A Method to Simulate Realistic Kinematic Trajectories on GNSS Signal Generators

Nabil Ghanem and Hisham Berjass

Abstract:	GNSS simulators provide an efficient mean to design, validate and test GNSS receivers, without the underlying costs and risks of field testing. The generated GNSS signals account for the satellite orbits as well as the satellite-to-user channel effects. These effects include among others the motion of the user’s vehicle. The GNSS receivers deployed on board of different vehicles in real life must sustain the corresponding maximum kinematics. In fact, tracking loop designs vary depending on the loop integrators, discriminator, filter noise bandwidth and order. Hence, GNSS signal tracking is platform dependent as it is generally subject to a tradeoff between the thermal noise error and the line-of-sight dynamic stress threshold. For instance, integrating an automotive GNSS receiver on an aircraft or a space shuttle, may cause a loss of tracking and hence a navigation failure. Therefore testing the receivers with actual signals under high dynamic stress can be very challenging as it implies pushing the vehicle under test to its kinematic limits. This work aims to provide GNSS signal simulators with a method to model a realistic motion by generating a trajectory that abides by the kinematic limits of the simulated vehicle. The proposed trajectory smoothening method generates from a set of input way-points a smoothened trajectory that minimizes the average travel time within a set of constraints. The output trajectory deviation from the input way-points is limited to user defined threshold suitable for a specific vehicle type. The generated trajectory is characterized by connected polynomials that can reach up to the sixth order. The input motion path is divided in segments by inserting control points that are used to shape the motion profile utilizing the defined kinematic limits. The number and location of these points are carefully chosen to prevent any undesired oscillations in position. This is achieved using a sinusoidal function template to define the kinematic conditions at each control point. Processing is performed using a window of three consecutive input way-points, between which the needed control points are determined. The inserted control points are sufficient to define the smoothened output trajectory within a given processing window. This approach reduces the processing time and the computational complexity, making it a feasible solution for real time applications. Moreover, the proposed algorithm presents a preprocessing technique to remove some of the user’s input way points based on the defined deviation tolerance threshold, which further improves the average travel and processing time of the smoothened output trajectory. Furthermore, the algorithm automatically inserts additional way-points along the great circle in order to avoid the earth surface penetration. The algorithm performance was tested and validated using a Rohde & Schwarz GNSS simulator with different vehicle configurations and receivers from different vendors.
Published in:	Proceedings of the ION 2015 Pacific PNT Meeting April 20 - 23, 2015 Marriott Waikiki Beach Resort & Spa Honolulu, Hawaii
Pages:	872 - 885
Cite this article:	Ghanem, Nabil, Berjass, Hisham, "A Method to Simulate Realistic Kinematic Trajectories on GNSS Signal Generators," Proceedings of the ION 2015 Pacific PNT Meeting, Honolulu, Hawaii, April 2015, pp. 872-885.
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