08-03-2011, 03:37 PM
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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)