Three-domain double-frequency low-altitude monitoring system and method

Abstract

The invention discloses a three-domain dual-frequency low-altitude monitoring system and method, and the system comprises a high-airspace monitoring module which is used for receiving flight state information broadcasted by an aircraft in a high-airspace through employing a 978MHz UAT frequency band, and transmitting information to a first aircraft in the high-airspace through employing the 978MHz UAT frequency band; the middle and low airspace monitoring module is used for receiving flight state information broadcasted by an aircraft in a middle and low airspace by adopting a 978MHz UAT frequency band, and sending information to a second aircraft in the middle and low airspace by adopting a 5GHz Remote ID frequency band; and the ultra-low-altitude domain monitoring module is used for receiving the broadcast flight state information of the aircraft in the ultra-low-altitude domain by adopting a 2.4 GHz Remote ID frequency band, and sending information to a third aircraft in the ultra-low-altitude domain by adopting the 2.4 GHz Remote ID frequency band. According to the invention, the coverage range is improved, and meanwhile, accurate target recognition is realized in a complex electromagnetic environment of a city.

Description

Technical Field

[0001] The present application relates to the field of low-altitude surveillance technology, and in particular to a three-domain dual-frequency low-altitude surveillance system and method. Background Art

[0002] With the rapid global rise of the low-altitude economy, emerging industries such as drone logistics and urban air mobility (UAM) are posing unprecedented challenges to low-altitude surveillance systems. Traditional ADS-B 1090ES-based surveillance technology, due to limited data capacity and significant multipath effects in urban areas, struggles to meet the demands for high-precision tracking in seconds or even sub-seconds in high-density airspace. Furthermore, the low-altitude electromagnetic environment is becoming increasingly complex due to spectrum penetration from 5G communications, the Industrial Internet of Things, and other services, significantly increasing the probability of signal collisions and interference.

[0003] In this context, the industry has proposed two technical paths: one is the 978MHz Universal Access Transceiver (UAT) technology led by the US FAA, which improves the robustness of aviation-specific links by optimizing frequency bands and communication protocols; the other is remote identification (Remote ID) technology based on the 2.4 / 5GHz frequency band, which aims to achieve mandatory broadcasting of drone identity and location.

[0004] However, due to issues such as poor spectrum isolation and protocol heterogeneity, these two technologies have yet to form a systematic collaborative solution, resulting in a fragmented low-altitude surveillance system. This fragmentation creates a conflict between wide-area coverage and high-precision identification, limiting the overall performance and reliability of the low-altitude surveillance system. Summary of the Invention

[0005] Based on this, in order to address the above technical problems, a three-domain dual-frequency low-altitude surveillance system and method are provided to improve the integrity and reliability of the low-altitude surveillance system.

[0006] In a first aspect, a three-domain dual-frequency low-altitude surveillance system is provided, the system comprising: a plurality of ground stations; the ground stations comprising a high-altitude surveillance module, a medium-low-altitude surveillance module, and an ultra-low-altitude surveillance module;

[0007] The high-altitude monitoring module is configured to receive flight status information broadcast by a first aircraft in the high-altitude area via the 978 MHz UAT frequency band using the 978 MHz UAT frequency band, and to send feedback or control information to the first aircraft in the high-altitude area via the 978 MHz UAT frequency band;

[0008] The mid- and low-altitude airspace monitoring module is configured to receive flight status information broadcast by a second aircraft in the mid- and low-altitude airspace via the 978 MHz UAT frequency band, and to send feedback or control information to the second aircraft in the mid- and low-altitude airspace via the 5 GHz Remote ID frequency band.

[0009] The ultra-low airspace monitoring module is used to receive flight status information broadcast by a third aircraft in the ultra-low airspace via the 2.4GHz Remote ID frequency band using the 2.4GHz Remote ID frequency band, and to send feedback or control information to the third aircraft in the ultra-low airspace using the 2.4GHz Remote ID frequency band.

[0010] In the above scheme, optionally, the system also includes: a backup frequency band module, which is used to receive flight status information broadcast by a fourth aircraft in the narrowband interference area through the 978.5-979.5MHz backup frequency band through the 978.5-979.5MHz backup frequency band when narrowband interference is detected, and use the 978.5-979.5MHz backup frequency band to send feedback or control information to the fourth aircraft in the narrowband interference area.

[0011] In the above solution, optionally, the flight status information includes: position information, altitude information, and speed information.

[0012] In the above scheme, optionally, the altitude range of the high-altitude area is 300-1000 meters, the altitude range of the medium- and low-altitude area is 50-300 meters, and the altitude range of the ultra-low-altitude area is below 50 meters.

[0013] In the above scheme, optionally, the deployment spacing of the high-altitude surveillance ground stations is 10 kilometers.

[0014] In a second aspect, a three-domain dual-frequency low-altitude surveillance method is applied to an aircraft, the method comprising:

[0015] Determine the airspace the aircraft is in based on its own altitude;

[0016] When in high altitude, the aircraft broadcasts flight status information to the high altitude monitoring module of the ground station set on the ground through the 978MHz UAT frequency band, and receives feedback or control information sent by the high altitude monitoring module of the ground station through the 978MHz UAT frequency band;

[0017] When in low and medium altitude, the aircraft broadcasts flight status information to the low and medium altitude monitoring module of the ground station set up on the ground via the 978MHz UAT frequency band, and receives feedback or control information sent by the low and medium altitude monitoring module of the ground station via the 5GHz Remote ID frequency band;

[0018] When in ultra-low airspace, the flight status information is broadcast to the ultra-low airspace monitoring module of the ground station set on the ground through 2.4GHz Remote ID, and feedback or control information sent by the ultra-low airspace monitoring module of the ground station through the 2.4GHz RemoteID frequency band is received.

[0019] This application has at least the following beneficial effects:

[0020] This application uses the flight status information broadcast by the first aircraft in high altitude through the 978MHz UAT frequency band, and the feedback or control information sent by the high altitude monitoring module to the first aircraft in high altitude through the 978MHz UAT frequency band; the flight status information broadcast by the second aircraft in medium and low altitude through the 978MHz UAT uplink, and the feedback or control information sent by the medium and low altitude monitoring module to the second aircraft in medium and low altitude through the 5GHz Remote ID frequency band; the flight status information broadcast by the third aircraft in ultra-low altitude through the 2.4GHz Remote ID frequency band, and the feedback or control information sent by the ultra-low altitude monitoring module to the third aircraft in ultra-low altitude through the 4GHz Remote ID frequency band. Since UAT focuses on high-precision tracking in urban medium and low altitudes, and Remote ID serves the fine management of dense drone groups at ultra-low altitudes, this application enables UAT and Remote ID to be implemented in a coordinated manner, so as to achieve wider coverage and high-precision identification. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A block diagram of the architecture of a three-domain dual-frequency low-altitude surveillance system provided in one embodiment of the present application;

[0022] Figure 2 A three-dimensional city modeling diagram is provided for one embodiment of the present application;

[0023] Figure 3 In one embodiment of the present application, the number of buildings over 20 meters in radius of 1 km is 30, and the frequency and intensity distribution of interference sources are shown;

[0024] Figure 4 For one embodiment of the present application, a spectrum diagram of the signal power within the 1UAT operating frequency band is provided with the UAT 978MHz frequency point as the center;

[0025] Figure 5 For one embodiment of the present application, a spectrum diagram within the UAT operating frequency band is provided when the signal power of the UAT transmitter is 10W;

[0026] Figure 6For one embodiment of the present application, a distribution diagram of interference source frequency and intensity is provided when the number of buildings over 20 meters in a 1 km range reaches 200;

[0027] Figure 7 For one embodiment of the present application, a spectrum analysis diagram of the UAT working area is provided when the signal power of the UAT transmitter is 1W and the number of buildings over 20 meters within a 1km range reaches 200;

[0028] Figure 8 For one embodiment of the present application, a diagram of the interference source frequency distribution and spectrum analysis is provided when there are 30 buildings in an urban area and an electromagnetic environment composed of 100 interference sources such as Wi-Fi base stations, industrial Internet of Things base stations, and 4G / 5G base stations.

[0029] Figure 9 For one embodiment of the present application, a spectrum analysis diagram of the UAT working area with a UAT transmitter signal power of 1W and 100 interference sources is provided;

[0030] Figure 10 A diagram showing the relationship between ADS-B UAT signal detection probability, transmission power, and distance is provided for one embodiment of the present application.

[0031] Figure 11 An embodiment of the present application provides an adaptive power control strategy diagram suitable for all low-altitude scenarios. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of this application more clear, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0033] In the description of this application: unless otherwise specified, "plurality" means two or more. The terms "first," "second," "third," etc. in this application are intended to distinguish the objects referred to and do not have any special technical connotations (for example, they should not be understood as emphasizing the degree of importance or order, etc.). Expressions such as "including," "comprising," and "having" also mean "not limited to" (certain units, components, materials, steps, etc.).

[0034] In recent years, domestic and international scholars have conducted multi-dimensional explorations of low-altitude surveillance technology. MITRE Corporation in the United States verified the signal penetration advantages of UAT in urban environments through simulation, but its research did not address interference suppression with existing avionics systems. European scholars such as Han R and Li H proposed an algorithm based on multi-agent deep reinforcement learning, but this mainly targets the optimization of drone traffic management based on cellular networks and does not cover cross-band collaboration between UAT and Remote ID. Domestic teams have made progress in low-altitude surveillance networking architectures, such as the framework for future low-altitude intelligent transportation systems proposed by Changqing Huang, but its electromagnetic compatibility analysis is limited to a single technical scenario. While these achievements have partially addressed the issue of technical isolation, they still lack in-depth discussion of core challenges such as spectrum efficiency optimization and cross-layer data fusion under the coexistence of multiple protocols.

[0035] This application aims to establish a collaborative operation mechanism for UAT and Remote ID, focusing on solving core issues such as multi-band interference suppression, continuous tracking of highly maneuverable targets, and enhancing system-level robustness. This provides a verifiable technical implementation path for typical applications such as urban logistics drone swarms and emergency rescue eVTOLs. Through ray tracing simulation, protocol stack integration, and hardware-in-the-loop verification, this paper proposes a hierarchical airspace management architecture and adaptive power control algorithm to enhance the efficiency of wide-area surveillance and peripheral identification, providing theoretical support for frequency band planning and equipment selection by airspace management departments.

[0036] The core value of this application lies in breaking through the isolated thinking of the existing technical routes, and systematically demonstrating for the first time the feasibility of collaboration between UAT and Remote ID in complex electromagnetic environments, providing key technical reserves for the transformation of my country's low-altitude economic regulatory system from "passive response" to "active adaptation".

[0037] In one embodiment, Figure 1 As shown, a three-domain dual-frequency low-altitude surveillance system is provided, the system comprising: a plurality of ground stations; the ground stations comprising a high-altitude surveillance module, a medium-low-altitude surveillance module, and an ultra-low-altitude surveillance module;

[0038] The high-altitude monitoring module is configured to receive flight status information broadcast by a first aircraft in the high-altitude area via the 978 MHz UAT frequency band using the 978 MHz UAT frequency band, and to send feedback or control information to the first aircraft in the high-altitude area via the 978 MHz UAT frequency band;

[0039] The mid- and low-altitude airspace monitoring module is configured to receive flight status information broadcast by a second aircraft in the mid- and low-altitude airspace via the 978 MHz UAT frequency band, and to send feedback or control information to the second aircraft in the mid- and low-altitude airspace via the 5 GHz Remote ID frequency band.

[0040] The ultra-low airspace monitoring module is used to receive flight status information broadcast by a third aircraft in the ultra-low airspace via the 2.4GHz Remote ID frequency band using the 2.4GHz Remote ID frequency band, and to send feedback or control information to the third aircraft in the ultra-low airspace using the 2.4GHz Remote ID frequency band.

[0041] In this embodiment, a comparison of surveillance technologies in a low-altitude electromagnetic environment is first proposed:

[0042] (1) Comparison of surveillance technologies in low-altitude electromagnetic environments:

[0043] The complexity of the low-altitude electromagnetic environment stems from the dual challenges of a highly dynamic spectrum competition landscape and physical propagation characteristics. Below 300 meters, especially in urban built-up areas, electromagnetic signals face non-line-of-sight (NLOS) propagation caused by densely populated buildings, multipath effects caused by reflections from metal structures, and co-channel interference from ground-based communication infrastructure (such as 5G base stations and Wi-Fi hotspots). The following is a comparison of three mainstream surveillance technologies: 1090ES ADS-B, UAT, and Remote ID, based on their technical principles, performance parameters, and application scenarios.

[0044] 1. Technical principles and core parameters:

[0045] As the current mainstream aviation surveillance technology, 1090MHz ADS-B (1090ES) is based on the Mode S Extended Squitter protocol and PPM modulation. Each frame transmits 112 bits of data, including a 24-bit aircraft identification code, latitude and longitude, and pressure altitude information. Its operating frequency band is fixed at 1090MHz ± 1MHz, with a channel bandwidth of 1MHz, a symbol rate of 1Mbps, and a data update rate of 1Hz. Although this technology has been globally deployed through the ICAO Annex 10 standard, its applicability in low-altitude scenarios is severely limited: the narrow 1MHz bandwidth increases the probability of signal collisions in dense airspace, severely reducing the continuity and availability of target surveillance.

[0046] To address the inherent limitations of 1090ES, the 978 MHz Universal Access Transceiver (UAT) was developed. UAT (Universal Access Transceiver) technology is one of the core data links of the Automatic Dependent Surveillance-Broadcast (ADS-B) system, designed to provide efficient surveillance and information services for general aviation. UAT uses the 978 MHz frequency band and transmits data via continuous phase frequency shift keying (CPFSK) modulation. The symbol rate is 1.0416 Mbps, the modulation index h = 0.6, and the carrier frequency is offset by ±312.5 kHz when transmitting bits 1 and 0, respectively. The UAT frame structure is strictly synchronized to Coordinated Universal Time (UTC). Each frame lasts one second and is divided into 618 time slots (approximately 1.618 ms each). Aircraft select a time slot using a random algorithm to broadcast a 272-bit fixed-length message containing information such as position and velocity. Reed-Solomon forward error correction (RS(255,249)) is used to enhance anti-interference capabilities.

[0047] Unlike aviation-specific technologies, Remote ID, as a mandatory means of drone regulation, is designed with a focus on low power consumption and wide compatibility. According to the ASTM F3411-22a standard, Remote ID supports two transmission modes: the broadcast mode uses the 2.4GHz ISM band or the 5GHz UNII band, based on the Wi-Fi 802.11n or Bluetooth 5.0 protocol, to periodically broadcast drone ID, location, and speed information with a transmission power of ≤1W[6]; the network mode forwards data to the cloud server via the cellular network (3.8-4.2GHz licensed band), and the end-to-end delay must be controlled within 2 seconds. Although the network mode can improve the horizontal accuracy to 10 meters with the help of base station positioning, its dependence on operator infrastructure limits its applicability in remote areas.

[0048] The differences in the parameters of these three technologies reflect the diverse application scenarios they address: 1090ES pursues global aviation standard uniformity, UAT focuses on enhancing robustness in complex electromagnetic environments, and Remote ID is dedicated to low-cost monitoring of consumer drones. This diverse technical approach provides a rich pool of elements for the integrated design of low-altitude surveillance systems, but also poses a significant challenge to the efficient coordination of spectrum resources.

[0049] The performance comparison of the three types of technologies is shown in Table 1 below:

[0050] Table 1

[0051]

[0052]

[0053] 2. Analysis of technical advantages and applicable scenarios:

[0054] The differentiated advantages of low-altitude surveillance technology determine the specific directionality of its application scenarios. As a global standard authorized by the International Civil Aviation Organization (ICAO), 1090ES ADS-B remains the preferred solution for high-altitude wide-area surveillance due to its wide deployment of airborne equipment and compatibility with air traffic control systems. This technology can achieve continuous track tracking within a radius of 200 kilometers under line-of-sight propagation conditions in high-altitude airspace (>3000 meters) without the need for additional modifications to existing ground station infrastructure. However, its limitations in low-altitude scenarios are significant, and the 1MHz narrowband channel is prone to message collisions in areas with dense drones. Therefore, 1090ES currently mainly serves the surveillance tasks of high-altitude, low-speed targets such as civil airliners and cargo flights, and is not suitable for surveillance in low-altitude airspace.

[0055] The technological innovation of 978MHz UAT directly targets the core pain points of the complex electromagnetic environment at low altitudes. Its core technology lies in the use of the 978MHz frequency band and CPFSK modulation, with a data rate of 1.0416Mbps. Combined with RS (255,249) forward error correction coding, it significantly improves the anti-interference capability and data reliability [5]. Compared with the traditional 1090ES (1090MHz extended message) technology, UAT achieves dynamic allocation of 7200 time slots per second through the time division multiple access (TDMA) architecture, supports aircraft to broadcast information such as position, speed, and identification code in random access time slots, and is compatible with ground stations to push enhanced services such as meteorological (FIS-B) and traffic (TIS-B) to aircraft, forming a "ground-air" and "air-ground" two-way data interaction. This feature gives it a significant advantage in low-altitude high-density surveillance scenarios.

[0056] The technical positioning of Remote ID is very different from the traditional aviation surveillance system. As a regulatory tool for consumer drones, its design philosophy emphasizes low cost and mandatory universality. The broadcast mode uses the 2.4GHz ISM band and utilizes the existing Wi-Fi / Bluetooth hardware ecosystem to control the cost of a single module to less than US$20, which is much lower than the US$500 cost of UAT equipment. This enables the technology to meet the economic requirements of regulatory agencies such as the FAA for large-scale drone registration and management. However, the spectrum congestion problem caused by the open frequency band seriously restricts its performance: according to the non-line-of-sight (NLOS) propagation characteristics in urban areas, multipath effects and obstacle penetration losses can cause the distance to be reduced by 6-10 times[7]. In actual measurements in urban environments, the maximum transmission distance of consumer drones is about 1.3 kilometers[8], which is much lower than the theoretical 5 kilometers. Therefore, the core application scenarios of Remote ID are limited to ultra-low altitude (<50 meters) and small areas, such as electronic fence control of drone take-off and landing stations, or identity recognition during dense formation flight. It is worth noting that its network model achieves wide-area coverage through cellular links, but its reliance on operator base stations limits its availability in remote areas or emergency scenarios.

[0057] The complementary advantages of these three technologies provide the theoretical basis for the layered design of the low-altitude surveillance system: the 1090ES will continue to provide basic high-altitude, wide-area surveillance, the UAT will focus on high-precision tracking at low and medium altitudes in cities, and Remote ID will serve the precise management of dense drone swarms at ultra-low altitudes. This coordinated evolution of technological approaches marks a paradigm shift in low-altitude surveillance from a single technology-driven approach to a multimodal approach.

[0058] (2) UAT and Remote ID collaborative operation mechanism:

[0059] Therefore, the multi-system integration of the low-altitude surveillance system proposed in this application must first solve the problem of airspace hierarchical management. In view of the differences in aircraft altitude and motion characteristics, this paper proposes a "three-domain dual-frequency" collaborative architecture, such as Figure 2 As shown:

[0060] High-altitude airspace (300-1000 meters): Dominated by the UAT band, the 978MHz band leverages its wide coverage to monitor medium- and high-speed targets such as general aviation aircraft and cargo drones. The update rate is maintained at 1Hz to meet route tracking requirements. Ground station spacing is extended to 10 kilometers, and narrowband bandpass filters are used to suppress environmental interference. Power is dynamically adjusted from 5 to 10W, automatically optimized based on airspace density.

[0061] Low- to medium-altitude airspace (50-300 meters): UAT and Remote ID operate in a hybrid configuration, utilizing frequency division duplexing (FDD). The UAT uplink (ground to aircraft) uses 978 MHz, while the downlink (aircraft to ground) reuses Remote ID's 5 GHz frequency band to avoid co-channel interference. This layer focuses on addressing signal blind spots in urban canyons, leveraging reflective surfaces on buildings to create virtual multiple-input multiple-output (VMIMO) channels. Tests have shown that this can improve link budget by 3-5 dB.

[0062] Ultra-low airspace (<50 meters): Exclusively used by Remote ID, this technology leverages 802.11ax (Wi-Fi 6) OFDMA technology to enable high-density drone swarm management. A single access point (AP) can simultaneously serve 150 drones with latency under 10ms. To avoid harmonic interference with UAT, the 2.4 GHz frequency band is mandatory.

[0063] (3) Data fusion and effectiveness verification:

[0064] To verify the effectiveness of the collaborative mechanism, a simulation of a simultaneous UAT / Remote ID dual-band operation scenario in an urban environment was conducted. After generating a simulation model of urban buildings, ray tracing calculations were performed on 978MHz and 5GHz signals, simulating diffraction and reflection paths in complex terrain. Interference from urban industrial frequency bands and 4G / 5G base station frequency bands was also introduced. The UAT operating spectrum was analyzed to determine the relationship between signal power strength and propagation distance.

[0065] Simulation scenario setting: The base station is usually erected at a height of 20 meters. To simulate a general urban scenario, 30 buildings over 20 meters high are set within a radius of 1 km. At the same time, a drone equipped with a UAT transmitter is set to send signals at a power of 1W and a frequency of 1Hz. On this basis, an electromagnetic environment consisting of 40 Wi-Fi base stations, industrial IoT base stations, 4G / 5G base stations and other interference sources is constructed. The frequency distribution of the interference sources and the UAT working spectrum are as follows: Figure 2 and Figure 3 shown.

[0066] It can be seen that due to factors such as third-order intermodulation, transmitter spectrum leakage, and operating frequency, there are 14 interference signals in the ±10MHz bandwidth with the UAT 978MHz frequency as the center frequency, and more than 5 of the interference signals are of high intensity. Figure 4 shown.

[0067] The power spectrum density fluctuates significantly across the entire frequency range. Near the UAT operating frequency band (978 MHz), the power spectrum density is higher, indicating a stronger signal strength within this frequency band.

[0068] In the same scenario, when the signal power of the UAT transmitter is increased from 1W to 10W, the spectrum in the UAT working frequency band is as follows: Figure 5 .

[0069] At this time, the signal power within the UAT working frequency band (978MHz±2MHz) is significantly increased, and the signal-to-noise ratio is significantly improved.

[0070] When the scene moves further to the city center, the number of high-rise buildings increases significantly. When the number of buildings over 20 meters high within a 1km range reaches 200, the frequency distribution of the interference source and the UAT working spectrum are as follows: Figure 6 shown.

[0071] The simulation results show that the multipath and fading effects caused by the further increase in the number of buildings do not change much. When the number of interference sources is effectively controlled, the UAT frequency band spectrum in the urban area and city center area will not change significantly.

[0072] Furthermore, in the urban area (30 buildings), when constructing an electromagnetic environment composed of 100 WIFI base stations, industrial Internet of Things base stations, 4G / 5G base stations and other interference sources, the frequency distribution and spectrum analysis of the interference sources are as follows: Figure 7 and Figure 8 .

[0073] It can be seen that the number of interference signals in the range of 978MHz±10MHz has increased to 27. However, the spectrum within the UAT operating bandwidth is relatively clean. At the same time, the spectrum energy near 960MHz is relatively high. It is necessary to carefully design the base station filter to ensure that the impact of out-of-band signals is isolated in the engineering implementation.

[0074] In summary, the introduction of the UAT working frequency band is an excellent means of low-altitude surveillance in complex urban electromagnetic environments. Its wavelength has good penetration into buildings. At the same time, this frequency point belongs to the ICAO's clear aviation surveillance band standard and naturally has a relatively pure spectrum in the urban background. It is a good supplement for the monitoring of aircraft such as drone logistics and eVTOL in future low-altitude economic scenarios.

[0075] In the above-mentioned three-domain dual-frequency low-altitude surveillance system, the flight status information broadcast by the first aircraft in the high altitude domain through the 978MHz UAT frequency band, and the high altitude domain surveillance module sends feedback or control information to the first aircraft in the high altitude domain through the 978MHz UAT frequency band; the flight status information broadcast by the second aircraft in the medium and low altitude domain through the 978MHz UAT uplink, and the medium and low altitude domain surveillance module sends feedback or control information to the second aircraft in the medium and low altitude domain through the 5GHz Remote ID frequency band; the flight status information broadcast by the third aircraft in the ultra-low altitude domain through the 2.4GHz Remote ID frequency band, and the feedback or control information is sent to the third aircraft in the ultra-low altitude through the ultra-low altitude surveillance module through the 4GHz Remote ID frequency band. Since UAT focuses on high-precision tracking in the medium and low altitude of the city, and Remote ID serves the fine management of dense drone groups at ultra-low altitude, this application enables UAT and Remote ID to be implemented in a coordinated manner, so as to achieve wider coverage and high-precision identification.

[0076] In one embodiment, the system further includes: a backup frequency band module, which is used to receive flight status information broadcast by a fourth aircraft in the narrowband interference area through the 978.5-979.5 MHz backup frequency band through the 978.5-979.5 MHz backup frequency band when narrowband interference is detected, and to use the 978.5-979.5 MHz backup frequency band to send feedback or control information to the fourth aircraft in the narrowband interference area.

[0077] In one embodiment, the flight status information includes: position information, altitude information, and speed information.

[0078] In one embodiment, the altitude range of the high-altitude area is 300-1000 meters, the altitude range of the medium-low-altitude area is 50-300 meters, and the altitude range of the ultra-low-altitude area is below 50 meters.

[0079] In one embodiment, the ground stations are deployed at a distance of 10 kilometers.

[0080] In one embodiment, when the high-altitude monitoring module receives flight status information broadcast by a first aircraft in the high-altitude area through the 978 MHz UAT frequency band, when the first aircraft is in a cruising phase, the power of the 978 MHz UAT frequency band of the first aircraft is 10 W;

[0081] When the ultra-low airspace monitoring module receives the flight status information broadcast by the third aircraft in the ultra-low airspace through the 2.4GHzRemote ID, if the third aircraft is in the take-off and landing phase, the 2.4GHzRemote ID of the first aircraft is 2W.

[0082] In this embodiment, based on the good spectral characteristics of the ADS-B UAT system signal, the relationship between signal power and transmission distance in an urban environment can be further analyzed. In this environmental simulation model, the Hata city model is introduced as a propagation model for UAT signals. This model is designed for macrocellular scenarios and is particularly suitable for predicting the path loss between base stations and mobile terminals in urban environments. The model simplifies the complex calculation of radio wave propagation loss through the following mathematical formula, which is very suitable for link propagation evaluation in the field of drone communications in urban environments.

[0083] The basic formula of the Hata model is as follows:

[0084] PL=69.55+26.16log 10 (f)-13.82log 20 (h b )-a(h m )+[44.9-6.55log 10 (h b )log 10 (d)(1)

[0085] Where PL is the path loss, f is the operating frequency, hb is the base station antenna height, hm is the UAV platform antenna height, and a(h m ) is the UAV platform height correction factor, and d is the signal propagation distance.

[0086] The environmental simulation model also incorporates a constant false alarm rate (CFAR) model to assess signal reception. The core concept of the CFAR model is to dynamically estimate local noise power and adaptively adjust the detection threshold. This allows it to accurately simulate the spatial heterogeneity and temporal nonstationarity of noise power in real environments, such as variations in clutter intensity caused by building reflections in urban environments or the rise in noise bases caused by sudden industrial interference.

[0087]

[0088] Where n is Gaussian white noise and s is the target signal.

[0089] On this basis, the false alarm probability Pfa is defined as the probability of misjudging H1 under H0:

[0090] P fa =P r(|x| 2 >T|H0) (3)

[0091] For Gaussian noise, the false alarm probability is:

[0092]

[0093] Where Q(.) is the Gaussian Q function:

[0094]

[0095] Finally, the relationship between the detection probability of ADS-B UAT signal and the transmission power and distance is obtained, as shown in Figure 10 As shown in the figure, when the signal detection probability reaches 90%, the effective range increases with increasing transmit power. When the ADS-B UAT signal strength is 1W, the propagation distance in the Hata metropolitan model is 2.5 kilometers. When the transmit power is increased to 10W, the effective propagation distance is 5 kilometers, which is significantly shorter than the traditional free-space propagation model. This result closely reflects the real-world environment, considering the influence of various buildings on the propagation path and the spectrum pollution caused by various industrial noises in metropolitan environments.

[0096] Combined with the simulation results, Figure 11 In response to the communication needs of UAVs in different mission scenarios, the power-frequency band joint optimization strategy proposed in this paper can significantly improve system reliability and energy efficiency by dynamically adjusting the transmission parameters.

[0097] During the cruise phase, the UAT transmit power is set to 10W, ensuring both 100km line-of-sight coverage and 5km penetration in densely populated urban areas. The Remote ID module is also disabled to reduce overall energy consumption, addressing the issue of excessive power consumption during long-duration missions.

[0098] During takeoff and landing, the UAT mode is turned off to avoid near-field signal saturation, and the Remote ID power is increased to 2W, enhancing the ability to penetrate buildings and terrain obstructions in the ultra-low altitude range of 30-500 meters, ensuring recognition reliability in complex environments around airports.

[0099] In response to sudden interference scenarios, the system can autonomously switch to the 978.5-979.5MHz backup frequency band and dynamically increase power to maintain signal continuity in narrowband interference or electromagnetic suppression environments.

[0100] This multi-mode adaptive mechanism enables the drone to achieve a balance between coverage capability, energy consumption control and anti-interference performance. It is particularly suitable for high-dynamic scenarios such as urban logistics and border patrols that require frequent switching of flight states.

[0101] This application establishes a collaborative mechanism for UAT and Remote ID, providing a theoretical framework and practical path for resolving the conflict between wide-area coverage and high-precision identification in low-altitude surveillance systems. This study conducted spectrum analysis on the urbanized simulation model of the UAT 978MHz signal, confirming the feasibility of collaborative UAT and Remote ID. A joint simulation based on the Hata model and a constant false alarm rate (CFAR) detection algorithm demonstrated that, in the complex electromagnetic environment of urban environments, the UAT 978MHz signal can dynamically optimize its effective surveillance range with a 90% detection probability by adjusting its transmit power. The design of a hierarchical airspace management strategy reveals the complementary advantages of different frequency bands: UAT leverages its L-band diffraction capabilities to maintain continuous tracking in airspace above 300 meters, while Remote ID, relying on multi-node networking technology of 4G / 5G base stations, achieves millisecond-level latency control for multi-UAV status monitoring at ultra-low altitudes below 50 meters. The two technologies work together to significantly improve system-level surveillance efficiency.

[0102] In one embodiment, a three-domain dual-frequency low-altitude surveillance method is applied to an aircraft, the method comprising:

[0103] Determine the airspace in which the aircraft is located based on its own altitude;

[0104] When in high altitude, the aircraft broadcasts flight status information to the high altitude monitoring module of the ground station set on the ground through the 978MHz UAT frequency band, and receives feedback or control information sent by the high altitude monitoring module of the ground station through the 978MHz UAT frequency band;

[0105] When in low and medium altitude, the aircraft broadcasts flight status information to the low and medium altitude monitoring module of the ground station set up on the ground via the 978MHz UAT frequency band, and receives feedback or control information sent by the low and medium altitude monitoring module of the ground station via the 5GHz Remote ID frequency band;

[0106] When in ultra-low airspace, the flight status information is broadcast to the ultra-low airspace monitoring module of the ground station set on the ground through 2.4GHz Remote ID, and feedback or control information sent by the ultra-low airspace monitoring module of the ground station through the 2.4GHz RemoteID frequency band is received.

[0107] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0108] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A three-domain dual-frequency low-altitude surveillance system, characterized by: The system includes: multiple ground stations; the ground stations include a high-altitude monitoring module, a medium-low-altitude monitoring module, and an ultra-low-altitude monitoring module; The high-altitude monitoring module is configured to receive flight status information broadcasted by a first aircraft in the high-altitude area via the 978 MHz UAT frequency band using the 978 MHz UAT frequency band, and to send feedback or control information to the first aircraft in the high-altitude area via the 978 MHz UAT frequency band; The mid- and low-altitude airspace monitoring module is configured to receive flight status information broadcast by a second aircraft in the mid- and low-altitude airspace via the 978 MHz UAT frequency band, and to send feedback or control information to the second aircraft in the mid- and low-altitude airspace via the 5 GHz Remote ID frequency band. The ultra-low airspace monitoring module is used to receive flight status information broadcast by a third aircraft in the ultra-low airspace via the 2.4GHz Remote ID frequency band using the 2.4GHz Remote ID frequency band, and to send feedback or control information to the third aircraft in the ultra-low airspace using the 2.4GHz Remote ID frequency band.

2. The three-domain dual-frequency low-altitude surveillance system according to claim 1 is characterized in that: The system also includes: a backup frequency band module, which is used to receive flight status information broadcast by a fourth aircraft in the narrowband interference area through the 978.5-979.5 MHz backup frequency band through the 978.5-979.5 MHz backup frequency band when narrowband interference is detected, and to use the 978.5-979.5 MHz backup frequency band to send feedback or control information to the fourth aircraft in the narrowband interference area.

3. The three-domain dual-frequency low-altitude surveillance system according to claim 1 is characterized in that: The flight status information includes: position information, altitude information, and speed information.

4. The three-domain dual-frequency low-altitude surveillance system according to claim 1 is characterized in that: The altitude range of the high-altitude area is 300-1000 meters, the altitude range of the medium- and low-altitude area is 50-300 meters, and the altitude range of the ultra-low-altitude area is below 50 meters.

5. The three-domain dual-frequency low-altitude surveillance system according to claim 1 is characterized in that: The ground station deployment spacing is 10 kilometers.

6. A three-domain dual-frequency low-altitude surveillance method, characterized in that: Applied to an aircraft, the method comprises: Determine the airspace in which the aircraft is located based on its own altitude; When in high altitude, the aircraft broadcasts flight status information to the high altitude monitoring module of the ground station set on the ground through the 978MHz UAT frequency band, and receives feedback or control information sent by the high altitude monitoring module of the ground station through the 978MHz UAT frequency band; When in low and medium altitude, the aircraft broadcasts flight status information to the low and medium altitude monitoring module of the ground station set up on the ground via the 978MHz UAT frequency band, and receives feedback or control information sent by the low and medium altitude monitoring module of the ground station via the 5GHz Remote ID frequency band; When in ultra-low airspace, the flight status information is broadcast to the ultra-low airspace monitoring module of the ground station set on the ground through 2.4GHz Remote ID, and feedback or control information sent by the ultra-low airspace monitoring module of the ground station through the 2.4GHz Remote ID frequency band is received.

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