📄 page_259.html
字号:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd"> <html> <head> <title>page_259</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_258.html">< previous page</a></td> <td id="ebook_previous" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_259</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_260.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 259</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">be determined from the pseudorange. By combining these two measurements with their different characteristics, the hope is to develop accurate estimates of position over time. Initially, the estimation process should rely on </font><font face="Symbol" size="3">r</font><font face="Times New Roman, Times, Serif" size="3"> because of the large uncertainty in the phase range (i.e., <i>N</i>). As samples are accumulated and <i>N</i> is estimated, the estimation process should rely more heavily on </font><font face="Symbol" size="3"><i>f</i></font><font face="Times New Roman, Times, Serif" size="3">. The velocity and the acceleration accuracy should rapidly converge, as they depend on the change in phase, which is independent of <i>N</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"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Example To illustrate the achievable performance, consider the one-dimensional inertial-frame INS example aided by pseudorange and L1 phase measurements from a single satellite. The common mode error dynamics are modeled as described in Sec. 5.4.8. The integer ambiguity is modeled as a random constant. The ionospheric and code multipath errors are modeled as scalar Gauss-Markov processes. This results in three INS error states and six GPS error states. The ionospheric model has </font><font face="Symbol" size="2"><i>b</i></font><font face="Times New Roman, Times, Serif" size="2"> = 1/300 1/s and <i>Q</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="2"> = var(</font><font face="Symbol" size="2"><i>w</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="2">) = 4 for a steady-state ionospheric error variance of 600 m<sup>2</sup>. The multipath model has </font><font face="Symbol" size="2"><i>b</i></font><font face="Times New Roman, Times, Serif" size="2"> = 1/60 1/s and <i>Q</i></font><font face="Times New Roman, Times, Serif" size="1"><sub>MP</sub></font><font face="Times New Roman, Times, Serif" size="2"> = var(</font><font face="Symbol" size="2"><i>w</i></font><font face="Times New Roman, Times, Serif" size="1"><sub>MP</sub></font><font face="Times New Roman, Times, Serif" size="2">) = 0.3 for a steady-state ionospheric error variance of 9 m<sup>2</sup>. The white code and phase measurement noise have error variances of 0.0943 and 1 脳 10<sup>-4</sup> m<sup>2</sup>, respectively. As a point of reference, a GPS-aided-INS implementation with the same assumptions, but using only the single-frequency code measurement in nondifferential mode, achieves a steady-state position error standard deviation of 36.67 m.</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"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Figure 7.8 illustrates the performance of an approach in which both the phase and the pseudorange measurements are used in a standard GPS-aided-INS application. The uncertainty in the integer ambiguity is still large after 30 min, so that the integer ambiguity cannot be fixed. The position error standard deviation is slightly improved relative to the pseudorange-only aiding performance. The Kalman filter gain plots show that the position estimation is predominantly based on the pseudorange, even after 30 min.</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"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Figure 7.9 illustrates the performance of an approach in which both the phase and the range measurements are used in a nondifferential GPS-aided-INS application with a two-frequency receiver. This is modeled by setting <i>P</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="2"> = <i>Q</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="2"> = 0 in the above model. In comparison with the single-frequency results of Fig. 7.8, the position-estimation accuracy improves only slightly, since the remaining common-mode errors are dominant and are common to both the code and the phase measurements. The uncertainty of the integer estimate is substantially reduced and the filter is relying predominantly on the phase measurement to compensate the position 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"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Figure 7.10 illustrates the performance of using both the phase and the range measurements in a differential GPS-aided-INS application. This is simulated by setting <i>P</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="2"> = <i>Q</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="2"> = 0 and P</font><font face="Times New Roman, Times, Serif" size="1"><sub>cm</sub></font><font face="Times New Roman, Times, Serif" size="2"> = Q</font><font face="Times New Roman, Times, Serif" size="1"><sub>cm</sub></font><font face="Times New Roman, Times, Serif" size="2"> = 0 in the error model. Although the ambiguity estimate error standard deviation decreases only slightly from the two-frequency simulation shown in Fig. 7.9, the position-estimate accuracy has greatly improved. A code-only differential implementation achieves a position-estimation error variance of 3.02 m. Therefore, differential carrier-smoothed-code operation offers the potential for significant performance improvements. Even in this full model implementation, the significant level of multipath error prohibits the estimation of a specific integer-valued ambiguity, without search, during the 30 min of the simulation.</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"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td> <td colspan="3" height="12"></td> <td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="24" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td></tr><tr><td colspan="3"></td></tr><tr><td></td> <td><font face="Times New Roman, Times, Serif" size="2">Based on the above analysis, the reduction of ionospheric error by any method increases the ability to estimate the integer ambiguity. This is because the remaining</font><font face="Times New Roman, Times, Serif" size="2" 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_258.html">< previous page</a></td> <td id="ebook_next" align="center" width="40%" style="background: #EEF3E2"><strong style="color: #2F4F4F; font-size: 120%;">page_259</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_260.html">next page ></a></td> </tr> </table> </body> </html>⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -