Global positioning system (GPS) provides the position accuracy of 15 m standard positioning service (SPS). By differencing measurements between receivers, common error sources such as the ionospheric error can be cancelled and the absolute coordinates is transformed to the relative coordinates. When carrier phase measurements are also used in determine position, the positioning precision increases compared to code only measurements. However, integer ambiguities have to be fixed before using carrier phase measurements, which takes considerable time to solve it.
Carrier-smoothed relative GPS (CS-RGPS) utilizes double differenced carrier and code measurements together and the integer ambiguities are roughly estimated using single- or several-epoch measurements. Once the integer ambiguity is determined, integer ambiguity estimation error would act like bias error. Not only high performance but also low cost receivers are suitable to use this method.
Carrier-smoothed GPS (CS-GPS) uses single differenced carrier and code measurements which cannot cancel ionospheric and tropospheric errors. On the other hands, the positioning error behaves as bias for a short time. When the visible satellite set is changed or cycle slip occurs in carrier measurement, this bias would be abruptly changed and the trajectory becomes discontinuous. To make the trajectory continuous, dead-reckoning (DR) sensors can be exploited. Moreover, performance of position estimate is improved when CS-GPS and DR are integrated together. Using CS-GPS, DR sensor errors are precisely compensated to provide accurate position estimate even when the GPS signals are blocked for a period of time. At the same time, continuous trajectory can be obtained regardless of cycle slip in carrier measurements and changes in visible satellite set. By field experiments, performance of the proposed methods are analyzed.