System-Level Analysis of the Directional Radar Coverage for UAV Localization in Dynamic Swarms

Numerous mission-critical unmanned aerial vehicle (UAV) operations, such as rescue and surveillance missions, are conducted in areas lacking access to external infrastructure providing precise positioning information. To enhance situational awareness in such scenarios, millimeter wave (mmWave, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{30}-\text{300}$</tex-math></inline-formula> GHz) and subterahertz (sub-THz, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\text{100}-\text{300}$</tex-math></inline-formula> GHz) range or Doppler radars promising large resolution can be employed. However, the small antenna apertures in these bands naturally call for the use of massive antenna arrays to achieve reasonable detection distances. By employing directional antenna arrays, these radars need to exhaustively scan the surroundings to ensure situational awareness of a UAV in a swarm. The aim of this article is to characterize the system-level performance of mmWave/sub-THz range and Doppler radars as a function of system parameters by accounting for the propagation specifics of the considered bands. To this aim, we combine the tools of stochastic geometry and antenna simulations to determine the optimal half-power beamwidth that minimizes the full scanning time while maximizing the detection probability of all UAVs in a swarm. Our results demonstrate that both types of radars are characterized by qualitatively similar performance. Detection performance is highly sensitive to both UAV density and coverage radius, as the increase in these parameters leads to an abrupt drop in the detection performance. At small distances, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\leq\!\text{50}$</tex-math></inline-formula> m, antenna arrays with a smaller number of elements result in the best tradeoff between scanning time and detection probability. Specifically, both types of radars provide perfect knowledge of the surroundings (with detection probability higher than 0.99) within a 50-m radius with a scanning time of less than 1 ms. At greater distances, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\geq\! \text{100}$</tex-math></inline-formula> m, the only option to improve performance is a drastic increase in the emitted power or receiver sensitivity.