1. 1 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Algorithms for Radio Networks Winter Term 2005/2006 19 Oct 2005 1st Lecture Christian Schindelhauer schindel@upb.de

2. Search Algorithms, WS 2004/05 2 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Contents  Introduction –Cellular Networks –Mobile Ad Hoc Networks (MANET) –Wireless Sensor Networks (WSN)  General background –Layers, Coding –Congestion, Energy, and Dilation  Mobility in networks –Mobility models –Analyzing Mobility  Network Coding  Topology Control  The Call Problem in Cellular Networks  Location based Routing

3. Search Algorithms, WS 2004/05 3 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Organization  Lecture: –Monday, 4pm - 6pm, F2.211  Exercise Class (Übung) –Stefan Rührup Tuesday, 1pm - 2pm, F2.211 Thursday, 1pm - 2pm, F1.110  Registration –By StudInfo-System –See web page: http://wwwcs.uni-paderborn.de/cs/ag-madh/WWW/Teaching/2005WS/AlgRadio/ –Go to http://studinfo.upb.de/cgi-bin/go?c=algradio_2005ws  Register for exercise classes as soon as possible!

4. Search Algorithms, WS 2004/05 4 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Organization  Material available at the web-site –Slides of the lecture (PDF/PPT) –Exercises –Schedule with upcoming topics and examination dates –Literature links  Web-site is ready on Oct 21 2005

5. Search Algorithms, WS 2004/05 5 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Examinations  Two types of exam –Written exams (45 minutes) Four written exams Dates to be announced (lecture/web-site) No registration Each covers 1/4th of the lecture Participation voluntary The best two of the four exams produce half of the overall grade –Oral exam (25 minutes) Participation mandatory Registration mandatory Passing the oral exam is necessary 23/24 Feb. 2006 or 27/28 Mar. 2006 Registration before 8 Feb 2006

6. Search Algorithms, WS 2004/05 6 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Chapter I Introduction to Radio Networks

7. Search Algorithms, WS 2004/05 7 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Types of Radio Networks  Cellular Networks –base stations distributed over the field –each base station covers a cell –used for mobile phones –WLAN can be seen as a special case  Mobile Ad Hoc Networks –self-configuring network of mobile nodes –node serve as client and router –no infrastructure necessary  Sensor Networks –network of sensor devices with controller and radio transceivers –base station with more resources

8. Search Algorithms, WS 2004/05 8 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Physics of Electro-magnetic Waves  Frequency f : number of oscilations per second –unit of measurement : Hertz –wave length  : distance (in meters) between wave maxima –The propagation speed of waves in vacuum is constant: –speed of light c  3  10 8 m/s  Note that:  f = c

9. Search Algorithms, WS 2004/05 9 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Amplitude Representation  Amplitude representation of a sinus curve –s(t) = A sin(2  f t +  ) –A : amplitude  : phase shift –f :frequency = 1/TT:period AtAt  T

10. Search Algorithms, WS 2004/05 10 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Fourier Transformation  Fourier transformation of a periodic function: –Decomposition into sinus curves  Dirichlet‘s conditions for a periodic function: –f(x) = f(x+2  ) –f(x) is continuous and monotone in finitely many intervals of (- ,  ) –If is non-coninuous in x 0, then f(x 0 )=(f(x 0 -0)+f(x 0 +0))/2  Theorem of Dirichlet: –f(x) satisfies Dirichlet‘s conditions. Then the Fourier coefficients a 0,a 1,a 2,…,b 1,b 2,… exist such that:

11. Search Algorithms, WS 2004/05 11 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Computation of Fourier coefficients  Fourier coeffizients a i, b i can be computed as follows – For k = 0,1,2,… – For k = 1,2,3,…  Example: saw tooth curve

12. Search Algorithms, WS 2004/05 12 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Frequency Bands LFLow FrequencyMFMedium Freq. HFHigh Freq. VHFVery High Freq.UHFUltra High F. SHFSuper High Fr. EHFExtra High FrequencyUVUltra Violet

13. Search Algorithms, WS 2004/05 13 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Radio Propagation  Propagation on straight line  Signal strength is proportional to 1/d² in free space –In practice can be modeled by 1/d c, for c up to 4 or 5  Energy consumption –for transmitting a radio signal over distance d in empty space is d²  Basic properties –Reflection –Refraction (between media with slower speed of propagation) –Interference –Diffraction –Attenuation in air (especially HV, VHF)

14. Search Algorithms, WS 2004/05 14 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Radio Propagation  VLF, LF, MF –follow the curvature of the globe (up zu 1000 kms in VLF) –pass through buildings  HF, VHF –absorbed by earth –reflected by ionosphere in a height of 100-500 km  >100 MHz –No passing through walls –Good focus  > 8 GHz absorption by rain

15. Search Algorithms, WS 2004/05 15 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Radio Propagation  Multiple Path Fading –Because of reflection, diffraction and diffusion the signal arrives on multiple paths –Phase shifts because of different path length causes interferences  Problems with mobile nodes –Fast Fading Different transmission paths Different phase shifts –Slow Fading Increasing or decreasing the distance between sender and receiver

16. Search Algorithms, WS 2004/05 16 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Signal Interference Noise Ratio  Receiving-power = Transmission-power  path-loss –path loss ~ 1/r β – β  [2,5]  Signal to Interference + Noise Ratio = SINR –S = receiving power from desired sender –I = receiving power from interfering senders –N = other interfering signals (e.g. noise)  Necessary for recognizing the signal:

17. Search Algorithms, WS 2004/05 17 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Theory of Wireless Routing

18. Search Algorithms, WS 2004/05 18 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer A Simple Physical Network Model  Homogenous Network of –n radio stations s 1,..,s n on the plane  Radio transmission –One frequency –Adjustable transmission range Maximum range > maximum distance of radio stations Inside the transmission area of sender: clear signal or radio interference Outside: no signal –Packets of unit length

19. Search Algorithms, WS 2004/05 19 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer (Omni-) Directed Antennae classical radio communication for sending and receiving omni-directed communikation directed communication

20. Search Algorithms, WS 2004/05 20 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Path System and Link network Link network Path system l (e) = load of edge e = # paths(messages) through this link

21. Search Algorithms, WS 2004/05 21 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer transmitted message acknowledgment interference Radio Interferences  Links (edges) interfere, if simultaneous transmission is not possible because radio signals interfere  Links are symmetric (because of acks)  Interference may be asymmetric

22. 22 HEINZ NIXDORF INSTITUTE University of Paderborn Algorithms and Complexity Christian Schindelhauer Thanks for your attention End of 1st lecture Next lecture:Mo 26 Oct 2005, 4pm, F2.211 Next exercise class: Tu 25 Oct 2005, 1.15 pm, F2.211 or Th 27 Oct 2005, 1.15 pm, F1.110