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Introduction to Wireless Technologies

Introduction to Wireless Technologies. Dr. Farid Farahmand. Wired Vs. Wireless Communication. Each cable is a different channel. One media (cable) shared by all. High signal attenuation. Signal attenuation is low. High interference

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Introduction to Wireless Technologies

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  1. Introduction to Wireless Technologies Dr. Farid Farahmand

  2. Wired Vs. Wireless Communication Each cable is a different channel One media (cable) shared by all Highsignal attenuation Signal attenuation is low High interference noise; co-channel interference; adjacent channel interference No interference

  3. Why go wireless ? Advantages • Sometimes it is impractical to lay cables • User mobility • Cost Limitations • Bandwidth • Fidelity • Power • (In)security

  4. Broadcast (analog) Wireless Systems: Examples • AM, FM Radio • TV Broadcast • Satellite Broadcast • 2-way Radios • Cordless Phones • Satellite Links • Mobile Telephony Systems • Wireless Local Loop (WLL) • Microwave Links • Wireless LANs • Infrared LANs 2-way communication (analog) 2-way communication (digital)

  5. Mobile Telephony, WLL MW Radio SW Radio Satellite Links FM Radio WLANs Blueooth IR Wireless Systems: Range Comparison 1 m 10 m 100 m 1 Km 10 Km 100 Km 1,000 Km

  6. ISM band 902 – 928 Mhz 2.4 – 2.4835 Ghz 5.725 – 5.785 Ghz VHF UHF SHF EHF LF MF HF  300MHz 30MHz 30GHz 300GHz 3GHz 3MHz 30kHz 300kHz  100mm 10cm 10m 1cm 1m 100m 10km 1km EM Spectrum FM radio S/W radio TV TV AM radio cellular X rays Gamma rays visible UV infrared  1 MHz 1 GHz 1 kHz 1 THz 1 EHz 1 PHz Propagation characteristics are different in each frequency band

  7. Frequency Band Allocations RADIO IR VISIBLE UV X-RAYS GAMMA RAYS RADIO VLF LF MF HF VHF UHF SHF EHF 300k 3k 30k 3M 30M 300M 3G 30G 300GHz VLF: Very Low Frequency LF: Low Frequency MF: Medium Frequency HF: High Frequency VHF: Very High Frequency UHF: Ultra High Frequency SHF: Super High Frequency EHF: Extremely High Frequency

  8. Wavelengths of Frequency Bands • VLF, LF  long waves • MF  medium waves • HF, VHF  short waves • UHF, SHF  microwaves  • EHF  millimeter waves • Above microwave region, only certain windows of frequencies propagate freely through air, rain, etc. • Infrared and visible light will not penetrate walls • X-rays and gamma rays interact with matter Propagate well beyond line of sight The distance the signal travels decreases as the frequency increases

  9. Electromagnetic Signals • Electromagnetic Signals are emitted and received in wireless systems • Requires a transmitting and receiving antenna • The EM signal goes through the unguided medium • Free space (vacuum) • Earth’s atmosphere • EM propagation is also referred to radio frequency propagation • Wireless communications examples • Terrestrial radio • Microwave radio • Broadband radio • Mobile radio • Cellular phone

  10. What is EM? • EM involves both a varying electric field (E) and a varying magnetic field (H) • E and H appear at right angles to each other and to the direction of travel of the wave (Z-axis) • The power passing a given signal is called the power density (P) • P (Watt/m2)= H.E http://info.ee.surrey.ac.uk/Teaching/Courses/EFT/transmission/html/TEMWave.html

  11. EM Propagation • Electromagnetic waves are invisible • We use the concept of rays to describe them • When radiating uniformly over a spherically we refer to it as isotropic radiation • Power Density (W/m2) = P_radiated / Area of sphere • As we get further from the source the radiation (received power) becomes smaller

  12. Example of Power Density • Assume the isotropic radiated power from an antenna is 100 W. Assuming the receiving antenna is 100 m away, calculate the received power density (assume vacuum). P(density) = 100W / 4p(100)2 =0.796 mW/m2 TX RX R=100 m

  13. Free Space Loss • The signal disperses with distance • Free space loss, ideal isotropic antenna • Pt = signal power at transmitting antenna (watt) • Pr = signal power at receiving antenna (Watt) •  = carrier wavelength • d = propagation distance between antennas • c = speed of light (»3 ´ 10 8 m/s) where d and  are in the same units (e.g., meters)

  14. Example of Power Radiation • Assume the isotropic radiated power from an antenna is 100 W. Assuming the receiving antenna is 100 m away, calculate the received power (assume vacuum and frequency of radiation is 100 MHz). P(received) =Pr =100W / (100x106x4p(100)/3x108)2 =0.057 mW  very little power received! TX RX R=100 m

  15. Attenuation • Strength of signal falls off with distance over transmission medium • Attenuation factors for unguided media: • Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal • Signal must maintain a level sufficiently higher than noise to be received without error Note: Attenuation in dB can be calculated by

  16. Signal Loss and Attenuation • Pulse spreading in free space • Attenuation in non-vacuum • Attenuation due to particles absorbing the EM energy • Called “wave absorption” • Remember: Attenuation = 10 log (Pout/Pin)

  17. Other Impairments • Multipath – obstacles reflect signals so that multiple copies with varying delays are received • Refraction – bending of radio waves as they propagate through the atmosphere • Atmospheric absorption – water vapor and oxygen contribute to attenuation

  18. The Effects of Multipath Propagation • Multiple copies of a signal may arrive at different phases • If phases add destructively, the signal level relative to noise declines, making detection more difficult • Intersymbol interference (ISI) • One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit

  19. Multipath Propagation & Fading • Reflection – occurs when signal encounters a surface that is large relative to the wavelength of the signal • Diffraction - occurs at the knife-edge of an impenetrable body that is almost the same compared to wavelength of radio wave • Scattering – occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less

  20. Multipath Propagation & Fading Three basic propagation mechanisms (D is the size of the material) Scattering λ >> D Diffraction λ  D Reflection λ << D

  21. Thin Air Dense Air Refraction • Refraction – bending of microwaves by the atmosphere • Velocity of electromagnetic wave is a function of the density of the medium • When wave changes medium, speed changes • Wave bends at the boundary between mediums

  22. References • Narayan Mandayam, • Tomasi

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