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Satellite “Satcom on the move” is an emerging concept. The United States calls it “Satcom on the move”. This concept is not the traditional mobile satellite communication service (MSS), because the International Telecommunication Union (ITU) has long defined satellite communication services as two categories, one is fixed satellite service (FSS) and the other is mobile satellite service (MSS), and has divided the satellite frequency bands used for their respective communications.

According to the traditional definition, the so-called satellite “Satcom on the move” cannot be simply classified under FSS or MSS. The reason is that the frequencies used by FSS are C, Ku, Ka, etc., and are characterized by large transmission bandwidth, high transmission rate, and fixed communication to transmit broadband information such as video; the frequencies used by MSS are L and S bands, and are characterized by small transmission bandwidth, low transmission rate, and mobile communication to transmit narrowband information such as voice data; and the current satellite “Satcom on the move” is a new application created to meet the needs of users to transmit broadband video information via satellite in dynamic motion. It uses the Ku band of fixed-orbit satellites for mobile communication to transmit broadband video information, and is a new business application that combines the advantages of FSS and MSS.

Satcom on the move  is the abbreviation of “Satellite Ground Station Communication System in Motion”. Through the mobile communication system, vehicles, ships, airplanes and other mobile carriers can track satellites and other platforms in real time during movement, and continuously transmit multimedia information such as voice, data, and images, which can meet the needs of various military and civilian emergency communications and multimedia communications under mobile conditions. The mobile communication system has effectively solved the difficulty of various vehicles, ships and other mobile carriers in real time and continuously transmitting multimedia information such as voice, data, high-definition dynamic video images, faxes, etc. through geosynchronous satellites during movement. It is a major breakthrough in the field of communications and an application field with strong demand and rapid development in the current satellite communication field. It has extremely broad development prospects in both military and civilian fields. It has been vigorously developed in the military, public security, armed police, fire protection, transportation, communications and other departments with emergency tasks or emergency nature. It has also made great progress in special industries such as geological exploration, petroleum, electricity, logistics, telemedicine, and distance education. As a new communication method, mobile communication has gradually become the preferred choice for video transmission, dedicated line command, and communication dispatch in special industries.

What exactly is Satcom on the move ?

Satcom on the move , which is the abbreviation of “communication system on the move”, uses the Satcom on the move wireless video transmission system to enable vehicles, ships, airplanes and other mobile carriers to track the platform in real time during movement and continuously transmit multimedia information such as voice, data, and images, which can meet the needs of various military and civilian emergency communications and multimedia communications under mobile conditions.

Currently, there are two types of mobile communications on the market: 
Satcom on the move  and 
ground micro-wave mobile communications .

The satellite-based mobile communication system is based on the satellite communication network, which combines satellites and other communication means together to complement and combine with each other to form a multi-means, multi-route, and multi-service communication network; the ground-based microwave-based mobile communication system is based on the microwave communication network, which combines ground base stations and other communication means together to complement and combine with each other to form a multi-means, multi-route, and multi-service communication network.

During the movement of the carrier, its posture and geographical location change, which may cause the original satellite antenna to deviate from the satellite, causing communication interruption. Therefore, these changes of the carrier must be isolated so that the antenna is not affected and always points to the satellite. This is the main problem that the antenna stabilization system needs to solve, and it is also the premise for the mobile carrier to carry out uninterrupted satellite communication.

The “Satcom on the move” automatic tracking system is a system that uses GPS, theodolite, and strapdown inertial navigation system to measure the heading angle, the longitude and latitude of the carrier’s location, and the initial angle relative to the horizontal plane in the initial static state. Then, according to its attitude, geographical location, and satellite longitude, it automatically determines the antenna elevation angle based on the horizontal plane, rotates the azimuth while keeping the elevation angle unchanged relative to the horizontal plane, and automatically aligns with the satellite in the signal maximum value mode. During the movement of the carrier, the change of the carrier’s attitude is measured, and through the operation of the mathematical platform, it is converted into the error angle of the antenna. The azimuth, pitch angle, and polarization angle of the antenna are adjusted through the servo mechanism to ensure that the antenna of the carrier is within the specified range during the change process, so that the satellite transmitting antenna can track the geosynchronous satellite in real time during the movement of the carrier. The system has two tracking modes: self-tracking and inertial navigation tracking. Self-tracking relies on satellite beacons to perform antenna closed-loop servo tracking; inertial navigation tracking uses the changes in the gyro-inertial navigation combination sensitive carrier to track the antenna. These two types of tracking can be automatically switched according to the on-site situation. When the system is aligned with the satellite and switches to automatic tracking, it works in self-tracking mode; at the same time, the inertial navigation system also enters the working state and continuously outputs antenna polarization, azimuth and pitch data. When the antenna beacon signal is interrupted due to occlusion or other reasons, the system automatically switches to the inertial navigation tracking mode. At the same time, the advanced mobile satellite communication system is used to transmit radio and television signals to achieve the effect of live broadcasting.

The “Satcom on the move” vehicle can transmit digital TV signals in both directions via satellite at a speed of 20 to 100 km/h, ensuring that the moving carrier can carry out uninterrupted broadband multimedia satellite communications during movement.

“Satcom on the move” has the following advantages in live broadcasting:

(1) During the relay process, the satellite is tracked in an autonomous tracking manner, making full use of the characteristics of satellite communication, such as large coverage area, strong anti-interference ability and stable line, to achieve point-to-point , point-to-multipoint and point-to-master station mobile satellite communications;

(2) The “Satcom on the move” vehicle has the characteristics of flexible and mobile broadcasting, which can ensure fast and real-time static and dynamic live broadcasting;

(3) The automatic recapture time is short, and communication can be quickly restored after leaving the communication blind area;

(4) Compared with OFDM “directionless” mobile microwave equipment, the “mobile communication” vehicle does not require the operators of the receiving and transmitting equipment to work in harsh environmental conditions, saving manpower and material resources, and reducing electromagnetic radiation pollution;

(5) The number of nodes in the signal transmission process is reduced, which improves the quality and reliability of the transmission;

(6) It can reduce the operating cost of live broadcasting of large-scale and complex scenes.

However, due to the limitations of current technology, “Satcom on the move” still has some shortcomings, mainly:

(1) In the case of complex broadcasting environment (too many or too high buildings, bridges, mountainous areas, etc.), signal interruption may occur;

(2) Using two “mobile communication” vehicles to transmit different television image signals makes it difficult to achieve a flash-free connection when the images are broadcast (the two vehicles encounter flash points at the same time);

(3) Signal transmission between the “mobile communication” vehicle and the mobile signal collection vehicle is difficult (the directions and positions of the two vehicles are constantly changing).