• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.11
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• pp.1050-1057
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• 2012

Super Wi-Fi is a newly emerging wireless Internet technology, which constitutes Wi-Fi networks using TV white space. A key technical challenge in the Super Wi-Fi applications is how to provide a seamless Internet service even when a Super WiFi user should give up the channel in use to the active incumbent user which is activated in the same service area, preventing from the service continuity in Super Wi-Fi. In this paper, we propose a channel handover method to support service continuity of Super Wi-Fi, in which an AP selects a new operational channel and provides the channel information for MSs. Therefore, the AP and the MSs can carry out seamless handover for Super Wi-Fi service. A performance evaluation shows that the proposed scheme is superior to the conventional Wi-Fi in channel mobility delay.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.12
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• pp.1327-1337
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• 2014

In cellular communication systems employing millimeter wave (mmWave) bands for a link, a large amount of training time and network resources will be required to find a serving BS with the best transmit and receive (Tx-Rx) beam pair if downlink control signals are used. In this paper, a tracking technique for OFDM-based cellular communication systems with a mmWave link, where an analog beamforer is used at the mobile station (MS) and a digital beamformer is used at the BS, is proposed using an uplink signal. A technique to select a serving BS with the best beam pair is described using the uplink preamble sequence based on Zadoff-Chu sequence and a metrics which can be used to identify parameters such as beam ID (BID), MS ID (MID), and direction-of-arrival (DoA). The effectiveness of the proposed technique is verified via simulation with the spatial channel model (SCM) for a moving MS in mmWave cellular systems.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.20 no.3
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• pp.31-36
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• 2020

The LTE-R system is a system consisting of a packet network that provides all IP-based services. Continuous failures related to the platform safety gate and subsequent safety accidents related to passengers and safety gate workers continue. The secondary damage caused by the failure of the platform safety door and the related human life damage have emerged as a major social issue.. By linking the beacon system to the Long Term Evoluton-Railway (LTE-R) network, an LTE-based railway wireless network currently in operation or being installed, it precisely locates trains and provides standardized fault alerts to train crews. When entering into the station, ultimately we will decelerate the train and reduce the accidents of metropolitabn railroad traffic by securing safe driving.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.1
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• pp.24-31
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• 2015

A differential codebook using M-ary phase shift keying (M-PSK) constellation as its codeword elements, is proposed for Long term evolution (LTE), LTE-Advanced (LTE-A), and/or WiMAX systems. Due to the temporal correlation of the adjacent channel, the consecutive precoding matrices are likely to be similar. This approach quantize only the differential information of the channel instead of the whole channel subspace, which virtually increase the codebook size to realize more accurate quantization of the channel. Especially, the proposed codebook has the same properties of LTE release-8 codebook that is, constant modulus, complexity reduction, and nested property. The mobile station can be designed by using a less expensive non-linear amplifier utilizing the constant modulus property. Computer simulations show that the capacity of the proposed codebook performs better than LTE release-8 codebook with the same amount of feedback information.

• Korean Journal of Construction Engineering and Management
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• v.10 no.1
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• pp.136-145
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• 2009

The objective of the Intelligent Excavation System (IES) is to recognize the work environment and produce work plan and automatically control the excavator through integrating sensor and robot technologies. This paper discusses one of the core technologies of IES development project, development of 3D work environment modeling. 3D laser scanner is used for 3-dimensional mathematical model that can be visualized in virtual space in 3D. This paper describes (1) how the most appropriate 3D imaging system has been chosen; (2) the development of user interface and customization of the s/w to control the scanner for IES project; (3) the development of the mobile station for the scanner; (4) and the algorithm for the automatic registration of laser scan segments for IES project. The development system has been tested on the construction field and lessons learned and future development requirements are suggested.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.12B
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• pp.2320-2334
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• 1999

In this paper, we propose multiple IS-MMBS service schemes for very low power and micro-size RMIMS (radio-interfaced micro information monitoring system) terminals. In MMBS service area, when new arrival RMIMS terminals have real-time traffic characteristic or large traffic bandwidth, only single IS-MMBS service scheme can not guarantee RMIMS terminal's QoS(quality of service) such as buffer overflow or packet loss. In this case, the proposed multiple IS-MMBS service schemes can be effectively used for QoS service of RMIMS terminal. According to clustering method of RMIMS terminals and MMBS segment method, the proposed schemes can be divided into terminal segment method, region segment method, application based segment method, traffic type based segment method, overlapping segment method and hybrid segment method

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.9B
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• pp.1624-1630
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• 1999

Code division multiple access (CDMA) is a promising air interface technique for cellular systems. When an MS (Mobile Station) moves to an adjacent cell, the handoff between the serving cell and the target cell is needed. Compared with the hard handoffs, the soft handoffs between two CDMA channels with the identical frequency assignments and frame offsets can provide a better quality of service by minimizing the undesirable ping pong phenomenon of back-and forth handoffs between two adjacent cells in conventional hard handoffs. For the soft handoff of a call to an adjacent cell to be successful, the adjacent cell should assign to the call the same frame offset as that being used in the original cell by the call. In this paper, considering the assignment states of the frame offsets of the adjacent cells, a frame offset assignment algorithm for the originated call is proposed. And analytic method for the handoff blocking probability due to the lack of the frame offset capacity is also presented to show the advantage of the proposed algorithm with respect to the soft handoff blocking probability.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.5
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• pp.123-129
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• 2018

Recently, as required wireless communication traffic increase, millimeter wave mobile technologies that can secure broadband spectrum are gaining attention. However, the path loss is high in the millimeter wave channel. Massive MIMO system is being researched in which can complement the path loss by beamforming by equiped large-scale antenna at the base station. While legacy beamforming techniques have analog and digital methods, practical difficulties exist for application to massive MIMO systems in terms of system complexity and cost. Therefore, this paper studies a hybrid beamforming scheme for massive MIMO system in the millimeter wave band. Also this paper considers spatial multiplexing scheme to serve multi-users with multiple received antennas. Gains of the beamforming and the spatial multiplexing schemes are evaluated by analyzing the spectral efficiency.

• The KIPS Transactions:PartC
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• v.11C no.6 s.95
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• pp.747-754
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• 2004

Today, wireless LANs are widely deployed in various places such as corporate office conference rooms, industrial warehouses, Internet-ready classrooms, etc. However, new concerns have been raised regarding suity. Currently, both virtual private network(VPN) and WEP are used together as a strong authentication mechanism. While security is increased by using VPN and WEP together, unnecessary redundancy occurs causing power consumption increase and authentication speed decrease in the authentication process. In this paper a new synchronization protocol for authentication is proposed which allows simple authentication, minimal power consumption at the mobile station, and high utilization of authentication stream. This is achieved by using one bit per a frame authentication, while main authentication process including synchronization is handled by access points. Computer simulation reveals that the proposed scheme significantly improves the authentication efficiency in terms of the number of authenticated frames and authentication speed compared with an earlier protocol employing a similar authentication approach.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.8A
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• pp.814-819
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• 2006

This paper presents the impacts of Ultra Wide-Band(UWB) system applied in Indoor and Handhold communications using frequency band from 3.1 GHz to 10.6 GHz on Wireless Broad-band(WiBro) system based on Orthogonal Frequency Division Multiplexing(OFDM) using frequency of 2.3 GHz. The Minimum Coupling Loss(MCL) method for the case of single interference and Monte Carlo(MC) simulation for multiple interference considering practical scenario were used to evaluate the interference effects of UWB system on WiBro system. As a result, the minimum separation distance between single interferer and the victim receiver required 34.4 m and above to guarantee the co-existence. Also, the UWB transmitting PSD of around - 81 dBm / MHz below should be required to meet the minimum throughput loss of WiBro mobile station in case of multiple UWB interference.