Transcript Satellite Communications - Dr. N.D. Gohar, HoD CSE

Cellular Mobile Communications-I
An Introduction
Dr. Nasir D. Gohar
Cellular Mobile Communications-I
An Introduction
 Cell Phone Growth in Pakistan & Worldwide
 According to a Media Report (Goliath, May 25, 2005), Cell
Phones in Pakistan to Touch 15M mark in December 2005
 Another Media Report (Middle East Times, June 20, 2006)
Predicts the number of Cell Phones will rise from 2.2 Billion to 3
Billion worldwide by the end of Year 2008
 According to MOBILEDIA (Jan 20, 2006)
 U.S. offers more room for growth than Russia, and Japan offers greater
future growth than South Africa
 The number of mobile subscribers worldwide reached over 2 billion by the
end of 2005, and is predicted to rise to 3.96 billion by 2011
 The Asia Pacific Region will account for 50% of the total number of
subscribers worldwide by the end of this decade with a staggering 1.067
billion subscribers shared between China and India alone, the world's two
biggest mobile markets
Cellular Mobile Communications-I
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]
Cellular Mobile Communications-I
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]
City 1
Land Line Link
Paging Terminal
PSTN
City 2
PAGING CONTROL
CENTRE
Land Line Link
Paging Terminal
City N
Paging Terminal
Cellular Mobile Communications-I
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
Cordless Handset
PSTN
Fixed Base
Station
Cellular Mobile Communications-I
An Introduction
 Limitations of Simple Mobile Radio Systems
 The Cellular Approach
 Divides the Entire Service Area into Several Small Cells
 Reuse the Frequency
 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
Cellular Mobile Communications-I
An Introduction
Cellular Mobile Communications-I
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
Cellular Mobile Communications-I
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
Cellular Mobile Communications-I
An Introduction
Frequency Reuse Factor

Frequency Reuse Factor N = No. of Distinct Channel Groups = Maximum Cluster Size
Cellular Mobile Communications-I
An Introduction
Frequency Reuse Example-2
 Suppose W = 25 MHz and B = 25 KHz/voice channel
 W/B = 1000 voice channels can be supported over the spectrum
 Scenario 1: a high power base station covering entire area (M = N = 1)
 system capacity n = 1000 users
 Scenario 2:
 Coverage area divided into M = 20 cells with reuse factor N = 4
 Each cluster accommodate 1000 active users
 5 clusters in coverage area  system capacity n = 5000 users
 Scenario 3:
 M = 100 cells, N = 4  system capacity n = 25000 users
 Scenario 4:
 M = 100 cells, N = 1  system capacity n = 100000 users
Cellular Mobile Communications-I
An Introduction
 Common Air Interface (CAI)
Common Air Interface: A Standard
that defines Communication between a
Base Station and Mobile
Specifies Four Channels [Voice
Channels and Control / Setup
Channels]
Reverse Channel
FVC: Forward Voice Channel
RVC: Reverse Voice Channel
FCC: Forward Control Channel
RCC: Reverse Control Channel
Forward Channel
Cellular Mobile Communications-I
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
 Call Setup Procedure (Cont’d)
3. Receives a Call
Initiation Request from
Base Station, and
Verifies that User has a
Valid MIN & ESN pair
MSC
4. Locates the
7. Connects the
Called Party,
Allocates a VFPs
and Instructs the
Base Stations via
FCC
Called Party[on
PSTN]/Mobile to the
Mobile
5. Pages for the Called
Mobile, the Mobiles are
instructed to move to the
Allocated VFPs
respectively
FCC
Base Station
RCC
2. Receives a Call
Initiation Request, with
MIN, ESN, SCM and
Called Part Number
8. Begins Voice
FVC
Transmission
8. Begins Voice
RVC
Reception
6. Receives [Called
Mobile] the Page and
Matches the MIN, the
Mobiles get ready to
move to the respective
Allocated VFPs
FCC
1. Makes a Call Initiation
Mobile
RCC
Request, with MIN and
Called Part Number
8. Begins Voice
FVC
Reception
8. Begins Voice
RVC
Transmission
TIME
Cellular Mobile Communications-I
An Introduction
 Handoff and Roaming
Handoff
When a Mobile is on the edge of a Cell
RSL of the Mobile in that Cell gets bellow a set Level
Base Station of the Cell originates a Handoff request
MSC gets RSL Info from all the Candidate Cells
MSC asks the Originating Cell and the Strongest
Candidate Cell to Coordinate
In Case the Handoff is Successful, the Mobile is asked
to switch to another VFP
All this happens in a matter of seconds and you hear a
little CLICK sound
Roaming
When SID of the Control Channel and that
programmed in the Mobile does not match:
The Mobile is in another Service Provider’s Area
MSC of the Cell contacts the MSC of the Mobile’s
Home System
After Verification, if the Mobile is Allowed, the new
MSC is ready to Serve.
MSC
Cellular Mobile Communications-I
An Introduction
 Comparison of Common Wireless Communication
Systems
Comparison of Mobile Communication Systems - Mobile/Base Station
System
Coverage
Range
Required
InfraStructure
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
Cellular Mobile Communications-I
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
Cellular Mobile Communications-I
An Introduction
 Cellular Mobile Access Technologies
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
Cellular Mobile Communications-I
An Introduction
 Cellular Mobile Access Technologies
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]
Cellular Mobile Communications-I
An Introduction
 Cellular System vs. Personal Communication
System/Network (PCS/PCN)
 Personal Communication Services [PCS] is a system, very similar
to Cellular Phone Service with great emphasis on personal
services (such as Paging, Caller ID, and E-mail] and mobility
 Originated in UK, to improve its competitiveness in the field
 PCS has smaller Cell size, therefore, requires more infra-structure
 PCS works in 1.85-1.99 GHz band
 PCS uses TDMA Technology but with 200 KHz Channel Bandwidth
with eight time-slots[as compared to 30 KHz and 3 time-slots used
by Digital Cellular Phone System IS-54/IS-136]
 GSM and Cellular Digital Packet Data[CDPD] also use PCS Tech.
Cellular Mobile Communications-I
An Introduction
 Dual Band/Dual Mode Cellular Phones
Dual Band Phone:
Supports both bands 800 MHz and
Dual Mode Phone:
Supports both FDMA and TDMA Access
1900 MHz
Technologies
Dual Band/Dual Mode Phone: Supports both Bands
and Both Access Technologies
Tri-Mode Phone: It can Support FDMA/TDMA/CDMA all
Access Tech. A popular version of Tri-Mode Cellular Phone is the
one which supports GSM [800 MHz as well as 1900 MHz (USA
version)] as well as FDMA.
Cellular Mobile Communications-I
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