Ece Viii Wireless Communication [10ec81] Notes

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(1)Wireless Communication Subject Code. 10EC81. : 10EC81. IA Marks. No. of Lecture Hrs/Week : 04 Total no. of Lecture Hrs. : 52. Exam Hours Exam Marks. : 25 : 03 : 100. PART - A UNIT – 1 Introduction to wireless telecommunication systems and Networks, History and evolution Different generations of wireless cellular networks 1G, 2g,3G and 4G etworks. 6 Hours UNIT - 2 Common Cellular System components, Common cellular network components, Hardware and software, views of cellular networks, 3G cellular systems components, Cellular component identification Call establishment.. 6 Hours UNIT - 3 Wireless network architecture and operation, Cellular concept Cell fundamentals, Capacity expansion techniques, Cellular backbone networks, Mobility management, Radio resources andpowermanagementWirelessnetwork 6 Hours UNIT - 4 GSM and TDMA techniques, GSM system overview, GSM Network and system Architecture,GSMchannelconcepts,GSM 6 Hours PART - B UNIT - 5 GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture. TDMA systems 6 Hours Department of ECE,SJBIT. Page 1.

(2) Wireless Communication. 10EC81. UNIT - 6 CDMA technology, CDMA overview, CDMA channel concept CDMA operations. 8 hours. UNIT - 7 Wireless Modulation techniques and Hardware, Characteristics of air interface, Path loss models, wireless coding techniques, Digital modulation techniques, OFDM, UWB radio techniques, Diversity techniques, Typical GSM Hardware.. 6 Hours UNIT - 8 Introduction to wireless LAN 802.11X technologies, Evolution of Wireless LAN Introduction to 802.15X technologies in PAN Application and architecture Bluetooth Introduction to Broadband wireless MAN, 802.16X technologies. 8 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS:. 1.. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.. 2.. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007.. 3.. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 2.

(3) Wireless Communication. 10EC81 INDEX SHEET. Sl.No. Unit & Topic of Discussion. Page no.. UNIT --- 1 1. Introduction to wireless telecommunication systems. 2. Introduction to wireless telecommunication Networks. 3. 5. History of different generations of wireless cellular networks Evolution of different generations of wireless cellular networks 1G,2G networks. 6. 3G and 4G networks. 4. 5 to 19. UNIT—2 7. Common Cellular System components. 8. Common cellular network components. 9. Hardware and software. 10. Views of cellular networks. 11. 3G cellular systems components. 12. Cellular component identification Call establishment. 13. Call release. 20 to 30. UNIT – 3 14. Wireless network architecture and operation. 15. Cellular concept , Cell fundamentals. 16 17. Capacity expansion techniques, Cellular backbone networks Mobility management. 18. Radio resources and power management. 19. Wireless network security. 31 to 42. UNIT --4 20. GSM and TDMA techniques. 21. GSM system overview. 22. GSM Network. 23. system Architecture. Department of ECE,SJBIT. 43 to 54. Page 3.

(4) Wireless Communication. 10EC81. 24. GSM channel concepts. 25. GSM identifiers UNIT – 5. 26. GSM system operation. 27. Traffic cases. 28. Call handoff. 29. Roaming. 30. GSM protocol architecture. 31. TDMA systems. 32. NA TDMA. 55 to 67. UNIT--6 33. CDMA technology. 34. CDMA overview. 35. CDMA channel concept CDMA operations. 36. CDMA channel concept CDMA operations. 37. CDMA channel concept. 38. CDMA channel assignement. 68 to 81. UNIT-7 40. Wireless Modulation techniques and Hardware. 41. Characteristics of air interface , Path loss models. 42. Wireless coding techniques. 43 44. Digital modulation techniques, OFDM, UWB radio techniques Diversity techniques. 45. Typical GSM Hardware. 82 to 94. UNIT-7 46. Introduction to wireless LAN 802.11X technologies. 47. Evolution of Wireless LAN. 48. Introduction. to. 802.15X. technologies. in. PAN. 95 to 108. architecture 49. 802.16X technologies. Department of ECE,SJBIT. Page 4.

(5) Wireless Communication. 10EC81. UNIT - 1 Introduction to wireless telecommunication systems and Networks, History and Evolution Different generations of wireless cellular networks 1G, 2g,3G and 4G networks.. 6 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS:. 1. 2. 3.. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 5.

(6) Wireless Communication. 10EC81. UNIT-1. Introduction to wireless telecommunication systems and networks 1.1. Introduction to wireless telecommunication systems and networks Communication is the transfer of information form one point to another. Invention of telephone by Bell in 1876 was the first manually switched wireline network. Radio or wireless was invented during 20th century which had the convenience of mobile operation to electronic communication. Advances in IC technology gave the cordless telephones during late 1970s , and in 1983 the public had the opportunity to subscribe for cellular telephone systems. These wireless systems gave access to public switched telephone network which had mobile access. The wireless and mobile communications was found useful in commerce, education, defense etc., according to the nature of particular application they can be used in home based, industrial, commercial, military environment. For example, in commercial wireless communications can be employed for purchase or selling of goods, services , playing audio and video, payment of telephone bills , airline , bus reservations etc.,. 1.2. History and Evolution of Wireless Radio Systems In 1887 , Heinrich Hertz performed laboratory experiments which proved the existence of EM waves . From 1895 to 1901 Marconi experimented with a wireless telegraph system who built several radio telegraph stations in England and started commercial service between England and France in 1899. Early AM wireless systems The early wireless transmitter consists of inductance and capacitance which is used to tune the output frequency of the spark gap. Max power is generated at lower freq and longer wavelength. The transmitter emits the signal either long or short duration depending on length of time telegraph key is closed. The transmitter signal is the EM noise produced by the spark gap discharge.. Department of ECE,SJBIT. Page 6.

(7) Wireless Communication. 10EC81. Fig 1. Typical early wireless transmitter. The transmitter signal propagates through the air to a receiver which is located at some distance . At the receiver the detected signal is interpreted by the operator as either a dot or dash depending upon its duration by use of Morse code.. Modern AM : Amplitude modulation is used for low frequency radio broadcasting the AM include quadrature amplitude modulation which is used for high speed data transmission at RF frequencies.. 1.2 The Development of Modern Telecommunications Infrastructure The early days of telecommunications The public switched telephone network • The local exchange • Intraoffice calls. Department of ECE,SJBIT. Page 7.

(8) Wireless Communication. 10EC81. Fig: 1.2 A PSTN intraoffice call through a local exchange. – – –. Circuit-switched calls Interoffice calls T-carrier transport. Fig: 1.3 A PSTN intraoffice call over an inter-exchange trunk line. Department of ECE,SJBIT. Page 8.

(9) Wireless Communication Signaling System #7 • • • •. 10EC81. Signal transfer points Service switching points Service control points Operations support systems. Signalling System No. 7 (SS7) is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls. Other uses include number translation, local number portability, prepaid billing mechanisms, short message service (SMS), and a variety of other mass market services. It is usually referenced as Signalling System No. 7 or Signalling System #7, or simply abbreviated to SS7. In North America it is often referred to as CCSS7, an abbreviation for Common Channel Signalling System 7. In some European countries, specifically the United Kingdom, it is sometimes called C7 (CCITT number 7) and is also known as number 7 and CCIS7 (Common Channel Interoffice Signaling 7). In Germany it is often called as N7 (Signalisierungssystem Nummer 7). There is only one international SS7 protocol defined by ITU-T in its Q.700-series recommendations.[1] There are however, many national variants of the SS7 protocols. Most national variants are based on two widely deployed national variants as standardized by ANSI and ETSI, which are in turn based on the international protocol defined by ITU-T. Each national variant has its own unique characteristics. Some national variants with rather striking characteristics are the China (PRC) and Japan (TTC) national variants. The Internet Engineering Task Force (IETF) has also defined level 2, 3, and 4 protocols that are compatible with SS7:   . Message Transfer Part (MTP) level 2 (M2UA and M2PA) Message Transfer Part (MTP) level 3 (M3UA) Signalling Connection Control Part (SCCP) (SUA). The public data network • Connectionless systems • Private data networks • Virtual private data networks • Tunneling protocols. Department of ECE,SJBIT. Page 9.

(10) Wireless Communication. 10EC81. Fig: 1.4 Network elements of the SS7 system. 1.3 Different Generations of wireless cellular networks: 1G Cellular Systems – AMPS system components and layout • Radio base stations • Communications links • Mobile switching office First-generation cellular systems have been around for a few decades now, and we expect them to remain in place for some time because of the significant infrastructure investments made by operators. All of these systems support circuit data services and may be utilized for various forms of mobile VPN, albeit not without difficulties. This section provides a high-level overview of the air interfaces utilized by most widely deployed 1G systems. AMPS. Department of ECE,SJBIT. Page 10.

(11) Wireless Communication. 10EC81. All 1G cellular systems rely on analog frequency modulation for speech and data transmission and in-band signaling to move control information between terminals and the rest of the network during the call. Advanced Mobile Phone System is a good example of first-generation analog technology mostly used in the United States. AMPS is based on FM radio transmission using the FDMA principle where every user is assigned their own frequency to separate user channels within the assigned spectrum (see Figure 3.2). FDMA is based on narrowband channels, each capable of supporting one phone circuit that is assigned to a particular user for the duration of the call. Frequency assignment is controlled by the system, and transmission is usually continuous in both uplink and downlink directions. The spectrum in such systems is allocated to the user for the duration of the call, whether it is being used to send voice, data, or nothing at all. As with other 1G technologies, in AMPS a circuit—represented by a portion of spectrum— is allocated to the user and must remain available for this user, similar to the telephone copper pair used for voice communications. Similar to the analog wireline connection, a modem is also used for data access (see Chapter 4 for more on this). Error correction protocols used by wireless modems tend to be more robust than their landline counterparts, because of the necessity of dealing with a more challenging physical environment with inherently higher interference and signal-to-noise ratios than copper or fiber. The peak data rate for an AMPS modem call under good conditions is usually up to 14.4 Kbps, and as low as 4.8 Kbps under poor conditions. It can take anywhere up 20 seconds or more to establish an AMPS data connection.. Fig 1.5 An early AMPS cellular system. Information flow over AMPS channels Department of ECE,SJBIT. Page 11.

(12) Wireless Communication – – – –. 10EC81. Analog color codes Digital color codes Transponder Signaling tones. Fig 1.6 AMPS forward and reverse control and voice channels. – Typical AMPS operations – AMPS security and identification – Summary of basic AMPS operations • Initialization. Fig 1.7 AMPS mobile phone initialization. –. AMPS ongoing idle mode tasks. Department of ECE,SJBIT. Page 12.

(13) Wireless Communication –. 10EC81. Mobile-to-land calls • Handshaking operations • Signaling operations • Service requests. Fig 1.8 AMPS mobile originated call. Land-to-mobile and mobile-to-mobile calls • Paging • ID information exchange • Signaling • Control messages. Department of ECE,SJBIT. Page 13.

(14) Wireless Communication. 10EC81. Fig 1.9 AMPS mobile terminated call. AMPS network operations • Radio base station operations • Base station control operations • Mobile switching center operations. Fig 1.10 AMPS network operations for a mobile originated call. Department of ECE,SJBIT. Page 14.

(15) Wireless Communication Handoff operations • • • •. 10EC81. Handshaking operations Signal strength measurements MSC operations during handoff Confirmation messages. Fig 1.11 AMPS handoff operation. 2G Cellular Systems. Second-generation (2G) digital cellular systems constitute the majority of cellular communication infrastructures deployed today. 2G systems such as GSM, whose rollout started in 1987, signaled a major shift in the way mobile communications is used worldwide. In part they helped fuel the transition of a mobile phone from luxury to necessity and helped to drive subscriber costs down by more efficient utilization of air interface and volume deployment of infrastructure components and handsets. Major geographical regions adopted different 2G systems, namely TDMA and CDMA in North America, GSM in Europe, and Personal Digital Cellular (PDC) in Japan. cellular systems. It effectively shows how the GSM system has been successful and why it is now being adopted in geographical areas other than Europe (such as North America, China, the Asia-Pacific region, and more recently, South America). CDMA, which Department of ECE,SJBIT. Page 15.

(16) Wireless Communication. 10EC81. originated in North America, has also proliferated in South America and later in the AsiaPacific region. TDMA remains to be widely deployed in North and South America regions, but it is expected to decline mostly because of the decisions taken by few major North American carriers to convert their TDMA networks to GSM. This second-generation system, widely deployed in the United States, Canada, and South America, goes by many names, including North American TDMA, IS-136, and D-AMPS (Digital AMPS). For the sake of clarity, we will refer to it as North American TDMA, as well as simply TDMA, when the context makes it clear. TDMA has been used in North America since 1992 and was the first digital technology to be commercially deployed there. As its name indicates, it is based on Time Division Multiple Access. In TDMA the resources are shared in time, combined with frequency-division multiplexing (that is, when multiple frequencies are used). As a result, TDMA offers multiple digital channels using different time slots on a shared frequency carrier. Each mobile station is assigned both a specific frequency and a time slot during which it can communicate with the base station. The TDMA transmitter is active during the assigned time slot and inactive during other time slots, which allows for power-saving terminal designs, among other advantages. North American TDMA supports three time slots, at 30 kHz each, further divided into three or six channels to maximize air interface utilization. A sequence of time-division multiplexed time slots in TDMA makes up frames, which are 40 ms long. The TDMA traffic channel total bit rate is 48.6 Kbps. Control overhead and number of users per channel, which is greater than one, decrease the effective throughput of a channel available for user traffic to 13 Kbps. TDMA is a dual-band technology, which means it can be deployed in 800-MHz and 1900-MHz frequency bands. In regions where both AMPS and TDMA are deployed, TDMA phones are often designed to operate in dual mode, analog and digital, in order to offer customers the ability to utilize coverage of the existing analog infrastructure.. Global System for Mobile Communications (GSM) There are still some analog cellular systems in operations in Europe, but their number is declining, and some regional networks are being completely shut down or converted to Global System for Mobile Communications. The GSM cellular system initiative was initiated in 1982 by the Conference of European Posts and Telecommunications Administrations (CEPT) and is currently governed by European Telecommunications Standards Institute (ETSI), which in turn has delegated GSM specifications maintenance and evolution to 3GPP (reviewed in part in Chapter 1). The intent behind GSM introduction was to have a common approach to the creation of digital systems across European countries, to allow—among other advantages of a common standard—easy international roaming and better economies of scale by decreasing handset and infrastructure components costs through mass production. In hindsight, this was a smart political decision, which contributed to the worldwide success of European cellular infrastructure providers and equipment manufacturers.. Department of ECE,SJBIT. Page 16.

(17) Wireless Communication. •. 10EC81. 2.5g Cellular Systems. "2.5G" is an informal term, invented solely for marketing purposes, unlike "2G" or "3G" which are officially defined standards based on those defined by the International Telecommunication (ITU). The term "2.5G" usually describes a 2G cellular system combined with General Packet Radio Services (GPRS), or other services not generally found in 2G or 1G networks.Wireless telecommunication technology like CDMA200 1xRTT, Enhanced Data Rates for GSM Evolution (EDGE) or Enhanced General Packet Radio Service (EGPRS), since they have data transmission rates of 144 kbps or higher, may qualify as 3G technology. However, they are usually classified as 2.5G technology because they have slower network speeds than most 3G services.. GPRS is a service commonly associated with 2.5G technology. It has data transmission rates of 28 kbps or higher. GPRS came after the development of the Global System for Mobile (GSM) service, which is classified as 2G technology, and it was succeeded by the development of the Universal Mobile Telecommunication Service (UMTS), which is classified as 3G technology.A 2.5G system may make use of 2G system infrastructure, but it implements a packet-switched network domain in addition to a circuit-switched domain. This does not necessarily give 2.5G an advantage over 2G in terms of network speed, because bundling of timeslots is also used for circuit-switched data services (HSCSD). The services and infrastructure of a 2.5G network may be used on a per-transaction basis rather than a per-minute-of-use basis, thanks to its packet-switched domain. This makes its infrastructure more efficient and improves the service delivery. This impetus is known as the "always-on" capability.2.5G networks may support services such as WAP, MMS, SMS mobile games, and search and directory.. 3G Cellular Systems. Cell phones and systems are classified by the generation they belong to. Third generation (3G) phones were developed in the late 1990s and 2000s. The goal was to improve the data capability and speed. 3G phones were defined by the Third Generation Partnership Project (3GPP) and later standardized by the ITU-T. Generally known as the Universal Mobile Telecomunications System (UMTS), this 3G system is based on wideband CDMA that operates in 5 MHz of bandwidth and can produce download data rates of typically 384 kb/s under normal conditions and up to 2 Mb/s in some instances. Another 3G standard, cdma2000, was developed by Qualcomm. It uses 1.25 MHz bands to produce data rates to 2 Mb/s. Another version of cdma2000 is an improved IS-95 version. It is a 3GPP2 standard. It can transmit data at a rate to 153 kb/s and up to 2 Mb/s in some cases.. Department of ECE,SJBIT. Page 17.

(18) Wireless Communication. 10EC81. 3G phone standards have been expanded and enhanced to further expand data speed and capacity. The WCDMA phones have added high speed packet access (HSPA) that use higher level QAM modulation to get speeds up to 21 or 42 Mb/s downlink (cell site to phone) and up to 7 and/or 14 Mb/s uplink (phone to cell site). AT&T and T-Mobile use HSPA technology. The cdma2000 phones added 1xRTT as well as Rev. A and Rev B modifications that boost speed as well. Verizon and Sprint use cdma2000 3G standard technology. Virtually all standard and smartphone models and most tablets still use some form of 3G.. Fig 1.12 3G operating environments. Department of ECE,SJBIT. Page 18.

(19) Wireless Communication. 10EC81. Table 1.1 3G characteristics by cell size and mobile speed. •. 4G Cellular Systems and Beyond. The fourth generation has been defined but we are not in it, yet. Yes, many if not most of the mobile carriers and the various phone and equipment manufacturers actually advertise 4G now. The formal definition of 4G as declared by the 3GPP and the ITU-T is something called Long Term Evolution-Advanced (LTE-A). The standard has not been fully completed but basically it is an improved and enhanced version of LTE that uses wider bandwidth channels and a greater number of MIMO antennas. The theoretical upper data rate is 1 Gb/s. That remains to be seen in practice. As for what the various companies are calling 4G, Verizon says that their LTE network is 4G. AT&T promotes their LTE and HSPA networks as 4G. T-Mobile indicates that their HSPA+ networks are 4G. Furthermore Sprint and Clearwire say that their WiMAX network is 4G. As mentioned, WiMAX is actually defined as a 3G technology by ITU-T like LTE.. Department of ECE,SJBIT. Page 19.

(20) Wireless Communication. 10EC81. UNIT - 2 Common Cellular System components, Common cellular network components, Hardware and software, views of cellular networks, 3G cellular systems components, Cellular component identification Call establishment.. 6 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS:. 1. 2. 3.. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 20.

(21) Wireless Communication. 10EC81. UNIT-2 COMMON CELLULAR SYSTEM COMPONENTS It is very much essential to implement increased system functionality to meet the demands of the increasing number of subscribers with the more sophisticated wireless cellular network. To achieve this the various hardware network elements used to create the wireless cellular network plays an important role. The network element scan be divided into three basic groups 1.The mobile or subscriber device (providers the user link to the wireless network. 2.Base station ( provides wireless system links to the subscriber over air interface) 3.Network switching system (provides interface to the PSTN and PDN ) 2.1 COMMON CELLULAR NETWORK COMPONENTS. Fig 2.1 Typical wireless cellular system components. During 1G wireless cellular system , it consists of several subsystems to perform certain operations in support of the entire system. For 2G and 2.5G cellular networks , the air interface functions are performed by fixed Radio Base Station and Mobile Station or Subscriber device that provide user mobility. The radio base station is controlled by a base station controller which is referred as base station system. The base station system is connected to a fixed switching system that handles the routing of both voice calls and data services to and from the mobile switching centre and various databases and functional nodes to support the mobility management and security operations of the system. The switching system is usually connected to the PSTN , the PDN , other public land mobile networks(PLMN ) and various data messaging networks through gate way switches. Department of ECE,SJBIT. Page 21.

(22) Wireless Communication. 10EC81. The various network elements that make up the wireless system are interconnected by communication links that transport system messages between network elements to facilitate network operations and deliver the actual voice call or data services information. SUBSCRIBER DEVICES: The subscriber device is the link between the customer and the wireless network. The SD must be able to provide a means for the subscriber to control and input information to the phone and display its operation status.. Fig 2.2 subscriber device. The subscriber device must be able to sample , digitize and process audio and other multimedia signals, transmit and receive RF signals, process system control messages and provide the power needed to operate the complex electronics subsystems . A SD consists of man machine interface, an RF transceiver section a signal processing section , a system control processor and a power supply/ management section. BASE STATION SYSTEM COMPONENTS: The Base station system handles all radio interface related functions for the wireless network .The BSS consists of several to many radio base stations , a base station contr5oller , Transcoder controller .The radio equipment required to serve one cell is typically called a base transceiver system. A single radio base station might contain three base transceiver systems which is used to serve a cell site that consists of three 120 degree sectors or cells.. Department of ECE,SJBIT. Page 22.

(23) Wireless Communication. 10EC81. Fig 2.3. components of base station system. Typical CDMA wireless system The base station controller functions as the interface between mobile switching centre and packet core network and all the radio base stations controlled by BSC. The BSC system provides timing signals and connectivity to every subsystem within it and computer interfaces to the entire system. The BSC will supply signaling towards the MSC using message transfer part protocol to transfer the message over a PCM link connected to SS7 signaling terminals located within MSC and the BSC. The TRC consists of subsystems that perform transcoding and rate adaptation which can be either stand alone or combined. REGISTERS IN WIRELESS SYSTEMS: VISITOR LOCATION REGISTER:. It is a database that temporarily stores information about any mobile station that attaches to a RBS in the area services by a particular MSC. This temporary subscriber information is required by the MSC to provide service to a visiting subscriber . HOME LOCATION REGISTER:. It is a data base that stores information about every user that has a cellular service contract with specific wireless service provider . This database stores permanent data about the networks subscribers, information about the subscribers present location. The HLR also plays a major role in the process of handling calls terminating at the MS. The HLR analyzes the information about the incoming call and controls the routing of the call. AUC Interconnection: The AUC provides authentication and encryption information for the MS being used in the cellular network. Upon a request from a VLR the HLR will be delivered a triplet for a particular mobile subscriber .the HLR receives the triplet information in response to a Department of ECE,SJBIT. Page 23.

(24) Wireless Communication. 10EC81. request to the AUC for verification of a subscriber. The HLR forwards the random number and returns it to the MSC/VLR and from there to the HLR .The AUC contains a processor, a database for the storage of key information for each subscriber maintenance functions for subscriber and an interface fro communication with HLR. EQUIPMENT IDENTITY REGISTER: Then EIR database is used to validate then status of mobile equipment . This global database is updated daily to reflect the current status of an MS. The MS can be black listed indicating that it has been reported stolen or missing and does not approve for network operation. INTERWORKING UNITS: IWUs are required to provide an interface to various data networks. These nodes are used to connect the base station controller and hence the radio base stations to various data services networks. GATEWAYS and its types 1. Gateway MSC: (GMSC)gateway MSC is an MSC that interfaces the wireless mobile network to other telecommunication networks. A cellular network will have numerous MSCs to facilitate coverage of large area but all switching centers need to be connected to other wireline network .to support its function as gateway the GMSC will have ability to reroute a call to an MS using the information provided by the HLR of a subscriber. 2. Billing gateway : (BGW) this collects billing information from various wireless network elements which becomes a file use by customer administrative system to generate billing information for the system subscribers like monthly access fees, home usage , roaming , data and special services etc., 3. Service order Gateway :(SOG) It is used to connect a customer administrative system to the switching system. This system is used to input new subscriber data to the HLR or to update current subscriber data already contained in the HLR. The SOG allows access to the AUC and EIR for equipment administration. When a customer signs a service contract with cellular service provider the information about the contract is entered into the customer administrative system.. 2.2 HARDWARE AND SOFTWARE VIEWS OF CELLULAR NETWORK: – Hardware view of a cellular network •. Serving areas. •. Cells MSC boundaries. Department of ECE,SJBIT. Page 24.

(25) Wireless Communication. 10EC81. Fig 2.4. –. Hardware view of cellular network. Software view of a cellular network •. Location area identity. •. Cell global identity. •. Mobile country code and network code. Fig 2.5. Software view of Cellular system. 2.3 3G Cellular System Components –. Core network. –. Radio access network. Department of ECE,SJBIT. Page 25.

(26) Wireless Communication. 10EC81. –. Radio network controller. –. Radio base station. Fig 2.6. The 3G radio network controller. 2.4 Cellular Component Identification –. Subscriber device identification •. Mobile station ISDN identification number –. North American version. –. The rest of the world. Department of ECE,SJBIT. Page 26.

(27) Wireless Communication. 10EC81. Fig 2.6. •. Formation of MSISDN number. Cellular Component Identification –. International mobile subscriber identity. –. International mobile equipment identity. Fig 2.7 Formation of IMSI number. Fig 2.8 Formation of IMEI number. Cellular system component addressing • Location area identity •. Cell global identity. •. Radio base station identity code. Department of ECE,SJBIT. Page 27.

(28) Wireless Communication. 10EC81. •. Location numbering. •. Addressing cellular network switching nodes. •. Global title and global title translation. • 2.5 Call Establishment – Mobile-terminated call •. PSTN messages. •. GMSC operations. •. MSC/VLR operations. •. BSC operations. Fig 2.9 Mobile terminated call operations. Mobile-originated call • Mobile operations •. Radio base station operations. •. Base station controller operations. •. MSC operations. Department of ECE,SJBIT. Page 28.

(29) Wireless Communication. 10EC81. Fig 2.10 Mobile originated call operations. – Call release •. Connection management operations. •. Radio resource operations. Department of ECE,SJBIT. Page 29.

(30) Wireless Communication. 10EC81. Fig 2.11 Call release. The above figure shows the operation during release of a mobile call through MSC . the steps involved as shown in detail which is self explanatory.. Department of ECE,SJBIT. Page 30.

(31) Wireless Communication. 10EC81. UNIT - 3 Wireless network architecture and operation, Cellular concept Cell fundamentals, Capacity expansion techniques, Cellular backbone networks, Mobility management, Radio resources and power management Wireless network security. 6 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS:. 1. 2. 3.. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 31.

(32) Wireless Communication. 10EC81. UNIT-3 WIRELESS NETWORK ARCHITECTURE AND OPERATION 3.1 The Cellular Concept Solves the problem of spectral congestion and user capacity,Offer very high capacity in a limited spectrum without major technological changes,Reuse of radio channel in different cells.Enable a fix number of channels to serve an arbitrarily large number of users by reusing the channel throughout the coverage region.Simplex and duplex. Each cellular base station is allocated a group of radio channels within a small geographic area called a cell.Neighboring cells are assigned different channel groups. By limiting the coverage area to within the boundary of the cell, the channel groups may be reused to cover different cells.Keep interference levels within tolerable limits. Frequency reuse or frequency planning seven groups of channel from A to G.footprint of a cell - actual radio coverage ,omni-directional antenna v.s. directional antenna. Steps for frequency reuse: Consider a cellular system which has a total of S duplex channels. • Each cell is allocated a group of k channels, . • The S channels are divided among N cells. • The total number of available radio channels • •. The N cells which use the complete set of channels is called cluster. The cluster can be repeated M times within the system. The total number of channels, C, is used as a measure of capacity. • • • • •. The capacity is directly proportional to the number of replication M. The cluster size, N, is typically equal to 4, 7, or 12. Small N is desirable to maximize capacity. The frequency reuse factor is given by Hexagonal geometry has – exactly six equidistance neighbors – the lines joining the centers of any cell and each of its neighbors are separated by multiples of 60 degrees. Only certain cluster sizes and cell layout are possible. The number of cells per cluster, N, can only have values which satisfy Co-channel neighbors of a particular cell, ex, i=3 and j=2.. • • • •. The Cellular Concept – Cellular hierarchy. Department of ECE,SJBIT. Page 32.

(33) Wireless Communication • • • •. 10EC81. Picocells Microcells Macrocells Megacells and femtocells. Fig 3.1 Cellular concept 3.2 Cell Fundamentals – The use of hexagons – Reuse number • Cellular reuse patterns. Fig 3.2 Frequency reuse concept •. Frequency reuse scheme – increases capacity. Department of ECE,SJBIT. Page 33.

(34) Wireless Communication. • •. •. •. 10EC81. – minimize interference Channel assignment strategy – fixed channel assignment – dynamic channel assignment Fixed channel assignment – each cell is allocated a predetermined set of voice channel – any new call attempt can only be served by the unused channels – the call will be blocked if all channels in that cell are occupied Dynamic channel assignment – channels are not allocated to cells permanently. – allocate channels based on request. – reduce the likelihood of blocking, increase capacity. Cell Fundamentals – Reuse number • Frequency reuse distance – The reuse distance can be calculated by using the equation:. Fig 3.3 Frequency Reuse number •. Cell Fundamentals – Cellular interference issues • Signal-to-interference ratio • Channel assignments. Fig 3.4 Cellular calculations. 3.3 Capacity Expansion Techniques Cell splitting Department of ECE,SJBIT. Page 34.

(35) Wireless Communication. • •. 10EC81. Split congested cell into smaller cells. – Preserve frequency reuse plan. – Reduce transmission power. Transmission power reduction from to Examining the receiving power at the new and old cell boundary. •. If we take n = 4 and set the received power equal to each other. •. The transmit power must be reduced by 12 dB in order to fill in the original coverage area. Problem: if only part of the cells are splited – Different cell sizes will exist simultaneously Handoff issues - high speed and low speed traffic can be simultaneously accommodated. • •. Fig 3.5 cell splitting •. Capacity Expansion Techniques – Cell sectoring • Sectoring concept. •. Decrease the co-channel interference and keep the cell radius R unchanged – Replacing single omni-directional antenna by several directional antennas – Radiating within a specified sector. Department of ECE,SJBIT. Page 35.

(36) Wireless Communication. 10EC81. Fig 3.6 Cell sectoring •. Capacity Expansion Techniques – Overlaid cells • Overlay concept. Fig 3.7 Cell overlaid •. Capacity Expansion Techniques – Channel allocation – Other capacity expansion schemes • Lee’s microcell technology • Smart antenna technology • Migration to digital technology • 3.4 Cellular Backhaul Networks – Introduction – Standards for PSTN carriers. Department of ECE,SJBIT. Page 36.

(37) Wireless Communication. 10EC81. Fig 3.8. cellular backhaul network. Fig 3.9. cellular backhaul network. 3.5 Mobility Management – Location management • Need • Frequency • Location updating. Department of ECE,SJBIT. Page 37.

(38) Wireless Communication. 10EC81. Fig 3.10 Location management in cellular network •. •. • • •. Mobility Management – Paging messages – Different paging schemes – Transmission of the location information between network elements Mobility Management – Handoff management • Handoff control • Handoff operation • Handoff algorithm When a mobile moves into a different cell while a conversation is in progress, the MSC automatically transfers the call to a new channel belonging to the new base station. Handoff operation – identifying a new base station – re-allocating the voice and control channels with the new base station. Handoff Threshold – Minimum usable signal for acceptable voice quality (-90dBm to -100dBm) – Handoff margin cannot be too large or too small. – If it is too large, unnecessary handoffs burden the MSC – If it is too small, there may be insufficient time to complete handoff before a call is lost.. Department of ECE,SJBIT. Page 38.

(39) Wireless Communication. 10EC81. Fig 3.10 Mobility management in cellular network •. Handoff must ensure that the drop in the measured signal is not due to momentary fading and that the mobile is actually moving away from the serving base station.. •. Running average measurement of signal strength should be optimized so that unnecessary handoffs are avoided. – Depends on the speed at which the vehicle is moving. – Steep short term average -> the hand off should be made quickly – The speed can be estimated from the statistics of the received short-term fading signal at the base station. •. Dwell time: the time over which a call may be maintained within a cell without handoff.. •. Dwell time depends on – propagation – interference – distance – speed. Department of ECE,SJBIT. Page 39.

(40) Wireless Communication •. 10EC81. •. Handoff measurement – In first generation analog cellular systems, signal strength measurements are made by the base station and supervised by the MSC. – In second generation systems (TDMA), handoff decisions are mobile assisted, called mobile assisted handoff (MAHO) Intersystem handoff: If a mobile moves from one cellular system to a different cellular system controlled by a different MSC. Handoff requests is much important than handling a new call.. •. Different type of users. •. High speed users need frequent handoff during a call. Low speed users may never need a handoff during a call. • • • •. Microcells to provide capacity, the MSC can become burdened if high speed users are constantly being passed between very small cells. Minimize handoff intervention – handle the simultaneous traffic of high speed and low speed users. Large and small cells can be located at a single location (umbrella cell) – different antenna height – different power level Cell dragging problem: pedestrian users provide a very strong signal to the base station – The user may travel deep within a neighboring cell. Handoff for first generation analog cellular systems ,10 secs handoff time, is in the order of 6 dB to 12 dB,Handoff for second generation cellular systems, e.g., GSM 1 to 2 seconds handoff time, mobile assists handoff , is in the order of 0 dB to 6 dB Handoff decisions based on signal strength, co-channel interference, and adjacent channel interference. IS-95 CDMA spread spectrum cellular system ,Mobiles share the channel in every cell.No physical change of channel during handoff ,MSC decides the base station with the best receiving signal as the service station Handoff within a cell, No channel reassignment, Switch the channel to a different zone site, Reduce interference, Low power transmitters are employed •. Frequency reuse - there are several cells that use the same set of frequencies – co-channel cells – co-channel interference. •. To reduce co-channel interference, co-channel cell must be separated by a minimum distance.. •. When the size of the cell is approximately the same. Department of ECE,SJBIT. Page 40.

(41) Wireless Communication. 10EC81. – –. •. co-channel interference is independent of the transmitted power co-channel interference is a function of • R: Radius of the cell • D: distance to the center of the nearest co-channel cell • Increasing the ratio Q=D/R, the interference is reduced.. •. Q is called the co-channel reuse ratio. Fig 3.11 Handoff management. Department of ECE,SJBIT. Page 41.

(42) Wireless Communication. 10EC81. Fig 3.12 analysis of handoff operation. 3.6 Radio Resources and Power Management – –. –. Power control Power saving schemes • Discontinuous transmission • Sleep modes • Energy efficient designs Radio resource management • Need • Schemes. 3.7 Wireless Network Security – – –. Wireless network security requirements Network security requirements Network security. Department of ECE,SJBIT. Page 42.

(43) Wireless Communication. 10EC81. UNIT - 4 GSM and TDMA techniques, GSM system overview, GSM Network and system Architecture, GSM channel concepts, GSM identifiers. 6 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS: 1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. 2. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. 3. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 43.

(44) Wireless Communication. 10EC81. Unit-4 GSM AND TDMA TECHNOLOGIES 4.1 Introduction to GSM and TDMA Global System for Mobile Communications (GSM) services are a standard collection of applications and features available to mobile phone subscribers all over the world. The GSM standards are defined by the 3GPP collaboration and implemented in hardware and software by equipment manufacturers and mobile phone operators. The common standard makes it possible to use the same phones with different companies' services, or even roam into different countries. GSM is the world's most dominant mobile phone standard. The design of the service is moderately complex because it must be able to locate a moving phone anywhere in the world, and accommodate the relatively small battery capacity, limited input/output capabilities, and weak radio transmitters on mobile devices. In order to gain access to GSM services, a user needs three things: .  . A billing relationship with a mobile phone operator. This is usually either where services are paid for in advance of them being consumed (prepaid), or where bills are issued and settled after the service has been consumed (postpaid). A mobile phone that is GSM compliant and operates at the same frequency as the operator. Most phone companies sell phones from third-party manufacturers. A Subscriber Identity Module (SIM) card, which is activated by the operator once the billing relationship is established. After activation the card is then programmed with the subscriber's Mobile Subscriber Integrated Services Digital Network Number (MSISDN) (the telephone number). Personal information such as contact numbers of friends and family can also be stored on the SIM by the subscriber.. After subscribers sign up, information about their identity (telephone number) and what services they are allowed to access are stored in a "SIM record" in the Home Location Register (HLR). Once the SIM card is loaded into the phone and the phone is powered on, it will search for the nearest mobile phone mast (also called a Base Transceiver Station/BTS) with the strongest signal in the operator's frequency band. If a mast can be successfully contacted, then there is said to be coverage in the area. The phone then identifies itself to the network through the control channel. Once this is successfully completed, the phone is said to be attached to the network. The key feature of a mobile phone is the ability to receive and make calls in any area where coverage is available. This is generally called roaming from a customer perspective, but also called visiting when describing the underlying technical process. Each geographic area has a database called the Visitor Location Register (VLR), which contains details of all the mobiles currently in that area. Whenever a phone attaches, or visits, a new area, the Visitor Location Register must contact the Home Location Register to obtain the details for that phone. The current cellular location of the phone (i.e., which BTS it is at) is entered into. Department of ECE,SJBIT. Page 44.

(45) Wireless Communication. 10EC81. the VLR record and will be used during a process called paging when the GSM network wishes to locate the mobile phone. Every SIM card contains a secret key, called the Ki, which is used to provide authentication and encryption services. This is useful to prevent theft of service, and also to prevent "over the air" snooping of a user's activity. The network does this by utilising the Authentication Center and is accomplished without transmitting the key directly. Every GSM phone contains a unique identifier (different from the phone number), called the International Mobile Equipment Identity (IMEI). This can be found by dialing *#06#. When a phone contacts the network, its IMEI may be checked against the Equipment Identity Register to locate stolen phones and facilitate monitoring.. TDMA It can be easily adapted to the transmission of data and voice communication. TDMA offers the ability to carry data rates of 64 kbps to 120 Mbps (expandable in multiples of 64 kbps). This enables operators to offer personal communication-like services including fax, voiceband data, and short message services (SMSs) as well as bandwidth-intensive applications such as multimedia and videoconferencing. It will not experience interference from other simultaneous transmissions Unlike spread-spectrum techniques which can suffer from interference among the users all of whom are on the same frequency band and transmitting at the same time, TDMA’s technology, which separates users in time, ensures that they will not TDMA is the only technology that offers an efficient utilization of hierarchical cell structures (HCSs) offering pico, micro, and macrocells. HCSs allow coverage for the system to be tailored to support specific traffic and service Department of ECE,SJBIT. Page 45.

(46) Wireless Communication. 10EC81. needs. By using this approach, system capacities of more than 40-times AMPS can be achieved in a cost-efficient way. TDMA allows service compatibility with the use of dual-mode handsets because of its inherent compatibility with FDMA analog systems.. 4.2 GSM Network and System Architecture Mobile station • Subscriber identity module Base station system – Network switching system. –. •. SMS gateway. •. Flexible numbering register. Operation and support system and other nodes •. Administrative and control system. Fig 4.1 components of GSM network GSM network interfaces and protocols • GSM interfaces –. Abis interface. –. A interface. Department of ECE,SJBIT. Page 46.

(47) Wireless Communication. 10EC81 –. Um interface. –. Layered structure/OSI model. Fig 4.2 interfaces in GSM. GSM network interfaces and protocols • GSM protocols and signaling model –. Um interface. –. Abis interface. –. A interface. –. Ater interface. The network structure is defined within the GSM standards. Additionally each interface between the different elements of the GSM network is also defined. This facilitates the information interchanges can take place. It also enables to a large degree that network elements from different manufacturers can be used. However as many of these interfaces were not fully defined until after many networks had been deployed, the level of standardisation may not be quite as high as many people might like.. 1. Um interface The "air" or radio interface standard that is used for exchanges between a mobile (ME) and a base station (BTS / BSC). For signalling, a modified version of the ISDN LAPD, known as LAPDm is used. 2. Abis interface This is a BSS internal interface linking the BSC and a BTS, and it has not been totally standardised. The Abis interface allows control of the radio equipment and radio frequency allocation in the BTS. 3. A interface The A interface is used to provide communication between the BSS and the MSC. The interface carries information to enable the channels, timeslots and the like to be allocated to the mobile equipments being serviced by the BSSs. Department of ECE,SJBIT. Page 47.

(48) Wireless Communication. 10EC81. The messaging required within the network to enable handover etc to be undertaken is carried over the interface. 4. B interface The B interface exists between the MSC and the VLR . It uses a protocol known as the MAP/B protocol. As most VLRs are collocated with an MSC, this makes the interface purely an "internal" interface. The interface is used whenever the MSC needs access to data regarding a MS located in its area. 5. C interface The C interface is located between the HLR and a GMSC or a SMS-G. When a call originates from outside the network, i.e. from the PSTN or another mobile network it ahs to pass through the gateway so that routing information required to complete the call may be gained. The protocol used for communication is MAP/C, the letter "C" indicating that the protocol is used for the "C" interface. In addition to this, the MSC may optionally forward billing information to the HLR after the call is completed and cleared down. 6. D interface The D interface is situated between the VLR and HLR. It uses the MAP/D protocol to exchange the data related to the location of the ME and to the management of the subscriber. 7. E interface The E interface provides communication between two MSCs. The E interface exchanges data related to handover between the anchor and relay MSCs using the MAP/E protocol. 8. F interface The F interface is used between an MSC and EIR. It uses the MAP/F protocol. The communications along this interface are used to confirm the status of the IMEI of the ME gaining access to the network. 9. G interface The G interface interconnects two VLRs of different MSCs and uses the MAP/G protocol to transfer subscriber information, during e.g. a location update procedure. 10. H interface The H interface exists between the MSC the SMS-G. It transfers short messages and uses the MAP/H protocol. 11. I interface The I interface can be found between the MSC and the ME. Messages exchanged over the I interface are relayed transparently through the BSS. Although the interfaces for the GSM cellular system may not be as rigorously defined as many might like, they do at least provide a large element of the definition required, enabling the functionality of GSM network entities to be defined sufficiently.. Department of ECE,SJBIT. Page 48.

(49) Wireless Communication. 10EC81. Fig 4.3 GSM network interfaces and protocols. 4.3 GSM Channel Concept –. Time division multiple access. –. Frames Multiframes. A single GSM RF carrier can support up to eight MS subscribers simultaneously. Each channel occupies the carrier for one eighth of the time. This is a technique called Time Division Multiple Access. Time is divided into discrete periods called â€œtimeslotsâ€•. The timeslots are arranged in sequence and are conventionally numbered 0 to 7. Each repetition of this sequence is called a â€œTDMA frameâ€•. Each MS telephone call occupies one timeslot (0â€“7) within the frame until the call is terminated, or a handover occurs. The TDMA frames are then built into further frame structures according to the type of channel. We shall later examine how the information carried by the air interface builds into frames and multi-frames and discuss the associated timing. For such a system to work correctly, the timing of the transmissions to and from the mobiles is critical. The MS or Base Station must transmit the information related to one call at exactly the right moment, or the timeslot will be missed. The information carried in one timeslot is called a â€œburstâ€•. Each data burst, occupying its allocated timeslot within successive TDMA frames, provides a single GSM physical channel carrying a varying number of logical channels between the MS and BTS.. Department of ECE,SJBIT. Page 49.

(50) Wireless Communication. 10EC81. Fig 4.4 TDMA time frame structure GSM Channel Concept – Logical channels •. –. –. –. Broadcast control channel. –. Frequency correction channel. Synchronization channel Logical channels •. –. Broadcast channels. Common control channels –. Paging channel. –. Random access channel. –. Access grant channel. Dedicated control channels •. Stand-alone dedicated control channel. •. Slow associated control channel. •. Fast associated control channel. •. Cell broadcast channel. Speech processing •. Operations Bit rate. GSM speech processing. Department of ECE,SJBIT. Page 50.

(51) Wireless Communication. 10EC81. Fig 4.5 GSM processing of speech Timeslots and TDMA frames • TDMA frames –. TDMA multiframes Hyperframes. –. Superframes. –. Multiframes. –. •. 26 frame. •. 51 frame. Timeslot bursts •. Normal burst. •. Frequency correction burst. •. Synchronization burst. •. Access burst Dummy burst. Department of ECE,SJBIT. Page 51.

(52) Wireless Communication. 10EC81. Fig 4.6 TDMA Hyperframe structure A hyperframe is a multiframe sequence that is composed of 2048 superframes and is largest time interval in the GSM system (3 hours, 28 minutes, 53 seconds). Every time slot during a hyperframe has a sequential number (represented by an 11 bit counter) that is composed of a frame number and a time slot number. This counter allows the hyperframe to synchronize frequency hopping sequence, encryption processes for voice privacy of subscribers' conversations. The hyperframe in an IS-136 TDMA system consists of 192 frames. The basic GSM frame defines the structure upon which all the timing and structure of the GSM messaging and signalling is based. The fundamental unit of time is called a burst period and it lasts for approximately 0.577 ms (15/26 ms). Eight of these burst periods are grouped into what is known as a TDMA frame. This lasts for approximately 4.615 ms (i.e.120/26 ms) and it forms the basic unit for the definition of logical channels. One physical channel is one burst period allocated in each TDMA frame. In simplified terms the base station transmits two types of channel, namely traffic and control. Accordingly the channel structure is organised into two different types of frame, one for the traffic on the main traffic carrier frequency, and the other for the control on the beacon frequency.. GSM multiframe Department of ECE,SJBIT. Page 52.

(53) Wireless Communication. 10EC81. The GSM frames are grouped together to form multiframes and in this way it is possible to establish a time schedule for their operation and the network can be synchronised. There are several GSM multiframe structures: . . Traffic multiframe: The Traffic Channel frames are organised into multiframes consisting of 26 bursts and taking 120 ms. In a traffic multiframe, 24 bursts are used for traffic. These are numbered 0 to 11 and 13 to 24. One of the remaining bursts is then used to accommodate the SACCH, the remaining frame remaining free. The actual position used alternates between position 12 and 25. Control multiframe: the Control Channel multiframe that comprises 51 bursts and occupies 235.4 ms. This always occurs on the beacon frequency in time slot zero and it may also occur within slots 2, 4 and 6 of the beacon frequency as well. This multiframe is subdivided into logical channels which are time-scheduled.. GSM Superframe Multiframes are then constructed into superframes taking 6.12 seconds. These consist of 51 traffic multiframes or 26 control multiframes. As the traffic multiframes are 26 bursts long and the control multiframes are 51 bursts long, the different number of traffic and control multiframes within the superframe, brings them back into line again taking exactly the same interval.. GSM Hyperframe Above this 2048 superframes (i.e. 2 to the power 11) are grouped to form one hyperframe which repeats every 3 hours 28 minutes 53.76 seconds. It is the largest time interval within the GSM frame structure. Within the GSM hyperframe there is a counter and every time slot has a unique sequential number comprising the frame number and time slot number. This is used to maintain synchronisation of the different scheduled operations with the GSM frame structure. These include functions such as: . . Frequency hopping: Frequency hopping is a feature that is optional within the GSM system. It can help reduce interference and fading issues, but for it to work, the transmitter and receiver must be synchronised so they hop to the same frequencies at the same time. Encryption: The encryption process is synchronised over the GSM hyperframe period where a counter is used and the encryption process will repeat with each hyperframe. However, it is unlikely that the cellphone conversation will be over 3 hours and accordingly it is unlikely that security will be compromised as a result.. Department of ECE,SJBIT. Page 53.

(54) Wireless Communication. 10EC81. UNIT - 5 GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture. TDMA systems. 6 Hours. TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS: 1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. 2. 3. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, Cambridge 2005.. Department of ECE,SJBIT. Page 54.

(55) Wireless Communication. 10EC81. UNIT-5 GSM SYSTEM OPERATIONS GSM Identities. 5.1. To switch a call to a mobile subscriber, the right identities need to be involved. It is therefore important to address them correctly. Followings are those identities; Mobile Station ISDN Number (MSISDN) The MSISDN is a number, which uniquely identifies a mobile telephone subscription in the public switched telephone network numbering plan. These are the digits dialed when calling a mobile subscriber. The MSISDN is consisted with followings;   . Country Code (CC) National Destination Code (NDC) Subscriber Number (SN) MSISDN = CC + NDC + SN. International Mobile Subscriber Identity (IMSI) The IMSI is a unique identity allocated to each subscriber to allow correct identification over the radio path and through the network and is used for all signaling in the PLMN. All network-related subscriber information is connected to the IMSI. The IMSI is stored in the SIM, as well as in the HLR and in the serving VLR. The IMSI is consisted with followings;   . Mobile Country Code (MCC) Mobile Network Code (MNC) Mobile Subscriber Identification Number (MSIN ) IMSI = MCC + MNC + MSIN. Temporary Mobile Subscriber Identity (TMSI) The TMSI is a temporary number used instead of IMSI to identify an MS. The TMSI is used for the subscriber’s confidentiality on the air interface. The TMSI has only local significance (that is, within the MSC/VLR area) and is changed at certain events or time intervals.. Department of ECE,SJBIT. Page 55.

(56) Wireless Communication. 10EC81. International Mobile Equipment Identity (IMEI) The IMEI is used for equipment identification and uniquely identifies a MS as a piece or assembly of equipment. The IMEI is consisted with followings;    . Type Approval Code (TAC), determined by a central GSM body Final Assembly Code (FAC), identifies the manufacture Serial Number (SNR), uniquely identifies all equipment within each TAC & FAC Spare, a spare bit for future use. IMEI = TAC + FAC + SNR + Spare. Mobile Station Roaming Number (MSRN) A MSRN is used during the call setup phase for mobile terminating calls. Each mobile terminating call enters the GMSC in the PLMN. The call is then re-routed by the GMSC, to the MSC where the called mobile subscriber is located. For this purpose MSRN is allocated by the MSC and provided to the GMSC. The MSRN is consisted with followings;   . Country Code (CC) National Destination Code (NDC) Subscriber Number (SN) MSRN = CC + NDC + SN. Location Area Identity (LAI) The LAI is used for paging, to indicate to the MSC in which Location Area (LA) the MS is currently situated and also for location updating of mobile subscribers. The LAI is consisted with followings;   . Mobile Country Code (MCC) Mobile Network Code (MNC) Location Area Code (LAC) LAI = MCC + MNC + LAC. Department of ECE,SJBIT. Page 56.

(57) Wireless Communication. 10EC81. Cell Global Identity (CGI) Each cell is identified by cell identity (CI). A CI is unique within a location area (LA). CGI is consisted with following;    . Mobile Country Code (MCC) Mobile Network Code (MNC) Location Area Code (LAC) Cell Identity (CI) CGI = MCC + MNC + LAC + CI. Base Station Identification Code (BSIC) In GSM, the mobile station uses BSIC to distinguish between neighboring base station. The BSIC is consisted with  . Network Colour Code (NCC) Base Transceiver Colour Code (BCC).. 5.2 GSM System Operations (Traffic Cases) Registration, call setup, and location updating • Call setup. •. –. Interrogation phase. –. Radio resource connection establishment. –. Service request. –. Authentication. GSM System Operations (Traffic Cases) –. Call setup •. Ciphering mode setting. •. IMEI check. •. TMSI reallocation. •. Call initiation procedure. Department of ECE,SJBIT. Page 57.

(58) Wireless Communication. •. 10EC81. •. Assignment of a traffic channel. •. Call confirmation, call accepted, and call release. GSM System Operations (Traffic Cases) –. Other aspects of call establishment •. Location updating –. Normal location updating (idle mode). –. IMSI detach/attach location updating. –. Periodic location updating. Fig 5.1 GSM channel assignment. Department of ECE,SJBIT. Page 58.

(59) Wireless Communication. 10EC81. Fig 5.2 GSM channel establishment GSM System Operations (Traffic Cases) Call handoff • Intra-BSC handover The process that occurs during the handover intra BSC as follows: A). During the call, MS will measure the strength and quality of the signal on the TCH and the signal strength from the neighboring cell. MS to evaluate and assess the average for each cell. MS send the results to the BTS measurements every two times in one second cell not only on their own but also the results of measurements from the BTS neighboring cell. B). The BTS will send the results of measurements on the TCH to the BSC. In the BSC, the function is activated when the placement is required to handover to another cell. C). When the handover is done, BSC will check whether the channel had requested be met by another cell, if not the BSC will be the new BTS to enable TCH. D). BSC will ask the BTS for a long time to send a message to MS with information about the frequency, time slot, and the output power for the change. E). MS choose a new frequency handover and access to the appropriate time slot. F). When the BTS to detect the handover, the BTS will send the information contains the physical "timing advance" (the distance between MS to the BTS) to Department of ECE,SJBIT. Page 59.

(60) Wireless Communication. 10EC81. MS. BTS also inform the BSC to send a "message HO detection" so that point on the new GS is connected. G). MS send a "HO complete message." H). Last time the BTS ordered not to activate the old TCH.. Fig 5.3 Intra BSC handover. Inter-BSC handover In this case BSC1, (old BSC) does not control the better cell which is the target for the handover. This means that the MSC will be part of the link procedure between BSC1 and BSC2 (new BSC). Handover request - BSC1 will use the MSC to send a handover request to BSC2. The MSC will know which BSC controls that cell. Activation of new channel - BSC2 will allocate a TCH in the targetcell and then order the BTS to activate it. The chosen HO ref. no. will be part of the activation message. The BTS will acknowledge that the activation has been made. Handover command - After the activation the new BSC commands the MS to change to the new channel. The message is sent on FACCH via the old channel and will contain a full description of the new channel and the HO ref. no.. Department of ECE,SJBIT. Page 60.

(61) Wireless Communication. 10EC81. 3. Handover bursts - When the MS has changed to the new channel, it will send handover bursts on the new channel. The information content is the HO ref. no. The bursts are as short as the access bursts. This is because the MS does not know the new Timing Advance (TA) value yet. On the detection of the handover bursts, and check of HO ref. no., the new BTS will send the new TA. 4. Handover complete - Now the MS is ready to continue the traffic and will send a handover complete message, which will be addressed to the old BSC as a clear command. 5. Release of old channel - When the old BSC receives the clear command from the MSC, the BSC knows that the handover was successful. The BSC orders the BTS to release the TCH and the BTS will acknowledge.. Fig 5.4 Inter BSC handover. Inter-MSC handover Handing over a GSM call is a complicated procedure. It is even more so when the source and target GSM cells are controlled by different MSCs. The following call flows analyze the different steps involved in a inter-MSC handover:  . The source BSC analyzes the signal quality measurement reports and initiates a handover. The source MSC finds that the call needs to be handed over to a cell controlled by a different MSC.. Department of ECE,SJBIT. Page 61.

(62) Wireless Communication   . 10EC81. The source MSC and target MSC interact and then command the UT to move to the new cell. The target MSC informs the source MSC when the call has been successfully handed over. The source MSC releases the radio resources for the call. Note that the call is still routed via the source MSC. Fig 5.5 Inter MSC handover. GSM Infrastructure Communications (Um Interface) A GSM network is a bearer data communication protocol families. Any protocol stack for data communication, for example TCP/IP, can be implemented to use a bearer. GSM protocol architecture is - as for ISDN - structured into three independent planes . User plane ,Control plane,Management plane The user plane defines protocols to carry connection oriented voice and user data. At the radio interface Um, user plane data will be carried by the logical traffic channel called TCH. The control plane defines a set of protocols for controlling these connections with signalling information, for example signalling for connection setup. Such signalling data is carried over logical control channels called D-channels (DmDepartment of ECE,SJBIT. Page 62.

(63) Wireless Communication. 10EC81. channels). As the control channels often have spare capacities, also user data, the packet oriented SMS data, is transported over these channels (see Figure gsm8). All logical channels, however, will be finally multiplexed onto the physical channel.. Management plane function are:  . plane management functions related to the system as a whole including plane coordination functions related to resources and parameters residing in the layers of the control and/or user plane.. Management of network element configuration and network element faults are examples of management plane functionality The basic GSM bearer service, Circuit Switched Data (CSD), simply consists of transmitting and receiving signals representing data instead of voice across the air interface. Modems are used for the conversion between data bit streams and modulated radio signals. Data transmission is either transparent or non-transparent.. Department of ECE,SJBIT. Page 63.

(64) Wireless Communication. 10EC81. Fig: 5.6 Three layers of interface in GSM. Department of ECE,SJBIT. Page 64.

(65) Wireless Communication. 10EC81. Fig: 5.7 Linking of Three layers of interface in GSM. •. GSM Infrastructure Communications (Um Interface) –. Layer 3: Networking layer operations •. Connection management. •. Mobility management. •. Radio resource management. Department of ECE,SJBIT. Page 65.

(66) Wireless Communication. 10EC81. Fig: 5.8 Linking of RR, RM and MM in GSM. •. GSM Infrastructure Communications (Um Interface) –. •. Layer 2: Data Link layer operations •. LAPD operations. •. Service access points. •. Data link procedures. •. Physical services required by the Data Link layer. •. Data link timers. North American TDMA –. TIA/EIA-136 basics. –. TIA/EIA-136 channel concept. –. TIA/EIA-136 timeslots and frame details. Department of ECE,SJBIT. Page 66.

(67) Wireless Communication. 10EC81. Fig: 5.9 NA -TDMA structure. Department of ECE,SJBIT. Page 67.

(68) Wireless Communication. 10EC81. UNIT - 6 CDMA technology, CDMA overview, CDMA channel concept CDMA operations.. 8 Hours TEXT BOOK: 1.. Wireless Telecom Systems and networks, Mullet: Thomson Learning 2006.. REFERENCE BOOKS: 1. Mobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. 2. Wireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. Fundamentals of Wireless Communication, David Tse, Pramod Viswanath, 3. Cambridge 2005.. Department of ECE,SJBIT. Page 68.

(69) Wireless Communication. 10EC81. UNIT- 6 CDMA TECHNOLOGY. 6.1 Introduction to CDMA Cellular services are now being used every day by millions of people worldwide. The number of customers requiring such services is increasing exponentially, and there is a demand for integration of a variety of multimedia services. The range of services includes short messaging, voice, data, and video. Consequently, the bit rate required for the services varies widely from just 1.2 kbps for paging up to several Mbps for video transmission. Furthermore, supporting such a wide range of data rates with flexible mobility management increases network complexity dramatically. The CDMA is a digital modulation and radio access system that employs signature codes (rather than time slots or frequency bands) to arrange simultaneous and continuous access to a radio network by multiple users. Contribution to the radio channel interference in mobile communications arises from multiple user access, multipath radio propagation, adjacent channel radiation and radio jamming. The spread spectrum system’s performance is relatively immune to radio interference. Cell sectorisation and voice activity used in CDMA radio schemes provide additional capacity compared to FDMA and TDMA. However, CDMA still has a few drawbacks, the main one being that capacity (number of active users at any instant of time) is limited by the access interference. Furthermore, Near-far effect requires an accurate and fast power control scheme. The first cellular CDMA radio system has been constructed in conformity with IS95 specifications and is now known commercially as cdmaOne.. Fig 6.1 comparison of different techniques. Department of ECE,SJBIT. Page 69.

(70) Wireless Communication. 10EC81. Fig 6.2 channel allocation. 6.2 CDMA Network and System Architecture. There is increasing demand for data traffic over mobile radio. The mobile radio industry has to evolve the current radio infrastructures to accommodate the expected data traffic with the efficient provision of high-speed voice traffic. The General Packet Radio Service (GPRS) is being introduced to efficiently support high-rate data over GSM. GPRS signalling and data do not travel through GSM network. The GPRS operation is supported by new protocols and new network nodes: Serving GPRS support node (SGSN) and Gateway GPRS support node (GGSN). One prominent protocol used to tunnel data through IP backbone network is the GPRS tunnel protocol (GTP). GPRS obtains user profile data using location register database of GSM network. GPRS supports quality of service and peak data rate of up to 171.2 kbps with GPRS using all 8 timeslots at the same time. GPRS uses the same modulation as that used in GSM, that is Gaussian Minimum Shift Keying (GMSK) with 4 coding schemes. GPRS packetises the user data and transports it over 1 to 8 radio channel timeslots using IP backbone network. The Enhanced Data Rates for GSM Evolution (EDGE) employs an Enhanced GPRS (EGPRS) to support data rate up to 384 kbps through optimised modulation. EGPRS support 2 modulation schemes, namely GMSK with 4 coding schemes and 8-PSK with 5 coding schemes. Unlike GPRS where header and data are encoded together, headers are encoded separately in EGPRS.. Fig 6.3 Network architecture of CDMA. CDMA Network and System Architecture Department of ECE,SJBIT. Page 70.

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