Unmanned Aerial Vehicle (UAV) networks have emerged as a promising technique to rapidly provide wireless coverage to a geographical area, where a flying UAV can be fast deployed to serve as cell site. Existing work on UAV-enabled wireless networks overlook the fast UAV deployment for wireless coverage, and such deployment problems have only been studied recently in sensor networks.Unlike sensors, UAVs should be deployed to the air and they are generally different in flying speed, operating altitude and wireless coverage radius. By considering such UAV heterogeneity to cover the whole target area, this paper studies two fast UAV deployment problems: one is to minimize the maximum deployment delay among all UAVs (min-max) for fairness consideration, and the other is to minimize the total deployment delay (min-sum) for efficiency consideration. We prove both minmax and min-sum problems are NP-complete in general. When dispatching UAVs from the same location, we present an optimal algorithm of low computational complexity O(n 2 ) for the min-max problem. When UAVs are dispatched from different locations, we propose to preserve their location order during deployment and successfully design a fully polynomial time approximation scheme (FPTAS) of computation complexity O(n 2 log 1 ) to arbitrarily approach the global optimum with relative error .The min-sum problem is more challenging. When UAVs are dispatched from the same initial location, we present an approximation algorithm of linear time. As for the general case, we further reformulate it as a dynamic program and propose a pseudo polynomial-time algorithm to solve it optimally. Index TermsUnmanned Aerial Vehicle Networks, Wireless Coverage, Fast Deployment, Approximation Algorithm. X. Zhang and L. Duan are with Engineering Systems and Design Pillar, Recent years have witnessed increasingly more exercises and uses of Unmanned Aerial Vehicle (UAV) networks for rapidly providing wireless coverage [1]. This flying cell site technology enabled by UAV rapidly expands the wireless coverage of the static territorial base stations on the ground, where UAVs serve as flying base stations to serve a geographical area (e.g., a disaster zone) out of the reach of the cellular networks. For example, Verizon has developed airborne LTE service allowing communications between a UAV and hurricane disaster victims [2]. Moreover, Project Loon [3] uses balloons as flying base stations to provide high speed internet coverage to people in rural and remote areas worldwide. In addition, traditional base stations or access points [4] are deployed at fixed locations for a long term by meeting the average traffic load, while flying UAVs are mobile and do not have such constraint to meet varying traffic load [5]. Thanks to such advantage, wireless carriers such as AT&T have started to use UAVs to opportunistically boost wireless coverage for crowds in big concerts or sports, where people continuously post their selfies and videos online [6].There is increasingly more research work to deploy UAV...

In traditional sensorless control of the interior permanent magnet synchronous motors(IPMSMs) for medium and high speed domains, a control strategy based on a sliding-mode observer(SMO) and phase-locked loop (PLL) is widely applied. A new strategy for IPMSM sensorless controlbased on an adaptive super-twisting sliding-mode observer and improved phase-locked loop isproposed in this paper. A super-twisting sliding-mode observer (STO) can eliminate the chatteringproblem without low-pass filters (LPFs), which is an effective method to obtain the estimated backelectromotive forces (EMFs). However, the constant sliding-mode gains in STO may causeinstability in the high speed domain and chattering in the low speed domain. The speed-relatedadaptive gains are proposed to achieve the accurate estimation of the observer in wide speed rangeand the corresponding stability is proved. When the speed of IPMSM is reversed, the traditionalPLL will lose its accuracy, resulting in a position estimation error of 180°. The improved PLL basedon a simple strategy for signal reconstruction of back EMF is proposed to ensure that the motor canrealize the direction switching of speed stably. The proposed strategy is verified by experimentaltesting with a 60-kW IPMSM sensorless drive.

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