"With the increasing availability of wireless networks, the continuous development of new wireless technologies and recent technological advancements in the area of unmanned aerial systems, it is essential to optimize the users' connection to meet the increased demands in terms of throughput and delay. In conventional infrastructure-based networks, the devices are connected to a central entity that is responsible for coordinating the network. Although infrastructure networks may be available in many situations, infrastructure-less or ad-hoc networks are necessary in situations where infrastructure-based networks are difficult to deploy (e.g., disaster or rural areas) or are inefficient to support connectivity. Therefore analyzing, optimizing, and selecting the best connection, whether it is through an existing infrastructure or an ad-hoc network, is vital for optimizing the users' performance and meeting the quality of service (QoS) requirements. My dissertation examines various approaches to optimize network connectivity for both wireless sensor networks and for mobile users. For example, I have used real elephants' movement data and a multi-sink extension to the epidemic routing with vaccine protocol in Network Simulator (ns-3) to analyze the performance ofWi-Fi infrastructure mode and multi-hopWi-Fi ad-hoc mode in a real life animal tracking sensor network application called JumboNet. Based on simulation results, Wi-Fi adhoc mode with epidemic routing outperforms infrastructure mode Wi-Fi in terms of packet delivery ratio. On the other handWi-Fi in infrastructure mode results in a lower delay and energy consumption per packet with the cost of a lower number of delivered packets. Additionally, I developed an Android application that scans and collects information about the accessibility, quality and attributes of Wi-Fi access points, and cellular base stations. Moreover, the application measures the throughput and delay of the infrastructure networks. Based on the collected data, about 10% of the scanned locations have only 0-2 Wi-Fi access points (APs), and for more than 20% of the locations, all the available APs are private and inaccessible due to security restrictions. Using an ad-hoc network can allow devices that do not have a direct access to the infrastructure network to be connected through other devices that do have access to the Wi-Fi APs. In this regard, I developed an Android application that connects a Wi-Fi Direct ad-hoc network to the Internet via a gateway node that is connected to an infrastructure network. The application can be used to evaluate the impact of extending access to the Internet to devices that do not have direct access. Moreover, based on energy consumption models for LTE, Wi-Fi and Wi-Fi Direct, I evaluated the tradeoffs between throughput, delay, and energy consumption of infrastructure and multi-hop ad-hoc networks. Based on the collected data, the throughput of infrastructure and multihop ad-hoc networks increases with increasing data size. Furthermore,Wi-Fi Direct multi-hop ad-hoc networks withWi-Fi connection from the gateway node are more energy efficient when uploading and downloading data compared with a direct cellular connection in some cases. Furthermore, I investigated the 3D placement problem for multiple unmanned aerial vehicles base stations (UAV-BSs) that maximizes the number of covered users with the same as well as with different QoS requirements. First, I presented a mathematical formulation of the multiple UAV-BSs placement problem, and showed that it is a non-convex optimization problem. Then, I proposed two heuristic algorithms, and I showed that for users with the same as well as with different QoS requirements, the proposed algorithms achieve near optimal performance and outperform the Linear Approximation (LA) state-of-the-art algorithm in terms of the average number of covered users and execution time. Finally, I explored the 3D placement problem for multiple UAV-BSs that maximizes the number of covered ground users both with and without support of multi-hop ad hoc ground networks. First, I presented a mathematical formulation of the single UAV-BS placement problem, then I proposed a heuristic algorithm that maximizes the number of directly and indirectly covered ground users considering users with the same as well as with different quality of service (QoS) requirements. Simulation results show the merits of utilizing the multi-hop capabilities of the ground users in terms of reducing the number of UAV-BSs required to cover the users. Overall, this dissertation contributes to the design, analysis, and optimization of infrastructurebased, aerial and multi-hop ad-hoc networks in various applications ranging from WSNs to mobile networks. Furthermore, these contributions will give new insights to the design of next generation wireless networks that are able to meet the users' demands and QoS requirements."--Pages x-xii.