Minho Shin

This paper presents a fault-tolerant estimator using a probabilistic voting algorithm (PVA) for the safe maneuvering of multirotor unmanned aerial vehicles (UAVs). UAVs are widely utilized in numerous applications, but any malfunction can lead to secondary accidents. The safety and robustness of the UAV component should be guaranteed to minimize fatal accidents during flight. A flight control computer (FCC) with various sensors is one of the most important components, the robustness of which should be guaranteed. In this paper, a hybrid FCC including both hardware and software is developed to improve the robustness and safety of the FCC by both hardware and analytical redundancy. Triple modular FCCs for hardware redundancy are utilized to deal with various faults. The PVA is designed to estimate the reference state of the UAV and make the consensus to select the fault-free FCC by the fault probabilities of each state measurement from the FCC estimators. Moreover, multiplexers switch the FCC channel based on the consensus result to compensate for faults. Then, the fault identification algorithm identifies the source of the estimator faults by information on the residual signals between the estimated states and the sensor measurements. The PVA is validated through numerical simulations and experiments. This method achieves approximately a 93% correct detection rate and a fault detection time of less than 1 second, which is sufficient to maintain the dynamic responses of the UAV. These results show that the PVA improves and ensures the safe maneuvering of the UAV in various fault situations.

This article presents a robust predictor-based sliding-mode control (RPSMC) for multirotor unmanned aerial vehicles (UAVs) to ensure desired tracking control under time delays, which appear in practice by communications, complex computation, and actuator delays. Many UAV applications have difficulty in control and operation due to various types of time delays, resulting in repeated commands, severe control instability, and then mission failure. However, existing controllers have limitations in solving time delay problems. In this article, the RPSMC with the prediction of future disturbance and reference trajectory is developed for the multirotor UAV to minimize the effects of time delay, robustly deal with external disturbances, and further achieve desired tracking control. The performance of RPSMC for the multirotor UAV is verified under various time delays and disturbances in numerical simulations. The results show the robustness and fast control convergence compared with proportional-integral-differential and conventional predictor-based controllers. Experimental results with step response and tracking of circular trajectory demonstrate the feasibility and performance of the RPSMC for UAVs in the presence of various time delays and disturbances.

Ultra-Wide Band (UWB) radar has a number of advantages of resolving multipath, exceptional spatial resolution, and ranging performance. However, several difficulties are confronted for multiple target tracking using UWB radars such as clutter signals which contaminate target signals, and unidentified number and behavior of the targets. Hence, this paper presents to develop a multiple moving target tracking algorithm, consisting of preprocessing and multiple target tracking steps. In the preprocessing step, static clutter reduction and constant false alarm rate (CFAR) detection extract the target candidate range measurements from each UWB radar. Then, two multiple target tracking (MTT) steps are developed: range- based MTT and position-based MTT. The range-based MTT is mainly based on existing linear multi-target integrated probabilistic data association (LM-IPDA) from each UWB radar measurement. Then the outputs of each LM-IPDA are gathered in the positioning center to estimate the position of multiple targets. On the other hands, the position-based MTT is based on multiple sensor LM-IPDA (msLM-IPDA) as an accurate target tracking method for various uncertainties by improving the probabilistic model of LM-IPDA. The tracking performance of two MTT methods is investigated with both numerical simulation and experiments.

As location-based services have become popular, thereby exposed user locations raised serious privacy concerns. A typical measure for location privacy is to report blurred locations and ensure that other users coexist in the reported region. However, additional knowledge about the user's maximum speed and the territorial information in user's vicinity can allow for the adversary to effectively compromise the user's location privacy. In this paper, we present an anonymization algorithm that effectively counters such attacks while achieving k-anonymity requirements as well as minimum acceptable cloaked region size. We evaluate our anonymization scheme using state-of-the-art simulators for both vehicular movements and pedestrian movements. The experimental results demonstrate the effectiveness and efficiency of our proposed algorithm.

As healthcare in many countries faces an aging population and rising costs, mobile sensing technologies promise a new opportunity. Using mobile health (mHealth) sensing, which uses medical sensors to collect data about the patients, and mobile phones to act as a gateway between sensors and electronic health record systems, caregivers can continuously monitor the patients and deliver better care. Although some work on mHealth sensing has addressed security, achieving strong security and privacy for low-power sensors remains a challenge. We make three contributions. First, we propose Adapt-lite, a set of two techniques that can be applied to existing wireless protocols to make them energy efficient without compromising their security or privacy properties. The techniques are: adaptive security, which dynamically modifies packet overhead; and MAC striping, which makes forgery difficult even for small-sized MACs. Second, we apply these techniques to an existing wireless protocol, and demonstrate a prototype on a Chronos wrist device. Third, we provide security, privacy, and energy analysis of our techniques.

In recent years the popularity of multi-hop wireless networks has been growing. Its flexible topology and abundant routing path enables many types of applications. However, the lack of a centralized controller often makes it difficult to design a reliable service in multi-hop wireless networks. While packet routing has been the center of attention for decades, recent research focuses on data discovery such as file sharing in multi-hop wireless networks. Although there are many peer-to-peer lookup (P2P-lookup) schemes for wired networks, they have inherent limitations for multi-hop wireless networks. First, a wired P2P-lookup builds a search structure on the overlay network and disregards the underlying topology. Second, the performance guarantee often relies on specific topology models such as random graphs, which do not apply to multi-hop wireless networks. Past studies on wireless P2P-lookup either combined existing solutions with known routing algorithms or proposed tree-based routing, which is prone to traffic congestion. In this paper, we present two wireless P2P-lookup schemes that strictly build a topology-dependent structure. We first propose the Ring Interval Graph Search (RIGS) that constructs a DHT only through direct connections between the nodes. We then propose the ValleyWalk, a loosely-structured scheme that requires simple local hints for query routing. Packet-level simulations showed that RIGS can find the target with near-shortest search length and ValleyWalk can find the target with near-shortest search length when there is at least 5% object replication. We also provide an analytic bound on the search length of ValleyWalk.