• Journal of Satellite, Information and Communications
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• v.5 no.2
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• pp.57-63
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• 2010

Many efficient frequency sharing methods are issued in present because of increasing users with various wireless communication terminals. In the satellite communications, the service coverage is generally very wide so frequency sharing with terrestrial system is essentially needed, and the research is progressing dynamically related on this frequency sharing method. But if we adopt the terrestrial system which is commonly used, it can't avoid the interference from terrestrial service to satellite service. Therefore, this paper will introduce methods for reducing the interference from terrestrial station to earth station using cognitive radio system Satellite system is guaranteed with decreasing interference from terrestrial stations using Genetic Algorithm based power control method. Furthermore, terrestrial systems can have increased QoS because the frequency reuse factor in proposed method is higher than existing methods.

• The Journal of the Korea institute of electronic communication sciences
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• v.9 no.10
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• pp.1145-1152
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• 2014

The RFID (Radio-Frequency Identification) system is a technology to discern things by radio and an epoch-making new method to improve product management such as distribution, transport, mobilization, inventory control. However, RFID, which uses radio, is at risk for information leakage and falsification due to the vulnerability of security of the communication section. We designed the new authentication protocol by applying the tent map, which is the representative complex systems, to the RFID communication system. A more solid and simple authentication system was designed by applying the initial value sensitivity and irregularity, which are the representative characteristics of the complex system, to the reader and tag of RFID. The purpose of this paper is to verify the usability of the RFID authentication protocol design that uses the nonlinear system shown in this thesis by the new system differentiated from the authentication system that depends on the existing hash function or random numbers.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.55-60
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• 2009

This paper deals with the analysis of characteristics of the scale non-uniformly formed on the surface of the steel during the steel production processes. The steel made at the high temperature contacts with the oxygen in the air, so forms the scale immediately. The scale has a role to protect the surface of the steel product as a oxide-layer, but the scale formed non-uniformly spoils the exterior of the steel product and occurs the problems about the next processes. There is a pickling process to remove the scale of the steel products, but the real situation is that the pickling process is not also based on the analysis of the characteristics of the scale. Therefore, this paper describe the procedures of the analysis of the scale more effectively using the radio-frequency wave. Using the radio-frequency wave, this paper introduce the experimentations to analyze the distributions of scale, the junction characteristics between the surface of steel and scale and the distributions of scale on the produced steel coil. Also, according to the simple simulations, this paper proves the proprieties about the above contents.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.9 no.3
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• pp.179-185
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• 2009

Cognitive radio (CR), which is proposed as a technology that utilizes the frequency resources effectively, has studied to relive scarcity of the frequency resources. CR provides opportunistically unused frequency to the secondary user when the primary user is not detected. Spectrum sensing is the most important technology to detect primary user. However, in the wireless channels, according to the effect of multipath fading channel, spectrum sensing performance is compromised. Therefore, in this paper, we apply diversity scheme that is a useful technique for combating multiple fading in wireless communications. There are several classes of diversity scheme, which are time diversity, antenna diversity, muitipath diversity, frequency diversity, and so on. In this paper, we adopt antenna diversity that is a kind of space diversity. By using the proposed method, we can overcome fading effect and improve spectrum sensing performance.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.20 no.3
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• pp.22-27
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• 2012

In oceanic flight routes, HF radio and satellite data links have been used for air-to-ground communication, but these systems have long propagation delay and low data throughput. In this paper, we propose a reliable system to overcome the weakness of current HF radio and satellite communication systems for oceanic aeronautical flight routes. The proposed scheme uses only one aeronautical VHF channel in multi-hop oceanic communication environments and supports a hybrid type of multiple access, which consists of random access and TDMA (Time Division Multiple Access) scheme. The proposed system improves performance on delay and throughput as an effective solution to communicate end-to-end on the oceanic flight routes and strengthens the reliability of oceanic aeronautical communication.

• Journal of information and communication convergence engineering
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• v.14 no.3
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• pp.147-152
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• 2016

In radio-over-fiber (RoF) systems, nonlinear compensation is essential to improve performance. Among the several existing nonlinear compensation techniques, we investigate a predistortion technique for a directly modulated laser in an RoF system. First, we obtain the input-to-output response of a directly modulated laser at 160, 820, and 1,540 MHz. The results show that the laser response is dependent on the frequency band. Second, we design an optimal predistortion circuit to compensate for the nonlinear responses of three frequency bands. We design the predistortion circuit with two options: each predistortion circuit for each frequency band and one single predistortion circuit for all the three frequency bands. Finally, we present the simulation results of the predistortion system obtained using a commercial simulator. These results show that the third intermodulation distortion (IMD3) is improved by 0.6-9 dB for the three frequency bands with only a single predistortion circuit.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.6
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• pp.1055-1059
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• 2004

A RFID(Radio Frequency Identification) system is a kind of radio frequency communication system and a branch of automatic data collection system. RFID system consists of RFID tags(or transponders) and RFID readers(controllers). This paper deals with the wireless communication that acquires tag IDs through RFID readers, and show the implementation of the target system which transmits tag IDs and related information to the server on the Internet through the wireless local area network. Today's RFID systems are usually implemented with the wired communication environment. In this paper, however, RFID system is effectively realized with the widely deployed wireless local area network and various RFID data can be collected by the readers which are communicating with the wireless access points of the local area network. Through the Internet, users also can have easy access to the server on the web and retrieve, analyze, and utilize tags' information.

• ETRI Journal
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• v.39 no.2
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• pp.245-254
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• 2017

In-band full-duplex (IFD) communication has recently attracted a great deal of interest because it potentially provides a two-fold spectral efficiency increase over half-duplex communications. In this paper, we propose a novel digital self-interference cancelation (DSIC) algorithm for an IFD communication system in which two nodes exchange orthogonal frequency-division multiplexing (OFDM) symbols. The proposed DSIC algorithm is based on the least-squares estimation of a self-interference (SI) channel with block processing of multiple OFDM symbols, in order to eliminate the fundamental and harmonic components of SI induced through the practical radio frequency devices of an IFD transceiver. In addition, the proposed DSIC algorithm adopts discrete Fourier transform processing of the estimated SI channel to further enhance its cancelation performance. We provide a minimum number of training symbols to estimate the SI channel effectively. The evaluation results show that our proposed DSIC algorithm outperforms a conventional algorithm.

• The Journal of the Korea institute of electronic communication sciences
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• v.7 no.1
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• pp.135-139
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• 2012

A majority of 4G Mobile communication manufacturers have launched separated-type base stations composed of DU (digital unit) and RU (ratio unit). DUs are usually installed in the central office, while RUs with antennas are installed on the top of building or pole. Therefore, the allowable distance between DU and RU is very important for cell planning. In this paper, we analyze the allowable distance between DU and RU induced by closed-loop MIMO (mulitple input multiple output) technology in 4G FDD (frequency division duplexing) mobile communication systems. In conclusion, the distance limit between DU and RU is dependent on the frequency of the wireless communication, and the allowable distance is about 11 km when assuming the operating frequency is 2 GHz.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.227-234
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• 2022

Covert Underwater Communication (CUC) signals should not be detected by other unintended users. Similar to the method used in Radio Frequency (RF), covert communication technique sending information underwater is designed in consideration of the characteristics of Low Probability of Detection (LPD) and Low Probability of Intercept (LPI). These conventional methods, however, are difficult to be used in the underwater communications because of the narrow frequency bandwidth. Unlike the conventional methods of reducing transmission power or increasing the modulation bandwidth, a method of mimicking the acoustic signal of an underwater mammal is being studied. The biomimetic underwater acoustic communication mainly mimics the click or whistle sound produced by dolphin or whale. This paper investigates biomimetic communication method and introduces research trends to understand the potential for the development of such biomimetic covert underwater acoustic communication and future research areas.