Mobile Communications

Transcription

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

2 Organization Lehrstuhl für Informatik 4 Lecture Dates Monday, 16:30 18:00, AH5 Wednesday, 13:30-15:00, 5052 Exercise Dates Wednesday, 13:30-15:00, 5052 Material (Slide Copies and Video Recordings) content/teaching/lectures/sub/mobil/ws0708/index.html Literature J. Schiller: Mobile Communications. 2 nd Edition, Addison Wesley, 2003 V. Garg: Wireless Communications and Networking. Morgan Kaufmann, 2007 Contact Dirk Thißen Lehrstuhl für Informatik 4, Room 4105B (Building E1) Phone: 0241 / thissen@informatik.rwth-aachen.de Page 2

3 What is Mobile Communications? Two aspects of mobility: User mobility: a user communicates anytime, anywhere, using any access technology 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 Cellular phone The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: In the local range: standardization of IEEE (Wireless LAN, WLAN) considering existing wired standards like Ethernet In wide area range: e.g. internetworking of GSM and ISDN In the Internet protocols: Mobile IP as enhancement of normal IP Page 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 Page 4

5 Types of Wireless Networks Cellular Networks Base stations distributed over the area to be covered Each base station covers a cell Need of an infrastructure network connecting all base stations Used for mobile phone networks and data networks like Wireless LAN Mobile Ad-Hoc Networks (MANETs) Self-configuring network of mobile nodes Each node serves as client and router No infrastructure (base stations) necessary, direct connections between any pair of nodes E.g. Bluetooth Mesh Networks Enhancement of above concepts: Ad-hoc network with infrastructure Allow a whole mesh of connections between wireless nodes Increased fault tolerance E.g. used in WiMAX Page 5

6 Possible Applications Vehicles Transmission of news, road condition, weather, music, e.g. via DAB (Digital Audio Broadcasting) Personal communication using the Global System for Mobile Communication (GSM) Location tracking via the Global Positioning System (GPS) Local ad-hoc networks 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,... Page 6

7 Typical Application: Road Traffic UMTS, WLAN, DAB, GSM,... ad hoc Personal Travel Assistant, DAB, PDA, Laptop, GSM/UMTS, WLAN, Bluetooth,... Page 7

8 Possible Applications 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 Page 8

9 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? Page 9

10 Wireless Networks in Comparison to Wired Networks Higher loss-rates due to interference Emissions of e.g. engines, lightning Restrictive regulations of radio 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 (shared medium), base station can be simulated, thus attracting calls from mobile phones Very different device capabilities New concepts necessary in protocol design, e.g. energy efficiency Page 10

11 Characteristics of 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 Page 11

12 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) Page 12

13 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 Page 13

14 History of Wireless Communication Many TV broadcast trials (across Atlantic, color TV, TV news) Frequency modulation (E. H. Armstrong) A-Netz in Germany Analogue, 160MHz, connection setup only from the mobile station, no handover, 80% coverage, customers B-Netz in Germany Analogue, 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 Page 14

15 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,... Page 15

16 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, 2.4GHz 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 Page 16

17 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 licenses!) Start of 3G systems Cdma2000 in Korea, UMTS in Europe, Foma (almost UMTS) in Japan since 2002 Standardization of high-capacity wireless networks IEEE as WMAN, IEEE (WWAN), IEEE (WRAN) Page 17

18 Wireless Systems: Overview of the Evolution cellular phones satellites cordless wireless LAN phones 1 st generation: analogue 2 nd generation: digital 3 rd generation (3G): integration of voice and data 4 th generation (4G): integration with Internet Chapter (When 1: and Introduction how?) 1981: NMT : NMT : GSM analogue digital 1994: DCS : CDMA 2000: GPRS 1983: AMPS 1991: D-AMPS 1993: PDC 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 since 2002: IEEE /20/22 Page 18

19 Wireless Systems transmission rate (MBit/s) wired devices WMAN WLAN CORDLESS (DECT) Office Building stationary walk drive Indoor HIPERLAN UMTS CELLULAR (GSM) Outdoor mobility 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 in very short range Page 19

20 Network Categories: Personal Area Networks (PAN) Personal Area Networks (very small range) IEEE (WPAN, Bluetooth): Data rates up to 2 MBit/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),... Page 20

21 Network Categories : 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/WiMAX), (WirelessWAN), (Wireless Regional Area Network) mainly supports mobility, more focuses on connecting buildings Higher data rates ( Mb/s), larger range Page 21

22 Network Categories: 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. Page 22

23 Overlay Networks integration of heterogeneous fixed and mobile networks with varying transmission characteristics regional Vertical Handover (IEEE ) metropolitan area campus Horizontal Handover indoor Page 23

24 Mobility is not only Wireless Networks Invalid IP address in foreign network Routing problems TCP connections break down TCP/IP modifications necessary! /24 home network router Internet router /24 foreign network Page 24

25 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... Page 25

26 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 Page 26

27 Tasks on Protocol Layers 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) Page 27

28 Structure of the Lecture Chapter 2 Technical Basics: Layer 1 Methods for Medium Access: Layer 2 Chapter 3 Wireless Networks: Bluetooth, WLAN, WirelessMAN, and variants 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 Page 28