Topic “cellular phone”

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Group MembersMuhammad Azam Sohu

Makhno SharSyed Muhammad Raghib Shah

Abdul Razique Bilal jatt

Cellular Phone Cellular telephone, sometimes called mobile

telephone, is a type of short-wave analog or digital telecommunication in which a subscriber has a wireless connection from a mobile phone to a relatively nearby transmitter. The transmitter's span of coverage is called a cell. As the cellular telephone user moves from one cell or area of coverage to another, the telephone is effectively passed on to the local cell transmitter.

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Cellular Phone The first cellular telephone for commercial

use was approved by the Federal Communications Commission (FCC) in 1983. The phone, a Motorola DynaTAC 8000X, weighed 2 pounds, offered just a half-hour of talk time for every recharging and sold for $3,995

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Cellular Phone-Use Cellular phone is used by any person

to communicate with each other and this is mostly used device which is easy to keep track of about the people and also used to communicate the important messages and also mostly used by business people even during the journey.So it makes life easy for people as they can communicate even though they are traveling.

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Cellular refers to communications systems, especially the Advance Mobile Phone Service (AMPS), that divide a geographic region into sections, called cells.The purpose of this division is to make the most use out of a limited number of transmission frequencies.

Each connection, or conversation, requires its own dedicated frequency, and the total number of available frequencies is about 1,000. To support more than 1,000 simultaneous conversations, cellular systems allocate a set number of frequencies for each cell. Two cells can use the same frequency for different conversations so long as the cells are not adjacent to each other. 5

Evolution to cellular networks communication anytime,

anywhere radio communication was invented by Nikola Tesla and Guglielmo Marconi: in 1893, Nikola Tesla made the first public demonstration of wireless (radio) telegraphy; Guglielmo Marconi conducted long ditance (over see) telegraphy 1897

in 1940 the first walkie-talkie was used by the US military

in 1947, John Bardeen and Walter Brattain from AT&T’s Bell Labs invented the transistor (semiconductor device used to amplify and switch electronic signals)6

In 1979 the first commercial cellular phone service was launched by the Nordic Mobile Telephone (in Finland, Sweden, Norway, Denmark).

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Cellular Systems Generations 1G (first generation) – voice-oriented

systems based on analog technology; ex.: Advanced Mobile Phone Systems (AMPS) and cordless systems

2G (second generation) - voice-oriented systems based on digital technology; more efficient and used less spectrum than 1G; ex.: Global System for Mobile (GSM) and US Time Division Multiple Access (US-TDMA)

3G (third generation) – high-speed voice-oriented systems integrated with data services; ex.: General Packet Radio Service (GPRS), Code Division Multiple Access (CDMA)

4G (fourth generation) – still experimental, not deployed yet; based on Internet protocol networks and will provide voice, data and multimedia service to subscribers.8

Frequency Reuse Is a method used by service providers to

improve the efficiency of a cellular network and to serve millions of subscribers using a limited radio spectrum.

Is based on the fact that after a distance a radio wave gets attenuated and the signal falls bellow a point where it can no longer be used or cause any interference.

A transmitter transmitting in a specific frequency range will have only a limited coverage area.

Beyond this coverage area, that frequency can be reused by another transmitter.

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Network Cells The entire network coverage area is divided into

cells based on the principle of frequency reuse. A cell = basic geographical unit of a cellular

network; is the area around an antenna where a specific frequency range is used; is represented graphically as a hexagonal shape, but in reality it is irregular in shape.

When a subscriber moves to another cell, the antenna of the new cell takes over the signal transmission.

A cluster is a group of adiacent cells, usually 7 cells; no frequency reuse is done within a cluster.

The frequency spectrum is divided into sub bands and each sub band is used within one cell of the cluster.

In heavy traffic zones cells are smaller, while in isolated zones cells are larger. 10

Network cells

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Types of cells Macro cell – their coverage is large used

in remote areas, high-power transmitters and receivers are used

Micro cell – their coverage is small (half a mile in diameter) and are used in urban zones; low-powered transmitters and receivers are used to avoid interference with cells in another clusters

Pico cell – covers areas such as building or a tunnel

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Other cellular concepts Handover = moving a call from one

zone (from the transmitter-receiver from one zone) to another zone due to subscriber’s mobility

Roaming = allowing the subscriber to send/receive calls outside the service provider’s coverage area

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The control channel

This channel is used by a cellular phone to indicate its presence before a frequency/time slot/code is allocated to him

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Cellular services

voice communication Short Messaging Service (SMS) Multimedia Messaging Service (MMS) Global Positioning System (GPS) Wireless Application Protocol (WAP) –

to access the Internet

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Components of a cellular phone (MSU – Mobile

Subscriber Unit) Radio transceiver – low power radio

transmitter and receiver Antenna, usually located inside the

phone

Control circuitry – formats the data sent to and from the BTS; controls signal transmission and reception

man-machine interface – consists from a keypad and a display; is managed by the control circuitry

Subscriber Identity Module (SIM) – integrated circuit card that stores the identity information of subscriber

Battery, usually Li-ion, the power unit of the phone.

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Multiple access schemes

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Frequency Division Multiple Access- when the subscriber enters another cell a unique frequency is assigned to him; used in analog systems

Time Division Multiple Access- each subscriber is assigned a time slot to send/receive a data burst; is used in digital systems

Code Division Multiple Access- each subscriber is assigned a code which is used to multiply the signal sent or received by the subscriber

Global System for Mobile Communication

(GSM)

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GSM (Global System for Mobile communications) is an open, digital cellular technology used for transmitting mobile voice and data services.

Cellular network components

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GSM system architecture

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The base station sub system(BSS) is the section of a GSM network which is responsible for handling the traffic and signaling between a mobile phone and a network Switching sub system

The BSS carries out allocation of radio channels to mobile Phone paging quality management of transmissions and Receptions over the air interface

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Base station sub system

The BSS consist of following elements one or more

BTS (base transceiver station)in one BSC(base station controller)

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Base station sub system

The base transceiver station or BTS contains the equipment for transmission and receiving of radio signals Transceiver antennas and equipment for encrypting and decrypting communications with the base station controller BSC

BTS is a plan transceiver which receive information from the MS (mobile station)through the air interface and send it towards the BSC

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Base transceiver station

BSC has 10s or even 100s of BTS under its control.

The BSC handles allocation of radio channels receive measurements from the mobile phone BTS to BTS and BTS to BSC

A key function of the BSC is connection towards the Mobile switching center (MSC) overall this means that networks are often structured to have many BSC distributed into regions near there BTS which are then connected to large centralized MSC sites

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Base station controller

The mobile switching center or MSC is a sophisticated Telephone exchange which provide circuit switching calling ,mobility management and GSM services to the mobile phones roaming within the area that is serves

That means voice data and fax services as well as SMS And call divert

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Mobile switching center

home location register The home location register or HLR is a central database has

contains the details of each phone subscriber that is authorized to use the GSM core network.

There is one HLR in one public land mobile network ,HLR is a single

database but can be maintained as separate database when the data to be stored is more then capacity.

HLR stores details of every SIM card issued by the mobile phone operator

Each SIM has a unique identity ,IMSI (International Mobile Subscriber Identity)which is one of the primary key to each HLR

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The VLR is a database contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers.

The VLR is always integrated with the MSC when

a mobile stations roams into a new MSC area the VLR connected to the MSC will request data about the mobile station from HLR later if mobile station makes a call the VLR have the information needed for call setup without having to interrogate the HLR each time

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VISITOR LOCATION REGISTER

AUTHENTICATION CENTER(AUC)

A unit call AUC provide authentication and encryption and encryption parameters that verify the user identity and ensure the confidentiality of each call.

The AUC protected network operator from different type of fraud found in Today’s cellular world.

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EQUIPEMENT IDENTITY REGISTER The EIR is a database that contains

information about the identity of mobile equipment that prevents calls from stolen, unauthorized

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GSM Call Processing

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Initializing a call1. when the cell phone is turned on it scans

all the available frequencies for the control channel

2. All the BTS in the area transmit the FCCH, SCH and BCCH that contain the BTS identification and location

3. Out of available beacon frequencies from the neighboring BTSs, the cell phone chooses the strongest signal

4. Based on the FCCH of the strongest signal, the cell phone tunes itself to the frequency of the network

5. The phone send a registration request to the BTS 31

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6. The BTS sends this registration request to the MSC via the BSC

7. The MSC queries the AUC and EIR databases and based on the reply it authenticates the cell phone

8. The MSC also queries the HLR and VLR databases to check whether the cell is in its home area or outside

9. If the cell phone is in its home area the MSC gets all the necessary information from the HLR if it is not in its home area, the VLR gets the information from the corresponding HLR via MSCs then the cell phone is ready to receive or make calls.

Initializing a call

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Making a call1. when the phone needs to make a call it sends an access

request (containing phone identification, number) using RACH to the BTS; if another cell phone tries to send an access request at the same time the messages might get corrupted, in this case both cell phones wait a random time interval before trying to send again

2. then the BTS authenticates the cell phone and sends an acknowledgement to the cell phone

3. the BTS assigns a specific voice channel and time slot to the cell phone and transmits the cell phone request to the MSC via BSC

4. the MSC queries HLR and VLR and based on the information obtained it routes the call to the receiver’s BSC and BTS

5. the cell phone uses the voice channel and time slot assigned to it by the BTS to communicate with the receiver

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Making a call

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Receiving a call1. When a request to deliver a call is made in the network,

the MSC or the receiver’s home area queries the HLR; if the cell phone is located in its home area the call is transferred to the receiver; if the cell phone is located outside its home area, the HLR maintains a record of the VLR attached to the cell phone

2. Based on this record, the MSC notes the location of the VLR and indicated the corresponding BSC about the incoming call

3. The BSC routes the call to the particular BTS which uses the paging channel to alert the phone

4. The receiver cell phone monitors the paging channel periodically and once it receives the call alert from the BTS it responds to the BTS

5. The BTS communicates a channel and a time slot for the cell phone to communicate now the call is established

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Receiving a call

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GSM Security

Personal Identification Number (PIN) User Authentication TMSI-based Security

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Personal Identification Number (PIN)

The PIN is stored on the SIM card of the cell phone

When the cell phone is turned on, the SIM checks the PIN; in case of 3 consecutive faulty PIN inputs a PUK (Personal Unblocking Key) is asked for in case of 10 faulty PUK inputs, the SIM is locked and the subscriber must ask a new SIM.

This security measure is within the cell phone and the service provider is not involved. 39

User Authentication A mechanism for encrypting messages in a GSM

network The network sends random data to the cell phone

(RAND) Each cell phone is allocated a secret key (KI) Using RAND and KI and the A3 encryption

algorithm the cell phone generates a signed result (SRES) which is then sent to the network

A similar process takes place in the network which generates a signed result specific to the cell phone

The network compares its SRES with the SRES generated by the phone and in case of a match the cell phone is connected to the network

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TMSI-Key Based Security Is most used in a GSM cellular network

A TMSI key provides a temporary identification to a cell phone and is provided by the network upon authentication

A TMSI key keeps changing according to the location of the cell phone this way preventing unauthorized access to a channel and preventing intruder from tracing location

The mapping between IMSI and TMSI keys is handled by the VLR

ISMI are used only when the SIM is used for the first time

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