• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2015.10a
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• pp.87-90
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• 2015

Equipments that can transmit maritime distress signals in accordance to Global Maritime Distress Safety System are the followings: A1 water(Very High Frequency, SART), A2 water(MF/HF Radio Equipment), A3 water(INMARSAT), A4 water(Emergency Position Indicating Radio Beacon). Institutions with the capacity to receive distress signals are Korea Coast Guard affiliated radio stations, patrol ships, Rescue Coordination centers, Vessel Traffic centers, Complex problems regarding repetitive distress alarms, inaccurate statistics, multiple control towers are existent. Consequently, effective measurement to resolve dispersed operating maritime distress signal system are in time of need. Moreover, current KCG Headquarter is considering to integrate five distress radio stations dispersed across nation into a single international safety communication center. The integration of radio stations are efficient in terms of information coordination between nations, however, it cannot support efficient response to real-time maritime incident. Therefore, in this study, a new system that can rapidly response to real-time maritime incident will be proposed.

• Journal of Navigation and Port Research
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• v.35 no.9
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• pp.701-706
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• 2011

Radio waves including GPS signals, various TV communications, and radio broadcasting can be disturbed by a strong solar storm, which may occur due to solar flares and produce an ionospheric delay anomaly in the ionosphere according to the change of total electron content. Electron density irregularities can cause deep signal fading, frequently known as ionospheric scintillation, which can result in the positioning error using GPS signal. This paper proposes a detection algorithm for the ionosphere delay anomaly during a solar storm by using multi-reference stations. Different TEC grid which has irregular electron density was applied above one reference station. Then the ionospheric delay in zenith direction applied different TEC will show comparatively large ionospheric zenith delay due to the electron irregularity. The ionospheric slant delay applied an elevation angle at reference station was analyzed to detect the ionospheric delay anomaly that can result in positioning error. A simulation test was implemented and a proposed detection algorithm using data logged by four reference stations was applied to detect the ionospheric delay anomaly compared to a criterion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.8C
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• pp.689-695
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• 2007

Wireline relay stations(RS's) are connected to cellular base stations(BS's) via radio-over-fiber(RoF) to enhance system capacity and to reduce shadow areas. Unlike wireless multi-hop systems, BS-to-RS signaling is transmitted out-of-band, thus reducing the effect of interference caused by frequency reuse. In this paper, antenna arrays used in addition to the wireline RS's are considered to evaluate the transmission capacity gain and performance variations according to the may structures. In particular, RS locations to maximize the gain, may distribution patterns for a given number of antenna elements, performance enhancement for a varying number of elements are experimentally determined to suggest a proper utilization of antenna ways in conjunction with wireline RS's.

• Proceedings of the IEEK Conference
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• 1998.06a
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• pp.74-77
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• 1998

We consider connection-oriented wireless cellular networks. These networks employ dedicated radio channels for the transmission of signaling information. A forward signaling channel is a common signaling channel assigned to carry the multiplexed stream of paging and channel allocation(virtual circuit allocation) packets from a base station to mobile stations. The delay levels experienced by paging and channel allocation packets have serious effect on the utilization level of the limited radio channel capacity. While a slotted mode operation is used to reduce the power consumption level at mobile stations, it may induce an increase in packet delay levels. In this paper, we thus consider a multiplexing scheme for paging and channel allocation packets under which slots are dynamically allocated for the paging packet transmission. For this dynamic scheme, we develop an analytical method for deriving the delay characteristics exhibited by paging and channel allocation packets, and investigate the effect of network parameters on the delay level by using this method.

• International journal of advanced smart convergence
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• v.9 no.2
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• pp.58-67
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• 2020

In this paper, we propose a data-driven-based beam selection scheme for massive multiple-input and multiple-output (MIMO) systems in ultra-dense networks (UDN), which is capable of addressing the problem of high computational cost of conventional coordinated beamforming approaches. We consider highly dense small-cell scenarios with more small cells than mobile stations, in the millimetre-wave band. The analog beam selection for hybrid beamforming is a key issue in realizing millimetre-wave UDN MIMO systems. To reduce the computation complexity for the analog beam selection, in this paper, two deep neural network models are used. The channel samples, channel gains, and radio frequency beamforming vectors between the access points and mobile stations are collected at the central/cloud unit that is connected to all the small-cell access points, and are used to train the networks. The proposed machine-learning-based scheme provides an approach for the effective implementation of massive MIMO system in UDN environment.

• Journal of electromagnetic engineering and science
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• v.1 no.1
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• pp.43-47
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• 2001

A compact size microstrip antenna element using FR-4 substrate is proposed for use in repeater and base stations. Two stacked patches are aperture-coupled by two split feedlines. Rectangular stubs on the split feedlines are laid under the aperture and have the effect of considerably lowing the magnitude of $S_{11}$ [dB] and broadening impedance bandwidth. The designed structure has been fabricated and measured. Based on 20 dB, the return loss bandwidth is about 16.8% (1.86 GHz~2.20 GHz), which covers the frequency range assigned for IMT-2000 with a large margin. The overall dimension of the proposed antenna structure is 37 mm$\times$41 mm$\times$19mm (very compact). The antenna gain is more than 7.5 dBi over the required frequency range.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.6
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• pp.1255-1261
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• 2014

Based on the radio wave measurement of korean ocean-based DGPS by season, in this paper, the service coverages of ocean-based DGPS reference stations were analyzed according to the climate and season. The signal strengths and signal-to-noise ratios in the land service areas that are provided by ocean-based DGPS reference stations were measured. The ocean-based DGPS reference station except reference stations on the mountainous terrain and the low ground conductivity provide more than 68% service area in comparison with the designed land service coverage providing by the ocean-based DGPS reference stations. To provide the designed service area that is unrelated to a season, it is necessary to install and operate the DGPS reference station with good ground conductivity and high efficiency antenna. Also, the poor service regions which is generated by obstacles of electric wave on pathway can be resolved by the double service area providing by land-based DGPS reference stations.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.3
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• pp.1074-1086
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• 2015

We Relay-assisted cellular network architecture has been developed to cover cell-edge users and to improve capacity. However, the deployment of relay stations (RSs) in cellular networks may increase the total energy consumption. Though energy efficiency has become a major concern in cellular networks, little work has studied the energy efficiency of relay-assisted cellular networks by sleep scheduling. In this paper, a distributed base stations (BSs) sleep scheduling scheme in relay-assisted cellular networks is proposed. The goal is to maximize the energy efficiency under the spectral efficiency constraint. Firstly, whether the BSs should be sleeping or active is determined by the traffic profile. Then, the transmission powers of the active BSs are optimized within the game-theoretic framework, by using an interior-point method, so as to maximize the energy efficiency. Simulation results demonstrate that the effectiveness of the proposed scheme is superior to that turning on all the BSs without sleep scheduling.

• Journal of the Korean Operations Research and Management Science Society
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• v.31 no.3
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• pp.145-154
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• 2006

WiBro (Wireless Broadband Internet) system is going to be 9ot down to commercialization. The high portable internet system is able to be connected to the high-speed internet using 2.3 GHz frequency bandwidth, anytime and anywhere. An effective scheduling for UGS, rtPS, nrtPS and BE requiring different QoS, which are service types of the WiBro, is necessary to increase the efficiency of radio channels that are the limiting resource. This paper researches an uplink scheduling that plays a role in assignment for the radio channels from subscribers to base stations. The suggested scheduling provides priorities with each service type considering QoS of them but reserves some bandwidth for lower priory services. After deciding effective amount of bandwidth for reservation, we suggest analytical result on mean delayed time of packet transmission for each terminal, transmission rate for the data, and capacity for uplink. This research can be used as basic data for the standard in the high portable internet system and as data to predict the capacity of base stations.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.5
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• pp.833-841
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• 2011

In this paper, we propose uncoordinated dynamic frequency(channel) allocation schemes based on cognitive radio in mobile cellular networks(MCNs). Under the assumptions that mobile base stations are equipped with cognitive radio(CR) function and they construct uncoordinated network, the proposed scheme enables the MCNs by suppression of successive channel switching and management of channel allocation in a dynamic and distributed manner. The proposed scheme is composed of two phase processes. In the first phase, highly orthogonal sequences are generated and assigned to mobile base stations. In the second phase, each mobile base station is allocated a channel according to the pre-assigned orthogonal sequences. Simulation results show that the number of successive spectrum switching is reduced significantly compared with the random switching scheme.