# Drone-Based Parcel Delivery Using the Rooftops of City Buildings: Model and Solution
## 2 Related Works  
### Urban Logistics  
There are many definitions of urban logistics, but common to each of them is finding efficient and effective ways to transport goods in urban areas while taking into account the negative effects on congestion, safety, and environment. As mentioned above, the trends of growing e-commerce and urbanization have led to an increasing number of transport activities in cities. To make our approach more relevant for practical urban applications, concentration is shifted on the optimization and operational perspective of last-mile delivery. Within the supply chain of goods, the last mile represents the final and most expensive section of the transport chain [12]. Today, trucks and light commercial vehicles perform the majority of urban logistic activities. However, different strategies and concepts are likely to be needed to improve the efficiency and effectiveness of last-mile delivery in general. It is believed that the problem of last-mile delivery can be addressed in innovative ways thanks to the development of information and communication technologies (ICTs) and environmentally-friendly vehicles. Therefore, many studies with several approaches for urban logistics (e.g., parcel lockers, crowdsourcing, food delivery, and electric vehicles) have been published. [PERSON] et al. [13] focused on the analysis of the usability and efficiency of parcel locker logistics in a case study of a Polish company. They showed that the most important factor for efficiency in this kind of solution is the location of the machines. Then, [PERSON] and [PERSON] [14] considered designing a parcel locker network as a solution to the last-mile problem in logistics. They formulated a 0-1 integer linear program to solve the problem and applied it to an industrial-sized network. In their model, the optimal number of locations and the optimal size of the parcel lockers were addressed. [PERSON] et al. [15] investigated peoples' motivation to participate in crowdsourced delivery. It was found that using friends in a social network to assist in last-mile delivery greatly reduced delivery costs and total emissions while ensuring fast and reliable delivery. [PERSON] et al. [16] considered urban parcel deliveries where trucks serve a network of transshipment points and crowdshippers perform the last-mile deliveries from those points to the customers. Here, crowdshippers are neither restricted by existing trips nor by an upper bound on detouring. Instead, they place bids on delivery jobs. The authors developed a tailored tabu search-based algorithm to solve the system design problem. [PERSON] and [PERSON] (2017) addressed an open multidepot vehicle routing problem (VRP) for distributing fresh meat from depots to customers located in an area of the city of Athens. To solve the problem, a new stochastic meta-heuristic search algorithm termed the list-based threshold accepting algorithm was proposed. [PERSON] and [PERSON] (2018) also solved the food delivery problem in metropolitan cities. Generally, the problems of last-mile route planning for cold-chain distribution can be modeled as a VRP with time windows, which considers the costs involved in cold-chain logistics and the characteristics of temperature-sensitive products. The authors developed a nonlinear mathematical model and a heuristic algorithm to generate efficient vehicle routings with the objective of maximizing the total level of customer satisfaction, which is dependent on the freshness of delivered food products. In addition, there have been some studies that considered adopting electric vehicles to urban logistics and assessed the environmental effects. [PERSON] et al. (2019) proposed green vehicle distribution in a public transportation network. The problem was defined as one of nonlinear optimization requiring neuro-fuzzy logic. They tested their solution on a part of the public transport system in central Belgrade, Serbia. [PERSON] et al.