MOBILE COMMUN

ANKIT

11090105

BRANCH: COE

GOLBAL SYSTEM FOR MOBILE COMMUNICATION

PREFACE

Practical training in an industry is an essential part of an engineering curriculum towards making a successful engineer, as in an industry only a student can realize the theory thought in classroom and it also gives an exposure to modern technology. In the field of Electronics Computer engineering there has been rapid development to

support the ever increasing volume information, so Electronics students has an opportunity

during Training period to knowledge about the latest technologies.

The training period of 28 days is not much sufficient to take complete knowledge of

technology used but one is expected to identify components, the process flow in an industry for

high efficiency and about the knowledge of product technology.

Practical knowledge means the visualization of the knowledge, which we read in books. For this we perform experiments and get observations. Practical knowledge is very important in every field. One must be familiar with the problems related to that field so that we may solve them and became successful person.After achieving the proper goal of life an Engineer has to enter in professional life. According to this life he has to serve an industry, may be public or private sector or self-own. For the efficient work in the field he must be well aware of practical knowledge as well as theoretical knowledge.To be a good Engineer, one must be aware of the industrial environment & must know about management, working in industry, labor problems etc., so we can tackle them successfully.Due to all the above reasons & to bridge the gap between theory and practical, our

engineering curriculum provides a practical training course of 28 days. During this period a

student in industry and gets all type of experience and knowledge about the working and

maintenance of various types of machinery. Since time immemorial, a man has tried hard to

bring the world as close to himself as possible. His thirst for information is hard to quench so

he has continuously tried to develop new technologies, which have helped to reach the

objective.

I have undergone by 28 days of training (after II yr.) at BAHRAT SANCHAR NIGAM

LIMITED, ROHTAK. This report has been prepared on the basis of the knowledge which I

acquired during my 28 days training at Company.

ACKNOWLEDGEMENT

Practical training has an important role in a shaping up an engineering student for practical knowledge how a keeping him update with latest technology. First of all, I would like to express my attitude towards Mr. Manjeet Singh Laddar (Training cum placement officer MMEC, Ambala) and towards Er. Sandeep Goel (H.O.D., Electronics department, MMEC,Ambala) for providing me a great opportunity to undertake training at BSNL, Rohtak.

I would also like to thanks to Mr. Jignesh Sehgal (SDE, BSNL ROHTAK) and the co-operative management helpful staff for giving me a knowledge of their services and helping me time to time.

Last but not least I would like to thanks to our teacher Er. Govind for providing moral support to me.

With extreme regards and obligations.

COMPANY PROFILE

Bharat Sanchar Nigam Limited (abbreviated BSNL) is a state- wnedtelecommunications company headquartered in New Delhi, India. BSNL is one of the largest Indian cellular service providers, with over 87.1 million subscribers as of April 2011, and the largest land line telephone provider in India BSNL is India's oldest and largest communication service provider (CSP) It is fourth largest departement of TeleCommunication Company in Asia and seventh

in world today. Which is one of the most earning revenue in India. Above more than 3 laces employees, officer and engineers working in BSNL at present. Previously electro mechanically exchanges for use in India namely Strowger type exchange, cross bar exchange were there.These manual telephone exchanges suffered from some disadvantages.To overcome these an automatic exchange was introduced in this system. In 1980’s PITHROTHA LTD. Introduced “ C-DOT ” exchange in India. These exchanges replaced by electro mechanical exchange. These exchange which has wide range of capacity replaced electro mechanical exchange, C-DOT-128, C-DOT-256, C-DOT-512, C-DOT- 1024(SBM) exchange, C-DOT-2048(MBM) exchange and so on.Besides C-DOT exchange ILT exchange, E-10B exchange also proved of mild stone in Telecommunication Sector to replace electromechanical exchanges, which were most sophisticated and modern latest techniques electronics exchanges. There after it was OCB-283 exchange which proved very important exchange in this series to replace electro mechanical exchanges.

CONTENTS

1. MOBILE TELEPHONY2. THE FIRST GENERATION CELLULAR SYSTEM

3. THE SECOND GENERATION CELLULAR SYSTEMS

4. GSM TECHNOLOGY

4.1 CELLULAR RADIO NETWORK

4.2 FREQUENCY RE-USE

4.3 ADVANTAGES OF GSM

4.4 GSM CARRIER FREQUENCIES

4.5 GSM SPECIFICATIONS

4.6 GSM SUBSCRIBER SERVICES

4.7 SUPPLIMENTARY SERVICES

4.8 NETWORK STRUCTURE

4.8.1 MOBILE STATION

4.8.2 BASE STATION SUBSYSTEM (BSS)

4.8.3 NETWORK SWITCHING SUBSYSTEM (NSS)

4.8.4 GSM NETWORK INTERFACES

4.9 PHYSICAL AND LOGICAL CHANNELS

4.9.1 GSM PHYSICAL CHANNELS

4.9.2 GSM LOGICAL CHANNELS

4.10 CALL SETUP IN GSM NETWORK

4.10.1 CASE 1- FIXED LINE TO GSM MOBILE

4.10.2 CASE 2- GSM MOBILE TO GSM MOBILE

4.10.3 CASE 3- GSM MOBILE TO FIXED LINE

4.11 HANDOVER PROCESS

5. INTRODUCTION TO RF PLANNING

5.1 CLUTTER

5.2 TOOLS USED FOR RF PLANNING (ATOLL TOOL WORK)

6. REFERENCES AND BIBLOGRAPHY

1. Mobile Telephony Standards

2. First Generation Cellular Systems

1st Generation Cellular Characteristics

Widespread Introduction in early 1980’s. Analogue modulation. Frequency Division Multiple Access. Voice traffic only. No inter-network roaming possible.

Insecure air interface.

In early networks, the emphasis was to provide radio coverage with little consideration for the number of calls to be carried. As the subscriber base grew, the need to provide greater traffic capacity had to be addressed.

1st Generation Standards

AMPS (Analogue Advanced Mobile Phone System) North American Standard in cellular band (800MHz).

TACS (Total Access Communications System) UK originated Standard based on AMPS in 900MHz band. NMT (Nordic Mobile Telephony System)

Scandinavian Standard in 450MHz and 900MHz bands. C-450

German Standard in 450MHz band. JTACS (Japanese Total Access Communications System)

Japanese Standard in 900MHz band.

1st Generation Planning

Macro cellular High sites for coverage driven planning. Antennas above roof height. Frequency planning required

For networks with more cells than frequencies these must be planned.

Large cell size Order 30km. Hard handover Mobile only ever connected to a single cell. Hexagonal Grid Representation

The First Generation – Problems

Problems with the analog systems included:

Limited capacity – could not cope with increase in subscribers. Bulky equipment. Poor reliability. Lack of security – air interface analogue signals could be intercepted. Incompatibility between systems in different countries - no roaming.

To improve on the analog systems, the European Conference of Posts and Telecommunications Administrations (CEPT) established ‘Groupe Speciale Mobile’ (GSM) to

set a new standard. The system developed became the Global System for Mobile Communications (also GSM).

3. Second Generation Cellular Systems

Digital systems offer considerable advantages in terms of capacity and security and introduce new possibilities for data traffic.

2nd Generation Characteristics

Widespread Introduction in 1990’s Uses digital modulation Variety of multiple access strategies More efficient use of radio spectrum Voice and low rate circuit switched data International roaming capability Secure air interface Compatibility with ISDN

While first generation systems used a cellular structure and frequency re-use patterns, digital systems developed this concept to include multi-layer cellular patterns (micro cells and macro cells). The greater immunity to interference inherent in digital transmission allowed tighter frequency re-uses patterns to be implemented.

4. GSM TECHNOLOGY

GSM (Global System for Mobile Communications: originally from Special Mobile) is the most popular standard for mobile telephony systems in the world. The GSM Association, its promoting industry trade organization of mobile phone carriers and manufacturers, estimates that 80% of the global mobile market uses the standard. GSM is used by over 4.3 billion people across more than 212 countries and territories. Its ubiquity enables international roaming arrangements between mobile phone operators, providing subscribers the use of their phones in many parts of the world. GSM differs from its predecessor technologies in that both signaling and speech channels are digital, and thus GSM is considered a second generation (2G) mobile phone system. This also facilitates the wide-spread implementation of data communication applications into the system.

The ubiquity of implementation of the GSM standard has been an advantage to consumers, who may benefit from the ability to roam and switch carriers without replacing phones, and also to network operators, who can choose equipment from many GSM equipment vendors. GSM also pioneered low-cost implementation of the short message service (SMS), also

called text messaging, which has since been supported on other mobile phone standards as well. The standard includes a worldwide emergency telephone number feature.

4.1 Cellular Radio Network

GSM is a cellular network, which means that mobile phones connect to it by searching for cells in the immediate vicinity. There are five different cell sizes in a GSM network - macro, micro, Pico, femto and umbrella cells. The coverage area of each cell varies according to the implementation environment.

Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average roof top level.

Micro cells are cells whose antenna height is under average roof top level; they are typically used in urban areas.

Pico cells are small cells whose coverage diameter is a few dozen meters; they are mainly used indoors.

Femto cells are cells designed for use in residential or small business environments and connect to the service provider’s network via a broadband internet connection.

Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells.

Cell horizontal radius varies depending on antenna height, antenna gain and propagation conditions from a couple of hundred meters to several tens of kilometers. The longest distance the GSM specification supports in practical use is 35 kilometers (22 mi). There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain and the timing advance.

Indoor coverage is also supported by GSM and may be achieved by using an indoor Pico cell base station, or an indoor repeater with distributed indoor antennas fed through power splitters, to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. These are typically deployed when a lot of call capacity is needed indoors; for example, in shopping centers or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of the radio signals from any nearby cell.

The modulation used in GSM is Gaussian minimum-shift keying (GMSK), a kind of continuous-phase frequency shift keying. In GMSK, the signal to be modulated onto the carrier is first smoothed with a Gaussian low-pass filter prior to being fed to a frequency

modulator, which greatly reduces the interference to neighboring channels (adjacent-channel interference).

Cell: Hexagonal in shape, this is the area which is covered by a single Base Station. The number of cells in any geographic area is determined by the number of MS subscribers who will be operating in that area, and the geographic layout of the area(hills, lakes, buildings etc).

Large CellsThe maximum cell size for GSM is approximately 70 km in diameter, but this is dependent on the terrain the cell is covering and the power class of the MS.

Generally large cells are employed in: Remote areas. Coastal regions. Areas with few subscribers. Large areas which need to be covered with the minimum number of cell sites.

Small CellsSmall cells are used where there is a requirement to support a large number of MS’s, in a small geographic region, or where a low transmission power may be required to reduce the effects of interference. Small cells currently cover 200 m and upwards.

Typical uses of small cells: Urban areas. Low transmission power required. High number of MSs.

4.2 Frequency Re-useStandard GSM has a total of 124 frequencies available for use in a network. Most network providers are unlikely to be able to use all of these frequencies and are generally allocated a small subset of the 124. The network provider must re-use the same frequencies over and over again, in what is termed a “frequency re-use pattern”. When planning the frequency re-use pattern the network planner must take into account how often to use the same frequencies and determine how close together the cells are, otherwise co-channel and/or adjacent channel interference may occur. The network provider will also take into account the nature of the area to be covered. This may range from a densely populated city (high frequency re-use, small cells, and high capacity) to a sparsely populated rural expanse (large omni cells, low re-use and low capacity).

Co-channel InterferenceThis occurs when RF carriers of the same frequency are transmitting in close proximity to each other; the transmission from one RF carrier interferes with the other RF carrier.

Adjacent Channel InterferenceThis occurs when an RF source of a nearby frequency interferes with the RF carrier.

Sectorization: The problem with employing omni-directional cells is that as the number of MS’s increases in the same geographical region, using omni-directional cells we can only go so far before we start introducing co-channel and adjacent channel interference, both of which degrade the cellular network’s performance.To gain a further increase in capacity within the geographic area we can employ a technique called “sectorization”. A sectorization split a single site into a number of cells, each cell has transmit and receive antennas and behaves as an independent cell. This has a number of advantages: firstly, as we are now concentrating all the energy from the cell in a smaller area 60, 120, 180 degrees instead of 360 degrees, we get a much stronger signal, which is beneficial in locations such as “in-building coverage”. Secondly, we can now use the same frequencies in a much closer re-use pattern, thus allowing more cells in our geographic region which allows us to support more MSs.

4site/ 3cell

4.3 Advantages of GSMDue to the requirements set for the GSM system, many advantages will be achieved. These advantages can be summarized as follows:

GSM uses radio frequencies efficiently, and due to the digital radio path, the system together more intercell disturbances.

The average quality of speech achieved is better than in analogue Cellular systems.

Data transmission is supported throughout the GSM system.

Speech is encrypted and subscriber information security is guaranteed.

Due to the ISDN compatibility, new services are offered compared to the analogue systems.

International roaming is technically possible within all countries using the GSM system.

The large market increases competition and lowers the prices both for investments and usage.

4.4 GSM Carrier Frequencies

GSM networks operate in a number of different carrier frequency ranges (separated into GSM frequency ranges for 2G and UMTS frequency bands for 3G), with most 2G GSM networks operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the 850 MHz and 1900 MHz bands were used instead (for example in Canada and the United States). In rare cases the 400 and 450 MHz frequency bands are assigned in some countries because they were previously used for first-generation systems.

Most 3G networks in Europe operate in the 2100 MHz frequency band.

Regardless of the frequency selected by an operator, it is divided into timeslots for individual phones to use. This allows eight full-rate or sixteen half-rate speech channels per radio frequency. These eight radio timeslots (or eight burst periods) are grouped into a TDMA frame. Half rate channels use alternate frames in the same timeslot. The channel data rate for all 8 channels is 270.833 kbit/s, and the frame duration is 4.615 ms.

The transmission power in the handset is limited to a maximum of 2 watts in GSM900 and 1 watt in GSM1800.

Sr. no Frequency band Uplink Downlink ARFCN( 200 KHz)

1. 900 GSM 890-915 MHz 935-960 MHz 124

2. 1800 GSM 1710-1785 MHz 1805-1880 MHz 374

Uplink (MS to BTS) band is always kept lower than the downlink (BTS to MS) band due to the fact that mobile station is operating at lower power than the BTS (base transceiver station).

4.5 GSM Specifications

The various GSM specifications are as follows:

1) Frequency band - the frequency range specified for GSM is 1850 to 1990 MHz (mobile station to the base station).

2) Duplex distance - the duplex distance is 80 MHz. Duplex distance is the distance between the uplink and the downlink frequencies. A channel has two frequencies, 80 MHz apart.

3) Channel separation - the separation between adjacent carrier frequencies. In GSM, this is 200 kHz.

4) Modulation - it is the process of sending a signal by changing the characteristics of the carrier frequency. This is done via Gaussian Minimum Shift Keying (GMSK).

5) Transmission rate - GSM is a digital system with an over the air bit rate of 270 kbps.

6) Access method - GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.

7) Speech coder - GSM uses liner predictive coding (LPC) the purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through the filter, leaving behind a residual signal. Speech is encoded at 13 kbps.

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4.6 GSM subscriber services

There are two basic types of services offered through GSM telephony and data (bearer services).Telephony services provide subscribers with complete capability (including necessary terminal equipment) to communicate with the other subscribers. Data services provide the capacity necessary to transmit appropriate date signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following services are supported by GSM-

1) Dual-tone multi frequency (DTMF) - DTMF is a tone signaling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF.

2) Facsimile group III - GSM supports CCITT Group 3 facsimile as standard fax

machines are designed to be connected to a telephone using analog signals, a special

fax converter connected to the exchange is used in the GSM system. This enables a

GSM–connected fax to communicate with any analog fax in the network.

3) Short message services - A convenient facility of the network is the short message

service. A message consisting of a maximum of 160 alphanumeric characters can be

sent to or from a mobile station. This service can be viewed as an advanced form of

alphanumeric paging with a number of advantages. If the subscriber's mobile unit is

powered off or has left the coverage area, the message is stored and offered back to

the subscriber when the mobile is powered on or has reentered the coverage area of

the network. This function ensures that the message will be received.

4) Cell broadcast - A variation of the short message service is the cell broadcast facility. A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents.

5) Voice mail - This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber's voice-mail box and the subscriber checks for messages via a personal security code.

6) Fax mail - With this service, the subscriber can receive fax messages at any fax

machine. The messages are stored in a service center from which they can be

retrieved by the subscriber via a personal security code to the desired fax number.

4.7 Supplementary Services

A list of supplementary services is as follows:

1) Call forwarding – This service gives the subscriber the ability to forward incoming calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply or if call forwarding is allowed unconditionally.

2) Barring of outgoing calls – This service makes it possible for a mobile subscriber to prevent all outgoing calls.

3) Barring of incoming calls – This function allows the subscriber to prevent incoming calls. The following two conditions for incoming call barring exists baring of all incoming call and barring of incoming calls when roaming outside the home PLMN.

4) Call hold – This service enables the subscriber to interrupt an ongoing call and then

subsequently reestablish the call. The call hold service is only applicable to normal

telephony.

5) Call waiting – This service enables the mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using a circuit-switched connection.

6) Multiparty service – The multiparty service enables a mobile subscriber to establish a multiparty conversation—that is, a simultaneous conversation between three and six subscribers. This service is only applicable to normal telephony.

7) Calling line identification presentation/restriction – These services supply the called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation.

8) Closed User Groups (CUGs) – CUGs are generally comparable to a PBX. They are a group of subscribers who are capable of only calling themselves and certain numbers.

4.8 Network structure

The network is structured into a number of discrete sections:

Mobile station (mobile equipment + SIM). The Base Station Subsystem (the base stations and their controllers). The Network and Switching Subsystem (the part of the network most similar to a fixed

network). This is sometimes also just called the core network. The GPRS Core Network (the optional part which allows packet based Internet

connections). The Operations support system (OSS) for maintenance of the network.

4.8.1 Mobile station

It mainly consists of the mobile equipment (ME) and the SIM card.

Mobile Handset

Mobile Hand set is one of the most complicated GSM devices. It provides user the access to the Network. Each handset has unique identity no. called IMEI (international mobile equipment identity). It has a slot provided for inserting the SIM card. It carries a battery to provide the power required for carrying out the functions of mobile station. It also has the input (keyboard and microphone) and output devices (speaker), to enable the user use the device in a user friendly interface.

The Subscriber Identity Module

From the user’s point of view, the first and most important database is inside the mobile phone: the Subscriber Identity Module (SIM) or UICC (Universal Integrated Circuit Card).The SIM is a small memory device mounted on a card and contains user specific identification. The SIM card can be taken out of one mobile equipment and inserted into another. In the GSM network, the SIM card identifies the user just like a traveler uses a passport to identify himself.

Example of SIM card

The SIM card contains the identification numbers of the user, a list of the services that the user has subscribed to and a list of available networks. In addition, the SIM card contains tools needed for authentication and ciphering and, depending on the type of the card, there is also storage space for messages such as phone numbers, etc. A so-called “Home Operator” issues a SIM card when the user joins the network by making a service subscription.

4.8.2 Base Station Subsystem (BSS)

The Base Station Subsystem consists of the following elements:

1) BSC (Base Station Controller)2) BTS (Base Transreceiver Station)3) TC (Transcoder)

Base Station Controller (BSC) is the central network element of the BSS and it controls the radio network. This means that the main responsibilities of the BSC are: Connection establishment between MS (mobile station) and NSS (network switching subsystem), Mobility management, Statistical raw data collection, Air and A interface signaling support.

BSC controls several BTSs. BSC manages channel allocation, & Handover is from one BTS to another BTS. BSC is connected to MSC via A interface. Transmission rate on an I/f is 2 Mbps. Interface between BSC & BTS is called A’Bis I/f. BSC has database for all of its BTS’s parameters. BSC provides path from MS to MSC.

Fig. A base station controller

Base Transceiver Station (BTS) is a network element maintaining the Air interface. BTS contains the equipment for transmitting and receiving radio signals (transceivers), antennas, and equipment for encrypting and decrypting communications with the base station controller

(BSC). It is a plain transceiver which receives information from the MS (mobile station) through the Um (air interface) and then converts it to a TDM (PCM) based interface, the A’bis interface, and sends it towards the BSC. It takes care of Air interface signalling, Air interface ciphering and speech processing. In this context, speech processing refers to all the functions the BTS performs in order to guarantee an error-free connection between the MS and the BTS.

BTS has a set of Transceivers to talk to MS. One BTS covers one or more than one cell. Capacity of BTS depends on no of Transceivers. BTS is connected to BSC via A’Bis interface. Transmission rate on A’Bis is 2 Mbps (G.703). Interface between MS & BTS is called Air I/f. Transmission rate on Air interface is 13 Kbps. BTS controls RF parameters of MS.

Fig. A base transceiver stationThe Transcoder (TC) is a BSS element taking care of speech transcoding, i.e. it is capable of converting speech from one digital coding format to another and vice versa. For transmission over the air interface, the speech signal is compressed by the mobile station to 13Kbits/s (Full

Rate) or 5.6Kbits/s (Half Rate). However, the standard bit rate for speech in the PSTN is 64Kbits/s. Therefore, a converter has to be provided in the network to change the bit rate from one to another. This is called the Transcoder (TC). If the TC is located as close as possible to the MSC with standard PCM lines connecting the network elements, we can, in theory, multiplex four traffic channels in one PCM channel. This increases the efficiency of the PCM lines. But when connecting to the MSC, the multiplexed lines have to be de-multiplexed. In this case the unit is called Transcoder and Sub multiplexer (TCSM).

4.8.3 Network Switching Subsystem (NSS)

The elements of Network Switching Subsystem are:

MSC (Mobile Services Switching Centre)

VLR (Visitor Location Register)

HLR (Home Location Register)

AUC ( Authentication centre)

EIR ( Equipment identity register)

Fig. Network Switching Subsystem

Mobile Services Switching Centre (MSC)

The MSC is included in the GSM system for call-switching. Its overall purpose is the same as that of any telephone exchange.However, because of the additional complications involved in the control and security aspects of the GSM cellular system and the wide range of subscriber facilities that it offers, the MSC has to be capable of fulfilling many additional functions. The MSC will carry out several different functions depending upon its position in the network. When the MSC provides the interface between the PSTN and the BSS’s in the GSM network it will be known as a Gateway MSC. In this position it will provide the switching required for all MS originated or terminated traffic.Each MSC provides service to MSs located within a defined geographic coverage area, the network typically contains more than one MSC. One MSC is capable of supporting a regional capital with approximately one million inhabitants. An MSC of this size will be contained in about half a dozen racks. The functions carried out by the MSC are listed below: Call ProcessingIncludes control of data/voice call setup, inter-BSS and inter-MSC handovers and control of mobility management (subscriber validation and location). Operations and Maintenance SupportIncludes database management, traffic metering and measurement, and a man–machine interface. InterworkingManages the interface between the GSM network and the PSTN. BillingCollects call billing data.

Home Location Register (HLR)

Various identification numbers and addresses are stored, as well as authentication parameters. This information is entered into the database by the network provider when a new subscriber is added to the system. The HLR database contains the master database of all the subscribers to a GSM PLMN. The data it contains is remotely accessed by all the MSCs and the VLRs in the network and, although the network may contain more than one HLR, there is only one database record per subscriber - each HLR is therefore handling a portion of the total subscriber database. The subscriber data may be accessed by either the IMSI or the MSISDN number. The data can also be accessed by an MSC or a VLR in a different PLMN, to allow inter-system and inter-country roaming. The HLR contains the following information:-

Subscriber ID ( IMSI & MSISDN) Current subscriber VLR ( current location) Supplementary services subscribed to Supplementary service information (eg. Current forwarding number) Subscriber status ( registered /deregistered) Authentication key and AUC functionality Mobile subscriber roaming numberVisitor Location Register (VLR)

The VLR contains a copy of most of the data stored at the HLR. It is, however, temporary data which exists for only as long as the subscriber is “active” in the particular area covered by the VLR. The VLR database will therefore contain some duplicate data as well as more precise data relevant to the subscriber remaining within the VLR coverage.The VLR provides a local database for the subscribers wherever they are physically located within a PLMN, this may or may not be the “home” system. This function eliminates the need for excessive and time-consuming references to the “home” HLR database.

The additional data stored in the VLR is listed below: Mobile status (busy/free/no answer etc.). Location Area Identity (LAI). Temporary Mobile Subscriber Identity (TMSI). Mobile Station Roaming Number (MSRN).

Location Area Identity (LAI)Cells within the Public Land Mobile Network (PLMN) are grouped together into geographical areas. Each area is assigned a Location Area Identity (LAI), a location area may typically contain 30 cells. Each VLR controls several LAI’s and as a subscriber moves from one LAI to another, the LAI is updated in the VLR. As the subscriber moves from one VLR to another, the VLR address is updated at the HLR.

Temporary Mobile Subscriber Identity (TMSI)The VLR controls the allocation of new Temporary Mobile Subscriber Identity (TMSI) numbers and notifies them to the HLR. The TMSI will be updated frequently, this makes it very difficult for the call to be traced and therefore provides a high degree of security for the subscriber. The TMSI may be updated in any of the following situations:

Call setup. On entry to a new LAI. On entry to a new VLR.

Mobile Subscriber Roaming Number (MSRN)As a subscriber may wish to operate outside its “home” system at some time, the VLR can also allocate a Mobile Station Roaming Number (MSRN). This number is assigned from a list of numbers held at the VLR (MSC). The MSRN is then used to route the call to the MSC which controls the base station in the MS’s current location. The database in the VLR can be accessed by the IMSI, the TMSI or the MSRN. Typically there will be one VLR per MSC.

Authentication Centre (AUC)

The authentication centre (AUC) is a function to authenticate each SIM card that attempts to connect to the GSM core network (typically when the phone is powered on). Once the authentication is successful, the HLR is allowed to manage the SIM and services described above. An encryption key is also generated that is subsequently used to encrypt all wireless communications (voice, SMS, etc.) between the mobile phone and the GSM core networkIf the authentication fails, then no services are possible from that particular combination of SIM card and mobile phone operator attempted. Proper implementation of security in and around the AUC is a key part of an operator's strategy to avoid SIM cloning.

Equipment Identity Register (EIR)

The EIR contains a centralized database for validating the International Mobile Equipment Identity (IMEI).This database is concerned solely with MS equipment and not with the subscriber who is using it to make or receive a call. The EIR database consists of lists of IMEI’s (or ranges of IMEI’s) organized as follows:

- White ListContains those IMEI’s which are known to have been assigned to valid MS equipment.

- Black ListContains IMEI’s of MS which have been reported stolen or which are to be denied service for some other reason.

- Grey ListContains IMEI’s of MS which have problems (for example, faulty software). These are not, however, sufficiently significant to warrant a ‘‘black listing”.

The EIR database is remotely accessed by the MSCs in the network and can also be accessed by an MSC in a different PLMN. As in the case of the HLR, a network may well contain more than one EIR with each EIR controlling certain blocks of IMEI numbers. The MSC contains a translation facility, which when given an IMEI, returns the address of the EIR controlling the appropriate section of the equipment database.

VMSC & SMSC

Voice Mail Service Centre: To provide Voice Mail service. It has database for all the VMS subscribers & also stores voice messages for them.

Short Message Service Centre: To provide text message service. To send short messages from mobile to another mobile subscriber. Messages can also be sent by Manual Terminal connected to SMSC.

4.8.4 GSM network interfaces:

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 signaling, 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 standardized. 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 BSS’s. The messaging required within the network to enable handover etc to be undertaken is carried over the interface.

4. 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.

4.9 Physical and Logical ChannelsThe physical channel is the medium over which the information is carried, in the case of a terrestrial interface this would be a cable. The logical channels consist of the information carried over the physical channel.

4.9.1 GSM Physical ChannelsA 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 “timeslots”. The timeslots are arranged in sequence and are conventionally numbered 0 to 7. Each repetition of this sequence is called a “TDMA frame”. Each MS telephone call occupies one timeslot (0–7) 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 “burst”. 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.

4.9.2 GSM Logical Channels

There are two main groups of logical channels, traffic channels and control channels.

Traffic Channels (TCH)

The traffic channel carries speech or data information. The different types of traffic channel are listed below:

Full rate

TCH/FS: Speech (13 kbit/s net, 22.8 kbit/s gross) - Full rate speech channelTCH/EFR: Speech (12.2 kbit/s net, 22.8 kbit/s gross) - Enhanced full rate speechTCH/F9.6: 9.6 kbit/s – dataTCH/F4.8: 4.8 kbit/s – dataTCH/F2.4 2.4 kbit/s – data

Half rate

TCH/HS: speech (6.5 kbit/s net, 11.4 kbit/s gross) - Half rate speech channelTCH/H4.8 4.8 kbit/s – dataTCH/H2.4 2.4 kbit/s – data

Control Channels

Broadcast Control Channel (BCCH)

The Broadcast Control Channel is transmitted by the BTS at all times. The RF carrier used to transmit the BCCH is referred to as the BCCH carrier. The information carried on the BCCH is monitored by the MS periodically (at least every 30 sec), when it is switched on and not in a call. Broadcast Control Channel (BCCH) – Carries the following information (this is only a partial list):

Location Area Identity (LAI). List of neighboring cells which should be monitored by the MS. List of frequencies used in the cell. Cell identity. Power control indicator. DTX permitted. Access control (for example, emergency calls, call barring). CBCH description.

The BCCH is transmitted at constant power at all times, and its signal strength is measured by all MS which may seek to use it. “Dummy” bursts are transmitted to ensure continuity when there is no BCCH carrier traffic.

Frequency Correction Channel (FCCH)

This is transmitted frequently on the BCCH timeslot and allows the mobile to synchronize its own frequency to that of the transmitting base site. The FCCH may only be sent during timeslot 0 on the BCCH carrier frequency and therefore it acts as a flag to the mobile to identify Timeslot 0.

Synchronization Channel (SCH)

The SCH carries the information to enable the MS to synchronize to the TDMA frame structure and know the timing of the individual timeslots. The following parameters are sent:

1) Frame number.2) Base Site Identity Code (BSIC).

The MS will monitor BCCH information from surrounding cells and store the information from the best six cells. The SCH information on these cells is also stored so that the MS may quickly resynchronize when it enters a new cell.

Common Control Channels (CCCH)

The Common Control Channel (CCCH) is responsible for transferring control information between all mobiles and the BTS. This is necessary for the implementation of “call origination” and “call paging” functions. It consists of the following:

Random Access Channel (RACH)

Used by the mobile when it requires to gain access to the system. This occurs when the mobile initiates a call or responds to a page.

Paging Channel (PCH)

Used by the BTS to page MS, (paging can be performed by an IMSI, TMSI or IMEI).

Access Grant Control Channel (AGCH)

Used by the BTS to assign a dedicated control channel to a MS in response to an access message received on the Random Access Channel. The MS will move to the dedicated channel in order to proceed with either a call setup, response to a paging message, Location Area Update or Short Message Service.

Cell Broadcast Channel (CBCH)

This channel is used to transmit messages to be broadcast to all MSs within a cell. The CBCH uses a dedicated control channel to send its messages, however it is considered a common channel because the messages can be received by all mobiles in the cell. Active MSs must frequently monitor both BCCH and CCCH. The CCCH will be transmitted on the RF carrier with the BCCH.

Dedicated Control Channels (DCCH)

The DCCH is a single timeslot on an RF carrier which is used to convey eight Stand-alone Dedicated Control Channels (SDCCH). A SDCCH is used by a single MS for call setup, authentication, location updating and SMS point to point. As we will see later, SDCCH can also be found on a BCCH/CCCH timeslot, this configuration only allows four SDCCHs.

Associated Control Channels (ACCH)

These channels can be associated with either an SDCCH or a TCH. They are used for carrying information associated with the process being carried out on either the SDCCH or the TCH.

Slow Associated Control Channel (SACCH)

Conveys power control and timing information in the downlink direction (towards the MS) and Receive Signal Strength Indicator (RSSI), and link quality reports in the uplink direction.

Fast Associated Control Channel (FACCH)

The FACCH is transmitted instead of a TCH. The FACCH ‘‘steals” the TCH burst and inserts its own information. The FACCH is used to carry out user authentication, handovers and immediate assignment. All of the control channels are required for system operation, however, in the same way that we allow different users to share the radio channel by using different timeslots to carry the conversation data, the control channels share timeslots on the radio channel at different times. This allows efficient passing of control information without wasting capacity which could be used for call traffic. To do this we must organize the timeslots between those which will be used for traffic and those which will carry control signalling.

Multiframes and TimingThere are eight timeslots within each TDMA frame, enabling eight physical channels to share a single physical resource – the RF carrier. In turn, each physical channel may be shared by a number of logical channels. In order to understand how a single physical channel is shared by various logical channels, it is necessary to introduce the GSM multiframe structures that make it possible.

The 26-frame Traffic Channel MultiframeThe illustration opposite shows the time relationship between time-slot, TDMA frame, and the 26-frame multiframe. Some of the times shown are approximate numbers as the GSM recommendations actually state the exact values as fractions rather than in decimal form (for example, the exact duration of a time-slot is 15/26 ms).

The 51-frame Control Channel MultiframeThe 51-frame structure used for control channels is considerably more complex than the 26-frame structure used for the traffic channels. The 51-frame structure occurs in several forms, depending on the type of control channel and the network provider’s requirements.

Superframes and HyperframesIt is not by accident that the control channel multiframe is not a direct multiple of the traffic channel multiframe. From the diagram, it can be seen that any given frame number will only occur simultaneously in both multiframes every 1326 TDMA frames (26 x 51). This number of TDMA frames is termed a “superframe” and it takes 6.12 s to transmit. This arrangement means that the timing of the traffic channel multiframe is always moving in relation to that of the control channel multiframe and this enables a MS to receive and decode BCCH information from surrounding cells. If the two multiframes were exact multiples of each other, then control channel timeslots would be permanently ‘masked’ by traffic channel timeslot activity. This changing relationship between the two multiframes is particularly important, for

example, to a MS which needs to be able to monitor and report the RSSI’s of neighbour cells (it needs to be able to ‘see’ all the BCCH of those cells in order to do this). The “hyperframe” consists of 2048 superframes; this is used in connection with ciphering and frequency hopping. The hyperframe lasts for over three hours, after this time the ciphering and frequency hopping algorithms are restarted.

4.10 Call Set-Up in a GSM Network

4.10.1 Case 1: Fixed line to GSM mobile

The first is a call originating from the fixed network. Setting up a call appears to be a quick and simple operation, but if we study the process more closely, we discover that it consists of a considerable number of sub operations.These operations include signalling between switching centers, identifying and locating the subscriber who is being called, making routing decisions and traffic connections etc. This section contains a step by step analysis of setting up a connection between a telephone in a fixed network and a GSM mobile station (i.e. a mobile phone).

1). A subscriber in a fixed network dials the number of a mobile station. This can be either a national or an international number. An example of a national number is: 040 2207959. There is no country code in this number. The following is an example of an international number: +358 40 2207959. The dialed number is called an MSISDN (Mobile Subscriber International ISDN Number) which contains the following elements:

CC= Country code (33=France, 358=Finland, etc.)NDC= National Destination CodeSN= Subscriber Number

The public switched telephone network (PSTN) also referred to as the Plain Old Telephone Service (POTS) is the network of the world's public circuit-switched telephone networks. It is a worldwide net of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables connected by switching centers, which allows any telephone in the world to communicate with any other. Originally a network of fixed-line analog telephone systems, the PSTN is now almost entirely digital in its core and includes mobile as well as fixed telephones.

The technical operation of the PSTN utilizes standards created by the ITU (International Telecommunication Union). These standards allow different networks in different countries to interconnect seamlessly. The combination of the interconnected networks and the single numbering plan make it possible for any phone in the world to dial any other phone.

Integrated Services Digital Network (ISDN) is a set of communications standards for simultaneous digital transmission of voice, video, data, and other network services over the traditional circuits of the public switched telephone network. The key feature of ISDN is that it integrates speech and data on the same lines, adding features that were not available in the classic telephone system. ISDN is a circuit-switched telephone network system, which also provides access to packet switched networks, designed to allow digital transmission of voice and data over ordinary telephone copper wires, resulting in potentially better voice quality than an analog phone can provide. It offers circuit-switched connections (for either voice or data), and packet-switched connections (for data), in increments of 64 kilobit/s. A major market application for ISDN in some countries is Internet access, where ISDN typically provides a maximum of 128 kbit/s in both upstream and downstream directions.

2). The PSTN exchange analyses the dialled number. The result of the analysis is the routing information required for finding the mobile network (Public Land Mobile Network, PLMN) in which the called subscriber has made his subscription. The PSTN identifies the mobile network on the basis of the NDC, after which it accesses the mobile network via the nearest Gateway Mobile Services Switching Centre (GMSC).

3). The GMSC analyses the MSISDN in the same way as the PSTN exchange did. As a result of the analysis, it obtains the HLR address in which the subscriber is permanently registered. Notice that the GMSC itself does not have any information about the location of the called subscriber. The subscriber’s location can only be determined by the two databases, the HLR and VLR. At this stage however, the GMSC only knows the HLR address and so it sends a message (containing the MSISDN) to the HLR. In practice this message is a request for locating the called subscriber in order to set up a call. This is called an “HLR Enquiry”.

4). The HLR analyses the message. It identifies the called subscriber on the basis of MSISDN and then checks its database to determine the subscriber’s location. As you remember, the HLR is informed every time the subscriber moves from one VLR area to another, i.e. the HLR knows in which VLR area the subscriber is currently registered. It has to be pointed out that the HLR does not handle network traffic at all.

A traffic connection requires two network elements that are able to provide speech connections. A speech connection is a network service and it can be handled only by an MSC. Therefore, to enable the traffic connection, maybe two MSC’s will have to be connected. The first MSC is the Gateway MSC which is contacted by the PSTN exchange. The HLR acts as a coordinator to set up the connection between the GMSC and the destination MSC (which could of course be the GMSC itself).

4.10.2 Case 2: GSM mobile to GSM mobile

Outgoing

Once a mobile phone has successfully attached to a GSM network as described above, calls may be made from the phone to any other phone on the global Public Switched Telephone Network.

The users dial the telephone number, press the send or talk key, and the mobile phone sends a call setup request message to the mobile phone network via the nearest mobile phone mast (BTS).

The call setup request message is handled next by the Mobile Switching Center, which checks the subscriber's record held in the Visitor Location Register to see if the outgoing call is allowed. If so, the MSC then routes the call in the same way that a telephone exchange does in a fixed network.

If the subscriber is on a Pay As You Go tariff (sometimes known as prepaid (for example, in Australia and India)), then an additional check is made to see if the subscriber has enough credit to proceed. If not, the call is rejected. If the call is allowed to continue, then it is continually monitored and the appropriate amount is decremented from the subscriber's account. When the credit reaches zero, the call is cut off by the network. The systems that monitor and provide the prepaid services are not part of the GSM standard services, but instead an example of intelligent network services that a mobile phone operator may decide to implement in addition to the standard GSM ones.

Incoming

Gateway MSC contact

When someone places a call to a mobile phone, they dial the telephone number (also called a MSISDN) associated with the phone user and the call is routed to the mobile phone operator's Gateway Mobile Switching Centre. The Gateway MSC, as the name suggests, acts as the "entrance" from exterior portions of the Public Switched Telephone Network onto the provider's network.

As noted above, the phone is free to roam anywhere in the operator's network or on the networks of roaming partners, including in other countries. So the first job of the Gateway MSC is to determine the current location of the mobile phone in order to connect the call. It does this by consulting the Home Location Register (HLR), which, as described above, knows which Visitor Location Register (VLR) the phone is associated with, if any.

Routing the call

When the HLR receives this query message, it determines whether the call should be routed to another number (called a divert), or if it is to be routed directly to the mobile.

If the owner of the phone has previously requested that all incoming calls be diverted to another number, known as the Call Forward Unconditional (CFU) Number, then this number is stored in the Home Location Register. If that is the case, then the CFU number is returned to the Gateway MSC for immediate routing to that destination.

If the mobile phone is not currently associated with a Visited Location Register (because the phone has been turned off) then the Home Location Register returns a number known as the Call Forward Not Reachable (CFNRc) number to the Gateway MSC, and the call is forwarded there. Many operators may set this value automatically to the phone's voice mail number, so that callers may leave a message. The mobile phone may sometimes override the default setting.

Finally, if the Home Location Register knows that the phone is roaming in a particular Visited Location Register area, then it will request a temporary number (called an MSRN) from that VLR. This number is relayed back to the Gateway MSC, and then used to route the call to the MSC where the called phone is roaming.

4.10.3 Case 3: Fixed line to GSM mobile

1. The subscriber pressing the ‘send’ key initiates a channel request message from the MS to the BSS. This is followed by assignment of dedicated control channel by the BSS and the establishment of the signaling link between the MS and BSS.

2. The message “request for service” is passed to the MSC which relays it to the VLR. The VLR will carry out the authentication process if the MS has been previously registered on this VLR – if not the VLR will have to obtain authentication parameters from the HLR. The diagram assumes the MS was previously registered to this VLR.

3. Subscriber authentication (optional) takes place using authentication messages and encryption algorithms and if successful the call setup can continue. If ciphering is to be used this is initiated at this time as the setup message contains sensitive information.

4. The message “set-up” is sent by the MS to the MSC accompanied by the call information (type of call, and number being called etc.) the message is forwarded from MSC to the VLR.

5. The MSC may initiate MS IMEI check (is MS stolen?). 6. In response to the message “set up” (sent in step4) the VLR sends a message “complete

call” to the MSC, which notifies the Ms with “call proceeding”.7. The MSC then assigns a traffic channel to the BSS (assignment commends) which in turn

assigns an air interface traffic channel. The MS responds to the BSS (which in turn responds to the MSC) with “assignment complete”.

8. An “initial and final address message (IFAM)” is sent to the PSTN. Ring tone is applied at the MS in response to “ alerting” , which the MSC sends to the MS when the PSTN responds with an “ address complete message( ACM)”

9. When answered the message “connect” is forwarded to the MS by the MSC, stopping the MS ring tone. The MSC then connects the GSM traffic channel to the PSTN circuit, thus completing the end to end traffic connection.

10.Conversation takes place for the duration of the call.

4.11 Handover Processes

Handovers take place as the MS moves between cells, gradually losing the RF signal of one and gaining that of the other. The MS switches from channel to channel and cell to cell as it moves to maintain call continuity. With analogue systems, handovers are frequently a problem area and the subscriber is often aware that a handover has occurred!When GSM was specified a great deal of thought went into the design and implementation of handovers. Although the GSM system is more complicated than analogue in this area, the flexibility of the GSM handover processes offer significant improvements which provide a much better quality of service to the subscriber.GSM provides handover processes for the following:

Quality (uplink/downlink). Interference (uplink/downlink). RF level (uplink/downlink). MS distance. Power budget.

More handover algorithms have been developed for specific applications, such as microcellular, and are currently being implemented.

Types of handovers:

Intra Cell / Intra BSC HO Inter Cell / Intra BSC HO Inter Cell / Inter BSC HO Inter Cell / Inter MSC HO

5. INTRODUCTION TO RF PLANNING

Designing a cellular system - particularly one that incorporates both Macrocellular and Microcellular networks is a delicate balancing exercise.

The goal is to achieve optimum use of resources and maximum revenue potential whilst maintaining a high level of system quality.

Full consideration must also be given to cost and spectrum allocation limitations.

A properly planned system should allow capacity to be added economically when traffic demand increases.

As every urban environment is different, so is every macrocell and microcell network. Hence informed and accurate planning is essential in order to ensure that the system will provide both the increased capacity and the improvement in network quality where required, especially when deploying Microcellular systems.

RF planning plays a critical role in the Cellular design process.

By doing a proper RF Planning by keeping the future growth plan in mind we can reduce a lot of problems that we may encounter in the future and also reduce substantially the cost of optimization.

On the other hand a poorly planned network not only leads to many Network problems, it also increases the optimization costs and still may not ensure the desired quality.

5.1 Clutter

Clutter refers to a Land Use/Land Cover classification of surface features which impact on radio wave propagation. These features are classed according to their physical and electrical properties.Average obstacle height, local absorption power loss, co-efficients of correction and distance to clearing are some of the clutter-specific parameters that can be set and adjusted in propagation modeling. Image classification for RF propagation studies must accurately model clutter in terms of its influence on radio wave propagation.Clutter is generally produced from multispectral satellite imagery where distinct classes of surface features can be delineated through spectral homogeneity and other characteristics. For certain classes such as water, forest and crop land we can employ supervised classification techniques. This is an automatic yet iterative process, the results of which are checked and rechecked for classification accuracy.

5.2 TOOLS USED FOR RF PLANNING

Network Planning Tool (Atoll)

Network Planning Tool (Atoll):

Planning tool is used to assist engineers in designing and optimizing wireless networks by providing an accurate and reliable prediction of coverage, doing frequency planning automatically, creating neighbor lists etc.

With a database that takes into account data such as terrain, clutter, and antenna radiation patterns, as well as an intuitive graphical interface, the Planning tool gives RF engineers a state-of-the-art tool to:

Design wireless networks Plan network expansions Optimize network performance Diagnose system problems

The major tools available in the market are Planet, Pegasus and Cell Cad. Also many vendors have developed Planning tools of their own like Netplan by

Motorola, TEMS by Ericsson and so on. More details regarding work with Atoll Planning Tool will discuss in next slides.

.

6. REFERENCES & BIBLIOGRAPHY

RF Planning – AASTER Presentation Motorola’s -- Introduction to GSM Cellular ,CP02 (V1 R2) [Manual] Nokia Systra Training Material [Manual] Cell Planning [Study Material] Capacity Planning [Study Material] FAQ’s in GSM 6 [Study Material] Channels.ppt [Study material] Call_flow_basics in GSM [Study Material] Frequency Hopping.pdf [Study Material] GSM TECHNOLOGY FOR ENGINEERS (Aircom International [Manual] Huawei “Handover-ISSUE2” [Manual] Wikipedia – the free Encyclopedia www.RadioElectronics.com Other Internet Resources