Mobile communications
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This document provides an overview of a lecture on mobile communications. It covers the history of mobile communication technologies, applications of mobile devices, challenges of wireless transmission, and media access protocols. It also discusses wireless telecommunication systems including GSM, UMTS, satellite systems, wireless LANs, and support for mobility in applications and transport protocols. The outlook section discusses potential future directions in mobile communication research and development.
Mobile communications
- 2. Overview of the lecture – Introduction • Use-cases, applications • Definition of terms • Challenges, history – Wireless Transmission • frequencies & regulations • signals, antennas, signal propagation • multiplexing, modulation, spread spectrum, cellular system – Media Access • motivation, SDMA, FDMA, TDMA (fixed, Aloha, CSMA, DAMA, PRMA, MACA, collision avoidance, polling), CDMA – Wireless Telecommunication Systems • GSM, HSCSD, GPRS, DECT, TETRA, UMTS, IMT-2000 – Satellite Systems • GEO, LEO, MEO, routing, handover – Broadcast Systems • DAB, DVB – Wireless LANs • Basic Technology • IEEE 802.11a/b/g, .15, Bluetooth – Network Protocols • Mobile IP • Ad-hoc networking • Routing – Transport Protocols • Reliable transmission • Flow control • Quality of Service – Support for Mobility • File systems, WWW, WAP, i-mode, J2ME, ... – Outlook
- 3. Chapter 1: Introduction A case for mobility – many aspects History of mobile communication Market Areas of research
- 4. Computers for the next decades? • Computers are integrated – small, cheap, portable, replaceable - no more separate devices • Technology is in the background – computer are aware of their environment and adapt (“location awareness”) – computer recognize the location of the user and react appropriately (e.g., call forwarding, fax forwarding, “context awareness”)) • Advances in technology – more computing power in smaller devices – flat, lightweight displays with low power consumption – new user interfaces due to small dimensions – more bandwidth per cubic meter – multiple wireless interfaces: wireless LANs, wireless WANs, regional wireless telecommunication networks etc. („overlay networks“)
- 5. Mobile communication • Two aspects of mobility: – user mobility: users communicate (wireless) “anytime, anywhere, with anyone” – device portability: devices can be connected anytime, anywhere to the network • Wireless vs. mobile Examples stationary computer notebook in a hotel wireless LANs in historic buildings Personal Digital Assistant (PDA) • The demand for mobile communication creates the need for integration of wireless networks into existing fixed networks: – local area networks: standardization of IEEE 802.11, ETSI (HIPERLAN) – Internet: Mobile IP extension of the internet protocol IP – wide area networks: e.g., internetworking of GSM and ISDN
- 6. Applications I • Vehicles – transmission of news, road condition, weather, music via DAB – personal communication using GSM – position 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, ...
- 7. Typical application: road traffic ad hoc UMTS, WLAN, DAB, DVB, GSM, cdma2000, TETRA, ... Personal Travel Assistant, PDA, Laptop, GSM, UMTS, WLAN, Bluetooth, ...
- 8. Mobile and wireless services – Always Best Connected UMTS 2 Mbit/s UMTS, GSM 384 kbit/s LAN 100 Mbit/s, WLAN 54 Mbit/s UMTS, GSM 115 kbit/s GSM 115 kbit/s, WLAN 11 Mbit/s GSM/GPRS 53 kbit/s Bluetooth 500 kbit/s GSM/EDGE 384 kbit/s, DSL/WLAN 3 Mbit/s DSL/ WLAN 3 Mbit/s
- 9. Applications II • Travelling 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 History Info
- 10. 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
- 11. Mobile devices performanceperformance Pager • receive only • tiny displays • simple text messages Mobile phones • voice, data • simple graphical displays PDA • graphical displays • character recognition • simplified WWW Palmtop • tiny keyboard • simple versions of standard applications Laptop/Notebook • fully functional • standard applications Sensors, embedded controllers www.scatterweb.net
- 12. Effects of device portability • Power consumption – limited computing power, low quality displays, small disks due to limited battery capacity – CPU: power consumption ~ CV2 f • C: internal capacity, reduced by integration • V: supply voltage, can be reduced to a certain limit • f: clock frequency, can be reduced temporally • Loss of data – higher probability, has to be included in advance into the design (e.g., defects, theft) • Limited user interfaces – compromise between size of fingers and portability – integration of character/voice recognition, abstract symbols • Limited memory – limited value of mass memories with moving parts – flash-memory or ? as alternative
- 13. 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, e.g., 53kbit/s with GSM/GPRS • 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
- 14. Early history of wireless communication • Many people in history used light for communication – heliographs, flags („semaphore“), ... – 150 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 (1831-79): theory of electromagnetic Fields, wave equations (1864) – H. Hertz (1857-94): 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)
- 15. History of wireless communication I • 1896Guglielmo Marconi – first demonstration of wireless telegraphy (digital!) – long wave transmission, high transmission power necessary (> 200kw) • 1907Commercial transatlantic connections – huge base stations (30 100m high antennas) • 1915Wireless voice transmission New York - San Francisco • 1920Discovery 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) • 1926Train-phone on the line Hamburg - Berlin – wires parallel to the railroad track
- 16. History of wireless communication II • 1928 many TV broadcast trials (across Atlantic, color TV, TV news) • 1933 Frequency modulation (E. H. Armstrong) • 1958 A-Netz in Germany – analog, 160MHz, connection setup only from the mobile station, no handover, 80% coverage, 1971 11000 customers • 1972 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 A, NL and LUX, 1979 13000 customer in D • 1979 NMT at 450MHz (Scandinavian countries) • 1982 Start of GSM-specification – goal: pan-European digital mobile phone system with roaming • 1983 Start of the American AMPS (Advanced Mobile Phone System, analog) • 1984 CT-1 standard (Europe) for cordless telephones
- 17. History of wireless communication III • 1986C-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, e-mail, 98% coverage • 1991Specification of DECT – Digital European Cordless Telephone (today: Digital Enhanced Cordless Telecommunications) – 1880-1900MHz, ~100-500m range, 120 duplex channels, 1.2Mbit/s data transmission, voice encryption, authentication, up to several 10000 user/km2 , used in more than 50 countries • 1992Start of GSM – in D as D1 and D2, fully digital, 900MHz, 124 channels – automatic location, hand-over, cellular – roaming in Europe - now worldwide in more than 200 countries – services: data with 9.6kbit/s, FAX, voice, ...
- 18. History of wireless communication IV • 1994 E-Netz in Germany – GSM with 1800MHz, smaller cells – As Eplus in D (1997 98% coverage of the population) • 1996 HiperLAN (High Performance Radio Local Area Network) – ETSI, standardization of type 1: 5.15 - 5.30GHz, 23.5Mbit/s – recommendations for type 2 and 3 (both 5GHz) and 4 (17GHz) as wireless ATM-networks (up to 155Mbit/s) • 1997 Wireless LAN - IEEE802.11 – IEEE standard, 2.4 - 2.5GHz and infrared, 2Mbit/s – already many (proprietary) products available in the beginning • 1998 Specification of GSM successors – for UMTS (Universal Mobile Telecommunication System) as European proposals for IMT-2000 • Iridium – 66 satellites (+6 spare), 1.6GHz to the mobile phone
- 19. History of wireless communication V • 1999 Standardization of additional wireless LANs – IEEE standard 802.11b, 2.4-2.5GHz, 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 – First step towards a unified Internet/mobile communicaiton system – Access to many services via the mobile phone • 2000 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 (50 B$ payed in Germany for 6 licenses!) • 2001 Start of 3G systems – Cdma2000 in Korea, UMTS tests in Europe, Foma (almost UMTS) in Japan
- 20. Wireless systems: overview of the development cellular phones satellites wireless LANcordless phones 1992: GSM 1994: DCS 1800 2001: IMT-2000 1987: CT1+ 1982: Inmarsat-A 1992: Inmarsat-B Inmarsat-M 1998: Iridium 1989: CT 2 1991: DECT 199x: proprietary 1997: IEEE 802.11 1999: 802.11b, Bluetooth 1988: Inmarsat-C analogue digital 1991: D-AMPS 1991: CDMA 1981: NMT 450 1986: NMT 900 1980: CT0 1984: CT1 1983: AMPS 1993: PDC 4G – fourth generation: when and how? 2000: GPRS 2000: IEEE 802.11a 200?: Fourth Generation (Internet based)
- 21. Foundation: ITU-R - Recommendations for IMT- 2000•M.687-2 – IMT-2000 concepts and goals •M.816-1 – framework for services •M.817 – IMT-2000 network architectures •M.818-1 – satellites in IMT-2000 •M.819-2 – IMT-2000 for developing countries •M.1034-1 – requirements for the radio interface(s) •M.1035 – framework for radio interface(s) and radio sub-system functions •M.1036 – spectrum considerations •M.1078 – security in IMT-2000 •M.1079 – speech/voiceband data performance •M.1167 – framework for satellites •M.1168 – framework for management •M.1223 – evaluation of security mechanisms •M.1224 – vocabulary for IMT-2000 •M.1225 – evaluation of transmission technologies •. . . •http://www.itu.int/imt
- 22. 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 – ...
- 23. Simple reference model used here Application Transport Network Data Link Physical Medium Data Link Physical Application Transport Network Data Link Physical Data Link Physical Network Network Radio
- 24. Influence of mobile communication to the layer model – service location – new applications, multimedia – adaptive applications – congestion and flow control – quality of service – addressing, routing, device location – hand-over – authentication – media access – multiplexing – media access control – encryption – modulation – interference – frequency Application layer Transport layer Network layer Data link layer Physical layer
- 25. Overlay Networks - the global goal regional metropolitan area campus-based in-house vertical handover horizontal handover integration of heterogeneous fixed and mobile networks with varying transmission characteristics