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Basic radio frequency communications - 1

Basic radio frequency communications - 1. Session 1. Contents. Definition and basic properties of radio waves Electromagnetic spectrum Radio frequency spectrum Modulation and demodulation Bandwidth Basic decibel computation. Radio waves.

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Basic radio frequency communications - 1

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  1. Basic radio frequency communications - 1 Session 1

  2. Contents • Definition and basic properties of radio waves • Electromagnetic spectrum • Radio frequency spectrum • Modulation and demodulation • Bandwidth • Basic decibel computation

  3. Radio waves • Wireless communications are based on electromagnetic phenomena • An oscillating electric field E(t) generates an oscillating magnetic field B(t) and vice versa, i.e. these two fields are alternate. • Together, these oscillating fields produce an electromagnetic wave.

  4. Radio waves • Maxwell (1864) mathematically predicted existence of such waves (Maxwell’s equations) and Hertz effectively first produced them. • Electromagnetic radiation includes radio wave, microwave, infrared light, visible light, ultraviolet light, X-rays and gamma rays.

  5. Radio waves

  6. Radio waves • Basic properties of electromagnetic waves (1) • Amplitude A – the height of the wave – (V/m) • The amplitude of the electric field is dominant, since B=E/v, v is the wave speed (light speed c in vacuum) • Frequency  – the number of oscillations per unit of time (the SI unit is Hertz (Hz) – 1 oscillation per second, i.e. s-1); period T=1/ • Wavelength – the distance the wave travels during one period (m)

  7. Radio waves • Basic properties of electromagnetic waves (2) • Speed v – the velocity of propagation of the wave through the medium (m/s)  is the magnetic permeability of the medium and  is electric permittivity of the medium. For vacuum

  8. Radio waves • Basic properties of electromagnetic waves (3) • Phase - The lag or lead of a wave to a reference wave (rad) • Polarization - The orientation of a wave’s electrical field () • Intensity I – The energy propagated in a wave (Wm-2)

  9. Radio waves

  10. Radio waves

  11. Radio waves • Wave speed v in different media

  12. Radio waves • The waveform need not be sine • Sine wave – analog wave • Other waveforms (typically square) – digital wave

  13. Electromagnetic spectrum

  14. Radio frequency spectrum

  15. Radio frequency spectrum

  16. Radio frequency spectrum

  17. Modulation and demodulation • Today’s communication is mostly digital • A digital information sequence (mostly binary) has to be transformed into an analog signal in order to be transmitted through a radio channel • Such a transformation is called modulation • Modulation techniques that are used for digital signal transmission can be the same as for analog signal transmission (AM – ASK, FM – FSK, PM – PSK etc.)

  18. Modulation and demodulation

  19. Modulation and demodulation • To use the radio channels in an optimal way and to prevent jamming, spread-spectrum techniques are often used in transmission of digital signals. • The most often used spread-spectrum techniques • Direct sequence spread-spectrum (DSSS) • Frequency hopping spread-spectrum (FHSS)

  20. Modulation and demodulation • DSSS The chip rate of the PN sequence is much higher then the data rate

  21. Modulation and demodulation • FHSS

  22. Bandwidth • Various radio signals occupy different bandwidth • With digital signals, this is mainly determined by the speed of transmission

  23. Bandwidth • Classification of communications according to bandwidth • Baseband • Narrowband • Wideband • Broadband

  24. Bandwidth • Baseband • A type of data transmission in which single digital or analog data signal is sent over the whole available channel. • Narrowband • A type of data transmission, whose transmission rate is up to 1.5 Mbit/s • Examples: dial-up networking, fax machines

  25. Bandwidth • Wideband • Wideband transmission uses multiple channels of a medium to provide high speed transmission • Wideband operates between narrowband and broadband with speed between 1.5 Mbps and 45 Mbps • Broadband • This is also a multiple-channel transmission, at even higher speeds.

  26. Basic decibel computation • Decibel • Logarithmic measure for comparing power levels (example: output/input) • N=10log10(P2/P1) [dB] • Sometimes, the power level is compared to a standard power level dBm – the power relative to 1mW • 0 dBm is the power of 1 mW • 1 dBm is the power of 1,259 mW

  27. Basic decibel computation

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