Seokhoon Yoon

AURP: An AUV-Aided Underwater Routing Protocol for Underwater Acoustic Sensor Networks

Deploying a multi-hop underwater acoustic sensor network (UASN) in a large area brings about new challenges in reliable data transmissions and survivability of network due to the limited underwater communication range/bandwidth and the limited energy of underwater sensor nodes. In order to address those challenges and achieve the objectives of maximization of data delivery ratio and minimization of energy consumption of underwater sensor nodes, this paper proposes a new underwater routing scheme, namely AURP (AUV-aided underwater routing protocol), which uses not only heterogeneous acoustic communication channels but also controlled mobility of multiple autonomous underwater vehicles (AUVs). In AURP, the total data transmissions are minimized by using AUVs as relay nodes, which collect sensed data from gateway nodes and then forward to the sink. Moreover, controlled mobility of AUVs makes it possible to apply a short-range high data rate underwater channel for transmissions of a large amount of data. To the best to our knowledge, this work is the first attempt to employ multiple AUVs as relay nodes in a multi-hop UASN to improve the network performance in terms of data delivery ratio and energy consumption. Simulations, which are incorporated with a realistic underwater acoustic communication channel model, are carried out to evaluate the performance of the proposed scheme, and the results indicate that a high delivery ratio and low energy consumption can be achieved.

Cooperative Search and Survey Using Autonomous Underwater Vehicles (AUVs)

In this work, we study algorithms for cooperative search and survey using a fleet of Autonomous Underwater Vehicles (AUVs). Due to the limited energy, communication range/bandwidth, and sensing range of the AUVs, underwater search and survey with multiple AUVs brings about several new challenges since a large amount of data needs to be collected by each AUV, and any AUV may fail unexpectedly. To address the challenges and meet our objectives of minimizing the total survey time and traveled distance of AUVs, we propose a cooperative rendezvous scheme called Synchronization-Based Survey (SBS) to facilitate cooperation among a large number of AUVs when surveying a large area. In SBS, AUVs form an intermittently connected network (ICN) in that they periodically meet each other for data aggregation, control signal dissemination, and AUV failure detection/recovery. Numerical analysis and simulations have been performed to compare the performance of three variants of SBS schemes, namely, Alternating Column Synchronization (ACS), Strict Line Synchronization (SLS), and X Synchronization (XS). The results show that XS can outperform other SBS schemes in terms of the survey time and the traveled distance of AUVs. We also compare XS with nonsynchronization-based survey and the lower bound on the survey time and traveled distance. The results show that XS achieves a close to optimal performance.

Coordinated Locomotion and Monitoring Using Autonomous Mobile Sensor Nodes

Stationary wireless sensor networks (WSNs) fail to scale when the area to be monitored is unbounded and the physical phenomenon to be monitored may migrate through a large region. Deploying mobile sensor networks (MSNs) alleviates this problem, as the self-configuring MSN can relocate to follow the phenomenon of interest. However, a major challenge here is to maximize the sensing coverage in an unknown, noisy, and dynamically changing environment with nodes having limited sensing range and energy, and moving under distributed control. To address these challenges, we propose a new distributed algorithm, Causataxis, which enables the MSN to relocate toward the interesting regions and adjust its shape and position as the sensing environment changes. (In Latin, causa means motive/interest. A taxis (plural taxes) is an innate behavioral response by an organism to a directional stimulus. We use Causataxis to refer to an interest driven relocation behavior.) Unlike conventional cluster-based systems with backbone networks, a unique feature of our proposed approach is its biosystem inspired growing and rotting behaviors with coordinated locomotion. We compare Causataxis with a swarm-based algorithm, which uses the concept of virtual spring forces to relocate mobile nodes based on local neighborhood information. Our simulation results show that Causataxis outperforms the swarm-based algorithm in terms of the sensing coverage, the energy consumption, and the noise tolerance with a slightly high communication overhead.

Improve Efficiency and Reliability in Single-Hop WSNs with Transmit-Only Nodes

Wireless Sensor Networks (WSNs) will play a significant role at the “edge” of the future “Internet of Things.” In particular, WSNs with transmit-only nodes are attracting more attention due to their advantages in supporting applications requiring dense and long-lasting deployment at a very low cost and energy consumption. However, the lack of receivers in transmit-only nodes renders most existing MAC protocols invalid. Based on our previous study on WSNs with pure transmit-only nodes, this work proposes a simple, yet cost effective and powerful single-hop hybrid WSN cluster architecture that contains not only transmit-only nodes but also standard nodes (with transceivers). Along with the hybrid architecture, this work also proposes a new MAC layer protocol framework called Robust Asynchronous Resource Estimation (RARE) that efficiently and reliably manages the densely deployed single-hop hybrid cluster in a self-organized fashion. Through analysis and extensive simulations, the proposed framework is shown to meet or exceed the needs of most applications in terms of the data delivery probability, QoS differentiation, system capacity, energy consumption, and reliability. To the best of our knowledge, this work is the first that brings reliable scheduling to WSNs containing both nonsynchronized transmit-only nodes and standard nodes.

A novel Qos-aware MAC scheme using optimal retransmission for wireless networks

This paper proposes a novel medium access control scheme for low cost, single-hop wireless networks where the source nodes have a transmitter module but no receiver module and hence they can only transmit data to a sink but cannot receive any control signals, like an ACK or NAK, from any other node. The goal of the proposed scheme is to provide QoS (in terms of packet delivery probability) to the nodes in such a network, where the existing schemes like polling or scheduled transmissions, CSMA and ARQ will be ineffective because of the unavailability of a receiver module at the nodes. The proposed scheme uses distributed control and allows the nodes to transmit each packet an optimal number of times at random instants in time within the packet generation interval. We define two optimization problems based on minimizing total network traffic and maximizing the delivery probability of the class of nodes requiring the highest QoS, respectively, and develop mathematical formulae and efficient algorithms to solve them. Numerical analysis and simulation results show that our scheme can provide high QoS to networks of different sizes.

Coordinated Locomotion of Mobile Sensor Networks

Stationary wireless sensor networks (WSNs) fail to scale when the area to be monitored is open (i.e borderless) and the physical phenomena to be monitored may migrate through a large region. Deploying mobile sensor networks (MSNs) alleviates this problem, as the self-configuring MSN can relocate to follow the phenomena of interest. However, a major challenge here is to maximize the sensing coverage in an unknown, noisy, and dynamic sensing environment while minimizing energy consumption. Another major challenge is to maintain network connectivity for each MSN node during relocations. To address these challenges, we propose a new distributed algorithm, Causataxis1, that enables the MSN to relocate toward the interesting regions and adjust its shape and position as the sensing environment changes. Causataxis achieves scalable control of the MSN via a backbone-tree infrastructure maintained over clusterhead nodes, and achieves agility via localized cluster formation and dissolution. Unlike conventional cluster-based systems with backbone networks, a unique feature of our proposed approach is its bio-system inspired growing and rotting behaviors with coordinated locomotion. We compare Causataxis with a custom tuned swarm algorithm, which uses the concept of virtual spring forces to relocate mobile nodes based on local neighborhood information. Our simulation results show that Causataxis can outperform the swarm based algorithm in terms of the sensing coverage, the energy consumption, and the noise tolerance with a slightly high communication overhead.

QoMOR: A QoS-aware MAC protocol using Optimal Retransmission for Wireless Intra-Vehicular Sensor Networks

The paper proposes a MAC layer protocol called QoMOR (QoS-aware MAC protocol using optimal retransmission) that is designed to provide QoS in a decentralized network with multiple sensor (source) nodes that do not have the capability to receive acknowledgements from the sink node. A minimum data delivery probability between the sensor and sink nodes is achieved by allowing each source node to transmit each new packet an optimal number of times in every interval of time. The paper first discusses the single QoS class case and derives the maximum achievable frame delivery probability and then extends the concepts to the multiple QoS class case. It also addresses a few design optimization criteria. Simulation and numerical analysis results show that QoMOR can effectively provide QoS guarantees under distributed control without using conventional ARQ-based schemes.

A New Search Algorithm using Autonomous and Cooperative Multiple Sensor Nodes

In this paper, we study search algorithms for using a set of autonomous and cooperative mobile sensor nodes (MSN) with limited sensing and communication ranges to search a large area. Our objectives include minimizing the total search time and the travel distance of MSNs while enabling fault tolerance to possible MSN failures. We propose a new rendezvous scheme, namely X synchronization (XS) to facilitate the exchange of both data and control signals among the MSNs during search. We also devise a way to calculate appropriate timeout periods used to detect an MSN failure at rendezvous points and describe how surviving MSNs subsequently carry out the search mission. Numerical analysis and simulations have been performed to evaluate the performance of XS. The results show that XS can outperform other rendezvous schemes in terms of the total search time and the average travel distance of MSNs.

VirFID: A Virtual Force (VF)-based Interest-Driven moving phenomenon monitoring scheme using multiple mobile sensor nodes

Abstract In this paper, we study mobile sensor network (MSN) architectures and algorithms for monitoring a moving phenomenon in an unknown and open area using a group of autonomous mobile sensor (MS) nodes. Monitoring a moving phenomenon involves challenges due to limited communication/sensing ranges of MS nodes, the phenomenon’s unpredictable changes in distribution and position, and the lack of information on the sensing area. To address the challenges and meet the objective of the maximization of weighted sensing coverage, we propose a novel scheme, namely VirFID (Virtual Force (VF)-based Interest-Driven moving phenomenon monitoring). In VirFID, MS nodes move toward the positions where more interesting sensing data can be obtained by utilizing the virtual force, which is calculated based on the distance between MS nodes and sensed values in the area of interest. MS nodes also perform network-wise information sharing to increase the weighted sensing coverage. Depending on the level of information used, three variants of VirFID are evaluated: VirFID-LIB (Local Information-Based), VirFID-GHL (Global Highest and Lowest), and VirFID-IBN (Interests at Boundary Nodes). In addition, an analytical model for estimating MSN speed is designed. Simulations are performed to compare the performance of three VirFID variants with other approaches. Our simulation results show that VirFID algorithms outperform other schemes in terms of the weighted coverage efficiency, and VirFID-IBN achieves the highest weighted coverage efficiency among VirFID variants.

HiCoDG: A Hierarchical Data-Gathering Scheme Using Cooperative Multiple Mobile Elements

In this paper, we study mobile element (ME)-based data-gathering schemes in wireless sensor networks. Due to the physical speed limits of mobile elements, the existing data-gathering schemes that use mobile elements can suffer from high data-gathering latency. In order to address this problem, this paper proposes a new hierarchical and cooperative data-gathering (HiCoDG) scheme that enables multiple mobile elements to cooperate with each other to collect and relay data. In HiCoDG, two types of mobile elements are used: the mobile collector (MC) and the mobile relay (MR). MCs collect data from sensors and forward them to the MR, which will deliver them to the sink. In this work, we also formulated an integer linear programming (ILP) optimization problem to find the optimal trajectories for MCs and the MR, such that the traveling distance of MEs is minimized. Two variants of HiCoDG, intermediate station (IS)-based and cooperative movement scheduling (CMS)-based, are proposed to facilitate cooperative data forwarding from MCs to the MR. An analytical model for estimating the average data-gathering latency in HiCoDG was also designed. Simulations were performed to compare the performance of the IS and CMS variants, as well as a multiple traveling salesman problem (mTSP)-based approach. The simulation results show that HiCoDG outperforms mTSP in terms of latency. The results also show that CMS can achieve the lowest latency with low energy consumption.