s09 Gsm Basics_tgengba110

8/12/2019 s09 Gsm Basics_tgengba110

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1TGENGBA110 GSM Basics

Module Id : TGENGBA110

GSM Basics


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Contents

Wireless as mediaTypes of Spectrum

Radio Wave Propagation

Modulation & Multiple Access Techniques

Historical developments in Mobile fieldMobile generations

Cellular principles

GSM areas

Mobile Identities


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Wireless as Media

Wireless belongs to unguided media categoryWireless as media can be used for several

applications such as

Microwave

UHF Systems

SatelliteGSM / CDMA Network

And the usage is forShip to shore communication

Air Traffic Control purposesMilitary / Police

Remote locations of private concerns

Commercial communication service providers etc.,


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Types of Spectrum

radio spectrum is the complete range of frequencies of

electromagnetic radiation useful in radio communicationLicensedPermission /registration for use is required

Coordination required

Interference is better controlledExample- microwave, satellite, GSM/CDMA networks

License-exempted (un-licensed)Anyone can use

no coordination is required

creates high interference is used in large unregulated

manner

Example- ISM band and UNII band


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License-exempt Bands

ISM (Industrial, Scientific, Medical) band 2.4 GHz : 2400-2483.5 MHz

U-NII (Unlicensed National Information

Infrastructure) bands 5.2 GHz (or Lower 5): 5150-5250 MHz

5.3 GHz (or Middle 5): 5250-5350 MHz

5.7 or 5.8 GHz (or Upper 5): 5725-5825 MHz


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1 2 3 124

890 MHz 915 MHz

UPLINK FREQUENCY

B

T

S

960 MHz

1 3 124

935 MHz

DOWNLINK FREQUENCY

2

Licensed- GSM 900Spectrum

Total Bandwidth = 25MHz & Channel Spacing 200kHzOut of Total 125 Frequencies & 1 frequency is Guard Bandand remaining 124 are used for GSM


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What Governs Distance?

Distance of propagation or radio coverage is governedby many factors like :

The radios technology The strength of the transmitted signal

The radios threshold specifications The radios frequency of operation Output power regulations Obstacles between the end points Climate/Terrain The antenna pattern


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Wireless Link Design Process

The whole process is methodical, systematic anditerative, hence sometimes lengthy and may go through

many redesign phases before the required quality and

availability are achieved

FrequencyPlanning

Link Budget

Quality and

Availability

Calculations

Fading

Predictions

Interference

analysis

Propagation

losses

Branching

losses

Other Losses

Rain

attenuation

Diffraction-

refraction

losses

Multipath

propagation


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Antenna Radiation Pattern


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A side lobe refers to any lobe of energy other than themain lobe.

The Front-to-Back Ratio (FBR), the differencebetween the power level at the peak of the beam and

the power level at a point 180o from that point, can beread directly from the radiation pattern.

A high FBR helps reduce interference betweenadjacent cell coverage areas.

Antenna Radiation Pattern


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Reflection

Refraction

Scattering

DiffractionAbsorption

Attenuation

Radio Wave Propagation


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Modulation

Modulation:The process, or result of theprocess, of varying a characteristic of a carrier,in accordance with an information-bearingsignal

Influencing Factors

Interference

Antenna Height

Attenuation Characteristics

Attenuation for RF is lower than for Audio

Frequency


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Modulation of Digital Signal

ASK (Amplitude Shift Keying)

FSK (Frequency Shift Keying)PSK (Phase Shift Keying)QAM (Quadrature Amplitude Modulation)


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Multiple Access

Multiple Access refers the sharing of

common resources in order to allow

simultaneous communication by multiple

users and this common resource is the RF

spectrumApplicable between BTS and MS

FDMA (Frequency Division Multiple Access)

TDMA (Time Division Multiple Access)

CDMA (Code Division Multiple Access)


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The Access Network

(E1)Radio Access N/W

Radio InterfaceFDMA/TDMA/CDMA

Local

Switch

or End

Office

BTS CustomerPremises


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Multiple Access Methods

Long distance wireless access to subscribers using

single channel systems

Multiple Access techniques are then deployed toshare the available spectrum in an efficient manner

FDMA -Frequency Division Multiple Access -

Individual transmissions separated in frequency TDMA -Time Division Multiple Access - Individual

transmissions are separated from one another in

time

CDMA- Code Division Multiple Access - Largenumber of transmissions are combined on the same

R.F.channel at the same time but are separated by

codes


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FDMA: Frequency Division Multiple Access

eg. Analogue AMPS

Each user defined full-time use of part of

the spectral allocation

TDMA : Time Division Multiple Access

eg. IS-136, GSMEach user has part time use of the

spectral allocation

CDMA: Code Division Multiple Accesseg. IS-95

Full time us of the full spectral allocation

Time

Multiple Access Methods

Time

TimeFREQUEN

CY

FREQUENCY

FREQUENCY


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Mobile Phone ! What ?

Phone on the move

Allows to communicate to people with

anybody while on move


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Objectives of Mobile Communication

Any time Any whereMobility & Roaming

High capacity & Subs density

Efficient use of Radio Spectrum

Seamless Network ArchitectureLow Cost

Flexibility

Innovative Services

Standard Interfaces


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Cellular Mobile Tele Systems

Cellular mobile Systems are Based on

"Re-use of available frequency

Allows greater density of users

Presently available Networks

1 . Analogue Cellular Radio2 . Digital Cellular Radio Standards being Used

1. Universal Mobile Telecommunication

System (UMTS), by ETSI2. International Mobile

Telecommunication System (IMTS) by ITU


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BTS

BTS

BTS

BSC MSC

DB DB DB

PSTN

SWITCH

PSTN

SWITCH

VOICE

SIGNAL

PSTNGSM N/W Comparison


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1G - Analogue (Cellular revolution)- Only Mobile Voice Services

- Used FDMA technique

- E.g., AMPS, NMT system

1G Limitations : Low service quality

Long call set up time

Inefficient use of band-width

Interference Bulky & Expensive equipments

Insecurity

Mobile Generations


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Digital (Breaking Digital Barrier) - MostlyVoice services & Data delivery Possible

FDMA & TDMA technique E.g., GSM, IS-95

(used in USA)

2G Advantages : Better service quality

Efficient use of band-width

Support data, speech & FAX services

Security mechanism Support power control

Advance mobility management

2G


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Voice & Data (Breaking Data Barrier)Provide both speech & data at very highspeed

Integrate all kinds of services (speech, data,

audio, video, fax etc.)Smaller call set up time

3G


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Generations of Cellular Technologies

Analogue

Cellular

Digital

PCS

Voice

+ DataPCS

3G2.5 G1G 2G 4G

IntegratedFixed/Mobile

NetworksBroadband

Multimedia

Wireless

Cellular PCS


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Cellular Systems

Cell is a Base Station (Transmitter) having anumber of RF channels Usually a Hexagonalshape

COVERAGE AREA : Each Cell covers alimited number of Mobile Subs within the Cellboundaries

CELL RADIUS : Radial distance of a CellApproximately :35 KMs ( Start up ) 200 m+ (Mature )


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Cellular Systems

In reality cell coverage is an irregularshaped circle

Exact coverage of the cell depend on the

terrain and many other factors

For design and as a first orderapproximation we assume that coverage

areas are regular polygons

Any regular polygon such as equilateral

triangle, a square, or a hexagon can beused for cell design


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Cell Representation

Theoretical

Cell Shape

Actual Cell

Shape

Hexagonal cell is used for two reasons.A hexagonal layout requires fewer cells and

therefore fewer transmitters sitesA hexagonal layout is less expensive

compared to square and triangular cells


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Large cells are planned in remote areas,

coastal regions, area with few subscribers &

large areas to be covered with min. cells.

Small cells are planned in urban areas, highsub. density & as advantage lowtransmission power required.

Applications


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Mobility to mobile subscriber

Flexibility to mobile subscriber

Expansion flexibility to network provider

Efficiency in using the spectrum

Easy to re-configure

Advantages of Cellular Systems


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Cell Sectorisation

Cell with

Omni Antenna

(360 degree)

Three Cell site with

Directional Antennas

(120 degree)

Sectorisation splits a single site into anumber of cells , each cell has Trans &

receive antennas


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GSM Service Area PLMN Service Area

MSC Service Area

Location Area

Cell Sector

GSM Network Structure


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GSM SERVICE AREA

PLMN Service Area

MSC Service Area

Location Area

CELL

Area Served

by BTS

Relation between GSM Areas


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Mobile Identities

SIM Subscriber Identity Module MSISDNMobile Station International Subscriber

Directory Number

IMSI International Mobile Subscriber Identity

TMSI Temporary Mobile Subscriber Identity

IMEI -- International Mobile Equipment Identity

MSRN Mobile Station Roaming/Routing Number


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In this module the basic concepts related towireless transmission are discussed.

The purpose & facility of various modulation &multiple access techniques are covered

Important information related to cellularprinciples, GSM areas ,mobile identities are

covered in this module.

Summary

Documents

s09 Gsm Basics_tgengba110