• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.1-8
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• 2020

The Ministry of Land, Infrastructure and Transport of Korea has been trying to spread integrated railway communication network technologies based on a major railway policy since 2012. As a result, the world's first commercial Long-Term Evolution - Railway (LTE-R) network was established on the Gangneung line (Manjong station - Gangneung station) and has been commercially operating as a railway communication system since 2017. Special function and performance requirements are needed for safe and efficient railway operations, such as group calls, emergency calls, functional addressing, and train control based on wireless communications. In this paper, we present functional and performance railway communications requirements that are based on European wireless railway communications systems. In addition, we measured communications characteristics and performance using a KTX field test on the Gangneung line to analyze the validity and reliability of the LTE-R network. Although the average Radio Frequency (RF) conditions were satisfied in the requirements, we found sudden communications quality degradation, such as Radio Link Failure (RLF) in some railway sections. We propose a way to improve performance and network installations based on in-depth analysis of LTE-R communications field-test results.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.9
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• pp.34-41
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• 2017

Wireless mesh networks contain multi-hop routing protocols between wireless nodes and are connected to the Internet through a gateway. These networks perform a role as a backbone and are scalable for main applications. We propose the design of QoS supporting mechanisms for wireless mesh networks using software defined networking. Our proposed scheme is cost-effective and features adaptive QoS mechanisms for wireless router's resource constraints. The QoS mechanisms use software defined networking technology with Openflow protocol based on diffserv and intserv models with MPLS mechanism and RSVP respectively. A performance evaluation model is suggested to verify the validity of the proposed scheme using several QoSmetrics of the wireless mesh networks.

• Journal of the Korean Operations Research and Management Science Society
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• v.41 no.2
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• pp.53-65
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• 2016

Static wireless multi-hop networks, such as wireless mesh networks and wireless sensor networks have proliferated in recent years because of they are easy to deploy and have low installation cost. Two key measures are used to evaluate the performance of a multicast tree algorithm or protocol : end-to-end delay and the number of transmissions. End-to-end delay is the most important measure in terms of QoS because it affects the total throughput in wireless networks. Delay is similar to the hop count or path length from the source to each destination and is directly related to packet success ratio. In wireless networks, each node uses the air medium to transmit data, and thus, bandwidth consumption is related to the number of transmission nodes. A network has many transmitting nodes, which will cause many collisions and queues because of congestion. In this paper, we optimize two metrics through a guaranteed delay scheme. We provide an integer linear programming formulation to minimize the number of transmissions with a guaranteed hop count and preprocessing to solve the aforementioned problem. We extend this scheme not only with the guaranteed minimum hop count, but also with one or more guaranteed delay bounds to compromise two key metrics. We also provide an explanation of the proposed heuristic algorithm and show its performance and results.

• Journal of Korea Society of Industrial Information Systems
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• v.11 no.2
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• pp.48-62
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• 2006

In recent years, wireless sensor networks(WSNs) have emerged as a new fast-growing application domain for wireless distributed computing and embedded systems. Recent Progress in computer and communication technology has made it possible to organize wireless sensor networks composed tiny sensor nodes. Furthermore, ad-hoc network protocols do not consider the characteristics of wireless sensor nodes, making existing ad-hoc network protocols unsuitable for the wireless sensor networks. First, we propose power-aware routing protocols based on energy-centered routing metrics. Second, we describe power management techniques for wireless sensor nodes using the spatial locality of sensed data. Many nodes can go into a power-down mode without sacrificing the accuracy of sensed data. Finally, combining the proposed techniques, we describe an overall energy-efficient protocol for data collection. Experimental results show that the proposed routing protocol can extend the routing path lifetime more than twice. The average energy consumption per sensing period is reduced by up to 30%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1342-1347
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• 2010

Various researches have been studied on WSN(wireless sensor network) for barbed wire entanglements surveillance applications such as industry facilities, security area, prison, military area, airport, etc. Currently, barbed wire entanglements surveillance is formed wire sensor network environment. Traditional wire sensor network guarantee high data transmission rate. Therefore, wire sensor network use fast fourier transform of data of high transmission rate for extraction of feature parameter. However, wireless sensor network in comparison with wire sensor network has very low data transmission rate. Therefore, wireless sensor network doesn't use fast fourier transform of wire sensor network for extraction of feature parameter. In this paper, proposed method use 1 level approximation coefficient of DTW(dynamic time-warped) algorithms based on DWT(discrete wavelet transform) for extraction of detection feature parameter and classification feature parameter for barbed wire entanglements surveillance. l level approximation coefficient have time information and frequency information of signal. Therefore, Dynamic time-warped algorithms based on discrete wavelet transform improve detection and classification of target rather than using energy of signal.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.12
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• pp.6081-6088
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• 2012

An unequal clustering method in wireless sensor networks is the technique that forms the cluster of different size. This method decreases whole energy consumption by solving the hot spot problem. In this paper, I propose a layer-based dynamic unequal clustering using the unequal clustering model. This method decreases whole energy consumption and maintain that equally using optimal cluster's number and cluster head position. I also show that proposed method is better than previous clustering method at the point of network lifetime.

• Proceedings of the IEEK Conference
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• 2009.05a
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• pp.290-292
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• 2009

With advance in technologies for wireless sensor networks(WSNs), 2.4 GHz band has become gradually attractive due to increase in low-power wireless communication devices. Especially ZigBee(IEEE 802.15.4-based) technology whose frequency band includes the 2.4GHz industrial, scientific and medical band providing nearly worldwide availability has been universally applicable to a various remote monitoring system and applications related home network system. However network throughput of these systems is significantly deteriorated due to this ISM band is a license-exemption used in a variety of low-power wireless communication devices. For instance, other IEEE 802 wireless standards such as Bluetooth, WLAN, Wi-Fi and others cause radio interference to ZigBee. The experiments was carried out to analyze radio frequency interference between heterogeneous devices using ISM bands to improve the limited frequency utility factor. Finally this paper suggests a frequency hopping-based adaptive multi-channel methods to decrease interference with empirical results.

• Journal of the Korean Society for Railway
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• v.12 no.1
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• pp.45-54
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• 2009

TETRA(Terrestrial Trunked Radio) is the standard of D-TRS(Digital Trunked Radio System) developed by the ETSI(European Telecommunications Standards Institute). Currently, TETRA has been selected as Electric Power IT Wireless Backbone Network. Traditional distribution automation system has used the wireless network of Mobile Service Provider using CDMA(Code-Division Multiple Access) and WCDMA(Wideband CDMA) modem. Therefore, the development of gateway platform is indispensable according to the change to TETRA network. In this paper, we propose an embedded Linux-based Gateway platform for transmitting Industrial Electric Power IT protocol using TETRA network.

• Industrial Engineering and Management Systems
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• v.16 no.1
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• pp.92-102
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• 2017

In this paper, we consider a typical health care system via the help of Wireless Sensor Network (WSN) for wireless patient tracking. The wireless patient tracking module of this system performs localization out of samples of Received Signal Strength (RSS) variations and tracking through a Particle Filter (PF) for WSN assisted by multiple transmit-power information. We propose a modified PF, Kullback-Leibler Distance (KLD)-resampling PF, to ameliorate the effect of RSS variations by generating a sample set near the high-likelihood region for improving the wireless patient tracking. The key idea of this method is to approximate a discrete distribution with an upper bound error on the KLD for reducing both location error and the number of particles used. To determine this bound error, an optimal algorithm is proposed based on the maximum gap error between the proposal and Sampling Important Resampling (SIR) algorithms. By setting up these values, a number of simulations using the health care system's data sets which contains the real RSSI measurements to evaluate the location error in term of various power levels and density nodes for all methods. Finally, we point out the effect of different power levels vs. different density nodes for the wireless patient tracking.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.7
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• pp.4554-4561
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• 2014

In recent years, several paradigms have been identified to simplify the design of fault-tolerant distributed applications in a conventional static system. Leader Election is among the most noticeable, particularly because it is closely related to group communication, which provides a powerful basis for implementing active replications among other uses. On the other hand, despite its usefulness, to our knowledge, no study has focused on this problem in a mobile computing environment. The aim of this paper was to propose an algorithm for the leader election protocol in a fixed station based wireless networks environment. The election algorithm is much more efficient than other election algorithms in terms of the fault tolerance.