1. Cellular Mobile Communications-I An Introduction
Dr. Nasir D. Gohar

2. 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 billion subscribers shared between China and India alone, the world's two biggest mobile markets

3. Cellular Mobile Communications-I An Introduction
Several Types of Mobile Radio Systems
Garage Door Controller [<100 MHz]
Remote Controllers [TV/VCR/DISH][Infra-Red: THz]
Cordless Telephone [<100 MHz]
Hand-Held Radio [Walki-Talki] [VHF-UHF: 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]

4. 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]

5. 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

6. 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

7. Cellular Mobile Communications-I An Introduction

8. 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

9. 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

10. Cellular Mobile Communications-I An Introduction
Frequency Reuse Factor
Frequency Reuse Factor N = No. of Distinct Channel Groups = Maximum Cluster Size

11. 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 = users
Scenario 4:
M = 100 cells, N = 1  system capacity n = users

12. 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]
FVC: Forward Voice Channel
RVC: Reverse Voice Channel
FCC: Forward Control Channel
RCC: Reverse Control Channel
Forward Channel
Reverse Channel

13. 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

14. Cellular Mobile Communications-I An Introduction
Call Setup Procedure (Cont’d)

15. 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.

16. Cellular Mobile Communications-I An Introduction
Comparison of Common Wireless Communication Systems

17. 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

18. 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

19. 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]

20. 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 ] 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 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.

21. Cellular Mobile Communications-I An Introduction
Dual Band/Dual Mode Cellular Phones
Dual Band Phone: Supports both bands 800 MHz and 1900 MHz
Dual Mode Phone: Supports both FDMA and TDMA Access 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.

22. 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 : 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