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Mobile communication

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Mobile communication

  1. 1. What is Wireless and Mobile Communication?
  2. 2. • Transmitting voice and data using electromagnetic waves in open space • Electromagnetic waves • Travel at speed of light (c = 3x108 m/s) • Has a frequency (f) and wavelength ( ) » c = f x • Higher frequency means higher energy photons • The higher the energy photon the more penetrating is the radiation
  3. 3. 3 Electromagnetic Spectrum 104 102 100 10-2 10-4 10-6 10-8 10-10 10-12 10-14 10-16 104 106 108 1010 1012 1014 1016 1018 1020 1022 1024 IR UV X-Rays Cosmic Rays Radio Spectrum 1MHz ==100m 100MHz ==1m 10GHz ==1cm < 30 KHz VLF 30-300KHz LF 300KHz – 3MHz MF 3 MHz – 30MHz HF 30MHz – 300MHz VHF 300 MHz – 3GHz UHF 3-30GHz SHF > 30 GHz EHF Micro wave Visible light
  4. 4. Wavelength of Some Technologies • GSM Phones: (Global System for Mobile) – frequency ~= 900 MHz – wavelength ~= 33cm • PCS Phones (Personal communication System) – frequency ~= 1.8 GHz – wavelength ~= 17.5 cm • Bluetooth: – frequency ~= 2.4GHz – wavelength ~= 12.5cm
  5. 5. Frequency Carries/Channels – The information from sender to receiver is carrier over a well defined frequency band. • This is called a channel – Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate) – Different frequency bands (channels) can be used to transmit information in parallel and independently.
  6. 6. Example – Assume a spectrum of 90KHz is allocated over a base frequency b for communication between stations A and B – Assume each channel occupies 30KHz. – There are 3 channels – Each channel is simplex (Transmission occurs in one way) – For full duplex communication: » Use two different channels (front and reverse channels) » Use time division in a channel Channel 1 (b - b+30) Channel 2 (b+30 - b+60) Channel 3 (b+60 - b+90) Station A Station B
  7. 7. Simplex Communication • Normally, on a channel, a station can transmit only in one way. • This is called simplex transmision • To enable two-way communication (called full- duplex communication) • We can use Frequency Division Multiplexing • We can use Time Division Multiplexing
  8. 8. Duplex Communication - FDD • FDD: Frequency Division Duplex Base Station B Mobile Terminal M Forward Channel Reverse Channel Forward Channel and Reverse Channel use different frequency bands
  9. 9. Duplex Communication - TDD • TDD: Time Division Duplex A singe frequency channel is used. The channel is divided into time slots. Mobile station and base station transmits on the time slots alternately. Base Station B Mobile Terminal M M B M B M B
  10. 10. Example - Frequency Spectrum Allocation in U.S. Cellular Radio Service 991 992 … 1023 1 2 … 799 991 992 … 1023 1 2 … 799 824-849 MHz 869-894 MHz Reverse Channel Forward Channel Channel Number Center Frequency (MHz) Reverse Channel 1 <=N <= 799 991 <= N <= 1023 Forward Channel 1 <=N <= 799 991 <= N <= 1023 0.030N + 825.0 0.030(N-1023) + 825.0 0.030N + 870.0 0.030(N-1023) + 870.0 (Channels 800-990 are unused) Channels (Forward and Reverse) are separated by is 45 MHz
  11. 11. What is Mobility • Initially Internet and Telephone Networks is designed assuming the user terminals are static • No change of location during a call/connection • A user terminals accesses the network always from a fixed location • Mobility and portability – Portability means changing point of attachment to the network offline – Mobility means changing point of attachment to the network online
  12. 12. Degrees of Mobility • Walking Users • Low speed • Small roaming area • Usually uses high-bandwith/low-latency access • Vehicles • High speeds • Large roaming area • Usually uses low-bandwidth/high-latency access • Uses sophisticated terminal equipment (cell phones)
  13. 13. The Need for Wireless/Mobile Networking • Demand for Ubiquitous Computing – Anywhere, anytime computing and communication • You don’t have to go to the lab to check your email – Pushing the computers more into background • Focus on the task and life, not on the computer • Use computers seamlessly to help you and to make your life more easier. – Computers should be location aware • Adapt to the current location, discover services
  14. 14. Some Example Applications of Ubiquitous Computing • You walk into your office and your computer automatically authenticates you through your active badge and logs you into the Unix system • You go to a foreign building and your (Personal Digital Assistant) PDA automatically discovers the closest public printer where you can print your schedule and give to your friend
  15. 15. What is PCS • Personal Communication Services – A wide variety of network services that includes wireless access and personal mobility services – Provided through a small terminal – Enables communication at any time, at any place, and in any form. • The market for such services is tremendously big – Think of cell-phone market
  16. 16. Several PCS systems • High-tier Systems – GSM: Global System for Mobile Communications • The mobile telephony system that we are using – IS-136 (Interim State) • USA digital cellular mobile telephony system • TDMA based multiple access – Personal Digital Cellular – IS-95 cdmaOne System • CDMA based multiple access
  17. 17. Several PCS systems • Low-tier systems – Residential, business and public cordless access applications and systems • Cordless Telephone 2 (CT2) • Digital Enhanced Cordless Telephone (DECT) • Personal Access Communication Systems (PACS) • Personal Handy Telephone System (PHS)
  18. 18. Several PCS systems • Wideband wireless systems – For Internet access and multimedia transfer • Cdma2000 • W-CDMA, proposed by Europe • SCDMA, proposed by Chine/Europe
  19. 19. Several PCS systems • Other PCS Systems – Special data systems • CDPD: Cellular Digital Packet Data • RAM Mobile Data • Advanced Radio Data Information System (ARDIS) – Paging Systems – Mobile Satellite Systems • LEO, MEO, HEO satellites for data/voice – ISM band systems: Bluetooth, 802.11, etc.
  20. 20. PCS Problems • How to integrate mobile and wireless users to the Public Switched Telephone Network (PSTN) (Voice Network) • Cellular mobile telephony system • How to integrate mobile and wireless users to the Internet (Data Network) • Mobile IP, DHCP, Cellular IP • How to integrate all of them together and also add multimedia services (3G Systems)
  21. 21. InternetPSTN (Telephone Network) Looking to PCS from different Angles Mobile Users -Cell phone users -Cordless phone users Mobile Users -Laptop users -Pocket PC users -Mobile IP, Dynamic Host Configurat computers Wireless Access Telecom People View Data Networking People View
  22. 22. Very Basic Cellular/PCS Architecture Base Station (BS) Mobile Station Base Station Controller Mobility Database Mobile Switching Center (MSC) Radio Network Public Switched Telephone Network
  23. 23. Wireless System Definitions – Mobile Station – A station in the cellular radio service intended for use while in motion at unspecified locations. They can be either hand-held personal units (portables) or installed on vehicles (mobiles) – Base station – A fixed station in a mobile radio system used for radio communication with the mobile stations. Base stations are located at the center or edge of a coverage region. They consists of radio channels and transmitter and receiver antennas mounted on top of a tower.
  24. 24. Wireless System Definitions – Mobile Switching Center – Switching center which coordinates the routing of calls in a large service area. In a cellular radio system, the MSC connections the cellular base stations and the mobiles to the PSTN (telephone network). It is also called Mobile Telephone Switching Office (MTSO) – Subscriber – A user who pays subscription charges for using a mobile communication system – Transceiver – A device capable of simultaneously transmitting and receiving radio signals
  25. 25. Wireless System Definitions – Simplex Systems – Communication systems which provide only one-way communication – Half Duplex Systems – Communication Systems which allow two-way communication by using the same radio channel for both transmission and reception. At any given time, the user can either transmit or receive information. – Full Duplex Systems – Communication systems which allow simultaneous two-way communication. Transmission and reception is typically on two different channels (FDD).
  26. 26. Wireless System Definitions – Handoff – The process of transferring a mobile station from one channel or base station to an other. – Roamer – A mobile station which operates in a service area (market) other than that from which service has been subscribed. – Page – A brief message which is broadcast over the entire service area, usually in simulcast fashion by many base stations at the same time.
  27. 27. PCS Systems Classification • Cordless Telephones • Cellular Telephony (High-tier) • Wide Area Wireless Data Systems (High-tier) • High Speed Local and Personal Area Networks • Paging Messaging Systems • Satellite Based Mobile Systems • 3G Systems
  28. 28. Major Mobile Radio Standards USA Standard Type Year Intro Multiple Access Frequency Band (MHz) Modulation Channel BW (KHz) AMPS Cellular 1983 FDMA 824-894 FM 30 USDC Cellular 1991 TDMA 824-894 DQPSK 30 CDPD(Cellular Digital Packet Data) Cellular 1993 FH/Packet 824-894 GMSK 30 IS-95 (Interim standard) Cellular/PCS 1993 CDMA 824-894 1800-2000 QPSK/BPSK 1250 FLEX( free Open source for web appl) Paging 1993 Simplex Several 4-FSK 15 DCS-1900 (GSM) PCS 1994 TDMA 1850-1990 GMSK 200 PACS Cordless/PCS 1994 TDMA/FDMA 1850-1990 DQPSK 300
  29. 29. Major Mobile Radio Standards - Europe Standard Type Year Intro Multiple Access Frequency Band (MHz) Modulation Channel BW (KHz) ETACS(Ex tended total access commn sys Cellular 1985 FDMA 900 FM 25 NMT-900 (Nordic mobile tech Cellular 1986 FDMA 890-960 FM 12.5 GSM Cellular/PCS 1990 TDMA 890-960 GMSK 200KHz C-450 Cellular 1985 FDMA 450-465 FM 20-10 ERMES (European radio Paging 1993 FDMA4 Several 4-FSK 25
  30. 30. Cordless Telephones • Characterized by – Low mobility (in terms of range and speed) – Low power consumption – Two-way tetherless (wireless) voice communication – High circuit quality – Low cost equipment, small form factor and long talk-time – No handoffs between base units • Appeared as analog devices • Digital devices appeared later with CT2, DECT standards in Europe and ISM band technologies in USA
  31. 31. Cordless Telephones • Usage – At homes – At public places where cordless phone base units are available • Design Choices – Few users per MHz – Few users per base unit • Many base units are connected to only one handset – Large number of base units per usage area – Short transmission range
  32. 32. Cordless Phone • Some more features – 32 Kb/s adaptive differential pulse code modulation (ADPCM) digital speech encoding – Tx power <= 10 mW – Low-complexity radio signal processing – No forward error correction (FEC) or whatsoever. – Low transmission delay < 50ms – Simple Frequency Shift Modulation (FSK) – Time Division Duplex (TDD)
  33. 33. Cellular Telephony • Characterized by – High mobility provision – Wide-range – Two-way tetherless voice communication – Handoff and roaming support – Integrated with sophisticated public switched telephone network (PSTN) – High transmit power requires at the handsets (~2W)
  34. 34. Cellular Telephony - Architecture Radio tower PSTN Telephone Network Mobile Switching Center
  35. 35. Cellular Telephony Systems • Mobile users and handsets – Very complex circuitry and design • Base stations – Provides gateway functionality between wireless and wireline links • Mobile switching centers – Connect cellular system to the terrestrial telephone network
  36. 36. Cellular Networks • First Generation • Analog Systems • Analog Modulation, mostly FM • AMPS • Voice Traffic • FDMA/FDD multiple access • Second Generation (2G) • Digital Systems • Digital Modulation • Voice Traffic • TDMA/FDD and CDMA/FDD multiple access • 2.5G • Digital Systems • Voice + Low-datarate Data • Third Generation • Digital • Voice + High-datarate Data • Multimedia Transmission also
  37. 37. 2G Technologies cdmaOne (IS-95) GSM, DCS-1900 IS-54/IS-136 PDC Uplink Frequencies (MHz) 824-849 (Cellular) 1850-1910 (US PCS) 890-915 MHz (Eurpe) 1850-1910 (US PCS) 800 MHz, 1500 Mhz (Japan) 1850-1910 (US PCS) Downlink Frequencies 869-894 MHz (US Cellular) 1930-1990 MHz (US PCS) 935-960 (Europa) 1930-1990 (US PCS) 869-894 MHz (Cellular) 1930-1990 (US PCS) 800 MHz, 1500 MHz (Japan) Deplexing FDD FDD FDD Multiple Access CDMA TDMA TDMA Modulation BPSK with Quadrature Spreading GMSK with BT=0.3 DQPSK Carrier Seperation 1.25 MHz 200 KHz 30 KHz (IS-136) (25 KHz PDC) Channel Data Rate 1.2288 Mchips/sec 270.833 Kbps 48.6 Kbps (IS-136) 42 Kbps (PDC) Voice Channels per carrier 64 8 3 Speech Coding CELP at 13Kbps EVRC at 8Kbps RPE-LTP at 13 Kbps VSELP at 7.95 Kbps
  38. 38. 2G and Data • 2G is developed for voice communications • You can send data over 2G channels by using modem • Provides a data rates in the order of ~9.6 Kbps • Increased data rates are requires for internet application • This requires evolution towards new systems: 2.5 G
  39. 39. 2.5 Technologies • Evolution of TDMA Systems – HSCSD (High speed Circuit Switched Data) for 2.5G GSM – Up to 57.6 Kbps data-rate – GPRS (General Packet Radio Services) for GSM and IS-136 – Up to 171.2 Kbps data-rate – EDGE (Enhanced Data For Global Evolution) for 2.5G GSM and IS-136 – Up to 384 Kbps data-rate • Evolution of CDMA Systems
  40. 40. 3G Systems • Goals – Voice and Data Transmission • Simultanous voice and data access – Multi-megabit Internet access • Interactive web sessions – Voice-activated calls – Multimedia Content • Live music
  41. 41. 3G Systems • Evolution of Systems • CDMA sysystem evaolved to CDMA2000 » CDMA2000-1xRTT: Upto 307 Kbps » CDMA2000-1xEV: » CDMA2000-1xEVDO: upto 2.4 Mbps » CDMA2000-1xEVDV: 144 Kbps datarate • GSM, IS-136 and PDC evolved to W-CDMA (Wideband CDMA) (also called UMTS) » Up to 2.048 Mbps data-rates » Future systems 8Mbps » Expected to be fully deployed by 2010-2015 • New spectrum is allocated for these technologies
  42. 42. Upgrade Paths for 2G Technologies IS-136 PDC GSMIS-95 2G IS-95B HSCSD GPRS EDGE W-CDMA EDGE TD-SCDMA cdma200-1xRTT cdma2000-1xEV,DV,DO cdma200-3xRTT 2.5G 3G
  43. 43. Issues related to 3G High input fees for the 3G service licenses. Inefficient to meet future need of the performance. Require wide bandwidth. Lack of coverage because it is still new. Multiple standard.
  44. 44. 4G Proposed in ITU-2003 >4G- Magic . Mobile multimedia anytime/anywhere global mobility support integrated wireless and customized personal service  Hardware-Smart Antennas- Find tune and turn up signal information Spectrum-UWB-(Ultra wide band)
  45. 45. Features • Interactive multimedia •User friendliness •High speed-1 Gbps for still and 1000 Mbps for user in mobility. •Network Heterogeneity •Terminal Heterogeneity
  46. 46. Setting up a Call in Cellular Mobile System When a cell phone is switched on, it scans for the FCC to determine the strongest strength and monitors it till it drops below a usable level. It again searches for the strongest signal available. Control channels are defined and standardized over the entire geographic area covered and typically it is about 5% of total available channels in the system . Due to the standardization, the same phone is capable to be used in different markets. MSC dispatches the request to all base stations. MIN of subscriber is broadcasted as a paging message over all FCC. The phone receives the message and acknowledges it on the RCC and base station forwards it to MSC for handshake. MSC instructs base station to move the call on unused voice channel. Base station indicates the phone to change it to unused frequency pair and at this time base station sends a data message to mobile station on the voice channel for ringing. (a) Call is made for mobile station
  47. 47. From Mobile station  A call initiation request is sent on RCC. The request consists of its own MIN, ESN and the telephone number of the called party. Mobile station also sends the station class mark (SCM) to indicate the maximum power level is for particular user.  Cell base station receives the data and sends it to MSC. MSC validates the request, makes connection to the called party through PSTN and instructs base and mobile stations to move to unused voice channel On Roaming When a mobile station enters the new service are other than in which it subscribed, it is registered as roamer and it is done with FCC. Every several minutes, the MSC issues a global command over each FCC in the system asking for all mobiles which are previously unregistered to report their MIN and ESN over the RCC. MSC sends MIN/ESN data to request billing status from the home location register (HLR). Once registered , mobile allowed to communicate and the billing is routed automatically to the home service provider

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