• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.14-18
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• 2010

The future of communication systems is expected to combine with the terrestrial and satellite networks. A commonality between wireless interfaces is important consideration for cost of user equipment in the integrated satellite and the terrestrial system. Because IMT-Advanced system take into account LTE based on the terrestrial system for the next generation of communication, a study of the LTE-based satellite system is especially required. A frame of the existing terrestrial wireless networks is designed to use for a random access up to the maximum cell radius of 100 km. However, the random access scheme for the terrestrial system cannot be used in the satellite system, because the satellite systems generally have large coverage than the terrestrial system. Therefore, we propose that the efficient random access procedure to reduce latency and complexity for the satellite system maintaining commonality with the terrestrial system in this paper.

• Journal of Satellite, Information and Communications
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• v.9 no.4
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• pp.38-41
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• 2014

Due to the diversity of device performances and the possibility of providing multimedia service through many networks, media consumption environment has been changed in various ways. In recent, mobile services and broadcasting services started to provided through IP network. According to this flow changes, there was great demand for various multimedia services through heterogenous networks. To solve this problem, MMT was suggested as a standard of multimedia transport which replaces MPEG-2 TS(Transport Stream) which is used for HD(High Definition) transport. MMT can be provided various broadcasting based on IP through terrestrial, satellite, cable broadcasting networks, and also deliver multimedia through many networks at the same time. MMT was risen as a method of servicing UHD broadcasting. In this paper, we present an implementation of service architecture for hierarchical UHD broadcasting over heterogenous networks using MMT.

• ETRI Journal
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• v.42 no.5
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• pp.712-720
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• 2020

Recently, to make the best use of limited and precious spectrum resources, spectrum sharing between satellite and cellular networks has received much interest. In this study, we mathematically analyze the success probability of a fixed (satellite) earth station (FES) based on a stochastic geometry framework. Both the FES and base stations (BSs) are assumed to be equipped with a directional antenna, and the location and the number of BSs are modeled based on the Poisson point process. Furthermore, an exclusion zone is considered, in which the BSs are prohibited from locating in a circular zone with a certain radius around the FES to protect it from severe interference from the cellular BSs. We validate the analytical results on the success probability of the cognitive satellite-terrestrial network with directional antennas by comparing it using extensive computer simulations and show the effect of the exclusion zone on the success probability at the FES. It is shown that the exclusion zone-based interference mitigation technique significantly improves the success probability as the exclusion zone increases.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.16 no.9
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• pp.3152-3171
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• 2022

This work investigates the physical layer secrecy of a multi-antenna hybrid satellite-terrestrial relay networks (HSTRN) with jamming, in which a satellite aims to make communication with a destination user by means of a relay, along with spatially random eavesdroppers. In order to weaken the signals of eavesdroppers, the conventional relay can also generate intentional interference, besides forwarding the received signal. Shadowed-Rician fading is adopted in satellite link, while Rayleigh fading is adopted in terrestrial link, eavesdropper link and jamming link. The analytical and asymptotic formulas for the system secrecy outage probability (SOP) are characterized. Practical insights on the diversity order of the network are revealed according to the asymptotic behavior of SOP at high signal-to-noise ratio (SNR) regime. Then, analysis of the system throughput is examined to assess the secrecy performance. In the end, numerical simulation results are presented to validate the theoretical analysis and point out: (1) The secrecy performance of the considered network is affected by the channel fading scenario, the system configuration; (2) Decrease of the relay coverage airspace can provide better SOP performance; (3) Jamming from the relay can improve secrecy performance without additional network resources.

• Proceedings of the KSRS Conference
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• 1999.11a
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• pp.296-298
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• 1999

Five institutions, which are very active in data utilization of environmental satellites NOAA and GMS, are connected via high speed networks to construct the databases based on the observations of A AVHRR (Advanced very High Resolution Radiometer) of NOAA satellite and VISSR (Visible and Infrared Scanning Radiometer) of GMS (Geostationary Meteorological Satellite) and to create scientific data sets for land, ocean and ,atmosphere. And vegetation index, sea surface temperature, cloud distribution maps and so on are generated by high speed and huge volume data Processing for studies on long term variations of land, ocean and atmosphere in Asia. In this paper the concept of this project and the activities at the Science University of Tokyo are briefly introduced

• Journal of the Korean Operations Research and Management Science Society
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• v.31 no.1
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• pp.117-129
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• 2006

In this paper, we consider broadband satellite networks using MF-TDMA (Multi-Frequency Time Division Multiple Access) scheme. We analyze the number of expected lost packets in each terminal, and mathematically formulate optimal buffer and timeslot allocation model to minimize the weighted sum of the numbers of expected lost packets. We also suggest optimal buffer and timeslot allocation scheme based on Lagrangean relaxation technique to solve the proposed model in a fast time. Extensive experiments show that the proposed scheme provides encouraging results.

• Journal of Aerospace System Engineering
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• v.14 no.6
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• pp.26-35
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• 2020

The national satellite operation network, which supports multiple satellites, was designated as a Critical Information Infrastructure (CII) in 2017. The network was designed independently from the control network and the information network to enhance physical security. Planning is underway to establish a bidirectional data interface between networks. The data transmission system allows data flow only to the physical layer and the data link layer; hence, only one file can be transferred at any one time. This means that when large amounts of data are being transmitted, no other data can be sent simultaneously in urgent situations. Thus, this paper discusses the design of flexible packets for the transmission of data between networks in an environment where physical security has been enhanced through network separation and based on this, presents a method for transmitting data effectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.2
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• pp.298-306
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• 2015

In this paper, we propose an efficient resource allocation scheme for the integrated satellite/terrestrial networks. The proposed scheme is a frequency sharing technique to mitigate the inter-component interferences which can be generated between a satellite beam and terrestrial cells that are operated in the same frequency. The proposed dynamic resource allocation scheme can mitigate the total inter-component interference by optimizing the total transmission power and it can expect a result of which can lead to an increase in capacity. In such a system, the interference situation can be affected by the distributed traffic demands or up/down link communications environments. In this point of view, we evaluate the performance of the total consumed power, the amount of inter-component interference with respect to different traffic distributions and interference environments between the satellite beam and terrestrial systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.1
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• pp.58-65
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• 2016

Satellite communication is a wide area network (WAN) which provides communication service worldwide. However, the performance of TCP can be seriously degraded in the satellite networks due to limited bandwidth, long round-trip time (RTT) and high bit error rate (BER) over satellite links. In order to improve the performance of TCP, this paper proposes cross-layer Performance Enhancing Proxy (PEP) in digital video broadcasting-return channel via satellite (DVB-RCS) networks. The proposed protocol sets TCP Congestion Window (CWND) size by using satellite resource allocation information exchanged between TCP and the link-layer. we implement PEP testbed based on Linux to evaluate the performance of the proposed protocol. The simulation results show that the proposed protocol performs better than standard TCP both in single and multiple sessions in variant BER, because the proposed protocol sets TCP CWND size by using satellite resource allocation.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.2
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• pp.137-147
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• 2024

This paper presents a novel Long Short-Term Memory (LSTM) network architecture for the integration of an Inertial Measurement Unit (IMU) and Global Navigation Satellite Systems (GNSS). The proposed algorithm consists of two independent LSTM networks and the LSTM networks are trained to predict attitudes and velocities from the sequence of IMU measurements and mechanization solutions. In this paper, three GNSS receivers are used to provide Real Time Kinematic (RTK) GNSS attitude and position information of a vehicle, and the information is used as a target output while training the network. The performance of the proposed method was evaluated with both experimental and simulation data using a lowcost IMU and three RTK-GNSS receivers. The test results showed that the proposed LSTM network could improve positioning accuracy by more than 90% compared to the position solutions obtained using a conventional Kalman filter based IMU/GNSS integration for more than 30 seconds of GNSS outages.