## 1 Introduction  
Recently, businesses in the logistics and transportation industry have developed rapidly. The emergence of the e-commerce industry has led to a significant revolution due to internet access to the general public as well as novel delivery methods. The volume of parcels to be delivered is predicted to be as high as 262 billion packages by the end of 2026 [1]. Customers also demand improved service in terms of delivery time and cost. Thus, it is an immense challenge for the service providers to ensure the package is being delivered to the destination as fast and as economically as possible. Furthermore, with the significant increase in the number of delivery packages, the freight costs are increasing due to the locations being widely spread throughout the city. Thus, the service providers are trying to find more effective ways to ensure better delivery service at reduced costs. For example, parcels with common destinations can be grouped to reduce transportation cost. The overall transportation of the delivery does not face any difficulties until the packages arrive near the destination. However, the unit cost per transportation increases because every package has its own unique delivery process, and the delivery costs are no longer shared. This is referred to as the \"last mile challenge\", which is encountered by many delivery service providers [2; 3; 4]. Therefore, e-commerce businesses have started exploring innovative delivery strategies to stay competitive and lower their delivery costs for customer retention and growth. An effective solution to the above-mentioned problem can be addressed by adopting an innovative autonomous drone-based delivery technique, which can mitigate the extra cost incurred by the increased delivery constraints. Such autonomous systems can provide reliable, swift, and efficient delivery services, which helps limit the last-mile transportation cost. This is particularly important in remote areas where the package delivery rate is minimal, such as small countryside cities and villages. In addition, the dispersion of delivery destinations adds to this problem. Thus, advanced techniques that consider all the practical constraints are required. The prospect of drone-based delivery has started to become a possibility for the future e-commerce, logistics industry, and integral part of smart city [5]. Reputed and well-known organizations such as Google, Federal Aviation Administration, and Amazon have started testing the use of drones to deliver parcels and packages to their destinations [6]. Recently, Amazon proposed using a giant flying warehouse that can carry drones, product inventory, and staff to address the limited payload capacity and service range problem [7]. The general drone-based delivery scenario can be envisioned as follows: Once the order of any package/meal has been confirmed, the delivery system assigns a drone to pick the package up from the source and deliver it to the actual destination. Afterward, a drone is selected to perform the mission based on the available battery and destination. When the trip ends, the drone may have several decisions to make, such as whether to recharge the battery, deliver the next parcel, or wait to receive the next parcel [4]. A general drone-based delivery scenario is presented in Figure 1. As the application of drones is growing popular due to technological advancements, the logistics industry is also trying to yield from the success being brought about by the drones. Thus, the rise of drone-based delivery systems come into picture. Employing drones for the delivery mission provide advantages over traditional logistics in various aspects. In comparison to the conventional truck delivery scheme, the advantages of drone-based delivery are as follows [6]: (1) Faster delivery can be ensured by reducing the delivery time and travel distance. (2) Cost can be reduced because drones are cheaper than trucks. (3) Delivery can be ensured even in emergency situations such as floods and earthquakes [8].