Cellular Mobile Communications 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]

Cellular Mobile Communications 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]

Cellular Mobile Communications 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

Cellular Mobile Communications 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

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

Cellular Mobile Communications 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

Cellular Mobile Communications 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

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 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