Switching & Transmission - Path Loss Prof Murat Torlak EE4367 Telecom Switching Transmission Radio Wave Propagation b The wireless radio channel

Switching & Transmission - Path Loss Prof Murat Torlak...

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Path Loss Prof. Murat Torlak EE4367 Telecom. Switching & Transmission
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Radio Wave Propagation boxshadowdwn The wireless radio channel puts fundamental limitations to the performance of wireless communications systems boxshadowdwn Radio channels are extremely random, and are not easily analyzed Prof. Murat Torlak EE4367 Telecom. Switching & Transmission boxshadowdwn Modeling the radio channel is typically done in statistical fashion
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Linear Path Loss boxshadowdwn Suppose s(t) of power P t is transmitted through a given channel boxshadowdwn The received signal r(t) of power P r is averaged over any random variations due to shadowing. boxshadowdwn We define the linear path loss of the channel as the ratio of transmit power to receiver power Prof. Murat Torlak EE4367 Telecom. Switching & Transmission boxshadowdwn We define the path loss of the channel also in dB
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Experimental results boxshadowdwn The measurements and predictions for the receiving van driven along 19th St./Nash St. Prof. Murat Torlak EE4367 Telecom. Switching & Transmission Prediction with distance And transmission frequency
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Line -of of -Sight Propagation Sight Propagation boxshadowdwn Attenuation boxshadowdwn The strength of a signal falls off with distance boxshadowdwn Free Space Propagation boxshadowdwn The transmitter and receiver have a clear line of sight path between them. No other sources of impairment! boxshadowdwn Satellite systems and microwave systems undergo free space propagation Prof. Murat Torlak EE4367 Telecom. Switching & Transmission boxshadowdwn The free space power received by an antenna which is separated from a radiating antenna by a distance is given by Friis free space equation
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Friis Free Space Equation boxshadowdwn The relation between the transmit and receive power is given by Friis free space equations: 2 2 (4 ) r t t r P PG G d λ π = d G G t P t P r Prof. Murat Torlak EE4367 Telecom. Switching & Transmission boxshadowdwn G t and G r are the transmit and receive antenna gains boxshadowdwn λ is the wavelength boxshadowdwn d is the T-R separation boxshadowdwn P t is the transmitted power boxshadowdwn P r is the received power boxshadowdwn P t and P r are in same units boxshadowdwn G t and G r are dimensionless quantities. r
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Free Space Propagation Example boxshadowdwn The Friis free space equation shows that the received power falls off as the square of the T-R separation distances boxshadowdwn The received power decays with distance by 20 dB/decade boxshadowdwn EX: Determine the isotropic free space loss at 4 GHz for the shortest path to a geosynchronous satellite from earth (35,863 km). boxshadowdwn P L =20log 10 (4x10 9 )+20log 10 (35.863x10 6 )-147.56dB Prof. Murat Torlak EE4367 Telecom. Switching & Transmission boxshadowdwn P L =195.6 dB boxshadowdwn Suppose that the antenna gain of both the satellite and ground- based antennas are 44 dB and 48 dB, respectively boxshadowdwn P L =195.6-44-48=103.6 dB boxshadowdwn Now, assume a transmit power of 250 W at the earth station.
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