On-field test campaign performance of VDE-SAT Link ID 20 over Norsat-2 LEO satellite

The latest technical recommendation by the International Telecommunication Union (ITU) for a data exchange system in the VHF maritime mobile band defines a random access channel (RAC) for communications on the uplink channel between vessels and satellites. The physical layer frame for random uplink channel is designed to allow for a more efficient use of the power amplifiers and includes features to assist the satellite receivers to resolve overlapping reception of multiple messages. This paper presents the performance results of an over-the-air test campaign carried out exploiting the NorSat-2 Low Earth orbit (LEO) satellite. After a review of the VDE-SAT RAC and Link ID 20 burst, a possible demodulator implementation is shown. Then, the VDE-SAT transmitter platform, located in Pisa, Italy, emulating a population of vessels transmitting to the NorSat-2 LEO satellite is introduced, and the test cases are described. Afterward, the analysis of the recorded signals is provided. The post-analysis first focuses on the demodulation performance in terms of probability of successful demodulation of the interfering bursts. Further investigation has also been carried out to better understand the interference environment in this frequency band for satellite signal reception. Tests indicate promising results of successfully detecting and demodulating up to 22 overlapping RAC messages, confirming the robustness of the protocol. Finally, capitalizing on the above analysis, conclusions suggest possible improvements.