| Multipath |
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In Wireless Telecommunication s, multipath is the Propagation phenomenon that results in Radio Signal s' reaching the receiving Antenna by two or more paths. Causes of multipath include Atmospheric Ducting , Ionospheric Reflection and Refraction , and Reflection from Terrestrial objects, such as Mountain s and Building s. The effects of multipath include constructive and destructive Interference , and Phase shifting of the Signal . This causes Rayleigh Fading , named after Lord Rayleigh . The standard statistical model of this gives a distribution known as the Rayleigh Distribution . Rayleigh Fading with a strong Line Of Sight content is said to have a Rician Distribution , or to be Rician fading. In Facsimile and Television Transmission , multipath causes Jitter and ghosting, seen as a faded duplicate image to the right of the main image. Source: from Federal Standard 1037C and from MIL-STD-188 In Radar processing, multipath causes ghost targets to appear, deceiving the radar Receiver . These ghosts are particularly bothersome since they move and behave like the normal targets (which they echo), and so the receiver has difficulty in isolating the correct target echo. These problems can be overcome by incorporating a ground map of the radar's surroundings and eliminating all echoes which appear to originate below ground or above a certain height. In digital radio communications (such as GSM ) multipath can cause Error s and affect the Quality of Communications . The errors are due to Intersymbol Interference (ISI). Equaliser s are often used to correct the ISI. Alternatively, Technique s such as Orthogonal Frequency Division Modulation and Rake Receiver s may be used. SEE ALSO |
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