Space based Automatic Identification system (Funded by Naval Research Board, Govt. of India)

The Automatic Identification System (AIS) is a maritime navigation safety communications system standardized by the International Telecommunication Union (ITU), adopted by the International Maritime Organization (IMO), that provides vessel information, including the vessel’s identity, type, position, course, speed, navigational status and other safety related information. AIS is designed as a ship collision avoidance system for terrestrial use and uses a communication scheme called Self-Organized Time Domain Multiple Access (SOTDMA). AIS also offer important ship monitoring services to coastal guards or search and rescue organizations.

Ship-to-shore and ship-to-ship communication is limited by the horizon, and the signal reception is highly dependent on the altitude of the transmitter antenna located onboard the ship. Satellite-based AIS is presented as a promising solution to overcome the terrestrial VHF coverage limitation with the potential to provide AIS detection service coverage on any given area on the Earth.

Problem:

The space-based AIS receiver typically receives signals from a large number of cells over the receiving antenna footprint. Therefore, a high number of SOTDMA cells are visible to the satellite and the organized structure is lost resulting in message collisions which the satellite receiver cannot process. All the received signals are sent back to ground station. The problem is to process the received complex signal and identify the ships from the collided messages and extract data of each ship separately.

Methodology:

Satellite receives the signal from various ships which are spatially separated and the signal received undergoes different Doppler frequency shifts and different time of arrivals with different signal strength. Our work is to develop an algorithm based on the above varying parameters to resolve the messages collision problem.