• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.777-786
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• 2003

The phase noise characteristics of the phase-locked loop frequency synthesizer were predicted based on the analysis for phase noise contribution of noise sources. The proposed phase noise model in this paper more accurately predicts the phase noise spectrum of frequency synthesizer. To accurately model the phase noise contribution of noise sources in frequency synthesizer, the phase noise sources were analyzed via modeling of the frequency divider and phase noise components using Leeson model for reference signal source and VCO. The phase noise transfer functions to VCO from noise sources were analyzed by superposition theory and linear operation of phase-locked loop. To evaluate the phase noise prediction model, the frequency synthesizers were fabricated and were evaluated by measured data and prediction data.

• The Journal of the Korea institute of electronic communication sciences
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• v.15 no.4
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• pp.643-650
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• 2020

The phased array antenna has an advantage enabling rapid beam aim without the mechanical rotation of the antenna, because it arranges multiple elements in a linear or planer (grid or circular) and electronically controls the phase for each element. The planar array antenna is generally used a grid array and a circular array, and the circular form has the higher resolution comparing to the grid form due to the its structural characteristics. However, a concentric circular array (CCA) or a concentric ring array (CRA) with multiple circular arrays which each has different radius is used in the limited area, because the entire radius should be increased for the circular array with a number of elements. In this paper, we introduce the angle-of-arrival (AOA) estimator for an adaptive beamforming satellite system based on CRA and provide the simulation results for performance evaluation. In addition, simulation results are compared and analyzed to the case for the circular array antenna.

• Journal of Satellite, Information and Communications
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• v.7 no.1
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• pp.39-47
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• 2012

Currently, most of the frequency spectrum resources are allocated and due to the lack of frequency, low frequency band, optimal for wireless communication environment is not used. Therefore, Cognitive Radio (CR) is a critical issue to solve the spectrum scarcity and to improve frequency spectrum utilization in wireless communication. In this paper, we implement data transmission and receive in a real CR system using the USRP(Universal Software Radio Peripheral) board and GNU Radio package of an open source development kit. Concretely, we detect the Primary User by spectrum sensing, and then we send Primary User information to the database. After receiving the information, because the database already sent optimal transmit power, bandwidth and channel information to CR equipment, CR can communicate without any interference to Primary User.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.4
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• pp.315-333
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• 2021

Due to the Global Navigation Satellite System (GNSS) modernization, recently launched GNSS satellites transmit signals at various frequency bands such as L1, L2 and L5. Considering the Korean Positioning System (KPS) signal and other GNSS augmentation signals in the future, there is a high probability of applying more complex communication techniques to the new GNSS signals. For the reason, GNSS receivers based on flexible Software Defined Radio (SDR) concept needs to be developed to evaluate various experimental communication techniques by accessing each signal processing module in detail. This paper proposes a novel SDR-based A-GNSS receiver capable of processing multi-GNSS/RNSS signals at multi-frequency bands. Due to the modular structure, the proposed receiver has high flexibility and expandability. For real-time implementation, A-GNSS server software is designed to provide immediate delivery of satellite ephemeris data on demand. Due to the sampling bandwidth limitation of RF front-ends, multiple SDRs are considered to process the multi-GNSS/RNSS multi-frequency signals simultaneously. To avoid the overflow problem of sampled RF data, an efficient memory buffer management strategy was considered. To collect and process the multi-GNSS/RNSS multi-frequency signals in real-time, the proposed SDR A-GNSS receiver utilizes multiple threads implemented on a CPU and multiple NVIDIA CUDA GPGPUs for parallel processing. To evaluate the performance of the proposed SDR A-GNSS receiver, several experiments were performed with field collected data. By the experiments, it was shown that A-GNSS requirements can be satisfied sufficiently utilizing only milliseconds samples. The continuous signal tracking performance was also confirmed with the hundreds of milliseconds data for multi-GNSS/RNSS multi-frequency signals and with the ten-seconds data for multi-GNSS/RNSS single-frequency signals.

• The Journal of the Korea institute of electronic communication sciences
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• v.18 no.5
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• pp.761-768
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• 2023

In the 4th Industrial Revolution, AI(Artificial Intelligence) and IoT(Internet of Things) technologies are being applied to across various fields, with particularly prominence in asset management, disaster management, and meteorological observation. In these fields, it is necessary to accurately determine the real-time and precise tracking of the object's location and status, and to collect various data even in situations that are difficult to detect with existing sensors. In order to address these demands, the use of GNSS(Global Navigation Satellite System) is essential, and this technology enables the efficient management of assets, disaster prevent and response, and accurate weather forecasting. In this paper, we provide the investigated results for the latest trends in the application of GNSS in the fields of asset management, disaster management, and weather observation, among various fields incorporating AI and IoT and analyze them.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.5
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• pp.1055-1062
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• 2015

A GPS based wave height meter system is proposed in this paper. The proposed system uses a dual-frequency measurements, a precise GPS satellite information and a PPP-based navigation algorithm to estimate the position with high accuracy. This method does not need to receive corrections from the reference stations. Therefore, unlike RTK based wave meter, regardless of the distance to the reference stations, it is possible to estimate position with high accuracy. This system is very simple and accurate system, but accelerometer-based system requires the other sensors such as GPS. Because position error is accumulated in the accelerometer system and must be removed periodically for high accuracy. In order to get the measurements and test the proposed wave height meter system, a buoy equipped with the test platform is installed on the sea near by Jukbyeon habor in Uljin, Korea. Then, to evaluate the performance, compares built-in commercial wave height meter with proposed system.

• Journal of Satellite, Information and Communications
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• v.1 no.2
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• pp.45-50
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• 2006

A satellite and ground stations which are developed in a program are tested whether the interface between the satellite and ground is well established before satellite operations. These compatibility tests are performed when the satellite is connected with the ground stations after all satellite and ground stations requirements are verified. The content of the RF compatibility test is to check whether the interface requirements which are described on the Interface Control Document are well developed. During the early operation phase and tentative contingency operations of the satellite, KARI ground station uses other oversea ground stations which are located worldwide according to contract between the KARI and the contractor. Since oversea ground stations were not developed for the designated space program, system integrator should check whether the oversea ground stations are satisfied with interface requirements. Using the RF suitcase, RF interface and the content of RF communication can directly be verified during RF compatibility test on oversea ground station without KARI ground station's support. The RF compatibility test using RF suitcase was performed oversea ground stations as well as KARI ground station located on Korea. The content of RF compatibility test was standardized in order to be used at any oversea ground stations, especially fitted for the operations concept of launch and early operations phase. The test content would be RF characteristics, protocol, command loop test, telemetry loop test, and ground station interface test.

• Journal of the Korean Institute of Navigation
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• v.16 no.2
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• pp.53-78
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• 1992

GMDSS-the Global Maritime Distress and Safety system which is utilizing the new technologies such as satellite communication system, DSC and NBCP-is effectuated not only by the amendment of SOLAS but also by the conference of RR and IMO's MSC, and will be the major factor of the variation of the demand and supply of Radio Operators. To cope with the GMDSS voluntarily, regulations relating to the radio installation, the posting of Radio Operators, the bounds of duty, etc. must be established and the demand and supply of Radio Operators which take charge of the system must be accomplished pertinently. In this study, the authors suggested some practical schemes to improve the effect of policy as follow. 1. The Ministry of Communication must supervise strictly the arrangement of Radio Operators, especially relating tot he legally qualified complement of Radio Station, and must review the official certification system to upgrade the quality of Radio Operators. 2. The Ministry of Communication must take overall charge of the qualitifications and technical standards of Radio Operators, the extent of their engagement, etc. which are provided by International Regulations. 3. Relating Administrations must cooperate with Shipping Companies in onboard-training to foster and ensure the manpower of Radio Operators. 4. Institutional devices to drive the resolute investment in education and training for mariners, especially for the ship's officers, must be prepared. 5. The Communication Administration and the Korea Maritime and Port Adminstration(KMPA) must cooperate mutually in the balance of the demand and supply of Radio Operators and use make their best to realize more harmonious policies on the demand and supply of manpower.

• Journal of Satellite, Information and Communications
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• v.10 no.1
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• pp.17-21
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• 2015

In this paper, we introduce satellite communication for new wireless disaster network to be built on the basis of amateur radio HR (HAM Radio) as a wireless package system, and channel environments of a D2D terminal that tries to connect and communicate with the wireless disaster network. In this disaster network, we propose a LOS component ratio based adaptive channel modeling approach to accurately estimate a variety of channels whose the D2D terminal could have and smoothly transfer to the level of multimedia data based on the Okumura-Hata channel model. As a result of computer simulation, performance of the proposed method was compared with the that of Okumura-Hata model of open area and urban area model and we were confirmed that there is a gain of BER performance from the results of the computer simulation.

• Electronics and Telecommunications Trends
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• v.33 no.6
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• pp.94-106
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• 2018

A quantum key distribution (QKD) provides in principle an unconditional secure communication unlike the standard public key cryptography depending on the computational complexity. In particular, free-space QKD can give a secure solution even without a fiber-based infrastructure. In this paper, we investigate an overview of recent research trends in the free-space QKD system, including satellite and handheld moving platforms. In addition, we show the key components for a free-space QKD system such as the integrated components, single photon detectors, and quantum random number generator. We discuss the technical challenges and progress toward a future free- space QKD system and components.