Initially, automatic identification system (AIS) was proposed to avoid collision between vessels and ensure effective traffic controlling off the coast or in harbors via navigational messages among mobile terminals and base stations in the VHF maritime mobile band.
Since it used typical VHF data exchange devices, AIS terminal equipment has been used for ocean monitoring. However, most ocean monitoring systems rely on satellites and no studies have been conducted on shore-based systems.
In the case of a long distance between the ground station and vessels, the received signal intensity decreases rapidly and there are a number of small cell areas around the base station. The rapid degradation of the strength of received signals due to troposphere propagation and the packet collision due to simultaneous signal transmission are main challenges to widening the communication range of AIS systems.
In order to extend the communication range of AIS ground stations, it is necessary to amplify received signals as much as possible to transfer to feed those with sufficient signal-to-noise ratio into the demodulation part, and the demodulation part should use coherent Viterbi detector and error correction codes to reduce the packet error rate.
O Myong Guk, a researcher at the Faculty of Communications, has proposed a new packet structure using error correction codes to reduce the packet error rate at the shore station, and a scheme to correctly decode it.
The simulation and experimental results show that the proposed scheme is suitable for reducing the packet error rate and increasing the coverage area of long-range AIS systems which depend on the troposphere wave propagation.