Mobile Communications

Mobile Communications A Brief Overview

Generations of Mobile Communications • 1 G – Analog (AMPS) • 2 G – Digital (GSM, CDMA) • 3 G – IMT 2000  International Mobile Telecommunications  2000 meant  Year it was supposed to go into service  Frequency to operate in MHz  Bandwidth in kHz

Introduction – Air Interface • FDMA : Frequency Division Multiple Access • TDMA : Time Division Multiple Access • CDMA : Code Division Multiple Access

FDMA FDMA puts each call on a separate channel (frequency band). Frequency

Channel

Time

TDMA TDMA assigns each call a certain portion of time on a designated frequency. Time Slot

Frequency Channel

0

1

2

3

4

5

6

7

Time

CDMA CDMA gives a unique code to each call and spreads it over the available frequencies and time slots

Multiple Band • A phone that has multiple-band capability can switch frequencies. • A quad-band GSM phone could use GSM service in the 850-MHz, 900-MHz, 1800-MHz or 1900-MHz band.

Multiple Mode • In cell phones, "mode" refers to the type of transmission technology used. • A phone that supports GSM and CDMA could switch back and forth as needed. • GSM and CDMA SIM cards available in single handset. • Introduced in INDIA by SPICE Telecom.

System Architecture

Mobile Station The Mobile Station is made up of two entities: •

Mobile Equipment (ME)

•

Subscriber Identity Module (SIM)

Mobile Station Mobile Equipment • • •

Produced by many different manufacturers Must obtain approval from the standardization body Uniquely identified by an IMEI (International Mobile Equipment Identity)

Mobile Station Subscriber Identity Module (SIM) • • • • •

Smart card containing the International Mobile Subscriber Identity (IMSI) Allows user to send and receive calls and receive other subscribed services Encoded network identification details Protected by a password or PIN Can be moved from phone to phone – contains key information to activate the phone

Base Station Subsystem Base Station Subsystem is composed of two parts that communicate with each other •

Base Transceiver Station (BTS)

•

Base Station Controller (BSC)

Base Station Subsystem Base Transceiver Station (BTS) • • •

Houses the radio transceivers that define a cell Towers that mark the boundaries of the cell Requirements for BTS: • • • •

Ruggedness Reliability Portability Minimum costs

Base Station Subsystem Base Station Controller (BSC) •

Manages resources for BTS

•

Handles call set up

•

Location update

•

Handover for each MS

Network Subsystem Mobile Switching Center (MSC) • Switch speech and data connections between: • • • •

Base Station Controllers Mobile Switching Centers GSM-networks Other external networks

• Three main jobs: 1) connects calls from sender to receiver 2) collects details of the calls made and received 3) supervises operation of the rest of the network components

Network Subsystem • Home Location Registers (HLR) contains administrative information of each subscriber current location of the mobile

• Visitor Location Registers (VLR) contains selected administrative information from the HLR authenticates the user tracks which customers have the phone on and ready to receive a call periodically updates the database on which phones are turned on and ready to receive calls

A MOBILE or A CELL phone??

CELL Structure • The carrier chops up an area, such as a city, into cells • Cell size depends on current load. E.g. IMT N • Additional traffic appears as noise to other users “Network Busy” • If the noise level is too high users drop out of calls. • Each cell has a base station that consists of a tower and a small building containing the radio equipment.

K=7

3 2

4 1 7

5 6

Handoff • Continuous signal strength measurement by the home base station • Coordination between the home BS and the one being approached through the MTSO • This handoff switches your phone to the new cell.

HANDOFF – HARD and SOFT Hard handover • When a call is in process the changes in location require more processing • Within a BSS the BSC, which knows the current radio link configuration, prepares an available channel in the new BTS • The MS is told to switch over to the new BTS

HANDOFF – HARD and SOFT Soft handover In a soft handover the MS is connected to two BTS’s simultaneously

Types of Handoff Intra MSC movement HLR VLR1

3

VLR2

2 MSC1

LA1

1

MSC2 4 LA2

Types of Handoff Inter-MSC movement

HLR

4

3

VLR2 2

MSC1

VLR1

5 MSC2 1

LA1

LA2

6

Types of Handoff Inter-VLR movement HLR 7 VLR1 MSC1 LA1

MSC2 LA2

8

3 2

4

5 VLR2 1 6

Call Flow Process Landline - Mobile • The telephone number associated with the phone user is dialled. • The call is routed to the mobile phone operator s GMSC. • The GMSC, as the name suggests, acts as the "entrance" from exterior portions of the network.

Call Flow Process Landline - Mobile • 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, knows which Visitor Location Register (VLR) the phone is associated with.

Determine how to route 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 HLR.

Determine how to route the call • 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 VLR then the HLR returns a number known as the Call Forward Not Reachable number to the Gateway MSC, and the call is forwarded there

Determine how to route the call • If the HLR knows that the phone is roaming in a particular VLR area, • then it will request a temporary number from that VLR. • This number is relayed back to the Gateway MSC • Then used to route the call to the MSC where the called phone is roaming

Ringing the phone • When the call arrives at the Visiting MSC • It pages all the mobile phone in the area in order to inform the phone that there is an incoming call for it. • If the subscriber answers, a speech path is created through the Visiting MSC and Gateway MSC back to the network of the person making the call, and a normal telephone call follows.

Wireless challenges • Path loss and fading – Buildings, trees etc. block or weaken signals • Reflected signals – Multiple copies of a signal with small timing differences – Even fading due to interference • Flash crowds – The customer's traffic patterns are difficult to predict

Revolutionising Urban INDIA • Business Transactions – Banking Industry • Mobile Banking • SMS Alerts

– Share Transactions – Ticketing

Revolutionising Urban INDIA • Facilitating Marketing – SMS Advertisements – Product Information – General Awareness – Mass Campaigning

Revolutionising Urban INDIA… • Booming Entertainment Industry • • • • • • •

RINGTONES VIDEO CLIPS WALLPAPERS MOBILE GAMES CAMERA RADIO MUSIC

Substituting Computers • MOBILE INTERNET • GRPS • GPS

Revolutionising life in Rural INDIA A Research By Nokia • HEALTH CARE Better connect rural communities Networks to share information & advice

• Education Via mobiles to children in remote villages

• Governance Platform to access Information & Services Using TEXT,DATA,AUDIO

Revolutionising Economic & Social life in Rural INDIA • Finance  Tool for financial transactions by swapping airtime for goods and services  Transfer credits into cash

• Micro-commerce  Significant distances Between markets  Change the logistical issues

• Transport  Provide real-time information about public transport services

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