Radio Communication. Presentation created by: András Balogh

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1 Radio Communication Presentation created by: András Balogh

2 AM and FM The goal is to transmit a modulating signal S(t) via a wave sin(ωt). In case of AM, the product of the modulation is f(t)=(a+s(t))*sin(ωt); In case of FM, the product is f(t)=a*sin((ω+s(t))*t); AM easily picks up noise, any random absorption of energy is a source Above a noise threshold, FM has a better signal to noise ratio

3 AM and FM

4 Quadrature AM Uses sine and cosine carrier waves Transmits 2 digital or analog signals f(t)=(a+s 1 (t))sin(ωt)+(a+s 2 (t))cos(ωt)

5 Stereo FM Transmits 2 audio signals, L(t) and R(t) Compatible with mono FM Main channel: L+R, decoded by mono, 30 Hz 15 khz Second channel: L-R, codes the stereo signal, 23 khz 53 khz Phase alignment: pilot wave, 19 khz

6 Stereo FM

7 Radiowave propagation on Earth The medium of propagation is the air, not vacuum, it has to be considered. The opacity of the atmosphere is highly dependant on the radio frequency The Earth can be considered as a conductor The ionosphere is also a conductor in the form of plasma

8 Atmospheric opacity

9 Direct mode propagation Direct mode or line-of-sight propagation is the free propagation of radiowaves in the air. The range of direct mode is limited by the curvature of the Earth. Small antennae: R horizon km = 3.57 h antenna [m] Very High Frequency (VHF) Tropospheric scatter and ducting can propagate waves over the horizon.

10 Direct mode propagation

11 Surface Modes The conducting properties of the ground can attach the radiowave to the surface A groundwave propagates along the curved surface of the Earth, beyond the horizon. The ground dissipates the energy of the groundwave Only low frequency waves ( Hz) can travel via groundwave modes.

12 Surface Modes

13 The Ionosphere

14 The Ionosphere The D layer: innermost layer from 60 km to 90 km. Solar radiation, only in daylight. High absorption for high frequency (HF) radiowaves, long distance AM communication impossible during daytime. The E layer: from 90 km to 150 km. It reflects radiowaves up to 10 MHz. Sporadic events: additional plasma clouds form, it can reflect up to 225 MHz. The F layer: 150 km to 500 km. Any radiowave that penetrates the layer will go out to space.

15 Ionospheric propagation Ionospheric propagation: skywave or skip, reflection and refraction from the Ionosphere s E and F layers. The radiowaves also reflect from the ground, they can reach the far side of the Earth. HF radiowaves can travel in this manner. The Earth and the Ionosphere also creates a waveguide effect, allowing an other form of propagation.

16 Skywave

17 Waveconduction

18 Signal weakening Absorption in the air Dissipation in the ground Scattering effects Scattering effects also generate noise Some examples of scattering sources: Rain, airplanes, lightning, meteors, auroras, tropospheric humidity, metal objects on the surface

19 Band acronym Band name Frequency range VLF Very Low Frequency Wavelength range Propagation modes 3-30 khz km Waveguide LF Low Frequency khz 10-1 km Waveguide, groundwave MF Medium Frequency khz m Groundwave, skywave HF High Frequency 3-30 MHz m Skywave VHF UHF SHF EHF Very High Frequency Ultra High Frequency Super High Frequency Extremely High Frequency MHz 10-1 m Direct wave, skywave, trop. duct GHz mm Direct wave, trop. duct GHz mm Direct wave GHz 10-1 mm Direct wave with absorption

20 Communication satellites Geostationary orbit: km, more than 100 satellites, no tracking required Low-Earth-orbit: 200 km, 90 min, visible in 1000 km, small signal strength, cheap to launch, satellite constellations, discontinuous data transmission Molniya orbit: highly elliptical orbit, 63.4 inclination, arctic communication, km apogee Medium-Earth-orbit: 8000 km to km, wider coverage than LEOs, more visible time, weaker signal, less satellites required for network Polar orbit: sun syncronous, less used

21 Geostationary orbits from Earth

22 Molniya orbit

23 Molniya orbit projection

24 Orbital altitude classification

25 Comsat applications Telephone communication: islands, sparsly populated areas, polar regions Television Digital Cinema: movies are digitalized, then distributed to theatres via satellites among other ways Internet Military

26 Thank you for your attention

Chapter 1: Telecommunication Fundamentals

Chapter 1: Telecommunication Fundamentals Block Diagram of a communication system Noise n(t) m(t) Information (base-band signal) Signal Processing Carrier Circuits s(t) Transmission Medium r(t) Signal