Improving MF R-Mode ranging performance with measurement-based correction factors

The advent of global satellite navigation systems (GNSS) has revolutionized the provision of position, navigation and timing (PNT) information. Thought to be always available and reliable, these systems may experience outages and they can be threatened by interference events. In such cases, alternative positioning, navigation and timing (APNT) systems play a key role. In the maritime domain Ranging Mode, called R-Mode, is a rising terrestrial alternative to GNSS. R-Mode exploits medium frequency (MF) signals transmitted by maritime radio beacons in one possible implementation. It is well-known that MF radio waves are affected by attenuation and distortion caused by a change in the electrical properties of the ground along the propagation path. Additionally, terrain elevation variation and large metallic infrastructures introduce further distortions in the signal, decreasing the overall ranging performance. In this paper we propose a novel approach to compensate for this effect based on direct range measurements. The theory is explained in depth and a test case, based on real measurement campaign data, to validate the technique is also presented.