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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>17.1.2 Low-earth-orbiting satellites</TITLE><META NAME="description" CONTENT="17.1.2 Low-earth-orbiting satellites"><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="previous" HREF="node197.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node197.html"><LINK REL="up" HREF="node196.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node196.html"><LINK REL="next" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html4324" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4318" HREF="node196.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node196.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4314" HREF="node197.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node197.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4320" 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="tex2html4322" 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="tex2html4325" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html">17.2 Using the satellite</A><B> Up:</B> <A NAME="tex2html4319" HREF="node196.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node196.html">17.1 Overview of satellite</A><B> Previous:</B> <A NAME="tex2html4315" HREF="node197.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node197.html">17.1.1 Geostationary satellites</A>   <B> <A NAME="tex2html4321" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4323" 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="SECTION031412000000000000000"></A><A NAME="sec:satellite_overview_leo"></A><BR>17.1.2 Low-earth-orbiting satellites</H2><P><DIV ALIGN="CENTER"><A NAME="fig:constellation"></A><A NAME="7679"></A><TABLE><CAPTION ALIGN="BOTTOM"><STRONG>Figure 17.1:</STRONG>Example of a polar-orbiting LEO constellation. This figurewas generated using the SaVi software package from the geometry center at theUniversity of Minnesota.</CAPTION><TR><TD><DIV ALIGN="CENTER">sat-constellation</DIV></TD></TR></TABLE></DIV><P>Polar orbiting satellite systems, such as Iridium and the proposed Teledesic system, canbe modelled in . In particular, the simulator supports the specificationof satellites that orbit in purely circular planes, for which the neighboring planes are co-rotating.There are other non-geostationary constellation configurations possible (e.g., Walker constellations)- the interested user may develop newconstellation classes to simulate these other constellation types. Inparticular, this would mainly require defining new intersatellite link handoff procedures.<P>The following are the parameters of satellite constellations that can currentlybe simulated:<UL><LI><B>Basic constellation definition</B> Includes satellite altitude,number of satellites, number of planes, number of satellites per plane.</LI><LI><B>Orbits</B> Orbit inclination can range continuouslyfrom 0 to 180 degrees (inclination greater than 90 degrees corresponds toretrograde orbits). Orbit eccentricity is not modeled. Nodal precession is not modeled. Intersatellite spacing within a given plane is fixed. Relativephasing between planes is fixed (although some systems may not control phasingbetween planes).</LI><LI><B>Intersatellite (ISL) links</B> For polar orbiting constellations,intraplane, interplane, and crossseam ISLs can be defined. Intraplane ISLsexist between satellites in the same plane and are never deactivated or handed off. Interplane ISLs exist between satellites of neighboring co-rotating planes. These links are deactivated near the poles (abovethe ``ISL latitude threshold'' in the table) because the antenna pointing mechanism cannot track these links in the polar regions. Like intraplane ISLs,interplane ISLs are never handed off. Crossseam ISLs may exist in a constellation between satellites in counter-rotating planes (where the planes form a so-called ``seam'' in the topology). GEO ISLs can also bedefined for constellations of geostationary satellites.</LI><LI><B>Ground to satellite (GSL) links</B> Multiple terminalscan be connected to a single GSL satellite channel. GSL links for GEO satellites are static, while GSL links for LEO channels are periodically handed off as described below. </LI><LI><B>Elevation mask</B> The elevation angle above which a GSL link can be operational. Currently, if the (LEO) satellite serving a terminaldrops below the elevation mask, the terminal searches for a new satelliteabove the elevation mask. Satellite terminals check for handoff opportunitiesaccording to a timeout interval specified by the user. Each terminalinitiates handoffs asynchronously; it would be possible also to definea system in which each handoff occurs synchronously in the system.</LI></UL><P>The following table lists parameters used for example simulation scriptsof the Iridium<A NAME="tex2html32" HREF="footnode.html#foot7689" tppabs="http://www.isi.edu/nsnam/ns/doc/footnode.html#foot7689"><SUP>17.1</SUP></A> and Teledesic<A NAME="tex2html33" HREF="footnode.html#foot7690" tppabs="http://www.isi.edu/nsnam/ns/doc/footnode.html#foot7690"><SUP>17.2</SUP></A> systems.<P><BR><P></P><DIV ALIGN="CENTER"><A NAME="7713"></A><TABLE><CAPTION><STRONG>Table 17.1:</STRONG>Simulation parameters used for modeling a broadband version ofthe Iridium system and the proposed 288-satellite Teledesic system.Both systems are examples of polar orbiting constellations.</CAPTION><TR><TD><DIV ALIGN="CENTER"><TABLE CELLPADDING=3 BORDER="1" ALIGN="CENTER"><TR><TD></TD><TD ALIGN="CENTER"><TT><B>Iridium</B> </TT></TD><TD ALIGN="CENTER"><TT><B>Teledesic</B></TT></TD></TR><TR><TD ALIGN="CENTER"><TT><B>Altitude</B> </TT></TD><TD ALIGN="CENTER">780 km</TD><TD ALIGN="CENTER">1375 km</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Planes</B> </TT></TD><TD ALIGN="CENTER">6</TD><TD ALIGN="CENTER">12</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Satellites per plane</B> </TT></TD><TD ALIGN="CENTER">11</TD><TD ALIGN="CENTER">24</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Inclination (deg)</B> </TT></TD><TD ALIGN="CENTER">86.4</TD><TD ALIGN="CENTER">84.7</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Interplane separation (deg)</B> </TT></TD><TD ALIGN="CENTER">31.6</TD><TD ALIGN="CENTER">15</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Seam separation (deg)</B> </TT></TD><TD ALIGN="CENTER">22</TD><TD ALIGN="CENTER">15</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Elevation mask (deg)</B> </TT></TD><TD ALIGN="CENTER">8.2</TD><TD ALIGN="CENTER">40</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Intraplane phasing</B> </TT></TD><TD ALIGN="CENTER">yes</TD><TD ALIGN="CENTER">yes</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Interplane phasing</B> </TT></TD><TD ALIGN="CENTER">yes</TD><TD ALIGN="CENTER">no</TD></TR><TR><TD ALIGN="CENTER"><TT><B>ISLs per satellite</B> </TT></TD><TD ALIGN="CENTER">4</TD><TD ALIGN="CENTER">8</TD></TR><TR><TD ALIGN="CENTER"><TT><B>ISL bandwidth</B> </TT></TD><TD ALIGN="CENTER">25 Mb/s</TD><TD ALIGN="CENTER">155 Mb/s</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Up/downlink bandwidth</B> </TT></TD><TD ALIGN="CENTER">1.5 Mb/s</TD><TD ALIGN="CENTER">1.5 Mb/s</TD></TR><TR><TD ALIGN="CENTER"><TT><B>Cross-seam ISLs</B> </TT></TD><TD ALIGN="CENTER">no</TD><TD ALIGN="CENTER">yes</TD></TR><TR><TD ALIGN="CENTER"><TT><B>ISL latitude threshold (deg)</B> </TT></TD><TD ALIGN="CENTER">60</TD><TD ALIGN="CENTER">60</TD></TR></TABLE></DIV></TD></TR></TABLE></DIV><P></P><BR><P><HR><!--Navigation Panel--><A NAME="tex2html4324" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4318" HREF="node196.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node196.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4314" HREF="node197.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node197.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4320" 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="tex2html4322" 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="tex2html4325" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html">17.2 Using the satellite</A><B> Up:</B> <A NAME="tex2html4319" HREF="node196.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node196.html">17.1 Overview of satellite</A><B> Previous:</B> <A NAME="tex2html4315" HREF="node197.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node197.html">17.1.1 Geostationary satellites</A>   <B> <A NAME="tex2html4321" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4323" 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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