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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_142</title> <link rel="stylesheet" href="reset.css" type="text/css" media="all"> <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> </head> <body> <table summary="top nav" border="0" width="100%"> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_141.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_142</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_143.html">next page ></a></td> </tr> <tr> <td id="ebook_page" align="left" colspan="3" style="background: #ffffff; padding: 20px;"> <table border="0" width="100%" cellpadding="0"><tr><td align="center"> <table border="0" cellpadding="2" cellspacing="0" width="100%"><tr><td align="left"></td> <td align="right"></td> </tr></table></td></tr><tr><td align="left"><p></p><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="right"><font face="Times New Roman, Times, Serif" size="2" color="#FF0000">Page 142</font></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="17"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">5.1<br />GPS System Overview</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">GPS consists of three major segments: <i>space, control</i>, and <i>user</i> (see Refs. 14, 34, 78, 81, and 141).</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The <i>space segment</i> consists of the GPS satellites. The GPS Operational Constellation comprises 24 satellites. The satellite vehicles (SVs) orbit the earth in six 12-h (11-h 58-min) orbital planes (four satellites in each plane). The orbits are nearly circular with inclination angles of 55掳 (relative to the equator) and radii of approximately 20,200 km. The six orbits are equally spaced around the equator, resulting in 60掳 separation. This constellation ensures that (barring obstructions) a user located anywhere on the globe has a direct line of sight to at least four satellites at any time. Since satellites are not in geosynchronous orbits, the geometric relation between the satellites in view is constantly changing with respect to an observer on earth. This changing geometry results in changing, but predictable, position-estimation accuracy for positions determined from a fixed set of satellites (see Sec. 5.5). The SVs emit coded radio signals that a GPS receiver will decode to determine important system parameters.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The <i>control segment</i> is responsible for monitoring the health and the status of the space segment. The control segment consists of a system of tracking stations located around the world, including six monitor stations, four ground antennas, and a master control station, as given in Table 5.1. The ground monitoring stations measure signals from the SVs that are transmitted to the master control station. The master control station determines the orbital model and the clock-correction parameters for each satellite. These parameters (and other data) are relayed to the ground antennas for transmission to the satellites for broadcast to the user segment.</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"></td> <td colspan="3" height="12"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="3">The <i>user segment</i> consists of antennas and receiver-processors that measure and decode the satellite transmissions to provide positioning, velocity, and precise timing information to the user. Since the user receiver operates passively (i.e., it does not transmit any signals), the GPS space segment can provide service to an unlimited number of users. It is important to note that the GPS</font><font face="Times New Roman, Times, Serif" size="3" color="#FFFF00"></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table><table cellpadding="0" cellspacing="0" border="0" width="100%"><tr><td height="12"></td></tr><tr><td><table cellspacing="0" width="487" cellpadding="4"><tr><td colspan="2" valign="top"><font face="Times New Roman, Times, Serif" size="2">TABLE 5.1 Locations of the Components of the Operation Control Segment</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Master control station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Falcon Air Force Base, Colorado Springs, CO</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Master control station (backup)</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Gaithersburg, MD</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Falcon Air Force Base, Colorado Springs, CO</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Remote monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Cape Canaveral, FL</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Remote monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Hawaii</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Remote monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ascension Island</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Remote monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Diego Garcia</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Remote monitor station</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Kwajalein</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ground antenna</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Cape Canaveral, FL</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ground antenna</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ascension Island</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ground antenna</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Diego Garcia</font></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Ground antenna</font></td><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Kwajalein</font></td></tr></table></td></tr></table><br /></td></tr></table><p><font size="0"></font></p>聽 </td> </tr> <tr> <td align="left" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_141.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_142</strong></td> <td align="right" width="30%" style="background: #EEF3E2"><a style="color: blue; font-size: 120%; font-weight: bold; text-decoration: none; font-family: verdana;" href="page_143.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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