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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_266</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_265.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_266</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_267.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 266</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">Therefore the synthetic range measurement based on this estimate of <i>N</i> will be biased by (2<i>E</i></font><i><font face="Times New Roman, Times, Serif" size="1"><sub>i</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3">/</font><font face="Symbol" size="3">l</font><font face="Times New Roman, Times, Serif" size="3">). Since <i>E</i></font><i><font face="Times New Roman, Times, Serif" size="1"><sub>i</sub></font></i><font face="Times New Roman, Times, Serif" size="1"><sub></sub></font><font face="Times New Roman, Times, Serif" size="3"> is time varying, the synthetic range would vary from the code range measurement over time. This is prevented in implementations by use of the code range to correct the prediction of synthetic range based on the phase change. This requires that <i>K</i>(<i>k</i>) not asymptotically approach zero. For example, in Ref. 89 the sequence</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"><img src="5827bf2a31891019979730a69a236d5e.gif" border="0" alt="0266-01.GIF" width="370" height="41" /></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">is proposed.</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">Another issue to consider is the case when <i>E</i></font><font face="Times New Roman, Times, Serif" size="1"><sub>cm</sub></font><font face="Times New Roman, Times, Serif" size="3"> is not zero. Since <i>E</i></font><font face="Times New Roman, Times, Serif" size="1"><sub>cm</sub></font><font face="Times New Roman, Times, Serif" size="3"> affects both the phase and the range measurements identically, it could be combined with the </font><font face="Symbol" size="3">r</font><font face="Times New Roman, Times, Serif" size="3"> term. It would therefore pass through the filter intact. Therefore, in nondifferential-mode carrier-smoothed-code operation, the effects of SA, ephemeris, tropospheric, and satellite clock errors are not reduced. Code multipath and measurement noise are still significantly attenuated. Effectively, this technique can produce high- (P-code) accuracy synthetic pseudorange measurements by use of lower-quality (C/A-code) pseudorange and phase measurements.</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">All the above techniques are based on the assumption that <i>N</i> is constant. This assumption is violated in the event of cycle slips. These occur when the phase tracking loop of the receiver loses phase lock. Such conditions must be detected. When cycle slips occur, the above estimation algorithms must be reinitialized.</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="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">7.5<br />Range-Space DGPS Base Station Design</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">In Sec. 5.8 the DGPS approach was motivated and a straightforward method for determining the pseudorange correction signals was described. The approach described in that section has a few disadvantages that are easily overcome. Appropriate methods are described in this section.</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">This section has five subsections. In Sec. 7.5.1 the calculation of the range-space corrections is reviewed and several issues to be addressed in base station design are summarized. The section also discusses compatibility with the RTCM DGPS conventions. In Sec. 7.5.2 issues related to removing the effects of the base station clock error from the range-space corrections are discussed. In Sec. 7.5.3 a design technique for single-frequency base stations is discussed. In Sec. 7.5.4 a design technique for two-frequency base stations is discussed. Finally, in Sec. 7.5.5 the generation of phase corrections 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">An understanding of this material is necessary for persons interested in designing a DGPS system. It should also be of interest to users of DGPS signals, so that they have a full understanding of the capabilities and limitations of DGPS corrections and can make educated decisions among the various sources of these corrections.</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_265.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_266</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_267.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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