MOBILE COMPUTING (TCS-054)
Anurag Malik Associate Professor Shivanshu Rastogi Assistant Professor
CE & IT Dept. M.I.T Moradabad B.Tech VIII CS / IT UNIT I Recommended Books:
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J. Schiller, Mobile Communications, Addison Wesley A. Mehrotra, GSM System Engineering Asok K. Talukder, Mobile ComputingTechnology, Applications & Service Creation, TMH Raj Kamal,Mobile Computing, Oxford University Press
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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 computer. 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.
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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 towers.
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
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Wireless characteristics
Variant Connectivity
Low bandwidth and reliability
Frequent disconnections
predictable or sudden Broadcast medium
Asymmetric Communication Monetarily expensive
Charges per connection or per message/packet
Connectivity is weak, intermittent and expensive
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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 subscribers. 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.
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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
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Two aspects of Mobility
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 X X ¥ ¥
Mobile X ¥ X ¥
Example Stationary computer Notebook in ahotel 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
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Portability Characteristics
Resource constraints Mobile computers are resource poor Reduce program size ± interpret script languages (Mobile Java?) Computation and communication load cannot be distributed equally 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 software 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 Network. 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)
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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 useragent 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.
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WHY WIRELESS NETWORK
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 users 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
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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: ³Ad-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
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Wireless Personal Area Network (WPAN)
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Wireless Local Area Network (WLAN)
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Wireless Metropolitan Area Network (WMAN)
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Wireless Wide Area Network (WWAN)
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Frequencies For Communication
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Limitations of Mobile Environments
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Limitations of the Wireless Network y heterogeneity of fragmented networks y frequent disconnections y limited communication bandwidth Limitations Imposed by Mobility y lack of mobility awareness by system/applications y route breakages Limitations of the Mobile Computer y short battery lifetime y limited capacities
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y
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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
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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
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Mobile Computing Architecture
Presentation Tier Application Tier Java Server Pages
RMI
Data Tier
Internet Explorer
SOAP
iPlanet Web Server
IBM WebSphere BEA WebLogic JBOSS IIOP iPlanet Jakarta SOAP Enterprise Java Beans SQL XML Servlets JDBC
XML Data Stores Database
Netscape Navigator
IIOP
Jigsaw
XSLT
Opera
Apache
HTML
LIB WWW
XML
Zeus
WML / HDML
Applications & Web Services ZOPE CGI (C. Perl, Python)
Aggregation Service Data Feeds
Java URL Class
HTTP
RPC ZEND PHP
XML
Lynx
HTTPS
Lotus Domino mail and Documents
Javascript
Roxen XML MS Transaction Server COM Applications Adapter Pike Equipment MS Exchange MS Commerce Server
WAP Browser
J2ME
Voice
Internet Information Server
COM
Legacy Applications
ASP
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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 design 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.
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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
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Mobile Computing Architecture
Database Management or Data Tier : This layer is for database access and management. 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 nonexclusive 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.
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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 maintain. 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 server. 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.
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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.
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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.
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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
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Typical Application : Road traffic
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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 ³high´ performance, color high-resolution display, mouse, hard disk typically, web pages optimized for design, not for communication; ignore endsystem 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
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Early Wireless Communication
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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
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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 Germany 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
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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 Telecommunications) 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, ...
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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
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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 ³members´ of a ³family´: 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)
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Cellular Concept
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 cluster. 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 changes. 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
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The
Example: N=7
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FundamentalsSystemsCellular Systems Of Fundamentals of Cellular
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
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Fundamentals Of Cellular Systems
Total number of frequency channels in the system : F 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 channels No. of channels per group: k= F/N Note: k must be integer! Reuse same channel group in cells that are far away Co-channel cells: cells that use the same set of frequency channels Co-channel interference: interference caused by signals from co-channel cells
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Fundamentals Of Cellular Systems
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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
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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 cells Involve MSC (mobile switching center) to supervise the borrowing procedure
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Channel Assignment Schemes
Dynamic channel assignment: Channels are allocated to cells on demand
MSC assign channels based on the co-channel & adjacent channel interference 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
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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
HLR VLR
MSC
HLR
To other MSCs
VLR
PSTN
PSTN
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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 ³visiting´ mobiles Interfacing with other MSCs Interfacing with PSTN (traditional telephone network) Standard ³Common 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
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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
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HLR - VLR
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.
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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.
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Handoff
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 UMTS. 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.
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Handoff
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 fasttraveling 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
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Handoff
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 Plus 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
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Handoff Features
1. 2. 3. 4.
The Effective handoff scheme should have the following features. Fast & Lossless Minimal no. of Control signal exchanges Scalable with network size 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.
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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.
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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.
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HandOffs
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
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Cellular Cellular Systems with small cells Concept Advantages of
higher capacity, higher number of users less transmission power needed more robust, decentralized base station deals with interference, transmission area etc. locally Disadvantages
Infrastructure Needed Handover Needed Frequency Planning
Problems: 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
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GSM
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.
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GSM
There are four different cell sizes in a GSM network²macro, 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.
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Functional Architecture of a GSM System
Cell MS MS Cell RSS BTS MS BSS
Abis
BSC
BTS BSC
A MSC MSC Signalling
RSS- Radio Subsystem MS- Mobile Station BSS- Base Station Subsystem BTS- Base Transceiver Station BSC- Base Station Controller NSS- Network & Switching Subsystem MSC- Mobile services Switching Centre VLR- Visitor Location Register HLR- Home Location Register GMSC- Gateway MSC OSS- Operation Subsystem EIR- Equipment Identity Register AUC- Authentication Centre OMC- Operation & Maintenance centre IWF- Inter-Working Function
VLR
NSS
VLR HLR
GMSC IWF
ISDN, PSTN PDN
O
OSS
EIR
AUC
OMC
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GSM
It is the most successful digital mobile telecommunication system in world. 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). 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)
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GSM
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.
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Intra _ MSC Handover
MS Measurement report BTS old Measurement report HO Required HO 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 BSC old MSC BSC new BTS new
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 network. 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.
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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
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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 operator. 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.
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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.
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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.
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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.
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GSM Channel Structure
2.
There are two types of TCHs that are differentiated by their traffic rates. 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 channels(11.4kbps). 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 correction Synchronization Channel (SCH) ± For synchronization
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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
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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 cell High transmission quality High audio quality and reliability for wireless, uninterrupted phone calls at higher speeds (e.g., from cars, trains)
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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 lock. GSM covers virtually all parts of the world so international roaming is not a problem.
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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
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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 them.
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.
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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. TMSI 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 procedures.
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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).
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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 network. Dual-tone multifrequency (DTMF)²DTMF 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 III²GSM 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 services²A 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.
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GSM Services
cell broadcast²A 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 mail²This 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 mail²With 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 forwarding²This 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 calls²This service makes it possible for a mobile subscriber to prevent all outgoing calls. barring of incoming calls²This 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.
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GSM Services
advice of charge (AoC)²The 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 hold²This 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 waiting²This 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 service²The multiparty service enables a mobile subscriber to establish a multiparty conversation²that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal telephony. calling line identification presentation/restriction²These 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)²CUGs are generally comparable to a PBX. They are a group of subscribers who are capable of only calling themselves and certain numbers.
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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).
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Access Scheme
FDMA 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 filtering. TDMA 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
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Access Scheme (CDMA)
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.
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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 spreadspectrum 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 multiplexing²predating, and distinct from cdmaOne²is 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 network. CDMA has been used in the OmniTRACS satellite system for transportation logistics.
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Idea of Communication with Coding Technique
d1 1 d1.c1 d1.C1 + d2.c2 + d3.c3 + d4.c4 Communication Channel D3.c3 3 d3 Data Representation in CDMA Data Bit 0 -1 Data Bit 1 +1 Silent -> 0 D4.c4 4 d4 D2.c2 2 d2
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Idea of Communication with Coding Technique
Chip Sequence
Data Representation in CDMA Data Bit 0 -1 Data Bit 1 +1 Silent -> 0
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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.
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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 encode0=vector0.data0 encode0=(1,-1).(1,-1,1,1) encode0=((1,-1),(-1,1),(1,-1),(1,-1)) signal0=(1,-1,-1,1,1,-1,1,-1) encode1=vector1.data1 encode1=(1,1).(-1,-1,1,1) encode1=((-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)
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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
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).
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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:
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.
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Synchronous CDMA They use orthogonal codes. completely reject arbitrarily strong signals using different codes, due to the orthogonality of these systems It can¶t use the spectrum more efficiently in mobile telephony applications. No such flexibility in allocation of resources. There are a fixed number of orthogonal codes, timeslots or frequency bands that can be allocated for CDM, Synchronous CDMA is ideally not suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals
Asynchronous CDMA It use unique "pseudo-random" or "pseudo-noise" (PN) sequences. This is not true for Asynchronous CDMA; rejection of unwanted signals is only partial. It can use the spectrum more efficiently in mobile telephony applications. offers a key advantage in the flexible allocation of resources There is no strict limit to the number of users that can be supported in an Asynchronous CDMA system Asynchronous CDMA is ideally suited to a mobile network where large numbers of transmitters each generate a relatively small amount of traffic at irregular intervals
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Advantages
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)
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Disadvantages
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 interference. 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 channel. 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.
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CDMA Applications
Applications:
GPSOne® Position Location Technology Position location concept applications. 1. 2. 3. 4. Get directions on the move Locate a lost pet Provide traffic and navigation services Locate Vehicles and Assets concepts applications
http://www.snaptrack.com/impact/index.jsp
Qtv Streaming Video and Audio Superior playback rates in a fully integrated software solution
2D and 3D Gaming Engine Life-like animation in 2D and 3D environments.
http://www.cdmatech.com/solutions/multimedia.jsp
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GSM Vs. CDMA
GSM is a widely spread standard GSM provided by BSNL, AIRTEL, ESCOTEL etc GSM users are almost 8 times in number than CDMA users worldwide GSM is far better than CDMA in voice quality GSM base stations consumes more power than CDMA and also covers a less distance cell size in GSM is small compared to GSM. CDMA is a patented technology CDMA provided by Reliance CDMA users are almost 8 times less in number than GSM users worldwide CDMA is poor than GSM in voice quality CDMA base stations consumes less power than GSM and also covers a large distance cell size in CDMA is larger compared to GSM.
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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 Module) Maximum 384kbps practice). download speed (around 140kbps of Maximum download speed of about 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
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GSM Vs. CDMA
It uses TDMA. It is 2nd generation Its year of first use was 1991 Roaming is worldwide Battery life is very good due to simple protocol, good coverage and mature, power efficient chipsets Hard Handoff It uses CDMA It is 3rd generation Its year of first use was 2000 Roaming is limited Battery life lower due to high demands of CDMA power control and young chipsets Soft Handoff
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GPRS
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.
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GPRS
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).
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GPRS
1.
2.
3.
4.
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. 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. Delay classes: Applications can request predictive delay classes which guarantee an average and 95% delay. Reliability class: application can request differing levels of reliability for its data depending on its tolerance of data loss. Throughput class: Applications can choose different profiles for throughput.
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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 (GGSN). 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.
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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 SGSNs. 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.
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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.
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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.
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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 (WAP) 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
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Limitations Of GPRS
GPRS does impact a network's existing cell capacity. Only limited resources. Use for one purpose precludes simultaneous use for another. 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
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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 ³always-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.
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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.
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INTERWORKING WITH THE EXTERNAL INTERNET
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.
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GPRS Transmission Plane Protocol Reference Model
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GPRS Transmission Plane Protocol Reference Model
All data within the GPRS backbone, i.e. between the GSNs (SGSNGGSN), 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 mechanisms. 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.
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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 GSM.
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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 frequency one uplink status flag (USF) per Packet Data Channel (PDCH), channel partition of up to 8 ms
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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
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GPRS: air interface
Physical Link Control adaptive forward error correction (FEC) dependent on shortterm 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
Scheme Code Rate 1/2 ~ 2/3 ~ 3/4 1 Payload BCS Precoded USF 3 6 6 12 Tail bits Coded bits 4 4 4 0 456 588 676 456 Punctured bits 0 132 220 0 Data rate (kbit/s) 9.05 13.4 15.6 21.4
GPRS Channel Encoding
CS-1 CS-2 CS-3 CS-4
181 268 312 428
40 16 16 16
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GPRS Applications
Chat Textual and visual information Still & moving images Web browsing Document sharing/Collaborate working Audio Email, File Transfer«
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GSM Vs. GPRS
It is circuit switched. It is not µAlways-on¶. It is packet switched. It is µAlways-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 customer with a dedicated channel all the way to the destination. The customer has exclusive use of the circuit for the duration of the call, With packet switching, the operator assigns one or more dedicated channels specifically for shared use. These channels are up and running 24 hours a day, and when you need to transfer data, you access a channel and transmit your data.
The standard data rate of a GSM It provides data rates from 56 up to 114 channel is 22.8 kbps Kbps.
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HSCSD Vs. GPRS
It is circuit switched. It is not µAlways-on¶. It is packet switched. It is µAlways-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 wireless links expensive wireless links HSCSD is not as widespread as GPRS with less
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. 57.6Kb.
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