Introduction To Cellular Mobile Communications

Cellular Mobile Communications-I An In tr oduction 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/Alphanumeric/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] FVC: Forward Voice Channel RVC: Reverse Voice Channel FCC: Forward Control Channel RCC: Reverse Control Channel

Reverse 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

Mobile

1. Makes a Call Initiation 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 infrastructure  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 IS54/IS-136]  GSM and Cellular Digital Packet Data[CDPD] also use PCS

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: Access

Supports both FDMA and TDMA

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