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Siwes it report

  1. 1. ATECHNICAL REPORTON STUDENTS INDUSTRIAL WORK EXPERIENCE SCHEME (SIWES)UNDERTAKEN ATNOKIA SIEMENS NETWORKS, 98/100 APAPA-OSHODI EXPRESSWAY,LAGOS STATE.SUBMITTED BYOLAFUSI MICHAEL O.EEE/04/2995TOTHE DEPARTMENT OF ELECTRICAL ELECTRONICS ENGINEERINGFEDERAL UNIVERSITY OF TECHNOLOGY, AKURE,ONDO STATEIN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OFBACHELOR OF ENGINEERING (B.ENG) DEGREE IN ELECTRICAL ANDELECTRONICS ENGINEERINGNOVEMBER 2008
  2. 2. DEDICATIONIn our lives three set of people matter mostFirst and greatest is God Almighty, who daily re-creates usSecond is our family, the people we love the mostThe third is our friends, the bright side of usTo them do I dedicate this reporti
  3. 3. ACKNOWLEDGEMENTFirst of all, I acknowledge the overwhelming help God gave me throughout thescheme. He encouraged me not to give up on getting a relevant (to my field of study)reputable company and when I was getting to the end of my rope, He came to my rescue.Without His support and miracles I would not have been alive, let alone have a successfulIndustrial training attachment.I appreciate my parents and siblings for their constant help and support, especially mymother who took my placement over-personal and my father for his constant financialsupport even when I could not give a reasonable report of expenditure.I heartily express my appreciation to Mr. Tope Akinkuowo (Transmission Manager,Zain Nigeria) and Mr. Zijad Demirovic (Project Manager, Nokia Siemens NetworksNigeria) for making it possible for me to do my Industrial Training attachment at NokiaSiemens Networks.I also appreciate Mr. Kehinde Oke (Senior Engineer, Nokia Siemens Networks) forsparing some of his precious time to teach me all I could understand aboutTelecommunications transmission and radio telephone network system. I also thank mycolleagues Ifekauche Onyeka and Agho Osasu for helping make my six months industrialtraining attachment a swell time.Sincerely, all the technicians at the Pre-installation and Transmission departmenttaught me so much that, even though they are too many for me list name by name I couldnot have had a very successful Industrial Training attachment without them.ii
  4. 4. ABSTRACTThe Student Industrial Work Experience Scheme (SIWES) is designed to giveUniversity undergraduates in Nigeria the relevant practical knowledge and industrialexposure they need to fully understand the application of the theoretical knowledge theyacquire within the four walls of the lecture halls. I was fortunate to serve my six monthsindustrial work experience at Nokia Siemens Networks, an internationaltelecommunications company involved in fixed telephone network system and mobiletelephone network system installation and servicing for telephone network operators andmultinational organizations all over the world.This report is a comprehensive summary of all that I learnt and was involved inthroughout my industrial attachment at the Radio access business unit of the Lagos,Nigeria branch of the company. I learnt the fundamentals of telecommunications, thedifferent type of telecommunications systems, the operational difference between a fixedtelephone line network and a mobile telephone network, and how the GSM network isimplemented. I was involved in a couple of site works, twice at the Twenty-first centurytelecommunications company fixed line switching and transmission capacity expansion,and twice at Zains Ibadan, Oyo state Base Transceiver Stations upgrade. At the companysTransmission Pre-installation Office (TPO), I was able to learn how the differenttransmission equipments operate, are installed, troubleshooted and remotely monitored. Iwas shown the different types of waveguides, coaxial cables, optical fibres and twistedcopper cable, and was made to understand their areas of application.The chapter one gives a brief introduction to the history and operations of NokiaSiemens Networks with an organogram of the company. Chapter two discusses the basicsof telecommunications and the media used in signal propagation. Chapter three delvesstraight into the core of the GSM network architecture and how the operate together tomake mobile phone calls possible. The last major chapter, chapter four talks extensively onthe Base Transceiver Station and its radio access link segment where I worked on at thesites.iii
  5. 5. LIST OF FIGURESFigure 1.1: Nokia Siemens Networks Organizational chart..................................................4Figure 2.1: Communication link between two telephones.....................................................5Figure 2.2: A four-pair copper cable......................................................................................7Figure 2.3: A typical coaxial cable.........................................................................................8Figure 2.4: A typical optic fibre..............................................................................................9Figure 2.5: Wireless communication links............................................................................10Figure 3.1: Frequency allocation in the GSM 900 and GSM 1800 band..............................12Figure 3.2: A mobile station..................................................................................................13Figure 3.3: Time Division Multiple Access principle............................................................15Figure 3.4: The Network Switching Subsystem (NSS)..........................................................17Figure 3.5: The Base Station Subsystem (BSS).....................................................................20Figure 3.6: A diagramatic representation of the management function of the NMS.............23Figure 3.7: Obanla trying to call Ajegunle.............................................................................23Figure 3.8: The frequency reuse chart....................................................................................25Figure 3.9: Synchronization of the mobile station with the network.....................................26Figure 3.10: Channel request and allocation..........................................................................27Figure 3.11: A summary of the GSM architecture.................................................................28Figure 4.1: The SRA 4 unit.....................................................................................................31Figure 4.2: Local Craft Terminal software.............................................................................31Figure 4.3: The NetBuilder software......................................................................................32Figure 4.4: On site testing of connectivity between two BTSs using the SRA 4 handset......32Figure 4.5: The SRA 4 unit fully connected to the other network units.................................33Figure 4.6: The coaxial cables connecting the indoor units to the outdoor units...................34Figure 4.7: The coaxial cables entering into the BTS shelter.................................................34Figure 4.8: An ODU...............................................................................................................35Figure 4.9: An antenna with two ODUs closely attached......................................................35Figure 4.10: The 6 – 13 GHz ODU........................................................................................36Figure 4.11: The 15 – 38 GHz ODU.....................................................................................36iv
  6. 6. Figure 4.12: The different polarizations.................................................................................37Figure 4.13: Directional high performance shielded antenna already installed......................38Figure 4.14: Mutual impedance between parallel /2 dipoles not staggered. Curves Re andIm are the resistive and reactive parts of the impedance.....................................39Figure 4.15: The 21 pair twisted cables being made into E1 transmission lines....................41Figure 4.16: The specialized crimper and clamp for fixing the E1 DB-32 connectors..........42Figure 4.17: A general tool box..............................................................................................43Figure 4.18: The Digital Distribution Frame (DDF)..............................................................44Figure 4.19: The Multiplexer (Surpass HiT 7070, under testing)..........................................45Figure 4.20: The Synchronous Radio Access XL (SRA XL)................................................46v
  7. 7. LIST OF TABLESTable 3.1: GSM 900 frequency channels............................................................................13Table 3.2: GSM 1800 frequency channels..........................................................................14Table 4.1: The standard frequency allocation table............................................................29vi
  8. 8. TABLE OF CONTENTSDEDICATION............................................................................................................................iACKNOWLEDGEMENT..........................................................................................................iiABSTRACT...............................................................................................................................iiiLIST OF FIGURES...................................................................................................................ivLIST OF TABLES.....................................................................................................................viTABLE OF CONTENTS..........................................................................................................vii1.0 INTRODUCTION.................................................................................................................11.1 NOKIA SIEMENS NETWORKS …........................................................................21.1.1 BRIEF HISTORY AND ORGANIZATIONAL STRUCTURE............21.1.2 ORGANIZATIONAL CHART..............................................................32.0 TELECOMMUNICATIONS BASICS.................................................................................52.1 TELECOMMUNICATIONS TRANSMISSION MEDIA.......................................62.1.1 COPPER.................................................................................................72.1.2 COAXIAL CABLES..............................................................................82.1.3 OPTIC FIBRES......................................................................................82.1.4 WIRELESS (ELECTROMAGNETIC WAVES)...................................93.0 GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS (GSM).................................113.1 GSM NETWORK ARCHITECTURE....................................................................163.2 NETWORK SWITCHING SUBSYSTEM (NSS)..................................................163.2.1 MOBILE SERVICES SWITCHING CENTRE (MSC)........................173.2.2 VISITOR LOCATION REGISTER (VLR)..........................................183.2.3 HOME LOCATION REGISTER (HLR)..............................................183.2.4 AUTHENTICATION CENTRE (AU).................................................183.2.5 EQUIPMENT IDENTITY REGISTER (EIR)......................................193.3 BASE STATION SUBSYSTEM (BSS).................................................................193.3.1 BASE STATION CONTROLLER (BSC)............................................203.3.2 BASE TRANSCEIVER STATION (BTS)...........................................203.3.3 TRANSCODER (TC)...........................................................................21vii
  9. 9. 3.4 NETWORK MANAGEMENT SUBSYSTEM (NMS)........................................223.5 PRACTICAL ILLUSTRATION...........................................................................234.0 BASE TRANSCEIVER STATION RADIO ACCESS LINK..........................................294.1 THE SYNCHRONOUS RADIO ACCESS STM-4 (SRA 4) UNIT....................304.2 THE COAXIAL CABLE.....................................................................................334.3 THE OUTDOOR FREQUENCY CONVERTER AND SIGNAL AMPLIFIERUNIT (ODU)........................................................................................................354.4 DIRECTIONAL ANTENNA...............................................................................374.5 TWISTED PAIR COPPER CABLE....................................................................415.0 CONCLUSION AND RECOMMENDATION................................................................47REFERENCES........................................................................................................................48viii
  10. 10. CHAPTER ONE1.0 INTRODUCTIONThe Student Industrial Work Experience Scheme (SIWES) was established in 1973 to enableundergraduates in various Nigerian universities to acquire relevant practical and industrial experiencein their various fields of study. This is to help the students better understand what they are beingtaught in the universities and to practically apply them.At Nokia Siemens Networks, where I observed the SIWES, I was exposed to many majortelecommunications equipment like the Nokia Siemens Networks Synchronous Radio Access STM-4(SRA 4) unit, Synchronous Radio Access Trunk (SRT) unit, Surpass HiT 7070 Multiplexer, DigitalDistribution Frame (DDF), EWSD high capacity switch, various optic fibres, waveguides, twistedpair copper cables and antennae.I was involved in the following projects,1. The expansion of the fixed line telephone network of the Twenty-first centurytelecommunications company branch at Ikeja, Lagos state.2. Another expansion of the fixed line telephone network of the Twenty-first centurytelecommunications company branch at Victoria Island, Lagos state.3. The powering of Zains Base Transceiver Station Synchronous Radio Access STM-4(SRA 4) system in Ibadan, Oyo state.4. The configuration of another Zains Base Transceiver Station Radio Access link atIbadan, and testing of connectivity between the station, another nearby station and thenearest Mobile services Switching Centre.5. The coupling of shielded twisted seven-pair copper cables into a standard E1 jack for usewith the Surpass HiT 7070 multiplexer and the Digital Distribution Frame (DDF).6. The installation of Very Small Arperture Terminal (VSAT) for data communications atthe Nokia Siemens Networks Lagos branch.I was able through the company and personal efforts to learn the following,1
  11. 11. 1. The use of AutoCAD and even used it on some occasions to reproduce in softcopysome company project site diagrams.2. The installation, multi-user capability and administration of the linux operatingsystem. I tried my hands on Ubuntu, Kubuntu and OpenSuse linux distributions.3. Microsoft windows XP operating software management and administration, use ofsystem restore, registry edit, and password reset through a bootable XP installationCD and a password breaker floppy disk.4. Use of Microsoft Excel to prepare stock lists and faulty equipments record.5. Oracle 10g R2 database mangement software and SQL relational query language.6. Medium size computer network ( less than a thousand computers involved) setup andmanagement using cisco switches, conventional routers and wireless routers.1.1 NOKIA SIEMENS NETWORKSNokia Siemens Networks started operations on the 1stApril, 2007 as a result of a mergerbetween the former Network Business Group department of Nokia and the Carrier-relatedoperations department of Siemens International.Nokia Siemens Networks operates in 150 countries located in all the major continents of theworld, ranking second in both Wireless networks infrastructure and Operator services, and thirdin Wireline networks infrastructure. They are headquartered in Espoo, Finland with over 60,000highly skilled professionals worldwide providing infrastructure and services to about 1,400corporate customers and infrastructural setup connecting over 1 billion people all over the world.1.1.1 BRIEF HISTORY AND ORGANIZATIONAL STRUCTURENokia Siemens Networks came out of two industry giants – Nokia and Siemens. Nokia is aworld leader in mobile telecommunications, connecting people to each other and the informationthat matters to them with easy-to-use and innovative products like mobile phones, devices andsolutions for imaging, gaming, media and businesses. Nokia has been in existence since 1865,2
  12. 12. though first as a furniture company which later evolved into a multinational telecommunicationscompany and a pioneer in mobile communications development.On the other hand, Siemens has been a global powerhouse in electrical engineering andelectronics since 1847, presently with over 461,000 employees in over 190 countries working todevelop and manufacture products, design and install complex systems. The company focuses onthe areas of Information and Communications, Automation and Control, Power, Transportation,Medical, and Lighting.On June 19, 2006, Nokia and Siemens announced that they intend to merge the NetworksBusiness Group of Nokia and the carrier-related operations of Siemens into a new company, to becalled Nokia Siemens Networks. This 50-50 joint venture eventually on April 1, 2007, created aglobal leader with strong positions in important growth segments of fixed and mobile networkinfrastructure and services.Nokia Siemens Networks has its operations grouped into five different business units,namely:1. Converged core business unit,2. IP Transport business unit,3. Radio Access business unit,4. Broadband Access business unit, and5. Operations and business software business unit.I worked in the Radio Access business unit which is concerned with the setting up of radiolinks between different network stations/nodes and configuration of the radio access equipments.The network nodes are usually branches of a bank or base stations of a mobile telephonenetwork.1.1.2 ORGANIZATIONAL CHARTNokia Siemens Networks organizational chart is as shown below.3
  13. 13. 4Figure1.1:NokiaSiemensNetworksOrganizationalchart
  14. 14. CHAPTER TWO2.0 THE BASICS OF TELECOMMUNICATIONSTelecommunications is the assisted transmission of signals over a distance for the purpose ofcommunication. A telecommunication system consists of three basic elements, namely:1. A transmitter that takes information and converts it to an easily transmittable signal,2. A transmission medium that carries the signal , and3. A receiver that receives the signal and converts it back to a useable information.Oftentimes, a single equipment can act as both a transmitter and a receiver and it is referredto as transceiver.Telecommunication that involves one transmitter and one receiver over a dedicated line oftransmission is called a point-to-point communication. While telecommunication that involvesone powerful transmitter and several receivers is called broadcast communication. An example ofa point-to-point communication is communication over a telephone line (phone call), eventhough there may be many transmitters and receivers along the communication path, only onetransmitter and receiver is actively used, others are simply serving as repeaters, to amplify and re-propagate the signal. Also, an example of a broadcast communication is the conventional free-to-air radio broadcast where a radio station uses one powerful transmitter to send signals tonumerous transistor radios.A simple illustration of telecommunications would be a Plain Old Telephone (POT) systemFigure 2.1: Communication link between two telephones5copper wire lineTelephone A Telephone B
  15. 15. The transmitter is the mouthpiece of each of the two telephones, the receiver is the earpieceof each of the two telephones and the transmission medium is the copper wire between the twotelephones. This is a point-to-point communication because the transmitter of telephone A isusing a dedicated link over the copper wire to communicate with the receiver of telephone B, andsame with the transmitter of telephone B and the receiver of telephone A.When you speak through the mouthpiece of telephone A, your voice which is in an analogueform and of low frequency (hence cannot of itself reach the other party of telephone B) is madeto alter the electrical properties of the mouthpiece in a predictable way. These electricalalterations (electrical signals) are transmitted through the copper wires to the receiver of the othertelephone which then regenerates the audio speech. This shaping of a signal to conveyinformation is called modulation.If we want to setup a plain old telephone network system for a town or large community, wewill probably need to run a copper wire from each telephone to every other telephone in thenetwork. This will be very cumbersome and uneconomical, so usually there are some copperwires that are made to carry communications signals for more than one point-to-pointcommunication. This will require a special device called a multiplexer to combine several point-to-point communication signals to be transmitted on one copper wire. There will also be ademultiplexer at the other end to separate the different communications signals. A modem isusually used to perform the operations of both the multiplexer and demultiplexer at bothcommunication ends. The combination of several communications signal to be transmitted overone transmission line is called multiplexing.A collection of several transmitters, receivers and/or transceivers that can communicate withone another is known as a network.2.1 TELECOMMUNICATION TRANSMISSION MEDIAThere are four basic types of transmission media used for transmission of signals intelecommunications, namely,1. Copper cable,2. Coaxial cable,6
  16. 16. 3. Optical fibre, and4. Wireless.2.1.1 COPPER CABLECopper cable is the most extensively used transmission media and often in conjunction withother media. It is very cheap to implement and in form of a twisted pair cable, it is quitesatisfactory for Public Switched Telephone Network (PSTN) lines and voice communications.But as data communications were been implemented in most telephone networks including thePSTN, copper became unsuitable due to the high degenerative effect it has on high frequencydata signals. Also, the load coils that are frequently added to copper loops longer than than18,000 feet to block frequencies higher than the standard 64kbits/s voice modulated signalsfrequency, are low-pass filters which greatly attenuate higher frequencies that characterize datasignals. Data signals require higher frequencies compared with voice modulated signals in otherto achieve a very high bandwidth.Copper cable is still much in use as a transmission medium, but it is not used for very high-traffic data communication. Since, all telecommunications networks now provide both voice anddata communication over the same set of infrastructure, copper cable as a transmission mediumis now limited to low traffic network areas and cover a relatively short distances.Figure 2.2: A four-pair copper cable7
  17. 17. 2.1.2 COAXIAL CABLECoaxial cable is a special adaptation of copper. It consists of a single strand of coppershielded by a foam-like insulator or air dielectric and an electromagnetic shield of a conductivefoil, with interwoven strands of wire between the outermost insulator and the foil. Coaxial cable ismore like an antenna than a regular cable because it carries an electromagnetic wave between theinner core and the shielding. It has superior signal quality because the shielding mostly preventsinterference from reaching the signal. Coaxial connectors are designed to have the same impedance asthe cable and to maintain its shielding. The main connector types are the BNC connector used forcomputer networking, and the F connector used for cable television. Cable terminators are closedconnectors that are placed on all open ends of a coaxial cable network to minimize signal loss andinterference. Because of its construction, the coaxial cable can conveniently transmit highfrequency signals for a longer distance and lower attenuation than the conventional copper cablewould. Usually, dozens of television channels each 6MHz wide can be multiplexed on a singlecoaxial cable for satellite television broadcast reception.But still, the coaxial cable still has the limitation of attenuating very high frequency signals,and is not usually used for very long distances.Figure 2.3: A typical coaxial cable8
  18. 18. 2.1.3 OPTICAL FIBREOptical fibre is simply a very thin strand of specially treated glass (about a few micrometersin diameter), padded with a flexible insulator material (cladding) with an outer jacket to preventbreakage. It transmits signals in form of refracted light rays. It is an ideal transmission mediumwith practically no attenuation for thousands of miles of very high frequency signal transmission.It can transmit bandwidths of 110 Gb/s on a single strand as tiny as 10 micrometer diameter.(Coring, 2006).Since most telecommunications signals are in electrical form, an electrical-to-optical signalconverter chip is used at each end of the optic fibre transmission line. Most telephone networkoperators use optic fibre backbone installation. Though, it is quite expensive to implement, but ona per-bandwidth basis, it is the cheapest form of telecommunication medium. Its only limitationis that it not economical for local network loops of low traffic load and short distances.Figure 2.4: A typical optic fibre2.1.4 WIRELESSWireless transmission involves the use of electromagnetic waves of various frequencies fortelecommunication transmission. In reality, a wireless transmission medium can be anythingranging from the atmosphere to even water body, as long as the electromagnetic waves is notreflected or absorbed completely. Hence, a wireless transmission medium goes beyond just airand free space media, it means any material that the signal can be propagated through. Wirelesstransmission can be implemented through several equipments like microwave transmitters,synchronous satellites, low-earth orbit satellites, cellular transmitters and personal9
  19. 19. communication services (PCS) devices. In fact, the GSM (Global System for Mobilecommunications) that I will discuss extensively in the following chapter, uses wireless.Wireless has the advantage of the fact that it could be implemented in remote ormountainous locations where wired connections will be too expensive or impossible toimplement. But wireless is the most expensive transmission mode per-bandwidth basis.Figure 2.5: Wireless communication links.10
  20. 20. CHAPTER THREE3.0 GLOBAL SYSTEM FOR MOBILE COMMUNICATIONS (GSM)The major application of wireless communication is for speech or voice communications.Though, radio telephony has been in use for many decades, but in a very limited way, usually forcommunications between different military bases and research institutes.The GSM is a radio telephony standard set up to allow commercial internationallystandardized cellular (use of cells in a network with frequency channels that can reused) radiotelephone networks in the world. More than 80 percent of the mobile telephone network systemsin the world uses the GSM standard. This makes it possible for companies to produce phones thatcomply with the standard and can work with any mobile telephone network operator that uses theGSM standard. For example, you can buy any of Nokia, Samsung or Siemens GSM phone anduse it with either Zain, MTN or Glo network operators in Nigeria.GSM operates in four standardized frequency ranges/bands namely,GSM 850,GSM 900,GSM 1800, andGSM 1900.In Nigeria, we use both the GSM 900 and 1800 bands.11
  21. 21. Figure 3.1: Frequency allocation in the GSM 900 and GSM 1800 bandThe uplink refers to a signal flow from the mobile station (MS) to the Base TransceiverStation (BTS), while the downlink refers to the signal flow from the Base Transceiver station tothe mobile station.The mobile station is a combination of a terminal equipment (usually a mobile phone) and asubscriber data usually stored on a subscriber Identity Module chip (SIM). Hence, mobile phone+ SIM = Mobile station.Figure 3.2: A mobile station12
  22. 22. The simultaneous use of separate uplink and downlink frequencies enables communicationin both the transmit (TX) and the receive (RX) directions. The radio carrier frequencies arearranged in pairs and the difference between these uplink and downlink frequencies is called theduplex frequency. Each of these uplink and downlink frequency ranges are divided into carrierfrequencies spaced at 200kHz.Table 3.1: GSM 900 frequency channels.CHANNEL UPLINK SIGNAL(MHz)DOWNLINK SIGNAL(MHz)1 890.1 – 890.3 935.1 – 935.32 890.3 – 890.5 935.3 – 935.53 890.5 – 890.7 935.5 – 935.74 890.7 – 890.9 935.7 – 935.95 890.9 – 891.1 935.9 – 936.16 891.1 – 891.3 936.1 – 936.37 891.3 – 891.5 936.3 – 936.58 891.5 – 891.7 936.5 – 936.79 891.7 – 891.9 936.7 – 936.910 891.9 – 892.1 936.9 – 937.111 892.1 – 892.3 937.1 – 937.312 892.3 – 892.5 937.3 – 937.513 892.5 – 892.7 937.5 – 937.714 892.7 – 892.9 937.7 – 937.9... ... ...13
  23. 23. 24 914.7 – 914.9 959.7 – 959.9Table 3.2: GSM 1800 frequency channels.CHANNEL UPLINK SIGNAL(MHz)DOWNLINK SIGNAL(MHz)1 1710.1 – 1710.3 1805.1 – 1805.32 1710.3 – 1710.5 1805.3 – 1805.53 1710.5 – 1710.7 1805.5 – 1805.74 1710.7 – 1710.9 1805.7 – 1805.95 1710.9 – 1711.1 1805.9 – 1806.16 1711.1 – 1711.3 1806.1 – 1806.37 1711.3 – 1711.5 1806.3 – 1806.58 1711.5 – 1711.7 1806.5 – 1806.79 1711.7 – 1711.9 1806.7 – 1806.910 1711.9 – 1712.1 1807.1 – 1807.311 1712.1 – 1712.3 1807.3 – 1807.512 1712.3 – 1712.5 1807.5 – 1807.713 1712.5 – 1712.7 1807.7 – 1807.914 1712.7 – 1712.9 1807.9 – 1808.1... ... ...374 1784.7 – 1784.9 1879.7 – 1879.914
  24. 24. In GSM 900, the duplex frequency is 45MHz and in GSM 1800, it is 95MHz. The lowestand highest channels are not used in both GSM 900 and 1800 bands to avoid interference withservices using neighbouring frequencies.The radio transmission in GSM networks is based on digital technology and is implementedusing the Frequency Division Multiple Acess (FDMA) for cell allocation to a Base TransceiverStation (BTS) and the Time Division Multiple Access (TDMA) for resource share among severalmobile stations in a cell. As for the FDMA, each BTS (covering a cell) is allocated different radiofrequency channels to avoid interference in adjacent cells. While in TDMA, each Mobile Stationis allocated a time slot to send and receive data.Figure 3.3: Time Division Multiple Access principle15
  25. 25. 3.1 GSM NETWORK ARCHITECTUREA connection between two people – the caller and the called person – is the basic service ofall telephone networks. In a GSM network, the establishment of this connection is quite complexbecause the users are allowed to move about provided they stay within the overall networkservice area of the network operator, unlike fixed telephone networks where each phone locationis fixed.In practice, the GSM network has to fnd solutions to the following three basic problemsbefore it can even set up a call,1. Who is the subscriber?2. Where is the subscriber?3. What does the subscriber want?In other words, the subscriber has to be located, identified and provided with the requestedservices.The GSM network is able to do these and many more through the use of a decentralisedintelligence subsystems, namely1. Network Switching Subsystem (NSS)2. Base Station Subsystem (BSS)3. Network management Subsystem (NMS)The actual network part needed for establishing call is the NSS and BSS. The NMS is theoperation and maintenance related part of the network and it is needed for the control of thewhole GSM network.3.2 NETWORK SWITCHING SUBSYSTEM (NSS)The network switching subsystem is the GSM network subsystem part that handles callcontrol, charging information, subscriber location information, signalling and subscriber datastorage. It is able to do all these through various component network elements , namely:16
  26. 26. 1. Mobile services Switching Centre (MSC)2. Home Location Registry (HLR)3. Visitor Location Registry (VLR)4. Authentication Centre (AC), and5. Equipment Identity Register (EIR)The GMSC stands for Gateway Mobile services Switching Centre and is used tointerconnect with the Public Switched Telephone Network (PSTN).Figure 3.4: The Network Switching Subsystem (NSS)3.2.1 MOBILE SERVICES SWITCHING CENTRE (MSC)The MSC is responsible for controlling calls in the mobile network. It identifies the originand destination of a call (mobile station or fixed telephone), as well as the type of call. An MSCalso initiates paging which is the process of locating a particular mobile station to receive acall.MSC also collects charging information.17
  27. 27. 3.2.2 VISITOR LOCATION REGISTRY (VLR)In the Nokia Siemens Networks implementation, the Visitor Location Register is integeratedwith the MSC. The Visitor Location Register is a database that contains information aboutsubscribers currently in the service area of the MSC/VLR, such as1. Identification numbers of subscribers.2. Security information for authentication of the SIM card and for ciphering.3. Services that the subscriber can us.The VLR database is temporary, in the sense that the data is held as long as the subscriber iswithin its service area. It also contains the address to every subscribers Home Location Register,which I will discus next.3.2.3 HOME LOCATION REGISTER (HLR)The Home Location Register maintains a permanent database of the subscribers, theiridentification numbers and subscribed services. Also, the HLR keeps track of the current locationof its customers. This makes it possble for the MSC to ask for call routing information from theHLR to get to the dialled number.In Nokia Siemens Networks implementation, the Authentication Centre (AC) and theEquipment Identity Register (EIR) are located in the HLR.3.2.4 AUTHENTICATION CENTRE (AC)The authentication centre provides security information to the network, so that SIM cardscan be verified. The AC provides authentication between the mobile station and the VLR. TheAC also issues a so-called authentication triplets upon request and ciphers the informationtransmitted between the mobile station and the Base Tranceiver Station.18
  28. 28. 3.2.5 EQUIPMENT IDENTITY REGISTER (EIR)Just like the Authentication Centre, the Equipment Identity Register is used for securityreasons. But while the AC provides information for verifying the SIM cards, the EIR isresponsible for the IMEI (International Mobile Equipment Identity) number checking to ascertainthe mobile phones validity on the network.The EIR contains three lists:1. White list containing the list of mobile phones allowed to operate normally on thenetwork,2. Grey list containing the list of mobile phones whose use will be monitored for securityreasons, and3. Black list containing the list of mobile phones reported stolen or just not allowed tooperate on the network for security reasons.3.3 BASE STATION SUBSYSTEM (BSS)The base station subsystem is responsible for managing the radio network, and it iscontrolled by the MSC. Typically, one MSC controls several BSSs. A BSS itself may cover aconsiderably large geographical area consisting of many cells.The BSS consists of the following network elements:1. Base Station Controller (BSC)2. Base Transceiver Station (BTS)3. Transcoder (TC)19
  29. 29. Figure 3.5: The Base Station Subsystem (BSS)3.3.1 BASE STATION CONTROLLER (BSC)The Base Station Controller is the central network element in the BSS and it controls theradio network. All calls to and from the mobile station are connected through the group switch ofthe BSC. The BSC is response for initiating the vast majority of all handovers, and it makes thehandover decision based on, among others, measurement reports sent by the mobile stationduring a call. Also, information from the Base Transceiver Stations, Transcoders and BSC arecollected in the BSC and forwarded via the Data Communications Network to the Networkmanagement Subsystem (NMS) where they are post-processed into statistical views, from whichthe network quality and status is obtained.It is the BSC that cordinates the operation of several BTSs, and Transcoders. And it iscapable of barring a BTS from the network and collecting alarm information.3.3.2 BASE TRANSCEIVER STATION (BTS)The Base Transceiver station is the network element responsible for maintainingcommunication with the mobile station. The BTS enables a lot of call and non-call signallingwith the mobile station, in order for the communication system to work well. For example, whena mobile station is just switched on in a new location area, it will need to send and receive a lot of20
  30. 30. information (as short data bursts) with the network through the BTS before it can begin to receiveand make calls.The BTS also performs speech processing in order to guarantee an error-free connectionbetween the mobile station and the network. This includes speech coding, channel coding anddata burst formatting.3.3.2 TRANSCODER (TC)For transmission between the mobile station and the Base Transceiver Station, the mediacarrying the traffic is a radio frequency. And to enable an efficient transmission of digital speechinformation, the digital speech signal is compressed. We must however, also be able tocommunicate with and through the fixed network whose speech compression format is different.So, somewhere between the BTS and the fixed network, we therefore have to convert from onespeech compression format to another, and this is where the Transcoder comes in.For transmission over the air interface, the speech signal is compressed using three formats,namely:1. FULL RATE compression of 13kbits/s using compression algorithm "Regular PulseExcitation with Long Term Prediction" (RPE-LTP).2. ENHANCED FULL RATE of also 13kbits/s (but better quality then the full rate) usingcompression algorithm "Algorithm Code Excited Linear Prediction" (ACELP).3. HALF RATE compression of 5.6kbits/s using compression algorithm "Vector SumExcited Linear Prediction" (VSELP).But the standard bit rate for speech in fixed network Public Switched Telephone Network(PSTN) is 64kbits/s using Pulse Code Modulation (PCM). The transcoder takes care of thechange from one bit rate to another. Also, the Transcoder enables Discontinuous Transmission(DTX) which is used during a call when there is nothing to transmit (no conversation) in order toreduce interference and mobile phones battery usage.21
  31. 31. In Nokia Siemens Networks the submultiplexing and transcoding functions are combined inone equipment called TCSME (Transcoder-Submultiplexer European version) or TCSMA(Transcoder-Submultiplexer American version).3.4 NETWORK MANAGEMENT SUBSYSTEM (NMS)The Network Management Subsystem is the third subsystem of the GSM network, workingin conjuction with the Network Switching Subsystem (NSS) and Base Station Subsystem (BSS)which I have already discussed. The purpose of the NMS is to monitor the various functions andelements of the network. In the Nokia Siemens Networks implementation, these tasks are carriedout by the NMS/2000, which consists of a number of workstations, servers, and a router whichconnects to a Data Communications Network (DCN).The operator workstations are connected to the database and communications servers via aLocal Area Network (LAN). The database stores the management information aboutcommunications between the NMS and the equipments in the GSM network known as "networkelements". These communications are carried over a Data Communication Network (DCN),which consists to the NMS via a router.The major functions of the NMS are:1. Fault management to ensure the smooth operation of the network and rapid correction ofany kind of problems detected.2. Configuration management to maintain up-to-date information about the operation andconfiguration status of network elements.3. Performance management through collection of measurement data from variousindividual network elements.22
  32. 32. Figure 3.7: A diagramatic representation of the management function of the NMS3.5 PRACTICAL ILLUSTRATIONLets take an MTN subscriber in Engineering building, Federal University of TechnologyAkure, Ondo state and call him Obanla.Figure 3.8: Obanla trying to call Ajegunle23
  33. 33. Let us take another MTN subscriber located in Ajegunle, Lagos state and call him Ajegunle.I am going to explain what happens when Obanla switches on his phone and dialsAjegunles mobile phone.Note the following already discussed items,1. A mobile station is a mobile phone that has a Subscriber Identity Module (SIM) connectedto it.2. A Base Station Subsystem (BSS) comprises the Base Station Controller (BSC), BaseTransceiver Station (BTS) and Transcoder (TC).3. The Network Switching Subsystem (NSS) comprises the Mobile services SwitchingCentre (MSC), Visitor Location Register (VLR), Home Location Register (HLR),Authentication Centre (AC) and Equipment Identity Register (EIR).4. Only the Base Station Subsystem (BSS) and Network Switching Subsystem (NSS) areneeded for establishing calls. The Network Management Subsystem (NMS) is foroperation monitoring and maintenance of the GSM network.The Base Transceiver Stations are arranged in such a way that one BTS covers anhexagonal area and the surrounding BTSs must use different frequency channels.24
  34. 34. Figure 3.9: The frequency reuse chart.When subscriber Obanla switches on his mobile station (mobile phone already with a validMTN SIM connected), the mobile station scans all the radio channel frequencies for broadcastsignals from all nearby MTN Base Transceiver Stations, measures the distance of each BTSthrough a special algorithm and also detects eachs signal strength. The mobile station will nowsynchronise with the BTS with the best signal sthrength (usually the nearest BTS) and tunes toits radio channel frequency. The radio frequency channel used by the BTS is divided intoconsecutive periods of time, each one called a Time Division Multiple Access (TDMA) frame.Each TDMA frame consists of eight shorter periods of time called timeslots. The radio carriersignal between the mobile station and the BTS is divided into a continuous stream of timeslotswhich in turn are transmitted in a continuous stream of TDMA frames.With the help of a synchronising signal in a TDMA frame broadcast from the BTS, Obanlasmobile station synchronises itself with the MTN network.25
  35. 35. Figure 3.10: Synchronization of the mobile station with the network.The timeslots of the TDMA frame represent the physical channels and their contents areorganized into logical channels which are divided into two types, namely:1. Dedicated channels, and2. Common channelsA dedicated channel is a logical channel that is allocated exclusively to one mobile station totransmit speech and data signals. A dedicated channel is also known as traffic cahnnel. But acommon channel is a logical channel used for broadcasting signals to numerous mobile station atthe same time.After Obanlas mobile station has synchronised itself with the MTN network, the nextprocess before he can be able to set up a call is registration. The mobile station will make arequest for a logical channel to establish connection with the VLR to inform it about its newlocation and routing information. The network acknowledges the request and allocates a logicalchennel. Then the mobile station moves into the allocated channel for further transmissions toinform the MTN network about its whereabout and how it can be reached.26
  36. 36. Figure 3.11: Channel request and allocation.Once the mobile station is registered in the network, Obanla can now dial Ajegunles phonenumber. When this done, Obanlas mobile station requests for a dedicated/traffic channel toAjegunles mobile station. This request is sent through the BTS that provides services forObanlas mobile station and the BSC that controls the BTS, to the MSC that controls the BSC,the MSC checks the information coded into Ajegunles phone number to determine his mobilestations HLR which will have the routing address to the MSC/VLR (MSC and VLR is usuallylocated in the same physical equipment) servicing Ajegunles mobile station. The MSC/VLRservicing Ajegunles mobile station is sent this traffic channel request, this MSC will now signalthe BTS servicing the mobile station, which will in turn page (send a special broadcast) to all themobile stations synchronised through it. Only Ajegunles mobile station will respond to thepaging signal, first by ringing and later sending an I am busy signal or a I am available signal,the MSC will now create a traffic channel from the mobile station through the other MSC toObanlas mobile station (provided the mobile station sent an I am available signal). This trafficchannel is then used to establish an audio conversation between Obanla and Ajegunle.27
  37. 37. The Network Management Subsystem only receives information about the call quality, timeof call, subscribers involved and possible faults, which MTN use for maintenance and upgradingof their network services.As for the charging, this is done by a separate network element called Biller.Figure 3.12: A summary of the GSM architecture.28
  38. 38. CHAPTER FOUR4.0 BASE TRANSCEIVER STATION RADIO ACCESS LINKThe Base Transceiver Station radio access link is the segment of the BTS that deals with thetransmission of the microwave frequency signals.The GSM network relies on microwave frequencies (3 – 30GHz) to transmit the digital signalsof large bandwidth between the BTSs, an MSC and a BTS. Only the MS operates on thestandardized GSM 800, 900, 1800 and 1900 frequency bands to communicate with the BTS at a datarate of 13kbits/s for full rate and enhanced full rate compression, or 5.6kbits/s for half ratecompression. The BTS multiplexes all these signals into a Synchronous Transport Module (STM) ofbandwidths 155.52Mbits/s for STM-1, 311Mbits/s for STM-2 and 622Mbits/s for STM-4, whichwill be transmitted to the next BTS, an MSC or a BSC. These high bandwidth signals can only beeffectively transmitted via a very high frequency electromagnetic wave commonly referred to asmicrowave.Table 4.1: The standard frequency allocation tableELECTROMAGNETICWAVE TYPEFREQUENCYRANGEWAVELENGTH(metres)CCIR CODEVery Low Frequency(VLF)300 Hz – 30KHz 10,000 – 100,000 4Low Frequency (LF) 30Khz – 300KHz 1,000 – 10,000 5Medium Frequency (MF) 300Khz – 3MHz 100 – 1,000 6High Frequency (HF) 3MHz - 30MHz 10 - 100 7Very High Frequency(VHF)30MHz - 300MHz 1 – 10 8Ultra High Frequency( UHF)300MHz - 3GHz 0.1 - 1 9Super High Frequency(SHF)3GHz – 30GHz 0.01 – 0.1 1029
  39. 39. Extremely High Frequency(EHF)30GHz - 300GHz 0.001 – 0.01 11The Base Transceiver Stations are arranged such that each BTS uses a frequency channel that isdistinct from all adjacent BTSs (to communicate with the mobile stations within its reach). This is toreduce co-channel interference that will result from two or more adjacent BTSs transmitting on thesame frequency channel, hereby leading to cross-talks and reduction in Quality of Service. Ideally,BTSs cover a circular area of radius, R, but for physical planning purpose this will give overlappedcells which will make planning extremely complex. So, hexagonal cells are used to represent theBTS coverage area because it gives no gap and overlap. The minimum distance which will allow thesame frequency channel to be reused will depend on many factors, such as the type of geographicterrain, the transmitter power, and the desired customer capacity per BTS. (William,1989).The Radio access link of the BTS in the latest Nokia Siemens Networks implementationcomprises,1. The Synchronous Radio Access STM-4 (SRA 4) unit,2. The coaxial cable,3. An outdoor frequency converter and signal amplifier unit (ODU), and4. Directional antenna.4.1 THE SYNCHRONOUS RADIO ACCESSS STM-4 (SRA 4) UNITThe SRA 4 is a Nokia Siemens Networks proprietary equipment that multiplexes several lowbandwidth signals into a high bandwidth signal for transmission via microwave frequencies or anoptical fibre.30
  40. 40. Figure 4.1: The SRA 4 unitThe SRA 4 is an intelligent device that does more than multiplexing but also, intelligently choosesthe modulation format to use and the path to use in getting to a specific destination/receiver. It isconfigured using the Local Craft terminal and the NetBuilder, and it can be used to monitor theoperation of most directly connected network elements.Figure 4.2: Local Craft Terminal software31
  41. 41. Figure 4.3: The NetBuilder software.Figure 4.4: On site testing of connectivity between two BTSs using the SRA 4 handset.32
  42. 42. Figure 4.5: The SRA 4 unit fully connected to the other network units4.2 THE COAXIAL CABLEThe Coaxial cable is a cable consisting of an inner conductor, surrounded by a tubular insulatinglayer typically made from a flexible material with a high dielectric constant, all of which is thensurrounded by another conductive layer (typically of fine woven wire for flexibility, or of a thinmetallic foil), and then finally covered again with a thin insulating layer on the outside. The termcoaxial comes from the inner conductor and the outer shield sharing the same geometric axis.Coaxial cables are often used as a transmission line for radio frequency signals. In a hypotheticalideal coaxial cable, the electromagnetic field carrying the signal exists only in the space between theinner and outer conductors. Practical cables achieve this objective to a high degree. A coaxial cableprovides protection of signals from external electromagnetic interference, and effectively guidessignals with low emission along the length of the cable. (Wikepedia, 2008).It is the coaxial cable that transmits signals between the SRA 4 and the Outdoor Unit (ODU).33
  43. 43. Figure 4.6: The coaxial cables connecting the indoor units to the outdoor units.Figure 4.7: The coaxial cables entering into the BTS shelter.34
  44. 44. 4.3 THE OUTDOOR FREQUENCY CONVERTER AND SIGNAL AMPLIFIER UNIT(ODU)The ODU is the unit always closely attached to the antenna which converts the signals from theantenna into a form that can easily transmitted down the coaxial cable by impedance matching, itconverts the high frequency microwave signal into a lower intermediate frequency, and amplifiesthe signal received from the antenna.Figure 4.8: An ODUFigure 4.9: An antenna with two ODUs closely attached35
  45. 45. In Nokia Siemens Networks implementation, the ODUs are of two major types, namely:1. The 6 – 13GHz ODUThis is the one used in all the Base Transceiver Stations setup by Nokia Siemens Networks inNigeria.Figure 4.10: The 6 – 13GHz ODU2. The 15 – 38 GHz ODU (Not currently used by Nokia Siemens Networks in Nigeria)Figure 4.11: The 15 – 38GHz ODU36
  46. 46. 4.4 DIRECTIONAL ANTENNAAn antenna is a tranducer that generates a radiating electromagnetic field in response to anapplied alternating voltage and the associated alternating electric current, or can be placed in anelectromagnetic field so that the field will induce an alternating current in the antenna and a voltagebetween its terminals. (Wikipedia, 2008)There are two fundamental types of antennae, namely:1. Omni-directional antenna that radiates or receives electromagnetic wave in all directionequally.2. Directional or uni-directional antenna that radiates or receive electromagnetic wave betterin a specific direction than in all other directions.In the GSM network, high performance shielded directional antennae are used to transmitsignals from one BTS to another BTS or an MSC. The polarization, which is the orientation of theelectric field vector of the electromagnetic wave produced by the antenna, is horizontal.Figure 4.12: The different polarizations37
  47. 47. Figure 4.13: Directional high performance shielded antenna already installed38
  48. 48. Figure 4.14: Mutual impedance between parallel /2 dipoles not staggered. Curves Re and Imare the resistive and reactive parts of the impedance.Current circulating in any antenna induces currents in all others. One can postulate a mutualimpedance between two antennas that have the same significance as the in ordinarycoupled inductors. The mutual impedance between two antennas is defined as:where is the current flowing in antenna 1 and is the voltage that would have to be appliedto antenna 2 – with antenna 1 removed – to produce the current in the antenna 2 that was producedby antenna 1.From this definition, the currents and voltages applied in a set of coupled antennas are:39
  49. 49. where:• is the voltage applied to the antenna i• is the impedance of antenna i• is the mutual impedance between antennas i and jNote that, as is the case for mutual inductances,Gain (directivity): This is a measure of the degree to which an antenna focuses power in agiven direction, relative to the power radiated by a reference antenna in the same direction. Units ofmeasure are dBi (isotopic antenna reference) or dBd (half-wave dipole reference). The two gainmeasurements can be converted using the following formula:dBi = dBd + 2.1If the directivity of the transmitting and receiving antennas is known, it is possible to computethe power received by the receiving antenna using either of the formulas below:When using dB:PRECEIVED = PTRANSMITTER + GT + GR + 20log(λ) – 20log(d) – 21.98Antenna gain should be expressed in dBi, wavelength and distances in m and powers in dBm ordBW.When using gain ratios and powers in W:PRECEIVED = PTRANSMITTERGTGRλ216π2d2Where, GT is the gain of the transmitterGR is the gain of the receiverd is the distance between the transmitter and the receiver in metresλ is the wavelength in metres40
  50. 50. 4.5 TWISTED PAIR COPPER CABLESometimes, remote connections are made to monitoring the Network Monitoring Subsystem ora Base Station Controller through twisted copper cables. In Nokia Siemens Networksimplementation, we use the 21 pair twisted copper cable to form the standard E1 (2.048 Mbits/s)European standard pleisynchronous transport module line.Figure 4.13: The 21 pair twisted cables being made into E1 transmission lines41
  51. 51. Figure 4.14: The specialized crimper and clamp for fixing the E1 DB-32 connectors42
  52. 52. Figure 4:15: A general tool box.Also, copper cables are used to connect between the Digital Distribution Frames, EWSDSwitches, and Multiplexers in the Gateway MSC connecting to the Public Land Mobile Networks.43
  53. 53. Figure 4.16: The Digital Distribution Frame (DDF)44
  54. 54. Figure 4.17: The Multiplexer (Surpass HiT 7070, under testing)45
  55. 55. Figure 4.18: The Synchronous Radio Access XL (SRA XL)46
  56. 56. CHAPTER FIVE5.0 CONCLUSION AND RECOMMENDATIONConclusively, the SIWES programme has given me the priviledge and opportunity ofunderstanding the fundamentals of telecommunications and how the mobile telecommunicationsnetwork operates. I now clearly see how all I have been taught in the lecture hall fit together to beapplied in the designing of telecommunications systems and in particular the GSM network. Fromthe elementary mathematics used in calculating and mapping the frequency reuse chart to theadvanced mathematics used in designing the compression codes, modulation techniques and cross-correlation of signals to eliminate interference. In this report, I explained in a much simplified formthe principle and system of operation of the GSM network with much emphasis on the BaseTransceiver Station Radio Access Link.I was able to train as a Cisco Certified Network Associate and a Oracle 10g DatabaseAdministration Certified Associate. I was also, able to work on the Linux edition of Unix OperatingSoftware and understand its peculiar use as a operating system for most backbone central computeror server. The experience and knowledge I have gained during the SIWES will be greatly beneficialto my career as an Electrical Electronics Engineer.I will like to make the following recommendations to help make the SIWES programme moreeffective:◦ The University should partner with some companies in order to send them in a specifiedpattern, some students from relevant departments to undertake their SIWES at thosecompanies. This will help lessen the problem of students not getting a company that willprovide experience that is relevant to their field of study.◦ The monthly stipend promised by the Industrial Training Fund (as stated in the SIWESplacement request letter) should be promptly paid to ease the financial pressure on studentsduring the SIWES programme.◦ The SIWES supervisors should be made to visit every student at their company ofplacement at least twice.47
  57. 57. REFERENCESMacario R. C. V. (1997): “Cellular Radio Principles and design” Second editions, MacmillanPress, London. pg7-12Nokia Networks (2002): “GSM Air Interface & Network Planning Training Document”. NokiaNetworks Oy, FinlandNokia Networks (2002): “GSM Architecture Training Document”. Nokia Networks Oy,FinlandWilliam C. Y. L. (1989): “Mobile Cellular Telecommunications System” McGraw-Hill, NewYork. pg26-27http://en.wikipedia.org/wiki/Antenna_(radio) (2008): “Antenna (radio) - Wikipedia, the freeencyclopedia”http://en.wikipedia.org/wiki/Base_Transceiver_Station (2008): “Base transceiver station -Wikipedia, the free encyclopedia”http://www.iec.org (2006):“Fiber-Optic Technology” Coringhttp://www.images.google.com_images_hl=en&q=telephone (2008): “Telephone – GoogleImage Search”http://www.images.google.com_images_hl=en&q=WIRELESS (2008): “WIRELESS - GoogleImage Search”http://www.nokiasiemensnetworks.com/about_us (2008): “Introduction to Nokia SiemensNetworks”http://www.tech-faq.com/coaxial-cable.shtml (2008): “What is a Coaxial Cable?”48

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