ECE-VIII-WIRELESS COMMUNICATION [10EC81]-NOTES.pdf

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Wireless Communication 10EC81

Subject Code : 10EC8110EC81 IA Marks : 25

No. of Lecture Hrs/Week : 04 Exam Hours : 03

Total no. of Lecture Hrs. : 52 Exam Marks : 100

PART - A PART - A UNIT

UNIT – 1 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 6 Hours UNIT - 2

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.

UNIT - 3

Wireless network architecture and operation, Cellular concept Cell fundamentals, Capacity expansion techniques, Cellular backbone networks, Mobility management, Radio resources andpowermanagementWirelessnetwork

UNIT - 4

GSM and TDMA techniques, GSM system overview, GSM Network and system Architecture,GSMchannelconcepts,GSM 6 Hours 6 Hours PART - B PART - B UNIT - 5 UNIT - 5

GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture. TDMA systems

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UNIT - 6 UNIT - 6

CDMA technology, CDMA overview, CDMA channel concept CDMA operations.. 8 hours 8 hours

UNIT - 7 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.

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 8 Hours

TEXT BOOK: TEXT BOOK:

1. Wireless Telecom Systems and networksWireless Telecom Systems and networks, Mullet: Thomson Learning 2006.

REFERENCE BOOKS: REFERENCE BOOKS:

1. Mobile Cellular TelecommunicationMobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002.

2. Wireless communicationWireless communication - D P Agrawal: 2nd Edition Thomson learning 2007. 3. Fundamentals of Wireless CommunicationFundamentals of Wireless Communication, David Tse, Pramod Viswanath,

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INDEX SHEET INDEX SHEET

Sl.No Unit

Sl.No Unit & & Topic Topic of of Discussion Discussion Page Page no.no. UNIT --- 1

UNIT --- 1

1 Introduction to wireless telecommunication systems

5 to 19 2 Introduction to wireless telecommunication Networks

3 History of different generations of wireless cellular networks

4 Evolution of different generations of wireless cellular networks

5 1G,2G networks

6 3G and 4G networks

UNIT UNIT — 22

7 Common Cellular System components

20 to 30

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

UNIT UNIT – 3 3

14 Wireless network architecture and operation

31 to 42 15 Cellular concept , Cell fundamentals

16 Capacity expansion techniques, Cellular backbone networks

17 Mobility management

18 Radio resources and power management 19 Wireless network security

UNIT --4 UNIT --4

43 to 54

20 GSM and TDMA techniques

21 GSM system overview

22 GSM Network

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Wireless Communication 10EC81 24 GSM channel concepts 25 GSM identifiers UNIT UNIT – 5 5 26 GSM system operation 55 to 67 27 Traffic cases 28 Call handoff 29 Roaming 30 GSM protocol architecture 31 TDMA systems 32 NA TDMA UNIT--6 UNIT--6 33 CDMA technology 68 to 81 34 CDMA overview

35 CDMA channel concept CDMA operations

36 CDMA channel concept CDMA operations

37 CDMA channel concept

38 CDMA channel assignement

UNIT-7 UNIT-7

40 Wireless Modulation techniques and Hardware

82 to 94 41 Characteristics of air interface , Path loss models

42 Wireless coding techniques

43 Digital modulation techniques, OFDM, UWB radio techniques

44 Diversity techniques

45 Typical GSM Hardware

UNIT-7 UNIT-7

46 Introduction to wireless LAN 802.11X technologies

95 to 108

47 Evolution of Wireless LAN

48 Introduction to 802.15X technologies in PAN architecture

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UNIT - 1 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 6 Hours

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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.

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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 : 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

1.2 The Developm

Development of

ent of Modern Telecommunicat

Modern Telecommunications Infrastructure

ions Infrastructure

The early days of telecommunications

The public switched telephone network • The local exchange • Intraoffice calls

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Fig: 1.2 A PSTN intraoffice call through a local exchange

– Circuit-switched calls – Interoffice calls – T-carrier transport

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Signaling System #7

• Signal transfer points • Service switching points • Service control points • Operations support systems Signalling System No. 7

Signalling System No. 7 (SS7SS7) 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.

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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

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Fig: 1.4 Network elements of the SS7 system

1.3 1.3 Different Gen

Different Generations of wire

erations of wireless cellular netwo

less cellular networks:

rks:

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.

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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 acircuit — 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.

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– 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

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– Mobile-to-land calls

• Handshaking operations • Signaling operations • Service requests

Fig 1.8 AMPS mobile srcinated call

Land-to-mobile and mobile-to-mobile calls • Paging

• ID information exchange • Signaling

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Fig 1.9 AMPS mobile terminated call AMPS network operations

• Radio base station operations • Base station control operations • Mobile switching center operations

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Handoff operations

• Handshaking operations • Signal strength measurements • MSC operations during handoff • Confirmation messages

Fig 1.11 AMPS handoff operation

2G Cellular Systems 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,

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srcinated in North America, has also proliferated in South America and later in the Asia-Pacific 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

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• 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 1x-RTT, 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 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.

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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.

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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.

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UNIT - 2 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 6 Hours

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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 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

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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

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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

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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

2.2 HARDWARE AND HARDWARE AND SOFTWARE VIEWS OSOFTWARE VIEWS OF CELLULAR F CELLULAR NETWORK:NETWORK: – Hardware view of a cellular network

• Serving areas • Cells

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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 2.3 3G

3G Cellular

Cellular System

System Components

Components

– Core network

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– Radio network controller – Radio base station

Fig 2.6 The 3G radio network controller 2.4

2.4 Cellular Component IdentificationCellular Component Identification – Subscriber device identification

• Mobile station ISDN identification number – North American version

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Fig 2.6 Formation of MSISDN number • Cellular Component Identification

– International mobile subscriber identity

Fig 2.7 Formation of IMSI number – International mobile equipment identity

Fig 2.8 Formation of IMEI number

Cellular system component addressing • Location area identity • Cell global identity

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• Location numbering

• Addressing cellular network switching nodes • Global title and global title translation • 2.5 Call Establishment 2.5 Call Establishment – Mobile-terminated call • PSTN messages • GMSC operations • MSC/VLR operations • BSC operations

Fig 2.9 Mobile terminated call operations Mobile-srcinated call

• Mobile operations

• Radio base station operations • Base station controller operations • MSC operations

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Fig 2.10 Mobile srcinated call operations – Call release

• Connection management operations • Radio resource operations

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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.

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UNIT - 3 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 6 Hours

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UNIT-3 UNIT-3

WIRELESS NETWORK ARCHITECTURE AND OPERATION WIRELESS NETWORK ARCHITECTURE AND OPERATION 3.1

3.1 The Cellular ConceptThe 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 acell .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 ofS duplex channels. • Each cell is allocated a group ofchannels, k .

• TheS channels are divided among N cells. • The total number of available radio channels

• The N cells which use the complete set of channels is calledcluster .

• 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.

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Wireless Communication 10EC81 • Picocells

• Microcells • Macrocells

• Megacells and femtocells

Fig 3.1 Cellular concept 3.2 Cell Fundamentals

3.2 Cell Fundamentals

– The use of hexagons – Reuse number

• Cellular reuse patterns

Fig 3.2 Frequency reuse concept • Frequency reuse scheme

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– 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 beblocked 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

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• 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 taken = 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 srcinal 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 theco-channel interferenceand keep the cell radius R unchanged – Replacing single omni-directional antenna by several directional antennas – Radiating within a specified sector

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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 3.4 Cellular Backhaul Networks

– Introduction

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Fig 3.8 cellular backhaul network

Fig 3.9 cellular backhaul network 3.5 Mobility Management 3.5 Mobility Management – Location management • Need • Frequency • Location updating

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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.

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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

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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 re-assignment, 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

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– 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 ratioQ=D/R, the interference is reduced. • Q is called the co-channel reuse ratio

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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

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UNIT - 4 UNIT - 4

GSM and TDMA techniques, GSM system overview, GSM Network and system Architecture, GSM channel concepts, GSM identifiers

6 Hours 6 Hours

1. Mobile Cellular TelecommunicationMobile Cellular Telecommunication, Lee W.C.Y, MGH, 2002. 2. Wireless communicationWireless communication - D P Agrawal: 2

nd

Edition Thomson learning 2007. 3. Fundamentals of Wireless CommunicationFundamentals of Wireless Communication, David Tse, Pramod Viswanath,

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Unit-4

GSM AND TDMA

GSM AND TDMA TECHNOLOGIES

TECHNOLOGIES

4.1 Introduction to GSM and TDMA

Global System for Mobile Communications (GSM) services

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

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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

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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

4.2 GSM Network and System ArchitectureGSM 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

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– 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 in terf ace 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 in terf ace 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 in terf ace The A interface is used to provide communication between the BSS and the MSC. The interface carries information to enable the channels, timeslots

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The messaging required within the network to enable handover etc to be undertaken is carried over the interface.

4. B in terf ace 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 in terf ace The C interface is located between the HLR and a GMSC or a SMS-G. When a call srcinates 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 in terf ace 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 in terf ace 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 inte rf ace 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 in terf ace 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 inte rf ace The H interface exists between the MSC the SMS-G. It transfers short messages and uses the MAP/H protocol.

11. I inte rf ace 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.

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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 ti meslot (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, occupy ing 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.

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Fig 4.4 TDMA time frame structure GSM Channel Concept

– Logical channels

• Broadcast channels

– Broadcast control channel – Frequency correction channel

Synchronization channel – Logical 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

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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

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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.

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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:

 Traff ic multifr ame: 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 m ul tif rame: 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 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 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:

 F r equency hoppin g: 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.

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UNIT - 5 UNIT - 5

GSM system operation, Traffic cases, Cal handoff, Roaming, GSM protocol architecture. TDMA systems

6 Hours 6 Hours

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UNIT-5

GSM SYSTEM OPERATIONS

5.1

5.1 GSM Identities

GSM Identities

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)

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 (CCCC)

 National Destination Code (NDCNDC)  Subscriber Number (SNSN)

MSISDN = CC + NDC + SN MSISDN = CC + NDC + SN International Mobile Subscriber Identity (IMSI) 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 (MCCMCC)

 Mobile Network Code (MNCMNC)

 Mobile Subscriber Identification Number (MSINMSIN )

IMSI = MCC + MNC + MSIN IMSI = MCC + MNC + MSIN Temporary Mobile Subscriber Identity (TMSI) 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.

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International Mobile Equipment Identity (IMEI) 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 (TACTAC), determined by a central GSM body  Final Assembly Code (FACFAC), identifies the manufacture

 Serial Number (SNR SNR ), uniquely identifies all equipment within each TAC &

FAC

 Spare, a spare bit for future use.

IMEI = TAC + FAC + SNR + Spare IMEI = TAC + FAC + SNR + Spare

Mobile Station Roaming Number (MSRN) 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 MSRN = CC + NDC + SN Location Area Identity (LAI)

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)

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Cell Global Identity (CGI) 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 CGI = MCC + MNC + LAC + CI Base Station Identification Code (BSIC)

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

5.2 GSM System Operations (Traffic Cases)

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

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• 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

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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

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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