Myounggyu Won

DistressNet: a wireless ad hoc and sensor network architecture for situation management in disaster response

Situational awareness in a disaster is critical to effective response. Disaster responders require timely delivery of high volumes of accurate data to make correct decisions. To meet these needs, we present DistressNet, an ad hoc wireless architecture that supports disaster response with distributed collaborative sensing, topology-aware routing using a multichannel protocol, and accurate resource localization. Sensing suites use collaborative and distributed mechanisms to optimize data collection and minimize total energy use. Message delivery is aided by novel topology management, while congestion is minimized through the use of mediated multichannel radio protocols. Estimation techniques improve localization accuracy in difficult environments.

Energy-Efficient Fault-Tolerant Data Storage and Processing in Mobile Cloud

Despite the advances in hardware for hand-held mobile devices, resource-intensive applications (e.g., video and image storage and processing or map-reduce type) still remain off bounds since they require large computation and storage capabilities. Recent research has attempted to address these issues by employing remote servers, such as clouds and peer mobile devices. For mobile devices deployed in dynamic networks (i.e., with frequent topology changes because of node failure/unavailability and mobility as in a mobile cloud), however, challenges of reliability and energy efficiency remain largely unaddressed. To the best of our knowledge, we are the first to address these challenges in an integrated manner for both data storage and processing in mobile cloud, an approach we call k-out-of-n computing. In our solution, mobile devices successfully retrieve or process data, in the most energy-efficient way, as long as k out of n remote servers are accessible. Through a real system implementation we prove the feasibility of our approach. Extensive simulations demonstrate the fault tolerance and energy efficiency performance of our framework in larger scale networks.

A wireless system for reducing response time in Urban Search & Rescue

Time is a critical factor in the Urban Search & Rescue operations immediately following natural and man-made disasters. Building on our collaboration with first responders we identify a set of areas for improving response times: victim detection in collapsed buildings, information storage and collection about buildings (collapsed or not), detection of first responder team separation and lost tools, and throughput and latency of data delivered to first responders. In this paper, we present the design (i.e., software/hardware architectures, and the guiding design principles), implementation and realistic evaluation of DistressNet, a system that targets the aforementioned areas for reducing the Urban Search & Rescue response time. DistressNet, built on COTS hardware and on open standards and protocols, pushes complexity that the very diverse Urban Search & Rescue scenarios pose, to user level applications (apps). Apps in DistressNet run on unmodified hardware ranging from smartphones, to motes and wireless routers. For the benefit of the research community, we also share some lessons learned during our experiences in the design, building and evaluation of DistressNet.

Towards robustness and energy efficiency of cut detection in wireless sensor networks

Reliable, full network connectivity in wireless sensor networks (WSN) is difficult to maintain. Awareness of the state of network connectivity is similarly challenging. Harsh, unattended, low-security environments and resource-constrained nodes exacerbate these problems. An ability to detect connectivity disruptions, also known as cut detection, allows WSN to conserve power and memory while reducing network congestion. We propose ER-CD and LR-CD, protocols that detect cuts while providing energy-efficiency and robustness to attack. Using distributed, cluster-based algorithms, ER-CD recognizes and determines the scope of disrupted connectivity while examining available data for evidence of an attack. For more resource-constrained networks, LR-CD enhances security through the use of a robust outlier detection algorithm. Extensive simulations and a hardware implementation provide experimental validation across a range of network sizes and densities. Results indicate that energy-efficiency can be improved by an order of magnitude in denser networks while malicious nodes are detected at deviations of 1% from expected behavior.

Destination-Based Cut Detection in Wireless Sensor Networks

Wireless Sensor Networks (WSNs) often suffer from disrupted connectivity caused by its numerous aspects such as limited battery power of a node and unattended operation vulnerable to hostile tampering. The disruption of connectivity, often referred to as network cut, leads to ill-informed routing decisions, data loss, and waste of energy. A number of protocols have been proposed to efficiently detect network cuts, they focus solely on a cut that disconnects nodes from the base station. However, a cut detection scheme is truly useful when a cut is defined with respect to multiple destinations (i.e., target nodes), rather than a single base station. Thus, we extend the existing notion of cut detection, and propose an algorithm that enables sensor nodes to autonomously monitor the connectivity to multiple target nodes. We introduce a novel reactive cut detection solution, the Point-to-Point Cut Detection, where given any pair of source and destination, a source is able to locally determine whether the destination is reachable or not. Furthermore, we propose a lightweight proactive cut detection algorithm specifically designed for a small set of target destinations. We prove the effectiveness of the proposed algorithms through extensive simulations.

A Low-Stretch-Guaranteed and Lightweight Geographic Routing Protocol for Large-Scale Wireless Sensor Networks

Geographic routing is well suited for large-scale wireless sensor networks (WSNs) because it is nearly stateless. One important challenge is that network holes may arbitrarily increase the routing path length. Fortunately, recent studies have shown that constant path stretch is achievable using nonlocal information. The constant stretch, however, is possible at the cost of high communication and storage overhead: a source node must complete a “path-setup” process prior to data transmission by exchanging a message with a destination node using a default geographic routing (e.g., GPSR). In this article, we propose the first geographic routing protocol (LVGR) that provably achieves worst-case stretch of Θ (D/γ) (where D is the diameter of the network and γ is the communication range of nodes) with low communication and storage overhead. LVGR represents a hole as a convex hull, the internal structure of which is represented as a local visibility graph. Based on the convex hulls and local visibility graphs, LVGR generates paths with guaranteed stretch. Through theoretical analysis and extensive simulations, we prove the worst-case stretch of LVGR and demonstrate that LVGR reduces communication overhead by up to 97% and storage overhead by up to 60%, compared with the state of the art.

Resource Allocation for Energy Efficient k-out-of-n System in Mobile Ad Hoc Networks

Resource Allocation has been widely used for improving various performance metrics in wireless networks. Applying resource allocation to a Mobile Ad Hoc Network (MANET), however, is a challenging problem because of dynamic network topology. In this paper, we develop a novel resource allocation scheme designed for MANETs that minimizes the communication cost for accessing distributed resources while improving the reliability by adopting the k-out-of-n system, a widely used technique for reliability control. Specifically, we propose a scheme that allocates resources to n nodes, called service centers, such that the expected energy consumption for nodes to access k service centers out of the n service centers (k ≤ n) is minimized. Our scheme accounts for dynamic network topology by estimating the failure probabilities of nodes and monitoring the network for significant topology changes. In addition, an Importance Sampling technique is used to reduce the computation-overhead. To evaluate the performance, we build a mobile distributed file system based on our resource allocation scheme. Through both extensive simulations and real hardware implementation on Smartphones, we show that our resource allocation scheme effectively reduces energy consumption by up to 45% and increases the successful data retrieval rate by up to 50% in comparison with a greedy algorithm.

On combining network coding with duty-cycling in flood-based wireless sensor networks

Network coding and duty-cycling are two major techniques for saving energy in wireless sensor networks. To the best of our knowledge, the idea to combine these two techniques for even more aggressive energy savings, has not been explored. This is not unusual, since these two techniques achieve energy efficiency through conflicting means, e.g., network coding saves energy by exploiting overhearing (i.e., nodes are awake), whereas duty-cycling saves energy by reducing idle listening (i.e., nodes sleep). In this article, we thoroughly investigate if network coding and duty cycling can be used together for more aggressive energy savings in flood-based wireless sensor networks. Our main idea is to exploit the redundancy sometimes present in flooding applications that use network coding, and put a node to sleep (i.e., duty cycle) when a redundant transmission takes place (i.e., the node has already received and successfully decoded a sequence of network-coded packets). We propose a scheme, called DutyCode, in which a multiple access control (MAC) protocol implements packet streaming and allows the network coding-aware application to decide when a node can sleep. We also present an algorithm for deciding the optimal coding scheme for a node to further reduce energy consumption by minimizing redundant packet transmissions. Finally, we propose an adaptive switching technique between DutyCode and an existing duty-cycling MAC protocol. We investigate our proposed solutions analytically and implement them on mote hardware. Our performance evaluation results, obtained from a 42-node indoor testbed, show that our scheme saves 30-46% more energy than network coding-based solutions.

GOAL: A parsimonious geographic routing protocol for large scale sensor networks

Geographic routing is well suited for large scale sensor networks, because its per node state is independent of the network size. However, the local minimum caused by holes/obstacles results in the worst-case path stretch of @W(c^2), where c is the path length of the optimal route. Recently, a geographic routing protocol based on the visibility graph (VIGOR) showed that a path stretch of @Q(c) can be achieved. This path stretch, however, is achieved at the cost of communication and storage overhead, which makes the practical deployment of VIGOR in large scale sensor networks challenging. To this end, we propose GOAL (Geometric Routing using Abstracted Holes), a routing protocol that provably achieves a path stretch of @Q(c), with lower communication and storage overhead. To compactly describe holes, we develop a novel distributed convex hull algorithm, which improves the message complexity O(n log^2n) of state of art distributed convex hull algorithm to O(n log n). The concise representation of a hole is used by nodes to make locally optimal routing decisions. Our theoretical analysis proves the correctness of the proposed algorithms and the path stretch of @Q(c). Through extensive simulations and experiments on a testbed with 42 EPIC motes, we demonstrate the effectiveness of GOAL and its feasibility for resource constrained wireless sensor networks; specifically, we show that GOAL eliminates part of communication overhead of VIGOR and reduces the memory overhead of VIGOR by up to 51%.

Asym-MAC: A MAC Protocol for Low-Power Duty-Cycled Wireless Sensor Networks with Asymmetric Links

Duty-cycling is a primary technique significantly improving the energy efficiency of Wireless Sensor Networks (WSNs). Thus, a large number of MAC protocols have been developed for duty-cycled WSNs. Especially, recently proposed receiver-initiated MAC protocols are well suited for extremely low duty-cycled WSNs. However, as it is shown in this paper, they perform poorly when highly asymmetric links are present. In this paper, a hybrid MAC protocol called Asym-MAC is proposed which takes advantage of both receiver-initiated and sender-initiated MAC protocols to combat performance degradation due to asymmetric links. Experimental results demonstrate that Asym-MAC has up to 2.8X higher packet reception ratio and up to 66.7% smaller packet transmission delay compared with A-MAC, the state-of-the-art receiver-initiated MAC protocol.