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this book can help you to get a better performance in the gps development

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</tr></table></td></tr><tr><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">24, 9, 4, 7</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"></td>
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  <td align="right"><font face="Times New Roman, Times, Serif" size="2">6.96</font></td>
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</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">7, 9, 4, 2</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="27" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td>
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  <td><font face="Times New Roman, Times, Serif" size="2">4.96</font></td>
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</tr></table></td></tr><tr><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">24, 9, 5, 7</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"></td>
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  <td align="right"><font face="Times New Roman, Times, Serif" size="2">4.89</font></td>
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</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">7, 9, 5, 2</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0"><tr><td rowspan="5"><img src="f7703d30723feae8ee39d997c6419c20.gif" border="0" width="27" height="1" alt="f7703d30723feae8ee39d997c6419c20.gif" /></td>
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  <td><font face="Times New Roman, Times, Serif" size="2">3.92</font></td>
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</tr></table></td></tr><tr><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">24, 9, 2, 7</font></td></tr></table></td><td valign="top"><table border="0" cellspacing="0" cellpadding="0" width="100%"><tr><td rowspan="5"></td>
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  <td align="right"><font face="Times New Roman, Times, Serif" size="2">13.10</font></td>
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  <td><font face="Times New Roman, Times, Serif" size="3">days of GPS, when a limited number of satellites were in view. Now they are generally avoidable by changing satellite combinations. Receivers with a small number of channels usually will select a near-optimal set of satellites to allocate to the available channels.</font></td>
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  <td><font face="Times New Roman, Times, Serif" size="3">A comparison of the above discussion with the discussion of observability in Sec. 3.3.6 shows that the various DOP factors are measures of how observable a given set of position states are at a given time instant (and location) for a given set of satellites. In Kalman filter implementations in which measurements are combined over various time instants, the state-estimation accuracy is quantified by P. If observability were temporarily lost (e.g., because of satellite occlusion), some of the DOP factors would become infinite. Therefore a full least-squares solution by Eq. (5.35) would not be possible. However, if the system is properly modeled, a Kalman filter implementation would continue to provide a full state estimate based on the previous state estimate, the currently available measurements, and the system model. The state-estimation variance (i.e., P) would grow in certain directions.</font></td>
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  <td><font face="Times New Roman, Times, Serif" size="2">Example Consider the following case for which six satellites are in view of the receiver antenna. The rows of the H matrix for each satellite are</font></td>
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  <td><font face="Times New Roman, Times, Serif" size="3"><img src="28e1ec86d14d638644d60f0d70d93105.gif" border="0" alt="0163-01.GIF" width="396" height="131" /></font></td>
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  <td><font face="Times New Roman, Times, Serif" size="2">For this set of 6 satellites, there are 15 different combinations of 4 satellites, as shown in Table 5.7. The GDOP figures for the various sets of four satellites range from 3.58 to 16.03. An alternative to selecting the best four satellites would be an all-in-view approach using all six satellites and Eq. (5.12). The all-in-view approach for this example would result in a GDOP of 2.96 [34].</font><font face="Times New Roman, Times, Serif" size="2" color="#FFFF00"></font></td>
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