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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_269</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_268.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_269</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_270.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 269</font></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">discussed in the example of Sec. 5.3, identical errors in all the range residuals are indistinguishable from clock error, the user clock estimate will include the bias </font><font face="Symbol" size="3"><i>t</i></font><font face="Times New Roman, Times, Serif" size="3">. Position accuracy would be unaffected, but time-transfer accuracy would be corrupted by errors in the base station clock estimate.</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">When the base station clock bias error is a function of time </font><font face="Symbol" size="3">t</font><font face="Times New Roman, Times, Serif" size="3">(<i>t</i>), user position accuracy may be affected, depending on the user algorithm. If the roving receiver uses double differencing, then </font><font face="Symbol" size="3">t</font><font face="Times New Roman, Times, Serif" size="3">(<i>t</i>) can change arbitrarily without affecting user position since all base and rover clock bias effects are removed. If any rover receiver uses single differences and the positioning algorithm involves a clock model, then the base station design must carefully consider the rate of change of </font><font face="Symbol" size="3">t</font><font face="Times New Roman, Times, Serif" size="3">(<i>t</i>). When a user navigation algorithm includes a clock model, the rate of change (i.e., bandwidth) of the clock error states is determined by the covariance of the clock state driving noise, the differential equation for the clock model, and the measurement error covariance. If the rate of change of </font><font face="Symbol" size="3">t</font><font face="Times New Roman, Times, Serif" size="3">(<i>t</i>) is greater than the rate of change expected based on the clock error model, then the position accuracy will be affected.</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">Because of the constraint that the correction bias be very slowly time varying, the estimate of Eq. (7.57) should be filtered before it is subtracted from the corrections, as in Eq. (7.54). An appropriate filter could be a Kalman filter incorporating the state-transition matrix and process-noise covariance described in Sec. 5.4.1, with H = [1, 0] and <i>R </i>> (30</font><font face="Times New Roman, Times, Serif" size="2"><sup>2</sup></font><font face="Times New Roman, Times, Serif" size="3">/<i>M</i>). The clock bias output by this filter [denoted as <img src="ed87ca03d3725f2be7303a79edfb40b9.gif" border="0" alt="C0269-01.GIF" width="49" height="20" /> may still be biased, since all the error processes have not been completely modeled; however, the bias that appears in the resulting corrections will vary slowly enough that the rover filter will be able to model the bias as clock error.</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 block diagram for a basic base station is shown in Fig. 7.12. The figure incorporates the principles described above to produce range corrections for each in-view satellite that are corrected for satellite clock error and filtered base station clock bias. In the following two sections the use of carrier-phase data to decrease the effects of pseudorange multipath and measurement noise is discussed.</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>7.5.3<br />Single-Frequency Base Station Design</i></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 effects of multipath and code receiver noise on the corrections can be greatly decreased by use of carrier information. This is because the carrier multipath and the measurement noise are approximately 100 times smaller than the</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 border="0" cellspacing="0" cellpadding="0" width="100%"><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 align="center"><font face="Times New Roman, Times, Serif" size="3"><img src="41b8a27c358371e278dc31f44e83302d.gif" border="0" alt="0269-01.GIF" width="408" height="150" /></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" width="100%"><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 align="center"><font face="Times New Roman, Times, Serif" size="2">Figure聽7.12<br />Base聽station聽clock聽bias聽estimation聽and聽smoothing.聽Thick聽lines聽represent聽vector<br />variables.</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_268.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_269</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_270.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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