Friday 26 August 2005

G6
1000-1200 hours

495
Developing and testing a virtual pseudolite (VPL) technique for GPS positioning
Chang, Chia-Chyang¹, Ker, Bin-Jung²
1 Chung Cheng Institute Of Technology, Tahsi, Taiwan
2 Armaments Bureau
The near-ground operation of a GPS-like signal transmitter, namely pseudolite (PL), is expected to provide the extra-measurements and improve the GPS positioning accuracy and availability. The GPS and PL observations were collected at a short baseline for three sessions and tested for the realization of the signal characteristics, differential operations, and bias removals. The results show that the average precision of the baseline solution can be improved by 7% and 30% for horizontal and vertical component, respectively, when PL's phase measurements were applied. Based on the 'true' measurements received from one PL during the field trial, a so-called 'virtual' PL (VPL) technique has been developed and implemented to duplicate the PL's measurements for any number and location of PL constellation. It is expected to effectively reduce the instrument cost, enhance the network geometry, improve the coordinate accuracy, and carry on the pure PL positioning. The results prove this virtual technique working properly as a better precision can be generally achieved for the tests based on different site of VPL, short session of measurement, or a wide range of VPL heights. The baseline precision demonstrates an impressive enhancement from the GPS only to the VPL solution for an average of 51% in three-dimensional component, especially when VPL network is designed as a reverse type of pyramid. Based on VPL technique, it is also possible to carry on an indoor-like pure PL positioning using one true PL and at least three virtual PL measurements. The point positioning with VPLs' phase data was carried out for the rovers and compared with the known coordinates. The coordinate recovery is found to be better than 1 cm for pure PL positioning. In summary, this study has preliminarily shown the effectiveness of the use of VPL in an auxiliary GPS positioning.

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