Urban Anti-UAV: Fundamentals of UAV Characteristics

To rationally construct an urban anti-UAV defense system, a clear understanding of the core composition and target characteristics of UAV systems is a primary prerequisite. The core architecture of a UAV system consists of two key parts: first, the hardware platform and supporting software of the remote controller (including the ground station system); second, the hardware platform of the UAV itself, the software system, and the integrated hardware and software module of the on-board payload. These two parts realize data interaction and command transmission through uplink and downlink bidirectional communication links. The operational effectiveness of UAVs is mainly supported by four core elements: remote control commands, image transmission, satellite navigation, and pre-set built-in programs. Therefore, targeted precision jamming and interception against the spectral characteristics of various electromagnetic signals at key links such as communication links, navigation and positioning, and mission payload transmission can effectively block information flow and significantly weaken the practical operational capabilities of UAVs.

Currently, the core target of UAV prevention and control in urban airspace is focused on "small, light, and micro" UAVs. Relying on the advantages of small size and strong concealment, such UAVs can flexibly carry out tasks such as covert reconnaissance, fixed-point surveillance, and precision strikes in complex urban environments, and can also perform tactical actions such as feint diversion, possessing significant inherent advantages in urban operations. Therefore, the effective countermeasure against "small, light, and micro" UAVs has become a core capability requirement in the construction of an urban anti-UAV operational system. According to their control mechanisms and technical characteristics, such UAVs can be subdivided into six categories, with the core technical parameters and operational characteristics of each category as follows:

1. Consumer-grade UAVs: Multi-rotor flight platforms are the mainstream. They feature low manufacturing costs and convenient market access channels, with low flight altitude, insignificant infrared radiation characteristics, and moderate flight speed. Such UAVs are highly dependent on satellite navigation signals and data transmission links. Once subjected to electromagnetic interference, they usually trigger safety protection strategies such as hovering on standby or forced landing. Although they have pre-set no-fly zone control mechanisms, these restrictions are easily technically cracked, posing the risk of modification and utilization by criminals; their communication frequency bands mostly adopt conventional frequencies of 2.4 GHz or 5.8 GHz, and the corresponding detection and control technology system is relatively mature.

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3. Fixed-wing UAVs: They rely on thrust or pull provided by power devices for flight and generate lift through fixed wings on the fuselage. They have advantages such as fast flight speed, wide operation coverage, long endurance time, and high mission efficiency. However, such UAVs have obvious limitations: high technical threshold for operation, high flight risk coefficient, relatively limited air endurance time, and high requirements for the flatness and openness of take-off sites; since they need to launch operational attacks from high altitudes in cities, their flight trajectories are easily captured by high-altitude detection equipment, resulting in low countermeasure difficulty.

4. 4G/5G UAVs: They rely on public 4G/5G communication base station networks to achieve remote control, which can break through the distance limit of traditional links, and have characteristics such as strong compatibility, large communication data transmission capacity, and long control distance. Their remote control mode greatly increases the difficulty of detecting and identifying control signals and image transmission signals, but their operational use is strictly limited by the radiation coverage of 4G/5G base stations, making it difficult to carry out high-altitude flight operations; they can exert good use efficiency in low-altitude environments below 50 m, but the communication latency is usually above 100~200 ms, which is difficult to meet the tactical needs of high-speed travel in complex urban environments.

5. WiFi UAVs: Equipped with WiFi image transmission modules, based on universal WiFi communication protocols, they can directly realize control and image preview through smart terminals such as mobile phones and tablets, with simple and convenient operation processes. With the popularization and application of 5G networks, the control accuracy and image transmission quality of WiFi UAVs have been further improved. However, limited by the technical characteristics of WiFi communication, the effective image transmission distance is mostly limited to a range of several hundred meters, and it is easily blocked by urban buildings leading to communication signal interruption. Usually, it can only be used in short-distance unobstructed line-of-sight environments.

6. UAVs equipped with special technologies: Such UAVs enhance operational capabilities by integrating dedicated technical modules, mainly including four types: satellite navigation-enhanced UAVs are equipped with GPS positioning modules, and even if the image transmission signal is lost, they can still complete the established tasks relying on the pre-set GPS track planning; inertial navigation UAVs have full-process autonomous flight control capabilities and do not need real-time control or image information interaction with the ground station, but the mission parameters need to be pre-loaded and cannot be modified during the flight; image-matching UAVs rely on pre-recorded target optical feature databases and can independently complete target search, dynamic tracking, precise locking, and strike tasks within a designated area; terrain-matching UAVs can automatically adjust flight altitude according to the terrain, usually flying at ultra-low altitudes ranging from several meters to tens of meters, and avoid radar and radio detection with the cover of ground clutter. However, in densely populated urban core areas, their use is extremely difficult due to the complexity of the environment.

Although multiple policies and regulations have been issued to regulate and control UAV flight activities in urban airspace, the phenomenon of illegal UAV flight (so-called "black flight") still persists, and sudden safety accidents such as UAV crashes, signal loss, and building collisions occur frequently. These problems not only pose severe hidden dangers to urban public security prevention and control work but also constitute a direct threat to urban core key targets, critical important areas, and major event security. Especially in the current context of escalating great power game confrontations, overlapping domestic and foreign contradictions, and frequent provocations from unstable factors in surrounding areas, once such UAVs are utilized by terrorists, hostile forces, or extreme criminals to carry out sabotage activities and create extreme air security threat incidents in key cities, it will trigger widespread social panic and adverse impacts, resulting in immeasurable casualties and property losses.