# Structured Urban Airspace Capacity Analysis: Four Drone Delivery Cases
###### Abstract  
A route network-based urban airspace is one of the initial operational concepts of managing the high-density very low-level (VLL) urban airspace for unmanned aircraft system (UAS) traffic management (UTM). For the conceptual urban airspace, it is necessary to perform a quantitative analysis of urban airspace to stakeholders for designing rules and regulations. This study aims to discuss the urban airspace capacity for four different operation types by applying different sequencing algorithms and comparing its results to provide insight and suggestions for different operation cases to assist airspace designers, regulators, and policymakers. Four drone delivery operation types that can be applied in the high-density VLL urban airspace are analysed using the suggested four metrics: total flight time; total flight distance; mission completion time; the number of conflicts. The metrics can be calculated from a flight planning algorithm that we proposed in our previous studies. The algorithm for multiple agents flight planning problems consists of an inner loop algorithm, which calculates each agent's flight plan, and an outer loop algorithm, which determines the arrival and departure sequences. For each operation type, we apply two different outer loops with the same inner loop to suggest an appropriate sequencing algorithm. Numerical simulation results show tendencies for each type of operation with regard to the outer loop algorithms and the number of agents, and we analyse the results in terms of airspace capacity, which could be utilised for designing structures depending on urban airspace situations and environments. We expect that this study could give some intuition and support to policymakers, urban airspace designers, and regulators. d rone delivery; flight planning algorithm; unmanned aircraft system (UAS) traffic management (UTM); graph theory; capacity analysis +
Footnote †: journal: Applied Sciences  
proposed capacity estimation approaches, which are evaluated from the human workload of air traffic controllers and pilots. These approaches are highly dependent on the subjective assessment or judgment of the air traffic controllers. However, such human-dependent airspace capacity estimation approaches are evaded and unsuitable for the UTM system which is expected to operate a large number of sUASs by a small number of people or by itself. In [21], authors presented a method to calculate air traffic conflict probabilities. The method is more scalable and robust than the previous approaches. Furthermore, the method can be applied for any arbitrary stochastic distribution under the condition that the method requires constant communication between the vehicles and cooperative operations. In [22], the authors showed that the threshold-based mathematical definition to estimate the capacity for free flight-based low-altitude airspace. The authors used two metrics to estimate the capacity: safety (total loss of flight per flight hour) and performance (percentage extension of travel distance). In [23], the authors investigated new deconfliction schemes for unmanned aerial vehicles in high-density very low-level (VLL) uncontrolled airspace, and assessed single-layered and multi-layered airspace designs. Their aim was to provide a framework for choosing resolution strategies for regulators and policymakers for the UTM system. In [13], the authors determined the situation-appropriate route network for unmanned aircraft in urban airspace. The authors suggested three different types of route networks (AirMatrix, Over Buildings, Over Roads), and showed the results of the capacity and throughput for each route network. The results were obtained by generating five two-way routes for aerial delivery missions from the supply point to five service points where the routing problem was solved with an assumption that once a sUAS occupies a segment, then any other sUASs cannot traverse the route.