Pseudo Dual-Polarization Antenna: NLOS Multipath Detection by Antenna Rotation

Taro Suzuki

Peer Reviewed

Abstract:	One of the unsolved issues in the global navigation satellite system (GNSS) is the degradation of positioning accuracy caused by multipath signals in urban environments. In these environments, signals reflected off building walls arrive at the antenna with delays, resulting in ranging errors known as multipath errors. When line-of-sight (LOS) signals from satellites are blocked by obstacles and only non-LOS (NLOS) signals are received, large positioning errors, known as NLOS multipath errors, occur. One method for detecting NLOS multipath signals is to use a dual polarization antenna. GNSS signals are right-hand circularly polarized (RHCP), and the rotation direction of circularly polarized signals reflected by building walls changes to left-hand circularly polarized (LHCP), the opposite rotation. A dual polarization antenna can detect these NLOS reflected multipath signals by simultaneously receiving and processing RHCP and LHCP signals with two types of antennas. However, dual polarization antennas had to be combined with special GNSS receivers, which was not practical. In this paper, we propose a method for detecting NLOS multipath signals using the difference in observations due to polarization direction. This method uses commercially available RHCP antennas and receivers for normal GNSS positioning. The proposed method involves rotating the RHCP antenna at a high speed (>5 Hz). By rotating the antenna, an additional Doppler frequency, called rotational Doppler, is generated when receiving circularly polarized waves. Since the signs of the rotational Doppler generated by RHCP and LHCP signals are opposite, this paper extracts the rotational Doppler from the Doppler observation to detect NLOS reflected multipath signals. Evaluation experiments of the proposed method were conducted in an environment surrounded by buildings where NLOS occurs, using a rotating antenna system. Using fisheye camera images as a reference, we evaluated the performance of the proposed method in detecting NLOS satellites. The experiments revealed that NLOS signals, or reflected multipath signals, exhibit rotational Doppler that differs from LOS signals. Evaluating the residual of this rotational Doppler demonstrated that the proposed method can detect NLOS satellites.
Published in:	Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025) September 8 - 12, 2025 Hilton Baltimore Inner Harbor Baltimore, Maryland
Pages:	1440 - 1450
Cite this article:	Suzuki, Taro, "Pseudo Dual-Polarization Antenna: NLOS Multipath Detection by Antenna Rotation," Proceedings of the 38th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2025), Baltimore, Maryland, September 2025, pp. 1440-1450. https://doi.org/10.33012/2025.20241
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