The development of low-orbit satellites has attracted attention from all walks of life in recent years under the development of resources injected by international science and technology companies. Large-scale satellite galaxies, unlike past satellite communication systems, can provide broadband transmission and global connectivity services.
What is a Low-Orbit Satellite?
Artificial satellites can be classified into three types: Geostationary Earth Orbits (GEO), Medium Earth Orbits (MEO), and Low Earth Orbits (LEO) according to their orbital heights.
Low earth orbit satellites are close to the ground, and the delay of data transmission is low. In the first quarter of 2021, specific counties in the United States were used as test areas. In the actual download speed measurement, the median regional speed was 40.36 Mbps, and the highest speed area could reach 93.09 Mbps. In the performance of the network latency section, the median zone latency was 31ms, and the highest latency zone was 88ms. In the area of these experiments, the network delay provided by the general telecommunications provider is between 8ms and 47ms. The current network transmission speed and delay are close to the level of the ground mobile network in the serviced area.
In addition to lower data transmission delay, low-orbit satellites also require less energy to transmit signals than satellites in geosynchronous orbit. However, because the orbital period of low-orbit satellites is different from the rotation period of the earth, they will not stay in the sky over a specific area. More satellites need to be deployed to avoid communication interruption in specific areas. Compared with satellites in geosynchronous orbit, there are more ground station antennas to track. The satellite, and the technical problem of the ground station passing the connection from this satellite to another satellite entering the connection area at the same time as the satellite leaves the ground station.
Communication Applications of Low Orbit Satellites:
In a remote and geographically complex environment, the network coverage in the area is often low. For vehicles such as airplanes and ships, the service signal is often interrupted and unstable. It is difficult to deploy infrastructure on the surface to obtain the network. If the use of a low-orbit satellite network can make up for the lack of ground network facilities. In addition to solving the problem of user networking, low-orbit satellite communication can provide networks in places where the geographical environment is not suitable for human activities, such as mountains and deserts. The application environment of IoT can extend to monitoring activities in harsh environments. Low-orbit satellite communication provides a stable communication network for remote and harsh surface environments due to its low latency and is not limited by the earth's terrain, whether it is a general civil network in remote areas, commercial shipping, and freight, as well as government or academic units. Applications such as monitoring special environments can benefit from the low-orbit satellite network complementing the lack of coverage and mobility of terrestrial networks.
The communication applications of LEO satellites mainly include:
- Traditional satellite phone and narrowband data transmission services, taking advantage of their wide coverage, can provide voice, SMS, and Internet services in areas where terrestrial communication cannot reach, such as mountains and seas. Since satellite phone services require the use of specially-designed user devices, the current main users of the related services are still corporate and government customers.
- Low-orbit satellites can provide satellite IoT services, which can be used in various vertical fields such as shipping, logistics, agriculture, energy, utilities, and construction. The satellite Internet of Things can directly receive and send data through the direct connection of the device to the satellite. It can also be used as a backhaul network for sensor data, using low-orbit satellites to transmit various data back to corporate networks, data centers, etc. for data analysis and application, such as helping companies track, monitor, and manage assets, and ensure employees. Personal safety and optimization of remote operation procedures, real-time monitoring of trucks transporting perishable goods, ensuring the safe driving of merchant ships in port, etc.
- Provide satellite broadband internet service. As the satellite communication system develops toward high frequency, at the same time High Throughput Satellite (HTS) significantly increases the bandwidth capacity through frequency reuse, which means that the bandwidth of each satellite can be greatly increased and the cost can be lower. Provide higher network performance, thereby reducing the unit transmission cost, and greatly improving the market competitiveness of satellite broadband communications. It can realize applications such as high-definition audio and video transmission, multi-party video conference, and real-time interactive map sharing.
Types and Comparisons of Artificial Satellites:
Artificial satellites can be roughly divided into high, medium, and low orbit satellites.
- The orbital period of the high-orbit satellite is synchronized with the earth, and it circles the earth in 24 hours. It mainly provides commercial communication satellites, radio, television, and auxiliary positioning systems.
- Medium-orbit satellites are commonly used in navigation.
- Low-orbit satellites are mainly used in earth observation and telephone communication, and the orbital distance is also proportional to the launch cost of the satellite and the life of the satellite. The growth potential of low-orbit satellites is the most significant.
Since the 5G signal is a high-frequency band, the shorter the wavelength, the smaller the effective coverage area. The number of small base stations must be increased to achieve its high-speed and low-latency goals. In the same area, the small base stations required for 5G will be More than ten times, and to make up for what the current network cannot cover, low-orbit satellite communication has become another solution.
Satellite Communication System Architecture and Operational Requirements Analysis:
The low-orbit satellite communication system includes the communication payload on the space side. The low-orbit satellite communication transceiver is mainly responsible for the transmission and reception of radio signals, and the signal is processed by the payload computer component so that the packets can be forwarded to different destinations. On the other hand, a user terminal is required on the ground side. The function of this device is like a network modem at home, providing Internet access services for the back-end machine. Through the gateway, the device also provides a satellite network operating system for remote management and control. The NMC (Network Management Center) will collect the information of each device and then analyze and manage it, while the NCC (Network Control Center) is responsible for the control of satellite communication resources to enable smooth radio communication between LEO satellite communication transceivers, user terminals, and gateways.
Network management requirements in low-orbit satellite communication systems:
In the low-orbit satellite communication system, many communications equipment will be included, including the payload part of the low-orbit satellite used for communication, the ground station that transmits signals and manages and controls the satellite network, and the satellite network terminal ground station. The information and health status of all equipment, and to reduce the cost of maintaining the low-orbit satellite communication network, need to centrally manage this information, so the need for network management is derived.
Control requirements in low-orbit satellite communication systems:
- Data collection, data analysis, and status monitoring:
All information about the low-orbit satellite communication system needs to be managed centrally. The network management system must at least be able to collect the raw data generated by the maintenance equipment, analyze the data to obtain available information, and the information can be monitored centrally. In the low-orbit satellite communication system, the network management can monitor whether there is any discrepancy in information, to judge the abnormal operation of the equipment, which can effectively help to make decisions, manage, and configure the equipment.
- Power management/scheduling, software/service update, event analysis/early warning capability:
In addition to basic requirements, it is necessary to further enhance network management from basic system status monitoring and fault management to power management/scheduling, software/service update, and event analysis/warning capabilities, so that the equipment in the system can achieve Automate management and reduce human intervention in monitoring and setup. The equipment is set with different events in advance, and these events are determined by the data generated by the equipment. If the event occurs, the management personnel will be notified or alerted, and necessary measures will be taken to maintain the communication system and reduce the maintenance labor cost of the low-orbit satellite communication network.
Because the wireless bandwidth, usage time, and regional communication resources of the low-orbit satellite network are relatively scarce and precious, the control requirements of the low-orbit satellite communication system mainly fall on the management and optimization of resource allocation. Since the resource management and configuration of the low-orbit satellite network is completed by the network control center of the ground station and the satellite payload, and the computing resources of the satellite payload are limited, the network control center is required to support most functions, simplifying the satellite Payload control function requirements.
At the same time, for the communication network architecture of multiple low-orbit satellites in the future, the control of the low-orbit satellite communication system needs to consider the continuous system architecture design requirements, which can be used as a development framework for subsequent payload and ground station resource management.
- The network control center cooperates with the satellite payload to complete the synchronization and login of the ground station. Session Control function requirements:
After the ground station is powered on, the synchronization of the signal is obtained through the dialogue control function, and then the signal is sent to the network control center via the satellite payload to log in to the low-orbit satellite network; after the login, the connection with the network control center must be maintained. , the network control center continuously grasps the connection status of the ground station in the low-orbit satellite network through the program of dialogue control and then can achieve the work of transmitting user data.
- The connection control function requirements of the ground station:
After a packet that is not attributed to an existing connection enters the ground station, to let the network control center know that the ground station has a new connection requirement, the ground station will need to initiate a connection control request packet to notify the network control center, the network control center needs to confirm whether the connection is acceptable, and after confirmation, it needs to respond to the confirmation result of the ground station. wireless resources.
- Resource scheduling (Radio Resource Management) functional requirements:
The core of the control requirement in the low-orbit satellite communication system is wireless resource allocation. It is necessary to calculate the resource allocation result through this function and send the information of the resource allocation result to all ground stations to inform (or control) the uplink of each ground station. Which time slots of the time to send the data. On the other hand, the computing resource allocation result also needs to reflect the Quality of Service (QoS) requirements of each connection to allocate a bandwidth configuration that meets the application requirements of the connection. At the same time, it must consider the control and management requirements of the overall satellite network operation. Bandwidth requirements to maintain the operation of the overall satellite network.
The management and control system of the low-orbit satellite communication network can improve the efficiency of network resource allocation and equipment management. In the future, the research and development results of the current network management and control system can also help manufacturers who intend to transform into system integrators to introduce network management and communication control subsystems, accelerate the process of the satellite industry from equipment foundry to system integration, and reduce transformation. development cost and time. Based on the technical energy accumulated by mobile communication, the development of B5G communication satellite technology is expected to first realize single satellite communication and then move towards galaxy communication.
Development Status and Prospects of Satellite Broadband Networking Services:
Satellite broadband networking services can be directly faced by consumers, and can provide enterprises and governments with networking needs. The consumer satellite broadband segment initially aims to provide household satellite broadband services. The follow-up will focus on the development of corporate broadband services, aviation, maritime, and other fields, hoping to replace traditional satellite communication services with high prices and low transmission speeds.
In addition to providing last-mile transmission services for homes and businesses, low-orbit satellite broadband can also be used as a mobile backhaul network to help telecom operators extend their signal coverage to remote islands and remote areas where wiring is difficult. The low-orbit satellite communication application that has recently received attention is as an emergency communication or backup communication system during disasters and wars. Because most of the main equipment of low-orbit satellite communication networks is built in space, compared with terrestrial networks such as mobile communication and wired broadband, it is less susceptible to natural disasters or man-made damage resulting in communication interruption. Therefore, it can be used as an alternative solution after the ground network is disconnected to maintain communication.
Driven by international information service providers, low-orbit satellite communication has attracted wide attention from all walks of life, but it has also been questioned by many, mainly because the establishment of galaxies by major operators has not yet been completed. Therefore, its communication performance and business models, such as transmission speed and network capacity, have not been verified in practice. Whether it can provide broadband networking services at reasonable prices in any corner of the world has been the focus of continuous attention from all walks of life. On the other hand, even if the commercial development of emerging low-orbit satellite communications is successful remains to be seen, telecommunications infrastructure is a part of national security, and it is important to have alternative networks to maintain communications in times of emergency. The low-orbit satellite communication can not only be used as an option for broadband services such as remote, mountainous, maritime, aviation, etc., but also as an emergency and backup network application potential, which also attracts all circles to pay more attention to its follow-up development.