  Accurate positioning, navigation, and timing (PNT) performance are
prerequisites for several technologies today. In a marine environment, it is
difficult to visually identify one's position accurately, leading to safety
concerns. Currently, PNT information is provided mainly from Global Navigation
Satellite Systems (GNSS); however, it is vulnerable to radio frequency
interference, spoofing, and ionospheric anomaly. Therefore, research on a
backup system is needed. Ranging Mode (R-Mode), a terrestrial integrated
navigation system, is being investigated for use in a marine environment.
R-Mode is a positioning technology that integrates terrestrial signals of
opportunity such as medium frequency (MF) differential GNSS (DGNSS), very high
frequency (VHF) automatic identification system (AIS), and enhanced long-range
navigation (eLoran) signals. Previous studies in Europe show that signals in
the MF band differ greatly in accuracy between daytime and nighttime. This
difference is primarily caused by skywave. In this study, the MF DGNSS R-Mode
signal transmitted from Chungju, Korea was received in Daesan and Daejeon,
Korea. The skywave effect during daytime and nighttime was compared and
investigated. In addition, the continuous wave intensity of the R-Mode signal
was increased during the nighttime to compare its effect on the measurement
accuracy.
