wireless telecommunication issue 1.0
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Basics Of Telecommunications: Wireless
Ameya Ashtamkar
Swapnil Ratnakar
Issue 1.0
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Overview
Topics to be covered:
Wireless Vs Wireline WLL
Wireless Access Technologies
GSM
CDMA
Generations of Mobile Systems
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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
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Wireless Local Loop
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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
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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.
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Wireless Local Loop Architecture
Coverage area
Radio Base station
(Wireless)
LE
B
S
C
Wireline
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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
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Global System for Mobile communications
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GSM
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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
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Cell Structure
Four Major Types of Cells
Macro Micro
Pico
Umbrella
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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
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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
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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.
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GSM C i d
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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
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GSM S i
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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
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Code Division Multiple Access
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Int od ction to CDMA
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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
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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
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CDMA Features
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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.
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Handoff
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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.
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Generations of Mobile Systems
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Generations of Mobile Systems
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
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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
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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
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Thank You
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