Development of FKP-DGPS Positioning Module with Low-priced GPS Receiver for Intelligent Vehicle

J. Kim, J. Song, H. No, C. Kee, M. Park

Abstract:	Nowadays, development of intelligent vehicle has been attracting world-wide attention. On the basis of autonomous driving, intelligent vehicle are expected to carry out various functions to provide convenience to people. The autonomous driving is considered as one of the most difficult problems to develop reliable intelligent vehicles. Thus, in order to solve the problem, many researches has been performing by using various sensors such as inertial sensors, gyros, laser sensors, and Global Positioning System (GPS) receivers. Among those sensors, positioning method by GPS sensor is one of the most popular methods and it is getting important to get precise positioning solution which is directly related to performance of the autonomous driving. In general, research about positioning method by GPS for autonomous driving is mainly conducted using Real Time Kinematic (RTK) which is widely known to be able to get cm level of positioning accuracy in basis of carrierphase measurements. However, expensive dual-frequency GPS receiver is necessary to obtain RTK solution. Furthermore, integer ambiguity resolution can be affected by cycle slips and it causes not continuous positioning solution. Therefore, though positioning method using pseudorange measurements are less accurate than that using carrierphase measurements, in this paper, considering mass production and cost-effectiveness, how to improve positioning accuracy of low-priced GPS receiver has been researched and novel FKP-DGPS positioning module has been developed. Commercial low-priced GPS receivers are operated based on pseudorange measurements. One of the typical augmentation systems for the low-priced GPS receivers is Differential GPS (DGPS). The DGPS consists of a Reference Station (RS) located at a known location that has been previously surveyed, and one or more DGPS users. DGPS is based on the principle that GPS receivers in the same vicinity will simultaneously experience common errors such as ionospheric delay, tropospheric delay, and satellite orbit error on a particular satellite ranging signal. Commercial low-priced GPS receivers can have 1~3 meter positioning accuracy using DGPS correction from RS. However, in the DGPS, the correlation of the common errors experienced at the reference station and the user location is dependent on the distance between them. Due to the separation of the user from the reference station, the probability of significant differing ionospheric and tropospheric conditions at the two sites increase. Therefore, bias error is caused by it in DGPS and it is commonly referred to as “Spatial Decorrelation”. In the DGPS, positioning error caused by spatial decorrelation is under noise level of pseudorange measurements. That is why it is treated as minor error source and just a few researches to deal with spatial decorrelation are in progress. The error due to spatial decorrelation is also present in RTK which is the augmentation system for carrierphase measurements. Compared to pseudorange measurements, carrierpahse measurements have got much smaller noise about centimeter level which is much smaller than bias error due to spatial decorrelation. It is very important error source which can affect integer ambiguity resolution in RTK. Therefore, many research such as Network-RTK (Network-Real Time Kinematic) to deal with spatial decorrelation in RTK have been carrying out rather than in DGPS. FKP is ‘Flaechen Korrektur Parameter’ in German. It is one of Network-RTK methods such as VRS (Virtual Reference Station), MAC (Master-Auxiliary Concept) and it means ‘Area Correction Parameters’. It is an information to deal with spatial decorrelation in CDGPS based on carrierphase measurements. According to RTCM standard, it can be easily modified to the correction for pseudorange measurements. In Korea, FKP has been being broadcasted since 2012. Thus, to use FKP correction for pseudorange measurement, it is not necessary to add more hardware system and to construct infrastructure. In this paper, to improve the DGPS positioning accuracy, FKP is modified to apply to the low-priced GPS receivers. In last year, possibility of FKP correction to improve DGPS positioning accuracy was verified by conducting post-processing FKP-DGPS tests based on MATLAB. After making sure about the possibility, real-time FKP-DGPS algorithm was designed and was also verified by several static and dynamic tests based on Visual C++. In the real-time static test, FKP-DGPS has 21% less 1CEP and 76% less bias error rather than DGPS. Also, in the dynamic test, FKP-DGPS has better positioning accuracy than DGPS. It has 19% improved 1CEP and 31% less bias error. Considering these result, it is clear that FKP correction eliminates effectively bias error due to spatial decorrelation in DGPS and it can be utilized for commercial low-priced GPS receivers effectively. Finally, this FKP-DGPS positioning method has been adapted for developed embedded positioning module based on LINUX with low-priced GPS receivers. Several static and dynamic tests with this module has been carried out and the results are almost equal to the test based on Visual C++. In conclusion, this developed novel FKP-DGPS positioning module is expected to mount in intelligent vehicle to calculate precise its positioning for trustworthy autonomous driving.
Published in:	Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015) September 14 - 18, 2015 Tampa Convention Center Tampa, Florida
Pages:	513 - 541
Cite this article:	Kim, J., Song, J., No, H., Kee, C., Park, M., "Development of FKP-DGPS Positioning Module with Low-priced GPS Receiver for Intelligent Vehicle," Proceedings of the 28th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2015), Tampa, Florida, September 2015, pp. 513-541.
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