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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_184</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_183.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_184</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_185.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 184</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">shown as they are essentially identical in performance to the single-differenced results.</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 main advantage of double-differencing techniques is that clock modeling is not required. The drawbacks are the potential processing of correlated measurements and the possible increase in range noise. In addition, for phase measurements, the integer ambiguity handling is more complex. In a double-differencing approach, the identified integer is that for the <i>i</i>th satellite minus that for the <i>j</i>th satellite. If either satellite loses lock, then the double difference is not available for positioning computations and requires another integer ambiguity search.</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>5.8.4<br />DGPS Methods Summary</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">Three methods for implementing a DGPS have been discussed. A comparison of the features of the three methods is summarized in Table 5.8. Because of increased flexibility at the rover, range-space techniques are preferred. Between single-difference and double-difference techniques, the comparison is not as straightforward. Single-differenced techniques require clock modeling, but may have smaller additive noise, which is also uncorrelated between simultaneous range measurements. Double differencing has the opposite characteristics, but is very easy to implement since no processing of the measured ranges (e.g., clock modeling) is required. Integer reacquisition processing will occur more frequently in double-differencing techniques, since lock loss to either satellite in the difference results in the integer ambiguity's changing. Last, the selection of satellites and satellite pairs to minimize DOP factors is a more difficult combinatorial problem in double-differencing techniques. These last two issues are often both addressed by selection of the satellite with the greatest elevation for double differencing with all other satellites. In Sec. 7.5 base station design for range-based DGPS systems 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">The difference in range noise amplification between single- and double-difference techniques is not straightforward to quantify in general because of the different measurement matrices associated with the two techniques. This is indicated in Table 5.8 by the terms PDOP</font><font face="Times New Roman, Times, Serif" size="1"><sub><i>H</i></sub></font><font face="Times New Roman, Times, Serif" size="3"> and PDOP</font><font face="Symbol" size="1"><sub>D</sub></font><sub><font face="Times New Roman, Times, Serif" size="1"><i>H</i></font></sub><font face="Times New Roman, Times, Serif" size="1"></font><font face="Times New Roman, Times, Serif" size="3">, where </font><font face="Symbol" size="3">D</font><font face="Times New Roman, Times, Serif" size="3"><i>H</i> indicates the differencing across satellites defined in Eq. (5.103). The </font><font face="Symbol" size="3"><i>m</i></font><font face="Times New Roman, Times, Serif" size="3"> in the last double-difference position standard deviation (STD) entry accounts for the upto four</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="509" cellpadding="4"><tr><td colspan="5" valign="top"><font face="Times New Roman, Times, Serif" size="2">TABLE 5.8 Comparison of Alternative Techniques for Differential Operation</font></td></tr><tr><td valign="bottom"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">Method</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">Requires clock modeling</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">Requires raw data handling</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">Requires Satellite set matching</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">Position error STD</font></td></tr></table></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Position-space</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">X</font></td></tr></table></td><td valign="top"></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">X</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2"><img src="9b0b247bf95de94885a77b528243514d.gif" border="0" alt="0184-01.GIF" width="68" height="17" /></font></td></tr></table></td></tr><tr><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="12" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="1"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">single difference</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"></td><td valign="top"></td><td valign="top"></td><td valign="top"></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Range-space</font></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">X</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">X</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">x</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2"><img src="fd6d2cda235a0a0dd9353f2fb8d651c8.gif" border="0" alt="0184-02.GIF" width="69" height="18" /></font></td></tr></table></td></tr><tr><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="12" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="1"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">single difference</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"></td><td valign="top"></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">x</font></td></tr></table></td><td valign="top"></td></tr><tr><td valign="top"><font face="Times New Roman, Times, Serif" size="2">Range-space</font></td><td valign="top"></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">X</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">x</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Symbol" size="2">s</font><font face="Symbol" size="1"><sub>r</sub></font><font face="Symbol" size="2">m</font><font face="Times New Roman, Times, Serif" size="2">PDOP</font><font face="Symbol" size="1"><sub>D</sub></font><sub><font face="Times New Roman, Times, Serif" size="1"><i>H</i></font></sub></td></tr></table></td></tr><tr><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="12" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="1"></td> <td rowspan="5"></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">double difference</font></td><td></td></tr><tr><td colspan="3"></td></tr><tr><td colspan="3" height="1"></td></tr></table></td><td valign="top"></td><td valign="top"></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2">x</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td align="center"><font face="Times New Roman, Times, Serif" size="2"><img src="55912dca01340dde346142ad9b387271.gif" border="0" alt="0184-03.GIF" width="59" height="16" /></font></td></tr></table></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_183.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_184</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_185.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
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