• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.8
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• pp.597-606
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• 2013

The performance of TCP depends on the degree of traffic congestion between the sender and the receiver. The traffic could increase, and this causes congestion which may cause trouble in data transfer. Then, TCP tries to eliminate the trouble by reducing the transfer speed with slowstart scheme. When a mobile node moves over heterogeneous wireless networks, TCP experiences dramatic change of the amount of traffic, and it performs slowstart. In this paper, we propose the efficient scheme of TCP slowstart that should performs after vertical handoff. In this scheme, TCP receiver forces slowstart, which is different form normal schemes. Its performance is better than the normal schemes in that TCP sender experiences traffic congestion and performs slowstart. We perform simulation to measure and to verify the improved performance.

• Proceedings of the Korea Information Assurance Society Conference
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• 2004.05a
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• pp.103-108
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• 2004

A Home Location Register(HLR) database system manages each subscriber's location information, which continuously changes in a cellular network. For this purpose, the HLR database system provides table management, index management, and backup management facilities. In this thesis, I propose using a two-level index method for the mobile directory number(MDN) as a suitable method and a chained bucket hashing method for the electronic serial number(ESN). Both the MDN and the ESN are used as keys in the HLR database system. I also propose an efficient backup method that takes into account the characteristics of HLR database transactions. The retrieval speed and the memory usage of the two-level index method are better than those of the T-tree index method. The insertion and deletion overhead of the chained bucket hashing method is less than that of the modified linear hashing method. In the proposed backup method, I use two kinds of dirty flags in order to solvethe performance degradation problem caused by frequent registration-location operations. I also propose using additional attributes in the HLR database scheme for location information secrecy as a suitable security method.

• The Journal of the Korea institute of electronic communication sciences
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• v.6 no.6
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• pp.909-914
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• 2011

In these days, according to the enhancement of the mobile communication technologies, location based services using the location and movements are vitalized. In this paper, we develop a private vehicle tracking system for garbage truck operation management using GPS and CDMA communication and Open map interface. The terminal equipment attached in vehicle receives the GPS signals and detect the position data including time, longitude, latitude, and altitude. And the terminal sends these data to the server PC through CDMA cellular network in fixed period. The server saves these data into database to process in map server program with which we can view real-time trace of moving vehicle. We apply our system to public garbage truck managing operation and we can increase operation efficiency by examine real-time working and moving path and by present reasonable operation rout.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.10B
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• pp.891-899
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• 2006

Generally, a geographical area consists of many regions called cells in wireless networks. Each mobile host(MH) in a cell communicates with a base station(BS) located in the center of the cell. The BSs are connected to each other by a static wired network. Since users are expected to move around during communication sessions, one of the most important QoS factors is related to the handoff. But, the handoff could fail due to unavailability of sufficient bandwidth in the next cell. As the individual cell size gradually shrinks to accommodate increasing the number of MHs, the probability of successful handoffs can be dropped. In this paper, we suppose a bandwidth reservation method to guarantee MHs against connection failure in case of frequent handoffs. This method predicts the mobility based on the geographical information and assigns the bandwidth reservation in proportion to the speed of MHs' motion. As a result, we can expect more exact moving path of MH and to reduce the waste of bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39B no.10
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• pp.654-663
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• 2014

Heterogeneous network (HetNet) with the various types of cells, e.g., with the different cell size and transmit power, has been introduced to improve the cell coverage and areal capacity in cellular mobile communication system. In this paper, we consider a practical situation in which all cells share the same wireless resource while some of them have a limited backhaul capacity. More specifically, we formularize a cell association problem that utilizes the minimum wireless resource while satisfying the quality of service (QoS) of all users in terms of their transmission time constraint, and propose a distributed algorithm to find the optimal solution. In the event of bottleneck at the backhaul link in some small cells, the proposed algorithm off-loads some users to the adjacent cell with the less congested backhaul capacity. Finally, we verify that the proposed algorithm supports the more numbers of users to satisfy the specified level of QoS than the conventional user association scheme under the limited access and backhaul capacities.

• The Journal of the Korea institute of electronic communication sciences
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• v.14 no.5
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• pp.917-926
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• 2019

At present, TICN has been developed and distributed for military command control. TICN is known as the 3.5G mobile communication technology based on WiBro, which shows technical limitation in the field operation situation. Accordingly, the drone-type base station platform is attracting attention as an alternative to overcome technical limitations such as difficulty in securing communication LoS and limiting expeditious network configuration. In this study, we performed simulation performance evaluation of drone-type base station operation in 28 GHz that is considered most suitable for cellular communication within mmWave frequency band. Specifically, we analyzed the changes in throughput and fairness performance according to radio resource management policies such as frequency reuse and scheduling in multi-cell topology. Through this, we tried to provide insights on the operation philosophy on drone-type base station.

• Journal of KIISE:Information Networking
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• v.29 no.3
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• pp.253-264
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• 2002

Recently, hierarchical architectures of databases for location management have been proposed in order to accommodate the increase in user population in future personal communication systems. In particular, a 3-level hierarchical database architecture is compatible with current cellular mobile systems. In the architecture, a newly developed additional databases, regional location database(RLR), are positioned between HLR and VLRs. We propose an efficient cache scheme, called the Double T-thresholds Location Cache Scheme. The cache scheme extends the existing T-threshold location cache scheme which is competent only under 2-level architecture of location databases currently adopted by IS-41 and GSM. The idea behind our scheme is to use two pieces of cache information, VLR and RLR serving called portables. The two pieces are required in order to exploit root only locality of registration area(RA) but also locality of regional registration area(RRA) which is the wide area covered by RLR. We also use two threshold values in order to determine whether the two pieces are obsolete. In order to model the RRA residence time, the branching Eralng-$\infty$ distribution is introduced. Our minute cost analysis shows that the double T-threshold location cache scheme yields significant reduction of network and database costs for molt patterns of portables.

• Journal of Korea Multimedia Society
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• v.14 no.1
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• pp.54-75
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• 2011

PoC(Push-to-talk Over Cellular) is an integrated technology of group voice calls, video calls and internet based multimedia services. If a PoC user can not participate in the PoC session for various reasons such as an emergency situation, lack of battery capacity, then the user can use the PoC Box which has a similar functionality to the MM Box in the MMS(Multimedia Messaging Service). The RTSP(Real-Time Streaming Protocol) method is recommended to be used when there is a transmission session between the PoC box and a terminal. Since the existing VOD service uses a wired network, the packet size of RTSP-based VOD service is huge, however, the PoC service has wireless communication environments which have general characteristics to be used in RTSP method. Packet loss in a wired communication environments is relatively less than that in wireless communication environment, therefore, a buffering latency occurs in PoC service due to a play-out delay which means an asynchronous play of audio & video contents. Those problems make a user to be difficult to find the information they want when the media contents are played-out. In this paper, the following techniques and methods were proposed and their performance and superiority were verified through testing: cross-over dual reception buffering technique, advance partition multi-reception buffering technique, and on-demand multi-reception buffering technique, which are designed for effective picking up of information in media content being transmitted in short amount of time using RTSP when a user searches for media, as well as for reduction in playback delay; and same-priority packetization transmission method and priority-based packetization transmission method, which are media data packetization methods for transmission. From the simulation of functional evaluation, we could find that the proposed multiple receiving buffering and packetizing methods are superior, with respect to the media retrieval inclination, to the existing single receiving buffering method by 6-9 points from the viewpoint of effectiveness and excellence. Among them, especially, on-demand multiple receiving buffering technology with same-priority packetization transmission method is able to manage the media search inclination promptly to the requests of users by showing superiority of 3-24 points above compared to other combination methods. In addition, users could find the information they want much quickly since large amount of informations are received in a focused media retrieval period within a short time.