• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
• /
• 2021.10a
• /
• pp.443-444
• /
• 2021

Security threats to information services are increasingly being developed, and the frequency and damage caused by security threats are also increasing. In particular, security threats occurring inside the organization are increasing significantly, and the size of the damage is also large. A zero trust model has been proposed as a way to improve such a security environment. In the zero trust model, a subject who has access to information resources is regarded as a malicious attacker. Subjects can access information resources after verification through identification and authentication processes. However, the initially proposed zero trust model basically focuses on the network and does not consider the security environment for systems or data. In this study, we proposed a zero trust-based access control mechanism that extends the existing zero trust model to the file system. As a result of the study, it was confirmed that the proposed file access control mechanism can be applied to implement the zero trust model.

• Journal of the Korea Society of Computer and Information
• /
• v.17 no.3
• /
• pp.85-93
• /
• 2012

In this paper, I designed the satellite system, using the MF-TDMA (Multi Frequency-Time Division Multiple Access) DAMA (Demand-Assigned Multiple Access) method, that allocates the satellite resources more effectively to prevent a large quantity data discard when Earth Terminals (ETs) request their satellite network resource to Network Controller (NC) by using their history information, such as traffic pattern or traffic class which have been receiving, and the network controller allocates the satellite network resource and send to earth terminals by using his history information that earth terminals have been requested already. The U.S. Military Warfighter Information Network-Tactical (WIN-T) community has selected the L-3 Linkabit MF-TDMA DAMA Network Centric Waveform (NCW) as the networking standard for full-mesh IP over SHF satellite communications. In the MF-TDMA DAMA satellite network, network controller allocates the satellite network resources and enables maximum 255 earth terminals to communicate each other for periodic satellite network resource requests of earth terminals.

• Journal of Astronomy and Space Sciences
• /
• v.37 no.2
• /
• pp.117-129
• /
• 2020

In a Satellite communication system, a link budget analysis is the detailed investigation of signal gains and losses moving through a channel from a sender to receiver. It inspects the fading of passed on data signal waves due to the process of spreading or propagation, including transmitter and receiver antenna gains, feeder cables, and related losses. The extent of the proposed tool is to make an effective, efficient, and user-friendly approach to calculate link budget analysis. It is also related to the satellite communication correlation framework by building up a graphical interface link analysis tool utilizing STK^® software with the interface of C# programming. It provides better kinds of graphical display techniques, exporting and importing data files, printing link information, access data, azimuth-elevation-range (AER), and simulation is also possible at once. The components of the link budget analysis tool include transmitter gain, effective isotropic radiated power (EIRP), free space loss, propagation loss, frequency Doppler shift, flux density, link margin, elevation plot, etc. This tool can be useful for amateur users (e.g., CubeSat developers in the universities) or nanosat developers who may not know about the RF communication system of the satellite and the orbital mechanics (e.g., orbit propagators) principle used in the satellite link analysis.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.30 no.7A
• /
• pp.578-586
• /
• 2005

We propose a random frequency hopping orthogonal frequency division multiple access (RFH-OFDMA) system based on statistical multiplexing for improving downlink user capacity. User capacity is defined as the maximum number of users served with a given basic data-rate in a cell. We compare the downlink user capacity of the proposed RFH-OFDMA system with that of the conventional frequency hopping OFDMA (FH-OFDMA) systems in the worst case where all users are located at the cell boundary. User capacity is limited by either the number of subcarriers or other-cell interference (OCI). Simulation results show that the proposed RFH-OFDMA system can accommodate 262 users in a 3-sectored cell, while the conventional FH-OFDMA systems can accommodate 51 users, when the user channel activity and the required Eb/I0 are 0.1 and 6 dB, respectively, and all users are assumed to be located at the cell boundary.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.23 no.8
• /
• pp.900-908
• /
• 2012

Owing to the proliferation of smart phone users, a proactive spectrum policy is needed in order to deal with increasing data traffic. Therefore, the prediction of frequency requirements for future wireless local area network (WLAN) as well as a licensed cellular communication is necessary. In this paper, we proposed a new prediction method for WLAN spectrum requirements. This method includes both a traditional prediction method and an offloading percentage from cellular network, Also, it can consider a frequency interference between access points using a statistical approach. Based on these approaches, we can predict the spectrum requirements of future domestic WLAN services considering the frequency interference. Finally, we suggest the spectrum policy for WLAN which can prevent spectrum shortage of future WLAN services.

• Journal of the Korea Society for Simulation
• /
• v.20 no.4
• /
• pp.81-89
• /
• 2011

Underwater wireless network can be useful in various fields such as underwater environment observation, catastrophe prevention, ocean resources exploration, ocean organism research, and vessel sinking exploration. We need to develop an efficient design for Medium Access Control (MAC) protocol to improve multiple data communication in underwater environment. Aloha protocol is one of the basic and simple protocols, but it has disadvantage such as collision occurs oftenly in communication. If there is collision occured in RF communication, problem can be solved by re-sending the data, but using low frequency in underwater, the re-transmission has difficulties due to slow bit-rate. So, Time Division Multiple Access (TDMA) based MAC protocol is going to be used to avoid collisions, but if there is no data to send in existing TDMA, time slot should not be used. Therefore, this paper proposes dynamic TDMA protocol mechanism with reducing the time slots by sending short "I Have No Data" (IHND) message, if there is no data to transmit. Also, this paper presents mathematic analysis model in relation to data throughput, channel efficiency and verifies performance superiority by comparing the existing TDMA protocols.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.2
• /
• pp.211-215
• /
• 2006

In this paper, design and applications of a generalized, versatile and customizable IF signal generator that can model the modernized GPS and Galileo signal is given. It generates IF sampled data that can be directly used by a software receiver. Entire constellation of satellites which is independent of satellite-user geometry is easily determined using a real or simulated ephemeris data. Since the IF center frequency, sampling frequency and quantization bit number are user location dependent parameters, their effects are also considered in IF signal generator. The generalized IF signal generator will be very well suited for the development phase of a software receiver due to its versatility. The full access to the sampling frequency, front-end filter definition and ADC parameters also offers a great opportunity for cost-effective analysis of tracking loops and error mitigation techniques at the receiver level. Interference sources can be easily added to the generator to simulate specific environments. This software IF signal generator can also be used to feed a multi-frequency multi-system software receiver for the prototyping of a combined GPS/Galileo receiver. The test result using the generated signals and a real software receiver shows the effectiveness of the implemented IF signal generator.

• Journal of Communications and Networks
• /
• v.12 no.1
• /
• pp.30-42
• /
• 2010

In this work we consider the problem of downlink resource allocation for proportional fairness of long term received rates of data users and quality of service for real time sessions in an OFDMA-based wireless system. The base station allocates available power and subchannels to individual users based on long term average received rates, quality of service (QoS) based rate constraints and channel conditions. We formulate and solve a joint bandwidth and power optimization problem, solving which provides a performance improvement with respect to existing resource allocation algorithms. We propose schemes for flat as well as frequency selective fading cases. Numerical evaluation results show that the proposed method provides better QoS to voice and video sessions while providing more and fair rates to data users in comparison with existing schemes.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.11C
• /
• pp.1059-1066
• /
• 2009

In this paper, we propose the precoder with superimposed pilots for orthogonal frequency-division multiple access (OFDMA) systems in order to enhance the transmission efficiency of the system and reduce peak-to-average power ratio (PAPR) which is the problem in OFDMA uplink. In wireless communication systems, the way to improve transmission efficiency is 1) to reduce bit error rate (BER) or 2) to increase data rate. In the proposed scheme, we design the precoder and superimposed pilots in the transmitter and use them in the receiver for increasing data rate, caused by the saved transmission bandwidth thanks to the superimposed pilots. In addition, we improve BER performance with the help of the frequency diversity gain caused by precoding. Also using superimposed pilots, we enhance the PAPR performance by increasing the average output power of the signal.

• Journal of Communications and Networks
• /
• v.7 no.1
• /
• pp.13-20
• /
• 2005

In this paper, a new multi carrier, direct sequence code division multiple access (MC-DS-CDMA) system is proposed. Our new signal construction is based on convolutional encoding of the transmitted data, serial-to-parallel (S/P) conversion of the encoded data, Walsh-Hadamard-transformation (WHT), a second S/P conversion of the WHT outputs, spread spectrum (SS) modulation with a common pseudo-noise (PN) sequence, and then multicarrier transmission. The system bit error rate (BER) performance in frequency selective fading channel in the presence of additive white Gaussian noise (AWGN) and a jamming tone is analyzed and simulated. The numerical results are compared with those from an orthogonal MC-DS-CDMA system of Sourour and Nakagawa [7]. It is shown that the two systems have almost the same BER performance, but the proposed scheme has better anti-jamming ability.