Mobile Communications

Transcription

1 Mobile Communications Lehrstuhl für Informatik 4 RWTH Aachen Dr. rer. nat. Dirk Thißen Prof. Dr. Otto Spaniol Seite 1

2 Organization Lehrstuhl für Informatik 4 Lecture Dates Wednesday, 13:30-15:00, in 5052 Material (Slide Copies and Video Recordings) content/teaching/lectures/sub/mobil/ws0506/index.html Literature J. Schiller: Mobile Communications. 2nd Edition, Addison Wesley, 2003 Contact Dirk Thißen Lehrstuhl für Informatik 4, Room 4226 (Building E1) Phone: 0241 / thissen@informatik.rwth-aachen.de Seite 2

3 What is Mobile Communications? Two aspects of mobility: User mobility: a user communicates (wireless) anytime, anywhere, with anyone Device portability: A device can connect to the network anytime and anywhere Wireless vs. Mobile Example stationary computer notebook in a hotel Wireless LAN in buildings Personal Digital Assistants (PDA) The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: In the local range: standardization of IEEE , ETSI HIPERLAN In the Internet: Mobile IP as enhancement of normal IP In wide area range: e.g. internetworking of GSM and ISDN Seite 3

4 Why Wireless Networks? Characteristics Mostly radio transmission, new protocols for data transmission are needed Advantages Spatial flexibility in radio reception range Ad hoc networks without former planning No problems with wiring (e.g. historical buildings, fire protection, esthetics) Robust against disasters like earthquake, fire and careless users which remove connectors! Disadvantages Generally very low transmission rates for higher numbers of users Often proprietary, more powerful approaches, standards are often restricted Consideration of lots of national regulations, global regulations are evolving slowly Restricted frequency range, interferences of frequencies Seite 4

5 Applications I Lehrstuhl für Informatik 4 Vehicles Transmission of news, road condition, weather, music via DAB (Digital Audio Broadcasting) Personal communication using GSM Location tracking via GPS Local ad-hoc network with vehicles close-by to prevent accidents, guidance system, redundancy Vehicle data (e.g., from busses, high-speed trains) can be transmitted in advance for maintenance Emergencies Early transmission of patient data to the hospital, current status, first diagnosis Replacement of a fixed infrastructure in case of earthquakes, hurricanes, fire etc. Crisis, war,... Seite 5

6 Typical Application: Road Traffic UMTS, WLAN, DAB, GSM, TETRA,... ad hoc Personal Travel Assistant, DAB, PDA, Laptop, GSM, UMTS, WLAN, Bluetooth,... Seite 6

7 Applications II Lehrstuhl für Informatik 4 Traveling salesmen Direct access to customer files stored in a central location Consistent databases for all agents Mobile office Replacement of fixed networks Remote sensors, e.g., weather, earth activities Flexibility for trade shows LANs in historic buildings Entertainment, education,... Outdoor Internet access Intelligent travel guide with up-to-date location dependent information Ad-hoc networks for multi user games Seite 7

8 Location Dependent Services Location aware services What services, e.g., printer, fax, phone, server etc. exist in the local environment Follow-on services Automatic call-forwarding, transmission of the actual workspace to the current location Information services Push : e.g., current special offers in the supermarket Pull : e.g., where is the Black Forrest Cherry Cake? Support services Caches, intermediate results, state information etc. follow the mobile device through the fixed network Privacy Who should gain knowledge about the location? Seite 8

9 Mobile Devices Pager receive only tiny displays simple text messages PDA simple graphical displays character recognition simplified WWW Laptop fully functional standard applications Sensors, embedded controllers Mobile phones voice, data simple graphical displays Palmtops tiny keyboard simple versions of standard applications Performance Seite 9

10 Wireless Networks in Comparison to Fixed Networks Higher loss-rates due to interference Emissions of e.g. engines, lightning Restrictive regulations of frequencies Frequencies have to be coordinated, useful frequencies are almost all occupied Low transmission rates Local some Mbit/s, regional currently up to 384 Kbit/s with GPRS/UMTS/ Higher delays, higher jitter Connection setup time with GSM in the second range, several hundred milliseconds for other wireless systems Lower security, simpler active attacking Radio interface accessible for everyone, base station can be simulated, thus attracting calls from mobile phones Always shared medium Secure access mechanisms important Seite 10

11 Early Wireless Communication Many people in history used light for communication Heliographs, flags ( semaphore ), BC smoke signals for communication (Polybius, Greece) 1794: optical telegraph, Claude Chappe Here electromagnetic waves are of special importance: 1831 Faraday demonstrates electromagnetic induction J. Maxwell ( ): theory of electromagnetic fields, wave equations (1864) H. Hertz ( ): demonstrates with an experiment the wave character of electrical transmission through space (1888, in Karlsruhe, Germany, at the location of today s University of Karlsruhe) Seite 11

12 History of Wireless Communication Guglielmo Marconi First demonstration of wireless telegraphy (digital!) Long wave transmission, high transmission power necessary (> 200kw) Commercial transatlantic connections Huge base stations (30 100m high antennas) Wireless voice transmission New York - San Francisco Discovery of short waves by Marconi Reflection at the ionosphere Smaller sender and receiver, possible due to the invention of the vacuum tube (1906, Lee DeForest and Robert von Lieben) Train-phone on the line Hamburg - Berlin Wires parallel to the railroad track Seite 12

13 History of Wireless Communication Many TV broadcast trials (across Atlantic, color TV, TV news) Frequency modulation (E. H. Armstrong) A-Netz in Germany Analog, 160MHz, connection setup only from the mobile station, no handover, 80% coverage, customers B-Netz in Germany Analog, 160MHz, connection setup from the fixed network too (but location of the mobile station has to be known) available also in Austria, Netherlands and Luxembourg, customers in Germany NMT at 450MHz (Scandinavian countries) Start of GSM-specification Goal: pan-european digital mobile phone system with roaming Start of the American AMPS (Advanced Mobile Phone System, analog) CT-1 standard (Europe) for cordless telephones Seite 13

14 History of Wireless Communication C-Netz in Germany Analog voice transmission, 450MHz, hand-over possible, digital signaling, automatic location of mobile device Was in use until 2000, services: FAX, modem, X.25, , 98% coverage Specification of DECT Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications) MHz, ~ m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several user/km2, used in more than 50 countries Start of GSM In Germany as D1 and D2, fully digital, 900MHz, 124 channels Automatic location, hand-over, cellular Roaming in Europe - now worldwide in more than 170 countries Services: data with 9.6kbit/s, FAX, voice,... Seite 14

15 History of Wireless Communication E-Netz in Germany GSM with 1800MHz, smaller cells As E-plus in Germany ( % coverage of the population) HiperLAN (High Performance Radio Local Area Network) ETSI, standardization of type 1: GHz, 23.5Mbit/s Recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz) as wireless ATM-networks (up to 155Mbit/s) Wireless LAN IEEE IEEE standard, GHz and infrared, 2Mbit/s Already many (proprietary) products available in the beginning Specification of GSM successors UMTS (Universal Mobile Telecommunication System) as European proposals for IMT-2000 Iridium: 66 satellites (+6 spare), 1.6GHz to the mobile phone Seite 15

16 History of Wireless Communication Standardization of additional wireless LANs IEEE standard b, GHz, 11Mbit/s Bluetooth for piconets, 2.4Ghz, <1Mbit/s Decision about IMT-2000 Several members of a family : UMTS, cdma2000, DECT, Start of WAP (Wireless Application Protocol) and i-mode Access to many (Internet) services via the mobile phone GSM with higher data rates HSCSD offers up to 57,6kbit/s First GPRS trials with up to 50 kbit/s (packet oriented!) UMTS auctions/beauty contests Hype followed by disillusionment (approx. 50 B$ payed in Germany for 6 UMTS licences!) Start of 3G systems Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan 2002 Standardization of high-capacity wireless networks IEEE als Wireless MAN Seite 16

17 Wireless Systems transmission rate (MBit/s) wired devices WMAN WLAN CORDLESS (CT, DECT) Office Building stationary walk drive Indoor HIPERLAN UMTS CELLULAR (GSM) Outdoor mobility CT - Cordless Telephony (analogous predecessor of DECT) DECT - Digital Enhanced Cordless Telecommunications (Standard for wireless phones in a local range) GSM - Global System for Mobile Communication (cellular phone system) UMTS - Universal Mobile Telecommunications System (universal system, comprising several different access systems) WLAN - Wireless Local Area Network (Standard for wireless networking of (portable) computer) HIPERLAN alternative LAN to WLAN, wireless ATM enhancement WMAN Wireless MAN (Bridging the last mile between a fixed network and the end user, wireless alternative to DSL) And furthermore: Satellite systems, Bluetooth/IrDA in very short range Seite 17

18 Wireless Systems: Overview of the Evolution cellular phones satellites cordless wireless LAN phones 1981: NMT : NMT : GSM analogue digital 1994: DCS : CDMA 2000: GPRS 1983: AMPS 1991: D-AMPS 1993: PDC 4G fourth generation: when and how? 1982: Inmarsat-A 1988: Inmarsat-C 2001: IMT-2000/UMTS 1992: Inmarsat-B Inmarsat-M 1998: Iridium 200?: Fourth Generation (Internet based) 1980: CT0 1984: CT1 1987: CT : CT : DECT 199x: proprietary 1997: IEEE : b, Bluetooth 2000: IEEE a 2002: IEEE Seite 18

19 Contents of this lecture: Personal Area Networks Personal Area Networks (very small range) IrDA (Infrared Data Association) Standard for connecting devices using infrared light Data rate up to 4 Mb/s gross, used only 115 Kb/s Range of some meters, only line of sight Susceptible to disturbances IEEE (WPAN, Bluetooth): Data rates up to 723 Kb/s Range up to ca. 10/15 meters (with higher transmission power, also 100 meters are no problem), forming of small radio cells Ad-hoc Networking: spontaneous (automatically) connection of several devices (maximally 8) to an independent network Used with cellular phones, Personal Digital Assistants (PDAs),... Seite 19

20 Contents of this lecture: Wireless Local Area Networks Wireless LANs (small range) IEEE (Wireless LAN, WLAN) The standard for supporting mobile computers High data rates: currently up to 54 MBit/s Physical layer and MAC: often called wireless variant of Ethernet Base stations (Access Point, AP) connect WLAN with fixed Ethernet, additionally WLAN enables forming ad-hoc networks Transmission medium: radio and infrared IEEE (WirelessMAN) mainly supports mobility, more focuses on connecting buildings Higher data rates ( Mb/s), larger range HIPERLAN (High Performance Radio Local Area Network) Several variants, from Type 1 with 23,5 Mb/s up to Type 4 with 155 Mb/s Range varies between 50 meter up to 5 kilometer No products Seite 20

21 Contents of this lecture: Telecommunication Networks Cordless Systems DECT (Digital Enhanced Cordless Telecommunications) Standard for cordless telephony Transmission of voice and data in short range (at home) Cellular Systems (medium range) GSM (Global System for Mobile Communications) Mainly designed for voice transmission, also used for data transmission (Wide Area Network) Low data rates (9,6 Kb/s) Enhancements for data transmission (EDGE, GPRS, HSCSD) UMTS (Universal Mobile Telecommunications System) Also: IMT-2000 (International Mobile Telecommunications) Integration of all types of data, rates up to 2 Mb/s and for word-wide coverage: satellites. Seite 21

22 Overlay Networks integration of heterogeneous fixed and mobile networks with varying transmission characteristics regional Vertical Handover metropolitan area campus Horizontal Handover indoor Seite 22

23 Areas of Research in Mobile Communication Wireless communication Transmission quality (bandwidth, error rate, delay) Modulation, coding, interference Media access, regulations... Mobility Location dependent services Location transparency Quality of Service support (delay, jitter, security)... Portability Power consumption Limited computing power, sizes of display,... Usability... Seite 23

24 Simple Reference Model used here Application Application Transport Transport Network Network Network Network Data Link Data Link Data Link Data Link Physical Physical Physical Physical Radio Medium Seite 24

25 Relation to OSI Reference Model Application Layer Transport Layer Network Layer Data Link Layer Physical Layer Service location Adaptive application New applications Congestion and flow control Quality of Service Addressing, routing Device location Handover Medium access control Multiplexing Authentication Frequencies, modulation Interferences, attenuation Encryption Seite 25

26 Structure of the Lecture Chapter 2 Technical Basics: Layer 1 Methods for Medium Access: Layer 2 Chapter 3 Wireless Networks: Bluetooth, WLAN, WirelessMAN, WirelessWAN Mobile Networks: GSM, GPRS, UMTS Satellites and Broadcast Networks Chapter 4 Mobility on the network layer: Mobile IP, Routing, Ad-Hoc Networks Mobility on the transport layer: reliable transmission, flow control, QoS Mobility support on the application layer Seite 26