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Cellular Communications

Cellular Communications

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  • 1. International Islamic University Malaysia Kulliyyah of Engineering Dept. of Computer & Information Engineering Cellular Communications & GSM Supervised by: Dr. Shihab Prepared by: Khalid Khalil Kamil Basheer Adamu Aliyu © 25/February/2004
  • 2. Contents CHAPTER ONE 1- INTRODUCTION: ------------------------------------------------------------------------------------------------ 3 CHAPTER TWO 2-CELLULAR COMMUNICATIONS:---------------------------------------------------------------------------- 6 2-1 DEFINITION AND OVERVIEW: ---------------------------------------------------------------------------------- 6 2-1-1 Definition: ----------------------------------------------------------------------------------------------- 6 2-1-2 Overview: ------------------------------------------------------------------------------------------------ 6 2-2 MOBILE COMMUNICATIONS PRINCIPLES:------------------------------------------------------------------- 6 2-3 EARLY MOBILE TELEPHONE SYSTEM ARCHITECTURE:------------------------------------------------------ 7 2-4 MOBILE TELEPHONE SYSTEM USING THE CELLULAR CONCEPT:-------------------------------------- 8 2-5 CELLULAR SYSTEM ARCHITECTURE: ------------------------------------------------------------------------ 9 2-5-1 Cells:-----------------------------------------------------------------------------------------------------10 2-5-2 Clusters: -------------------------------------------------------------------------------------------------10 2-5-3 Frequency Reuse: --------------------------------------------------------------------------------------11 2-5-4 Cell Splitting: -------------------------------------------------------------------------------------------12 2-5-5 Handoff: -------------------------------------------------------------------------------------------------12 2-6 NORTH AMERICAN ANALOG CELLULAR SYSTEMS: ----------------------------------------------------- 13 2-6-1 The Advanced Mobile Phone Service (AMPS) -----------------------------------------------------14 2-6-2 Narrowband Analog Mobile Phone Service (NAMPS): -------------------------------------------15 2-7 CELLULAR SYSTEM COMPONENTS: [1] -------------------------------------------------------------------- 15 2-7-1 PSTN:----------------------------------------------------------------------------------------------------15 2-7-2 Mobile Telephone Switching Office (MTSO) -------------------------------------------------------16 2-7-3 The Cell Site: -------------------------------------------------------------------------------------------16 2-7-4 Mobile Subscriber Units (MSUs) --------------------------------------------------------------------16 2-8 DIGITAL SYSTEMS: --------------------------------------------------------------------------------------------- 16 2-8-1 FREQUENCY DIVISION MULTIPLE ACCESS (FDMA): [2]----------------------------------------------- 18 2-8-2 Time Division Multiple Access (TDMA): -----------------------------------------------------------19 2-8-3 Extended Time Division Multiple Access (E–TDMA) ---------------------------------------------20 2-8-4 Fixed Wireless Access (FWA) ------------------------------------------------------------------------21 2-8-5 Personal Communications Service (PCS):----------------------------------------------------------21 2-8-6 Code Division Multiple Access (CDMA): -----------------------------------------------------------22 CHAPTER THREE 3- GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM) ---------------------------------------24 3-1 DEFINITION AND OVERVIEW: -------------------------------------------------------------------------------- 24 3-1-1 Definition:-----------------------------------------------------------------------------------------------24 3-1-2 Overview: -----------------------------------------------------------------------------------------------24 3-2 INTRODUCTION: THE EVOLUTION OF MOBILE TELEPHONE SYSTEMS: ----------------------------- 24 3-3 WHAT IS GSM: ------------------------------------------------------------------------------------------------- 26 3-3 GSM HISTORY: ------------------------------------------------------------------------------------------------- 27 3-4 GSM PARTS: ---------------------------------------------------------------------------------------------------- 28 3-4-1 GSM Mobile Station: ---------------------------------------------------------------------------------29 3-4-2 Base Station Subsystem: (BSS):---------------------------------------------------------------------30 3-4-3 Network and Switching Subsystem: ----------------------------------------------------------------31 3-4-4 Operation and Maintenance Subsystem: ----------------------------------------------------------34 3-5 GSM NETWORK AREAS: -------------------------------------------------------------------------------------- 35 3-6 BASIC OPERATION: -------------------------------------------------------------------------------------------- 37 3-6-1 Mobile Station Initialization: ------------------------------------------------------------------------37 1
  • 3. 3-6-2 Mobile Call Organization: ---------------------------------------------------------------------------38 3-6-3 Call Handover:-----------------------------------------------------------------------------------------40 3-6-4 Ending a Call:------------------------------------------------------------------------------------------42 3-6-5 Receiving a Call on a Mobile: -----------------------------------------------------------------------42 3-7 GSM SPECIFICATIONS:---------------------------------------------------------------------------------------- 43 3-8. GSM SUBSCRIBER SERVICES-------------------------------------------------------------------------------- 45 3-9 SUPPLEMENTARY SERVICES:----------------------------------------------------------------------------------- 46 CHAPTER FOUR 4- 3G MOBILE PHONES AND MULTIMEDIA APPLICATIONS ----------------------------------------48 4-1 INTRODUCTION:------------------------------------------------------------------------------------------------- 48 4-1-1 Overview: -----------------------------------------------------------------------------------------------48 4-2 TECHNICAL FEATURES: --------------------------------------------------------------------------------------- 50 4-3 3G APPLICATIONS: MESSAGING: -------------------------------------------------------------------- 52 4-4 3G SPECIFIC APPLICATIONS : ------------------------------------------------------------------------- 55 4-5 PROSPECTS AND FUTURE TRENDS: : ------------------------------------------------------------------------ 59 4-6 PROBLEMS AND CHALLENGES: ------------------------------------------------------------------------------ 60 CHAPTER FIVE CONCLUSION --------------------------------------------------------------------------------------------------------62 REFERENCES ------------------------------------------------------------------------------------------------------63 2
  • 4. Cellular Communications and GSM 1- Introduction: Millions of people around the world use cellular phones. They are such great gadgets with a cell phone; you can talk to anyone on the planet from just about anywhere! But, today, these days, cell phones provide an incredible array of functions, and new ones are being added at a breakneck pace. People use mobile-phones to Store contact information. • Make task or to-do lists. • Keep track of appointments and set reminders. • Send or receive e-mail . • Get information (news, entertainment, stock quotes) from the Internet . • Play simple games • Integrate other devices such as PDAs, MP3 players and GPS receivers. • Then came the new generation popularly called 3G's which have potential of full multi- media applications, in addition to the previously listed functions. These include: Multi-Media Messagemation. • Audio and Video services • Voice Over Internet Protocol • Enhance Still Image exchange • Moving Image services • Virtual Home Environment • Electronic Agent services • Software Download Capabilities and lots more... • This research introduces the different technologies behind the cellular mobile phones, GSM and 3G phones and shows how progress in these fields has made the access to distributed multimedia resources via mobile communications very easy and realizable. 3
  • 5. Chapter One Introduction 1.1 Aims and Objectives: The goals of this project can thus be summarized as follows: 1. To have a thorough understanding of the technologies behind GSM and 3G's phone. 2. To Study the application of these in a distributed Multi-Media environment. 3. To look at the current trends and future prospects in this field. 4. To have a closer look at the special demands, challenges and problems brought about by the introduction of Multimedia to Mobile communication. 1.2 Organization This report consists of five chapters organized as follows: Chapter One introduces the project, gives an overview of the various functions available in the application of GSM and 3G technologies to MM systems. Then the goals of the project are presented followed by a discussion of the layout of the report.. Chapter Two explains the cellular communication concept including both analog and digital systems, which forms the basis of both GSM and 3G phones. Various concepts, protocols and standards underlying this very important technology are presented and discussed. Chapter Three presents GSM concepts, specifications, networks, and services. The various stages of history and evolution of the mobile system is presented and detailed discussions on the various parts constituting GSM phone are discussed. Then, Networking and switching technologies involed are presented and different stages of communication and services provided by the GSM system are given. Chapter Four discusses 3G mobile Phones and Multimedia Applications. After presenting an overview, background, evolution and Technical features of the 3G are presented. Next comes a discussion of the various applications of 3G systems in Multimedia, starting with the most popular application – Messaging – followed by several other applications which are only possible in 3G systems or have gained added flexibilities with the development of 3G. Some of the disadvantages associated with this kind of system are presented, followed by prospects and future trends. Finally, some of the problems and challenges facing this new technology were presented. 4
  • 6. Cellular Communications and GSM Chapter five summarizes the issues presented and discusses some of the questions raised in the write-up and concludes the project by giving a discussion on the relevance of the project, possible areas of research. References are appended at the end of the report in addition to the table of contents at the beginning. 5
  • 7. Chapter Two Cellular Communications 2-Cellular Communications: 2-1 Definition and Overview: 2-1-1 Definition: A cellular mobile communications system uses a large number of low-power wireless transmitters to create cells—the basic geographic service area of a wireless communications system. Variable power levels allow cells to be sized according to the subscriber density and demand within a particular region. As mobile users travel from cell to cell, their conversations are handed off between cells to maintain seamless service. Channels (frequencies) used in one cell can be reused in another cell some distance away. Cells can be added to accommodate growth, creating new cells in unserved areas or overlaying cells in existing areas. 2-1-2 Overview: This chapter discusses the basics of radio telephony systems, including both analog and digital systems. It shows the basic components of a cellular system and identifies digital wireless technologies. 2-2 Mobile Communications Principles: Each mobile uses a separate, temporary radio channel to talk to the cell site. The cell site talks to many mobiles at once, using one channel per mobile. Channels use a pair of frequencies for communication—one frequency (the forward link) for transmitting from the cell site and one frequency (the reverse link) for the cell site to receive calls from the users. Radio energy dissipates over distance, so mobiles must stay near the base station to maintain communications. The basic structure of mobile networks includes telephone systems and radio services. Where mobile radio service operates in a closed network and has no access to the telephone system, mobile telephone service allows interconnection to the telephone network (see Figure( 2-1)). 6
  • 8. Cellular Communications and GSM Figure (2-1). Basic Mobile Telephone Service Network. [1] 2-3 Early Mobile Telephone System Architecture: Traditional mobile service was structured in a fashion similar to television broadcasting: One very powerful transmitter located at the highest spot in an area would broadcast in a radius of up to 50 kilometers. The cellular concept structured the mobile telephone network in a different way. Instead of using one powerful transmitter, many low-power transmitters were placed throughout a coverage area. For example, by dividing a metropolitan region into one hundred different areas (cells) with low-power transmitters using 12 conversations (channels) each, the system capacity theoretically could be increased from 12 conversations—or voice channels using one powerful transmitter—to 1,200 conversations (channels) using one hundred low-power transmitters. Figure (2-2) shows a metropolitan area configured as a traditional mobile telephone network with one high-power transmitter. 7
  • 9. Chapter Two Cellular Communications Figure (2-2). Early Mobile Telephone System Architecture. [1] 2-4 Mobile Telephone System Using the Cellular Concept: Interference problems caused by mobile units using the same channel in adjacent areas proved that all channels could not be reused in every cell. Areas had to be skipped before the same channel could be reused. Even though this affected the efficiency of the original concept, frequency reuse was still a viable solution to the problems of mobile telephony systems. Engineers discovered that the interference effects were not due to the distance between areas, but to the ratio of the distance between areas to the transmitter power (radius) of the areas. By reducing the radius of an area by 50 percent, service providers could increase the number of potential customers in an area fourfold. Systems based on areas with a one-kilometer radius would have one hundred times more channels than systems with areas 10 kilometers in radius. Speculation led to the conclusion that by reducing the radius of areas to a few hundred meters, millions of calls could be served. The cellular concept employs variable low-power levels, which allow cells to be sized according to the subscriber density and demand of a given area. As the population grows, cells can be added to accommodate that growth. Frequencies used in one cell cluster can be 8
  • 10. Cellular Communications and GSM reused in other cells. Conversations can be handed off from cell to cell to maintain constant phone service as the user moves between cells (see Figure (2- 3)). Figure (2-3). Mobile Telephone System Using a Cellular Architecture. [1] The cellular radio equipment (base station) can communicate with mobiles as long as they are within range. Radio energy dissipates over distance, so the mobiles must be within the operating range of the base station. Like the early mobile radio system, the base station communicates with mobiles via a channel. The channel is made of two frequencies, one for transmitting to the base station and one to receive information from the base station. 2-5 Cellular System Architecture: Increases in demand and the poor quality of existing service led mobile service providers to research ways to improve the quality of service and to support more users in their systems. Because the amount of frequency spectrum available for mobile cellular use was limited, efficient use of the required frequencies was needed for mobile cellular coverage. In modern cellular telephony, rural and urban regions are divided into areas according to specific provisioning guidelines. Deployment parameters, such as amount of cell-splitting and cell sizes, are determined by engineers experienced in cellular system architecture. 9
  • 11. Chapter Two Cellular Communications Provisioning for each region is planned according to an engineering plan that includes cells, clusters, frequency reuse, and handovers. 2-5-1 Cells: A cell is the basic geographic unit of a cellular system. The term cellular comes from the honeycomb shape of the areas into which a coverage region is divided. Cells are base stations transmitting over small geographic areas that are represented as hexagons. Each cell size varies depending on the landscape. Because of constraints imposed by natural terrain and man-made structures, the true shape of cells is not a perfect hexagon. 2-5-2 Clusters: A cluster is a group of cells. No channels are reused within a cluster. Figure(2- 4) illustrates a seven-cell cluster. Figure (2-4). A Seven-Cell Cluster. [1] 10
  • 12. Cellular Communications and GSM 2-5-3 Frequency Reuse: Because only a small number of radio channel frequencies were available for mobile systems, engineers had to find a way to reuse radio channels to carry more than one conversation at a time. The solution the industry adopted was called frequency planning or frequency reuse. Frequency reuse was implemented by restructuring the mobile telephone system architecture into the cellular concept. The concept of frequency reuse is based on assigning to each cell a group of radio channels used within a small geographic area. Cells are assigned a group of channels that is completely different from neighboring cells. The coverage area of cells is called the footprint. This footprint is limited by a boundary so that the same group of channels can be used in different cells that are far enough away from each other so that their frequencies do not interfere (see Figure (2- 5)). Figure (2-5). Frequency Reuse. [1] Cells with the same number have the same set of frequencies. Here, because the number of available frequencies is 7, the frequency reuse factor is 1/7. That is, each cell is using 1/7 of available cellular channels. 11
  • 13. Chapter Two Cellular Communications 2-5-4 Cell Splitting: Unfortunately, economic considerations made the concept of creating full systems with many small areas impractical. To overcome this difficulty, system operators developed the idea of cell splitting. As a service area becomes full of users, this approach is used to split a single area into smaller ones. In this way, urban centers can be split into as many areas as necessary to provide acceptable service levels in heavy-traffic regions, while larger, less expensive cells can be used to cover remote rural regions (see Figure 2-6)). Figure (2-6). Cell Splitting. [1] 2-5-5 Handoff: The final obstacle in the development of the cellular network involved the problem created when a mobile subscriber traveled from one cell to another during a call. As adjacent areas do not use the same radio channels, a call must either be dropped or transferred from one radio channel to another when a user crosses the line between adjacent cells. Because dropping the call is unacceptable, the process of handoff was created. Handoff occurs when the mobile telephone network automatically transfers a call from radio channel to radio channel as a mobile crosses adjacent cells (see Figure (2-7)). 12
  • 14. Cellular Communications and GSM Figure (2-7). Handoff between Adjacent Cells. [1] During a call, two parties are on one voice channel. When the mobile unit moves out of the coverage area of a given cell site, the reception becomes weak. At this point, the cell site in use requests a handoff. The system switches the call to a stronger-frequency channel in a new site without interrupting the call or alerting the user. The call continues as long as the user is talking, and the user does not notice the handoff at all. 2-6 North American Analog Cellular Systems: Originally devised in the late 1970s to early 1980s, analog systems have been revised somewhat since that time and operate in the 800-MHz range. A group of government, telco, and equipment manufacturers worked together as a committee to develop a set of rules (protocols) that govern how cellular subscriber units (mobiles) communicate with the cellular system. System development takes into consideration many different, and often opposing, requirements for the system, and often a compromise between conflicting requirements results. Cellular development involves the following basic topics: 13
  • 15. Chapter Two Cellular Communications frequency and channel assignments • type of radio modulation • maximum power levels • modulation parameters • messaging protocols • call-processing sequences • 2-6-1 The Advanced Mobile Phone Service (AMPS) AMPS was released in 1983 using the 800-MHz to 900-MHz frequency band and the 30-kHz bandwidth for each channel as a fully automated mobile telephone service. It was the first standardized cellular service in the world and is currently the most widely used standard for cellular communications. Designed for use in cities, AMPS later expanded to rural areas. It maximized the cellular concept of frequency reuse by reducing radio power output. The AMPS telephones (or handsets) have the familiar telephone-style user interface and are compatible with any AMPS base station. This makes mobility between service providers (roaming) simpler for subscribers. Limitations associated with AMPS include the following: low calling capacity • limited spectrum • no room for spectrum growth • poor data communications • minimal privacy • inadequate fraud protection • AMPS is used throughout the world and is particularly popular in the United States, South America, China, and Australia. AMPS uses frequency modulation (FM) for radio transmission. In the United States, transmissions from mobile to cell site use separate frequencies from the base station to the mobile subscriber. 14
  • 16. Cellular Communications and GSM 2-6-2 Narrowband Analog Mobile Phone Service (NAMPS): Since analog cellular was developed, systems have been implemented extensively throughout the world as first-generation cellular technology. In the second generation of analog cellular systems, NAMPS was designed to solve the problem of low calling capacity. NAMPS is now operational in 35 U.S. and overseas markets, and NAMPS was introduced as an interim solution to capacity problems. NAMPS is a U.S. cellular radio system that combines existing voice processing with digital signaling, tripling the capacity of today's AMPS systems. The NAMPS concept uses frequency division to get 3 channels in the AMPS 30-kHz single channel bandwidth. NAMPS provides 3 users in an AMPS channel by dividing the 30-kHz AMPS bandwidth into 3 10-kHz channels. This increases the possibility of interference because channel bandwidth is reduced. 2-7 Cellular System Components: [1] The cellular system offers mobile and portable telephone stations the same service provided fixed stations over conventional wired loops. It has the capacity to serve tens of thousands of subscribers in a major metropolitan area. The cellular communications system consists of the following four major components that work together to provide mobile service to subscribers. public switched telephone network (PSTN) • mobile telephone switching office (MTSO) • cell site with antenna system • mobile subscriber unit (MSU) • 2-7-1 PSTN: The PSTN is made up of local networks, the exchange area networks, and the long-haul network that interconnect telephones and other communication devices on a worldwide basis. 15
  • 17. Chapter Two Cellular Communications 2-7-2 Mobile Telephone Switching Office (MTSO) The MTSO is the central office for mobile switching. It houses the mobile switching center (MSC), field monitoring, and relay stations for switching calls from cell sites to wireline central offices (PSTN). In analog cellular networks, the MSC controls the system operation. The MSC controls calls, tracks billing information, and locates cellular subscribers. 2-7-3 The Cell Site: The term cell site is used to refer to the physical location of radio equipment that provides coverage within a cell. A list of hardware located at a cell site includes power sources, interface equipment, radio frequency transmitters and receivers, and antenna systems. 2-7-4 Mobile Subscriber Units (MSUs) The mobile subscriber unit consists of a control unit and a transceiver that transmits and receives radio transmissions to and from a cell site. The following three types of MSUs are available: the mobile telephone (typical transmit power is 4.0 watts) • the portable (typical transmit power is 0.6 watts) • the transportable (typical transmit power is 1.6 watts) • The mobile telephone is installed in the trunk of a car, and the handset is installed in a convenient location to the driver. Portable and transportable telephones are hand-held and can be used anywhere. The use of portable and transportable telephones is limited to the charge life of the internal battery. 2-8 Digital Systems: As demand for mobile telephone service has increased, service providers found that basic engineering assumptions borrowed from wireline (landline) networks did not hold true in mobile systems. While the average landline phone call lasts at least 10 minutes, mobile calls usually run 90 seconds. Engineers who expected to assign 50 or more mobile phones to the 16
  • 18. Cellular Communications and GSM same radio channel found that by doing so they increased the probability that a user would not get dial tone—this is known as call-blocking probability. As a consequence, the early systems quickly became saturated, and the quality of service decreased rapidly. The critical problem was capacity. The general characteristics of time division multiple access (TDMA), Global System for Mobile Communications (GSM), personal communications service (PCS) 1900, and code division multiple access (CDMA) promise to significantly increase the efficiency of cellular telephone systems to allow a greater number of simultaneous conversations. Figure (2-8) shows the components of a typical digital cellular system. Figure (2-8). Digital Cellular System. [1] The advantages of digital cellular technologies over analog cellular networks include increased capacity and security. Technology options such as TDMA and CDMA offer more channels in the same analog cellular bandwidth and encrypted voice and data. Because of the enormous amount of money that service providers have invested in AMPS hardware and software, providers look for a migration from AMPS to digital analog mobile phone service (DAMPS) by overlaying their existing networks with TDMA architectures. 17
  • 19. Chapter Two Cellular Communications Table (2-1). AMPS/DAMPS Comparison . [1] Analog Digital EIA–553 (AMPS) IS–54 (TDMA + AMPS) standard 824 MHz to 891 MHz 824 MHz to 891 MHz spectrum 30 kHz 30 kHz channel bandwidth 21 CC/395 VC 21 CC / 395 VC channels 1 3 or 6 conversations per channel 40 to 50 conversations per cell 125 to 300 conversations per cell subscriber capacity continuous time shared bursts TX/RCV type constant phase variable constant frequency variable carrier type frequency phase mobile slaved to base authority shared cooperatively mobile/base relationship poor better—easily scrambled privacy poor high noise immunity ESN plus optional password ESN plus optional password fraud detection (PIN) (PIN) 2-8-1 Frequency Division Multiple Access (FDMA): [2] It puts each call on a separate frequency. FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. To better understand FDMA, think of radio stations: Each station sends its signal at a different frequency within the 18
  • 20. Cellular Communications and GSM available band. FDMA is used mainly for analog transmission. While it is certainly capable of carrying digital information, FDMA is not considered to be an efficient method for digital transmission. See figure (2-9). Figure (2-9). In FDMA, each phone uses a different frequency. [2] 2-8-2 Time Division Multiple Access (TDMA): North American digital cellular (NADC) is called DAMPS and TDMA. Because AMPS preceded digital cellular systems, DAMPS uses the same setup protocols as analog AMPS. TDMA has the following characteristics: 1. IS–54 standard specifies traffic on digital voice channels 2. initial implementation triples the calling capacity of AMPS systems 3. capacity improvements of 6 to 15 times that of AMPS are possible 4. many blocks of spectrum in 800 MHz and 1900 MHz are used 5. all transmissions are digital 6. TDMA/FDMA application 7. 3 callers per radio carrier (6 callers on half rate later), providing 3 times the AMPS capacity 19
  • 21. Chapter Two Cellular Communications TDMA is one of several technologies used in wireless communications. TDMA provides each call with time slots so that several calls can occupy one bandwidth. Each caller is assigned a specific time slot. In some cellular systems, digital packets of information are sent during each time slot and reassembled by the receiving equipment into the original voice components. TDMA uses the same frequency band and channel allocations as AMPS. Like NAMPS, TDMA provides three to six time channels in the same bandwidth as a single AMPS channel. Unlike NAMPS, digital systems have the means to compress the spectrum used to transmit voice information by compressing idle time and redundancy of normal speech. TDMA is the digital standard and has 30-kHz bandwidth. Using digital voice encoders, TDMA is able to use up to six channels in the same bandwidth where AMPS uses one channel. See figure (2-10). Figure (2-10). TDMA splits a frequency into time slots. [2] 2-8-3 Extended Time Division Multiple Access (E–TDMA) The E–TDMA standard claims a capacity of fifteen times that of analog cellular systems. This capacity is achieved by compressing quiet time during conversations. E–TDMA divides 20
  • 22. Cellular Communications and GSM the finite number of cellular frequencies into more time slots than TDMA. This allows the system to support more simultaneous cellular calls. 2-8-4 Fixed Wireless Access (FWA) FWA is a radio-based local exchange service in which telephone service is provided by common carriers (see Figure (2-11)). It is primarily a rural application—that is, it reduces the cost of conventional wireline. FWA extends telephone service to rural areas by replacing a wireline local loop with radio communications. Other labels for wireless access include fixed loop, fixed radio access, wireless telephony, radio loop, fixed wireless, radio access, and Ionica. FWA systems employ TDMA or CDMA access technologies. Figure (2-11). Fixed Wireless Access. [1] 2-8-5 Personal Communications Service (PCS): The future of telecommunications includes PCS. PCS at 1900 MHz (PCS 1900) is the North American implementation of digital cellular system (DCS) 1800 (GSM). Trial networks were operational in the United States by 1993, and in 1994 the Federal Communications 21
  • 23. Chapter Two Cellular Communications Commission (FCC) began spectrum auctions. As of 1995, the FCC auctioned commercial licenses. In the PCS frequency spectrum, the operator's authorized frequency block contains a definite number of channels. The frequency plan assigns specific channels to specific cells, following a reuse pattern that restarts with each nth cell. The uplink and downlink bands are paired mirror images. As with AMPS, a channel number implies one uplink and one downlink frequency (e.g., Channel 512 = 1850.2-MHz uplink paired with 1930.2-MHz downlink). 2-8-6 Code Division Multiple Access (CDMA): CDMA is a digital air interface standard, claiming 8 to 15 times the capacity of analog. It employs a commercial adaptation of military, spread-spectrum, single-sideband technology. Based on spread spectrum theory, it is essentially the same as wireline service—the primary difference is that access to the local exchange carrier (LEC) is provided via wireless phone. Because users are isolated by code, they can share the same carrier frequency, eliminating the frequency reuse problem encountered in AMPS and DAMPS. Every CDMA cell site can use the same 1.25-MHz band, so with respect to clusters, n = 1. This greatly simplifies frequency planning in a fully CDMA environment. See figure (2-12). Figure 1-12. In CDMA, each phone's data has a unique code. [2] 22
  • 24. Cellular Communications and GSM CDMA is an interference-limited system. Unlike AMPS/TDMA, CDMA has a soft capacity limit; however, each user is a noise source on the shared channel and the noise contributed by users accumulates. This creates a practical limit to how many users a system will sustain. Mobiles that transmit excessive power increase interference to other mobiles. For CDMA, precise power control of mobiles is critical in maximizing the system's capacity and increasing battery life of the mobiles. The goal is to keep each mobile at the absolute minimum power level that is necessary to ensure acceptable service quality. Ideally, the power received at the base station from each mobile should be the same (minimum signal to interference). 23
  • 25. Chapter Three GSM 3- Global System for Mobile Communication (GSM) 3-1 Definition and Overview: 3-1-1 Definition: Global system for mobile communication (GSM) is a globally accepted standard for digital cellular communication. GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard that would formulate specifications for a pan-European mobile cellular radio system operating at 900 MHz. It is estimated that many countries outside of Europe will join the GSM partnership. 3-1-2 Overview: This chapter provides an introduction to basic GSM concepts, specifications, networks, and services. A short history of network evolution is provided in order set the context for understanding GSM. 3-2 Introduction: The Evolution of Mobile Telephone Systems: Cellular is one of the fastest growing and most demanding telecommunications applications. Today, it represents a continuously increasing percentage of all new telephone subscriptions around the world. Currently there are more than 45 million cellular subscribers worldwide, and nearly 50 percent of those subscribers are located in the United States. It is forecasted that cellular systems using a digital technology will become the universal method of telecommunications. By the year 2005, forecasters predict that there will be more than 100 million cellular subscribers worldwide. (see Figure( 3-1)). 24
  • 26. Cellular Communications and GSM Figure (3-1). Cellular Subscriber Growth Worldwide . [1] The concept of cellular service is the use of low-power transmitters where frequencies can be reused within a geographic area. The idea of cell-based mobile radio service was formulated in the United States at Bell Labs in the early 1970s. However, the Nordic countries were the first to introduce cellular services for commercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981. Cellular systems began in the United States with the release of the advanced mobile phone service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America, and Oceanic countries, creating the largest potential market in the world for cellular. In the early 1980s, most mobile telephone systems were analog rather than digital, like today's newer systems. One challenge facing analog systems was the inability to handle the growing capacity needs in a cost-efficient manner. As a result, digital technology was welcomed. The advantages of digital systems over analog systems include ease of signaling, lower levels of interference, integration of transmission and switching, and increased ability to meet capacity demands. Table (3-1) charts the worldwide development of mobile telephone systems. [1] 25
  • 27. Chapter Three GSM Table 3-1. The Development of Mobile Telephone Systems. [1] Year Mobile System 1981 Nordic Mobile Telephone (NMT) 450 1983 American Mobile Phone System (AMPS) 1985 Total Access Communication System (TACS) 1986 Nordic Mobile Telephony (NMT) 900 1991 American Digital Cellular (ADC) 1991 Global System for Mobile Communication (GSM) 1992 Digital Cellular System (DCS) 1800 1994 Personal Digital Cellular (PDC) 1995 PCS 1900—Canada 1996 PCS—United States 3-3 What is GSM: GSM is the abbreviation for Global System for Mobile Communication. Historically, GSM is referred to the original French name, Groupe Spécial Mobile. This was the name of the technical study group established by the European Conference of posts and Telecommunications administrations (CEPT) to investigate alternative proposals for a pan- European digital cellular technology. Both names are still visible, the French reference appears in older documents, the English reference in newer one. GSM is a digital cellular radio network which allows one network channel to support multiple conversations by means of time division multiplexing (TDM, or time division multiple access-TDMA). TDMA takes one network channel and divides it up into slices of time. The mobile phone user is given one of these slices of time for a brief pre-scheduled 26
  • 28. Cellular Communications and GSM interval. The interval is so short that neither the mobile user nor other mobile users on the same radio channel notice that they are only transmitting or receiving on a fraction of the channel. In this manner, the capacity of the network is significantly increased over standard analog cellular, which requires an entire channel for transmission. GSM was designed by the GSM design group during the latter part of the 1980s, and is the major digital cellular radio network in Europe, where it is used in the 900MHz radio band. The radio band is also known as the frequency of the network. GSM has been standardized to 900MHz, 1800MHz and 1900MHz, and continuous to grow through out Europe, Africa, Asia Pacific and the Americas. GSM is one of the major contenders for becoming the de facto technical standard for digital cellular networks and personal communications systems. [3] 3-3 GSM History: Cellular telecommunication is one of the fastest growing telecommunication applications ever developed. While the early 1980s were marked by the development of a number of national and incompatible radio networks, today cellular telecommunications represent a large and increasing percentage of all new telephone subscriptions around the world. In 1982 the Nordic Postal, Telephone and Telegraph administration (PTT) sent a proposal to the Conférence Européenne des Administrations des Postes et des Télécommunications (CEPT) to specify a common European telecommunication service at 900MHz. A standardization group, the Groupe Spéciale Mobile (GSM), was established in order to formulate the specification or this pan-european mobile cellular radio system. There were no guidelines on how the new mobile radio system was to transmit analog or digital speech and data. The decision to develop a digital mobile radio network was not made until the development stage. But it was agreed from the beginning that the system being a planned should incorporate and consider new technology from the area of telecommunications, such as Telecommunication Standardization Sector of ITU (ITU-T) Common Channel Signaling System No. 7(CCS7), Integrated Services Digital Network and the International Standards Organization (ISO)/ Open Systems Interconnection(OSI) reference model. In 1986 there was a field test in Paris where the GSM group tested a number of prototypes for digital cellular radio systems. In 1987 the GSM decided on a 27
  • 29. Chapter Three GSM standard that combined the best characteristic of different systems. At this time the first 17 countries signed the Memorandum of Understanding (MoU) committing themselves to fulfil the specifications and confirmed their commitment to introducing mobile radio based on the recommendation of the GSM. Figure (3-2) shows the milestones in the GSM history. Figure (3-2), Milestones in the GSM history. [4] Later, in March, 1989, the GSM working party was taken over by ETSI, and since 1991 has been called the Special Mobile Group (SMG). Today the abbreviation GSM stands for Global System for Mobile Communication, thereby underlining its claim as a worldwide standard. [4] 3-4 GSM Parts: A GSM network is comprised of several major portions: a mobile radio part, subscriber information part, a radio network, a switching system and network intelligence (Primarily databases). Figure (3-3) shows a basic GSM network. The mobile phone is called a mobile station. There are several types of mobile stations in GSM. High power mobile phones can 28
  • 30. Cellular Communications and GSM be used in vehicles and people typically carry low-power mobile phones (handhelds). An electronic card also called a chip that is stored inside the phone identifies each customer. The card is called a subscriber identity module (SIM). Mobile stations communicate with nearby radio towers called base stations. Base stations convert the radio signal for communication to a switching system. The switching system connects calls to other mobile stations or routes the call to the public telephone network. The switching is connected to several databases that hold customer information. These databases include equipment identification numbers (the numbers stored in the SIM card) and authorized feature lists (features the customer has subscribed to). [3] Figure (3-3). A basic GSM network. [3] 3-4-1 GSM Mobile Station: A GSM mobile station consists of two parts. The first part contains all the hardware and software components relating to the radio interface; the second part, known as the Subscriber Identity Module (SIM), stores all the subscriber’s personal data. The SIM is either installed into the terminal or provided as a smart card, which has the function of a key. Once it has been removed from a device, it can only be used for emergency calls, if the network so 29
  • 31. Chapter Three GSM allows. A mobile subscriber can use the SIM to identify himself over any mobile station in the network, and accordingly a mobile phone can be personalized using the SIM. In addition, each mobile station has its mobile Equipment Identity (EI). Figure (3-4). Mobile station and SIM card. [4] 3-4-2 Base Station Subsystem: (BSS): The radio parts of the GSM network equipment are contained within the Base Station Subsystem (BSS). The base station subsystem is divided into two main parts: the Base Transceiver Station (BTS) and the Base Station Controller (BSC). The BTS comprises several base radio transceivers. Each transceiver consists of a transmitter and a receiver which has a duplicated “front end” to match up with the two receiving antennas used in the base antenna assembly. The BSC comprises a control computer (typically a microprocessor central processing unit with memory), data communication facilities, and multiplexing and de-multiplexing equipment. The BSC can control the radio power levels of the various transceivers in the BTS, and also autonomously control the mobile stations’ radio transmitter power levels as well. The BSC passes certain types of control messages between the BTS and the Mobile Switching Center, and handles and handles certain types of control messages itself under appropriate conditions. A single BSC can control several BTS radio equipment transmitters. The BSC can be located in a base station or at an other remote site. Figure (3-5) shows a basic diagram of a GSM base station sub-system. The BTS consists of transmitters, receivers, antenna assembly, power supplies and test circuits. In this diagram, the BSC is located t the base station. Each transmitter operates on a different radio carrier frequency. Each radio carrier is divided into time slots and frames. For typical GSM handsets (called full rate), this allows up to 8 users to simultaneously share a single radio channel. A portion of one (or more) radio carrier frequencies is used as a control channel. The control 30
  • 32. Cellular Communications and GSM channel coordinates mobile station alerting and access to the GSM network. A base station may include a scanning receiver, although most GSM installations do not have one. The scanning receiver allows the base station to measure the radio signal strength of mobile stations that operate on any frequency to determine if they are good candidates for call handover. [3] Figure (3-5). GSM Base Station Subsystem. [3] 3-4-3 Network and Switching Subsystem: The GSM network requires a switching network and intelligence to interconnect calls between mobile phones and the public telephone network. The central switch of a GSM installation is called a Mobile-service Switching Center (MSC). In earlier documents, the word “service” was omitted, which gave some people the incorrect impression that the MSC was itself mobile or capable of motion while in service. The MSC is, in all modern GSM networks, an electronic digital telephone switch with digital multi-channel (trunk-type) telephone line inputs and outputs. Trunks are telephone channels that connect between one switch and another. Different subscribers in each successive connection use trunk channels. 31
  • 33. Chapter Three GSM In an MSC, some of the trunks connect the MSC to a BSC, while other trunks connect the MSC to the PSTN switches. Figure (3-6) shows the basic building blocks for the MSC. The MSC consists of a switching centre, power supplies, and alarm monitoring equipment. The switch is also connected to customer databases that maybe located at the MSC or located at a remote site. In this diagram, the switch allows connection between each base station and the public telephone network. While the diagram shows physical switches, most modern switching system uses Electronic Switching Systems (ESS). ESS systems use a process called Time Slot Interchange (TSI) to connect incoming and outgoing digital lines together through the use of temporary memory locations. The TSI system uses a computer to control the assignment of these temporary locations so that a portion of an incoming line can be stored in temporary memory and retrieved for insertion to an outgoing line. Figure (3-6). Mobile Switching Centre. [3] There are many network processing centers and databases used in a GSM network to check authorization for service and process call features. The most utilized network database parts store and process home customer subscriber lists, hold temporary customer information, validate equipment identity information (authentication), manage the fraudulent equipment identity list, and store and forward messages. 32
  • 34. Cellular Communications and GSM A Home Location Register (HLR) database holds the detailed subscriber service subscription information. This database can be located with the MSC, or it may be at a distant location. In some implementations, multiple MSCs share the same SLR. The HLR holds a user profile that indicates if a particular user subscribes to services such as call forwarding, call waiting, etc. The HLR also stores information about the present location of its subscribers who are presently visiting in the radio service area of another MSC, and indicates whether or not they have arranged to receive calls there. A Visitor Location Register (VLR) database holds temporary information about active subscribers that are operating within the control of that particular MSC. This includes both visiting and active local subscriber data. The word “visited” is somewhat misleading since the data here is not restricted to visitors. The data to a large extent is a copy of the corresponding subscriber data taken from the HLR. The VLR is usually built into the MSC. In some implementations, HLR and VLR are the same physical data base, with records active in the VLR specially/temporarily marked as required, rather than copied from one database to another. A Group Call Register (GCR) is a network database that holds the attributes for the set-up and processing of voice group and broadcast calls. These include group call membership lists, priority authorization, and locations of group callers. When a group call is initiated, the GCR provides the information necessary to setup the call to all the recipients of the group call. A Short Message Control Center (SMCC) stores and forwards short messages to and from the GSM network. An Interworking Function (IWF) is used to process and adapt information between dissimilar types of network systems. Figure (3-7) shows the basic parts of a GSM network. In this diagram, several databases are interconnected to each other and to a MSC. 33
  • 35. Chapter Three GSM Figure (3-8). GSM Network Parts. [3] 3-4-4 Operation and Maintenance Subsystem: The Operation and Maintenance Subsystem (OMS) includes alarms and monitoring equipment to help a network operator run, diagnose, and repair a communications network. This includes administrative subscriber and mobile station management systems such as billing, accounting and statistics. It also includes access security, system performance monitoring, system design changes and maintenance. There are several databases that support the operation and maintenance subsystem. These include a subscriber validation processing center and a fraudulent equipment database. A network operator including customer care, marketing and billing database nay use many other databases. An Authentication Center (AuC) is a database and processing center that is used to validate the identity of mobile stations. The AuC processes secret information (electronic keys) that is transferred between a mobile station and the GSM network. 34
  • 36. Cellular Communications and GSM An Equipment Identity Register (EIR) is a database that holds a list of unauthorized (black list) and suspected fraudulent (gray list) users. The EIR stores information about mobile stations but not about subscribers. The subscriber information is stored in the SIM card. If a certain handset, identified by its electronic identification number, is known to be stolen, lost, or malfunctioning, this information is stored here and used to prevent such a mobile station from being further used until it is returned to normal condition. 3-5 GSM Network Areas: The GSM network is made up of geographic areas. As shown in Figure( 3-9), these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas. Figure (3-9). Network Areas. [1] The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is 35
  • 37. Chapter Three GSM served by one or more base station controllers, yet only by a single MSC (see Figure(3-10)). Each LA is assigned a location area identity (LAI) number. Figure (3-10). Location Areas. [1] An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC (see Figure (3-11)). Figure (3-11). MSC/VLR Service Areas. [1] The PLMN service area is an area served by one network operator (see Figure( 3-12) ). Figure (3-12). PLMN Network Areas. [1] 36
  • 38. Cellular Communications and GSM 3-6 Basic Operation: There are many other processes a mobile station must perform to operate in a GSM network. The basic call processing operation if a mobile station includes initialization, system access, paging and handover. 3-6-1 Mobile Station Initialization: When a GSM handset is first powered on in a GSM network, it begins an initialization process prior to accessing the system. The initialization process involves finding a suitable radio carrier channel and capturing system information that allows the mobile station to access the system. When seeking a radio carrier signal with strong signal strength, it will typically find several frequencies. Having scanned for radio carrier channels, the MS then goes back and examines each frequency beginning with the strongest signals. It is seeking a radio carrier channel that contains a control channel. These channels are identified by beacon frequencies. After it has found a control channel, the MS begins to receive and store certain system broadcast information. This broadcast information includes data that allows the MS to access to the system. Figure (3-13) shows the basic information that is continuously sent by the system. This information includes system identification, the initial access power level at which the MS should transmit when requesting service, locations of paging and messaging channels, and other information that coordinates access to the GSM network. Figure (3-13). System Broadcast Information. [3] 37
  • 39. Chapter Three GSM Every installed GSM base service area has a unique Mobile Network Code (MNC), a number which it broadcasts periodically and which identifies it distinctly from other system operators in the same city or anywhere else in the world. Each base station also broadcast a number which tells mobile stations in that cell how much power they should use when transmitting a signal to the base station. Small cells request low power and large cells request high power. The mobile set also has the MNC of its own home system stored in the SIM chip. The mobile set is also able to measure the radio signal strength of each such a beacon frequency. Given all this information, the mobile station chooses the “best” beacon frequency and send an identifying message. The best frequency is one that has the home MNC stored in the SIM. If the MS is in its own home city, this rule will cause it to temporarily ignore the beacon frequencies of other system operators in that city in favor of its own home system. If that is not available in the vicinity (which would happen if the MS were roaming to another city at this time) the MS treats all MNCs equally. The MS then chooses the beacon frequency with the smallest cell so it can use the lowest transmit power, and transmits certain signals which identify the MS to the base system. Incidentally, when the MS has found the beacon frequencies that are in use in the various cells in the city, it stores these carrier beacon frequency numbers in the SIM chip. Then when the MS power is turned on and such a list is available in the SIM chip, the MS can be ready for service much sooner, because it only needs to scan the set of beacon frequencies, rather than every legally permitted frequency. 3-6-2 Mobile Call Organization: When a customer initiates a call from a mobile station, this is referred to as a call origination. This is typically accomplished by a subscriber entering a telephone number via the number buttons, and pressing the send button. Figure (3-14) shows a functional diagram of how an MS initiates a call to a GSM network. In step 1, the MS sends the dialed digits along with the phone’s identification information to a nearby base station. After the dialed digits have been received and the MS has been authorized for service, the MSC will seize an outside line (trunk) and dial the indicated number (step2). The GSM network will then command the MS to tune to a specified radio 38
  • 40. Cellular Communications and GSM carrier frequency and time slot for which the call will be connected (step 3). The MS tunes to the new channel (step 4) and conversation may begin (step 5). Figure (3-14). Mobile Cell Origination. [3] During the conversation, the Base Transceiver Station is continually measuring the signal strength of the received radio waves from the mobile transmitter. In addition, all of the digital information transmitted over the radio link consists of two portions. One portion is the actual information of significance, such as the encoded speech or the call control messages that cause the MS to re-tune to another frequency to other actions. The other portion is a smaller set of data bits called an error detection code. There is a method used at the radio receiver to examine the information bits and the error detection code bits for consistency. When these two portions are not mathematically consistent, this detects that errors have occurred during transmission via the radio channel. In many cases the number of erroneous data bits can be estimated with good accuracy. Then the Bit Error Rate (BER) can be computed, which is the ratio of erroneously received bits to the total of all received bits. Due to radio channel imperfections, about 1% of thee data bits (about erroneous bit out of each 100 bits received) transmitted are received in error. When there is a 2, 3or even up to 5% BER for a short interval of time, the voice codec is still able to produce sound with reasonable accuracy. But when the BER goes much above 5% for a long enough time, the sound output will be unacceptably bad, as is known from prior measurements. 39
  • 41. Chapter Three GSM 3-6-3 Call Handover: Call handover is the process of transferring a call between base stations. Handover is typically called handoff in North America. Handover is necessary because mobile stations often move out of range of one base station and into the radio coverage area of another base station. The GSM network has several advantages for handover when compared to analog systems. Because the GSM network is digital and divided in time, the received radio signal strengths and channel quality can be continually measured for multiple radio carrier channels. This allows the continual seeking of a better radio frequency and time slot related to an adjacent cell. This is determined necessary when there is either excessive BER and/or received signal strength below what is known to be adequate for this particular cell. This process of seeking a better target channel is the beginning of handover. In the GSM network we have several additional items of information, which are not available in older analog cellular system. Because the MS operates on a carrier frequency in a TDMA operating sequence during a conversation, it only transmits for 1/8th of the total time, and receives a signal from the base station during another 1/8th of the time. During the remaining six-eights (or three quarters) of the total time, the mobile receiver is idle and can be used to monitor the signal strength and quality from the beacon frequencies in adjacent radio cells. Keep in mind that the MS receiver can be quickly re-tuned to other radio carrier frequencies during each such time slot, and then tuned back to the frequency needed to communicate with the current base station in adequate time to keep up proper communication for support of the conversation. To facilitate this, a control message is initially sent to each MS when it begins a conversation in a particular cell. That message contains a command to scan the beacon frequencies of adjacent cells and then their frequency numbers are explicitly listed. The mobile scans the listed frequencies during the otherwise idle mobile receiver time slots, measures and reports the signal strength and BER of each nearby cell. These reports are transmitted back to the base station periodically in a special a scheduled manner that does not interfere with the transmission of the digitally coded speech signals. This process of using reports from the mobile station to assist in handover is called Mobile Assisted HandOver (MAHO). 40
  • 42. Cellular Communications and GSM The base station is then in possession of a dynamically generated list showing the signal strength and BER of signals from all adjacent cells, as measured by the MS at the present location. The base system also knows which adjacent cells have idle radio channels available as a handover target, and which do not. The control computer in the BSC (or in the MSC, as the case may be) selects the set of adjacent cells which have idle available channels, and from this set it selects that cell which have the best combination of signal strength and BER. A suitable channel (carrier frequency and slot) is assigned in that cell as the target, and the MS is commanded to re-tune to use that channel. At the same time, the base or land portion of the conversation is simultaneously switched over to that assigned target channel in the adjacent cell. When this is done properly, the retuning of the radio occurs during the previously mentioned idle time slots, so the mobile station is still in communication with the base station on the regular schedule of 1 in 8 for both transmit and receive. There is no lost information and no gap in the speech from the voice codec. This is called a “seamless” TDMA handover. Only in very exceptional circumstances is there a gap in the proper reception of TDMA GSM speech information; however, such a gap is an inherent problem that occurs for every handover with the earlier analog cellular system. Figure (3-15) shows the basic call handover process. In this diagram, an MS is communicating with base station #1. Base station #1 provides the MS with a list of the radio carrier channels to measure of nearby base station (step1). After the MS measures the quality of the radio carrier channels, it returning this information to the serving base station (step 2). Using this information and information from neighboring base stations, the serving base station sends a handover message (step 3) which instructs the MS to tune to a new radio carrier channel of the adjacent base station #2. The MS begins a transmission on the new channel by sending a short burst (step 4). The new base station uses this information to send a command to adjust the relative timing of the MS (step 5). After the MS has adjusted, the voice channel from the MSC is switched from base station #1 to base station #2 and voice conversation can continue (step6). 41
  • 43. Chapter Three GSM Figure (3-15). Call Handover. [3] 3-6-4 Ending a Call: Eventually, one of the two people involved in the telephone conversation hangs up the telephone (on the land end) or presses the END button on the mobile end. This causes an exchange of messages over the radio link which requests a disconnect, along with an acknowledgment message for an intentional disconnection. The system design is very paranoid in this situation, requiring repeated confirming messages in order to prevent an accidental disconnection. After the call is disconnected, the MS starts scanning again to find the best beacon frequency and be ready for another call. The base station marks the previous channel as free and ready for another use by another conversation. [3] & [4] 3-6-5 Receiving a Call on a Mobile: Receiving a call on a mobile phone is called call termination. A mobile terminated call is essentially similar to the mobile originated call just described, except for the beginning steps which involve alerting the mobile station of an incoming call (called paging). The paging process begins when another caller dials the telephone number of the mobile station. This results in an inquiry to the HLR (customer database) of the home MSC switch. The HLR 42
  • 44. Cellular Communications and GSM responds with the identification number of the MS along with an indication of the last registered location of the MS. If the mobile phone is operating in a visited system, the HLR response includes the system identification and routing information of the visited system. The system uses the mobile phone identification information to send a page message to the MS. The MS identification information is called the international mobile subscriber identity (IMSI). Because the IMSI is composed of many digits, systems typically use an abbreviated form of the paging message. The temporary identification number is assigned to the mobile phone when it first registers in a system (typically during initialization). This is called a temporary mobile subscriber identity (TMSI). The TMSI is much shorter than an IMSI. Figure (3-16). Receiving call on a mobile. [3] Figure(3-16) shows the basic process for receiving a call on the GSM network. In the first step, the MS receives the channel number of the paging channel to monitor. The MS will listen to this channel until it hears its identification number (step 2). The MS will then request service from the GSM network indicating in its request that it is responding to a page message (step 3). After the system validates the MS identification number, it will assign it to a radio carrier channel (step 4). 3-7 GSM Specifications: Before looking at the GSM specifications, it is important to understand the following basic terms: 43
  • 45. Chapter Three GSM bandwidth—the range of a channel's limits; the broader the bandwidth, the faster • data can be sent bits per second (bps)—a single on-off pulse of data; eight bits are equivalent to one • byte frequency—the number of cycles per unit of time; frequency is measured in hertz • (Hz) kilo (k)—kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits • per second megahertz (MHz)—1,000,000 hertz (cycles per second) • milliseconds (ms)—one-thousandth of a second • watt (W)—a measure of power of a transmitter • Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM. frequency band—The frequency range specified for GSM is 1,850 to 1,990 MHz • (mobile station to base station). duplex distance—The duplex distance is 80 MHz. Duplex distance is the distance • between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart. channel separation—The separation between adjacent carrier frequencies. In GSM, • this is 200 kHz. modulation—Modulation is the process of sending a signal by changing the • characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps. • access method—GSM utilizes the time division multiple access (TDMA) concept. • TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot. 44
  • 46. Cellular Communications and GSM speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to • reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps. 3-8. GSM Subscriber Services There 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. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM: dual-tone multifrequency (DTMF)—DTMF is a tone signaling scheme often used • for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF. facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax • machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM–connected fax to communicate with any analog fax in the network. short message services—A convenient facility of the GSM network is the short • message service. A message consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. 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. 45
  • 47. Chapter Three GSM cell broadcast—A variation of the short message service is the cell broadcast facility. • A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents. voice mail—This service is actually an answering machine within the network, which • is controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box and the subscriber checks for messages via a personal security code. fax mail—With this service, the subscriber can receive fax messages at any fax • machine. The messages are stored in a service center from which they can be retrieved by the subscriber via a personal security code to the desired fax number. [1] 3-9 Supplementary Services: GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services. Supplementary services are defined by GSM and are characterized as revenue-generating features. A partial listing of supplementary services follows. call forwarding—This service gives the subscriber the ability to forward incoming • calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply, or if call forwarding is allowed unconditionally. barring of outgoing calls—This service makes it possible for a mobile subscriber to • prevent all outgoing calls. barring of incoming calls—This function allows the subscriber to prevent incoming • calls. The following two conditions for incoming call barring exist: baring of all incoming calls and barring of incoming calls when roaming outside the home PLMN. advice of charge (AoC)—The AoC service provides the mobile subscriber with an • estimate of the call charges. There are two types of AoC information: one that provides the subscriber with an estimate of the bill and one that can be used for immediate charging purposes. AoC for data calls is provided on the basis of time measurements. 46
  • 48. Cellular Communications and GSM call hold—This service enables the subscriber to interrupt an ongoing call and then • subsequently reestablish the call. The call hold service is only applicable to normal telephony. call waiting—This service enables the mobile subscriber to be notified of an • incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using a circuit-switched connection. multiparty service—The multiparty service enables a mobile subscriber to establish • a multiparty conversation—that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal telephony. calling line identification presentation/restriction—These services supply the • called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation. closed user groups (CUGs)—CUGs are generally comparable to a PBX. They are a • group of subscribers who are capable of only calling themselves and certain numbers. [1] 47
  • 49. Chapter Four 3G Mobile Phones & Multimedia Applications 4- 3G MOBILE PHONES AND MULTIMEDIA APPLICATIONS 4-1 Introduction: In this chapter we will discuss 3G Mobile Phones, a new generation of mobile phones which has various Multimedia Applications. 4-1-1 Overview1: UMTS, or Universal Mobile Telecommunications System. Proposed by the Third Generation Interest Group (3GIG) is a Third Generation System promising a wide range of personal mobility features using a multimedia-like phone. Some of the new features promised with the new devices include home shopping, interactive education and training with virtual reality support, navigation, multi-media multi-party consultation, entertainment, multi-connection surveillance, information seeking and retrieval, communicating laptop PCs and video communication. It also promises to standardize cellular technology around the world, so that your phone will be just as useable in another corner of the world as it is in your home or office. International roaming is already a reality, but UMTS takes it one step further - to Global Roaming. Background2 This new generation of mobile phones is based on WAP (Wireless Application Protocol) which takes a client server approach. It incorporates a relatively simple microbrowser into the mobile phone, requiring only limited resources on the mobile phone. The Wireless Application Protocol is aimed at turning a mass-market mobile phone into a “network-based smartphone” utilizing as few resources as possible on the handheld device and compensate for the constraints of the device by enriching the functionality of the network. 1 Introduction to 3G Mobile Phones 2 www,YES2WAP.com 48
  • 50. Cellular Communications and GSM Indeed, the importance of WAP can be found in the fact that it provides an evolutionary path for application developers and network operators to offer their services on different network types, bearers and terminal capabilities. The design of the WAP standard separates the application elements from the bearer being used. This helps in the migration of some applications from SMS or Circuit Switched Data to GPRS for example. WAP will be compatible with any mobile network standard such as Code Division Multiple Access (CDMA), Global System for Mobiles (GSM), or Universal Mobile Telephone System (UMTS); has been designed to work with all cellular standards and is supported by major worldwide wireless leaders such as AT&T Wireless and NTT DoCoMo, multiple input terminals such as keypads, keyboards, touch-screens and styluses. Evolution3: Whenever a new service is introduced, there are a number of stages before it becomes established. 3G service developments will include standardization, infrastructure development, network trials, network roll out, availability of terminals, application development, and so on. These stages for 3G are shown in the table below: TIMELINES ON 3G EVOLUTION4 3G radio interface standardization took place, and initial 3G live Throughout 1999 demonstrations of infrastructure and concept terminals shown Continuing standardization with network architectures, terminal 2000 requirements and detailed standards The formal approval of the IMT-2000 Recommendations made at the ITU May 2000 Radio communication Assembly in early May 2000 3G licenses are awarded by governments around Europe and Asia 2001 2001 3G trials and integration commence 2001 3G launched in Japan by NTT DoCoMo Summer of 2001 First trial 3G services become available in Europe Start of 2002 Basic 3G capable terminals begin to be available in commercial quantities 3 Introduction to 3G Mobile Phones 4 SOURCE: MOBILE STREAMS 49
  • 51. Chapter Four 3G Mobile Phones & Multimedia Applications -Network operators launch 3G services commercially and roll out 3G. Throughout 2002 -Vertical market and executive 3G early adopters begin using 3G regularly for nonvoice mobile communications New 3G specific applications, greater network capacity solutions, more 2002/3 capable terminals become available, fuelling 3G usage 3G will have arrived commercially and reached critical mass in both 2004 corporate and consumer sectors 4-2 Technical features: Following are the main Features of the 3G system: 1. NETWORK REQUIREMENTS 3G networks will require new radio and core network elements. A new air interface is needed for 3G. This will require new Base Station Systems (BSSs). Specifically, the BSS changes needed are an RNC (Radio Network Controller) and Node B. RADIO NETWORK CONTROLLER A Radio Network Controller (RNC) will replace the Base Station Controller. The RNC will include support for connection to legacy systems and provide efficient packet connection with the core network packet devices (SSGN or equivalent). The RNC performs radio network control functions that include call establishment and release, handover, radio resource management, power control, diversity combining and soft handover. NODE B A Node B is equivalent to a Base Station in the 2G network but also incorporates support for the 3G air interfaces. 50
  • 52. Cellular Communications and GSM 2. CELL PLANNING New cell planning methods will be needed to support the new frequency allocations for 3G and the radio interface changes- more 3G base stations will be needed compared to the comparable 2G coverage area. This gives an advantage to GSM 1800 and 1900 network operators whose cells already cover a smaller coverage area than those for GSM 900 networks. GSM 900 network operators will need to “fill in” coverage in between existing cell sites. 3. CORE NETWORK The 3G core network will be an evolution from GPRS or equivalent 2.5G core network systems. Upgrades to the mobile and transit switching systems to deliver packets will also be needed. A new piece of network infrastructure for 3G is Media Gateways (MGW) that resides at the boundary between different networks to process end user data such as voice coding and decoding, convert protocols and map quality of service. The connectivity layer also provides access to backbone switches and non-mobile networks such as Cable Television. In some vendor solutions, MGWs are controlled remotely by the Mobile Switching Centre (MSC) and GSN servers by means of the Gateway Control Protocol. The ITU Study Group 16 and the IETF Megaco H.248 are working to ensure the GCP is an open standard protocol. Existing network operators can then upgrade their Mobile Switching Centre (MSC) and GSNs to implement 3G OR ALTERNATIVELY to implement a new standalone MGW that is controlled from the server part of an upgraded 2G node. 4. BACKBONE NETWORK The radio network will be connected to the core network by a backbone network allowing wideband access and interconnection of subscribers. The 3G backbone network can use any transport technology but is certain to be based on packet technologies such as Asynchronous 51
  • 53. Chapter Four 3G Mobile Phones & Multimedia Applications Transfer Mode (ATM) and Internet Protocol (IP). The backbone network is built as a mesh of IP routing or ATM switching nodes interconnected by point to point links. Technologies such as IP over ATM may be used that uses ATM switching to multiplex IP traffic. This IP over ATM architecture supports voice traffic alongside IP. Many vendors prefer a “pure” end to end IP approach whereas others (such as Fujitsu) prefer an ATM/ IP hybrid to guarantee quality of service. Alternatively, IP over SONET/ SDH is a different backbone network solution that eliminates the ATM layer by establishing point to point links between IP routers directly over SONET/ SDH rings which run over a Dense Wavelength Division Multiplexing (DWDM) layer that enables Terabits per second (Tbits/s) of aggregate network bandwidth. 5. SUPPORT SYSTEM CHANGES Of course, platforms and systems such as the value added service centers, gateways, billing systems, customer service elements, Intelligent Network systems and the like will also need to be upgraded. Once again, this is likely to be an evolution from 2.5G data centric services such as GPRS where packet charging elements and so on where introduced. There may also need to be a change in personnel as more applications specialists, alliance managers, Internet sector managers and the like are hired to develop content and applications over 3G networks. 4-3 3G APPLICATIONS: MESSAGING: Because of the special and important place Messaging has in 3G mobile communication, we will look at its application in 3g and how it differs from the previously used technologies. The Short Message Service (SMS) is the ability to send and receive text messages to and from mobile telephones. The text can comprise of words or numbers or an alphanumeric combination. SMS was created when it was incorporated into the Global System for Mobiles 52
  • 54. Cellular Communications and GSM (GSM) digital mobile phone standard. The first short message was sent in December 1992 from a Personal Computer (PC) to a mobile phone on the Vodafone GSM network in the UK. The Enhanced Messaging Service (EMS) is the ability to send a combination of simple melodies, pictures, sounds, animations, modified text and standard text as an integrated message for display on an EMS compliant handset. For example, when an exclamation mark appears in the enhanced message, a melody could be played. A simple black and white image could be displayed along with some text and this sound effect. EMS is an enhancement to SMS but is very similar to SMS in terms of using the store and forward SMS Centers, the signaling channel and the like to realize EMS. The first EMS compliant handsets were due by mid-2001, whilst no new network infrastructure is needed to handle EMS. The Multimedia Messaging Service (MMS) is as its name suggests the ability to send and receive messages comprising a combination of text, sounds, images and video to MMS capable handsets. The Multimedia Messaging Service (MMS) confers the ability to send still images such as mobile postcards, mobile pictures, mobile screensavers, mobile greeting cards, mobile maps and business cards. Additionally, moving images, cartoons and interactive video will also be supported by Multimedia Messaging (MMS). Thus, a New mobile network infrastructure is needed for Multimedia Messaging (MMS)- in addition to implementing the new bearer services such as 3G, new network elements such as Multimedia Messaging Relays and Stores will be needed. The first trials of Multimedia Messaging (MMS) infrastructure will took place in mid 2001 and the first MMS terminals were ready by the end of 2002. MMS uses WAP (Wireless Application Protocol, and MExE (Mobile Station Application Execution Environment, as protocols to enable a smooth migration path for messaging applications as mobile networks and handsets improve. 53
  • 55. Chapter Four 3G Mobile Phones & Multimedia Applications With this, the wireless industry is moving from text messages to icons and picture messages to photographs and blueprints to video messages and movie previews being downloaded and on to full blown movie watching via data streaming on a mobile device. The key technologies underlying these new services and applications are EMS and MMS. The main features of this transformation are shown in the table below5: CHARACTERISTICS CONTENT TIME FOR TYPE REFORMATTING APPLICATIONS SUPPORT AVAILABILITY FOR MOBILE NECESSARY? Simple Text person to 100-200 characters Yes All phones 1990s Messaging person messaging Simple person to Some Picture Simple rudimentary person networks 2000- Yes Messaging images and Nokia phones 2001 messaging with a only. visual feel Simple Text messages plus EMS person to sound, animation, standards Enhanced 2001 person Yes picture, text expected to Messaging onwards messaging formatting be widely with a enhancements adopted visual feel Simple MMS Messages in multiple person to standards Multimedia 2002 rich media formats person No expected to Messaging e.g. video, audio messaging onwards be widely plus text with a adopted visual feel 5 SOURCE: MOBILE STREAMS 54
  • 56. Cellular Communications and GSM 4-4 3G SPECIFIC APPLICATIONS 6: Apart from Messaging which was discussed in the previous section, there are several applications that will be enabled by the broadband bandwidth that will come with 3G. These applications include: 1. AUDIO Audio or video over the Internet is downloaded (transferred, stored and played) or streamed (played as it is being sent but not stored). The later tends to be of lower quality than the former. Content is transferred using various different compression algorithms such as those from Microsoft or Real Networks or the MPEG-1 Audio Layer 3 (better known as MP3) protocol. In fact, MP3 is a codec- a compression/ decompression algorithm. MP3 was invented in 1987 in Germany and approved by the Moving Pictures Experts Group, a part of the International Organization for Standardization, in 1992. With 3G, MP3 files will be downloadable over the air directly to your phone via a dedicated server. 2. VOICE OVER INTERNET PROTOCOL Another audio application for 3G is Voice over IP (VoIP)- the ability to route telephone calls over the Internet to provide voice telephony service at local call rates to anywhere in the world. With 3G and higher rate 2.5G technologies such as EDGE, VoIP will be available for the first time on mobile phones. To make a voice call, Voice Over IP can be used as an alternative to regular service. VoIP is not however a replacement for standard voice services since VoIP services are bandwidth demanding- there needs to be a high switching rate on the IP backbone to minimize the very high likelihood of delayed and lost packets.7 6 Introduction to 3G Mobile Phones 19 – 23 (quot;Yes 23 3Gquot; – White Paper, www.mobilestreams.com, February 2001. 7 Mobile Streams www.mobile3G.com Page 20 55
  • 57. Chapter Four 3G Mobile Phones & Multimedia Applications 3. STILL IMAGES Still images such as photographs, pictures, letters, postcards, greeting cards, presentations and static web pages can be sent and received over mobile networks just as they are across fixed telephone networks. Two variables affect the usability of such applications- bandwidth and time - and they are inversely related. The faster the bandwidth, the less time is needed to transmit images, and vice versa. This is the reason why transmission of image based rather than textual information has not been a popular nonvoice mobile application until now- it takes too long given the slow data transmission speeds that were available prior to the introduction of mobile packet data. Once captured, images can then be sent directly to Internet sites, allowing near real- time desktop publishing. The size of the file for a picture depends on the resolution and type of compression. Typically each picture is between 50K and 100K in the JPEG format. This can be transmitted quickly using mobile packet data. Still image transmission is a much touted application for lower packet data services such as GPRS and beyond. Many people see still images as a killer compelling applications for GPRS. 4. MOVING IMAGES Sending moving images in a mobile environment has several vertical market applications including (monitor sensor triggered) monitoring parking lots or building sites for intruders or thieves, and sending images of patients from an ambulance to a hospital. Videoconferencing applications, in which teams of distributed sales people can have a regular sales meeting without having to go to a particular physical location, is another application for moving images that is similar to the document sharing/ collaborative working applications reviewed below. Skeptics argue that vertical markets don’t need video and consumers don’t want it. However, with the Internet becoming a more multimedia environment, 3G will be able displaying those images and accessing web services. The transmission of moving images is one of the applications that GPRS and 3G terminal and infrastructure vendors routinely and repeatedly tout as a compelling application 56
  • 58. Cellular Communications and GSM area that will be enabled by greater data rates. And they are not incorrect to do so. However, it must be noted that even demonstrations of one megabyte of data over the air using Microsoft NetMeeting to perform a video conference facility do not deliver smooth broadcast quality video images. However, improving compression techniques should allow acceptable quality video images to be transmitted using 64 kbps of bandwidth.8 This is where 3G comes in- once again, the bandwidth uplift it enables allows for high quality image transmission over the mobile network. As such, we see all moving video and image transmission application migrating to the 3G bearer as soon as it becomes available. By the time 3G is here, full length movies could be downloadable from Internet sites. 5. VIRTUAL HOME ENVIRONMENT A Universal Mobile Telephone Service (UMTS) service that is often mentioned in the vendor’s brochures is so called Virtual Home Environment (VHE), a service that simply lets customers have seamless access with a common look and feel to their services from home, office or on the move and in any city as if they were at home. VHE is therefore aimed at roamers (a small subset of total mobile phone users). VHE could also allow some other more useful services by placing their Universal Identity Module (UIM) into ANY terminal- and those terminals could be something other than mobile devices if smart cards are more widely supported than they are today. 6. ELECTRONIC AGENTS This is an efficient way to get things done on the move. Electronic agents are defined as quot;mobile programs that go to places in the network to carry out their owners' instructions. They can be thought of as extensions of the people who dispatch them.quot; Agents are quot;self-contained programs that roam communications networks delivering and receiving messages or looking for information or services.quot; 8 Page 21 www.mobile3G.com Mobile Streams 57
  • 59. Chapter Four 3G Mobile Phones & Multimedia Applications Certainly, 3G terminals will give their owners much more control over their lives than today’s mobile phones. They will be eAssistants, eSecretaries, eAdvisors and eAdministrators. This kind of control is what Home Automation applications anticipate. Indeed Orange in the UK has a vision expects that within ten years, our mobiles will be waking us up, reading out our emails, ordering our groceries, telling us the best route to work, reminding us and translating our conference calls. The key question is the extent to which these processes are human initiated or computer generated and controlled and the extent to which devices can “learn” individual preferences and act accordingly. 7. DOWNLOADING SOFTWARE In the twenty-first century, software will increasingly be downloaded electronically from the Internet rather than purchased as boxed product in stores. This is a like file transfer applications that involve downloading the software itself. You might for example need WinZip or Abode Acrobat to read a file- and can download that over the 3G network to your 3G terminal. Downloading software has several advantages because it is: Environmentally friendly: there is no packaging to throw away or store. Quick and convenient: downloadable products are delivered direct to your computing device. It arrives in minutes, not days. Value for money: you pay no delivery charges. DOWNLOAD TIMES Download times vary depending on the speed of your modem and the size of the application. Typical download times vary from 10 minutes to two hours. Here are download times for a 5 Megabyte (MB) application: CONNECTION SPEED DOWNLOAD TIME Very fast corporate type 30 seconds connection (e.g. T1) 58
  • 60. Cellular Communications and GSM Corporate type connection (e.g. 12 minutes ISDN) Typical home modem (e.g. 28.8 104 minutes modem) Sites such as beyond.com and Mobiledatashop.com from Mobile Streams offer many software products for immediate electronic download. Additionally, the Application Service Provision (ASP) market in which software platforms and server software is being hosted by third parties and accessed by client software mimics this “thin client” world in which the bandwidth is high enough for applications and files to be retrieved from the Internet on the fly whenever they are needed. Since it relies on the bandwidth that 3G provides, 3G is likely to be the key bearer for downloading software. Disadvantages9: Since they are WAP based, the 3G's have the disadvantages of WAP with them: - It is very difficult to configure WAP phones for new WAP services, with 20 or so different parameters needing to be entered to gain access to a WAP service. - Compared with the installed base of Short Message Service (SMS) compliant phones, the relative number of handsets supporting WAP is tiny. - WAP services are expected to be expensive to use since the tendency is to be on-line for a long Circuit Switched Data (CSD) call as features such as interactivity and selection of more information are used by the end user. Without specific tariff initiatives, there are likely to be some surprised WAP users when they see their mobile phone bill for the first time after starting using WAP. 4-5 Prospects and Future Trends: : Following are some of the expected trends in the use of 3G's for MM applications: 9 www.YES2WAP.com 59
  • 61. Chapter Four 3G Mobile Phones & Multimedia Applications Bigger and better screen technology- screens will be color which is unusual today and • will be bright and have considerably larger screen areas in many cases than today’s phones. Video is central to the technology demonstration- of course, multimedia is the • biggest single new understandable thing about 3G. Videoconferencing is an application that many of the concept terminals anticipates. Consumer electronics and mobile phones converge, as cameras are built into • mobile phones. The majority of these devices include built-in miniature cameras. The most popular form factor that has been shown in the 3G concept devices is • the video palm- a device form factor that can be held in one hand and supports video applications with varying small, medium or large screen sizes. Nearly all of the devices are in form factors that are familiar to us today- we may • use the phone for different things and in different ways, but it will probably look similar to today’s mobile phones. The broadband bandwidth on 3G networks enables mobile multimedia as will the • devices. When the networks and the devices are in harmony and the customer is king, the Three Dimensions of the Third Generation will give enough level of applications and services never before possible on mobile networks. 4-6 Problems and Challenges: As is the case with any new technology, there are problems and challenges facing this great innovation. Some of these include: Handover between 3G and 2G networks remain a knotty problem for the o manufacturers. If a user in a data session goes out of a 3G cell and into GSM cell, the data session won't be maintained and provide the handover functionality. quot;You cannot handover between the two modes in one go. Once you fall off a 3G cell, you drop the call and you have to re-initiate it on GSM.quot; Says Chris Tunsley head of protocol software of Cambridge, a UK-based handset technology provider TTPCom. One of the 60
  • 62. Cellular Communications and GSM causes of the problems is lack of a free timeslots in 3G as there are in GSM system's TDMA-based technology, and hence, compressed mode gaps have to be created. Size of Handsets: since users are used to lightweight, low priced phones with o extensive battery life, 3G providers have to design with this in mind. Functionality is another thing to deal with, since 3G specification allows networks to o chose which functionality or parameters they wish to use, and there are a lot of optional features to choose from, manufactures are provide sets which support every feature in the specifications10. 10 Taking 3G in Hand, 3G Solutions for Operators – Issue 14/2003 - Lucent Technologies, http://www.lucent.com/livelink/09009403800541b6_Newsletter.pdf 61
  • 63. Chapter Five Conclusion 5- Conclusion: This project has shown the various systems underlying the Cellular phone, GSM and 3G systems and their various applications. Different stages of evolution passed through before finally arriving at the present state of affairs. Starting with the issue of frequency reuse - which is the underlying principle behind cellular phones – and the challenges brought by rapid changes in the technologies and the needs of handover whenever there is roaming outside the base station and the various standards employed by different countries in Europe and North America, to the issues of bandwidth and switching, especially with the introduction of digital systems to work side by sides with the traditional analog systems, this project has shown how all these challenges were overcome, providing the use with a seamless communication. With the acceptance of the Global System for Mobile (GSM) communication worldwide, came the demands of standards, switching and increasing number of users provided with flexibility in service. The operation and maintenance of this system and the different protocols involved in the process of sending and receiving calls, in addition to the system demands on the stations and network, especially when the user is roaming outside home base are part of the issues discussed in the section on GSM. Finally specifications and supplementary services were presented and each explained as briefly as possible. In discussing the use of 3G phones in Multimedia applications, the basic philosophy and the different stages of evolution passed by mobile communication before reaching the 3G are presented. Then, the network requirements and the needs for core and support systems to handle the high demands of the 3G applications were then discussed. After that, the application of 3G in Multimedia messaging and other applications ranging from Audio, Video, Still and Moving Images, VoIP and other applications are mentioned. 62
  • 64. References [1] - GSM Superphones, by Lawrence Harte, Richard Levine and Geoff Livingston, APDG Publishing, McGraw-Hill Telecommunications. ©1999. [2] - The GSM Evolution, Mobile Packet Data Services, by Peter Stukmann, Aachen University, John Wiley & Sons, Ltd. © 2003. [3] - Introduction to 3G Mobile Phones, [4] – quot;Success 4 WAPquot; (Wireless Application Protocol) – White Paper, Mobile Streams, February 2001. [5] – Taking 3G in Hand, 3G Solution for Operators – Lucent Technologies Newsletter, Issue 14/2003. [6] – Next Messaging, An Introduction to SMS, EMS and MMS, Mobile Streams Ltd. [7] quot;Yes 2 3Gquot; (Introduction to 3G) – White Paper, Mobile Streams, February 2001. [8] - www.mobilestreams.com [9] -www.iec.org [10] - www.howstuffworks.com [10] - www.YESWAP.com [11] - www.mobile3G.com [12] - www.lucent.com 63