Overcoming RFI with High Mask Angle Antennas and Multiple GNSS Constellations

L. Heng, T. Walter, P. Enge, G.X. Gao

Abstract:	Radio frequency interference (RFI) has been being a significant issue for global navigation satellite system (GNSS) users. An increasing number of satellites in multiple constellations enable a new, simple method to reduce RFI from terrestrial sources---using a multi-constellation GNSS receiver equipped with a high mask angle antenna. In general, an antenna with a higher mask angle can better suppress RFI signals coming from low elevation angles, and meanwhile can reject more useful signals from low elevation GNSS satellites, leading to worse user-satellite geometry. The purpose of this paper is to study the optimal antenna mask angle that maximizes the suppression of RFI but still maintains the dilution of precision (DOP) performance of a single constellation with a low mask angle antenna. The paper first introduces a novel lower bound of expected value of DOP. Our theoretical analysis based on the lower bound generates a closed-form expression that directly relates DOP to the antenna mask angle and the average number of visible satellites. Then, we conduct extensive numerical simulations based on actual and planned GNSS orbits. From the simulation results we derive a variety of optimal mask angles with respect to different constellation settings, different DOP metrics, and different assumptions of range accuracy. The optimal mask angles obtained from theoretical analysis highly agree with the simulation results based on similar assumptions. Furthermore, the optimal mask angle found with respect to the Vertical DOP performance is validated by a simulation of the Wide Area Augmentation System (WAAS) Vertical Protection Level (VPL). The theoretical analysis and simulation results show that two GNSS constellations can match performance of one with 5- to 14-degree higher mask, and three constellations can match performance of one with 11- to 23-degree higher mask, where the exact optimal mask angel depends on the DOP metric and the range error model used. The analysis and results also show diminishing marginal gain of mask angle obtained with the increase in number of satellites. In addition, using high mask angle antennas is more beneficial to users interested in positioning accuracy, especially horizontal accuracy, than users interested in time transfer accuracy. The results presented in this paper provide multi-constellation GNSS users accurate guidelines on designing and using high mask angle antennas to overcome RFI.
Published in:	Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013) September 16 - 20, 2013 Nashville Convention Center, Nashville, Tennessee Nashville, TN
Pages:	3433 - 3442
Cite this article:	Heng, L., Walter, T., Enge, P., Gao, G.X., "Overcoming RFI with High Mask Angle Antennas and Multiple GNSS Constellations," Proceedings of the 26th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2013), Nashville, TN, September 2013, pp. 3433-3442.
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