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UNIT - I Mobile Communication and Mobile Computing. Motivation. Speech- and Data Communication location independent and mobile Ä New application areas, flexibility, improved workflows Requirements: - Mobile end-devices - Radio transmission - Localization and signalization/management

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UNIT - I Mobile Communication and Mobile Computing


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    1. UNIT - IMobile Communication andMobile Computing

    2. Motivation Speech- and Data Communication location independent and mobile Ä New application areas, flexibility, improved workflows Requirements: - Mobile end-devices - Radio transmission - Localization and signalization/management - Standards - Application Concepts for mobile end-devices in distributed systems - Control of heterogeneous, dynamic infrastructures Mobile Computing

    3. Application example: Civil Engineering, Field Service Drafts, urgent modification Large archives, Videoconferences ATM ISDN Building of enterprise A (main office) Building of enterprise A (branch office) Architect X.25 ISDN ATM Selected drafts, Videoconferences GSM GSM Construction supervisor Material data, status data, dates Building site Building of enterprise B

    4. WAP-Example: Order processing Order book • Status of bond transactions. • Executed and deleted orders are indicated in the order book for some days more. • Partial execution of some order is presented as one open and one executed partial order in the order book. • Details to an order could be indicated via dial-up of correspondent Links.

    5. Perspective: Mobile Multimedia Systems Local Resources, Error Protocols Client Maintenance technician Product Data LAN-Access Main office Caching Mobile Access - very different performance and charges: radio networks versus fixed networks Software-technical, automatic adaptation to concrete system environment Example:Access to picture data/compressed picture data/graphics/text

    6. Application Structure Ethernet Ethernet Distributed Database DB E-Fax-Order Branch office Firm xDSL Application Resource Mobile Station Communication path GSM Ethernet Cache ManagementDB-Access Distributed Database Client X

    7. Traffic Telematics Systems Content Provider Main Office Content Provider ATM Internet GSM, RDS/TMC, DAB ... GSM Beam Radio, ISDN GSM GSM Radio/Infrared DAB: Digital Audio Broadcast RDS/TMC: Radio Data System/ Traffic Message Channel Infrastructure

    8. Mobile Communication Networks: Examples GSM (Global System for Mobile Communications): worldwide standard for digital, cellular Mobile Radio Networks UMTS (Universal Mobile Telecommunications System): European Standard for future digital Mobile Radio Networks AMPS (Advanced Mobile Phone System): analog Mobile Radio Networks in USA DECT (Digital Enhanced Cordless Telecommunications): European standard for cordless phones TETRA (Terrestrial Trunked Radio): European standard for circuit switched radio networks ERMES (European Radio Message System): European standard for radio paging systems (Pager) 802.11: International standard for Wireless Local Networks Bluetooth: wireless networking in close/local area Inmarsat: geostationary satellite systems Teledesic: planned satellite system on a non-geostationary orbit

    9. E (GSM1800) D (GSM900) CT2 DECT HSCSD Mobile Communication: Development C Mobile Phone Networks EDGE GPRS Cordless Telephony IMT2000/ UMTS Packet Networks Modacom Mobitex Circuit Switched Networks Tetra Iridium/ Globalstar Satellite Networks Inmarsat Radio-LAN Local Networks IEEE 802.11/ Hiperlan MBS IR-LAN 2005 1990 1995 2000

    10. Used Acronyms CT2: Cordless Telephone 2. Generation HSCSD: High Speed Circuit Switched Data GPRS: General Packet Radio Service EDGE: Enhanced Data Rates for GSM Evolution IMT2000: International Mobile Telecommunications by the year 2000 MBS: Mobile Broadband System

    11. 2. Mobile Communication

    12. Principles

    13. Mobile Communication Tied to electro-magnetic radio transmission radio transmission orbital (satellite) terrestrial broadcast radio equatorial orbit beam radio non-equatorial orbit cellular non-cellular • Principles: • Propagation and reception of electro-magnetic waves • Modulation methods and their properties • Multiplex methods • Satellite orbits/Sight- and overlap areas

    14. Cellular Networks: Principles Channels801-1600 3 4 2 1 4 2 1 5 2 1 5 7 6 Interference Zone 5 7 6 3 7 6 3 4 2 2 R 3 4 1 R 4 2 5 7 1 1 5 7 6 5R 5 7 6 3 4 6 3 4 2 4 2 1 5 Channels 1-800 Channels 1-800 7-Cell-Cluster (repeat sample of the same radio-channels) Supply- (radius R) and interference areas (5 R)

    15. Cellular Networks: Principles Cell structure: Example Reference cell Cell in the interference area of the reference cell Further cells, whose channel distribution should be known to the reference cell

    16. z x Kinds of antennas: directional & sectored • Energy is radiated in definite directions, for instance x-Direction • So called main propagation directions, for instance Satellite Antennas • Often also used in Mobile Radio Systems, such as GSM, for creation of sectored cells • Seamless radio supply via partial/overlay of sectors y x Directional Antenna Sectored Antenna

    17. Media Access Methods

    18. Principles • Multiplex • Multiple-shift usage of the medium without interference • 4 multiplex methods: • Space • Time • Frequency • Code • Media Access Methods • controls user access to medium

    19. SDMA (Space Division Multiple Access) • based on SDM (Space Division Multiplexing, Space Multiplex) • communication channel obtains definite Space for definite Time on the definite Frequency with definite Code • Space Multiplex for instance in the Analog Phone Systems (for each participant one line) and for Broadcasting Stations • Problem: secure distance (interferences) between transmitting stations is required (using one frequency) and by pure Space Multiplex each communication channel would require an own transmitting station • Space Multiplex is only reasonable in combination with other multiplex methods • SDMA for instance by base station dedication to an end-device via Media Access Methods or respectively by segmentation of a Mobile Radio Network to several areas

    20. SDMA: Example k1 k2 k3 k4 k5 k6 f1 s SDMA finds selection s – secure distance

    21. f k6 k5 k4 k3 k2 t k1 FDMA (Frequency Division Multiple Access) • Based on FDM (Frequency Division Multiplexing, Frequency Multiplex) • i.e. to transmission channels several frequencies are permanently assigned, for instance radio transmitting stations k1 k2 k3 k4 k5 k6 f1 f4 FDMA finds selection f2 f5 s f3 f6 s – secure distance

    22. f k1 k2 k3 k4 k5 k6 k1 t TDMA (Time Division Multiple Access) • Based on TDM (Time Division Multiplexing, Time Multiplex) • i.e. to transmission channels is the transmission medium is slot assigned for certain time, is often used in LANs • Synchronization (timing, static or dynamic) between transmitting and receiving stations is required k1 k2 k3 k4 k5 k6 TDMA finds selection f1

    23. TS0 TS0 TS0 TS0 TS0 TS0 TS1 TS1 TS1 TS1 TS1 TS1 TS2 TS2 TS2 TS2 TS2 TS2 TS3 TS3 TS3 TS3 TS3 TS3 TS4 TS4 TS4 TS4 TS4 TS4 TS5 TS5 TS5 TS5 TS5 TS5 TS6 TS6 TS6 TS6 TS6 TS6 TS7 TS7 TS7 TS7 TS7 TS7 TS0 TS0 TS0 TS0 TS0 TS0 Combination: FDMA and TDMA, for instance GSM • GSM uses combination of FDMA and TDMA for better use of narrow resources • the used band width for each carrier is 200 kHz f in MHz 960 downlink 25 MHz 935,2 915 200 kHz 45 MHz uplink 25 MHz 890,2 t

    24. CDMA (Code Division Multiple Access) • based on CDM (Code Division Multiplexing, Code multiplex) • i.e. to transmission channels the definite Code is assigned, this can be on the same Frequency for the same Time transmitted • derivates from military area • via development of cost-efficient VLSI components • via spread spectrum techniques a good communication security and tiny fault sensitivity • but: exact synchronization is required, code of transmitting station must be known to receiving station, complex receivers for signal separation are required • Noise should not be very high

    25. CDMA k1 k2 k3 k4 k5 k6 f1 CDMA decoded

    26. CDMA illustrated by example The Principle of CDMA can be good illustrated by the example of some party: • communication partners stand closely to each other, each transmission station (Sender) is only so loud, that it does not interfere to neighbored groups • transmission stations (Senders) use certain Codes (for instance, just other languages), they can be just separately received by other transmission stations • receiving station (Listener) attunes to this language (Code), all other Senders are realizing this only as background noise • if receiving station (Listener) cannot understand this language (Code), then it can just receive the data, but it cannot do anything with them • if two communication partners would like to have some secure communication line, then they should simply use a secret language (Code) • Potential Problems: • security distance is too tiny: interferences (i.e. Polish und Czech)

    27. CDMA-Example in the theory Sender A • Sends Ad =1, Key Ak = 010011 (set: „0“= -1, „1“= +1) • Transmit signal As =Ad *Ak = (-1, +1, -1, -1, +1, +1) Sender B • sends Bd =0, Key Bk = 110101 (set: „0“= -1, „1“= +1) • Transmit signal Bs =Bd *Bk = (-1, -1, +1, -1, +1, -1) Both signals superpose additively in air • Faults are ignored here (noises etc.) • C = As+ Bs =(-2,0,0,-2,+2,0) Receiver will listen to Sender A • uses Key Ak bitwise (internal product) • Ae = C * Ak =2 +0+0 +2 +2+0 = 6 • Result is greater than 0, so sent bit was „1“ • analog B • Be = C * Bk =-2 +0 +0 -2 -2 +0 = -6, also „0“

    28. Spread Spectrum Techniques • Signal is spread by the Sender before the transmission (overblown) • dP/df value corresponds with so called Power Density, Energy is constant (in the Figure: the filled areas) Objective: • Increase of robustness against small band-width faults • listening security: power density of spread-spectrum signals can be lower than that of background noise

    29. Spread Spectrum Techniques • small band-width faults are spread by de-spreading in receiving station • band-pass deletes redundant frequency parts t

    30. Mobile Radio Networks: Overview

    31. Development of Mobile Radio General technological development in mobile telephony Satellite Systems (LEO) UMTS HSCSD GPRS EDGE GSM Phase II+ Digital cellular Networks...1800 Mhz PCN GSM1800 Digital cellular Networks...900 Mhz GSM900 Prognoses Anal. cellular Networks...900 Mhz Anal. cellular Networks...450 Mhz Analog Networks...150Mhz before 1970 1970 1980 1990 2000 2005

    32. Correspondent data rates Satellites (GEO) (GEO)

    33. Participant quantities in Mobile Radio – world-wide November 2002: 1148 Mio. participants world-wide (1119 Mio. digital & 29 Mio analog) (Source: http://www.emc-database.com) 1... Europe: Western 4... Americas (thereof 15.4 Mio. analog) 2... Asia Pacific 5... USA/Canada (thereof 5.4 Mio. analog) 3... Middle East 6... Africa 7… Europe: Eastern

    34. Frequency Assignment Circuit Switched Radio Mobile Phones Cordless Phones Wireless LANs TETRA NMT TETRA CT2 CT1+ GSM900 CT1+ GSM900 380-400 410-430 453-457 450-470 (nationally different) 500Mhz 864-868 885-887 890-915 930-932 935-960 1GHz 463-467 TFTS (Pager, aircraft phones) GSM1800 TFTS GSM1800 DECT UMTS 1670-1675 1710-1785 1800-1805 1805-1880 1880-1900 (1885-2025 2110-2200) WLAN IEEE 802.11a: 5,15-5,25; 5,25-5,35; 5,725-5,825 IEEE 802.11b Bluetooth HIPERLAN1 HIPERLAN2 HIPER-Link MHz 2400-2483 2402-2480 5176-5270 (ca.5200,5600) (ca.17000) 2412-2472 Notes: - 2,4 GHz license free, nationally different - () written : Prognoses! - today speech over license free frequencies up to 61Ghz -> interesting for high data rates HomeRF...(approx.2400) TFTS - Terrestrial Flight Telephone System

    35. Broadcast/multicast networks • several carrier frequencies but participant obtains carrier for short time only • often in use by taxi- und logistics enterprises etc., each own separated frequency reaches • can use the same frequency packs with FDM- and TDM- techniques, i.e. more efficient handling with narrow resource frequency spectrum • improves transition to fixed network, speech- and data services • not for public access • very reliable, cost-efficient

    36. TETRA (Terrestrial Trunked Radio) • former name: Trans-European Trunked Radio • frequencies: 380-390, 410-420 MHz Uplink; 390-400, 420-430 MHz Downlink • bandwidth of each channel: 25 kHz • 1991 started by ETSI • replace of national networks like MODACOM, MOBITEX or COGNITO • Services: • Voice + Data (V+D)- Service: Speech and Data, channel-oriented, uni-, multi- and broadcast possible • Packet Data Optimized (PDO)- Service: packet-oriented, improves connection-oriented or connectionless service, as well as point-to-point and point-to-multipoint communication • carrier services with data rate up to 28,8 kbit/s unprotected; 9,6 kbit/s - protected

    37. TETRA, advantages compared with GSM, UMTS • confirmed and/or non-confirmed Group Call (however it’s already possible with GSM today: up to 16 participants) • Group call • listening is possible (so called “open-channel mode”) • very reliable • fast dialing: approx. 300 ms (so called “push to talk”), GSM: several seconds • certain independence of infrastructure (so called “direct mode” between end-devices) • cost-efficient, especially for limited user quantity, because of the „large“ cells x • 10 km • also especially suitable for emergency teams (fire department, ambulance etc.)

    38. Cordless Telephony - DECT (Digital Enhanced Cordless Telecommunications) • frequency reach: 1880 - 1990 MHz • other than GSM limited to short reaches (1km) • in buildings particularly under 50m • is not designed for use at high rates • mobile phones with GSM and DECT are available in the market • 120 full duplex channels • TDD (Time Division Duplex) for directional separation with 10ms frame length • frequency reach is divided into 10 carrier frequencies using FDMA • each station 10mW averaged, max. 250mW of transmitting power, GSM – radio phones transmit at 1 to 2W, fixed car phones up to 8W

    39. DECT – system architecture D4 D3 D2 HDB PA PT FT Local Networks VDB PA PT D1 FT Global Networks Local Networks FT.. Fixed Radio Termination PT.. Portable Radio Termination PA... Portable Terminations HDB.. Home Data Base VDB.. Visitor Data Base

    40. . . . . . . . . . DECT - Multiplex Used Data Used Data CRC Synchronization Signalization CRC Secure marker (Speech) (Speech) 32 bit 48 bit 160 bit 8 bit 160 bit 8 bit 64 bit 0,417 ms DECT-timeslot structure Transmission reach of fixed part (downlink) Transmission reach of mobile part (uplink) carrier frequency 1: 1 2 3 4 5 6 .... 11 12 1' 2' 3' 4' 5' 6' .... 11' 12' carrier frequency 2: 1728 1' 2' 3' 4' 5' 6' .... 11' 12' 1 2 3 4 5 6 .... 11 12 kHz carrier frequency 10: 1' 2' 3' 4' 5' 6' .... 11' 12' 1 2 3 4 5 6 .... 11 12 Transmission principle of DECT-system Channel 1 Channel 2 Channel 12 Channel 1’ Channel 2' Channel 12' . . . . . . fixed part to mobile part mobile part to fixed part Time duplex with 10 ms frame length Structure of DECT-time multiplex frame

    41. Pager systems: overview • Eurosignal • to each participant 4 different audio signals using 4 diverse call numbers are assigned. Meaning must be agreed. Receiving stations are at a size of a cigarette packet • 85 senders in the 87 MHz-reach (ultra short waves) • called person location must be approximately known: 3 area codes: North 0509, Middle 0279, South 0709 • Cityruf (city call) • additionally to 4 audio- or respectively optical signals transmission of short numerical (15 digitals) or alpha-numerical messages (80 characters) exists optionally, receiving station is smaller than with Eurosignal • PEP (Pan European Paging) • preparation for coupling of national services for ERMES • D: Cityruf, F: Alphapage, GB: Europage, I: SIP • ERMES (European Radio Message System) • ETSI-Standard for pan-European radio service, similar to PEP but in 169 MHz-reach with 60 Mio. addresses

    42. UNIT - IIGSM: Global System for Mobile Communications

    43. GSM: Properties • cellular radio network (2nd Generation) • digital transmission, data communication up to 9600 Bit/s • Roaming (mobility between different net operators, international) • good transmission quality (error detection and -correction) • scalable (large number of participants possible) • Security mechanisms (authentication, authorization, encryption) • good resource use (frequency and time division multiplexing) • integration within ISDN and fixed network • standard (ETSI, European Telecommunications Standards Institute)

    44. Providers in Germany (1) • D1 T-Mobile • subscribers: 24,6 Mio (Stand 2003) • Vodafone D2 • old name: Mannesmann Mobilfunk D2 • subscribers: 22,7 Mio (Stand 2003) • E-plus • O2 • old name: VIAG Interkom

    45. Providers in Germany (2)

    46. MS MS Call Management Network Management GSM: structure Fixed network Switching Subsystems Radio Subsystems OMC Data networks VLR HLR AuC EIR (G)MSC BSC BTS PSTN/ ISDN BTS BSS MS MS Mobile Station (G)MSC (Gateway) Mobile Switching Centre OMC Operation and Maintenance Centre PSTN Public Switched Telephone Network VLR Visitor Location Register ISDN Integrated Services Digital Network AuC Authentication Centre BSS Base Station Subsystem BSC Base Station Controller BTS Base Transceiver Station EIR Equipment Identity Register HLR Home Location Register

    47. GSM: Structure Operation and Maintenance Centre (OMC) • logical, central structure with HLR, AuC und EIR Authentication Centre (AuC) • authentication, storage of symmetrical keys, generation of encryption keys Equipment Identity Register (EIR) • storage of device attributes of allowed, faulty and jammed devices (white, grey, black list) Mobile Switching Centre (MSC) • arrangement centre, partial as gateways to other nets, assigned to one VLR each Base Station Subsystem (BSS): technical radio centre • Base Station Controller (BSC): control centre • Base Transceiver Station (BTS): radio tower / antenna

    48. Radio technical structure 1 TDMA-Frame, 144 Bit in 4,615 ms 8 TDMA-channels, together 271 kBit/s inclusive error protection information 124 radio frequency channels (carrier), each 200 kHz downlink 890 915 MHz uplink 960 MHz 935 2 frequency wavebands, for each 25 MHz, divided into radio cells • One or several carrier frequencies per BSC • Physical channels defined by number and position of time slots

    49. PSTN/ ISDN GSM: protocols, incoming call (4) (3) BSS HLR VLR (8) (7) (6) (4) (2) (11) (10) (8) (8) (5) (1) (9) (9) MSC GMSC BSS BSS (12) (12) (8) BSS (1) Call from fixed network was switched via GMSC (2) GMSC finds out HLR from phone number and transmits need of conversation (3) HLR checks whether participant for a corresponding service is authorized and asks for MSRN at the responsible VLR (4) MSRN will be returned to GMSC, can now contact responsible MSC

    50. PSTN/ ISDN GSM: protocols, incoming call (4) (3) BSS HLR VLR (8) (7) (6) (4) (2) (11) (10) (8) (8) (5) (1) (9) (9) MSC GMSC BSS BSS (12) (12) (8) BSS (5) GMSC transmits call to current MSC (6) ask for the state of the mobile station (7) Information whether end terminal is active (8) Call to all cells of the Location Area (LA) (9) Answer from end terminal (10 - 12) security check and connection construction