Sangkyung Kim

Design and Performance Evaluation of Hierarchical Protocol for Underwater Acoustic Sensor Networks

ABSTRACTAs underwater environment monitoring system’s interest has increased, the research is proceeding about underwater acoustic sensor network. Underwater sensor network can be applicable to many fields, such as underwater environment monitoring, underwater resource exploration, oceanic data collection, military purposes, etc. It is essential to define the PHY-MAC protocol for revitalization of the underwater acoustic sensor network which is available utilization in a variety of fields. However, underwater acoustic sensor network has to implement by consideration of underwater environmental characteristics, such as limited bandwidth, multi-path, fading, long propagation delay caused by low acoustic speed. In this paper, we define frequency of adjusted PHY protocol, network topology, MAC protocol, PHY-MAC interface, data frame format by consideration of underwater environmental characteristics. We also present system configuration of our implementation and evaluate performance based on our implementation with test in real underwater field.

Robot Control Using an Underwater Acoustic Modem

Underwater sensor network (USN) enables various services implemented over terrestrial wireless sensor network previously and underwater robot control service is one of the applications of USN. For wirelessly controlling an underwater robot, development of an underwater acoustic modem for transmitting robot control frame as well as analysis of the robot control protocol should be carried out properly. In this paper, we have developed an underwater modem suitable for underwater robot control and designed a protocol to handle the robot. We have also verified the robot control system by experimenting in an underwater environment.

FFFR-Based Resource Allocation Mechanism for Interference Mitigation of D2D Communications in LTE-Advanced Networks

D2D (Device-to-Device) communication underlaying LTE-advanced networks is a promising technology to improve the system capacity and spectral efficiency. By sharing the same radio resources with cellular user equipments, D2D communications can significantly enhance the overall spectral efficiency. However, it may cause interference between D2D link and cellular link. Careful resource allocation and interference coordination between cellular and D2D communications are very important and need to be properly handled. This paper proposes a radio resource allocation scheme based on FFFR (Flexible Fractional Frequency Reuse) for D2D communication underlaying cellular networks. The base station selects randomly resource blocks assigned to cellular users, and reuses them for a D2D pair. Through simulations, we have confirmed that the proposed scheme improves the system throughput, reduces the computational complexity, and mitigates the interference of D2D link and cellular link.

Specific Device Discovery Method for D2D Communication as an Underlay to LTE-Advanced Networks

Device discovery for D2D (device-to-device) communication enables a device to discover other devices in order to initiate communication with them. Devices should perform the discovery phase using a small quantity of radio resource in a short time and be able to reduce the load of the base station. Legacy device discovery schemes have focused on discovering as many target devices as possible. However, it is not appropriate for peer-to-peer D2D communication scenario. Further, synchronization problems are an important issue for discovery signal transmission. This paper proposes a discovery method that one requesting device discovers a specific target for communication. Multiple antenna beamforming is employed for the synchronization between the base station and a target device. The proposal can reduce the load of the base station using the information that it already maintains and improve the reliability of the device discovery because two times of synchronizations using beamforming among the base station and devices can make the exact discovery of a target device with mobility possible.

Aggregating Web Service matchmaking variants using web search engine and machine learning

Variety of Web Service discovery algorithms had been investigated for improvement of the retrieval quality. Combining the several algorithms according to their strong points, is proposed as enabling more refined discovery consequence. Now, many researches as OWL-Mx [6] are sited as examples, had already shown the method that join together and conclude for the specific domain. However, there are no way to conclude multi-algorithms results. Klusch [7] shows the brand-new way that leads the conclusion by using machine-learning algorithm Support Vector Machine (SVM) [1,4]. In this research, we attempted to apply the SVM aggregation and several new discovery algorithm using similarity based on search engine, shown on Trip Domain service discovery. And, 88 percent over score of precision, were gotten as the result from specifically prepared queries for Trip Domain. This experiment also had shown 10 percent missing which occurred by using web page count based similarity computation. In future work, we will conduct some comparison for getting more reliability of this proposed method.

Scalable Uniformly-Distributed Clustering Mechanism for Sensor Networks

The energy of a sensor network decides how long it will be alive. Therefore, energy efficiency is the critical part of network survivability. The most energy-consuming action of a sensor network is considered as communication between nodes. For energy efficient communication, many research activities for clustering mechanisms have been conducted. But, selecting cluster heads, selecting cluster range and communication mechanism between clusters are not clearly defined, and they are not suitable for applying to practical network environments. So, in the paper, we try to solve these problems and apply a new clustering mechanism for more efficient energy usage in sensor networks.

ELM-MAC: Energy Efficient Link Management by Using Optimal Transmission Power in MAC Protocol

Many studies on sensor network have focused on energy efficiency in several layers on communication protocol. In order to increase energy efficiency in sensor network communication, MAC-layer energy efficiency needs to be considered. Even though MAC layer protocols for increasing energy efficiency at MAC layer have been proposed in several papers, there have been few of researches that focused on energy efficiency methods in which transmission power is considered. In this paper we propose a new mechanism named as ELM-MAC that creates, uses, and manages the optimized transmission power level for energy efficiency in MAC layer.

An energy scheduling algorithm for ensuring the pre-determined lifetime in sensor network

Energy limitation of a sensor network is a very important feature which distinguishes it from traditional networks and a number of methods to saving energy consumption have been studied in sensor networks. Most of those works have focused on Network, MAC or PHY layer and the lifetime of a sensor network cannot be pre-determined. But some sensor network might be able to survive for some specified time. In this work, we propose an energy consumption scheduling model, at application level of a node, that ensures predetermined lifetime. To do this, first, we divide applications into six classes and define five operations of an application. Second, an energy consumption model is proposed using those five operations and consumption energies of each operation are calculated by a statistical method. Finally, energy consumption schedules of each application are rebuilt for a node to survive for predetermined lifetime, e.g. varying the period of response and sensing and the number of actuation, etc. Consequently, it is ensured for nodes to survive for the pre-determined lifetime.

TinyOS-based gateway for underwater acoustics/radio frequency communication

Currently, UWASN (Underwater Acoustic Sensor Network) has been researched as a branch of sensor networks. UWASNs use a transmission media different from terrestrial wireless sensor networks. That is, the former uses acoustic waves and the latter uses radio waves for communication. G/W (Gateway)s in UWASNs are nodes for relaying data transmission between a UWASN and a terrestrial wireless sensor network. So, it is necessary to design and realize the UWA communication module with the UWA/RF (Underwater Acoustics/Radio Frequency) protocol stack for the underwater environment. As TinyOS used most widely at operating system for sensor networks is not considering the underwater acoustic communication, the functions supported by it cannot be used. Therefore, The TinyOS-based UWA/RF G/W system and prototype suitable for the characteristic of UWASN is designed and realized in this paper.