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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>18.3.1 Backgroud</TITLE><META NAME="description" CONTENT="18.3.1 Backgroud"><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="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html"><LINK REL="previous" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><LINK REL="up" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><LINK REL="next" HREF="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html4634" HREF="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4628" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4622" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4630" 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="tex2html4632" 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="tex2html4635" HREF="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html">18.3.2 Using shadowing model</A><B> Up:</B> <A NAME="tex2html4629" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A><B> Previous:</B> <A NAME="tex2html4623" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A>   <B> <A NAME="tex2html4631" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4633" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H2><A NAME="SECTION031531000000000000000">18.3.1 Backgroud</A></H2><P>The free space model and the two-ray model predict the received poweras a deterministic function of distance. They both represent the communicationrange as an ideal circle. In reality, the received power at certain distanceis a random variable due to multipath propagation effects, which is alsoknown as fading effects. In fact, the above two models predicts the meanreceived power at distance . A more general and widely-used model iscalled the shadowing model [<A HREF="node589.html#Rappaport96" tppabs="http://www.isi.edu/nsnam/ns/doc/node589.html#Rappaport96">30</A>].<P>The shadowing model consists of two parts. The first one is known as pathloss model, which also predicts the mean received power at distance ,denoted by <!-- MATH $\overline{P_r(d)}$ -->. It uses a close-in distance asa reference. <!-- MATH $\overline{P_r(d)}$ --> is computed relative to as follows.<P><BR><DIV ALIGN="RIGHT"><!-- MATH \begin{equation}\frac{P_r(d_0)}{\overline{P_r(d)}} = {\left( \frac{d}{d_0} \right)}^\beta\end{equation} --><TABLE WIDTH="100%" ALIGN="CENTER"><TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="eqn:pathloss"></A></TD><TD WIDTH=10 ALIGN="RIGHT">(18.4)</TD></TR></TABLE><BR CLEAR="ALL"></DIV><P></P><P>is called the path loss exponent, and is usually empiricallydetermined by field measurement. From Eqn. (<A HREF="node216.html#eqn:freespace" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html#eqn:freespace">18.1</A>) weknow that for free space propagation. Table <A HREF="node219.html#tab:pathlossexp" tppabs="http://www.isi.edu/nsnam/ns/doc/node219.html#tab:pathlossexp">18.1</A>gives some typical values of .Larger values correspond to more obstructions and hence fasterdecrease in average received power as distance becomes larger. can be computed from Eqn. (<A HREF="node216.html#eqn:freespace" tppabs="http://www.isi.edu/nsnam/ns/doc/node216.html#eqn:freespace">18.1</A>).<P><BR><P></P><DIV ALIGN="CENTER"><A NAME="8843"></A><TABLE><CAPTION><STRONG>Table 18.1:</STRONG>Some typical values of path loss exponent </CAPTION><TR><TD><DIV ALIGN="CENTER"><DIV ALIGN="CENTER"><FONT SIZE="-1"> </FONT><TABLE CELLPADDING=3 BORDER="1" ALIGN="CENTER"><TR><TD ALIGN="CENTER" COLSPAN=2><FONT SIZE="-1"> </FONT><FONT SIZE="-1"><B>Environment</B></FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Outdoor </FONT></TD><TD ALIGN="LEFT"><FONT SIZE="-1"> Free space </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 2 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> </FONT></TD><TD ALIGN="LEFT"><FONT SIZE="-1"> Shadowed urban area </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 2.7 to 5 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> In building </FONT></TD><TD ALIGN="LEFT"><FONT SIZE="-1"> Line-of-sight </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 1.6 to 1.8 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> </FONT></TD><TD ALIGN="LEFT"><FONT SIZE="-1"> Obstructed </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 4 to 6 </FONT></TD></TR></TABLE><FONT SIZE="-1"> <A NAME="tab:pathlossexp"></A></FONT></DIV></DIV></TD></TR></TABLE></DIV><P></P><BR><BR><P></P><DIV ALIGN="CENTER"><A NAME="8937"></A><TABLE><CAPTION><STRONG>Table 18.2:</STRONG>Some typical values of shadowing deviation </CAPTION><TR><TD><DIV ALIGN="CENTER"><DIV ALIGN="CENTER"><FONT SIZE="-1"> </FONT><TABLE CELLPADDING=3 BORDER="1" ALIGN="CENTER"><TR><TH ALIGN="LEFT"><FONT SIZE="-1"> <B>Environment </B></FONT></TH><TD ALIGN="CENTER"><FONT SIZE="-1"> (dB) </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Outdoor </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 4 to 12 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Office, hard partition </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 7 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Office, soft partition </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 9.6 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Factory, line-of-sight </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 3 to 6 </FONT></TD></TR><TR><TD ALIGN="LEFT"><FONT SIZE="-1"> Factory, obstructed </FONT></TD><TD ALIGN="CENTER"><FONT SIZE="-1"> 6.8 </FONT></TD></TR></TABLE><FONT SIZE="-1"> <A NAME="tab:stddb"></A></FONT></DIV></DIV></TD></TR></TABLE></DIV><P></P><BR><P>The path loss is usually measured in dB. So from Eqn. (<A HREF="node219.html#eqn:pathloss" tppabs="http://www.isi.edu/nsnam/ns/doc/node219.html#eqn:pathloss">18.4</A>)we have<P><BR><DIV ALIGN="RIGHT"><!-- MATH \begin{equation}{\left[ \frac{\overline{P_r(d)}}{P_r(d_0)} \right]}_{dB} = -10 \beta \log \left( \frac{d}{d_0} \right)\end{equation} --><TABLE WIDTH="100%" ALIGN="CENTER"><TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="eqn:pathlossdb"></A></TD><TD WIDTH=10 ALIGN="RIGHT">(18.5)</TD></TR></TABLE><BR CLEAR="ALL"></DIV><P></P><P>The second part of the shadowing model reflects the variation of thereceived power at certain distance. It is a log-normal random variable,that is, it is of Gaussian distribution if measured in dB. The overallshadowing model is represented by<P><BR><DIV ALIGN="RIGHT"><!-- MATH \begin{equation}{\left[ \frac{P_r(d)}{P_r(d_0)} \right]}_{dB} = -10 \beta \log \left( \frac{d}{d_0} \right) + X_{dB}\end{equation} --><TABLE WIDTH="100%" ALIGN="CENTER"><TR VALIGN="MIDDLE"><TD ALIGN="CENTER" NOWRAP><A NAME="eqn:shadowing"></A></TD><TD WIDTH=10 ALIGN="RIGHT">(18.6)</TD></TR></TABLE><BR CLEAR="ALL"></DIV><P></P><P>where is a Gaussian random variable with zero mean andstandard deviation . is called theshadowing deviation, and is also obtained by measurement. Table <A HREF="node219.html#tab:stddb" tppabs="http://www.isi.edu/nsnam/ns/doc/node219.html#tab:stddb">18.2</A> shows some typical values of . Eqn.(<A HREF="node219.html#eqn:shadowing" tppabs="http://www.isi.edu/nsnam/ns/doc/node219.html#eqn:shadowing">18.6</A>) is also known as a log-normal shadowing model.<P>The shadowing model extends the ideal circle model to a richerstatistic model: nodes can only probabilistically communicate whennear the edge of the communication range.<P><HR><!--Navigation Panel--><A NAME="tex2html4634" HREF="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4628" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4622" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4630" 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="tex2html4632" 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="tex2html4635" HREF="node220.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node220.html">18.3.2 Using shadowing model</A><B> Up:</B> <A NAME="tex2html4629" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A><B> Previous:</B> <A NAME="tex2html4623" HREF="node218.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node218.html">18.3 Shadowing model</A>   <B> <A NAME="tex2html4631" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4633" 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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