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Mobile Communications

Lehrstuhl fr Informatik 4RWTH Aachen

Dr. Dirk Thien

Prof. Dr. Otto Spaniol

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Dirk Thien

Lehrstuhl fr Informatik 4, Room 4105B (Building E1)

Phone: 0241 / 80 - 21450

E-Mail: thissen@informatik.rwth-aachen.de

Contact

http://www-i4.informatik.rwth-aachen.de/content/teaching/lectures/sub/mobil/WS0708/index.html

Material (Slide Copies and Video Recordings)

Organization

Lecture Dates

Monday, 16:30 18:00, AH5 Wednesday, 13:30 - 15:00, 5052

J. Schiller: Mobile Communications. 2nd Edition, Addison Wesley, 2003

V. Garg: Wireless Communications and Networking. Morgan Kaufmann, 2007

Literature

Exercise Dates

Wednesday, 13:30 - 15:00, 5052

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What is Mobile Communications?

Two aspects of mobility:

User mobility: a user communicates anytime, anywhere, using anyaccess technology

Device portability: A device can connect to the network anytime andanywhere

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 ofwireless networks into existing fixed networks:

In the local range: standardization of IEEE 802.11 (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

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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 whichremove 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 evolvingslowly

Restricted frequency range, interferences of frequencies

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Types of Wireless Networks

Cellular Networks

Base stationsdistributed over the area to be covered

Each base station covers a cell

Need of an infrastructure networkconnecting all base stations

Used for mobile phone networks and data networks like Wireless LAN

Mobile Ad-Hoc Networks (MANETs)

Self-configuring networkof mobile nodes

Each node serves as client and router

No infrastructure(base stations) necessary, direct connections between any pairof nodes

E.g. Bluetooth

Mesh Networks

Enhancement of above concepts: Ad-hoc network with infrastructure

Allow a whole mesh of connectionsbetween wireless nodes

Increased fault tolerance

E.g. used in WiMAX

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Possible Applications

Vehicles

Transmission of news, road condition, weather, music, e.g. via DAB (DigitalAudio Broadcasting)

Personal communication using the Global System for MobileCommunication (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 inadvance for maintenance

Emergencies

Early transmission of patient data to the hospital, current status, firstdiagnosis

Replacement of a fixed infrastructure in case of earthquakes, hurricanes,fire etc.

Crisis, war, ...

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Typical Application: Road Traffic

adhocUMTS, WLAN,

DAB, GSM, ...

Personal Travel Assistant,DAB, PDA, Laptop,

GSM/UMTS, WLAN,Bluetooth, ...

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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

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Location Dependent Services

Location aware services

What services, e.g., printer, fax, phone, server etc. exist in the localenvironment

Follow-on services

Automatic call-forwarding, transmission of the actual workspace to thecurrent 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 mobiledevice through the fixed network

Privacy

Who should gain knowledge about the location?

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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 alloccupied

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 hundredmilliseconds for other wireless systems

Lower security, simpler active attacking

Radio interface accessible for everyone (shared medium), base station canbe simulated, thus attracting calls from mobile phones

Very different device capabilities

New concepts necessary in protocol design, e.g. energy efficiency

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Characteristics of Mobile Devices

PerformancePerformance

Pager receive only tiny displays simple text messages

Mobile phones voice, data simple graphical

displays

PDA simple graphical displays character recognition simplified WWW

Palmtops tiny keyboard simple versions of

standard applications

Laptop fully functional standard applications

Sensors,embeddedcontrollers

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Early 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 electromagneticfields, wave equations (1864)

H. Hertz (1857-94): demonstrateswith an experiment the wave characterof electrical transmission through space(1888, in Karlsruhe, Germany, at the

location of todays University of Karlsruhe)

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Network Categories :

Wireless Local Area Networks

Wireless LANs(small range)

IEEE 802.11 (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 802.16 (WirelessMAN/WiMAX),802.20 (WirelessWAN),802.22 (Wireless Regional Area Network)

802.11 mainly supports mobility, 802.16 more focuses on connecting buildings

Higher data rates (32-134 Mb/s), larger range

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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.

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Overlay Networks

regional

metropolitan area

campus

indoor

VerticalHandover(IEEE 802.21)

HorizontalHandover

integration of heterogeneous fixed andmobile networks with varyingtransmission characteristics

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Mobility is not only Wireless Networks

router

router

home network

foreign network

Internet

137.226.12/24

141.17.63/24

137.226.12.98

Invalid IP address in foreign network

Routing problems

TCP connections break down

TCP/IP modifications necessary!

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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

...

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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

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Tasks on Protocol Layers

Physical Layer

Data Link Layer

Network Layer

Transport Layer

Application Layer

Frequencies, modulation

Interferences, attenuation (Encryption)

Medium access control

Multiplexing

(Authentication)

Addressing, routing

Device location

Handover

Congestion and flow control

Quality of Service

Service location

Adaptive application

New applications

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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