• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1521-1531
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• 2015

According to the service attributes, D2D communications establish 1-1, or 1-n channels and require the differentiated device discovery technology. This paper proposes a sector-based device discovery mechanism for 1-n D2D communication scenario in LTE-Advanced networks that a disaster happened. Our proposal is a mechanism that can extend the coverage in a disaster situation which a number of devices(survivors) need to be discovered in a short time. In the single cell environment, a larger discovery coverage can be obtained, and in the multi-cell, it is possible to mitigate the interference with adjacent links due to sector-based coverage control. Through a set of simulations, we have confirmed that our proposal has better performance in the number of devices discovered and the interference than the legacy broadcast device discover mechanism.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.3A
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• pp.287-295
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• 2010

In wireless sensor networks(WSNs), the studies that support sink mobility without global position information exploit a Backbone-based Virtual Infrastructure (BVI) which considers one-hop clusters and a backbone-based tree. Since the clusters of a sink and a source node are connected via flooding into the infrastructure, it causes high routing cost. Although the network could reduce the number of clusters via multi-level clusters, if the source nodes exist at nearest clusters from the cluster attached by the sink and they are in different branches of the tree, the data should be delivered via detour paths on the tree. Therefore, to reduce the number of clusters, we propose a novel multi-hop cluster based communication protocol supporting sink mobility without global position information. We exploit a rendezvous cluster head for sink location service and data dissemination but the proposed protocol effectively reduces data detour via comparing cluster hops from the source. Simulation shows that the proposed protocol is superior to the existing protocols in terms of the data delivery hop counts.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.4
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• pp.229-239
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• 2013

Recently, device-to-device (D2D) communications have been highlighted to improve the spectral efficiency and offer various user experiences in cellular networks. In this paper, we survey standards and literatures related to the D2D technology and address various advantages of D2D technology, and the problems to be resolved before practically implemented. Especially, by considering an important interference issue between cellular and D2D links, five resource allocation and interference management scenarios are provided and their performances are evaluated through the system level simulations. The simulation results show that the use of D2D significantly improve the cell capacity and the D2D user rate due to the effects of frequency reuse and data off-loading. Notably, it is also shown that an optimal D2D communication range exists to maximize the system performance.

• Journal of Internet Computing and Services
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• v.18 no.2
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• pp.1-11
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• 2017

There are two kinds of wireless network access to a certain place by using smart devices - 1) open (anonymous) - access and 2) user-authorized access. The open-access is a non-authorization connection method which does not need to require Smart device's user authorized information. It means open-access use only user's SSID (Service Set Identifier) information to access the wireless AP devices following public wireless network standard. This access mechanism is not suitable to use all of public wireless networks because users have to get all wireless network information around them. As a result, huge data for smart devices should be one of the most critical overload problems for them. Secondly, the user-authorized access method uses wireless network information (SSID and password) chosen by the users. So, the users have to remember and use the network access information data manually whenever accessing the network. Like open-access, this access method also has the operational and inconvenient problem for the users - manually inputting access information whenever connecting to the network. To overcome this problem in both schemes, we propose two improved wireless network access methods: 1) the implementation of automatic AP connection mechanism using user-authorization and iBeacon messages, and 2) SSID registration form for public wireless networks.

• Journal of Korean Society of Transportation
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• v.26 no.6
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• pp.93-101
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• 2008

With a spread of mobile devices, the growing trend of integrating wireless communications technologies into transportation systems is advanced. In particular, vehicular ad hoc networks (VANETs) enable vehicles to share traffic information that they have through intervehicle communications. This research focused on the design of an integrated transportation and communication simulation framework to build an environment that is more realistic than previous studies developed for studying VANETs. Developing a VANET-based information model, this research designed an integrated transportation and communication simulation framework in which these independent simulation tools not supporting High Level Architecture (HLA) were tightly coupled and finely synchronized. As a case study, a VANET-based traffic information system was demonstrated based on a real road network and real traffic data. The experiment results showed that the simulation framework was well integrated. The simulation framework designed in this study is expected to contribute to developing the environment to experiment a wide range of VANET applications.

• Journal of the Korean Regional Science Association
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• v.12 no.2
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• pp.99-116
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• 1996

This study investigates the nature and patterns of interrelation between the emerging information and communication technology(ICT) and the organization of corporate space, both theoretically and empirically. In this work, ICT is conceptualized not so much a space-adjusting technology as an organizational technology. ICT is considered as a governance technology which is related to coordination function within a firm. Therefore, it is supposed to have a great relevance to the spatial reorganization of functions within a firm. Both questionnaire and case study method are used to gather necessary data from Korean electronics manufactures. The results of this study can be summarized as follow. First, the spatial structure of a firm, which is operationalised as the number and type of spatially separated establishments, is turned out to have a great explanatory power to its adoption of computer networks. Computer networks in muli-locational companies are introduced to overcome the limits of its spatial structure, such as duplication of functions, such as duplication of functions, loss of time spent in proceeding a job between different functional units, and unresponsiveness to the change of market demand. Second, new spatial division of labor and function could be possible through a series of business process reengineering, not through the mere adoption of ICT. Case studies reveal that computer network could help a firm to realize new forms of spatial division of labor, especially in those functions which is mainly based on the flow of information. Such function as ICT management, sales logistics and after-sales service are major parts where a new operational unit has appeared with the help of ICT. From above results, it can be concluded that the interrelations between ICT and organizational space should be approached intimately integrated with the change of industrial structure and it's organizational implications.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.5
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• pp.1569-1586
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• 2015

This paper considers the optimal cell association and resource allocation for load balancing in a heterogeneous cellular network subject to user's quality-of-service (QoS) constraints. We adopt the proportional fairness (PF) utility maximization formulation which also accommodates the QoS constraints in terms of minimum rate requirements. With equal resource allocation this joint optimization problem is either infeasible or requires relaxation that yields a solution which is difficult to implement. Nevertheless, we show that this joint optimization problem can be effectively solved without any priori assumption on resource allocation and yields a cell association scheme which enforces single BS association for each user. We re-formulated the joint optimization problem as a network-wide resource allocation problem with cardinality constraints. A reweighted heuristic l₁-norm regularization method is used to obtain a sparse solution to the re-formulated problem. The cell association scheme is then derived from the sparsity pattern of the solution, which guarantees a single BS association for each user. Compared with the previously proposed method based on equal resource allocation, the proposed framework results in a feasible cell association scheme and yields a robust solution on resource allocation that satisfies the QoS constraints. Our simulations illustrate the impact of user's minimum rate requirements on cell association and demonstrate that the proposed approach achieves load balancing and enforces single BS association for users.

• Convergence Security Journal
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• v.20 no.3
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• pp.47-52
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• 2020

The introduction of virtualization technology in the broadcasting field is actively progressing broadcasting service automation and intelligence based on the effective operation of IT resources throughout the broadcasting industry ecosystem. In recent years, there is increasing interest in increasing the flexibility of various broadcasting resources and increasing the efficiency of interworking with other networks through network virtualization of the broadcasting network infrastructure. The fundamental transformation from the broadcasting network to the IP paradigm is facing a situation where it is necessary to solve various problems for the effective interworking of Internet-based service platforms and 5G networks and the development of new convergence services. In other words, for organic and effective interworking with the next-generation broadcasting network represented by ATSC 3.0, a mobile communication network represented by 5G, and the Internet, a number of difficulties must be solved. In this paper, the basic technology and status for the convergence of ATSC 3.0 broadcasting network and mobile communication network represented by 5G was examined, and a plan for the ATSC 3.0 broadcasting network and 5G network to interwork with each other as a network was described.

• Journal of Communications and Networks
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• v.14 no.6
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• pp.653-661
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• 2012

High-availability seamless redundancy (HSR) is a redundancy protocol for Ethernet networks that provides two frame copies for each frame sent. Each copy will pass through separate physical paths, pursuing zero fault recovery time. This means that even in the case of a node or a link failure, there is no stoppage of network operations whatsoever. HSR is a potential candidate for the communications of a smart grid, but its main drawback is the unnecessary traffic created due to the duplicated copies of each sent frame, which are generated and circulated inside the network. This downside will degrade network performance and might cause network congestion or even stoppage. In this paper, we present two approaches to solve the above-mentioned problem. The first approach is called quick removing (QR), and is suited to ring or connected ring topologies. The idea is to remove the duplicated frame copies from the network when all the nodes have received one copy of the sent frame and begin to receive the second copy. Therefore, the forwarding of those frame copies until they reach the source node, as occurs in standard HSR, is not needed in QR. Our example shows a traffic reduction of 37.5%compared to the standard HSR protocol. The second approach is called the virtual ring (VRing), which divides any closed-loop HSR network into several VRings. Each VRing will circulate the traffic of a corresponding group of nodes within it. Therefore, the traffic in that group will not affect any of the other network links or nodes, which results in an enhancement of traffic performance. For our sample network, the VRing approach shows a network traffic reduction in the range of 67.7 to 48.4%in a healthy network case and 89.7 to 44.8%in a faulty network case, compared to standard HSR.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.1
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• pp.121-127
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• 2017

In the land mobile satellite (LMS) communication, a hybrid satellite-terrestrial relay networks (HSTRNs) using a maximal ratio combining (MRC) scheme are widely used to enhance the quality of signal from a satellite. In this paper, we derive equations for the TCP throughput and the spectral efficiency in the HSTRN and analyze results of the performance evaluation for TCP in various environments. In the simulation results, it is shown that increasing the number of terrestrial relays can enhance the TCP throughput and spectral efficiency thanks to the MRC scheme. However, the usage of the static number of terrestrial relays considering no channel states would cause the overhead. Furthermore, it has a limitation to enhance the network performance by only MRC scheme in HSTRN because the TCP performance is sensitive to the packet los rate. Therefore, we discuss the possible solutions that can additionally enhance the network performance and reduce the overhead.