Distributed Construction of Connected Cover Graph in Wireless Sensor Networks

( Duc Tai Le ),( Thang Le Duc ),( Boram Hwang ),( Hyunseung Choo ) 한국정보처리학회 2012 한국정보처리학회 학술대회논문집 Vol.19 No.1

In this paper, we consider the problem of scheduling sensor activity to prolong the network lifetime while guaranteeing both discrete target coverage and connectivity among all the active sensors and the sink, called connected target coverage (CTC) problem. We proposed a distributed scheme called Distributed Lifetime- Maximizing Scheme (DLMS) to solve the CTC problem. Our proposed scheme significantly reduces the cost of the construction of the connected cover graphs in comparison with the some conventional schemes. In addition, the energy consumption is more balanced so that the network lifetime will be increased. Our simulation results show that DLMS scheme performs much better than the conventional schemes in terms of the network lifetime.

미래형 생체모방 자율 컴퓨팅

Thang Le Duc,Dung Tien Nguyen,Duc Tai Le,추현승 한국통신학회 2016 정보와 통신 Vol.33 No.5

미래의 IoT, 클라우드 빅데이터, 모바일 환경에서 퍼베이시브 정보통신(Pervasive information network)은 우리 사회에 스며들어 다양한 기기를 통해 접근한다. 이를 실현하기 위해, 새로운 네트워크 아키텍처와 서비스 플랫폼이 요구된다. 현재의 네트워크 환경에서 이러한 형태의 퍼베이시브 정보통신을 지원하는 것은 매우 어렵다. 실제 환경과 가상 공간 사이의 간극을 극복하기 위한 연구는 도전적인 주제이다. 관련 연구 결과 중 가장 발전된 형태의 성과를 보이는 것으로 일본 AKARI 프로젝트와 유럽 FP6 BIONETS 프로젝트가 있다. AKARI 프로젝트는 차세대 네트워크의 구현을 목표로 하고 있으며, 이를 위해 완전히 새로운 형태의 미래인터넷 아키텍처를 설계했다. BIONETS 프로젝트는 미래인터넷 환경에서의 새로운 서비스 프레임워크를 확립했다. 이러한 프로젝트의 연구 및 결과물 융합을 통해 미래 사회에 기여할 수 있는 보다 발전된 형태의 네트워크를 준비한다.

Design of a Cyber Emergency Monitoring and Evacuation System

Duc Tai Le,Thang Le Duc,Sanggil Yeoum(염상길),Hyunseung Choo(추현승) 한국정보과학회 2014 한국정보과학회 학술발표논문집 Vol.2014 No.6

무선 네트워크에서 사전 핸드오버를 위한 프레임워크

( Thang Le Duc ),( Duc Tai Le ),( Hyunseung Choo ) 한국정보처리학회 2014 한국정보처리학회 학술대회논문집 Vol.21 No.2

Handover is constantly a challenging issue in wireless networks. Most of the existing solutions are host-based, which are implemented on the wireless terminals and leave the decision making to the terminals. This paper studies the problem of network-based handover in the wireless networks with the constraints of low latency as well as low computational time. To address this problem, we employ the software-defined network (SDN) architecture to facilitate handover. According to the operational model of the SDN, we define a workflow for all involved network entities, and then design a framework implementing the workflow as a complete handover system. The proposed framework aims to establish a channel conveying the mobility-related information of devices and the context information of their vicinity from the switches/access routers to the controllers. Based on collected information, the controller can optimally execute the handover.

Characterization of ternary (Ni,Co,Mn)₃O₄ thin films for microbolometer applications

Le, Duc Thang,Jeon, Chang Jun,Lee, Kui Woong,Jeong, Young Hun,Yun, Ji Sun,Yoon, Dae Ho,Cho, Jeong Ho Elsevier 2015 Journal of alloys and compounds Vol.650 No.-

<P><B>Abstract</B></P> <P>A liquid flow deposition (LFD) technique was successfully applied to grow (Ni<SUB>0.1</SUB>Mn<SUB>2.9−<I>x</I> </SUB>Co<SUB> <I>x</I> </SUB>)O<SUB>4</SUB> (NMC<I>x</I>, <I>x</I> = 0.015, 0.027, 0.048, 0.065, 0.082, 0.097, 0.119 and 0.145) thin films onto Si wafer substrates at a low temperature (50 °C). The microstructure of the films was studied by field-emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). X-ray diffraction (XRD) analysis results showed that heat treatment at a temperature of 400 °C leads to the formation of a cubic spinel AB<SUB>2</SUB>O<SUB>4</SUB> structure in the films. Measurements of the electrical resistance–temperature (<I>R–T</I>) dependence in a temperature range of 293–373 K revealed a very good negative temperature coefficient of resistance (NTC) characteristic for all annealed films. Films with a very low resistivity (<I>ρ</I>) of 613–831 Ω cm were obtained from solutions when <I>x</I> was varied in a range of 0.065–0.082, without substantially affecting the sensitivity. The difference in the electrical properties of the films was attributed to a valence state shift of manganese in accordance with the Co dopant concentration and this was also confirmed by an X–ray photoelectron spectroscopy (XPS) analysis. On the basis of their high NTC characteristic, low processing temperature, and very low specific resistivity, the NMC<I>x</I> thin films have a promising application in the integrated microbolometer devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Highly quality (Ni,Co,Mn)<SUB>3</SUB>O<SUB>4</SUB> thin films were grown using liquid flow deposited (LFD) technique. </LI> <LI> The formation of a cubic spinel AB<SUB>2</SUB>O<SUB>4</SUB> structure was found in all films after heat treatment at 400 °C. </LI> <LI> Films possess technical parameters of a <I>TCR</I> <SUB> <I>300</I> </SUB> larger than −2.43 and very low resistivity, i.e., <I>ρ</I> <SUB> <I>300</I> </SUB> = 613–831 Ω cm. </LI> <LI> Liquid flow deposited (Ni,Mn,Co)<SUB>3</SUB>O<SUB>4</SUB> thin films are very potential for microbolometer applications. </LI> </UL> </P>

Delay-Efficient Data Aggregation Tree Construction in Wireless Sensor Networks

Duc Tai Le,Thang Le Duc,Sanggil Yeom(염상길),Hyunseung Choo(추현승) 한국정보과학회 2015 한국정보과학회 학술발표논문집 Vol.2015 No.12

An Energy-Efficient MAC Protocol for Duty-Cycled Wireless Sensor Networks

Thang Le Duc,Duc Tai Le,Hyunseung Choo(추현승) 한국정보과학회 2013 한국정보과학회 학술발표논문집 Vol.2013 No.6

Critical-Path Aware Scheduling for Latency Efficient Broadcast in Duty-Cycled Wireless Sensor Networks

Le, Duc-Tai,Im, Giyeol,Le Duc, Thang,Zalyubovskiy, Vyacheslav V.,Kim, Dongsoo S.,Choo, Hyunseung WILEY INTERSCIENCE 2018 WIRELESS COMMUNICATIONS AND MOBILE COMPUTING Vol.2018 No.-

<P>Minimum latency scheduling has arisen as one of the most crucial problems for broadcasting in duty-cycled Wireless Sensor Networks (WSNs). Typical solutions for the broadcast scheduling iteratively search for nodes able to transmit a message simultaneously. Other nodes are prevented from transmissions to ensure that there is no collision in a network. Such collision-preventions result in extra delays for a broadcast and may increase overall latency if the delays occur along critical paths of the network. To facilitate the broadcast latency minimization, we propose a novel approach, critical-path aware scheduling (CAS), which schedules transmissions with a preference of nodes in critical paths of a duty-cycled WSN. This paper presents two schemes employing CAS which produce collision-free and collision-tolerant broadcast schedules, respectively. The collision-free CAS scheme guarantees an approximation ratio of <TEX>$ (\Updelta -\mathrm{1})T$</TEX> in terms of latency, where <TEX>$ \Updelta $</TEX> denotes the maximum node degree in a network. By allowing collision at noncritical nodes, the collision-tolerant CAS scheme reduces up to 10.2 percent broadcast latency compared with the collision-free ones while requiring additional transmissions for the noncritical nodes experiencing collisions. Simulation results show that broadcast latencies of the two proposed schemes are significantly shorter than those of the existing methods.</P>

무선센서네트워크에서 데이터 병합 트리를 위한 자기치유 방법

( Duc Tai Le ),( Thang Le Duc ),염상길 ( Sanggil Yeom ),( Vyacheslav V. Zalyubovskiy ),추현승 ( Hyunseung Choo ) 한국정보처리학회 2015 한국정보처리학회 학술대회논문집 Vol.22 No.1

Data aggregation is a fundamental problem in wireless sensor networks that has attracted great attention in recent years. On constructing a robust algorithm for minimizing data aggregation delay in wireless sensor networks, we consider limited transmission range sensors and approximate the minimum-delay data aggregation tree which can only be built in networks of unlimited transmission range sensors. The paper proposes an adaptive method that can be applied to maintain the network structure in case of a sensor node fails. The data aggregation tree built by the proposed scheme is therefore self-healing and robust. Intensive simulations are carried out and the results show that the scheme could adapt well to network topology changes compared with other approaches.

Collision-tolerant broadcast scheduling in duty-cycled wireless sensor networks

Le, Duc Tai,Le Duc, Thang,Zalyubovskiy, Vyacheslav V.,Kim, Dongsoo S.,Choo, Hyunseung Academic Press 2017 Journal of parallel and distributed computing Vol.100 No.-

<P><B>Abstract</B></P> <P>The minimum-latency broadcast problem in duty-cycled wireless sensor networks has received significant attention over the last few years. A common approach for the problem is to assign collision-free transmitting times to forwarding nodes for disseminating a message from one source node to all other nodes according to their given duty-cycle schedules and transmission ranges. However, preventing collision for all transmissions may increase latency in the broadcast schedules. This paper proposes a novel strategy of Collision-Tolerant Scheduling (CTS) that offers an opportunity to reduce broadcast latency by allowing collisions at non-critical nodes to speed up the broadcast process for critical ones. The completion of broadcast scheduling, i.e. all nodes receive a broadcast message, is ensured by additionally transmitting the message to non-critical nodes experiencing collision. We employ the scheduling strategy in two proposed broadcast schemes: Degree-based CTS (DCTS) and MIS-based CTS (MCTS), which select forwarding nodes based on the node degree and maximal independent set information, respectively. The results of both theoretical analysis and simulation reveal the remarkable advantages of CTS in minimizing broadcast latency in duty-cycled WSNs. DCTS and MCTS guarantee approximation ratios of ( Δ − 1 ) T and 12 T in terms of broadcast latency, where Δ and T denote the maximum node degree and the number of time slots in a working period, respectively. The two schemes reduce to at least 94 percent of the broadcast latency compared with existing schemes, while slightly increasing the number of transmissions due to the additional transmissions. Thanks to the latency reduction, the proposed schemes require 93 percent less energy than existing ones.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel scheduling strategy for broadcast latency minimization in duty-cycled WSNs. </LI> <LI> Allowing collisions at non-critical nodes to speed up the broadcast process. </LI> <LI> The completion of broadcast scheduling is ensured by additional transmissions. </LI> <LI> Achieving significant improvement in both theoretical and simulation results. </LI> </UL> </P>