Satellite communications have been widely used in the emergency communications of science and technology integration in various countries around the world due to their wide coverage, no geographical restrictions, and easy deployment and expansion. They are an effective supplement and extension of the ground communication network. In the event of serious natural and social disasters, especially when the ground wired and wireless communication systems are destroyed and cannot provide normal communication services, satellite communications become the most effective or even the only means of communication. For example, the ice and snow disaster in southern my country in early 2008 was the worst in 50 years, and the Sichuan earthquake on May 12 of the same year caused serious damage to the power grid and ground communication network. Satellites have undoubtedly become the best means of communication and have played a huge role in the process of disaster rescue.

 According to the type of service, satellites can include fixed satellite services, mobile satellite services, broadcasting services and navigation and positioning services. The ITU Radio Regulations define these services as follows:

       (1) Fixed-Satellite Service (FSS)

       A radiocommunication service between earth stations at a given location using one or more satellites. The given location may be a designated fixed point or any fixed point within a designated area. In some cases, this service may also include satellite-to-satellite links used in inter-satellite services, and feeder links for other space radiocommunication services.

       (2) Mobile-Satellite Service (MSS)

       A radiocommunication service between a mobile earth station and one or more space stations, or a radiocommunication service between space stations used by the service, or a radiocommunication service between mobile earth stations using one or more space stations.

       (3) Broadcasting-Satellite Service (BSS)

       A radiocommunication service that uses space stations to send or retransmit signals for direct public reception (including individual and collective reception).

       (4) Satellite radio navigation service and satellite radio positioning service

       Satellite radionavigation service refers to the satellite radio determination service used for radio navigation. Satellite radio positioning service refers to the radio determination service used for radio positioning. Herein, satellite radionavigation service and radio positioning service are collectively referred to as satellite navigation and positioning service.

       These services have different characteristics and their application modes in science and energy integrated emergency communications are also different, as shown in the table below.

Table 1 Application modes of different satellite communication service types in emergency communications:

Business Type	Space segment	Ground users	Function	business
Satellite fixed communications services	Fixed service communications satellite	Fixed station, vehicle-mounted station, portable station	• Emergency command and dispatch: communication of command and disaster information between command centers at different levels, on-site consultation on disaster situations, etc. • Interconnection with other public networks: access to telecommunications, computer and television networks • Ground network support: replace damaged ground networks and reconstruct emergency communication networks	Video, image, data, voice
Satellite mobile communications services	Mobile business communications satellite	Fixed station, vehicle-mounted station, portable station, handheld device	• Emergency command and information collection: issuing on-site rescue orders, collecting and reporting disaster information, etc. • Interconnection with other public networks: access to telecommunications, computer and television networks • Ground network support: replacing damaged ground networks and reconstructing emergency communication networks	Video, image, data, voice
Satellite broadcasting service	Broadcast Satellite	Fixed station, mobile receiving station, handheld device	•Disaster information release: real-time release of weather forecast and warning information, etc. •Propaganda program broadcast: real-time broadcast of disaster relief and self-help comfort programs to the masses, etc.	Video, image, data, voice
Navigation and positioning services	Navigation and positioning satellite system	Fixed station, vehicle-mounted station, portable station, handheld device	• Intelligent path navigation: Realize the path navigation of disaster relief aircraft and vehicles so as to quickly reach the disaster relief site • Fixed-point rescue: In the actual disaster relief process, use satellite positioning technology to achieve accurate information point positioning and carry out effective search and rescue for missing persons in a targeted manner	Video, image, data, voice

1.1. Emergency application mode of satellite fixed service

       Satellite fixed services can be used for issuing command orders and reporting on-site disaster situations at the emergency command center and sub-centers at all levels. They can also quickly replace the ground network and restore communication capabilities after the ground public network is damaged or paralyzed.

1.2. Emergency application mode of satellite mobile service

       Satellite mobile services are widely used in emergency communications that integrate science and energy due to their outstanding advantages such as flexible networking, strong mobility, and little impact from terrain and objects. Satellite mobile services can be used for guidance and information transmission of disaster situations at all levels of emergency command centers and disaster sites, and establish intercommunication with ground networks.

1.3. Emergency application mode of satellite broadcasting service

       Satellite broadcasting service is an auxiliary service in satellite science and technology integrated emergency communications. It can be used by command centers at all levels to distribute disaster information such as weather conditions and warning information to lower levels and disaster areas, and to send self-rescue and comfort publicity programs to the general public in disaster areas.

1.4. Emergency application mode of satellite navigation and positioning service

       Satellite navigation and positioning technology can be used to achieve path navigation for disaster relief aircraft and vehicles so that they can quickly reach the disaster relief site, and through accurate information point positioning, effective search and rescue of missing persons can be carried out in a targeted manner.

       Their space segments, ground users, functions and services can be represented in the following table. These four services have their own advantages and are mutually integrated and complementary, and can play an important role in the application of emergency communication in which science and energy are integrated.

2.1 System Introduction

Generally, the satellite fusion emergency communication system consists of three parts: space segment, ground segment and user segment. The space segment can be geostationary orbit satellites and non-geostationary orbit satellites; the ground segment generally includes satellite measurement and control centers, network control centers and various gateway stations; the user segment generally includes fixed stations, mobile stations, portable stations and handheld devices. The ground segment can be connected to the public network through various gateway stations. The schematic diagram of the satellite fusion emergency communication system is shown in the figure below.

Schematic diagram of satellite science and energy integration emergency communication system

Space segment and ground segment

The space segment and ground segment are mainly based on the existing satellite communication network. At present, the satellite networks used more in my country’s science and energy integration emergency communication include VSAT communication network, satellite mobile communication system, broadband satellite communication system, navigation and positioning satellite system, etc.

VSAT Communication Network

Traditional VSAT network technology is mature, highly reliable, and flexible in design. It can achieve very high transmission rates and is the main system type in emergency satellite communications. Emergency command and management departments in many countries around the world have basically built dedicated emergency communication VSAT systems.

       In 1997, my country built a dedicated VSAT emergency satellite communication network, covering 30 provinces and cities across the country. After the split of Telecom, the VSAT National Satellite Science and Technology Integration Emergency Communication Network is jointly maintained by China Netcom (i.e. China Unicom (merged on January 6, 2009 on the basis of the former China Netcom and the former China Unicom, referred to as China Unicom)) and China Telecom. The network consists of the main control station in Beijing (network management center), the backup control station in Shanghai, 17 regional fixed stations and more than 200 VSAT mobile stations. The regional fixed station is the gateway for the entire network to enter the public network. Each mobile station has the ability to transmit two voice channels, one fax or low-speed data transmission. The entire network is dependent on the public network but calls itself a system. It is a satellite communication network that mainly provides voice services and also has data services. The main control stations, fixed stations, and mobile stations communicate with each other through satellite voice, forming a scientific and technological network. The backbone of the energy-integrated emergency communication network provides reliable guarantee for the energy-integrated emergency communication. In 2002, after the north-south split of China Telecom, according to the principle of territorial division, the 12 mobile communication bureaus of the energy-integrated emergency communication were also divided into the north and south parts, with 7 mobile bureaus assigned to China Telecom and 5 mobile communication bureaus assigned to China Netcom. The energy-integrated emergency communication network uses the Zhongwei-1 satellite, which operates in the Ka band. At present, the energy-integrated emergency communication equipment equipped by each emergency communication bureau is mainly a satellite communication vehicle, which can transmit 1 SCPC or MCPC digital video signal and receive 1 digital video signal at the same time; send and receive 2 IBS/IDR digital carriers at the same time; and use the DCME equipment system to transmit up to 480 digital voice signals.

Satellite mobile communication system

 According to the satellite orbit position, satellite mobile communication systems can be divided into geostationary orbit satellite mobile communication systems and non-geostationary orbit satellite mobile communication systems.

       The geostationary orbit satellite mobile communication systems commonly used in my country’s emergency communications include the Inmarsat maritime satellite system, and the non-geostationary orbit satellite mobile communication systems include the Iridium system and the Globalstar system.

       The main function of satellite mobile communication system in the emergency field is to serve as an access means for mobile science and technology fusion emergency communication terminals. Mobile emergency communication terminals can be various vehicle-mounted communication systems or personal communication systems. Such systems are highly mobile and need to establish communication connections with emergency command systems anytime, anywhere and under various conditions.

Broadband satellite communication system

Broadband satellite communication systems refer to various high-speed satellite communication systems that carry new broadband services. In addition to supporting all digital services previously operated on the third-generation satellites, the fourth-generation Inmarsat satellite system has also launched BGAN (Broadband Global Area Network, Global Broadband Network) services, Fleet Broadband services and Swift Broadband services for land, sea and aviation users, and can provide global mobile voice and high-speed data services at the same time. BGAN is the first mobile communication system that provides voice and broadband data to the world through handheld terminals. It can provide global users with network data transmission at a rate of up to 492kbit/s, mobile video, video conferencing, fax, email, LAN access and other services and a variety of additional functions. Inmarsat-4 is generally considered a broadband satellite communication system.

       The IPSTAR system is the first broadband satellite communication system introduced by my country and put into actual operation. The Thai IPSTAR satellite was launched in August 2005 and is located at 119.5 degrees east longitude. It is a large-capacity commercial broadband communication satellite with a total communication capacity of 45Gbps, and the capacity available for use in China is 12Gbit/so. The IPSTAR system consists of three gateway stations built in Beijing, Shanghai and Guangzhou and terminal stations throughout the country. It is an all-IP satellite communication network.

       The characteristics of IPSTAR satellite broadband service are large capacity, which can accommodate hundreds of thousands of users at most. Due to its IP-based characteristics, one terminal can provide integrated telecommunication services of voice, data and video transmission at the same time, and its weight and volume are suitable for transportation and carrying. The figure below is a schematic diagram of IPSTAR’s integrated emergency communication. Several sets of IPSTAR portable stations, IP phones, PCs, video decoders, etc. are configured at the front disaster site, and IPSTAR fixed stations, IP phones, PCs, video decoders, etc. are configured at the rear command center accordingly, so that voice, data and video services can be transmitted in real time between the front disaster site and the rear command center.

Navigation and positioning satellite system

The navigation and positioning satellite system can send real-time high-precision positioning information, provide continuous, reliable, accurate and efficient positioning services, and play an important role in emergency rescue command, disaster investigation and tracking, disaster relief material dispatch, safe transfer of disaster area personnel and search and rescue in disaster reduction and relief work. At present, the main navigation and positioning satellite systems are GPS, GLO¬NASS. Galileo satellite navigation system, and the Beidou-1 regional satellite navigation system independently developed by my country.

  The user segment generally includes fixed stations, mobile stations, portable stations and handheld devices.

       Fixed station: generally located in the emergency command and communication center to realize communication and information exchange with mobile stations and portable stations.

       Mobile station: mainly used for emergency communication in areas that cannot be covered by ground communication networks, including “communication in motion” and “communication in static”, of which “communication in static” can also be called a portable station. “Communication in motion” ensures communication and information exchange with the emergency command and communication center while on the move, and can conduct command and communication of voice, data and images while in motion. “Communication in static” is communication and information exchange with the emergency command and communication center after being set up on site.

       Portable station: Mainly used in areas that cannot be reached by vehicle-mounted stations, such as mountains and canyons. It has a high degree of system integration, is lightweight and flexible, can be carried by one person, has a user connection interface, and can provide information communications such as video, data, and voice.

       Handheld device: a satellite mobile phone that can provide voice, low-speed data and other functions.

       Commonly used satellite science and technology integration emergency communication equipment mainly includes communication earth stations, VSAT stations, satellite science and technology integration emergency communication vehicles, portable broadband terminals, satellite mobile phones, etc. Some of these devices are fixed stations, some can realize “communication in motion” and “communication in static”, and some are also portable devices. These typical satellite science and technology integration emergency communication equipment will be introduced.

3.1 Communication earth station

The communication earth station consists of antenna feeder equipment, transmitting equipment, receiving equipment, channel terminal equipment, etc.

(1) Antenna feeder equipment

       An antenna is a device that directional radiates and receives electromagnetic waves. It radiates the signal output by the transmitter to the satellite, and collects the electromagnetic waves sent by the satellite and sends them to the receiving device. The receiving/transmitting branches are mainly separated by the duplexer in the feed device.

Depending on the function of the earth station, the antenna aperture can be as large as 32m or as small as 1m or smaller. Large-aperture antennas generally require a tracking servo system to ensure that the antenna is always aimed at the satellite. Small-aperture antennas generally use manual tracking.

(2) Transmitter

       The transmitting device converts the intermediate frequency signal output by the channel terminal device into a radio frequency signal and amplifies the power of this signal to a certain value. The power amplifier can work with a single carrier or multiple carriers, and the output power can range from a few watts to several kilowatts.

       Large earth stations with large traffic usually use klystron power amplifiers with an output power of up to 3000Wo. Medium-sized earth stations often use traveling wave tube power amplifiers with a power level of 100~400W. With the development of microwave integrated circuit technology, solid-state field effect transistor amplifiers are widely used in small earth stations, with power levels ranging from 0.25 to 125W. For example, the TES earth station is a small earth station and uses two types of 10W and 20W solid-state power amplifiers.

(3) Receiving equipment

       The task of the receiving device is to first perform low-noise amplification on the extremely weak satellite relay signal received, and then convert it into an intermediate frequency signal for demodulation and other processing by the channel terminal equipment.

       Early large stations often used cold parametric amplifiers as low noise amplifiers, with noise temperatures as low as 20K; medium-sized earth stations often used room temperature parametric amplifiers as low noise amplifiers, with noise temperatures as low as 55K; small earth stations mostly used field effect transistor amplifiers, with noise temperatures ranging from 40-80K.

(4) Channel terminal equipment

      For the sending branch, the basic task of the channel terminal is to process the signal input by the user equipment (telephone, computer, fax machine, etc.) through the transmission line interface and convert it into a signal form suitable for satellite channel transmission. For the receiving branch, the opposite processing of the sending branch is performed to restore the signal sent by the receiving device into the user signal.

       The processing of user signals includes analog digital signals, source encoding/decoding, channel encoding/decoding, modulation and demodulation of intermediate frequency signals, etc. The main features of various satellite communication systems currently in existence are concentrated on the technology used by channel terminal equipment.

3.2 VSAT Small Station

VSAT small station equipment is simple, small in size, light in weight, and low in cost. It can be mounted on a vehicle or carried by one person. The networking is flexible and convenient, and a single VSAT small station can be easily connected to the network. It supports multiple communication methods, including point-to-point communication between VSAT stations, duplex communication between multiple VSAT stations, and broadcast communication from the master station to the small station. It has a large communication capacity and a long transmission distance, and is suitable for a variety of services and rates. It has high communication quality, fewer routes, fewer link links, and a low bit error rate. It can be equipped with various terminal devices and easily interconnected with other networks. It is currently the most widely used communication equipment in scientific and energy-integrated emergency communications.

        VSAT stations are generally composed of three parts: a small-diameter antenna, an outdoor unit, and an indoor unit. Most VSAT station antennas use offset feeding, and their diameters are 1.2m, 1.8m, and 2.4m in the C band. In the Ku band, the antenna diameter is even smaller, with diameters of 0.6m, 0.75m, and 1.0m. In addition to the band, the size of the antenna also depends on the transmission rate, the geographical location of the installation, and the EIRP value of the satellite transponder. The outdoor unit is often suspended on the antenna bracket, and its electronic units are sealed into an integrated component with a heat sink on the outer surface to reduce the heat caused by the power amplifier. The indoor unit is installed in a cabinet in the form of components and circuit boards. The back of the cabinet is connected to the outside by many sockets, including intermediate frequency interface sockets and data and voice interface sockets.

  VSAT small stations generally include moving stations, static stations and portable stations.

(1) VSAT small station

       The carriers of the mobile communication system include: cars, trains, airplanes, helicopters, drones and ships. One of the core issues of the mobile communication VSAT communication system is the antenna stabilization platform or antenna tracking system. Since the communication distance between it and the geostationary satellite is very long and the antenna beam is very narrow, in order to ensure that the antenna beam of the carrier is always accurately aligned with the satellite during high-speed movement, a high-performance servo tracking system is required. The “mobile communication” vehicle can generally transmit signals bidirectionally through the satellite at a speed of 20~100km/h, ensuring that the moving carrier can communicate uninterruptedly during the movement.

(2) VSAT small station

        The VSAT system works when the carrier platform is stationary. One of the differences between it and the portable station is that it does not need to be removed from the carrier platform when it is working. The antenna can be directly unfolded and pointed at the satellite to start working. Most of the existing VSAT satellite communication systems have a “one-touch” satellite pointing function, that is, the antenna can be pointed at the satellite and polarization adjusted by pressing a button.

(3) Portable VSAT station

       Portable VSAT stations are called Fly-Away satellite communication stations abroad because they can be quickly transported to the place of use by air or helicopter. This type of satellite communication station has very important practical significance for many emergency communication systems that integrate science and energy, especially the emergency communication needs caused by natural disasters such as earthquakes. my country has a vast territory and complex terrain. There are many mountainous areas and remote rural areas with very inconvenient transportation. Disasters such as earthquakes have caused the interruption of existing road traffic. When general satellite communication systems in motion and in stillness cannot enter the disaster site, small portable stations suitable for people to carry on their backs or horses can play a role.

Portable stations generally have the following features:

       1) Higher antenna efficiency and performance: Under the same EIRP requirement, the antenna aperture of the portable base station should be minimized.

       2) Light system weight and volume. The system equipment generally does not exceed 2~3 packaging boxes, and each box does not exceed 25kgo

       3) Easy to install and open, and easy to store and pack.

       4) Adapt to local natural and environmental conditions. The system should be able to work normally under windy and rainy conditions.

       5) It has multiple transmission functions and can be connected to a variety of different user terminal devices.

       6) It is power-saving and can adapt to different power supplies, including car generators, small diesel generators, and batteries. Usually portable stations have built-in lithium batteries that can provide the system with 1~2 hours of operation.

3.3 Satellite Fusion Emergency Communication Vehicle

Since satellite fusion emergency communication vehicles have good mobility and a series of advantages of satellite communication, they are widely used in science and energy fusion emergency communication and have shown great effectiveness. There are many types of satellite science and energy fusion emergency communication vehicles. From the use of bands, there are C-band satellite science and energy fusion emergency communication vehicles, Ku-band satellite science and energy fusion emergency communication vehicles, and Ka-band satellite science and energy fusion emergency communication vehicles; from the working status, there are “mobile communication” and “static communication”.

       Satellite fusion emergency communication vehicle is a vehicle that integrates satellite communication earth station equipment and various information collection and processing equipment, and has an independent power supply system and certain life support devices. It can complete the tasks of large-capacity voice, data, image and other multimedia integrated services under various emergency conditions alone or in conjunction with other vehicles.

       The satellite science and technology fusion emergency communication vehicle is generally composed of a carrier vehicle, a satellite antenna subsystem for mobile communication, a satellite communication subsystem, a private network communication dispatching subsystem, a wireless image acquisition and transmission subsystem, a video conferencing subsystem, an IP phone subsystem, computer network equipment, audio and video equipment, a central control subsystem, a power supply, an air conditioning subsystem, office and living facilities, etc. According to different needs, different vehicle models, communication equipment configurations, antenna calibers, business types and wireless access methods can be selected. Among them, the key technology of the “mobile communication” satellite science and technology fusion emergency communication vehicle can also be applied to the satellite communication systems of other moving carriers such as ships, trains, and airplanes.

       Satellite fusion emergency communication vehicles generally have functions such as command and dispatch, satellite communication, video conferencing, telephone and fax, data transmission, image acquisition, on-site office, broadcasting, on-site power supply, and comprehensive support.

4. Satellite mobile phone

Satellite mobile phones are small in size, low in power consumption, easy to use, and the entire communication network is basically not affected by ground environmental conditions. They are easy to carry or airdrop, and can be transported to the disaster site as soon as possible. Before other communication facilities are restored, they are the only channel for rescue workers and the public to contact the outside world. Therefore, in various emergencies, the first to be used are often various models of satellite mobile phones. The disadvantage of satellite mobile phones is that the call charges are relatively expensive, and the communication is greatly affected by factors such as climate and space shielding. The satellite mobile phones that are widely used in my country include maritime satellite phones, Istar phones, and Globalstar phones.

       Satellite mobile phones are generally dual-mode or multi-mode phones that can roam to other public mobile networks and have multiple functions such as calls and short messages.

5. Portable broadband terminal

With the application of broadband multimedia satellites, a type of terminal that is lighter and easier to use than portable stations has been launched on the market, providing people with voice, broadband access and other communications. Herein, it is called a portable broadband terminal. The BGAN terminal equipment of the Inmarsat-4 maritime satellite is a typical example.

       BGAN terminal equipment weighing about 1-2.5kg can provide users at almost any land location in the world with network data transmission at a rate of up to 492kbit/s, mobile video, video conferencing, fax, email, LAN access and other services and a variety of additional functions. BGAN can provide voice and broadband data services at the same time, that is, voice communication is carried out while high-speed data transmission is carried out; during data communication, data packets are transmitted in the BGANIP network in a packet switching manner through IP routers; during voice communication, voice is transmitted in a circuit switching manner through switches.

       BGAN expands the broadband data network communication capabilities based on the original maritime satellite’s portability, security and reliability. It supports both circuit switching and packet switching, and provides the following types of services:

       1) Standard IP service : users can send emails, transfer files and access the Internet, with a maximum transfer rate of up to 492kbit/s

       2) Streaming IP service : It can provide smooth live video service with a transmission rate of up to 256kbit/8, providing streaming-level service quality. Users can flexibly choose the data transmission rate according to their own applications and actual conditions: 32kbit/s, 64kbit/s, 128kbit/s, 256kbit/s. It also supports ISDNO at a rate of 64kbit/s.

       3) Voice service : Provide 4kbit/s circuit-switched voice service through a handset or headset. 

BGAN’s voice service also has enhanced services of terrestrial fixed telephone network and mobile network standards, such as voice mail, call waiting, call barring, call hold, call forwarding, etc.

       4) Other services : including text messaging, short message services between terrestrial mobile networks, roaming, use of 3G and GPRS SIM cards, prepayment and billing, etc.

       Therefore, BGAN can provide applications such as video conferencing, data image transmission, information browsing, network access, etc., and can be used for news media (real-time interview reports), mobile communications, etc. in the integration of science and energy emergency communications.