• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.3
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• pp.1373-1392
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• 2017

WiFi Direct (WD) is a state of the art technology for a Device-to-Device (D2D) communication in 802.11 networks. The performance of the WD system can be significantly affected by some key factors such as the type of application, specifications of MAC and PHY layer parameters, and surrounding environment etc. It is, therefore, important to develop a system model that takes these factors into account. In this paper, we focus on investigating the design parameters of the PHY layer that could maximize the efficiency of the WD 802.11 system. For this purpose, a basic theoretical model is formulated for a WD network under a 2x2 Multiple In Multiple Out (MIMO) TGn channel B model. The design level parameters such as input symbol rate and antenna spacing, as well as the effects of the environment, are thoroughly examined in terms of path gain, spectral density, outage probability and Packet Error Rate (PER). Thereafter, a novel adaptive algorithm is proposed to choose optimal parameters in accordance with the Quality of Experience (QoE) for a targeted application. The simulation results show that the proposed method outperforms the standard method thereby achieving an optimal performance in an adaptive manner.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.6
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• pp.915-920
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• 2011

P2P technology is the concept to share resources efficiently in distributed environments that a lot of research is underway. a lot. In these P2P systems, the server to support the contents-information have less overloads than the composed system as the server to have resources generally. In this paper, we suggest a P2P system to support conveniences to choice time for users that were connected with the information of joint-buying based on social network. Social networks based on co-purchasing information and price alerts using the P2P system is provided by the peer, this relay information is provided by the P2P server.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.2
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• pp.312-318
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• 2011

USN technology will be applied to various fields such as logistics, transportation, government, health, welfare and environment and will be settled down by basic infrastructure of a future society. In this study, we analyzed sensor networks structure based on IEEE 802.15.4 and implemented the sensor monitoring system using Zigbee modules. For implementation of real-time sensor monitoring system, we designed Linux-based development environment and the sensor-specific component. The result of this paper may be utilized in such areas lighting system, intrusion detection, fire detection, detection and notification of abnormal conditions.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.6
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• pp.588-594
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• 2010

In a multi-hop wireless sensor network, broadcasting is an elementary operation to support command message sending, route discovery and other application tasks. Broadcasting by flooding may cause serious redundancy, contention, and collision in the network, which is referred to as the broadcast storm problem. Many broadcasting schemes have been proposed to give better performance than simple flooding in wireless sensor network. How to decide whether re-broadcast or not also poses a dilemma between reach ability and efficiency under different host densities. In this paper, we present popular broadcasting schemes, which can reduce re-broadcast packets and improve SRB(Saved ReBroadcast). Simulation results show different levels of improvement over the simple flooding scheme.

• International journal of advanced smart convergence
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• v.5 no.1
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• pp.23-29
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• 2016

The information is to be considered as important part of any network, the communication nodes within network can able to communicate and transmit information by the means of configured LAN/WAN, or/and using internet technology. Thus, vast enhancement has been made in- exchanging of information over transmission media, this should be beneficial in various disciplines of modern client/server applications but at other side, several massive vulnerabilities have been directly/in-directly associated with them. To resolve the security issues, a security mechanism is proposed which hide the sensitive information of images before transmitting to networks. Random size image samples have used and encrypted to protect them from unauthorized entities. The encryption mechanism manipulates the sample images, and corresponding secret codes are generated which help to protect the images from adversaries. To provide an indestructible security mechanism, cryptography algorithms are deployed and considered as best solutions to keep the secret information of images.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.12 no.3
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• pp.83-88
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• 2012

This paper studies the effects of wavelength conversion on self-healing optical networks. We examined the effects of wavelength conversion capability on the backup routing and the spare wavelength utilization. The efficiency of spare wavelength utilization is proportionally increased as the wavelength conversion capability increases, different from the call blocking probability for which about 30% of wavelength conversion capability shows nearly the same performance as full wavelength conversion capability. The spare resource utilization efficiency can be improved by using alternate routing and wavelength assignment algorithms.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.4
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• pp.41-48
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• 2010

In this paper, a new type of integrated AFCI is designed and implemented by combining individual circuit breaker characteristics, which can effectively detect arc fault signals in real-time. The proposed integrated AFCI satisfies the UL1699, the USA certification standard, and the Korean circuit breaker standards such as KS C4613 and KS C8321. Data signals are transferred to the management server via ZigBee network to analyze dangerous factors and to prevent unwanted trip. It is also shown by experiments that arc fault signals are detected and analyzed by using the integrated AFCI with ZigBee networks.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.14 no.6
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• pp.229-234
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• 2014

As association between sensor networks that collect environmental information by using numberous sensor nodes and smartphones that are equipped with various sensors, many applications understanding users' context have been developed to interact users and their environments. Collected data should be stored with XML formatted metadata containing semantic information to share the collected data. In case of distance based clustering schemes, the efficiency of data collection decreases because metadata files are extended and changed as the purpose of each system developer. In this paper, we proposed a clustering scheme considering the structural similarity of metadata to reduce clustering construction time and improve the similarity of metadata among member nodes in a cluster.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.4
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• pp.35-42
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• 2008

Since Bianchi's 2-D Markov Chain Model considers collision problem only in ideal channel condition, it does not reflect real channel impaired by fading, interference, and noise. Distributed Coordination Function(DCF) doubles its contention window(CW) when transmission fails regardless of collision or transmission error. Increase of CW caused by transmission error degrade throughput and increase the delay. In this paper, we present quantitative analysis of the impact of the parameters such as contention window size(CW), transmission probability for a given time slot(${\Im}$), transmission failure probability($p_f$), on the system performance and provide a method how to decrease the initial CW to achieve equivalent performance.

• Journal of the Korea Institute of Military Science and Technology
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• v.11 no.1
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• pp.5-14
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• 2008

In this paper, we propose operational concepts and technology requirements for guard and surveillance robots in military field. After surveying on current trend of guard robots, we present an operational scenario and technology requirements. To begin with, we discriminate the use of fixed type guard robots(fixed robots) and mobile guard and surveillance robots(mobile robots). Fixed robots are used for substituting daily guard by human soldier. In contrast, mobile robots are used for compensating shadow area where not to be covered by fixed type robots. To be specific, mobile robots adopt communication relays to extend operational range and sensor networks to collecting information. In addition, we present technology requirements composed of wireless communication system, platform, sensor nodes, unmanned driving technology, power supply system and IFF etc. In conclusion, in order to maximize co-operational functionality, fixed robots and mobile robots should be tightly related.