Optimal GPS-Tracking Even in Case of Line-of-Sight Loss

K. Kaindl, N. Niklasch

Abstract:	Conventional GPS receiver technique consists of several parallel scalar DLL-banks which estimate pseudorange independently. This has some severe disadvantages. The most negative one is the loss of the delay lock loop in case of loosing satellite positioning, following a lack of pseudo-range and line-of-sight calculations. This is mostly the case if less then four satellites are tractable, or the number of satellites varies a lot. In these cases the parallel DLL fails completely [SPIL], p. 297. So improvement of this situation is desirable. More advanced solutions propose coupled correlator technique [SEN]. This approach does not take into account representation of the nonlinear terms. The VDLL (vector delay lock loop) is a generalization of the conventional Kalman filtering technique and a optimal estimation process. EKF filtering technique is having two separate sets of loops, delay lock loop and EKF loop, in-stead VDLL integrates these two loops into one and can remain in lock, when parallel DLLs outage. It can be argued that all loops are linearized and so the EKF is still optimum. However, if the independent DLL moves into nonlinear region, this argument is not valid. The nonlinear behaviour is represented by second order terms in Taylor's series expansion of the pseudorange function .
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	638 - 645
Cite this article:	Kaindl, K., Niklasch, N., "Optimal GPS-Tracking Even in Case of Line-of-Sight Loss," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 638-645.
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