1. Lecture 4: Propagation Models, Antennas and Link Budget Anders Västberg vastberg@kth.se 08-790 44 55

2. Digital Communication System Source of Information Source Encoder ModulatorRF-Stage Channel RF-Stage Information Sink Source Decoder Demodulator Channel Encoder Digital Modulator Channel Decoder Digital Demodulator [Slimane]

3. Propagation between two antennas (not to scale) No Ground Wave for Frequencies > ~2 MHz No Ionospheric Wave for Frequencies > ~30 Mhz

4. The Radio Link Design considerations –The distance over which the system meets the performance objectives –The capacity of the link. Performance determined by –Frequency –Transmitted Power –Antennas –Technology used [Black et. al]

5. Performance of Radio Systems Signal attenuation –path loss –multipath fading Additive noise –Thermal noise –Atmospheric noise –Cosmic Noise –Man-made noise

6. Noise Thermal noise – White Noise Spectral density:(W/Hz) kBoltzmann’s constant (1.38 10 -23 J/K) TAbsolute temperature (in Kelvins) Noise power (in W) BBandwidth (Hz)

7. Signal to noise ratio (SNR)

8. Link Budget EIRP=Effective Isotropic Radiated Power

9. Propagations Models Free Space Model Plane Earth Model Power Law Model

10. Dipole antenna Omnidirectional L=  II Half-wave dipole –Gain 1,64 = 2.15 dBi –Linear Polarisation Quarter-wave dipole –Conducting plane below a single quarter wave antenna. Acts like a half- wave dipole L= /4 I

11. Yagi-antenna Directional http://www.urel.feec.vutbr.cz/~raida/multimedia_en/chapter-4/4_3A.html 3-30 element and a gain of 8-20 dBi

12. Parabolic antenna Directional Effective area A e =  d 2 /4  [Stallings, 2005]

13. Corner Reflectors Multiple images results in increased gain Example: G=12 dBi  Driven Element Images

14. Loop-antenna - Directional http://www.ycars.org/EFRA/Module%20C/AntLoop.htm Linear Polarisation Gain 1,76 dBi

15. Helical antenna Directional Normal mode Axial mode http://hastingswireless.homeip.net/index.php?page=antennas&type=helical

16. Microwave Communication [Slimane]

17. Propagation in the Atmosphere The atmosphere around the earth contains a lot of gases (10 44 molecules) It is most dense at the earth surface (90% of molecules below a height of 20 km). It gets thinner as we reach higher and higher attitudes. The refractive index of the air in the atmosphere changes with the Height This affects the propagation of radio waves. The straight line propagation assumption may not be valid especially for long distances. [Slimane]

18. Effective Earth Radius [Slimane]

19. Line-of-Sight Range [Slimane]

20. Ray Paths and Wave fronts

21. Fresnel Zone [Slimane]

22. Ionospheric Communication [Davies, 1993]

23. Indoor models

24. Slow and Fast Fading

25. Homework before F6 Describe the following modulation methods: –AM, FSK, BPSK, QAM Order ASK, FSK, PSK and DPSK in order of least efficient to most efficient.