M.V. RAGHUNADHAssistant Professor, Dept. of ECE    NIT, Warangal – 506004.raghu@nitw.ac.in
INTRODUCTION        TOMOBILE & CELLULAR COMMUNICATIONS
Wireless systemWhat is a wireless system? Provides communication without  the use of wire Computing and communication at...
“ Mobile communications isnot Cellular communications              butCellular communications isMobile communications ” .
Mobile Com            Ex :Public emergency services               Police, Fire, Ambulance                 Single frequenc...
“ Portablecommunicators are not     mobile butmobile communicators   are Portable ”
Communication devices exhibit followingCharacteristicsa. Fixed & Wired:  Typical desktop PC, Telephone large, Data  Logger...
d. Mobile & Wireless Today’s Cell Phones, PDAs, Personal Communicators        Most interesting case, no cable restriction...
Applications:1.Vehicles:Cars with a) Digital Audio Broadcast (DAB) at 1.5 Mbps    Music ,news, weather and GPS datab) UM...
2.Emergencies Ambulance  high quality wireless adhoc nets               – accidents, natural disasters.3.Business      ...
5. Location Dependent Services Mobile computing and WLANs applications need toknow the mobile unit location.a. Follow on ...
Wi-Fi Stands for “Wireless Fidelity” High-bandwidth category of wireless  communications Short range (300-1600ft) Used to...
Mobile & Wireless Devices:a. Sensors         :     Control state information sourcesb. Embeded Controllers: Keyboards, mic...
MOBILE, CELLULAR          &PERSONAL COMMUNICATIONS
Mobility   : Mobility of Talker ( Transmitter )             Mobility of Listener ( Receiver )             Mobility of Both...
What is Mobility?A device that moves Between different geographical locations Between different networksA person who moves...
Device mobilityPlug in laptop at home/work on Ethernet  Wired network access only  Network address changes  May want acces...
People mobilityPhone available at home or at work  Multiple phone numbers to reach me  Breaks in my reachability when I’m ...
Mobility means changesHow does it affect the following?  Hardware     Lighter     More robust     Lower power  Wireless co...
Example changesAddresses  Phone numbers, IP addressesNetwork performance  Bandwidth, delay, bit error rates, cost,  connec...
Enabling TechnologiesSoftware Defined RadiosAdvanced media access technology to connectdifferent cores to different access...
Goal of emerging mobile & PCS systems      Toenable communication with any person, at anytime, at any place (Home office i...
Technological Trends• All Digital Optical Fiber or Satellite media ,• Hyper media content• Intelligent Networks• Universal...
The Electromagnetic Spectrum               Short Wave Radio    FM Broadcast                AM Broadcast         Television...
Wireless Network Area Definitions       GSM                                  Courtesy of IEEE                             ...
Hierarchical Layers for 4G                                               IP-based backboneGlobal layer                    ...
Inter-Working                        Billing         SIP Proxy     Signalling WAP   Accounting      ISP                   ...
ENABLING CONCEPTS      FORMOBILE & PERSONAL COMMUNICATIONS.
These concepts enable us to provide UniversalPCS with standardized systems & services atlocal, regional, national and inte...
TERMINAL MOBILITY• The terminal mobility systems can locate and  identify a mobile terminal as it moves• Allows a mobile t...
PERSONAL MOBILITY• Terminal and user have DYNAMIC Relationship.  Call Delivery & Billing are based on Personal        Iden...
SERVICE PORTABILITY• Network is capable to provide subscribed  services at a terminal or location designated by  the user....
CELLULAR CONCEPT          &INITIAL IMPLEMENTATION
Conventional Mobile Tele phone SystemA Land mobile system in which availablefrequency spectrum is divided into mobile radi...
1. Limited service capability• Larger coverage area zones• High Power Transmissions• Re-initiation of call in every zone  ...
3. Inefficient frequency spectrum Utilization• Smaller Frequency Utilization factor  Mo = max. no. of customers/channel at...
SOLUTIONCellular approach• Reuse of frequencies• Multiple Access• Cell Splitting• Smaller coverage area (cell)
Starting point :   AMPS by Bell Labs, 1983, USACellular System :   A high capacity land mobile system in whichavailable sp...
A cellular system: The tower represent basestation (BS) which provide     radio accessbetween mobile users and the mobile ...
Cellular Advantages:  • Lower Power Transmissions  • Frequency Reusability  • Multiple Access capability  • Lower Antenna ...
• Efficient Power control• Handsets – Light weight, compact, Pocket held• Digital Communication transceivers• Value added ...
CELLULAR   SYSTEMARCHITECTURE
Basic Cellular system components :1. Mobile Station / Unit / Site (MS)2. Cell site / Base station (BS)3. Mobile Telephone ...
Mobile Station : (MS)Mobile station/unit contains     a   Transceiver,control unit and an Antenna.Cell Site : (MSC)Cell si...
MTSO or MSC• This is the mobile switching exchange• The central coordinating system for all the cells• Contains cellular s...
• Coverage area is partitioned into nearly  hexagonal shaped areas called radio cells• Each cell is served by one Base sta...
• MSC is connected to PSTN because majority of  calls originate from or terminate at fixed PSTN  phones.• Every cellular s...
Radio System Planning:  • Cell size design  • Cell location    identification/assignment  • Allocation of group of channel...
• In each cell, one Radio Channel is set aside  permanently assigned to carry signaling  information between the cellular ...
Location Updating MS always monitors overhead information           broadcast by network on the signaling channel• MS upda...
Mobile station initialization:• Whenever a user activates the receiver of Mobile  unit, the receiver scans SETUP CHANNEL l...
• This is done in Idle State also, transparently to  user.• But, it can’t provide location information to  BS. Thus BS mus...
Mobile originated call set up:• Exact procedure depends on particular cellular  standard.• More or less similar in princip...
• The BS receives this call request signal and  sends a request to MTSO (MSC) via high speed  data link.• BS selects an ap...
NETWORK ORIGINATED CALL SETUP               (Mobile Terminated Call)• A Landline phone dials a mobile unit number• The PST...
• The serving MTSO initiates a paging message  over the downlink-signaling channel toward the  cells contained in the pagi...
• Only the intended mobile now sends back a  response to its nearest cell site (BS) on the  signaling channel.• Now the re...
Call Termination:• When mobile user turns OFF the transmitter, a  signaling tone is sent to the BS.• Both the sides free u...
Hand Off:• During a call, serving BS monitors mobile signal  strength• If signal strength falls below a threshold, Network...
Data and Communications ConvergenceMediaStreaming videoVideo on demandInteractive video servicesTelecommunication         ...
Convergence of High Speed Internet & MobilityA major driver of future wireless  The Wireless Industry has grown at enormou...
Wireless Network EvolutionFirst generation (1G): Analog voice systems   No standardizationSecond Generation (2G): Digital ...
Third Generation (3G)Two basic proposals to handle voice and data   Ericsson: Universal Mobile Telecommunications systems ...
Fourth Generation (4G)Supporting heterogeneous multitude of systems   Includes multiple networks:       Digital video broa...
 
G-points in Mobile Comms History                           2G                 2.5G       1G                               ...
GSM Global System for MobileCommunications Digital cellular system for voice, fax, data >200 million customers >320 ne...
Countries with GSMwith GSMno GSM
Wireless NetworksMotivated by people-on-the-go  - PCs availability, Internet usage,     Mobile lifeAimed is to establish w...
Wireless Network Area Definitions           GSM                             Courtesy of IEEE           GPRS               ...
WLAN Network Architecture                       Mobile                       Agent                                Laptop  ...
WAN:                                                                 everywhere outside of the                            ...
Convergence  Convergence of Cellular Mobile Networks and WLANsBenefitsFor cellular mobile operators  Higher bandwidths. ...
These future networks will have the following inherent characteristics :1. Broadband Internet access.2. High (guaranteed) ...
The Internet is the driver           World Internet users (1999 – 2004) Million   1999   2000 2001        2002         200...
Mobile Broadband Network               Categories PAN      Personal Area NetworksW-LAN     Wireless Local Area NetworksW-W...
Wireless Networking Standards             OverviewMarket Name       GPRS/GSM       Wi-Fi       Bluetooth       ZigBee     ...
Future PAN TechnologiesTechnology Max      Introduction Advantages Dis-         Bottomline           Speed                ...
W-WAN CategoriesAnalogue    • AMPS        • TACS  (1G)      • N-AMPS      • NMT            • GSM         • CDMA/cdmaOne/IS...
Technolog Max        Introducti Advantage Dis-              Bottomliny         Speed      on         s         advantag   ...
Mobile TransactionsTransaction - Based• Mobile Banking• Mobile Stock Trading                    Technology Enabler:• Trave...
NEXT GENERATION MOBILE VISION &CONCEPTUbiquitous connectivity for slow and fast movingusers, accessing high speed internet...
Higher Data, Superior Radio Resource Management,Seamless mobility, Aggregation of Generations                             ...
Evolution towards better Data rates                                and higher mobilityMobility                            ...
Convergence of High Speed Internet & MobilityA major driver of future wireless The Wireless Industry has grown at enormous...
GENERAL REQUIREMENTS Handling multimedia Traffic Data, Video, Voice Seamless Services on the move User friendly smart ...
WIRELESSTRANSMISSION
WIRELESS TRANSMISSIONMobile Radio (Wireless) signals undergo manyimpairments during transmission / propagationthrough the ...
SIGNALS: Mostly SINUSOIDAL(AM/FM)         or its variants (ASK, PSK)         spectrum has side bonds or         frequencie...
ANTENNAS:Energy Translators /Couplers from TX to CH.Hence Radiation pattern.Ideal Isotropic: Equal power in all directions...
zReal Directive: DIPOLE                    λ /2omni directional uniform                                                xra...
SIGNAL      Onlyone direction ofPROPAGATION    transmission unlike wired               transmission               Fixed ...
SIGNAL IMPAIRMENTS Free space Loss or Los loss                 Squared law  pr α 1/d2                 - Due to equal dis...
Blocking or Shadowing :      - due to large obstaclesReflection : When λ < size of obstacle                     - Mobile...
Scattering : obstace size ≤ λIncoming signal is scattered in multiple directionsand become weak signals, due to many obje...
Multi Path Effects : Delay Spread                    POWERISI Fading –       Short term                            tLong ...
MULTIPLE ACCESS OR MULTIPLEXING : Means of combining several user signals onto acommon channel Multiple users access and...
SPACE DIVISION MULTIPLEXING : Assignment of space to each communicationchannel i.e., actually a source signal, with minim...
 Analogous to road traffic      separate lanes  Analog fixed Telephone Network                                 separate w...
FREQUENCY DIVISION MULTIPLEXING(FDM / FDMA)• Subdivision of frequency dimension into several  non-overlapping frequency bo...
TIME DIVISION MULTIPLEXING TDM(A)• A channel Ki is given whole bandwidth, but only for  a fixed period of time• Time dimen...
HYBRID-FTDMA:• A channel Ki use a certain frequency band fi for only a  certain amount of time ti• More robust against fre...
CODE DIVISION MULTIPLEXING : CDM(A) All channels use same  frequency at the same          ctime. Separation throughcodin...
 Due to VITERBI. Ex:- Different telephone calls use same bandwidth but different languages (Codes), at same time.If langu...
AM                         ANALOG  MODULATION                       FM                                   BINARY         AS...
SPREAD SPECTRUM MODULATION Developed for secured communication Means of transmitting a data sequence thatoccupies larger...
 Purposeful bandwidth spread to make the signal topossess noise like appearance so as to blend intothe back ground noise....
STEP i) Narrow band user input data     ii) Tx Spreads the signal into a wide bandsignal. But energy is same as original. ...
MOBILE RADIO SIGNAL PROPAGATION &              ENVIRONMENTMobile radio signals propagating through acommunication medium a...
• Scattering and Multipath effects :  - Signal gets scattered at ≤ λ obstacle points    and travel in multipaths.  - Resul...
• Instantaneous Signal Strength :    S(t)                  MS Stationary                                              avg ...
• Depends on whether Mobile station (MS) is inmovement or stationary.• Fading is always present due to     multipatheffect...
• Short term fading is obtained by r0(t) = r(t) - m(t)    In db         r0(t)                                      - multi...
PROPAGATION PATH LOSS:• Due to the presence of radio wave scatterers along  the path.• No. of scatterers depend on the con...
Specular Reflection from smooth flat andslopy terrains :• Occurs when radio waves encounter a smooth interface between two...
Diffuse Reflection: • Occurs when radio waves encounter a rough  textured surface with roughness of order of λ • Unlike sp...
• Hygen’s principle explains this.• In tensing of signals is smaller than that of specular reflected wave• Both these refl...
Diffraction:• Occurs when the propagation path is obstructed by  the features of an intervening terrain between two  anten...
Path Loss : Propagation             frequency   distance    ►                  Path Loss                       ►          ...
Received carrier powered is inversely proportional to R 4.         -4      - For Mobile Radio Channel.C αR  α R -2        ...
Result : Multipath Fading due to net sum of multiple path arriving signals with different  phase.         Fading fluctuati...
Multi path fading occurs inThree situations :1. Mobile unit and surrounding scatterers are still   / stationary2. Static M...
Static Multipath Signal :              N                    τ   s(t) = ∑ai s0(t − i )             i=1                     ...
Case 2 : MS still     τi , a are                             i   uniquely different        scatterers    along ith path at...
Case 3 : MS Moving – a) Scatters are absent   s0(t)             b) only one scatterer present            ▼      v c) Many ...
Thus concept of standing waves is applied to radio signals to understand the multipath effects. A resultant signal due to ...
Scatterers (Houses)                                  As a mobile unit                                  proceeds in a      ...
Why 800 MHz Band?ITU - T and FCC chose 800 MHz initially because.- Severe spectral limitations at lower frequency    Bands...
Even though not an ideal frequency for mobileradio, the 800 MHz band demonstrated thefeasibility.History of 800 MHz spectr...
FCC assigned frequencies in 20 MHz groups, as   Ban        Mobile                Base               System     A    824-83...
TRUNKING EFFICIENCY:No. of calls per hour per cell = Φ = Offered traffic load / average calling timeTrunking efficiency de...
UNIQUENESS OF MOBILE     RADIO ENVIRONMENTPropagation path loss increases with    - Frequency   - distance                ...
Cell antenna height:                30-100 mMobile antenna height:Received carrier Power   C =α R3m       -4Difference in ...
R1Free Space- c α R   -2          ∆C = 20 log    = 20 dB/dec                                            R2                ...
PATH LOSS MODEL• Different, often complicated, models are used for different environments. • A simple model for path loss,...
PATH LOSS LIMITATIONS• The received signal-to-noise power ratio, SNR, is                            Pr      KP         1  ...
SHADOW FADING• The received signal is shadowed by obstructions such as  hills and buildings.• This results in variations i...
First order statistics of Fading => Average power                                    CDF, BER                             ...
NOISE LEVEL IN CELLULAR BANDS:THERMAL NOISE  -129 dBm at B = 30 KHz, T=290KIGNITION NOISE    -124 to –104 dBm at B=30 KH...
DELAY SPREAD• Base station sends an impulse signal to the mobile station.                                                 ...
• Because of multipath scattering, the impulse gets  reflected many times and thus many impulses  (echos) arrive at mobile...
• As number of scatterers (N) increases, the receivedimpulse sequence becomes a continuous signal pulse,with a pulse lengt...
DELAY SPREAD       FREQUENCY DOMAIN INTERPRETATIONH(f)                                       Bs = signal bandwidth ≈ 1/T  ...
Parameter            Open      Urban     Suburban                      Area       Area      AreaMean Delay Time d, μs 0.2-...
DOPPLER SPREAD          • A measure of the spectral broadening caused           by the channel time variation.            ...
COHERENCE BANDWIDTH:• Bandwidth in which either the amplitudes or the phasesof two received signals have high degree of si...
E(t)                      Specular component                                    Scattered component                       ...
NOISE IN MOBILE RADIO CHANNEL:        THERMAL NOISE  WIDEBRAND        NARROWBAND  WHITE NOISE   GAUSSIAN WHITE NOISE      ...
HUMAN MADE NOISE    URBAN          SUBURBAN         EXTERNAL NOISESOLAR     ATMOSPHERIC      GALACTIC
NF       atmospheric                                       UR                           SU               BA               ...
ELEMENTS OF CELLULAR MOBILE     RADIO SYSTEM DESIGNGENERAL DESCRIPTION OF PROBLEM:CONCEPT  efficient Spectrum Utilization...
Limitation / constraint In system design                Frequency ResourceChallenge / goal  greatest no. of customers wi...
Ex :- A BUSY Traffic area of 12 Km radius is divided intoseven 2 Km cells. Assume a traffic situation with thebusiest traf...
MAX. No. of Frequency Channels per cell (N)• depends on average calling time T• depends on maximum calls per hour per cell...
Problems in wireless communication• Available unlicensed spectrum allocation  (government regulation)• Only low transmissi...
RADIO ENVIRONMENT• Path Loss• Shadow Fading• Multipath• Interference• Infrared Versus Radio• Path Loss               Limit...
FREQUENCY REUSE                BASE              STATION• Frequencies (or time slots or codes) are reused at  spatially-se...
DESIGN CONSIDERATIONS• Reuse Distance (D) – distance between cells using the same frequency,   time slot, or code – smalle...
History of Mobile Radio &Cellular Communication Systems Year                Telecom Event 1880     Initial radio demo by H...
1984 AMPS cellular system introduced by AT&T in US1986 FCC added 5 MHz extended band; two operators per       market1988 T...
It is widely believed that the fixed landline telecomnetwork (Telephone, fax, etc) are the largest andmost complete integr...
Plain old telephone:
DTMF Keypad for number dialing:
Features of land phone:i) Telephone Number is registered solely in the local   exchange.ii) Numbers are dialed from DTMF k...
Features of mobile/cellular phone:i) There is no dial tone and cradle switch (i.e. on/off Hook)                           ...
Fundamental principles of cellular  communications:Cellular technology had evolved from the mobile radiotelephone technolo...
Cellular radio phone and its components:
There are many ways of providing wireless andmobile communicationsFor ex:- cordless phones used at homes employwireless te...
Radio Cell Shape:
All users in a cell are served by central BS -gateway of cell !Ideally all the cells are circular in shape for omnidirecti...
The limited bandwidth allocated to operator is divided intonumber of radio channels, which are further grouped intosubsets...
Radio coverage in a single cell:The fundamental radio cell and parameters thatdictate the radio coverage are shown below
Different cellular ranges for mobile radio communicationsare indicated. The reverse path (MS to BS) limits the radiorange,...
Typical cellular system layout and signal powerdistribution are shown below. One can see theextensive signal processing re...
MULTIPLE CEL LAYOUT:The  intracellular communication       is  duplex     radiocommunication between cell site (BS) and mo...
Basic cellular system architecture:Cellular technology replaced a large coverage areamobile radio system with many smaller...
The mobile and wireless devices used by subscribers arecell phones, PDAs, palmtop/laptop PCs, web phone s, etc.All devices...
Cellular system architecture:
Home location register (HLR) and visitor locationregister (VLR) are two database pointers that supportmobility and enable ...
BS and MS signaling and voice communication:In any cellular system, four simplex radio channels areneeded to exchange sync...
The control channels are used to exchange controlmessages like, authentication, subscriber identity, callparameter negotia...
Handshaking protocols in cellular call setup:Simplified handshaking steps for a cellular call setupare illustrated in foll...
steps for a call set up from MS to BS:MS                                        BS       1. Call for MS # pending     2. R...
Wireless LANs and PANs:Mobile wireless networks find extensive use in differentfacets of human life.Already we are accusto...
It is predicted that the percentage of nonvoicemultimedia data traffic is increasing heavily.Also the digital voice techno...
MOBILE ADHOC NETWORKS (MANNET):Adhoc networks are basically peer to peer multihopmobile networks for freely moving mobile ...
Typical adhoc network is shown below.
Wireless Sensor Networks:Sensor networks are the newest members of a specialclass of wireless networks.A large no. of tiny...
Typical wireless sensor network:
WLAN and PAN characteristics and featuresType of      Range of Primary function        Deployednetwork     node           ...
HANDOFFHandoff is defined as a process used to allowa call/data transfer to continue uninterruptedas the mobile terminal m...
Hard handoff vs. Soft handoffHard handoff- break before makeSoft handoff – Make before breakVertical Handoff vs. Horizonta...
CHANNEL ASSIGNMENT• Fixed Channel Assignment (FCA)         – each cell is assigned a fixed number           of channels   ...
METHODS TO IMPROVE          SPECTRUM UTILIZATION• Interference Averaging (CDMA)• Interference Reduction   (power adaptatio...
PHYSICAL LAYER ISSUES• Link Performance Measures• Modulation Tradeoffs• Flat Fading Countermeasures• Delay Spread Counterm...
LINK PERFORMANCE MEASURES            PROBABILITY OF BIT ERROR• The probability of bit error, Pb, in a radio environment  i...
HOW DO WE OVERCOME THE  LIMITATIONS IMPOSED BY THE        RADIO CHANNEL?• Flat Fading Countermeasures         – Fade Margi...
DIVERSITY                                           16                                           The chance that two deep ...
DIVERSITY COMBINING TECHNIQUES                                           • • •              α1     α2      α3             ...
THANK YOU
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cellular communications-1

  1. 1. M.V. RAGHUNADHAssistant Professor, Dept. of ECE NIT, Warangal – 506004.raghu@nitw.ac.in
  2. 2. INTRODUCTION TOMOBILE & CELLULAR COMMUNICATIONS
  3. 3. Wireless systemWhat is a wireless system? Provides communication without the use of wire Computing and communication at anytime and anyplace Small size, portable device Uses radio wave, to send voice, data, internet and video signals Good energy management Access to resources
  4. 4. “ Mobile communications isnot Cellular communications butCellular communications isMobile communications ” .
  5. 5. Mobile Com  Ex :Public emergency services Police, Fire, Ambulance Single frequency communications over entire area using one BSand many mobile vehiculartransceiver setsCellular Com  Public com services with frequency reuse over multiple cells in entire area using one BS and many cellular phones in every cell.
  6. 6. “ Portablecommunicators are not mobile butmobile communicators are Portable ”
  7. 7. Communication devices exhibit followingCharacteristicsa. Fixed & Wired: Typical desktop PC, Telephone large, Data Loggers  weight / high powerb. Mobile & Wired: Today’s laptop PCs  mobile but connection to company via wired line of PSTN & Modemc. Fixed & Wireless: WLL  last mile in PSTN, in house wireless networks, local net in tradeshows.
  8. 8. d. Mobile & Wireless Today’s Cell Phones, PDAs, Personal Communicators  Most interesting case, no cable restriction, full mobility, roaming between cities and even different networks Ex: GSM , CDMA > 900 million users worldwide
  9. 9. Applications:1.Vehicles:Cars with a) Digital Audio Broadcast (DAB) at 1.5 Mbps  Music ,news, weather and GPS datab) UMTS for Wireless Cell Telephony – voice & Data at 384 kbpsc) Adhoc Networks with emergency services Accidents, Maintenance Logistics.d) Wireless Pico Nets PDA, Laptops, Mobile Phones ,Bluetooth / Wi-Fi.e) Rail / Air Traffic
  10. 10. 2.Emergencies Ambulance  high quality wireless adhoc nets – accidents, natural disasters.3.Business  Sales  Database consistency, wireless LAN hot spots at supermarkets, gas stations, laptop connections via LAN,DSL…4.Infotainment  Up-to-date info over wireless net i. Travel guide ii. Cash payment iii. Adhoc gaming networks
  11. 11. 5. Location Dependent Services Mobile computing and WLANs applications need toknow the mobile unit location.a. Follow on Services  Call forwarding, e-mail, multimedia conferencing.b. Location aware Services  Printing service from a hotel control room.c. Privacy  Time dependent access/forwarding at the will & wish of userd. Info. Services Travel guidee. Support services Caching of data on mobile device via a wireless net access.
  12. 12. Wi-Fi Stands for “Wireless Fidelity” High-bandwidth category of wireless communications Short range (300-1600ft) Used to connect laptops, PDAs, and even workstationsDigital Cellular Telephony CDMA, TDMA, GSM Smart phones and some PDAs Longer range than Wi-Fi
  13. 13. Mobile & Wireless Devices:a. Sensors : Control state information sourcesb. Embeded Controllers: Keyboards, mice, headset, washing machine, TV set, …..c. Pager : One or two line message service, fast replaced by cell phone.d. Mobile Phones : Vehicular Sets, Cell phonese. PDA : Personal Communicators, Pocket/Palm Computersf. Notebook / Laptop : Portable PCs
  14. 14. MOBILE, CELLULAR &PERSONAL COMMUNICATIONS
  15. 15. Mobility : Mobility of Talker ( Transmitter ) Mobility of Listener ( Receiver ) Mobility of Both ( TX & RX )Definition : Communication facility between stationary and mobile or mobile and mobile users ( units )UserTypes : Walking Pedestrians automobile computers car, bus, train, plane, ship.
  16. 16. What is Mobility?A device that moves Between different geographical locations Between different networksA person who moves Between different geographical locations Between different networks Between different communication devices Between different applications
  17. 17. Device mobilityPlug in laptop at home/work on Ethernet Wired network access only Network address changes May want access to information when no network is available: hoard information locallyCell phone with access to cellular network Continuous connectivity Phone # remains the same (high- level network address) Network performance may vary from place to placeCan we achieve best of both worlds? Continuous connectivity of wireless access Performance of better networks
  18. 18. People mobilityPhone available at home or at work Multiple phone numbers to reach me Breaks in my reachability when I’m not inCell phone Only one number to reach me Continuously reachable Sometimes poor quality and expensive connectivityCell phone, networked PDA, etc. Multiple numbers/addresses for best quality connection Continuous reachability Best choice of address may depend on sender’s device or message content
  19. 19. Mobility means changesHow does it affect the following? Hardware Lighter More robust Lower power Wireless communication Can’t tune for stationary access Network protocols Name changes ; Delay changes ; Error rate changes Fidelity High fidelity may not be possible Data consistency Strong consistency no longer possible Location/transparency awareness Transparency not always desirable Names/addresses
  20. 20. Example changesAddresses Phone numbers, IP addressesNetwork performance Bandwidth, delay, bit error rates, cost, connectivityNetwork interfaces PPP, eth0, stripBetween applications Different interfaces over phone & laptopWithin applications Loss of bandwidth triggers change from color to B&WAvailable resources Files, printers, displays, power, even routing
  21. 21. Enabling TechnologiesSoftware Defined RadiosAdvanced media access technology to connectdifferent cores to different access technologiesVariable spreading factor ( VSP )All-IP networks and protocolsAd-Hoc Networking algorithmsUltra Wideband , variable power HardwareRadioNetwork-layer mobility protocolsSmart antennaeMIMO (Multi Input Multi Output) devicesOpen platform architecturesSmart mediation devices for HandsetsSmart mediation devices for overlay network
  22. 22. Goal of emerging mobile & PCS systems Toenable communication with any person, at anytime, at any place (Home office in public inTransit), in any form / device ( Home /normaltelephone, cellular/mobile phone , PC phone,PDA, fax, Multimedia terminal). On the basis of “any time, any where, any one, any service”Information Services:Voice, Video, Text, Fax ,Image, Data, Files
  23. 23. Technological Trends• All Digital Optical Fiber or Satellite media ,• Hyper media content• Intelligent Networks• Universal Reachability & Accessibility• User specific & Interactive service• Global Roaming & Interoperability• Mobile ATM and Mobile Internet• Mobile data and computing• Guaranteed Quality of Service (QOS)• Standardized Universal ID Numbers/ Addresses• Personalization
  24. 24. The Electromagnetic Spectrum Short Wave Radio FM Broadcast AM Broadcast Television Infrared wireless LAN Cellular MicrowaveExtremely Very Low Medium High Very Ultra Super Infrared Visible Ultra- X-Rays Low Low High High High Light violet 2.4 – 2.4835 GHz GSM: 5 GHz 802.11b (11 Mbps) US ISM: 902-928 MHz 802.11a (54 Mbps) 802.11g (54 Mbps)
  25. 25. Wireless Network Area Definitions GSM Courtesy of IEEE 802.15 Press Kit. Jan. GPRS 2001 CDMA IEEE802.11 WAN HyperLan Bluetooth WAN-MAN PAN MAN MAN-LAN LAN-PAN Pico-Cell ~50km ~2km 0km ~10m
  26. 26. Hierarchical Layers for 4G IP-based backboneGlobal layer SatelliteRegional layer DAB and DVB-TNational layer 2G, 3G CellularLocal area layer Wireless LANsPersonal network layer Wireless PANs Vertical Handover Horizontal Handover
  27. 27. Inter-Working Billing SIP Proxy Signalling WAP Accounting ISP VHE Server Gateway The InterneSatellite FES Context-aware information Centre IP backboneBroadcast Networks (DAB, DVB-T) GSM / GPRS UMTS IP-based micro-mobility Wireless LANs
  28. 28. ENABLING CONCEPTS FORMOBILE & PERSONAL COMMUNICATIONS.
  29. 29. These concepts enable us to provide UniversalPCS with standardized systems & services atlocal, regional, national and international levels.They are :Terminal Mobility  with wireless AccessPersonal Mobility  with personal NumberService Portability  with Intelligent NetworkThese are for location independent availability ofcustomized telecom services.
  30. 30. TERMINAL MOBILITY• The terminal mobility systems can locate and identify a mobile terminal as it moves• Allows a mobile terminal to access telecom services from any location – even in movements• Uses wireless Access• User must carry wireless terminal and be within a radio coverage area• Functional parts reside on portable IC / Smart card• Terminal and User have STATIC Relationship• Terminal and Network have DYNAMIC Relation• Call delivery and Billing are based on Terminal /
  31. 31. PERSONAL MOBILITY• Terminal and user have DYNAMIC Relationship. Call Delivery & Billing are based on Personal Identity / Personal Number assigned to the user.• Locate and identify the end users as they move• Allows end users to access subscribed telecom services on any terminal, any location• More broader access whether fixed or wireless
  32. 32. SERVICE PORTABILITY• Network is capable to provide subscribed services at a terminal or location designated by the user.• Depends on terminal capabilities• Uses intelligent Network concepts• Maintains User profile in a Database• User can access, query, modify to manage & control subscribed services.• Intelligent services – seamless international roaming
  33. 33. CELLULAR CONCEPT &INITIAL IMPLEMENTATION
  34. 34. Conventional Mobile Tele phone SystemA Land mobile system in which availablefrequency spectrum is divided into mobile radiotelephone channels using FDM without reusefacility, serving an area with large size..A dedicated channel is allocated for each user,whether uses it or not.Principle of operation is similar to cellular radiotelephonyAs a result, It has several limitations that aregiven below.
  35. 35. 1. Limited service capability• Larger coverage area zones• High Power Transmissions• Re-initiation of call in every zone (no auto handoff)• One frequency per channel• No. of active users is equal to No. of channels allocated to zone2. Poor Service Performance:• Higher blocking probabilities due the smaller number of radio channels.
  36. 36. 3. Inefficient frequency spectrum Utilization• Smaller Frequency Utilization factor Mo = max. no. of customers/channel at Busy Hour.• Each channel can serve only one customer at a time in whole area.
  37. 37. SOLUTIONCellular approach• Reuse of frequencies• Multiple Access• Cell Splitting• Smaller coverage area (cell)
  38. 38. Starting point : AMPS by Bell Labs, 1983, USACellular System : A high capacity land mobile system in whichavailable spectrum is divided into discretechannels, which are assigned in groups togeographic cells covering an area and thefrequencies are reused, thus low powertransmissions. Principle : Divide large area into cells with 2 to 50 km diameter, each cell allocated with a set of RF channels
  39. 39. A cellular system: The tower represent basestation (BS) which provide radio accessbetween mobile users and the mobile switchingcenter (MSC). BS MS BS BS
  40. 40. Cellular Advantages: • Lower Power Transmissions • Frequency Reusability • Multiple Access capability • Lower Antenna Heights • Unlimited capacity and range coverage • Cell splitting & Micro cells • Automatic hand off transparency • Multi Level roaming
  41. 41. • Efficient Power control• Handsets – Light weight, compact, Pocket held• Digital Communication transceivers• Value added & intelligent information services• Mobile Multimedia broadband communication• Minimal Blocking• More than one license operator, Competition• Better propagation models.
  42. 42. CELLULAR SYSTEMARCHITECTURE
  43. 43. Basic Cellular system components :1. Mobile Station / Unit / Site (MS)2. Cell site / Base station (BS)3. Mobile Telephone switching office/ Centre4. Data Links
  44. 44. Mobile Station : (MS)Mobile station/unit contains a Transceiver,control unit and an Antenna.Cell Site : (MSC)Cell site contains a fixed Base station that has atower antenna, Transceivers (BS) for MS andFixed links to MTSO
  45. 45. MTSO or MSC• This is the mobile switching exchange• The central coordinating system for all the cells• Contains cellular switch, control computer, mobile management software, user location mobile management software, user location registers, Interfaces and links to BS & PSTN.• MTSO is the central administrator & Manager• Cellular switch is Analog or Digital and switches the calls to connect mobile – mobile or mobile – fixed
  46. 46. • Coverage area is partitioned into nearly hexagonal shaped areas called radio cells• Each cell is served by one Base station for radio coverage of all mobile units in that cell.• Radio Link carries the VOICE and SIGNALLING information (Channels) between the MS and BS in that cell only.• Base stations are connected to MSC through fixed circuits (cables or fiber or microwave)• MSC interacts with a database of subscriber data and location information, to provide dynamic terminal (MS) location to the switching computer.
  47. 47. • MSC is connected to PSTN because majority of calls originate from or terminate at fixed PSTN phones.• Every cellular system has some number of radio channels for its use, depending on cellular standard and RF band.• The available radio channels are partitioned into groups of channels, each group being allocated to an individual cell.• These individual group of channels can be reused in distant cells without causing interference.
  48. 48. Radio System Planning: • Cell size design • Cell location identification/assignment • Allocation of group of channels to each cell • Performance criteria • Handoff mechanism • Propagation modeling
  49. 49. • In each cell, one Radio Channel is set aside permanently assigned to carry signaling information between the cellular network (base station) and all the mobile stations in that cell.MS  BS Signaling Channel  Location updating , call set up. Paging response , user dataBS  MS Signaling Channel  Operating parameters (identities) Paging call, location updating, and control.
  50. 50. Location Updating MS always monitors overhead information broadcast by network on the signaling channel• MS updates the operating parameters as and when necessary• MS Checks Location information (area identity) broadcast by new cell, if it is in new cell location.• MS advices the network about its new location• Then network updates its location registers.• This location information is used to route / switch the incoming calls or determining paging
  51. 51. Mobile station initialization:• Whenever a user activates the receiver of Mobile unit, the receiver scans SETUP CHANNEL list designated.• It selects a strongest one and locks to it• Each site has one set up channel only. Thus strongest channel selection is the nearest BS (Cell site) selection.• This process is called SELF LOCATION
  52. 52. • This is done in Idle State also, transparently to user.• But, it can’t provide location information to BS. Thus BS must search for idle mobile unit by paging.• In future, registration scheme will be used, in which, the vehicles (MS) must register/update location regularly, as shown above.
  53. 53. Mobile originated call set up:• Exact procedure depends on particular cellular standard.• More or less similar in principle• User places/keys in the called telephoned number into an originating register and checks for correctness in LCD display.• Then user pushes ‘SEND’ button.• This call request is sent on the already set up channel on the uplink signaling channel  there is no dial tone at all.
  54. 54. • The BS receives this call request signal and sends a request to MTSO (MSC) via high speed data link.• BS selects an appropriate voice channel for the call and sends a speech channel (number) allocation message to mobile unit.• MS now locks on to this allocated radio channel• Network MSC proceeds now to set up the connection to the called party.
  55. 55. NETWORK ORIGINATED CALL SETUP (Mobile Terminated Call)• A Landline phone dials a mobile unit number• The PSTN exchange recognizes that the number is a Mobile number• PSTN exchange forwards this request to MTSO (MSC)• MTSO first establishes current location area for the called mobile through signaling between Home Location Register (HLR) and Visiting Location Register (VLR).• This process allows the call to be routed to the current serving MTSO (MSC)
  56. 56. • The serving MTSO initiates a paging message over the downlink-signaling channel toward the cells contained in the paging area, through a cell search algorithm• Each cell site further transmits this paging signal on its own set up channel.• If mobile is in ON state, it receives paging message, recognizes its own identification number in it and locks to the strongest set up channel (nearest BS).
  57. 57. • Only the intended mobile now sends back a response to its nearest cell site (BS) on the signaling channel.• Now the respective BS, sends a speech channel allocation message to the mobile and informs the network so that connection can be established.• The mobile unit tunes to the assigned voice channel tend initiates user alert of an incoming call
  58. 58. Call Termination:• When mobile user turns OFF the transmitter, a signaling tone is sent to the BS.• Both the sides free up the voice channel.• BS and MTSO recognize this and disconnect the connections and refresh the switch.• MS resumes monitoring the pages through the strongest setup channel, i.e. expects a paging message from nearest / strongest BS (current cell)
  59. 59. Hand Off:• During a call, serving BS monitors mobile signal strength• If signal strength falls below a threshold, Network requests all the neighboring cell BS to measure signal strength from this mobile.• If any nearest BS indicates better quality and strength than the current serving BS, the MSC commands the current BS to send a signaling message to the mobile, asking it to retune to a free channel in neighboring cell.• The MS retunes to new channel and network MSC switches call to new BS
  60. 60. Data and Communications ConvergenceMediaStreaming videoVideo on demandInteractive video servicesTelecommunication InternetPSTN and cellular servicesVideo telephonyWideband data servicesComputer Broadband WirelessInternet accessElectronic mailMobile computing
  61. 61. Convergence of High Speed Internet & MobilityA major driver of future wireless The Wireless Industry has grown at enormous pace over the past decade. More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move. With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure. The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective.
  62. 62. Wireless Network EvolutionFirst generation (1G): Analog voice systems No standardizationSecond Generation (2G): Digital voice systems Currently deployed systems CDMA, GSM (Global System for Mobile communication) PDC (Japan) D-AMPS (Digital Advanced Mobile Phone System) PCS SystemsSecond Generation – advanced (2.5G): Combining voiceand data communications Providing enhanced data rate Two basic technologies: GSM-based (high baud rate) GPRS (General Packet Radio Service) Utilizes voice time slots to send packet traffic An overlay over the existing voice system Should really be called 2.1G!! Any standards?
  63. 63. Third Generation (3G)Two basic proposals to handle voice and data Ericsson: Universal Mobile Telecommunications systems (UMTS) Compatible with European GSM Backed by ETSI and Japan Qualcom: CDM2000 Not compatible with GSM Compatible for IS-95 (supported by U.S)3G Standards 1999 UMTS took over and an agreement was made over setting some standardsMajor competing technologies Bluethood Wireless LAN (IEEE 802.x standards) – also known as WiFi Short range wireless communications Highly utilized and very popular: offices, airports, coffee shops, universities and schools Two basic modes of operations: • Ad-hoc networking: computers send data to one another • Access point:: sending data to the base station
  64. 64. Fourth Generation (4G)Supporting heterogeneous multitude of systems Includes multiple networks: Digital video broadband Digital audio broadband Wireless LAB, Bluethood-based networks Open communication network: infrastructure independent which can access to any services and applications Complete compatibility between wireless and wired networks through gatewaysSupports statistical multiplexing of heterogeneous data over-the-air Latency, noisy environment, unpredictable discontinuities and loss, etc.High-speed wireless transmission over the air High performance physical layer 20Mbps (2G: 28Kbps, 3G: 2Mbps) Scarce bandwidth availability Efficient frequency spectrum utilization Efficient hand off Dynamic bandwidth allocation Advanced digital transmission technology (modulation, low power devices, etc.)
  65. 65.  
  66. 66. G-points in Mobile Comms History 2G 2.5G 1G digital analog digital (analog) - voice + data- voice only - voice (data) - flexible- inflexible - inflexible - optimised- not optimised - optimised - transparent- very transparent - transparent 3G 3.5G 4G digital digital digital/analog?- data + voice - more data (IP) - even more- very flexible - very flexible data- ‘optimisable’ - ‘optimisable’ - very flexible- not transparent - not transparent - ‘optimisable’ - transparent
  67. 67. GSM Global System for MobileCommunications Digital cellular system for voice, fax, data >200 million customers >320 networks 137 countries Annual growth rate of 100% - 200% 4 new customers every secondGreater “presence” than MacDonalds!
  68. 68. Countries with GSMwith GSMno GSM
  69. 69. Wireless NetworksMotivated by people-on-the-go - PCs availability, Internet usage,  Mobile lifeAimed is to establish wide-area  voice data communicationsIncludes mobile systems (cellular  telecommunication systems) 
  70. 70. Wireless Network Area Definitions GSM Courtesy of IEEE GPRS 802.15 Press Kit. CDMA Jan. 2001 WAN IEEE802.11 Bluetooth WAN-MAN HyperLan PAN MAN MAN-LAN LAN-PAN Pico-Cell ~50km ~2km 0km ~10m
  71. 71. WLAN Network Architecture Mobile Agent Laptop Access point Fixed Fixed Workstation WorkstationMobile MobileAgent Agent Wired Network WorkstationPDA Access Access point point Printer Fixed Workstation DBMS
  72. 72. WAN: everywhere outside of the hotspots, where wireless GPRS, 3G – UMTS Wide Area Internet connection are provided< 400 Kb/s – xx Mls, Kms MAN: Building to Building Metropolitan Area connectionMMDS; LMDS; 802.1610M > 155 Mb/s - Kms LAN: Local Area collection of secure “hot spot” connections, 802.11b; 802.11a; 802.11g providing broadband 2M > 54Mb/s – > 300 ft, 100 m access to the Internet Personal Area Bluetooth; PAN: collection of secure < 800 Kb/s – < 30 ft, 10 m connections between devices in a “very” local area
  73. 73. Convergence Convergence of Cellular Mobile Networks and WLANsBenefitsFor cellular mobile operators  Higher bandwidths.  Lower cost of networks and equipment.  The use of licence-exempt spectrum.  Higher capacity and QoS enhancement.  Higher revenue.For users Access to broadband multimedia services with lower cost and where mostly needed (e.g. in Central Business Districts and Business Customer Premises).  Inter-network roaming.
  74. 74. These future networks will have the following inherent characteristics :1. Broadband Internet access.2. High (guaranteed) QoS.3. Seamless access – fixed and mobile.4. Intelligence.
  75. 75. The Internet is the driver World Internet users (1999 – 2004) Million 1999 2000 2001 2002 2003 2004USA 97 118 135 145 148 152Japan 23 32 38 43 47 50Asia Pac 32 70 104 120 135 150W.Europe 54 81 114 145 164 179ROW 35 72 105 118 130 140Total 241 373 496 571 624 671
  76. 76. Mobile Broadband Network Categories PAN Personal Area NetworksW-LAN Wireless Local Area NetworksW-WAN Wireless Wide Area Networks
  77. 77. Wireless Networking Standards OverviewMarket Name GPRS/GSM Wi-Fi Bluetooth ZigBee IrDA UWBStandard 1xRTT/CDMA 802.11b 802.15.1 802.15.4 802.15.3aApplication Wide Area Web, Email, Cable Monitoring & CableFocus Voice & Data Video Replacement Control replacementSystem 16MB+ 1MB+ 250KB+ 4KB - 32KB ?Resources ?Battery Life 1-7 .5 - 5 1-7 100 - 1,000+(days) ?Network Size 1 32 7 255 / 65,000 1Bandwidth 64 - 128+ 11,000+ 720 20 - 250(KB/s) 9.6-115Transmission 1,000+ 1 - 100 1 - 10+ 1 - 100+Range (meters) 1-5 Success Reach Speed, Cost, Reliability, Metrics quality Flexibility Convenience Power, Cost
  78. 78. Future PAN TechnologiesTechnology Max  Introduction Advantages Dis- Bottomline Speed advantagesBluetooth 723.2Kbps 2001 Low cost Interference,  Replace  security cablesInfrared 115Kbps In use Very low  LOS Replaced by  cost Bluetooth802.15.1 723.2Kbps 2002 Low cost Interference,  Formalized  security Bluetooth802.15.3 >20Mbps 2003 High data  Expensive,  Case not High rate rates proven yet Source: Gartner (2001)
  79. 79. W-WAN CategoriesAnalogue • AMPS • TACS (1G) • N-AMPS • NMT • GSM • CDMA/cdmaOne/IS-95A Digital • CDPD • TDMA / IS-136 (2G) • PDC • GPRS • EDGE Compact • PDC-P 2.5G • HSCSD • CDMA / IS-95B • EDGE Classic • cdma2000 1xMC • W-CDMA • CDMA 1 XTREME 3G • cdma2000 3xMC • CDMA 1x EVDV 4G • Undefined
  80. 80. Technolog Max  Introducti Advantage Dis- Bottomliny Speed on s advantag e esGPRS 171.2Kbp 2001 Packet data  Data rates  Will be  s for GSM  may  most  world disappoint successful  technology  through  2005HSCSD 115Kbps In use Dedicated  Low  Will not be  channels deployment mainstrea , expensive mEDGE 384Kbps 2003 Higher data  Expensive,  Will not be Classic rates for  little  able to  both packet  terminal  compete  & circuit support with W- CDMA.EDGE 250Kbps 2002 Higher data  AT&T  Unlikely to Compact rates for  (main  be  both packet  proponent)  successful & circuit  has  TDMA  changed  networks direction
  81. 81. Mobile TransactionsTransaction - Based• Mobile Banking• Mobile Stock Trading Technology Enabler:• Travel Reservation & Payment (Rail, LRT, Bus, Flights, Taxi, Dual – Slot Hand Phone Hotel, Insurance)• Entertainment Reservation & Payment (Cinema, Theater, Concerts)• Pre-Paid Voucher Recharge• Vending Machine Purchases• Electronic Cash Download• Payment of Utility Bills (Electricity, Water, Astro, etc)• Other Payments (Restaurant Bills, Takeaways, Parking)• Online Auctions 2 nd• Online Shopping (eg. CDs, Books) SIM Smart • Credit Card• Music MP3 Downloads • Debit Card Card Card • eCash Card • Customisable with SIM Toolkit • Pre-Paid Car • Remote Upgrading • Loyalty Card
  82. 82. NEXT GENERATION MOBILE VISION &CONCEPTUbiquitous connectivity for slow and fast movingusers, accessing high speed internet and relatedmultiple services at affordable cost andreasonable QOSCooperation between content providers andWireless access providers- Virtual operatorsMulti-Media, Multi-Environment, Multi-OperatorEnvironmentUser Driven, User Controlled, Context AwareApplicationsConvergence of services, aggregation and inter-working of existing and emerging technologiesand networksVertical and Horizontal Seamless Handover
  83. 83. Higher Data, Superior Radio Resource Management,Seamless mobility, Aggregation of Generations 4G Cost efficient, Higher Data 3G evolutionMultimedia messages, multiple services 3G Packet Data, On 2G evolution Digital Voice, data 2GAnalog Voice 1G 80’s 90’s 00’s 10’s
  84. 84. Evolution towards better Data rates and higher mobilityMobility 4G ResearchV E-Mail 4.2 sec in 2G to 0.002s in 4G Targets Movie Download 926 hours in 2G to 1minute in 4G N TIO OLU d vo s EV ve E m G ste CDMA 1X , l 3 y EDGE CD S M A2P 00 0, W CD M 802.11a,g 1X A EV 1X -D V W-LAN EVS 802.11b DO 0.1 1 10 100 1000
  85. 85. Convergence of High Speed Internet & MobilityA major driver of future wireless The Wireless Industry has grown at enormous pace over the past decade. More than half a billion subscribers to cellular services are enjoying the benefits of staying connected while on the move. With the growth in Internet , a wide range of services are accessed by users through a wired infrastructure. The introduction of mobile Internet brought about by the convergence of Mobile & Internet technologies is the future objective. 
  86. 86. GENERAL REQUIREMENTS Handling multimedia Traffic Data, Video, Voice Seamless Services on the move User friendly smart devices Diversified wireless access Under One Umbrella, Seamless access Advanced Mobility Management Independent of the IP version Proactive, always-on Intelligent integrated control
  87. 87. WIRELESSTRANSMISSION
  88. 88. WIRELESS TRANSMISSIONMobile Radio (Wireless) signals undergo manyimpairments during transmission / propagationthrough the radio channel (atmosphere / free space/ any medium)Frequencies• Radio signals are modulated signals with carrierfrequency allotted in any of the frequency bonds.• ITU Region 1. Europe, Middle East, Africa 2. Greenland, North & South America 3. Far East, Australia, New Zealand• LAND / SATELLITE CELLULAR RADIO BANDS
  89. 89. SIGNALS: Mostly SINUSOIDAL(AM/FM) or its variants (ASK, PSK) spectrum has side bonds or frequencies. Fundamental + Harmonics 90° Ф = m sinФ Phase Zero phase f ) Ф I = m cosФ
  90. 90. ANTENNAS:Energy Translators /Couplers from TX to CH.Hence Radiation pattern.Ideal Isotropic: Equal power in all directions y x z SMART ANTENNAS→ Use DSP
  91. 91. zReal Directive: DIPOLE λ /2omni directional uniform xradiation in one planefig.of 8 in other two planes y yDIRECTIONAL ANTENNA: x z Main lobe in only y y zone direction x z xSECTORIZED ANTENNA:Several directed antennas z zcombined on a single pole x x 3 sector 8 sector
  92. 92. SIGNAL  Onlyone direction ofPROPAGATION transmission unlike wired transmission  Fixed error limited transmission range d  Fixed error limited detection range  Interference range
  93. 93. SIGNAL IMPAIRMENTS Free space Loss or Los loss Squared law  pr α 1/d2 - Due to equal distribution of energy Over the surface of energy sphere. Path Loss : Signal attenuation due to rain,fog,dust,smog,air,snow Signal penetration mediumattenuation frequency 
  94. 94. Blocking or Shadowing : - due to large obstaclesReflection : When λ < size of obstacle - Mobile signal reflects from sky scrapers, Walls, Trucks,Mountains,Towers, Birds. Reflected signal is not as strong as the original. Reflection  Signal strength 
  95. 95. Scattering : obstace size ≤ λIncoming signal is scattered in multiple directionsand become weak signals, due to many objects inatmosphere or space .Diffraction :Similar to scattering Radio waves get deflected atedges signals become weak
  96. 96. Multi Path Effects : Delay Spread POWERISI Fading – Short term tLong term
  97. 97. MULTIPLE ACCESS OR MULTIPLEXING : Means of combining several user signals onto acommon channel Multiple users access and share a common channel with no interference (Hope fully) Simple ex :1. Athletic tracks / Swimming lanes 2. Many cars/Buses/Trucks share amultiple lane road due to separationof lanes Space Division Multiplexing However, needs a special identification and controlmechanism for proper MUX & DEMUX. For Wireless Communication,4 types of Multiplexing
  98. 98. SPACE DIVISION MULTIPLEXING : Assignment of space to each communicationchannel i.e., actually a source signal, with minimum interference and a maximum medium utilization Assume 3D space represented as shown CH k1 k2 k3 k4 k5 k6 code c c time t t s1 frequency s2 s3 f Κ f Coverage Space is represented via circles Channels K1, K2, K3 can be mapped into three spaces S1,S2, S3 with clear separation and no overlapWhat about K4, K5, K6 ?
  99. 99.  Analogous to road traffic separate lanes Analog fixed Telephone Network separate wire pair / local loop For wireless, SDM implies , a separate sender for each channel with wide space separations. ex: FM radio stations.• Problems arise if two or more channels occupy the same space
  100. 100. FREQUENCY DIVISION MULTIPLEXING(FDM / FDMA)• Subdivision of frequency dimension into several non-overlapping frequency bounds or slots. c • Each channel Ki is allotted its own (dedicated) band f • Sender uses this band S1 S2 S3 continuously • Guard spaces do exist for no interferences. t Ex:- Am radio stations• Receivers must TUNE into the specific senders.• Draw backs : Tremendous wasted frequency as user maynot transmit all the time (usually less than 1Hr per day).
  101. 101. TIME DIVISION MULTIPLEXING TDM(A)• A channel Ki is given whole bandwidth, but only for a fixed period of time• Time dimension is partitioned into several Time slots• Each channel is allocated one Time slot. c t1 S1 t2 f S2t3 • Needs precise S3 . . synchronizatio . n in timings fort TX or Rx.
  102. 102. HYBRID-FTDMA:• A channel Ki use a certain frequency band fi for only a certain amount of time ti• More robust against frequency selective interference / jamming.• Better protection against Tapping / Intruder.• But needs coordination between senders. c ft
  103. 103. CODE DIVISION MULTIPLEXING : CDM(A) All channels use same frequency at the same ctime. Separation throughcoding each channelwith its own code. Guard space is thedistance in code space t fEx:- ORTHOGONAL CODES
  104. 104.  Due to VITERBI. Ex:- Different telephone calls use same bandwidth but different languages (Codes), at same time.If language is same, then SDM is needed. Thus secret codes (Languages) provide security Code space is huge. Hence better protection against interference and tapping . However, the intended receiver must know thecode and also must synchronize with Tx forcorrect decoding .
  105. 105. AM ANALOG MODULATION FM BINARY ASK, PSK, FSK DIGITAL M - ary MSK, QAM, GMSK, QPSK, DQPSK Analog Base band Digital signal Data Digital Analog Modulation Modulation101101001 Radio Carrier
  106. 106. SPREAD SPECTRUM MODULATION Developed for secured communication Means of transmitting a data sequence thatoccupies larger bandwidth than the original base hand Spreading of bandwidth is through the use of a code that is independent of data Chief Advantages: 1. Resistance to narrow band interference or jamming 2. Multiple Access Communication.
  107. 107.  Purposeful bandwidth spread to make the signal topossess noise like appearance so as to blend intothe back ground noise. Power P P P f f f i) ii ) iii ) P P BPF f f iv ) v)
  108. 108. STEP i) Narrow band user input data ii) Tx Spreads the signal into a wide bandsignal. But energy is same as original. iii) A Wide band interference and Narrowband interference get added to wide band signal during transmission iv) Receiver dispreads the signal into narrowband. Thus narrow band interference gets spread and wide band interference gets left as it is. v) Receiver uses a BPF to band limit the user signal to original bandwidth and yield high SNR
  109. 109. MOBILE RADIO SIGNAL PROPAGATION & ENVIRONMENTMobile radio signals propagating through acommunication medium are subjected to manychanges or modifications. Propagation path loss :- - Due to beam Divergence (Free space Loss) - Proportional to 1/d2Terrestrial Losses :- Terrain Dependent (Path Loss) - Texture, roughness of terrain tends to dissipate propagated energy.
  110. 110. • Scattering and Multipath effects : - Signal gets scattered at ≤ λ obstacle points and travel in multipaths. - Result is different delay spreads of signal. - Thus severe FADING of the received signal (sum total of multipath signals). - Because of low mobile antenna height and near ground communication.
  111. 111. • Instantaneous Signal Strength : S(t) MS Stationary avg Pr m(t) Local mean MS moving r(t) Time or distance
  112. 112. • Depends on whether Mobile station (MS) is inmovement or stationary.• Fading is always present due to multipatheffects due to multiple scattering points,reflection points, dissipations.• Delay spread is the smearing of received signal due to lengthening of time period as a result of different multipath signals arriving withdifferent phases.
  113. 113. • Short term fading is obtained by r0(t) = r(t) - m(t) In db r0(t) - multipath fading Received Long term - Rayleigh fading fading - due to multiple reflections from r(t) = r0(t) m(t) Model buildings, structures. m(t) - Local mean long term fading due to terrain contour• Signal fades about 40 dB• Nulls around λ / 2• Rate of fading α vehicle speed.
  114. 114. PROPAGATION PATH LOSS:• Due to the presence of radio wave scatterers along the path.• No. of scatterers depend on the contour variations, terrain roughness T BS antenna MS antenna ▼ ▼ Snell’s law ▲ θ( )θ Ф • Therefore changes in the propagation as a result of specular Reflection, DiffuseT Reflection and Diffraction.
  115. 115. Specular Reflection from smooth flat andslopy terrains :• Occurs when radio waves encounter a smooth interface between two dissimilar media and linear dimension of interface is larger than λ Ex: Mirror reflection defined by Snells law. Elevation  • Reflected wave at point θ h1 due to reflection of incident wave from BS antenna T h1 can be thought of as ▼ originated from a fictitious image antenna TI and passed through the surface Distance without refraction.
  116. 116. Diffuse Reflection: • Occurs when radio waves encounter a rough textured surface with roughness of order of λ • Unlike specular reflection, this scatters energy and focus a divergent radio path. 1 hp < 2 1 1 ( + ) λ d1 d2 BS LOS €  MS LOS  ▼h1 LOS h2 d1 d2
  117. 117. • Hygen’s principle explains this.• In tensing of signals is smaller than that of specular reflected wave• Both these reflections correspond to LOS propagation of reflected signals.
  118. 118. Diffraction:• Occurs when the propagation path is obstructed by the features of an intervening terrain between two antennas.•Thus out of sight propagation. • Attenuation depends onElevation whether obstruction extends through the path or protrudes into LOS path. BS • Knife edge diffraction modals €h1 are used. hp ▼ l h2 Distance
  119. 119. Path Loss : Propagation frequency distance ► Path Loss ► Ә1 ( 100m ▼ ► 3m Ә2 ( > 2 km Ә1 - incident angle / elevation angle Ә2 - reflected anglePropagation path loss is 40 dB / decade or 10 km.
  120. 120. Received carrier powered is inversely proportional to R 4. -4 - For Mobile Radio Channel.C αR α R -2 - For Free space Radio Channel. -γ - For Real Mobile radio model αR 2<γ<5FADING:• Antenna height of Mobile unit is less than its surroundings.• Carrier signal wavelength is smaller than sizes of surrounding structures.
  121. 121. Result : Multipath Fading due to net sum of multiple path arriving signals with different phase. Fading fluctuation range about 40 dB. (10 dB above, 30 dB below avg / mean). λ• Nulls of fluctuation at the base band at about every 2 in space, but not with same levels.• Rate of fluctuation α vehicle speed.
  122. 122. Multi path fading occurs inThree situations :1. Mobile unit and surrounding scatterers are still / stationary2. Static Multipath Mobile unit standing still scatterers moving3. Mobile unit and scatterers moving.
  123. 123. Static Multipath Signal : N τ s(t) = ∑ai s0(t − i ) i=1 { i 2 Π f 0 ( t - τ ) + i Φ 0} s(t) = x ( t - τ ) eEnvelope x(t) = a0 ∑ ai e - j 2 Π f 0 ∆ τi ai → attenuation factor of ith path. N signal paths, τi → Propagation time ∆τi → additional relative delay on i th path.
  124. 124. Case 2 : MS still τi , a are i uniquely different scatterers along ith path at any instant. moving cars j Φ 0 - j 2 Π f0 t ∴ s(t) = x(t) e e - j2 Πf0τ i(t) x(t) = ∑ a0 ai(t) e - jψ (t) = A(t) e = a0 {R - js} A(t) = a0 R + S 2 2 -1 S ψ(t) = Tan R
  125. 125. Case 3 : MS Moving – a) Scatters are absent s0(t) b) only one scatterer present ▼ v c) Many scatterers present θ near MS. 2π s(t) = a0 Exp [ j ( ω0t + φ0 − β vt cosθ ) ] β= λ Doppler effect contributes additional frequency due to movement of Mobile vVoltage fdoppler = fm cosθ = cosθ λ = ± depending on direction of travel X(t)
  126. 126. Thus concept of standing waves is applied to radio signals to understand the multipath effects. A resultant signal due to an incident signal and a perfect scatterer reflected signal, reaching a mobile of speed V is j [ ω0 t + φ0 - β vt] [ j ( ω0 t + φ0 + β vt - ω0 τ ) ]s(t) = a0 e - a0 eThe envelope of S(t) looks like a standing wave pattern. 2 x2(t) = 4a02 sin2(β vt - ) ω0 τ ∴ Fading Frequency → 2V/λ
  127. 127. Scatterers (Houses) As a mobile unit proceeds in a ▼ street, it is passing v through an avenue of scatterers as shown.Highest Doppler Frequency fd is v v fm = max ( fd ) = max ( cosθ ) = λ λ W(f) v fd 2 λ
  128. 128. Why 800 MHz Band?ITU - T and FCC chose 800 MHz initially because.- Severe spectral limitations at lower frequency Bands- Maritime (ship) mobile service at 160 MHz- Fixed station services from 30 to 100 MHz- FM and VHF/UHF TV Bands from 80-600 MHz- No Mobile radio transmission beyond 10 GHz due to propagation path loss, multipath fading and rain loss.- 800 MHz allocated to educational TV Channels was heavily under utilized.
  129. 129. Even though not an ideal frequency for mobileradio, the 800 MHz band demonstrated thefeasibility.History of 800 MHz spectrum:1958 -Bell lab proposal for 75 MHz system at 800 MHz.1974 -FCC allocated 40 MHz spectrum for one cellular operator licensed per market area.1980 -FCC revised its policy and introducedcompetition with two licensed carriers perservice area of course this resulted in trunkefficiency degradation
  130. 130. FCC assigned frequencies in 20 MHz groups, as Ban Mobile Base System A 824-835,845-846.5 869-880, 890-891.5 non wire line. B 835-845, 846.5-849 880-890, 891.5-894 Wire line1986 – FCC added 5 MHz to each band. old 333 + new 83 = 416 channels per band with 30 KHz per channel.
  131. 131. TRUNKING EFFICIENCY:No. of calls per hour per cell = Φ = Offered traffic load / average calling timeTrunking efficiency degradation factor η = {φOne carrier – φ Multi carrier} / φOne carrier η% 30 5 ca reer /m arke t 20 2 career/m 10 arket 0 1 2 5 Blocking30 10 probability %
  132. 132. UNIQUENESS OF MOBILE RADIO ENVIRONMENTPropagation path loss increases with - Frequency - distance θ1  elevation angle θ2  incident angle h ▼ Dire ct path Re fle 30 – 100 m cte d pa θ1( ▼ th θ2 ( 2 km d
  133. 133. Cell antenna height: 30-100 mMobile antenna height:Received carrier Power C =α R3m -4Difference in Powers C1 R2 - 4 =( ) C2 R1 R1 ∆ C = C2 - C1 in dB = 40 log R2 General Rule =>40 dB/dec path loss Δc = - 40dB
  134. 134. R1Free Space- c α R -2 ∆C = 20 log = 20 dB/dec R2 R1 ∆C = 40 log = 40 dB/decMobile radio CH- c α R-4 R2 Received signal fading levels: 10 dB above and 30 dB below mean. - R2CDF P(R) = R e − (R) = βν × ηlcr Level crossing rate η R 2πafd Average fading duration - 2π - t (R) = × tR βν
  135. 135. PATH LOSS MODEL• Different, often complicated, models are used for different environments. • A simple model for path loss, L, is L= Pr =K 1 f dα 2 Pt where Pr is the local mean received signal power Pt is the transmitted power d is the transmitter-receiver distance f is frequency, K is a transmission constant. The path loss exponent α = 2 in free space; 2 ≤ α ≤ 4 in typical environments.
  136. 136. PATH LOSS LIMITATIONS• The received signal-to-noise power ratio, SNR, is Pr KP 1 SNR = = • αt Pn d NoB where No is the one-sided noise power spectral density B is the signal bandwidth. • Given the performance requirement SNR ≥ SNRo, the path loss imposes limits on the bit rate and the signal coverage. KPt KPt 1/α B≤ or d ≤ ( ) dα NoSNRo NoBSNRo
  137. 137. SHADOW FADING• The received signal is shadowed by obstructions such as hills and buildings.• This results in variations in the local mean received signal power, Pr (dB) = Pr (dB) + Gs where Gs ~ N(0, σ 2 ), 4 ≤ σ s ≤ 10 dB. s• Implications – nonuniform coverage – increases the required transmit power
  138. 138. First order statistics of Fading => Average power CDF, BER ∴ independent of time Second order statistics of Fading =>lcr, afd, word Error Rate ∴time/velocity dependent _ 2 - A A2Rayleigh Fading : CDF P(x ≤ A) = 1- e _ P(y ≤ L) = 1− e −L L
  139. 139. NOISE LEVEL IN CELLULAR BANDS:THERMAL NOISE  -129 dBm at B = 30 KHz, T=290KIGNITION NOISE  -124 to –104 dBm at B=30 KHz, T=290K Ni + (Na G) AMPLIFIER NOISE  NF = KTB
  140. 140. DELAY SPREAD• Base station sends an impulse signal to the mobile station. error s0(t) = a0 s(t) BS a0 Antenna 1 3 ▼ t τ 1 τ2 τ3 τ4 t 4 ▼ 2 4 scatter case Delay spread N=4
  141. 141. • Because of multipath scattering, the impulse gets reflected many times and thus many impulses (echos) arrive at mobile unit at different times. a0 N>>4 t ∆ N-scatter case delay spread• Received impulse signal is s(t) = a0 ∑ aj δ(t - τ ) e jωt jωt = E(t) e
  142. 142. • As number of scatterers (N) increases, the receivedimpulse sequence becomes a continuous signal pulse,with a pulse length Δ (called DELAY SPREAD).• Delay envelopes contain multiple peaks.• Shortest path signal need not necessarily producehighest peak as the scatterer could be absorb in nature.• Mean delay time d is the first moment or average. ∞ d =∫t E(t) dt 0• Standard deviation or delay spread Δ is t=0 → Leading edge of ∞ envelope E(t). ∆ = ∫ t E(t)dt - d 2 2 2 0
  143. 143. DELAY SPREAD FREQUENCY DOMAIN INTERPRETATIONH(f) Bs = signal bandwidth ≈ 1/T Bs 1 f 2τ • τ small flat fading T • τ large frequency-selective fading T
  144. 144. Parameter Open Urban Suburban Area Area AreaMean Delay Time d, μs 0.2-0.5 1.5-2.5 0.1-2.0Path Length, km 20–300 450-750 30-600Max. Delay Time 0.5-2 5-12 0.3-7(-30dB)Path Length, Km 0.5-1 1.5-3.6 0.9-2.1Range of delay spread 0.1-2.0 1-3 0.2-2 Δi, μsMean Delay Spread <0.2 3 0.5Delay spread is assumed independent of frequency.
  145. 145. DOPPLER SPREAD • A measure of the spectral broadening caused by the channel time variation. v fD ≤ λ Example: 900 MHz, 60 mph, fD = 80 Hz 5 GHz, 5 mph, fD = 37 Hz • Implications – signal amplitude and phase decorrelates after a time period ~ 1/fD8C32810.87-Cimini-7/98
  146. 146. COHERENCE BANDWIDTH:• Bandwidth in which either the amplitudes or the phasesof two received signals have high degree of similarity orcorrelated.• Different delays in two fading signals that are closelyspaced in frequency can cause the two signals to becomecorrelated.• The frequency spacing that allows this conditiondepends on the delay spread Δ .• This frequency interval is called coherence or correlationBandwidth Bc.
  147. 147. E(t) Specular component Scattered component t d dt Δ Channel input response modelCorrelation C(f) function Scattered component f Coherence bandwidth 1 1 Bc = or Bc ≈ 2Π Δ AM 8Δ• A typical definition of Bc → 1 FM = PM 4ΠΔ
  148. 148. NOISE IN MOBILE RADIO CHANNEL: THERMAL NOISE WIDEBRAND NARROWBAND WHITE NOISE GAUSSIAN WHITE NOISE n(t) = nc(t) + jns(t)
  149. 149. HUMAN MADE NOISE URBAN SUBURBAN EXTERNAL NOISESOLAR ATMOSPHERIC GALACTIC
  150. 150. NF atmospheric UR SU BA B N UR RU BA RA N L INTERNAL RECEIVER GA 0 RUR AL Q LA CT SOLA UITE IC R 2 4 6 8 100 1000 105 109 f -10 10Mean Noise Figure Fa : 28 db / decade slopes for all.Automotive Traffic Noise Power increases with trafficdensity decreases with frequency
  151. 151. ELEMENTS OF CELLULAR MOBILE RADIO SYSTEM DESIGNGENERAL DESCRIPTION OF PROBLEM:CONCEPT  efficient Spectrum UtilizationMajor Elements of System Design  1. Frequency Reuse Channels 2. Co channel Interference Reduction Factor 3. Carrier-Interference Ratio 4. Handoff Mechanism 5. Cell Splitting
  152. 152. Limitation / constraint In system design  Frequency ResourceChallenge / goal  greatest no. of customers with a specified system quality. Ex :- Max. no. of calls/hour/cell Q Max. No. of frequency Channels /cell - N Q depends on - cell size - traffic conditions
  153. 153. Ex :- A BUSY Traffic area of 12 Km radius is divided intoseven 2 Km cells. Assume a traffic situation with thebusiest traffic cell cover 4 freeways and 10 heavy trafficstreets, with a total length of • 64 Km of TWO 8 lane roads • 48 Km of Two 6 lane freeways • 588 Km of forty three 4 lane roadsaverage spacing of cars is 10m during busy periods. Onehalf cars have phones and eight tenths of them make a call(ηc= 0.8) during the busy hour. Total length of roads = 64 + 48 + 588 = 700km 700km Total number of cars = = 70000 10m 70,000 No.of calls in busy hour = × 0.8 = 28,000 2
  154. 154. MAX. No. of Frequency Channels per cell (N)• depends on average calling time T• depends on maximum calls per hour per cell Qi• Determined from a plot or Table that shows N,B and A• OFFERED TRAFFIC LOAD = Q IT A= Erlangs 60
  155. 155. Problems in wireless communication• Available unlicensed spectrum allocation (government regulation)• Only low transmission power levels allowed (No brute force possible: strong signal in narrow band)• Multi-path propagation echoes• Interference• Noise
  156. 156. RADIO ENVIRONMENT• Path Loss• Shadow Fading• Multipath• Interference• Infrared Versus Radio• Path Loss Limit the Bit Rate• Shadow Fading and/or Coverage• Multipath
  157. 157. FREQUENCY REUSE BASE STATION• Frequencies (or time slots or codes) are reused at spatially-separated locations.• Introduces interference ⇒ system capacity is interference-limited.• Mainly designed for circuit-switched communications• Base stations perform centralized control functions. (call setup, handoff, routing, etc.)
  158. 158. DESIGN CONSIDERATIONS• Reuse Distance (D) – distance between cells using the same frequency, time slot, or code – smaller reuse distance packs more users into a given area, but also increases their co-channel interference• Cell Radius – decreasing the cell size increases system capacity, but complicates the network functions of handoff and routing
  159. 159. History of Mobile Radio &Cellular Communication Systems Year Telecom Event 1880  Initial radio demo by Hertz 1897  First radio transmission by Marconi 1921  Police car radio at 2 MHz in Detroit 1933  FCC permitted 4 channels in 30-40 MHz 1956  Simplex radio telephony system-450 MHz 1964  FCC – 152 MHz duplex radio telephony  1974 1979  FCC allots 40 MHz bandwidth in 800-900 MHz band 1981 First cellular system by NTT in Japan First US cellular land mobile phone service in 800- 900 MHz band with 40 MHz bandwidth
  160. 160. 1984 AMPS cellular system introduced by AT&T in US1986 FCC added 5 MHz extended band; two operators per market1988 TDMA digital cellular standard in North America (NA)1992 GSM operable in Germany D2 cellular system1993 CDMA chosen as digital cellular standard in NA1994 American TDMA started in Seattle; PDC in Tokyo, Japan1995 CDMA in Hong Kong1996 Six PCS licensed bands at 120 MHz given in US1997 Broadband CDMA chosen as 3G Technology for UMTS1999 ITU decides nextG standards- W-CDMA, CDMA2000, TD-SCDMA2001 First commercial W-CDMA service in Japan2002 FCC approves additional band for UWB
  161. 161. It is widely believed that the fixed landline telecomnetwork (Telephone, fax, etc) are the largest andmost complete integrated systems at present in theworld.The cellular radio has rapidly evolved and hadalready crossed the size of the fixed land telephonenetwork.Let us consider the important differences betweenthe conventional landline telephone network and thecellular radio telephone network.Let us recall the basic features of the plain old landtelephone network (Public switched telephonenetwork – PSTN).
  162. 162. Plain old telephone:
  163. 163. DTMF Keypad for number dialing:
  164. 164. Features of land phone:i) Telephone Number is registered solely in the local exchange.ii) Numbers are dialed from DTMF keypad as shown above.iii)Central Battery supplies power to telephone handset.iv)Subscriber loop is a 2 wire half duplex circuit.v) Trunk circuits employ 4 wire circuits with Hybrid coil doing 2/4 wire conversion.vi)ON/OFF HOOK state of cradle switch is an indication to the exchange about call REQ/ Disconnect signaling information.vii) subscriber can start dialing (entering telephone no.) only after receiving the dial tone from the exchange.viii) User must go to instrument to make a land phone call.
  165. 165. Features of mobile/cellular phone:i) There is no dial tone and cradle switch (i.e. on/off Hook) Hookii) User types in/ calls from memory and presses ‘SEND’ button to transmit telephone number of called partyiii)Power comes from the local Battery (LB), not from CBiv)Local exchange is replaced by a base station (BS) and a mobile switching centre (MSC)v) Local 2 wire loop is replaced by 2 way HDX radio channelvi)Cellular user talks on Reverse channel (MS to BS radio link) and listens on forward channel (BS to MS radio link)vii) signaling information is exchanged via separate set up or control channels in each direction, user transparently
  166. 166. Fundamental principles of cellular communications:Cellular technology had evolved from the mobile radiotelephone technology.Mobile radio telephone (R/T):It is basically a transceiver handset with a 2 way duplexlink connecting to a base station and switching centre.Mobile unit carries its own telephone number in a SIM /smart card, which allows roaming using same number.BS and MS always keep in touch by handshakingprotocols via control channels, transparent to the user.The following figure depicts the components of a R/T.
  167. 167. Cellular radio phone and its components:
  168. 168. There are many ways of providing wireless andmobile communicationsFor ex:- cordless phones used at homes employwireless technology, with a low power transmitterand hence has small coverage area(<100 m)Such phones used in adjacent homes do notexperience any interference, even by operating atsame frequency exactlyThis is a perfect example for frequency reuseThe same principle of frequency interferenceavoidance is used in cellular systems also, evenwith much more transmission powers
  169. 169. Radio Cell Shape:
  170. 170. All users in a cell are served by central BS -gateway of cell !Ideally all the cells are circular in shape for omnidirectionalcoverage, with BS located at its centre as shown below.Cell area and periphery are decided by minimum signalstrength, height of BS antenna, presence of hills, talltrees/buildings and atmospheric conditions.Thus actual shape of cell and coverage area is an irregularzigzag circle, but modeled by a hexagonal building blocks.Ex:- Bee hives are 3D hexagonsMultiple accessing is employed in cellular systems to allowmultiple cellular subscribers to access the same BS in a cellThey are FDMA, TDMA and CDMA
  171. 171. The limited bandwidth allocated to operator is divided intonumber of radio channels, which are further grouped intosubsets, to assign one group of channels to a particular cellThis is the principle of FDMA employed in firstgeneration cellular systems.Because of unique frequency sets allocated for eachcell, it is possible to use the same frequency set in adistant cell, as long as the two transmissions do notinterfere with each other.This is the principle of frequency reuse, a central themeof cellular communications
  172. 172. Radio coverage in a single cell:The fundamental radio cell and parameters thatdictate the radio coverage are shown below
  173. 173. Different cellular ranges for mobile radio communicationsare indicated. The reverse path (MS to BS) limits the radiorange, due to limited TX. Power of mobile unit.The no. of subscribers covered by a single cell depends onthe radius or area of the cell, as given in the table. Cell area and number of subscribers coveredCell radius Coverage Number of km area km2 subscribers covered 1 3.14 100 3 28.3 900 10 314 10,000 25 1960 60,000
  174. 174. Typical cellular system layout and signal powerdistribution are shown below. One can see theextensive signal processing required to meet this.
  175. 175. MULTIPLE CEL LAYOUT:The intracellular communication is duplex radiocommunication between cell site (BS) and mobile unit (MS).It needs a block allocation of frequencies for the control andvoice radio channelsAdjacent cells are not assigned the same frequency sets toavoid the cochannel and adjacent channel interferences.A handoff mechanism is required to automatically handoveran ongoing mobile call from one group to another frequencygroup used in the next cell, as and when mobile unit iscrossing cell boundaries.That means the cellular phone circuits must be frequencyagile to retune to a new frequency without call disconnects.
  176. 176. Basic cellular system architecture:Cellular technology replaced a large coverage areamobile radio system with many smaller cells, with asingle BS covering one particular cell only, asdepicted in the following figure.
  177. 177. The mobile and wireless devices used by subscribers arecell phones, PDAs, palmtop/laptop PCs, web phone s, etc.All devices are referred to as Mobile Stations/Units (MS)An MS can communicate only with its nearest BS of acell in which it is located ( i.e., belongs to).Hence a BS (with a base transceiver) acts as a gatewayswitch/router to the rest of the world, to any MS.Every BS is controlled by one base station controller(BSC), which in turn is connected to a mobile switchingcentre (MSC) as shown in the following figure.Several MSCs are interconnected to PSTN and ATMbackbone networks.
  178. 178. Cellular system architecture:
  179. 179. Home location register (HLR) and visitor locationregister (VLR) are two database pointers that supportmobility and enable the use of same telephone numberworldwide in cellular communications.HLR is located at the home MSC where MS is registeredVLR stores all the visiting mobiles in that particularareaAuthentication centre (AUC) provides authentication foran user attempting to make a cellular call.This uses a 15 digit unique IMEI number programmedinto the MS at registration time and also stored inEquipment identity register (EIR).Network management and operations control are thefunctions of the centers NMC and OMC.
  180. 180. BS and MS signaling and voice communication:In any cellular system, four simplex radio channels areneeded to exchange synchronization and data betweenBS and MS, as shown below.
  181. 181. The control channels are used to exchange controlmessages like, authentication, subscriber identity, callparameter negotiation, power control, etc.Traffic (information) channels are used to transferactual data (voice/digital data)Forward CH/ Downlink  BS to MS transmissionsReverse CH/ Uplink  MS to BS transmissionsControl information shall be exchanged before theactual data transfer can take place.This necessitates the use of handshaking protocols forcellular call setup, maintenance and disconnection.
  182. 182. Handshaking protocols in cellular call setup:Simplified handshaking steps for a cellular call setupare illustrated in following figure. BS MS 1. Need to establish path 2. Frequency/time slot/code assigned 3. Control information acknowledgement 4. Start communication fig. steps for a call set up from MS to BS
  183. 183. steps for a call set up from MS to BS:MS BS 1. Call for MS # pending 2. Ready to establish a path 3. Use of frequency/timeslot/code 4. Ready for communication 5. Start communication
  184. 184. Wireless LANs and PANs:Mobile wireless networks find extensive use in differentfacets of human life.Already we are accustomed to line orientd to Local AreaNetworks (LAN) and Wide Area Networks (WAN). Ex:- Internet access, a value added service offered by landline telephone network PSTNWireless LANs (WLAN) are being developed to providemobile access to data users.Personal access Networks (PAN) cover very small areasreferred to as Pico cells using low powers in ISM band.WLANs and PANs are becoming popular choice andinfluence the wholesome home and office automation.
  185. 185. It is predicted that the percentage of nonvoicemultimedia data traffic is increasing heavily.Also the digital voice technology is permitting theintegration of voice and nonvoice traffic into unifieddata stream.Thus convergence of voice and nonvoice networks intoa single unified network supporting multimediacommunications is the order of the day.Standards like IEEE 802.11, Bluetooth, HomeRF,HiperLAN etc., are being developed and deployedworldwide.Adhoc networks are being devised for commercial andmilitary applications.
  186. 186. MOBILE ADHOC NETWORKS (MANNET):Adhoc networks are basically peer to peer multihopmobile networks for freely moving mobile users andhosts interconnected by nodes (mobile transceivers).Information packets are transmitted using a store andforward protocol as shown in the fig.Nodes are very small transceivers with antennas andcan be located inside airplanes, ships, trains, trucks,cars, homes, offices, etc.This adhoc network topology (multihop graph) maychange with time as the nodes move or adjust theirtransmission or reception parameters.
  187. 187. Typical adhoc network is shown below.
  188. 188. Wireless Sensor Networks:Sensor networks are the newest members of a specialclass of wireless networks.A large no. of tiny immobile sensors are planted on theadhoc basis to sense and transmit some physicalcharacteristics of the environment.An associated BS collects the information reported bythe sensors on a data centric basis.Ex:- Battlefield surveillance of enemy territory/war frontby sensors dropped from a low flying aircraft.Potential commercial uses include machineryprognosis, biosensing and environment monitoring.
  189. 189. Typical wireless sensor network:
  190. 190. WLAN and PAN characteristics and featuresType of Range of Primary function Deployednetwork node locationsIEEE    30 m Standard for Any peer-peer802.11 wireless nodes connectionHiper-    30 m High speed indoor Airports,LAN connectivity warehousesAdhoc   ≥ 500m    mobiles, wireless, Battlefields,Networks similar to wired disaster networks connectivitySensor     2 m Monitor Nuclear,Networks inaccessible, chemical plants, inhospitable terrain oceansHome RF    30 m Resource sharing, Homes device connectionsBluetooth    10 m Avoid wire clutter, offices, buildings low mobility indoors
  191. 191. HANDOFFHandoff is defined as a process used to allowa call/data transfer to continue uninterruptedas the mobile terminal moves between cells
  192. 192. Hard handoff vs. Soft handoffHard handoff- break before makeSoft handoff – Make before breakVertical Handoff vs. Horizontal HandoffVertical Handoff- Between Different NetworksHorizontal Handoff- Between Same NetworksDecision to handoff is based on the receivedsignal strength or S/I ratio.
  193. 193. CHANNEL ASSIGNMENT• Fixed Channel Assignment (FCA) – each cell is assigned a fixed number of channels – channels used for both handoff and new calls• Reservation Channels with FCA – each cell reserves some channels for hand off calls• Channel Borrowing – a cell may borrow free channels from neighboring cells• Dynamic Channel Assignment
  194. 194. METHODS TO IMPROVE SPECTRUM UTILIZATION• Interference Averaging (CDMA)• Interference Reduction (power adaptation, sectorization)• Interference Cancellation (smart antennas, multi user detection)• Interference Avoidance (dynamic resource allocation)
  195. 195. PHYSICAL LAYER ISSUES• Link Performance Measures• Modulation Tradeoffs• Flat Fading Countermeasures• Delay Spread Countermeasures
  196. 196. LINK PERFORMANCE MEASURES PROBABILITY OF BIT ERROR• The probability of bit error, Pb, in a radio environment is a random variable. – average Pb, Pb – Pr [Pb > Pbtarget] ∆ outage, Pout = • Typically only one of these measures is useful, depending on the Doppler frequency and the bit rate.
  197. 197. HOW DO WE OVERCOME THE LIMITATIONS IMPOSED BY THE RADIO CHANNEL?• Flat Fading Countermeasures – Fade Margin – Diversity – Coding and Interleaving – Adaptive Techniques• Delay Spread Countermeasures – Equalization – Multicarrier – Spread Spectrum – Antenna Solutions
  198. 198. DIVERSITY 16 The chance that two deep fades• Independent signal paths have a low probability occur simultaneously is rare. of experiencing deep fades simultaneously. 4 8 12• The basic concept is to send the same information over independently fading radio• Independent fading paths can be achieved by separating the signal in time, frequency, space, polarization, etc. 0 0 -20 -40 -80 -60 -100 (dBm) Received Signal Power
  199. 199. DIVERSITY COMBINING TECHNIQUES • • • α1 α2 α3 αM Combiner Output• Selection Combining: picks the branch with the highest SNR.• Equal-Gain Combining: all branches are coherently combined with equal weights.• Maximal-Ratio Combining: all branches are coherently combined with weights which depend on the branch SNR.
  200. 200. THANK YOU

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