But in this chapter, an algorithm is proposed to calculate the multipath error affecting GPS L1 pseudorange range measurement. These parameters limit the efficiency of the conventional multipath modeling methods. The multipath error originating at the receiver is very sensitive to geometry (like size and surface texture) and the reflection coefficients of the nearby reflectors. In precise positioning applications, multipath is a major error source and impact needs to be calculated especially in urban canyon while setting up GPS receiver antenna. Apart from these methods the filter-based techniques are also implemented to extract or eliminate multipath effects, such as wavelet filters, Vondrak filter and adaptive filter. Some techniques also rely on the analysis of the signal-to-noise ratio values of GPS signals. Mitigation of the error and the performance of the receivers are analyzed for dual frequency receiver as well. A choke ring antenna with ground plane to absorb multipath signals was proved to mitigate the error to large extent. There are several studies mitigating the multipath error by antenna based mitigation methods. Multipath due to water bodies and its impact on the precision of GNSS positioning in marine application was also studied and similar studied were done for static and kinematic receivers. multipath effect due to large water bodies like sea surface. For the same GPS receiver, multipath error differs depending on the reflecting surfaces, viz. This problem in tracking loop was addressed by several authors. The GPS receiver cannot distinguish the direct signal from the several multipath signals. The multipath effect on carrier phase measurements was also detected. The pseudorange multipath error in an urban environment is characterized by considering signal to noise ratio and elevation angle for DGPS. But the effect of multipath on pseudorange is much higher than the carrier phase. The signal transmitted by the satellite, taking multiple paths, affects both the pseudorange and carrier phase measurements. In this chapter, the error originating at the receiver which is due to GPS signal multiple paths is addressed. Hence, error estimation and correction is a primary concern in precise navigation applications. In addition to these errors, the accuracy of the navigation solution is also affected by GPS satellites location as viewed by the receiver. Also, the propagation medium contributes to the delays in the GPS signal, as it passes through the ionosphere and troposphere. whereas, the receiver clock errors, multipath errors, receiver noise, and antenna phase center variations are the errors originating at the receiver. However, the accuracy, availability, reliability, and integrity of GPS navigation solution are impaired by various errors which are originating at the satellites, like orbital errors, satellite clock errors, etc. precise farming, surveying, missile guidance, military and civil aviation. GPS finds its applications in most of the day to day activities of human life, viz. This mitigation technique will be useful in selecting the site for GPS receiving antenna, where reflection coefficients are difficult to measure. This resulted in maximum error reduction of 30 m in receiver position estimates. GPS receiver position is calculated by considering multipath error corrected pseudoranges of all the visible satellites. Implementation of the algorithm shows pseudorange error due to multipath varied from 7 to 52 m, where the signals of low elevation satellites are most affected. The multipath error is mitigated for standalone GPS receiver located in Indian subcontinent. This algorithm exploits the random nature of the multipath error and it avoids complex calculations involving sensitive parameter like reflection coefficient of the nearby reflectors. The error is estimated considering the linear combination of the GPS measurements and carrier frequencies of L band, viz. In this chapter, an algorithm is proposed to mitigate the multipath error on the pseudorange measured from L1 carrier frequency. The predominant errors in range measurements are due to propagation path delays, making the measured range longer than it would be, if the signal has not reflected or refracted while propagating. The performance of GPS receiver depends on the accuracy of the range measurements.
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