• Journal of KIISE:Information Networking
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• v.36 no.4
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• pp.339-350
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• 2009

In wireless sensor networks, the limited battery resources of sensor nodes have a direct impact on network lifetime. To reduce unnecessary power consumption, it is often the case that only a minimum number of sensor nodes operate in active mode while the others are kept in sleep mode. In such a case, however, the network service can be easily unreliable if any active node is unable to perform its sensing or communication function because of an unexpected failure. Thus, for achieving reliable sensing, it is important to maintain the sensing level even when some sensor nodes fail. In this paper, we propose a new fault-tolerance scheme, called FCP(Fault-tolerant Coverage Preserving), that gives an efficient way to handle the degradation of the sensing level caused by sensor node failures. In the proposed FCP scheme, a set of backup nodes are pre-designated for each active node to be used to replace the active node in case of its failure. Experimental results show that the FCP scheme provides enhanced performance with reduced overhead in terms of sensing coverage preserving, the number of backup nodes and the amount of control messages. On the average, the percentage of coverage preserving is improved by 87.2% while the additional number of backup nodes and the additional amount of control messages are reduced by 57.6% and 99.5%, respectively, compared with previous fault-tolerance schemes.

• Journal of Advanced Navigation Technology
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• v.20 no.3
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• pp.232-237
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• 2016

As a possible standardization of wireless local area network (WLAN), IEEE 802.11 LRLP is under discussion in order to support long range and low power (LRLP) communication for internet of things (IoT) including drones and many other IoT devices. In this paper, an efficient adaptive resource unit allocation scheme for uplink multiuser transmission in IEEE 802.11 LRLP networks is proposed. In the proposed scheme, which adopts OFDMA random access based transmission scheme of IEEE 802.11ax, in order to enhance the efficiency of the slotted OFDMA random access, access point (AP) traces the history of the sizes of successfully transmitted uplink data, and adjusts the sizes of resource units for the next uplink multiuser transmission adaptively. Our simulation results corroborate that the proposed scheme significantly improves the system throughput.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.6
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• pp.359-366
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• 2018

Social infrastructure facilities that have been under construction since the country's high-growth period are undergoing rapid aging, and safety assessments of large structures such as bridge tunnels, which can be directly linked to large-scale casualties in the event of an accident, are necessary. Wireless smart sensor networks that improve SHM(Structural Health Monitoring) based on existing wire sensors are difficult to construct economical and efficient system due to short signal reach. The LPWAN, Low Power Wide Area Network, is becoming popular with the Internet of Things and it is possible to construct economical and efficient SHM by applying it to structural health monitoring. This study examines the applicability of LoRa LPWAN to structural health monitoring and proposes a channel usage pre-planning based LoRa network operation method that can efficiently utilize bandwidth while resolving conflicts between channels caused by using license - exempt communication band.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.7 no.2
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• pp.175-181
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• 2006

Wireless sensor network forms the self-organization network, and transfers the information among sensor nodes that have computing technology ability and wireless communication ability. The recent sensor network is study for low-power, micro, low cost of node is proceeded. Recently, the research of application services in wireless sensor networks is proceeded. Therefore, in this paper, we design the prototype of the real-time information service that support a user the information of temperature, illumination etc. And, we implement the alarm application service fer the disaster prevention on Internet base on IPv4/IPv6. We develop the module of the extract information using the query processing based on TinyOS, and the module of the server's database using MySQL data base management system and JDBC. Additionally, we develop the client module that receive the real-time sensing data using ODBC in Internet based on IPv4/IPv6.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2010.05a
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• pp.856-859
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• 2010

WSN is composed of a lot of small sensors with the limited hardware resources. In WSN, at the initial stage, sensor nodes are randomly deployed over the region of interest, and self-configure the clustered networks by grouping a bunch of sensor nodes and selecting a cluster header among them. Specially, in Mobile-WSN environment, in which the administrator's intervention is restricted, the self-configuration capability is essential to establish a power-conservative Mobile-WSN which provides broad sensing coverage and communication coverage. In this paper, we propose a self-configuration routing protocol for Mobile-WSN, which consists of step-wise novel protocols for initial deployment, effective joining and removal of sensor nodes, which result in reducing overall power consumption, and extending the lifetime of network.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.22 no.1
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• pp.202-210
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• 2018

The modern battlefield is being developed as a network-centric warfare where priority is given to rapid status grasp and power deployment through scientification and modernization. Therefore, tactical data link has been continuously improving the network speed, and recently, security technology is required for wireless communication with the UAV and various devices for reconnaissance. In addition, the future information warfare will utilize advanced IT technology positively. Efforts are needed to integrate various systems and networks. However, these efforts are meaningful only when they can assume sufficient security in a newly changing information and communication environment. In this paper, we propose a new cryptographic synchronization for link encryption suitable for tactical data links. The proposed cryptographic synchronization is useful for T4 UAV link encryption, and it is also adaptable for lower BER, then we analyze the performances analysis of that.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.18 no.4
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• pp.1042-1058
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• 2024

Terahertz (THz) communication is becoming a key technology for future 6G wireless networks because of its ultra-wide band. However, the implementation of THz communication systems confronts formidable challenges, notably beam splitting effects and high computational complexity associated with them. Our primary objective is to design a hybrid precoder that minimizes the Euclidean distance from the fully digital precoder. The analog precoding part adopts the delay-phase alternating minimization (DP-AltMin) algorithm, which divides the analog precoder into phase shifters and time delayers. This effectively addresses the beam splitting effects within THz communication by incorporating time delays. The traditional digital precoding solution, however, needs matrix inversion in THz massive multiple-input multiple-output (MIMO) communication systems, resulting in significant computational complexity and complicating the design of the analog precoder. To address this issue, we exploit the characteristics of THz massive MIMO communication systems and construct the digital precoder as a product of scale factors and semi-unitary matrices. We utilize Schatten norm and Hölder's inequality to create semi-unitary matrices after initializing the scale factors depending on the power allocation. Finally, the analog precoder and digital precoder are alternately optimized to obtain the ultimate hybrid precoding scheme. Extensive numerical simulations have demonstrated that our proposed algorithm outperforms existing methods in mitigating the beam splitting issue, improving system performance, and exhibiting lower complexity. Furthermore, our approach exhibits a more favorable alignment with practical application requirements, underlying its practicality and efficiency.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.2
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• pp.228-238
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• 2003

We believe that existing wire solutions such as HomePNA2.0 using phone lines and HomePlug using power line and wireless solution such as HomeRF are the most promising solutions, because of its cost-effectiveness. However, MAC protocols of these solutions provide only Class of Service(CoS) using priority mechanism like HomePNA and HomePlug or consider only voice among real-time traffics like HomeRF. For these reasons, we perceive the needs of the new MAC protocol which is no new wire solution and provides guaranteed Quality of Service (QoS) for not only voice but also video and audio. In light of this, we present the design and software implementation of a new MAC protocol for Home Networks. Our evaluation results of software implementation verify that proposed MAC protocol can provide low delay, low loss, and low jitter to real-time traffic by reserving bandwidth.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.7
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• pp.1465-1470
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• 2011

In this paper, we propose a new MAC protocol, namely DM-MMAC (Doze Mode Multi-Channel MAC) for ad hoe wireless networks which can utilize multiple channels effectively, thereby enhancing the network throughput considerably. Basically, the IEEE 802.11 specification allows for the use of multiple channels available at the physical layer, but its MAC protocol is designed only for a single channel with the fatal drawback, so called multi-channel hidden terminal problem in multi-channel environments. In this vein, several multi-channel MAC protocols have been proposed, but most of them demonstrate the performance problem that its throughput drastically decreases as the number of mobile hosts residing in a given network increases with small number of available channels. In this work, we tried to improve the performance of multi-channel MAC protocols in terms of network throughput as well as power saving effects by simplifying the channel assignment and channel capturing procedures and reducing the possibility of collisions between mobile hosts.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.16 no.1
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• pp.105-114
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• 2006

Ubiquitous Sensor Network consists of a number of sensor nodes with a limited computation power and limited communication capabilities, and a sensor node is able to communicate with each other at anytime and in any place. Due to the rapid research and development in sensor networks, it will rapidly grow into environments where hmm beings can interact in an intuitive way with sensing objects which can be PDAs, sensors, or even clothes in the future. We are aiming at realizing an Unattended Secure Security System to apply it to Ubiquitous Sensor Network. In this paper, the vulnerabilities in the Unattended security system are identified, and a new protocol called OMAC-SNEP is proposed for the Unattended Secure Security System. Because the CBC-MAC in SNEP is not secure unless the message length is fixed, the CBC-MAC in SNEP was replaced with OMAC in SNEP. We have shown that the proposed protocol is secure for my bit length of messages and is almost as efficient as the CBC-MAC with only one key. OMAC-SNEP can be used not only in Unattended Security System, but also any other Sensor Networks.