• Journal of the Korea Society of Computer and Information
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• 제25권2호
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• pp.83-92
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• 2020

In this paper, we propose an efficient session management scheme for low-latency communications in 5G systems. The main idea of the proposed scheme is to prevent unnecessary reattempt signalling overhead when the session establishment for low-latency communications fails. Also, this method avoids network resource waste and battery drain of mobile devices. If a UE(User Equipment) fails to establish an Always-on PDU session for low-latency communications with the 5G systems because of network failure or resource unavailability, the proposed method prevents the UE's re-establishment of the Always-on PDU session by the specific information in the NAS(Non-Stratum) message from the 5G systems. Through simulation, we show that the proposed efficient session management scheme (ESMS) minimizes unnecessary signalling overhead and improves battery efficiency of mobile devices compared to existing legacy mechanism in 5G systems.

• International Journal of Precision Engineering and Manufacturing
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• 제8권2호
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• pp.70-74
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• 2007

This paper describes the development of a nano-positioning system for nanoscale science and engineering. Conventional positioning systems, which can be expensive and complicated, require the use of laser interferometers or capacitive transducers to measure nanoscale displacements of the stage. In this study, a new self-displacement sensing (SDS) nano-stage was developed using mechanical magnification of its displacement signal. The SDS nano-stage measured the displacement of its movement using a position-sensitive photodiode (PSPD), a laser source, and a hinge-connected rotating mirror plate. A beam from a laser diode was focused onto the middle of the plate with the rotating mirror. The position variation of the reflected beam from the mirror rotation was then monitored by the PSPD. Finally, the PSPD measured the amplified displacement as opposed to the actual movement of the stage via an optical lever mechanism, providing the ability to more precisely control the nanoscale stage. The displacement amplification process was modeled by structural analysis. The simulation results of the amplification ratio showed that the distance variation between the PSPD and the mirror plate as well as the length L of the mirror plate could be used as the basic design parameters for a SDS nano-stage. The PSPD was originally designed for a total travel range of 30 to 60 mm, and the SDS nano-stage amplified that range by a factor of 15 to 25. Based on these results, a SDS nano-stage was fabricated using principle of displacement amplification.

• Korean Journal of Materials Research
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• 제11권3호
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• pp.207-214
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• 2001

Silica glass is a core material for optical fiber in optical telecommunications, but its centrosymmetry eliminates the second order nonlinearity. But it is experimentally well known that the space charge polarization induces the Second Harmonic Generation (SHG) when a strong DC voltage is applied to silica glass for a long period of time with metal blocking electrodes. In this report, the results of a theoretical calculation of the nonlinear optical property caused by the space charge polarization, and a model of a numerical analysis to predict the small chance in nonlinear optical property as functions of time and space are provided. Assuming that amorphous silica is a solid state electrolyte and sodium ion is the only mobile charge carrier, 'Finite Difference Method' was employed for modeling of numerical analysis. The distributions of the concentration of sodium ion and electric field as functions of a normalized length of the specimen and a normalized applied voltage were simulated.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제30권4B호
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• pp.210-217
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• 2005

With rapid advance in wireless communication technologies, many researches are conducted for providing Internet data services while users are roaming around. Efficient management of mobility of mobile nodes is essential as the use of real-time application program grows. In this paper, we propose a multicast-based localized mobility support scheme in IPv6 networks. The proposed scheme utilizes a class of multicast routing protocol for the localized mobility support. Features of the proposed scheme are use of join to a multicast group and leave from that group to localize binding update information and provision of an extended multicast group management mechanism to reduce leave latency. The results of simulation show that the proposed scheme out-performs Mobile IPv6 and Hierarchical Mobile IPv6 in UDP and TCP traffic performance and in wasted bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제31권11A호
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• pp.1101-1112
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• 2006

With the recent growth in demand for high-data rate multimedia services in the wireless environments, the Mobile Broadband Wireless Access (MBWA) technologies, such as WiBro (Wireless Broadband internet) system, are gradually coming into the spotlight. Unlike the conventional mobile communication networks based on cellular system, the WiBro system basically consists of IP based backbone networks that will be ultimately deployed by Ipv6 (IP version six) based backbone networks according to the All-IP trend for the network evolution. In such wireless mobile environments, it is needed to support the mobility management protocol on network layer as well as physical layer and Medium Access Control (MAC) layer in WiBro system. Accordingly, in this paper, we propose a fast handover scheme for improving the handover performance in IPv6 based WiBro system and show that the proposed scheme achieves loss-free and low handover latency during inter-subnet movement of the mobile stations through the simulation.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제35권8B호
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• pp.1141-1149
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• 2010

Next Generation Networks (NGN) is defined as IP-based networks with multi-services and with multi-access networks. A variety of services and access technologies are co-existed within NGN. Therefore there are numerous transport technologies such as Differentiated Services (DiffServ), Multi-protocol Label Switching (MPLS), and the combined transport technologies. In such an environment, flows are aggregated and de-aggregated multiple times in their end-to-end paths. In this research, a method for calculating end-to-end delay bound for such a flow, provided that the information exchanged among networks regarding flow aggregates, especially the maximum burst size of a flow aggregate entering a network. We suggest an admission control mechanism that can decide whether the requested performance for a flow can be met. We further verify the suggested calculation and admission algorithm with a few realistic scenarios.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제33권12B호
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• pp.1066-1074
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• 2008

In this paper, we proposed an efficient algorithm using pulse signal based on group-node-contention in LR-WPAN. The purpose of IEEE 802.15.4 is low speed, low cost and low power consumption. Recently, as applications of LR-WPAN have been extended, there is a strong probability of collision as well and almost collision occurs because of hidden node problem. Moreover, if the collision continuously occurs due to hidden node collision, network performance could be decreased. Nowadays, although several papers focus on the hidden node collision, algorithms waste the channel resource if continuous collisions frequently occur. In this paper, we assume that PAN has been already formed groups, and by using pulse signal, coordinator allocates channel and orders, and then, nodes in the allocated group can compete each other. Hence, contention nodes are reduced significantly, channel wastage caused by collision is decreased, and data transmission rate is improving. Finally, this algorithm can protect the network from disruption caused by frequent collisions. Simulation shows that this algorithm can improve the performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제39C권11호
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• pp.1177-1184
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• 2014

An wired ship area network has functionality of remote control and autonomous management of various sensors and instruments embedded or boarded in a ship. For such environment, the DiffServ (Differentiated Services) realizes that the high-speed real-time flow with the higher priority has the guaranteed minimum data rate and is delivered faster. As a result of this DiffServ effect, the intelligent Ship Area Networks can be implemented. In this paper, an packet drop technique is proposed to outperform the previous RIO (RED In and Out) drop mechanism for DiffServ in ship area networks. the proposed packet drop technique does not manage the individual flows and divides them into several flow groups according to a criterion. And it guarantees the fairness between individual flows in the same QoS class through the group-based control. In simulation results of the proposed packet drop technique, the link utilization decreases than RIO. But it guarantees more data rates to DiffServ flows passing multiple bottleneck links.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제38A권10호
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• pp.858-864
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• 2013

In the 4G wireless environment, one of the important issues is to discover and select an access network suited for users. In this thesis, we propose a new network selection mechanism using group decision making and evaluate the effect of network selection schemes for vertical handover in heterogeneous wireless networks. We consider the group of users with similar QoS requirements search for the available access network simultaneously and a service area consist of multiple access networks with various characteristics. We divide the access networks with similar characteristics split into a group. Between each group, the one group is selected and within that group, the best access networks will be assigned according to priority order by network selection algorithm. We evaluate and compare the performance of three representative MADM schemes: GRA, SAW and TOPSIS. The MATLAB simulation results indicate the proposed algorithm can make a more effective choice according to the networks' characteristics and user's preference.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제38B권7호
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• pp.572-580
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• 2013

IEEE 802.15.4e is a prospective standard for low latency control application in industries. This paper proposes a framework to evaluate the closed loop IEEE 802.15.4e based WNCS performance. The framework consists of two models: closed loop control system model and network model. The network model focuses on the PHY parameters of wireless link and takes the channel parameters into consideration. The PHY model combining with MAC model gives the control system model the probability of packet loss in a super-frame. In addition, redundancy mechanism is considered in IEEE 802.15.4e to reduce to data frame loss probability. The simulation is implemented in Matlab, PHY model takes the channel parameters from empirical results. Hence our evaluation gives insight into behavior of WNCS in different environments and it provides us a tool to design wireless network to achieve a good performance for control system.