Frequency Window with Homogeneous Time of Flight (ToF) for Near Vertical Incidence Skywave (NVIS) Propagation Determined Based on Ionograms

The Multi-Carrier Modulation (MCM) technique in the Near Vertical Incidence Skywave (NVIS) propagation mode poses a challenge due to the ionosphere’s dynamic behavior. The selection of the main bandwidth and transmission frequency in the MCM-NVIS system should consider the different ionospheric refraction indexes within each available frequency of the ionosphere channel. This ensures that all transmitted sub-carriers arrive at the receiver at an acceptable time. It is important to note that not all transmission frequencies may reach the receiver, and the propagation time of each received frequency may differ significantly. Using sub-carrier frequencies with varying propagation times in the MCM technique may negatively impact the system’s performance. Therefore, information on the NVIS propagation mode frequency window with homogeneous Time of Flight (ToF) values is crucial for successfully implementing the MCM technique. In this paper, we explore the frequency window with homogeneous ToF values for NVIS propagation based on ionograms. The width of the frequency window and its center frequency variation can be used to determine the main bandwidth and transmission frequency of the MCM-NVIS system. Our numeric simulation with the inputs of the widest frequency window based on the ionograms at Kupang in 2022 shows that the maximum value of ergodic capacity is up to 10
⁶
bps at 20 dB SNR during the daytime.