The Composition of the Maritime Satellite Communication System

The Brief Introduction of Maritime Satellite Communication System

The maritime satellite communication system is a kind of ship radio communication system using communication satellites as relay stations. It has remarkable advantages such as global (except in the southern Arctic), all-time, all-weather, stable, reliable, high-quality, large capacity, and automatic communication. It can not only improve ship operation and management efficiency, and close ship shore relations but also help to ensure the safety of human life at sea. INMARSAT is a kind of mobile service satellite communication system (MSS). It includes communication between mobile stations, between mobile stations and fixed stations, and between fixed stations and users of the public communication networks. INMARSAT is the first global mobile service satellite communication system in the world.

The Composition of the Maritime Satellite Communication System

The maritime satellite communication system is mainly composed of the maritime satellite communication earth station installed on the ship (referred to as the ship station), the maritime satellite communication earth station located on the coast (referred to as the shore station), and the maritime communication satellite.

The ship station is the communication terminal of the system. It is equipped with a parabolic antenna with a diameter of about 1m and corresponding communication equipment. It adopts L-band, with a transmitting frequency of 1.6 GHz and a receiving frequency of 1.5 GHz. The telegraph communication adopts phase shift keying modulation, with a transmission rate of 4800 bits / s and a reception rate of 1200 bits / s. Telephone communication adopts FM mode.

The shore station plays the role of network control in the communication circuit of the system. It is equipped with a Cassegrain antenna with a diameter of about 13 meters and corresponding communication equipment and is connected with the land communication network. C-band is adopted. The transmission frequency is 6 GHz band and the reception frequency is 4 GHz band. In order to eliminate the influence of frequency offset in the process of radio wave propagation, L-band frequency is also used as the pilot frequency of automatic frequency control, and as the frequency of service circuit and test circuit between shore stations.

The maritime communication satellite is the relay station of the system, transmitting signals sent by the ship station and shore station. Geostationary satellites and spherical beams are used, and the configuration is based on three ocean regions: the Atlantic Ocean, the Pacific Ocean, and the Indian Ocean. Each satellite is equipped with L → C band and C → L band transponders, which provide Telegraph and telephone (including fax and data transmission) channels, as well as common call channels. Each telegraph channel is divided into 22 channels by TDMA, and the telephone channel adopts single channel single carrier technology.

In order to make full use of the communication capacity of each satellite, the system adopts a more complex channel allocation method, and the network coordination station set up at the designated shore station is responsible for allocating the satellite communication channel in each ocean region. The telegraph channel is pre-allocated to each shore station, which is responsible for allocating the time slot for telegraph communication with the ship station as required. The telephone channel is controlled by the network coordination station and allocated according to the application of the ship station and shore station.

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