Wireless Telecommunication Issue 1.0

8/4/2019 Wireless Telecommunication Issue 1.0

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© Tech Mahindra Limited 2007 Tech Mahindra Limited confidential

Basics Of Telecommunications: Wireless

Ameya Ashtamkar

Swapnil Ratnakar

Issue 1.0



Overview

Topics to be covered:

Wireless Vs Wireline WLL

Wireless Access Technologies

GSM

CDMA

Generations of Mobile Systems

CONFIDENTIAL© Copyright 2007 Tech Mahindra Limited



Wireless Vs Wireline

Wireline

Pros

“Higher Data speeds ‘ compared to wireless

More suited for “Business customers”

Cons

High upfront Capital investment

Uncertainty about customer uptake of services

Problems associated with “Right of way permission”

Problems of digging and laying cables in congested areas




Wireless Local Loop




Wireless Local Loop (WLL)

Wireless local loop (WLL), also called Broadband Wireless Access(BWA) radio in the loop (RITL) or fixed-radio access (FRA) or fixed-wireless access (FWA) or Fixed Wireless Terminal (FWT), is the useof a wireless communications link as the "last mile / first mile"

connection for delivering plain old telephone service (POTS) andbroadband Internet to telecommunications customers




WLL Continued…

WLL replaces the ‘wire’ in the Access network between subscriberand the Switching node by means of Radio communication .

Unlike wired line telephone, WLL can have “Limited Mobility” as

long as it receives signal from the Central Radio Base Station

WLL Does Not provide mobile communications anywhere andeverywhere like Cellular Mobile Systems.




Wireless Local Loop Architecture

Coverage area

Radio Base station

(Wireless)

LE

B

S

C

Wireline




WLL Vs Full Blown Mobile Communications

Pure WLL

Coverage limited to Radio BaseStation (RBS)

No “handover “ between RadioBase Stations

No “Roaming”

Just a wireless extension of “switch”- Not too “Intelligent”

Cellular Mobile

Coverage“everywhere”

Automatic handover betweenRBSs

Roaming nationally & internationally

An “Intelligent” system




Global System for Mobile communications




GSM




GSM Radio Interface

Most Commonly Used Bands :

900 MHz 1800 MHz

850 MHz

1900 MHZ

25 MHz Bandwidth each for uplink & downlink

Subdivided into 124 carrier frequency channels

Each spaced 200 KHz apart Modulation technique used: GMSK




Cell Structure

Four Major Types of Cells

Macro Micro

Pico

Umbrella




GSM Continued…

Sw itching System:

The Switching System is responsible for performing call processing& subscriber related functions. Following are the functional units of the switching system

Home Location Register (HLR) : All the subscriber related information

Services, Authentication parameters

Location of MS




GSM Continued…

Mobile services Sw itching Centre (MSC):

Telephony switching functions Controls call to & from other telephone & data systems

Network interfacing, Common Channel Signaling

Visitor Location Register (VLR):

Temporary information about visiting subscribers

Authentication Centre (AUC): Authentication & encryption parameters for verifying user’s identity




GSM Continued…

Equipment Identity Register (EIR):

Contains a unique hardware identity no. of the mobile equipment Checks for the validity of the equipment

Mobile Station

MS = Equipment + SIM

SIM contains subscription information, authentication key etc.


GSM C i d



GSM Continued…

Base Station System (BSS):

All radio-related functions are performed Consists of Base Station Controller (BSC) Base Transceiver Stations

(BTS).

BSC provides all control functions & control links between MSC &

BTS BTS handles the radio interface to the mobile station


GSM S i



GSM Services

GSM Subscriber Services:

In addition to the normal telephony & emergency calling services,GSM supports following additional services,

Dual Tone Multi Frequency

Facsimile Group III

Short Message Service (SMS)

Cell Broadcast

Voice Mail

Fax Mail




Code Division Multiple Access


Int od ction to CDMA



Introduction to CDMA

Code division multiple access (CDMA) is a form of multiplexing

and a method of multiple access that divides up a radio channelnot by time (as in time division multiple access), nor by frequency(as in frequency-division multiple access), but instead by usingdifferent pseudo-random code sequences for each user

CDMA also refers to digital cellular telephony systems that makeuse of this multiple access scheme, such as those pioneered byQualcomm, and W-CDMA by the International TelecommunicationUnion or ITU




The GSM standard is a specification of an entire network

infrastructure & the CDMA interface relates only to the airinterface—the radio part of the technology. For example GSMspecifies an infrastructure based on internationally approvedstandard while CDMA allows each operator to provide the networkfeatures as it finds suited


CDMA Features



CDMA Features

Narrowband message signal multiplied by wideband spreading

signal or pseudo noise code Each user has his own pseudo noise (PN) code

Soft capacity limit: system performance degrades for all users asnumber of users increases

Cell frequency reuse: no frequency planning needed

Soft handoff increases capacity

Near-far problem

Interference limited: power control is required

Wide bandwidth induces diversity: rake receiver is used

Extended battery life because of effective power control.


Handoff



Handoff

As the CDMA phone roams through the network, it detects the PN

offsets of the neighbouring cells and reports the strength of eachsignal back to the reference cell of the call (usually the strongestcell). If the signal from a neighbouring cell is strong enough, themobile will be directed to "add a leg" to its call and starttransmitting and receiving to and from the new cell in addition to

the cell (or cells) already hosting the call. Likewise, if a cell's signalbecomes too weak the mobile is directed to drop that leg. In thisway, the mobile can move from cell to cell and add and drop legsas necessary in order to keep the call up without ever dropping the

link.






First Generation (1G ):

Analog cell phone standards introduced in 80s Radio signals that 1G networks use are analog

Second Generation (2G):

2G networks are digital

GSM is TDMA based

IS-95 is CDMA based




Third Generation (3G):

The services associated with 3G provide the ability to transfersimultaneously both voice data (a telephone call) and non-voice

data

In Asia, Europe, and the USA, telecommunication companies use

The most significant feature offered by third generation mobiletechnologies is the capacity to support greater numbers of voiceand data customers




Fourth Generation (4G):

There is no set definition to what 4G is The Wireless World Research Forum (WWRF) defines 4G as a

network that operates on Internet technology, combines it withother applications and technologies such as Wi-Fi and WiMAX, and

runs at speeds ranging from 100 Mbps (in cell-phone networks) to1 Gbps (in local Wi-Fi networks




Thank You


Wireless Telecommunication Issue 1.0

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