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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_154</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_153.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_154</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_155.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 154</font></td></tr></table><table cellpadding="0" cellspacing="0" border="0" width="100%"><tr><td height="12"></td></tr><tr><td><table cellspacing="0" border="2" width="380" cellpadding="4"><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">TABLE聽5.6聽Algorithm聽for聽Compensating聽Residuals聽for聽Clock聽Resetting</font></td></tr><tr><td valign="top"><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"><img src="f4b08cec5b96e00400bb7984520a950a.gif" border="0" alt="0154-01.GIF" width="224" height="105" /></font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td></tr></table></td></tr></table><br /><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">not erroneously classifying other events (e.g., outliers or sensor failure) as clock resets. Failure to correctly account for the effects of clock bias resetting will result in undesirable (usually large) transients in the position and the velocity estimates of the filter.</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">Table 5.6 contains an algorithm that essentially counts the clock resets and adds a compensating offset to the residual. Before the algorithm is entered, <img src="9308fc82f539c1e31c3b7d3e4dea4da7.gif" border="0" alt="C0154-01.GIF" width="14" height="15" />, h, and x</font><font face="Times New Roman, Times, Serif" size="1"><sub>0</sub></font><font face="Times New Roman, Times, Serif" size="3"> are calculated as usual. After the algorithm is completed, the residual is used as normal. The result is that the discrete jumps in the clock bias estimate are removed and the clock bias drifts monotonically.</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">An alternative approach is to not alter the residual, but to artificially increase the Kalman filter clock bias error covariance (the component of P</font><font face="Times New Roman, Times, Serif" size="1"><sub>_</sub></font><font face="Times New Roman, Times, Serif" size="3"> corresponding to the clock estimate) to a large number [e.g., (0.001<i>c</i>)</font><font face="Times New Roman, Times, Serif" size="2"><sup>2</sup></font><font face="Times New Roman, Times, Serif" size="3">] when either of the reset conditions in Table 5.6 is satisfied. This tells the Kalman filter algorithm which component of the state vector is responsible for the large residual.</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"><i></i></font><i><font face="Symbol" size="3"></font><font face="Times New Roman, Times, Serif" size="3">5.4.2<br />Satellite Clock Bias c</font><font face="Symbol" size="3">D</font><font face="Times New Roman, Times, Serif" size="3">t</font><font face="Times New Roman, Times, Serif" size="1"><sub>sv</sub></font></i></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">Each satellite clock is free running and will, over time, drift away from the GPS system time. The control segment is responsible for estimating and monitoring the satellite clock error. The ground stations do not actually correct the satellite clock, but monitor the errors and send the correction formula parameters to the user. The user reads these parameters and corrects the predicted portion of the satellite clock error (see Table E.2). The remaining satellite clock error will bias the corrected range.</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 satellite clock correction should be used to correct the transit time before calculating time of transmission, satellite position, or corrected pseudorange. In addition to the actual satellite clock drift, one implementation of the policy of SA is the addition of apparent clock error. The SA portion of the satellite clock error is not accounted for in the broadcast clock corrections.</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">Satellite clock error affects all users (i.e., those using C/A code, P code, or two-frequency receivers) in the same fashion. The error is independent of the location of the user relative to the satellite. Therefore the satellite clock component of differential corrections is accurate for all users, regardless of position.</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></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_153.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_154</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_155.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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