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Home > Archive > CWNP > May 2004 > Need info on Multipath vs. Scattering
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Need info on Multipath vs. Scattering
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| npo3po 2004-04-30, 6:54 pm |
| Hey what's up guys, could someone point out what exactly is the difference between multipath(resulting from reflection) vs scattering?
thanx
Amir | |
| NovellRed 2004-05-03, 3:06 pm |
| Multipath occurs when the signal is reflected off objects large enough for the signal to remain recognizable after the reflection. This signal will then arrive at the receiver at a slightly different time than the original signal. A reasonable analogy is standing in a canyon with high steep walls and yelling “hello”. You hear the original “hello” when you yelled and the echoed “hello” after some delay. If your canyon has the proper acoustics you may even hear the “hello” a number of times as it reflects off the canyon walls.
Scattering occurs when the signal is reflected off objects too small for the signal to remain recognizable after the reflection. Only parts of the wave are reflected in the new direction instead of the whole wave. This renders the signal unrecognizable. To keep with the canyon analogy let’s get out the miracle grow and cover the canyon with leafy trees, bushes, and assorted ground cover. Now yell “hello” again. Why no echo this time? Because the original “hello” wasn’t reflected off the canyon walls, it was scattered by the vegetation. Since the vegetation presents a reflecting surface much smaller than the sound wave, only parts of the sound wave get reflected rendering the original “hello” unrecognizable at a relatively short distance from you.
So when the reflecting object is large in relation to the wave size, the entire signal gets reflected causing the receiver to receive multiple signals from multiple paths at slightly different times. When the reflecting object is small in relation to the wave size, only parts of the signal get reflected and the signal is degenerated by the loss of the parts of it that get reflected away.
This is what causes your “hello” to go further in the smooth walled canyon than in the one filled with vegetation. The smooth walls reflect the sound but the vegetation scatters the sound.
Hope his helps. | |
| npo3po 2004-05-03, 4:02 pm |
| thanks for that clarification! |
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