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I am studying about wireless communications and I need to understand the two-ray ground-reflection model for one of my assignments. However, I fail to understand it. Could anyone provide a description of the two-ray ground-reflection model in plain English that could be helpful to me and others in future.

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  • \$\begingroup\$ Are you asking about the Two-ray ground-reflection model? If not, could you give a little more background about what you've already learned about the "2-way propagation model"? \$\endgroup\$ – The Photon Jul 11 '14 at 17:37
  • \$\begingroup\$ yes, I am asking about the "Two-ray ground-reflection model", i just used the name that my teacher has used in the slides... will modify the questions now \$\endgroup\$ – Kristof Tak Jul 11 '14 at 17:42
  • \$\begingroup\$ Frankly I guessed you were translating from another language...No worries though, it should be easier to get a good answer now. \$\endgroup\$ – The Photon Jul 11 '14 at 17:57
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Whenever there are multiple paths from transmitter to receiver, each of these paths combine at the receiver. When the paths are of different length, then the phase of each path at the receiver differs in phase. If the phase of the two paths are identical, then they add together and no fading occurs. When the phase of the two paths differ by 180 degrees, then they cancel each other and fading occurs.

In general, this is called multipath interference. The two ray ground reflection model is a mathematical formulation of one kind of multipath interference when the interference is considered to consist of two paths:

  • from transmitter to receiver directly
  • from transmitter, reflected off the ground, to receiver

illustration

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  • \$\begingroup\$ so fading occurs only when the phase of the arriving waves is different? \$\endgroup\$ – Kristof Tak Jul 12 '14 at 12:53
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    \$\begingroup\$ @WolfgangKuehne yes, precisely. When the phase difference is 0, or some multiple of 360 degrees, you actually end up with a gain over the case where there was no ground because you are receiving the energy from the blue ray, plus the red ray. \$\endgroup\$ – Phil Frost Jul 12 '14 at 13:13
  • \$\begingroup\$ is there a formula which can be used to calculate the attenuation (or signal-strength) on the receiver based on the Two ray ground reflection model \$\endgroup\$ – Kristof Tak Jul 13 '14 at 13:53
  • \$\begingroup\$ @PhilFrost: For pure sines multiple of 360° sounds logical, but for real datatransfer wouldn't that be a problem because the signal is modulated somehow? \$\endgroup\$ – PlasmaHH Mar 6 '15 at 10:55
  • \$\begingroup\$ @PlasmaHH Maybe, maybe not. If the difference in delay between the two paths is very small relative to the modulation rate, then the difference between the two paths will be very small. If the difference in delay between the two paths isn't small relative to the modulation rate, then it's called "multipath interference". \$\endgroup\$ – Phil Frost Mar 6 '15 at 12:54

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