According to Cisco, more than 500 Billion of Internet of Things (IoT) devices are expected to be installed worldwide by 2030. At the same year, the estimated global data traffic per month would be around 5000 Exabyte (i.e., 5000*10^18 bytes) according to ITU traffic estimation report. A key enabler for the next generation cellular networks to support the explosive growth of traffic demand and the massive number of IoT devices is the intensive deployment of the base stations (BSs). Mimicking the over-engineered planning approach of traditional wireless networks for future networks is not feasible because it will lead to excessive energy and monetary waste. Unmanned aerial vehicles (UAVs) equipped with communication transceivers can be employed to act as on-demand flying/aerial base stations (ABSs). They can be used to offload traffic, relay, broadcast, and collect information. The interest in using the UAVs is mainly due to their mobility and deployment flexible as well as their ability to provide line-of-sight (LoS) communication links. The main challenges to effectively use the ABSs to assist the IoT networks are how to efficiently find the optimal location of the ABSs and how to design their trajectory such as the number of ABSs, the IoTs’ energy consumption, the ABSs’ travel time is minimized.