0                       decode1=pattern.vector1
2   decode0=((0,-2),(-2,0),(2,0),(2,0)).(1,-1)    decode1=((0,-2),(-2,0),(2,0),(2,0)).(1,1)
3   decode0=((0+2),(-2+0),(2+0),(2+0))           decode1=((0-2),(-2+0),(2+0),(2+0))
4   data0=(2,-2,2,2)=(1,0,1,1)                    data1=(-2,-2,2,2)=(0,0,1,1)

   Further, after decoding, all values greater than 0 are interpreted as 1 while
    all values less than zero are interpreted as 0. For example, after decoding,
    data0 is (2,-2,2,2), but the receiver interprets this as (1,0,1,1).

CDMA Coding scheme
   We can also consider what would happen if a receiver
    tries to decode a signal when the user has not sent
    any information. Assume signal0=(1,-1,-1,1,1,-1,1,-1)
    is transmitted alone. The following table shows the
    decode at the receiver:

Step     Decode sender0                             Decode sender1
0 vector0=(1,-1), pattern=(1,-1,-1,1,1,-1,1,-1) vector1=(1,1), pattern=(1,-1,-1,1,1,-1,1,-1)
1 decode0=pattern.vector0                        decode1=pattern.vector1
2 decode0=((1,-1),(-1,1),(1,-1),(1,-1)).(1,-1)) decode1=((1,-1),(-1,1),(1,-1),(1,-1)).(1,1)
3 decode0=((1+1),(-1-1),(1+1),(1+1))             decode1=((1-1),(-1+1),(1-1),(1-1))
4 data0=(2,-2,2,2)=(1,0,1,1)                     data1=(0,0,0,0)

   When the receiver attempts to decode the signal using sender1‘s code, the
    data is all zeros, therefore the cross correlation is equal to zero and it is clear
    that sender1 did not transmit any data.

Synchronous CDMA                                 Asynchronous CDMA
They use orthogonal codes.                       It use unique "pseudo-random" or
                                                 "pseudo-noise" (PN) sequences.
completely reject arbitrarily strong signals     This is not true for Asynchronous CDMA;
using different codes, due to the                rejection of unwanted signals is only partial.
orthogonality of these systems
It can‘t use the spectrum more efficiently       It can use the spectrum more efficiently in
in mobile telephony applications.                mobile telephony applications.
No such flexibility in allocation of             offers a key advantage in the flexible
resources.                                       allocation of resources
There are a fixed number of orthogonal           There is no strict limit to the number of
codes, timeslots or frequency bands that         users that can be supported in an
can be allocated for CDM,                        Asynchronous CDMA system
Synchronous CDMA is ideally not suited to        Asynchronous CDMA is ideally suited to a
a mobile network where large numbers of          mobile network where large numbers of
transmitters each generate a relatively          transmitters each generate a relatively
small amount of traffic at irregular intervals   small amount of traffic at irregular intervals


   Can share a common bandwidth without
    interfering each other.
   Flexible network planning (planning is no longer needed)
   Greater coverage (larger area for a given amount of power )
   High capacity (greater coverage capacity)
   Cost (larger profit for providers due to increased capacity, less infrastructure)
   Clarity
   Customer satisfaction (privacy, better call quality longer battery life due
          to less power consumption, prevent cross talks)

   Compatibility (dual mode analog and digital)

   Poor Synchronization
    Difficulty to satisfy synchronization requirements.

   Self jamming
    Self jamming is a steep deterioration of performance as a result of poor
    synchronization. Poor synchronization causes partial-correlation with the
    codes of other users and the result will be a vast increase of the

   Near-far problem
    power control is necessary for mitigating the Near-far problem. There are
    some factors for imperfect power control such as: feedback delays,
    imperfect power estimates, traffic conditions, errors in the feedback

   Network complexity
    Complex network support is needed for implementing soft handoff, and
    also for countering multipath and fading effects.

   Throughput
    Low throughput efficiency for large number of users.
CDMA Applications


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GSM is a widely spread standard         CDMA is a patented technology

GSM provided by BSNL, AIRTEL,           CDMA provided by Reliance
GSM users are almost 8 times in         CDMA users are almost 8 times less
number than CDMA users worldwide        in number than GSM users worldwide
GSM is far better than CDMA in voice    CDMA is poor than GSM in voice
quality                                 quality
GSM base stations consumes more         CDMA base stations consumes less
power than CDMA and also covers a       power than GSM and also covers a
less distance                           large distance
cell size in GSM is small compared to   cell size in CDMA is larger compared
GSM.                                    to GSM.

                    GSM Vs. CDMA
It covers a large area of more than 25 user cannot go beyond a short
Kms.                                   distance charging area (SDCA) -
                                       which is roughly a radius of 25 km.

GSM offers slower data download      CDMA offers faster data download

On a GSM phone your account On a CDMA phone, your account
information along with your contact information is programmed into your
list and other personal data are stored cellular phone
on a SIM card (Subscriber Identity
Maximum       download   speed    of Maximum download speed of about
384kbps      (around   140kbps    in 2mb/s (about 700kbps in practice)

Europe, South Africa, Australia, and CDMA is mostly used in America and
many Middle and Far East countries some parts of Asia
have chosen to adopt GSM

It uses TDMA.                      It uses CDMA

It is 2nd generation               It is 3rd generation

Its year of first use was 1991     Its year of first use was 2000

Roaming is worldwide               Roaming is limited

Battery life is very good due to   Battery life lower due to high
simple protocol, good coverage     demands of CDMA power control
and mature, power efficient        and young chipsets
Hard Handoff                       Soft Handoff

   General Packet Radio Service (GPRS) is a Mobile Data Service available to
    users of Global System for Mobile Communications (GSM) and IS-136 mobile
    phones. It provides data rates from 56 up to 114 Kbps.
   GPRS data transfer is typically charged per kilobyte of transferred data, while
    data communication via traditional circuit switching is billed per minute of
    connection time, independent of whether the user has actually transferred data
    or has been in an idle state. GPRS can be used for services such as Wireless
    Application Protocol (WAP) access, Short Message Service (SMS), Multimedia
    Messaging Service (MMS), and for Internet communication services such as
    email and World Wide Web access.
   2G cellular systems combined with GPRS is often described as "2.5G", that is,
    a technology between the second (2G) and third (3G) generations of mobile
    telephony. It provides moderate speed data transfer, by using unused Time
    division multiple access (TDMA) channels in, GPRS is integrated into GSM
    Release 97 and newer releases.
    It was originally standardized by European Telecommunications Standards
    Institute (ETSI), but now by the 3rd Generation Partnership Project (3GPP).
   The General Packet Radio Service (GPRS) is a new nonvoice value added
    service that allows information to be sent and received across a mobile
    telephone network. It supplements today's Circuit Switched Data and Short
    Message Service. GPRS is NOT related to GPS (the Global Positioning System),
    a similar acronym that is often used in mobile contexts.

  GPRS Handset Classes: There are three different classes of devices.
1. Class A handsets can do both voice and data at the same time
   (simultaneously). If you were to receive a voice call will using the
   Internet, say, the connection would be placed on busy while you
   answer the call, rather than have it disconnected.
2. Class B handsets are voice and packet data capable, but not at the same
   time. It can only support either a voice or data service at a time. But
   like in Class A above, a voice call would put the data call on hold, and
   vice versa.
3. Class C handsets can handle only non-simultaneous data and voice
   calls. The user must manually select the service they wish to connect
   to. (SMS is also optional for Class C terminals).

    Classes of GPRS Services: Mobile devices can request different types
     of traffic to be prioritized in a attempt to give the user their desired
     level of connectivity. There are 4 types of classes.
1.   Precedence Class: An application can be assigned precedence classes
     1,2, or 3. If an application has higher precedence (1) than another(3)
     then its traffic will be given a higher priority.
2.   Delay classes: Applications can request predictive delay classes which
     guarantee an average and 95% delay.
3.   Reliability class: application can request differing levels of reliability
     for its data depending on its tolerance of data loss.
4.   Throughput class: Applications can choose different profiles for

GPRS Network System Architechture
   A GSM network mainly consists of four components.
   Mobile Station (MS) carried by the subscriber .
   Base Station Subsystem (BSS) controls radio link with mobile station .
   Mobile Switching Center (MSC) is the central component of the NSS.
    Operates all switching functions for the mobiles within its jurisdiction.
    Interface between mobile and other (including fixed) network.
   Network Databases : Home Location Register and Visitor Location
    Register together with MSC provides the call routing and roaming
    capabilities of GSM.
   In order to integrate GPRS into the existing GSM network, two major
    new core network elements are introduced: the Serving GPRS
    Support Node (SGSN) and the Gateway GPRS Support node
   Serving GPRS Support Node (SGSN): An SGSN is responsible for the
    delivery of data packets from and to the mobile stations within its
    service area. SGSNs send queries to Home Location Registers (HLRs)
    to obtain profile data of GPRS subscribers. SGSNs detect new GPRS
    mobile stations in a given service area; and, finally, SGSNs process
    registration of new mobile subscribers and keep a record of their
    location inside a given service area.

GPRS Network System Architechture

   Gateway GPRS Support Node (GGSN) : GGSNs are used as
    interfaces between the GPRS backbone network and the
    external Public Packet Data Networks. GGSNs maintain routing
    information that is necessary to tunnel the Protocol Data Units
    (e.g IP) to the SGSNs that service particular mobile stations.
    Other functions include network and subscriber screening and
    address mapping. One or more GGSNs may support multiple
   In addition to the new GPRS components, following existing
    GSM network elements must also be enhanced in order to
    support GPRS.
   Base Station System (BSS): must be enhanced to recognize
    and send user data to the SGSN that is serving the area.
   Home Location Register (HLR): must be enhanced to register
    GPRS user profiles and respond to queries originating from
    SGSNs regarding these profiles.

GPRS Network System Architecture

 As can be seen, there are a number of new standardized network interfaces introduced:
Gb Frame relay connection between the SGSN and the PCU within the BSS. This transports both
user data and signaling messages to/from the SGSN. (SNDCP,LLC,BSSGP,NS)
•Gn The GPRS backbone network, implemented using IP LAN/WAN technology. Used to provide
virtual connections between the SGSN and GGSN.
•Gi The point of connection between GPRS and the external networks, each referenced by the
Access Point Name. This will normally be implemented using IP WAN technology.
•Gr Interface between the HLR and SGSN that allows access to customer subscription information.
This has been implemented using enhancements to the existing GSM C7 MAP interface.
To use GPRS, users specifically need:

   A mobile phone or terminal that supports GPRS (existing GSM phones do
    NOT support GPRS)

   A subscription to a mobile telephone network that supports GPRS;

   Use of GPRS must be enabled for that user. Automatic access to the GPRS
    may be allowed by some mobile network operators, others will require a
    specific opt-in;

   Knowledge of how to send and/or receive GPRS information using their
    specific model of mobile phone, including software and hardware
    configuration (this creates a customer service requirement);

   A destination to send or receive information through GPRS. Whereas with
    SMS this was often another mobile phone, in the case of GPRS, it is likely
    to be an Internet address, since GPRS is designed to make the Internet
    fully available to mobile users for the first time. From day one, GPRS users
    can access any web page or other Internet applications- providing an
    immediate critical mass of uses.

GPRS Services
   Multimedia Messaging Service (MMS)
   Push to talk over Cellular PoC / PTT
   Instant Messaging and Presence -- Wireless Village
   Internet Applications for Smart Devices through Wireless Application Protocol
   Point-to-point (PTP) service: internetworking with the Internet (IP protocols)
   Short Message Service (SMS)
   Future enhancements: flexible to add new functions, such as more capacity,
    more users, new accesses, new protocols, new radio networks.
   USB GPRS modem:USB GPRS modems use a terminal-like interface USB 2.0
    and later, data formats V.42bis, and RFC 1144 and external antennas. Modems
    can be add in cards (for laptop) or external USB devices which are similar in
    shape and size to a computer mouse.
   GPRS can be used as the bearer of SMS. If SMS over GPRS is used, an SMS
    transmission speed of about 30 SMS messages per minute may be achieved.
    This is much faster than using the ordinary SMS over GSM, whose SMS
    transmission speed is about 6 to 10 SMS messages per minute

Limitations Of GPRS
   GPRS does impact a network's existing cell capacity.
    Only limited resources.
   Use for one purpose precludes simultaneous use for
   Maximum speed of 171.2 kbps only theoretically.
   Single user would need all 8 time slots.
   Network operator would never allow that.
   Bandwidth limited.
   Limited cell capacity for all users
   Speeds much lower in reality

Features of GPRS
   Faster data transfer rates
    GPRS currently supports an average data rate of 115 Kbps, but this speed is only
    achieved by dedicating all eight time slots to GPRS. Instead, carriers and terminal
    devices will typically be configured to handle a specific number of time slots for
    upstream and downstream data. The aggregate cell site bandwidth is shared by voice and
    data traffic. GPRS operators will vary in how they allocate the bandwidth. Typically,
    they will configure the networks to give precedence to voice traffic; some may dedicate
    time slots to data traffic to ensure a minimum level of service during busy voice traffic
    periods. Unused voice capacity may be dynamically reallocated to data traffic.

   Always-on connection
    An ―always-on‖ connection eliminates the lengthy delays required to reconnect
    to the network to send and receive data. Information can also be pushed to the
    end user in real time.

   Robust connectivity
    GPRS improves data transmission integrity with a number of mechanisms. First,
    user data is encoded with redundancies that improve its resistance to adverse
    radio conditions. The amount of coding redundancy can be varied, depending
    on radio conditions. GPRS has defined four coding schemes CS1 through CS4.
    Initially, only CS1 and CS2 will be supported, which allows approximately 9 and
    13 Kbps in each time slot.If an error is detected in a frame received in the BSS,
    the frame may be repeatedly retransmitted until properly received before
    passing it on to the GPRS core network.

Features of GPRS
   Broad application support
    Like the Internet, GPRS is based on packet-switched data. This means
    that all native IP applications, such as email, Web access, instant
    messaging, and file transfers can run over GPRS. In addition, its faster
    data transfer rates enable GPRS to accommodate higher-bandwidth
    applications (such as multimedia Web content) not suited to slower
    GSM dial-up connections. GPRS is particularly well suited for
    applications based on the Wireless Application Protocol (WAP).

   Security support
    GPRS builds on the proven authentication and security model used by
    GSM. At session initiation, a user is authenticated using secret
    information contained on a smart card called a Subscriber Identity
    Module (SIM). Authentication data is exchanged and validated with
    records stored in the HLR network node. GPRS enables additional
    authentication using protocols such as RADIUS before the subscriber is
    allowed access to the Internet or corporate data networks.


   Before a GPRS mobile station can use GPRS services it must obtain an
    address used in the packet data network (a PDP address) and create a PDP
    context. The context describes the characteristics of the connection to the
    packet data network (PDP type, PDP address, service precedence, reliability,
    delay, throughput and GGSN). With an active PDP context, packets from mobile
    station will be sent to its current SGSN first, then this SGSN encapsulates the IP
    packets, examines the PDP context, and routes them to appropriate GGSN. The
    GGSN decapsulates the packets and sends them out on the IP network.
    Similarly packets from the external packet data network will be routed to the
    GGSN first, which then queries the HLR and obtains the information where the
    MS is currently located in. It encapsulates the incoming packets and tunnels
    them to the current SGSN of the mobile user. The SGSN decapculates the
    packets and delivers them to MS. Each GGSN has an IP address and each
    mobile station has been assigned an IP address by its GGSN. Thus the MS's IP
    address has the same network prefix as the IP address of its GGSN.
   In GPRS network, user's current locations are managed in two levels: Micro
    mobility management tracks the current routing area or cell of the mobile
    station. It is performed by the SGSN. Macro mobility management keeps track
    of the mobile station's current SGSN and stores it in the HLR, VLR, and GGSN.

GPRS Transmission Plane Protocol
Reference Model

GPRS Transmission Plane Protocol
Reference Model
   All data within the GPRS backbone, i.e. between the GSNs (SGSN-
    GGSN), is transferred using the GTP (GPRS tunnelling protocol).
    GTP can use two different transport protocol, either reliable TCP
    for X.25 packets or the non-reliable UDP used for IP packets.
   To adapt to the different characteristics of the underlying
    networks, the Subnetwork Dependent Convergence Protocol
    (SNDCP) is used between an SGSN and the MS
   On top of SNDCP and GTP user packet data is tunneled from the
    MS to the GGSN and vice versa.
   To achieve high reliability of packet transfer between SGSN and
    MS, a special LLC is used, which comprises ARQ and FEC
   A Base Station Subsystem GPRS Protocol (BSSGP) is used to
    convey routing and QoS -related information between the BSS and
    SGSN. BSSGP doesn’t perform error correction and works on top
    of Frame relay (FR) network.

GPRS Transmission Plane Protocol
Reference Model
   Radio link dependent protocols are needed to
    transfer data over the Um interface. The Radio Link
    Protocol (RLC) provides a reliable link.
   The MAC controls access with signaling procedures
    for the radio channel and their maping of LLC
    frames onto the GSM physical channels.
   The radio interface at Um needed for GPRS doesn‘t
    require fundamental changes compared to standard

GPRS: air interface
 Radio Link Control (RLC)
  Segmentation of the LLC-Frames in RLC blocks
  Block size dependent on short-term channel conditions
  Backward error correction and data flow control by Automatic
   Repeat Request (ARQ) protocol
    repeating not repairable RLC blocks selectively

 Medium Access Control ( MAC)
  Channel                   reservation               contains:
    - one/several time slots (Packet Data Channels PDCH) of
    one uplink status flag (USF) per Packet Data Channel
      (PDCH), channel partition of up to 8 ms

GPRS: air interface
    Medium Access Control ( MAC)
    Reservation in the uplink (MS to BSS):
    MS sends reservation request on a Random Access Channel
     (Slotted ALOHA)
      BTS allocates a (split) channel and sends packet assignment

      MS sends data depending on the current priority (USF flag)

    Reservation in the Downlink (BSS to MS):

        BTS displays transmitting request and informs about the
         reserved channel
        MS supervises the reserved channel and receives

GPRS: air interface
    Physical Link Control
    adaptive forward error correction (FEC) dependent on short-
     term channel conditions
    temporal scrambling (Interleaving) of the bursts and Mapping
     on reserved PDCH (Packet Data Channel)
    procedure to recognize overbooking situations on the
     physical channel
 GPRS Channel Encoding
        Scheme   Code    Payload   BCS    Pre-   Tail bits Coded   Punctured    Data
                 Rate                    coded              bits      bits       rate
                                          USF                                  (kbit/s)

         CS-1    1/2      181      40     3        4       456        0         9.05

         CS-2    ~ 2/3    268      16     6        4       588       132        13.4

         CS-3    ~ 3/4    312      16     6        4       676       220        15.6

         CS-4     1       428      16     12       0       456        0         21.4

GPRS Applications

   Chat
   Textual and visual information
   Still & moving images
   Web browsing
   Document sharing/Collaborate working
   Audio
   Email, File Transfer…

It is circuit switched.                     It is packet switched.
It is not ‘Always-on’.                      It is ‘Always-on’.

You’re charged for the time the channel - You’re charged for the amount of data
is reserved.                            that’s being transported, not for the time
                                        that the unit is online.

The System uses the same TDMA (Time The GPRS connection in the t610 can
Division Multiple Access) link with one use as many as 4+1 time slots.
out of seven time slots.
Circuit     switching     provides    the   With packet switching, the operator
customer with a dedicated channel all       assigns one or more dedicated channels
the way to the destination. The             specifically for shared use. These
customer has exclusive use of the           channels are up and running 24 hours a
circuit for the duration of the call,       day, and when you need to transfer data,
                                            you access a channel and transmit your
The standard data rate of a GSM It provides data rates from 56 up to 114
channel is 22.8 kbps            Kbps.

It is circuit switched.                       It is packet switched.
It is not ‗Always-on‘.                        It is ‗Always-on‘.
supports guaranteed quality of service , Doesn‘t supports guaranteed quality of service
better     protocol    for   timing-sensitive ,so not a better protocol for timing-sensitive
applications such as image or video transfer. applications such as image or video transfer

is less bandwidth efficient with expensive is more bandwidth efficient           with   less
wireless links                             expensive wireless links

HSCSD is not as widespread as GPRS            GPRS is not as widespread as HSCSD

CSD is just your normal dial up where you GPRS on the other hand is the internet
dial a number to connect to an internet connection provided by the mobile phone
service provider and is limited to 9.6kbps on operator
most                                 networks

HSCSD utilizes up to four 9.6Kb or 14.4Kb It provides data rates from 56 up to 114
time slots, for a total bandwidth of 38.4Kb or Kbps.

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