• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2012.05a
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• pp.896-898
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• 2012

Recently, many countries are making efforts for the development of ocean resources because the necessity and importance of the ocean resources are increased. Underwater sensor networks have emerged as a very powerful technique for many applications, including monitoring, measurement, surveillance and control and envisioned to enable applications for oceanographic data collection, ocean sampling, environmental and pollution monitoring, offshore exploration, disaster prevention, tsunami and seaquake warning, assisted navigation, distributed tactical surveillance, and mine reconnaissance. The idea of applying sensor networks into underwater environments (i.e., forming underwater sensor networks) has received increasing interests in monitoring aquatic environments for scientific, environmental, commercial, safety, and military reasons. The data obtained by observing around the environment are wireless-transmitted by a radio set with various waves. According to the technical development of the medium set, some parameters restricted in observing the ocean have been gradually developed with the solution of power, distance, and corrosion and watertight by the seawater. The actual matters such as variety of required data, real-time observation, and data transmission, however, have not enough been improved just as various telecommunication systems on the land. In this paper, a wireless management system will be studied through a setup of wireless network available at fishery around the coast, real-time environmental observation with RF sensor, and data collection by a sensing device at the coastal areas.

• The Journal of the Korea Contents Association
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• v.9 no.12
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• pp.515-527
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• 2009

IEEE 802.11n is an ongoing next-generation WLAN(Wireless Local Area Network) standard that supports a very high-speed connection with more than 100Mb/s data throughput measured at the MAC(Medium Access Control) layer. Study trends of IEEE 802.11n show two aspects, enhanced data throughput using aggregation among packets in MAC layer, and better data rates adapting MIMO(Multiple-Input Multiple-Output) in PHY(Physical) layer. But, the former doesn't consider wireless channel and the latter doesn't consider aggregation among packets for reality. Therefore, this paper analyzes data throughput for IEEE 802.11n considering MAC and PHY connection. A-MPDU(Aggregation-MAC Protocol Data Unit) and A-MSDU(Aggregation-MAC Service Unit) is adapted considering multi-service in MAC layer, WLAN MIMO TGn channel using SVD(Singular Value Decomposition) is adapted considering MIMO and wireless channel in PHY layer. Consequently, Simulation results shows throughput between A-MPDU and A-MSDU. Also, We use Ns-2(Network simulator-2) for reality.

• Journal of KIISE:Information Networking
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• v.27 no.2
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• pp.160-174
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• 2000

Nowadays, most widely used transport protocol, TCP is tuned to perform well in traditional networks where packet losses occur mostly because of congestion. TCP performs reliable end-to-end packet transmission under the assumption of low packet error rate. However, networks with wireless links suffer from significant losses due to high error rate and handoffs. TCP responds to all losses by invoking congestion control and avoidance algorithms, resulting in inefficient use of network bandwidth and degraded end-to-end performance in that system. To solve this problem, several methods have been proposed. In this paper, we analyse and compare these methods and propose appropriate model for improving TCP performance in the network with wireless links. This model uses TCP selective acknowledgement (SACK) option between TCP ends, and also uses caching method at the base station. Our simulation results show that using TCP SACK option with base station caching significantly reduces unnecessary duplicate retransmissions and recover packet losses effectively.

• Journal of Digital Convergence
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• v.12 no.2
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• pp.271-276
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• 2014

The life-time and performance of a wireless sensor network is closely related to energy-efficiency of sensor nodes. In this paper, to increase energy-efficiency, each sensor node operates in one of three operational modes which are normal, power-saving, and inactive. In normal mode sensor nodes sense and transmit data with normal period, whereas sensor nodes in power-saving mode have three-times longer period. In inactive mode, sensor nodes do not sense and transmit any data, which makes the energy consumption to be minimized. Plus, the proposed algorithm can avoid unnecessary energy consumption by preventing transmitting duplicate sensed data. We implemented and simulated the proposed algorithm using Tiny OS based ZigbeX platfom and NS-2, respectively. Performance evaluation results show that the proposed algorithm can prolong sensor networks' lifespan by efficiently reducing energy consumption and its standard deviation of all sensor nodes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.14 no.3
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• pp.943-961
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• 2020

With the advent of IoT technology and Big Data computing, the importance of WSNs (Wireless Sensor Networks) has been on the rise. For energy-efficient and collection-efficient delivery of any sensed data, lots of novel wireless medium access control (MAC) protocols have been proposed and these MAC schemes are the basis of many IoT systems that leads the upcoming fourth industrial revolution. WSNs play a very important role in collecting Big Data from various IoT sensors. Also, due to the limited amount of battery driving the sensors, energy-saving MAC technologies have been recently studied. In addition, as new IoT technologies for Big Data computing emerge to meet different needs, both sensors and sinks need to be mobile. To guarantee stability of WSNs with dynamic topologies as well as frequent physical changes, the existing MAC schemes must be tuned for better adapting to the new WSN environment which includes energy-efficiency and collection-efficiency of sensors, coverage of WSNs and data collecting methods of sinks. To address these issues, in this paper, a self-organization scheme for mobile sensor networks with mobile multiple sinks has been proposed and verified to adapt both mobile sensors and multiple sinks to 3-dimensional group management MAC protocol. Performance evaluations show that the proposed scheme outperforms the previous schemes in terms of the various usage cases. Therefore, the proposed self-organization scheme might be adaptable for various computing and networking environments with big data.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1369-1376
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• 2015

A wireless bridge is essential to transmit control and managing information to sensors or instruments from a central integrated ship area network station. In this paper, a WiMedia Distributed-MAC(D-MAC) protocol is adopted for development of a seamless N-Screen wireless service in Indoor and Ship Area Networks. Furthermore, to provide the OSMU(One Source Multi Use) N-screen service through P2P streaming in the seamless D-MAC protocol, a Dynamic Threshold-based Multicast(DTM) technology is proposed and analyzed. For this technology, a new Hard/Soft Vertical Region(HVR-SVR) based time slot allocation and a multicast resource reservation scheme are combined. From simulation results, proposed DTM scheme expands the number of time slots available for unicast and multicast realtime N-Screen reservations with various service time interval requests. Furthermore, it enhances performances in vewpoints of realtime N-Screen data reservation conflict and throughput.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4B
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• pp.165-173
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• 2008

In this paper, we propose a new reliable broadcast protocol referred to as timer-based reliable broadcast (TRB) for wireless sensor networks (WSNs). The proposed TRB scheme exploits (1) bitmap based explicit ACK to effectively reduce the unnecessary error control messages and (2) randomized timer for ACK transmission to substantially reduce the possibility of contentions. Although it has been argued that 100% reliability is not necessary in WSNs, there should be messages (such as mission-critical message, task assignment, software updates, etc.) that need to be reliably delivered to the entire sensor field. We propose to use the TRB algorithm for such cases. Performance evaluation shows that the TRB scheme achieves 100 % reliability significantly better than other schemes with expense of slightly increased energy consumption.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.3
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• pp.239-246
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• 2014

In the context of wireless sensor networks, one of major issues is energy conservation. For low power communication, by utilizing our experimental results for the relation between clock drift and synchronization interval, we designed a new protocol which can support a wide range of duty cycles for applications with very low traffic rate and insensitive delay. The transmission (TX) node in the protocol synchronizes with the reception (RX) node very before transmitting a packet, and it can adaptively estimate the synchronization error size according to the synchronization interval from minutes to hours. We conducted simulations and a testbed implementation to show the efficacy of the proposed protocol. We found that our protocol substantially outperforms other state-of-the-art protocols, resulting in order-of-magnitude increase in network lifetime over a variety of duty cycles.

• Journal of the Korea Society of Computer and Information
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• v.13 no.2
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• pp.203-210
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• 2008

Home networking has been noticed as a key technology for the home automation because it is possible to remotely monitor and control the in-house appliances and devices through the network. Wireless home networking method is easily applied to the conventional houses compared to the wired home networking method because of low cost and small effort due to no extra wired works. Especially, home networking using the ZigBee protocol is one of the most attractive technologies in the wireless networking area because of its low cost and low power consumption characteristics. However, there are a lot of practical problems to be solved in implementing the ZigBee module and constructing the wireless network. In this paper, one of the practical structures of the hardware and software modules for implementing the ZigBee protocol is proposed. Moreover, problems in constructing the home networking with the proposed ZigBee module are introduced, and the effective solutions to solve these problems are described through various tests.

• Journal of Internet Computing and Services
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• v.15 no.2
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• pp.9-18
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• 2014

The sensors attached on/in a person are moved since human body frequency changes their activity, therefore in wireless body area networks, nodal mobility and non-line-of-sight condition will impact on performance of networks such as energy efficiency and reliable communication. We then proposed schemes which study on forwarding decisions against frequent change of topology and channel conditions to increase reliable connections and improve energy efficiency. In this work, we control the size of packets, forwarding rate based on ratio of input links and output links at each node. We also robust the network topology by extending the peer to peer IEEE 802.15.4-based. The adaptive topology from chain-based to grid-based can optimal our schemes. The simulation shows that these approaches are not only extending network lifetime to 48.2 percent but also increase around 6.08 percent the packet delivery ratio. The "hot spots" problem is also resolved with this approach.