A brief introduction to cellular-mobile-communications.ppt

Cellular Mobile Communications
An Introduction

An Introduction
Several Types of Mobile Radio Systems
 Garage Door Controller [<100 MHz]
 Remote Controllers [TV/VCR/DISH][Infra-Red: 1-100 THz]
 Cordless Telephone [<100 MHz]
 Hand-Held Radio [Walki-Talki] [VHF-UHF:40-480 MHz]
 Pagers/Beepers [< 1 GHz]
 Cellular Mobile Telephone[<2 GHz]
Classification
 Simplex System: Communication is possible in only one direction : Garage Door
Controller, Remote Controllers [TV/VCR/DISH] Pagers/Beepers
 Semi-Duplex System: Communication is possible in two directions but one talks
and other listens at any time[Push to Talk System]: Walki-Talki
 Duplex System: Communication is possible in both directions at any time: Cellular
Telephone [FDD or TDD]

An Introduction
Paging System: For Transmission of Brief Numeric/Alpha-
numeric/Voice Messages [Pages] to Subscriber
 To Notify/Alert the User
 Simplex Service
 Modern Paging Systems Can Send News Head-Lines, Stock Info, or Fax
 Application Dependent System Range [2 Km to World-wide]
PAGING CONTROL
CENTRE
Paging Terminal
PSTN
Land Line Link
Land Line Link
Paging Terminal
Paging Terminal
City 1
City 2
City N

An Introduction
Cordless Telephone System: To Connect a Fixed
Base Station to a Portable Cordless Handset
 Early Systems (1980s) have very limited range of few tens of
meters [within a House Premises]
 Modern Systems [PACS, DECT, PHS, PCS] can provide a limited
range & mobility within Urban Centers
PSTN
Fixed Base
Station
Cordless Handset

An Introduction
 Basic Components of a Cellular Telephone System
 Cellular Mobile Phone: A light-weight hand-held set which is an
outcome of the marriage of Graham Bell’s Plain Old Telephone
Technology [1876] and Marconi’s Radio Technology [1894] [although a
very late delivery but very cute]
 Base Station: A Low Power Transmitter, other Radio Equipment
[Transceivers] plus a small Tower
 Mobile Switching Center [MSC] /Mobile Telephone
Switching Office[MTSO]
 An Interface between Base Stations and the PSTN
 Controls all the Base Stations in the Region and Processes User ID and
other Call Parameters
 A typical MSC can handle up to 100,000 Mobiles, and 5000 Simultaneous
Calls
 Handles Handoff Requests, Call Initiation Requests, and all Billing & System
Maintenance Functions

An Introduction
 The Cellular Concept
RF spectrum is a valuable and scarce commodity
RF signals attenuate over distance
Cellular network divides coverage area into cells, each
served by its own base station transceiver and antenna
Low (er) power transmitters used by BSs; transmission
range determines cell boundary
RF spectrum divided into distinct groups of channels
Adjacent cells are (usually) assigned different channel
groups to avoid interference
Cells separated by a sufficiently large distance to avoid
mutual interference can be assigned the same channel group 
frequency reuse among co-channel cells

An Introduction
 An Example of Frequency Reuse
 Suppose we have spectrum
for 100 voice channels
 Scenario 1: a high power
base station covering entire
area – system capacity = 100
channels
 Scenario 2: divide spectrum
into 4 groups of 25 channels
each; cells (1, 7), (2, 4), (3,
5), 6 are assigned distinct
channel groups – system
capacity = 175 channels

An Introduction
Frequency Reuse Factor
 Frequency Reuse Factor N = No. of Distinct Channel Groups = Maximum Cluster Size

An Introduction
 Common Air Interface (CAI)
Forward Channel
Reverse Channel
Common Air Interface: A Standard
that defines Communication between a
Base Station and Mobile
Specifies Four Channels [Voice
Channels and Control / Setup
Channels]
FVC: Forward Voice Channel
RVC: Reverse Voice Channel
FCC: Forward Control Channel
RCC: Reverse Control Channel

An Introduction
 Call Setup Procedure
Cellular Phone Codes: Special Codes are associated with each Cell
Phone to identify the phone, its owner, and service provider:
Electronic Serial Number(ESN) -A Unique 32-bit Code
Mobile Identification Number(MIN): A Subscriber’s Telephone Number
 Station Class mark (SCM): Indicates the Max Tx Power for the User
When a Cellular Phone is turned on and Initiates a Call:[see
next slide]
Monitors the Control Channels and gets hold on to the strongest one
Makes a Call Initiation Request[Dials the Called part Number, MIN , ESN and SCM
automatically transmitted]
Validation Procedure at MSC & Voice-Frequency pair Allocation
Base Station Pages the Information for the Mobile
MSC Connects the Mobile with the Called Party[Another Mobile/Landline Phone]
Call is Established and Communication Starts

Cellular Mobile Communications-I
An Introduction
 Comparison of Common Wireless Communication
Systems
System
Coverage
Range
Required
Infra-
Structure
Complexity
Hardware
Cost
Carrier
Frequency
Functionality
Tv Remote Control Low Low Low Low Infra-Red Tx/Rx
Garage Door Contol Low Low Low Low <100 Mhz Tx/Rx
Paging System High High Low/High Low/High <1GHz Rx/Tx
Cordless Phone Low Low Moderate/Low Low/Moderate <100 MHz Transceiver
Cellular Phone High High High Moderate/High <1 GHz Transceiver
Tx = Transmitter Rx = Receiver
Comparison of Mobile Communication Systems - Mobile/Base Station

An Introduction
 Cellular Mobile Access Technologies
FDMA Assigns each Call a Separate Frequency
Works like Radio Stations
Mainly Analogue Technology-used by AMPS, NAMPS, E-TACS, NMT-450, JTACS
Not an Efficient Method for Digital Transmission
849 MHz
869 MHz

An Introduction
TDMA Assigns each Call a
certain Time-Slot on a Designated
Frequency
Each Mobile/User gets one-third of
a total Channel Time-Slot[6.7 ms]
Courtesy of Compression
Techniques: Speech Data in Digital
Form takes considerably less time
Optimal Frequency Usage: System
Capacity improves by three times
Operates both in 800 MHz[IS-54]
and 1900 MHz[IS-136]
Digital Access Technology use by
GSM, USDC, IDEN, PDC and PCS

An Introduction
CDMA Assigns a Unique Code to
each Call and Spreads it over the entire
bandwidth available
 A form of Spread Spectrum
Technology
Speech Data is sent in small pieces
over number of Discrete Frequencies
available at any time in a specified range
 Receiver uses the same unique Code
to Recover the Speech Data
GPS used for Exact Time Stamp
Can handle 8-10 Calls in the same
Channel Space as one Analogue Channel
An Access Technology for 3G Mobile
Systems[IMT-2000]
Supports both Bands [800 MHz and
1900 MHz]

An Introduction
 Trends in Cellular radio and Personal
Communications
 PCS/PCN: PCS calls for more personalized services whereas
PCN refers to Wireless Networking Concept-any person,
anywhere, anytime can make a call using PC. PCS and PCN
terms are sometime used interchangeably
 IEEE 802.11: A standard for computer communications using
wireless links[inside building].
 ETSI’s 20 Mbps HIPER LAN: Standard for indoor Wireless
Networks
 IMT-2000 [International Mobile Telephone-2000
Standard]: A 3G universal, multi-function, globally compatible
Digital Mobile Radio Standard is in making
 Satellite-based Cellular Phone Systems
 A very good Chance for Developing Nations to Improve
their Communication Networks

A brief introduction to cellular-mobile-communications.ppt

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