Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Numerical modeling of a Global Navigation Satellite System in a general
  relativistic framework   In this article we model a Global Navigation Satellite System (GNSS) in a
Schwarzschild space-time, as a first approximation of the relativistic geometry
around the Earth. The closed time-like and scattering light-like geodesics are
obtained analytically, describing respectively trajectories of satellites and
electromagnetic signals. We implement an algorithm to calculate Schwarzschild
coordinates of a GNSS user who receives proper times sent by four satellites,
knowing their orbital parameters; the inverse procedure is implemented to check
for consistency. The constellation of satellites therefore realizes a
geocentric inertial reference system with no \emph{a priori} realization of a
terrestrial reference frame. We show that the calculation is very fast and
could be implemented in a real GNSS, as an alternative to usual post-Newtonian
corrections. Effects of non-gravitational perturbations on positioning errors
are assessed, and methods to reduce them are sketched. In particular,
inter-links between satellites could greatly enhance stability and accuracy of
the positioning system.

23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
36
The categories of this paper are: cmp-lg
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
1
The categories of this paper are: cs
32
The categories of this paper are: atom-ph
9
The categories of this paper are: nlin
25
The categories of this paper are: patt-sol
11
The categories of this paper are: hep-lat