ee392f - RADIO ENVIRONMENT 8C32810.71-Cimini-7/98 Path Loss...

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Unformatted text preview: RADIO ENVIRONMENT 8C32810.71-Cimini-7/98 Path Loss Shadow Fading Multipath Interference Infrared Versus Radio RADIO ENVIRONMENT 8C32810.83-Cimini-7/98 Path Loss Shadow Fading Multipath Limit the Bit Rate and/or Coverage where P r is the local mean received signal PATH LOSS MODEL Different, often complicated, models are used for different environments. A simple model for path loss, L, is The path loss exponent = 2 in free space; 2 4 in typical environments. power, P t is the transmitted power, d is the transmitter-receiver distance, f is frequency, and K is a transmission constant. 7C29822.011-Cimini-9/97 P r 1 P t f 2 d = K L = PATH LOSS LIMITATIONS Given the performance requirement SNR SNR o , the path loss imposes limits on the bit rate and the signal coverage. The received signal-to-noise power ratio, SNR, is SNR = = P r KP t 1 P n d N o B ( ) B or d KP t d N o SNR o KP t N o BSNR o 1/ where N o is the one-sided noise power spectral density and B is the signal bandwidth. 8C32810.12-Cimini-7/98 SHADOW FADING 8C32810.84-Cimini-7/98 The received signal is shadowed by obstructions such as hills and buildings. This results in variations in the local mean received signal power, Implications nonuniform coverage increases the required transmit power P r (dB) = P r (dB) + G s where G s ~ N(0, s ), 4 s 10 dB. 2 COVERAGE AREA For a desired received power P r the coverage area C defines the percentage of the cell with received power P P r . For P(R) = P r 7C29822.66-Cimini-9/97 C = [ 1 + exp ( )( 1 - erf ( ))] , b = 1 1 1 10 log e 2 b 2 b s 2 4 8 12 2 77% 67% 63% 4 85% 77% 71% 6 90% 83% 77% s R P = P r MULTIPATH Constructive and Destructive Interference of Arriving Rays Received Power Delay Spread t dB With Respect to RMS Value 0.5 0.5 1.5-30-20-10 10 1 t, in seconds 10 30 20 x, in wavelength 8C32810.85-Cimini-7/98 h(t) = a i e j i (t-t i ) i FLAT FADING The delay spread is small compared to the symbol period. The received signal envelope, r, follows a Rayleigh or Rician distribution. Implications increases the required transmit power causes bursts of errors shadow fading Rayleigh fading path loss log (distance) Received Signal Power (dB) P r (dB) = P r (dB) + G s + 20 log r 8C32810.86-Cimini-7/98 DOPPLER SPREAD A measure of the spectral broadening caused by the channel time variation. Implications signal amplitude and phase decorrelate after a time period ~ 1/f D Example: 900 MHz, 60 mph, f D = 80 Hz 5 GHz, 5 mph, f D = 37 Hz 8C32810.87-Cimini-7/98 f D v DELAY SPREAD TIME DOMAIN INTERPRETATION larg e T small T 1 1 T 2T Channel Input Channel Output T 2T T 2T 8C32810.88-Cimini-7/98 Two-ray model = rms delay spread 2 Delay Received Power T small negligible intersymbol interference large significant intersymbol interference, which causes an irreducible error floor T DELAY SPREAD...
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This note was uploaded on 01/20/2012 for the course EE 301 taught by Professor Ahmetçakar during the Spring '11 term at Gazi Üniversitesi.

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ee392f - RADIO ENVIRONMENT 8C32810.71-Cimini-7/98 Path Loss...

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