Mobile Communication

[seminar class]

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Mobile Communications
Chapter 1: Introduction
Computers for the next century?
Computers are integrated
 small, cheap, portable, replaceable - no more separate devices
Technology 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)
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“)
Mobile communication
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
û û stationary computer
û ü notebook in a hotel
ü û wireless LANs in historic buildings
ü ü 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
Applications
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,
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
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
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., 9.6kbit/s with GSM
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 importantEarly 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): demonstrateswith an experiment the wave character of electrical transmission through space(1886, in Karlsruhe, Germany, at the location of today’s University of Karlsruhe)