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<html><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><!--Converted with jLaTeX2HTML 2002 (1.62) JA patch-1.4patched version by: Kenshi Muto, Debian Project.LaTeX2HTML 2002 (1.62),original version by: Nikos Drakos, CBLU, University of Leeds* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan* with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --><HTML><HEAD><TITLE>18.2 Two-ray ground reflection model</TITLE><META NAME="description" CONTENT="18.2 Two-ray ground reflection model"><META NAME="keywords" CONTENT="everything"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"><META NAME="Generator" CONTENT="jLaTeX2HTML v2002 JA patch-1.4"><META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css"><LINK REL="STYLESHEET" HREF="everything.css" tppabs="http://www.isi.edu/nsnam/ns/doc/everything.css"><LINK REL="next" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><LINK REL="previous" HREF="node216.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html"><LINK REL="up" HREF="node215.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node215.html"><LINK REL="next" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html4604" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4598" HREF="node215.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node215.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4592" HREF="node216.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4600" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html"><IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="file:/usr/share/latex2html/icons/contents.png"></A> <A NAME="tex2html4602" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html"><IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="file:/usr/share/latex2html/icons/index.png"></A> <BR><B> Next:</B> <A NAME="tex2html4605" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A><B> Up:</B> <A NAME="tex2html4599" HREF="node215.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node215.html">18. Radio Propagation Models</A><B> Previous:</B> <A NAME="tex2html4593" HREF="node216.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html">18.1 Free space model</A>   <B> <A NAME="tex2html4601" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4603" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H1><A NAME="SECTION031520000000000000000"></A><A NAME="sec:tworay"></A><BR>18.2 Two-ray ground reflection model</H1><P>A single line-of-sight path between two mobile nodes is seldom the only meansof propation. The two-ray ground reflection model considers both the directpath and a ground reflection path. It is shown [<A HREF="node589.html#Rappaport96" tppabs="http://www.isi.edu/nsnam/ns/doc/node589.html#Rappaport96">30</A>] that thismodel gives more accurate prediction at a long distance than the free spacemodel. The received power at distance is predicted by<P><BR><DIV ALIGN="RIGHT"><!-- MATH \begin{equation}P_r (d) = \frac{P_t G_t G_r {h_t}^2 {h_r}^2}{d^4 L}\end{equation} --><TABLE WIDTH="100%" ALIGN="CENTER"><TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="eqn:tworay"></A></TD><TD WIDTH=10 ALIGN="RIGHT">(18.2)</TD></TR></TABLE><BR CLEAR="ALL"></DIV><P></P><P>where and are the heights of the transmit and receive antennasrespectively. Note that the original equation in [<A HREF="node589.html#Rappaport96" tppabs="http://www.isi.edu/nsnam/ns/doc/node589.html#Rappaport96">30</A>] assumes. To be consistent with the free space model, is added here.<P>The above equation shows a faster power loss than Eqn. (<A HREF="node216.html#eqn:freespace" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html#eqn:freespace">18.1</A>)as distance increases. However, The two-ray model does not give a good resultfor a short distance due to the oscillation caused by the constructive anddestructive combination of the two rays. Instead, the free space model isstill used when is small.<P>Therefore, a cross-over distance is calculated in this model. When, Eqn. (<A HREF="node216.html#eqn:freespace" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html#eqn:freespace">18.1</A>) is used. When , Eqn.(<A HREF="node217.html#eqn:tworay" tppabs="http://www.isi.edu/nsnam/ns/doc/node217.html#eqn:tworay">18.2</A>) is used. At the cross-over distance, Eqns. (<A HREF="node216.html#eqn:freespace" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html#eqn:freespace">18.1</A>)and (<A HREF="node217.html#eqn:tworay" tppabs="http://www.isi.edu/nsnam/ns/doc/node217.html#eqn:tworay">18.2</A>) give the same result. So can be calculated as<P><BR><DIV ALIGN="RIGHT"><!-- MATH \begin{equation}d_c = \left( 4\pi h_t h_r \right) / \lambda\end{equation} --><TABLE WIDTH="100%" ALIGN="CENTER"><TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="eqn:crossover"></A></TD><TD WIDTH=10 ALIGN="RIGHT">(18.3)</TD></TR></TABLE><BR CLEAR="ALL"></DIV><P></P><P>Similarly, the OTcl interface for utilizing the two-ray ground reflection modelis as follows.<P><PRE>$ns_ node-config -propType Propagation/TwoRayGround</PRE><P>Alternatively, the user can use<P><PRE>set prop [new Propagation/TwoRayGround]$ns_ node-config -propInstance $prop</PRE><P><HR><!--Navigation Panel--><A NAME="tex2html4604" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4598" HREF="node215.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node215.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4592" HREF="node216.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4600" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html"><IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="file:/usr/share/latex2html/icons/contents.png"></A> <A NAME="tex2html4602" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html"><IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="file:/usr/share/latex2html/icons/index.png"></A> <BR><B> Next:</B> <A NAME="tex2html4605" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A><B> Up:</B> <A NAME="tex2html4599" HREF="node215.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node215.html">18. Radio Propagation Models</A><B> Previous:</B> <A NAME="tex2html4593" HREF="node216.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html">18.1 Free space model</A>   <B> <A NAME="tex2html4601" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4603" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <!--End of Navigation Panel--><ADDRESS>2003-09-23</ADDRESS></BODY></HTML>⌨️ 快捷键说明
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