ECE8708_2010_ch2-3B

ECE8708_2010_ch2-3B - ECE-8708 2010 Spring ECE-8708 2010...

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ECE-8708 2010 Spring Wireless Communications Lecture 2 ECE8708 ECE8708 - 2010 Spring 2010 Spring Yimin Zhang, PhD Center for Advanced Communications Villanova University http://www.yiminzhang.com 1 p// y g Yimin Zhang, Villanova University ECE-8708 2010 Spring ireless Channel Modeling Wireless Channel Modeling (cont’d) 2 Yimin Zhang, Villanova University ECE-8708 2010 Spring Wireless Channels Wireless Channels 0 10 / 2 ath ss R T T R G G P d g P ) ( 10 Path loss Shadowing effect Log-normal Multipath fading Rayleigh Ricean Yimin Zhang, Villanova University 3 ECE-8708 2010 Spring Fading Channel In addition to the signal strength, there are other significant effects to be considered. l t i i Frequency-Selective Slow Fading Frequency-Selective Fast Fading ective sive) Flat Slow Fading Flat Fast Fading ency-sel e -disper s me- lective frequ (tim 4 time selective (frequency-dispersive) Yimin Zhang, Villanova University
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ECE-8708 2010 Spring Doppler Frequency Shift Doppler Shift mobile moves at a constant velocity along a path – A mobile moves at a constant velocity v , along a path segment having length d between points X and Y . ath length difference – Path length difference hase change cos cos t v d l Phase change cos 2 2 t v l – Doppler shift s 1 v cos 2 t f d Yimin Zhang, Villanova University ECE-8708 2010 Spring Doppler Frequency Spread t l f d Moving direction Multipath arrivals at different directions are likely to yield varying Doppler frequencies, causing Doppler spread. Yimin Zhang, Villanova University ECE-8708 2010 Spring Doppler Spread and Coherent Time When a pure sinusoidal tone of f c is transmitted, the received signal spectrum, called the Doppler spectrum, will have components in the range f c f d and f c + f d , where f d is the Doppler shift. Channel f f f f f For Rayleigh fading with a vertical receive antenna with equal sensitivity in all directions, the Doppler power spectral density is c f c d c d c y , pp p p y 2 1 ) ( v v s which is U-shaped. 1 d d f f Yimin Zhang, Villanova University ECE-8708 2010 Spring Rate of Fading Radian Doppler frequency or ceived ignal presented s k k v cos 2 For received signal represented as L k k k c k R t t t a t s 1 0 ] ) ( cos[ ) ( signal level a Root mean square vel of signal level R a E 2 ] [ 2 level of signal level time Yimin Zhang, Villanova University
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ECE-8708 2010 Spring Rate of Fading signal level a Root mean square level of signal level R a E 2 ] [ 2 R The average level cross rate 2 time 2 2 2 2 2 2 e f e R f R m R R m c R R R a E R 2 ] [ 2 2 Average fade duration m f f e 2 1 Probability that amplitude fades below level R : c f R e R a P 2 1 ) ( Yimin Zhang, Villanova University ECE-8708 2010 Spring Doppler Spread and Coherent Time Coherent time T c is the time domain dual of Doppler spread.
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ECE8708_2010_ch2-3B - ECE-8708 2010 Spring ECE-8708 2010...

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