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Unformatted text preview: Lecture 6 - EE 359: Wireless Communications - Fall 2011 Fading Distributions and Duration. Markov Model. Wideband Fading. Doppler and Delay Spread Lecture Outline • Signal Envelope (Fading) Distributions • Level Crossing Rate and Average Fade Duration • Markov Models • Wideband Channel Models • Scattering Function • Multipath Intensity Profile, Delay Spread, and Coherence Bandwidth • Doppler Power Spectrum, Doppler Spread, and Coherence Time 1. Signal Envelope (Fading) Distribution: • CLT approximation leads to Rayleigh distribution (in-phase and quadrature zero mean and jointly Gaussian): p Z ( z ) = 2 z P r exp[- z 2 / P r ] = z σ 2 exp[- z 2 / (2 σ 2 )] , z ≥ . • A LOS component leads to a received signal with non-zero mean. The Rician distri- bution models signal envelope in this case, with K factor dictating the relative power of the LOS component: p Z ( z ) = z σ 2 exp bracketleftBig- ( z 2 + s 2 ) 2 σ 2 bracketrightBig I parenleftBig zs σ 2 parenrightBig , z ≥ 0. • Experimental results support a Nakagami distribution for some environments. Similar to Rician, but can model “worse than Rayleigh.” Model generally leads to closed-form expressions in BER and diversity analysis: p Z ( z ) = 2 m m z 2 m- 1 Γ( m ) P m r exp bracketleftBig- mz 2 P r bracketrightBig , m ≥ . 5 . 2. Level Crossing Rate and Average Fade Duration • Level crossing rate L R is the rate at which a signal envelope crosses the threshold R ....
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This note was uploaded on 10/16/2011 for the course ELECTRICAL EE251202 taught by Professor Rejaei during the Spring '10 term at Sharif University of Technology.
- Spring '10