Two approaches to precise kinematic GPS positioning with miniaturized L1 receivers

The present paper deals with precise kinematic GPS positioning applications for which requirements to the receiver such as low-cost, light weight, low power consumption and high measurement rate are becoming increasingly more important (e.g. flight maneuver reconstructions). It is investigated whether cheap and miniaturized L1 GPS receivers such as the TIM modules from μ-blox and the new Septentrio AsteRx may provide raw data of sufficient quality as to obtain high-precision (sub-dm) kinematic positioning accuracy. In this paper carrier phase (and code) data at the L1 frequency are processed by means of two approaches. In the first approach, based on a traditional RTK strategy, data of a low-cost miniaturized receiver are processed relative to data of a base station. Here, the rapidity of the integer phase ambiguity resolution is crucial for success. The second approach, a time relative method, abstains from ambiguity resolution, as the phase ambiguities are eliminated when forming time-differences. In this approach, not requiring a base receiver, navigation is demanded to be highly accurate relative to an initial position during time-intervals restricted to a few minutes. Here, the application of correction models compensating for time-drifting effects such as ephemeris error, satellite clock error and tropospheric and ionospheric delays is crucial. The potential of both approaches is demonstrated in various experiments. For the RTK-approach, L1 ambiguity resolution turned out to be feasible for all experiments, even for a baseline length of 4.5 krn, however requiring an ambiguity initialization time of up to 11 min. Comparing the RTK and time-difference method, maximum deviations observed during kinematic experiments of up to 3 min duration do not exceed the sub-decimeter range. The (slow) drift of the solution found by the time relative method is balanced in the context of the actual application by the fact that neither base receiver nor initialization time is needed.