China Unicom Research Institute conscientiously implement the national strategic plan, bear the service level of science and technology self-reliance and self-improvement of the mission of the times, since 2017 to set up a professional drone team and actively carry out the systematic innovation of the network connection drone industry, the first in the industry to put forward the "end, network, industry, management," a four-in-one network connection drone solutions. Recently, the team's latest research result, the "End, Network, Industry, and Management", was published. Recently, the team's latest research result "Key Issues of 5G Networked UAV System Application" was published in the journal "Communication Information Technology". The article discusses three aspects of low altitude network optimization, system network transformation and system security construction, and gives corresponding solutions around potential security issues such as navigation systems, flight control signals, and communication links affecting the application of the 5G networked UAV system, which can ensure the effective and efficient application of the 5G networked UAV system. Net-connected UAS applications are effectively realized.
The following is the full text of the article:
Introduction.
As, the concept of low altitude economy is written into the national plan for the first time [1], the low altitude application market it pulls is growing at a rate visible to the naked eye and is gradually moving towards the stage of high-quality development. UAV is an important carrier of new technology and advanced productivity, has become a strategic opportunity for intensive innovation and high-speed growth of the low-altitude economy industry [2], thanks to the system has unmanned, intelligent, safe, efficient and other significant advantages, the front to the vertical field of continuous penetration, and thus create a "drone + industry applications" of the new digital governance The model of digital governance. However, while UAV applications have good development prospects, there are also pain points such as difficult supervision and backward measurement and control technologies, which have never led to real commercial scale. The existing UAS consists of a flight platform (drone) and a ground control station, and the flight platform is selectively paired with relevant functional payloads for different tasks, such as optical pods, shouting devices, and special operational equipment (fire extinguishers, water samplers, etc.). Within this system, communication and data interaction is limited to between the UAV and the ground control station. In terms of supervision, the data and information generated by the system are scattered within each of the aforementioned UAS, creating great difficulties for centralized management. In terms of measurement and control, the system adopts point-to-point communication, which is limited by the limited radio transmission power of the equipment and the problem of keeping the visual communication environment unobstructed, so that the effective distance range cannot meet the demands of diversified industries.
Based on this, there is an urgent need to revolutionize the inherent application limitations of the existing UAS by technological means. 5G network has the advantages of ultra-high bandwidth, millisecond latency, and ultra-high-density links, etc. [3], and since its commercialization to date, it has rapidly conquered many fields that are looking for a favorable grip for innovation and transformation, and the application of the UAV industry is one of them.
5G network-connected UAV, as the name suggests, is an unmanned aircraft that is remotely or programmatically controlled by using 5G network [4], which is based on the existing UAV system, and through the transformation and replacement, replaces the original point-to-point communication link with the 5G communication link, and at the same time further integrates all the functions of the ground control station into the cloud platform, so as to solve the core pain-point problem of limited measurement and control distance and isolated data islands, and to reduce professional personnel input and enhance the system. It reduces the input of professionals, improves the intelligent unmanned level of the system, contributes to the integration of industry, and empowers a wide range of industry application needs.
However, if 5G network-connected UAVs want to achieve the above application results, they still need to make substantial breakthroughs in the following key aspects. First, the most significant feature of 5G network-connected UAVs is the use of 5G communication links to realize UAV network access, and thus the signal quality of the low-altitude network determines the reliability of 5G network-connected UAV system applications. It can be said that the construction, planning and optimization of the low altitude network is a prerequisite for the implementation of 5G network-connected UAVs. Secondly, how UAS can be transformed for 5G network connectivity and how the transformed system can be widely applied to more scenarios will be an important issue affecting the effective application of 5G network-connected UAVs. Finally, the frequent occurrence of UAV "black flight" events [5], for the safety of 5G network connected UAS need to focus on the argumentation, on the one hand, combined with the differences in the requirements of industry applications, on the other hand, the need to take into account the application of the implementation of the risk of avoidance.
1. Low-altitude network problem analysis and recommendations
The main difference between low altitude network and terrestrial network exists for the terrestrial network in the process of wireless signal propagation blocking more, interference, and low altitude network due to the relative purity of the airspace, line-of-sight propagation, resulting in low altitude network signals are more messy, and at the same time there is due to the kilometers away from the base station through the atmospheric waveguide [6] and the interference coverage across a number of cells, resulting in the low altitude network network network environment more complex and difficult to handle.
1.1 Actual flight test situation of low altitude network
Aiming at the uncertainty of the low altitude network environment, an area of 31.38km2 in Changde, Hunan Province is selected for the actual flight test, and the frequency bands and bandwidths are 5GN1 20/40MHz, 4G B3 20MHz, 4G B1 20MHz, and 4G B810MHz.A multi-rotor UAV mounted with a self-developed onboard terminal is used for the in-flight data collection, and the data of the low altitude network is analyzed in the flight by means of the collected log files. The low altitude network data in flight is analyzed through the collected log files, and the overall situation of the flight test is shown in Table 1.
The following main conclusions can be drawn through the test:
1) Although the antenna of the base station is downward sloping, because the free space propagation conditions make up for the reduction of the antenna gain, the terminal can still receive a fairly strong signal at a height of 200m~300m under the premise of a suitable horizontal distance from the site;
2) Limited by the fact that there are fewer 5G cells compared to 4G cells, and because the 5G frequency band is significantly higher than the 4G frequency band resulting in the coverage of 5G cells being significantly weaker than the coverage of 4G cells;
3) Lower SINR (Signal to Interference plus Noise Ratio, which describes the ratio of the received signal strength to the interfering signals in reception, one of the important parameters for expressing link quality) was observed simultaneously in the low altitude network environment for both 5G and 4G cells compared to the ground, suggesting that, compared to the ground (i.e., signal to interference plus noise ratio, which describes the ratio of received signal strength to received interference signal), indicating that the interference is higher at the altitude of the low altitude environment used for the test compared to the ground;
4) Signals from several cells several kilometers away can be observed in the flight test log without any throughput test operational process;
5) Neither 5G to 4G switching nor at the same time 4G to 5G switching is observed in the flight test log. The terminal only re-registers to the 4G network after a radio link failure as well as a stoppage of service on the 5G cell and stays on the 4G network, making switching between the different systems more difficult in a high-speed flight. The specific performance of the uplink throughput test is shown in Table 2. The following conclusions can also be drawn from the specifics of the uplink throughput test:
1)The UL scheduling rate reaches more than 88%, which indicates that the overall volume of uplink services received by the base station during the flight test is low, even when using a commercial network for public terrestrial users;
2) The physical uplink shared channel transmit power is close to the terminal's maximum transmit power of 23dBm on both 4G and 5G, indicating that the terminal carries out nearly full power transmission during uplink services.
The RSRP at different heights of 200m and 300m are shown in Fig. 1. The following conclusions can be drawn from Fig. 1:
1)At the height of 200m and 300m, the floating range of RSRP is basically between -110~-100dBm, which can basically satisfy the channel conditions for 1080P video transmission;
2) The distribution of RSRP at 200m and 300m heights is basically the same, i.e., the height below 300m has less impact on RSRP. the SINR at 300m height is shown in Fig. 2.
As can be seen from Fig. 2, several factors such as limited BTS coverage, absence of qualified primary service cell signals, and relatively high inter-cell interference due to good free-space propagation conditions at high altitude contribute to the overall low downlink SINR, with the probability of SINR ≤ 12 dB reaching 63%.
1.2 Low Altitude Network Construction Planning Recommendations
1.2.1 Public network mode
UAVs share a ground network with ground users, which involves the following two aspects of adjustment and optimization.
1) Initial planning of base station: in order to make most of the signal energy emitted by the base station can be radiated into the UAV's flight area, and at the same time reduce the interference to the adjacent inter-cell area, when initially setting up the antenna's upward inclination angle, the half-power point of the antenna's main flap is aligned as much as possible with the edge of the coverage area, in order to achieve the optimum of the SINR, and to solve the problem of the airborne SINR difference. Meanwhile, the PRACH leading sequence Preamble is selected as a long format [7] to increase the coverage distance of the base station.
2) Adopt the mechanism of slicing or QoS independent guarantee: UAV users and ordinary ground terminal users share the ground basic service network. For drones that are carrying out services, QoS and slicing and other guarantee mechanisms can be used to differentiate QoS or slicing and other settings according to the needs of different operating scenarios of drones, dividing different latency, reliability requirements, etc., so as to separate drones' services from ordinary ground terminal users from the perspective of the logical network. At the same time, adopting the guarantee mechanism of slicing, as the slices are isolated from each other, each slice has its own logically independent network components and network resources, so that the slices do not interfere with each other, further guaranteeing the independence and security of the business processes.
1.2.2 Private network mode
In dedicated network mode [8], UAV services and ordinary ground end-users are completely isolated in physical and logical networks, and an exclusive physical network is built for users to serve specific UAV business scenarios according to demand. The dedicated network mode requires the construction of a new physical network channel covering frequency, wireless, transmission network, core network and other links, the disadvantage lies in the high investment cost, and the advantage lies in the network service exclusivity, with the highest network quality and stability guarantee, which can provide users with the best business experience.
2. 5G network-connected unmanned aircraft system realization scheme
The existing system is composed of air subsystems, ground subsystems, wireless communication subsystems and other components together. Among them, the air subsystem is the most basic and important component within the UAS, consisting of flight platforms, power units, control and navigation, mission loads and other unit modules. The ground subsystem mainly includes mission planning, control processing, data processing, integrated wireless communication and other functions. Among them, mission planning is responsible for predetermined mission content, control processing undertakes execution and interaction, and data processing is responsible for acquisition, storage and transmission. The wireless communication subsystem is the key unit to maintain the contact between the front-end and the back-end, and the transmission medium is based on radio waves. The wireless communication link is divided into uplink and downlink. The uplink is responsible for sending and receiving remote control commands from the ground station to the UAV, and the downlink is mainly responsible for sending and receiving telemetry data, load data, etc. from the UAV to the ground station [9].
The 5G network-connected UAS will replace the point-to-point communication link by incorporating the 5G communication link without destroying the synergistic relationship of the original UAV subsystems, and complete the upgrading of the overall system's unmanned intelligence.The 5G network-connected UAS is specifically realized through the reshaping of the air subsystems, the ground subsystems, and the wireless communication subsystems in the original UAS.
2.1 Net-connected transformation for UAV airborne subsystems
The network linkage transformation for the UAV air subsystem mainly focuses on the flight platform by adapting to load or embedding and integrating the airborne communication terminal with 5G network access capability, i.e., the 5G airborne network linkage communication terminal. The 5G airborne NFC terminal will be connected with the control and navigation, mission payload and other unit modules for software and hardware adaptation. Among them, the 5G airborne NFC terminal is connected to the UAV control and navigation module through hardware standard serial communication interfaces such as RS232/422/485, TTL, etc., and the former polls to obtain the corresponding flight data, and then transmits this part of the data to the back-end equipment or server with the help of the 5G communication link. At the same time, the 5G airborne NFC terminal can parse, secondary encapsulate and forward the definition and format of the UAV control and navigation module information.The 5G airborne NFC terminal and the UAV mission payload module (video transmission is the main business of the UAV application [10], take the optical pod as an example) can be connected through the hardware of the high-definition multimedia interface and the digital component serial interface, to obtain the video data generated by the UAV flight, and then transmit this part of data to the back-end equipment or server with the help of the 5G communication link to obtain real-time data. The video data generated by the UAV flight can be processed and forwarded by open source or private streaming media standards such as real-time messaging protocol (RTMP), real-time transmission protocol (RTC), secure and reliable transmission protocol (SRT), and codec standards such as high-level video coding (H.264/AVC) and high-efficiency video coding (H.265/HEVC), and can be connected by network cable such as RJ45 interface, which can be used by 5G aircrafts. It can also be connected through RJ45 and other network cable interfaces, and the 5G airborne network-connected communication terminal provides transmission link resources for the optical pods that support network data transmission, realizing the transmission of video data to the back end.
2.2 Grid-connected modification of UAV ground subsystems
The UAV ground subsystem for network modification refers to the equipment that can execute commands to the UAV and receive various types of (flight and operational) data, which is called the ground control station. The existing ground control station does not have the ability to access the network, so it needs to be retrofitted with hardware such as a network card to communicate and interact with the back-end based on the network. As shown in Figure 2, in the scenario where the airborne forward link adopts point-to-point communication, the ground control station carries out bidirectional data interaction with the UAV through the original point-to-point link, and the commands given and the data acquired are interacted with the back-end in a bidirectional way through broadband/5G/fiber optics. However, it should be noted that although this solution improves the degree of data openness of the overall system, the measurement and control distance is still maintained at the original level, which is only a compromise that cannot be fully realized by 5G network-connected UAVs (when the low-altitude network is not able to strongly support it), and it does not help to realize a highly intelligent and unmanned overall system in the true sense. On the premise that the low-altitude network can bear all the requirements of the 5G network-connected UAV, all the software functions of the ground control station can be further integrated into the cloud server, and accordingly be completely eliminated from the overall system, and the 5G airborne network-connected communication terminals integrated inside the UAV at the front end can complete the bidirectional data interactions with the back end through the 5G wireless link. Such a system breaks through the original unmanned aircraft system measurement and control distance is limited, that is, as long as there is a low-altitude network signal coverage to ensure that the 5G network connected unmanned aircraft can not be restricted by time and space for applications, such as off-site operations, and to the intelligent unmanned a big step forward, the application of the proximity no longer need to be manipulated by professionals to operate the operation.
2.3 Net connection modification for wireless communication subsystem of UAVs
In the wireless communication subsystem of UAVs, due to the adoption of point-to-point communication, there are hardware devices for digital transmission, graphic transmission, or digital-graphic transmission as a whole, and at the same time, the ground side also needs hardware devices that match with them in order to realize the bidirectional transmission of the relevant data, but it creates the situation of information islands of one UAS after another. In addition, point-to-point communication mostly adopts public unauthorized wireless point frequency band, bandwidth resources are relatively limited, in the case of the number of UAV applications concentrated in the emergence of the UAV system will bring serious mutual same-frequency communication interference problems, the same frequency band only through the use of a limited number of different frequency points staggered circumvention, the effect of the number of unmanned aircraft when the number of small is still available, but in the number of a substantial increase in the number of times, it is difficult to be sustained. In addition, due to the gradual trend of complexity in industry application scenarios, often a set of UAS operations need to take into account multiple applications. As an example, in the field of public security, when UAVs operate in the region, from the initial only shooting video images, has slowly changed to both shooting video images and emergency disposal (e.g., shouting dispersal, putting out fire bombs, etc.). This will be point to point link communication resources limited drawbacks further amplified, even when a single video image shooting task requires 4K and higher definition, stretched to the limit.
As mentioned earlier, the substitution of 5G wireless communication for the original point-to-point communication of UAVs will enable UAV communication to have more spectrum resources, and will be able to perform with greater ease when responding to the demands of complex and demanding applications. At the same time, the convergence of 5G wireless links allows drone application data to be gathered to the back-end cloud platform, where the information silos of the original system are solved, making supervision and management simple, and the value of data timeliness is further brought into play, growing into the role of an enabler for more industries.
3. Security Analysis and Countermeasures of 5G Network-connected UAV System
With the rapid development of technology in the pan-low-altitude field, UAVs, as a typical form in the pan-low-altitude economy, are widely used in agricultural plant protection, electric power patrol, urban road inspection, emergency rescue and other industrial application fields. However, while the industrial application field is expanding, the system and network security problems faced after entering various vertical fields are also becoming increasingly obvious. Traditional drones are exposing a series of security risks and regulatory loopholes in the process of large-scale use in various scenarios, and such security issues will have a certain impact on society and individuals, and need to be improved and strengthened at the technical level.
3.1 Types of UAS security risks
1) Navigation system attack. The principle of navigation information spoofing is to send false geographic location coordinates to the control system of the UAV, thus controlling the navigation system and inducing the UAV to fly to the wrong location. Since the UAV always receives GPS signals from the source with the strongest signal, the artificial GPS signals on the ground can override the real GPS signals as long as they are strong enough, thus spoofing the UAV's positioning receiver module.
2) Flight control signal hijacking. Since wireless signals are the main means of communication between the UAV and the controller, attacks on wireless signals can directly affect the normal operation of the UAV and even gain control of the UAV. Attackers use jammers to generate UAV flight control jamming signals as well as satellite positioning jamming signals, by blocking the uplink flight control channel and satellite positioning channel of the UAV, thus making it lose the flight control instructions and satellite positioning information, so that it can't fly normally, and according to the different designs of the UAV, it will have the effect of returning to the flight, landing, and crashing for the control of the UAV.
3) Communication link attack. Information security attacks such as jamming, eavesdropping and even interception and tampering against these communication links can have direct consequences on the UAV. The current major UAV ground and air communication links also generally have serious problems such as open frequency points, transparent links, and lack of confidentiality measures, which are very easy to become the target of various attack methods [11].
3.2 5G Networked UAV Security Technology Strategies
This thesis proposes several network security techniques to safeguard wireless air port confidentiality, integrity and availability mainly through 5G networks. Through RF fingerprint identification, lightweight authentication, wireless transmission encryption, signal anti-jamming and other security protection, it safeguards legitimate terminal access to the network at all levels, including the physical layer, link layer and network layer, and defends against eavesdropping, hijacking, tampering and other UAS attacks [11].
1) RF fingerprint identification. For the net-connected UAS, before the UAV terminal accesses the platform system through the communication network, it needs to carry out signal identification and authorization to ensure the legitimacy of the UAV, and the UAS can realize the authentication of the communication signal through the RF fingerprint identification technology. RF fingerprint identification technology through signal processing means, extract the collected wireless signal characteristics, establish the UAV terminal RF fingerprint library, communication between the two sides using RF fingerprint identification and detection methods, so as to realize the identification of the UAV terminal, to realize the individual identification of the radiation source equipment, to discover and block the illegal terminal connection. In recent years, the theory and practical application related to radiation source individual identification technology have been continuously improved, and the research on fingerprint feature extraction method has made great progress.
2) Lightweight authentication. Aiming at the characteristics of dynamic changes and narrow communication bandwidth of net-connected UAVs, the use of lightweight authentication protocols can realize the security authentication of UAVs and prevent the access of illegal and fake users. Lightweight authentication protocol focuses on lightweight authentication algorithms, the main purpose of which is to simplify the number of authentication interactions, the amount of interactive data, while taking into account the confidentiality, integrity and non-repudiation of the communication, and the protocol mainly realizes the functions of UAV key management and identity authentication. Lightweight authentication methods are mainly divided into centered UAV network authentication and centerless UAV network authentication, in which centered UAV network authentication is the management center to distribute keys for UAVs and provide UAV identity authentication functions; centerless UAV network authentication is the use of threshold key technology, and multiple nodes in the network are jointly involved in the generation of the key and authentication [12].
3) Wireless transmission encryption. Since a large amount of important and sensitive data are transmitted between the UAV terminal and the platform system, it is necessary to encrypt the sensitive data transmitted through the wireless network at the link layer and the network layer, including the use of the state secret SM, Zu Chongzhi algorithm, etc., to realize the end-to-end encryption between the UAV terminal and the platform system, and to ensure the confidentiality and completeness of the data transmitted in the wireless network. Important data is encrypted and transmitted to the network through encryption module or software, and the data packet is always in the encrypted state during the whole network transmission process, and the decryption module or software of platform system decrypts the data information of the opposite end and then stores them, so as to realize the security and confidentiality of data transmission in the air.
4) Signal anti-interference. At present, the research direction of UAV network anti-jamming technology at home and abroad mainly focuses on frequency hopping spread spectrum, spectrum resource allocation optimization and other aspects. Frequency hopping spread spectrum technology is mainly used to actively avoid interference attacks by quickly switching frequency carriers, and has been used for a long time to improve the anti-jamming ability of wireless communication. Spectrum resource optimization technology is to achieve anti-interference through the optimal use of available spectrum resources, using adaptive methods to achieve the optimal resource allocation effect. In addition, the "honeypot" spoofing mechanism can be utilized to improve the transmission performance of transmission pairs in the network by disguising idle nodes in the network as transmission nodes and tricking the interfering party into interfering with them [13].
4. Conclusion
In the future, with the continuous construction and completion of ground communication infrastructure and the iteration of functional technology, 5G network-connected UAS will vividly interpret the meaning of unmanned and intelligent, and the 5G network-connected capability will help UAVs to transform into a more intelligent and autonomous application system to meet the more diversified and rich industry application fields and scenarios, so that the UAV application will no longer be limited by the constraints of the threshold of professionalism, and will help the development of the low altitude economy to continue to grow. This will enable the application of UAVs to be no longer limited by the threshold of specialization, and help the low altitude economy to develop continuously. In addition, it will really step into planning and promotion, thus ushering in a brand new chapter in the high-quality development of low-altitude economy.