T-79.7001 Postgraduate Course in Theoretical Computer ... · • C. Siva Ram Murthy and B. S. Manoj: "Ad Hoc Wireless Networks: Architectures and Protocols • Stefano Marinoni:”

Hannu H. Kari/HUT/CS/TCS Page 1/25T.79.7001/5401:Spring 2007

Helsinki Universityof Technology

T-79.7001 Postgraduate Course in Theoretical Computer Science

T-79.5401 Special Course in Mobility Management: Ad hoc networks

(2 - 10 cr) P V

professor Hannu H. KariLaboratory for Theoretical Computer Science

Department of Computer Science and EngineeringHelsinki University of Technology (HUT), Espoo, Fin land

email: Kari [at] tcs [dot] hut [dot] fi


Helsinki Universityof Technology Practical issues

• How many credits: • 2 cr (ECTS) for one presentation (30 minutes) +slid es

+summary paper. • 1 cr (ECTS) for reviewing two summary papers and

opponenting two other participants' presentations.• Either of them can be taken several times.• Additional credits can be achieved based on the num ber of

presentations:• A presentation includes archivable slides and short summary.

Credits are given with the following rules: • 3 ECTS per topic (for dissertation) • 2 ECTS per topic for master's thesis and • 1 ECTS for journal/proceeding.


Helsinki Universityof Technology Practical issues

• Dates:• Seminar schedule: Wednesdays 14-16• Topic selection deadline: 31.1.2007


Helsinki Universityof Technology Credits

• Material based on • C. Siva Ram Murthy and B. S. Manoj: "Ad Hoc Wireless

Networks: Architectures and Protocols • Stefano Marinoni:” Performance of wireless ad hoc r outing

protocols — a simulation study in realistic environm ents”, Master's thesis http://www.tcs.hut.fi/Publications/bibdb/MarinoniMs c.pdf


Helsinki Universityof Technology Spectrum


Helsinki Universityof Technology Radio spectrum


Helsinki Universityof Technology Radio propagation mechanisms

• Direct signal• Reflection• Diffraction• Scattering


Helsinki Universityof Technology Path loss: Open space

P r P t Gt G r 4 d

2

whereP r receive powerP t transmission powerGt transmission gainG r receive gain

wavelengthd distance betweentransmitter receiver



Path loss: Two ray ground model

P r P t Gt G r

ht hr

d 2

2

wherehr receiver height from groundh t transmitter height from groundor

P r P t Gt G r 4 d

2 4 ht hr

d

2

P t Gt G r 4 d

2 d tresh

d

2

where

d tresh

4 ht hr



Path loss: Two ray ground model

1.E-15

1.E-14

1.E-13

1.E-12

1.E-11

1.E-10

1.E-09

1.E-08

1.E-07

1.E-06

1.E-05

1.E-04

1.E-03

1.E-02

1.E-01

1.E+00

1 2 4 8 16 32 64 128

256

512

1024

2048

4096

Pwr-2

Pwr-4

Two-rayground

Distance d [m]

Sign

al s

tren

gth

[db]



Path loss: Strong attenuation

P r P t Gt G r4

21

dwhere

propagation coefficient between2 (open space) and 5 (strong fading)


Helsinki Universityof Technology Impact of antenna


Helsinki Universityof Technology Impact of obstacles


Helsinki Universityof Technology Fading

• Fast fading (small-scale fading)• Rapid fluctuation of signal (amplitude, phase, inte rference due

to multi-path transmission• If no line-of-sight signal: Rayleigh fading

• If line-of-sight signal available: Ricean distribution (indoor situation)

• Slow fading (large-scale fading)• Attenuation due to objects between transmitter and receiver• Fading lasts longer time (seconds or minutes)


Helsinki Universityof Technology Interference

• Adjacent channel interference• Signal disturbed by adjacent frequency

transmission

• Co-channel interference• Interference caused by transmission at the same

frequency


Helsinki Universityof Technology Doppler shift

• Caused by movement of transmitter and receiver (actually relative movement of them)

f dv

wheref d doppler effect on frequencyv relative frequency

wavelenght



Transmission rate constraints

• Nyquist’s theorem

• Shannon’s theorem

C 2 B log2 LwhereC maximum channel capacityB used bandwidth [Hz]L number of discrete signal levels

S/N bit/s/Hz SNR1 1 02 1.584963 34 2.321928 6

10 3.459432 10100 6.658211 20

C B log2 1 S NwhereC maximum data rateB bandwidth [Hz]S signal powerN noice powerSNR 10 log10 S N



Modulation techniques: Analog modulations



Modulation techniques: Digital modulations



FDMA: Frequency Division Multiple Access



TDMA: Time Division Multiple Access



CDMA: Code Division Multiple Access



SDMA: Space Division Multiple Access


Helsinki Universityof Technology Error control

• Detection• Parity check• Cyclic Redundancy Check• Digital signatures

• Forward error correction (FEC)• Hamming coding• Convolutional coding• Turbo codes

• Automatic Retransmission reQuest (ARQ)


Helsinki Universityof Technology Questions

• Why X-rays or Gamma rays are not used in communication?

• Which modulation mechanism is best for ad hoc networks: • FDMA, TDMA, CDMA, or SDMA?

• Is there need to consider doppler shift in ad hoc networks

• Impact of Fast/Slow fading in ad hoc networks and simulating them?

• Impact of asymmetry of antenna?• Impact of obstacles?

Documents

T-79.7001 Postgraduate Course in Theoretical Computer ... · • C. Siva Ram Murthy and B. S. Manoj: "Ad Hoc Wireless Networks: Architectures and Protocols • Stefano Marinoni:”