Lect-5 Introduction to Cellular Mobile Communications (1)

Cellular Mobile Communications-IAn Introduction Dr. Nasir D. Gohar

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Cellular Mobile Communications-IAn 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

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Cellular Mobile Communications-IAn Introduction Paging System: For Transmission of Brief Numeric/Alpha-numeric/Voice Messages [Pages] to SubscriberTo Notify/Alert the UserSimplex ServiceModern Paging Systems Can Send News Head-Lines, Stock Info, or FaxApplication Dependent System Range [2 Km to World-wide]

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Cellular Mobile Communications-IAn Introduction Cordless Telephone System: To Connect a Fixed Base Station to a Portable Cordless HandsetEarly 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

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Cellular Mobile Communications-IAn Introduction Limitations of Simple Mobile Radio SystemsThe Cellular ApproachDivides the Entire Service Area into Several Small Cells Reuse the FrequencyBasic Components of a Cellular Telephone SystemCellular Mobile Phone: A light-weight hand-held set which is an outcome of the marriage of Graham Bells Plain Old Telephone Technology [1876] and Marconis Radio Technology [1894] [although a very late delivery but very cute]Base Station: A Low Power Transmitter, other Radio Equipment [Transceivers] plus a small TowerMobile Switching Center [MSC] /Mobile Telephone Switching Office[MTSO]An Interface between Base Stations and the PSTNControls all the Base Stations in the Region and Processes User ID and other Call ParametersA 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

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Cellular Mobile Communications-IAn Introduction

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Cellular Mobile Communications-IAn Introduction The Cellular Concept

RF spectrum is a valuable and scarce commodityRF signals attenuate over distanceCellular network divides coverage area into cells, each served by its own base station transceiver and antennaLow (er) power transmitters used by BSs; transmission range determines cell boundaryRF spectrum divided into distinct groups of channelsAdjacent cells are (usually) assigned different channel groups to avoid interferenceCells separated by a sufficiently large distance to avoid mutual interference can be assigned the same channel group frequency reuse among co-channel cells

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Cellular Mobile Communications-IAn Introduction An Example of Frequency Reuse

Suppose we have spectrum for 100 voice channelsScenario 1: a high power base station covering entire area system capacity = 100 channelsScenario 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

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Cellular Mobile Communications-IAn Introduction Frequency Reuse Factor

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

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Cellular Mobile Communications-IAn Introduction Frequency Reuse Example-2

Suppose W = 25 MHz and B = 25 KHz/voice channelW/B = 1000 voice channels can be supported over the spectrumScenario 1: a high power base station covering entire area (M = N = 1) system capacity n = 1000 usersScenario 2:Coverage area divided into M = 20 cells with reuse factor N = 4Each cluster accommodate 1000 active users5 clusters in coverage area system capacity n = 5000 usersScenario 3:M = 100 cells, N = 4 system capacity n = 25000 usersScenario 4:M = 100 cells, N = 1 system capacity n = 100000 users

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Cellular Mobile Communications-IAn Introduction Common Air Interface (CAI)

Common Air Interface: A Standard that defines Communication between a Base Station and MobileSpecifies Four Channels [Voice Channels and Control / Setup Channels]

FVC: Forward Voice ChannelRVC: Reverse Voice ChannelFCC: Forward Control ChannelRCC: Reverse Control Channel

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Cellular Mobile Communications-IAn 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 Subscribers Telephone Number Station Class mark (SCM): Indicates the Max Tx Power for the UserWhen a Cellular Phone is turned on and Initiates a Call:[see next slide]Monitors the Control Channels and gets hold on to the strongest oneMakes 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 MobileMSC Connects the Mobile with the Called Party[Another Mobile/Landline Phone]Call is Established and Communication Starts

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Cellular Mobile Communications-IAn Introduction Call Setup Procedure (Contd)

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Cellular Mobile Communications-IAn Introduction Handoff and Roaming

HandoffWhen a Mobile is on the edge of a CellRSL of the Mobile in that Cell gets bellow a set LevelBase Station of the Cell originates a Handoff requestMSC gets RSL Info from all the Candidate CellsMSC asks the Originating Cell and the Strongest Candidate Cell to CoordinateIn Case the Handoff is Successful, the Mobile is asked to switch to another VFPAll this happens in a matter of seconds and you hear a little CLICK soundRoamingWhen SID of the Control Channel and that programmed in the Mobile does not match:The Mobile is in another Service Providers AreaMSC of the Cell contacts the MSC of the Mobiles Home SystemAfter Verification, if the Mobile is Allowed, the new MSC is ready to Serve.

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Cellular Mobile Communications-IAn Introduction Comparison of Common Wireless Communication Systems

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Cellular Mobile Communications-IAn Introduction Cellular Mobile Access Technologies

FDMA Assigns each Call a Separate FrequencyWorks like Radio StationsMainly Analogue Technology-used by AMPS, NAMPS, E-TACS, NMT-450, JTACSNot an Efficient Method for Digital Transmission

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Cellular Mobile Communications-IAn 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 timeOptimal Frequency Usage: System Capacity improves by three timesOperates both in 800 MHz[IS-54] and 1900 MHz[IS-136]Digital Access Technology use by GSM, USDC, IDEN, PDC and PCS

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Cellular Mobile Communications-IAn 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 TechnologySpeech 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 DataGPS used for Exact Time StampCan handle 8-10 Calls in the same Channel Space as one Analogue ChannelAn Access Technology for 3G Mobile Systems[IMT-2000]Supports both Bands [800 MHz and 1900 MHz]

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Cellular Mobile Communications-IAn 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 mobilityOriginated in UK, to improve its competitiveness in the fieldPCS has smaller Cell size, therefore, requires more infra-structurePCS works in 1.85-1.99 GHz bandPCS 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.

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Cellular Mobile Communications-IAn Introduction Dual Band/Dual Mode Cellular PhonesDual Band Phone: Supports both bands 800 MHz and 1900 MHzDual Mode Phone: Supports both FDMA and TDMA Access TechnologiesDual Band/Dual Mode Phone: Supports both Bands and Both Access TechnologiesTri-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.

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Cellular Mobile Communications-IAn 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 interchangeablyIEEE 802.11: A standard for computer communications using wireless links[inside building].ETSIs 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 makingSatellite-based Cellular Phone SystemsA very good Chance for Developing Nations to Improve their Communication Networks

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