Enhancement of MF R-Mode ranging accuracy by exploiting measurement-based error mitigation techniques

Abstract

Nowadays, the maritime sector strongly relies on global navigation satellite systems (GNSS) for the provision of position, navigation, and timing (PNT) information. The standard functionality of several ships’ bridge instruments depends on such information, which becomes critical to have a safe and reliable navigation. Nevertheless, the possibility of GNSS outages combined with unintentional and intentional interference to GNSS signals, which have been increasing over the last years, can severely threaten the nominal activity of the crew onboard of vessels. For these reasons, alternative position, navigation, and timing (APNT) systems become fundamental in order to provide operational continuity. R(anging)-Mode is a terrestrial alternative system to GNSS for the maritime domain. In one of its possible implementation, it exploits synchronized medium frequency (MF) signals transmitted by maritime radio beacons. In the MF band, the radio waves are attenuated and distorted by the change of electrical properties of the ground along the propagation path. Moreover, these signals are affected by terrain elevation changes and large metallic infrastructures which induce an overall loss in the accuracy of the system. In this paper, we propose a mitigation technique based on the estimation of these additional error sources by using in-field range measurements. The theoretical details are explained in depth and the technique is validated with real data gathered on a measurement campaign. A clear and significant performance improvement is achieved on the range accuracy when the proposed approach is applied.

Prediction of Ground Wave Propagation Delay for MF R-Mode

“…where 24(1 + 7/(4q 3 ) + 5/(4q 6 ) + 21/(64q 9 )), A 10 = −1(32/945 + 64/(945q 3 ) + 11/(189q 6 ) + 7/(270q 9 )) (13) Finally, the R-Mode AGDF is based on the phase delay ϕ GW of the ground wave over a homogeneous propagation path with respect to free space propagation in vacuum, and is given as…”

“…To compensate for the effects of ground wave propagation and atmospheric delays, we developed a method to predict and correct the propagation delay of MF R-Mode signals, called the Atmospheric and Ground Wave Delay Factor (AGDF) [ 13 , 14 ]. This paper is the first detailed description and performance analysis of the approach.…”