Presentation is loading. Please wait.

Presentation is loading. Please wait.

Dr. Farid Farahmand. Wired Vs. Wireless Communication WiredWireless Each cable is a different channelOne media (cable) shared by all Signal attenuation.

Similar presentations


Presentation on theme: "Dr. Farid Farahmand. Wired Vs. Wireless Communication WiredWireless Each cable is a different channelOne media (cable) shared by all Signal attenuation."— Presentation transcript:

1 Dr. Farid Farahmand

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

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

4 Broadcast (analog) 2-way communication (digital) 2-way communication (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

5 Wireless Systems: Range Comparison Satellite Links SW Radio MW Radio FM Radio Mobile Telephony, WLL WLANs Blueooth IR 1,000 Km100 Km10 Km1 Km100 m10 m1 m

6 EM Spectrum Propagation characteristics are different in each frequency band UV 1 MHz 1 kHz 1 GHz 1 THz 1 PHz 1 EHz infrared visible X rays Gamma rays AM radio S/W radio FM radio TV cellular LFHF VHFUHFSHFEHF MF 30kHz300kHz 3MHz 30MHz 300MHz 30GHz300GHz 10km 1km 100m 10m 1m 10cm 1cm 100mm 3GHz 902 – 928 Mhz 2.4 – Ghz – Ghz ISM band

7 7 RADIO IR VISIBLEUVX-RAYSGAMMA RAYS VLFLFMFHFVHFUHFSHFEHF 3k30k 300k 3M30M300M3G30G300GHz VLF: Very Low FrequencyLF: Low Frequency MF: Medium FrequencyHF: High Frequency VHF: Very High FrequencyUHF: Ultra High Frequency SHF: Super High FrequencyEHF: Extremely High Frequency Frequency Band Allocations RADIO

8 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 8 Wavelengths of Frequency Bands 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/m 2 )= H.E

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/m 2 ) = 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). R=100 m RX TX P(density) = 100W / 4  (100) 2 =0.796  W/m 2

13 Free Space Loss The signal disperses with distance Free space loss, ideal isotropic antenna P t = signal power at transmitting antenna (watt) P r = 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). R=100 m RX TX P(received) =P r =100W / (100x10 6 x4  (100)/3x10 8 ) 2 =0.057  W  very little power received!

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) Reflection λ << D Diffraction λ  D Scattering λ >> D

21 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 Thin Air Dense Air

22 References Narayan Mandayam, Tomasi


Download ppt "Dr. Farid Farahmand. Wired Vs. Wireless Communication WiredWireless Each cable is a different channelOne media (cable) shared by all Signal attenuation."

Similar presentations


Ads by Google