• Journal of IKEEE
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• v.15 no.1
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• pp.49-56
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• 2011

In this paper, a compact doppler sensor with oscillator type active antenna operating at 2.4GHz frequency band is proposed to measure the distance or speed of a moving object. The active antenna has been realized by oscillator using radiator, patch antenna, as its resonator. The oscillation frequency is shifted depending on approaching of the object, and a detection circuit discriminates the frequency deviation. The oscillator type active antenna has been designed and simulated. The prototype fabricated has a very small circular disk type of diameter 30mm and height 4.2mm. As for antenna performance, broadside radiation pattern with beamwidth of $130^{\circ}$ and oscillation frequency of 2.373GHz has been measured. Test results as a doppler sensor shows that doppler signal voltage of about 190mV has been obtained for conducting plate moving 1 meter away from the sensor. And, doppler signal voltage has been linearly increased to the ground from 4.5m height by free-falling the sensor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.3
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• pp.212-217
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• 2016

The S-band receiver for Low Earth Orbit satellite is designed and fabricated as engineering model. Demodulator is implemented by using FPGA for extension of demodulator method. The receiver consists of RF Block, Digital demodulator and Power stage and has a Doppler tracking function to compensate a frequency shift that occur on the operation. The measured results of fabricated receiver show BER of less than $1.0{\times}10^{-6}$ at -110dBm RF input power and equipped a frequency tracking of ${\pm}100KHz$ relative to the center frequency. TID test was satisfied with the results of the test criterion is 10krad.

• Journal of Satellite, Information and Communications
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• v.3 no.1
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• pp.8-14
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• 2008

In this paper, we analyze throughput performance of MF-TDMA scheme and QS MC-DS/CDMA(quasi-synchronous MC-DS/CDMA) scheme based on scrambling on WH sequence and PPGC sequence in early frequency offset caused by high speed transfer terminal. QS MC-DS/CDMA scheme with scrambled WH sequence shows 5.7% higher throughput than MF-TDMA scheme and 8% higher throughput than QS MC-DS/CDMA with PPGC sequence in high speed transfer terminal environment such as maximum 1000Km/h speed with high frequency of Ka-band. Finally, we show that QS MC-DS/CDMA scheme with scrambled WH sequence is more efficient than traditional MF-TDMA scheme at the aspect of throughput in DVB-RCS system with Ka frequency band.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.3
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• pp.208-216
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• 2017

This paper presents the design method of an FMCW(frequency-modulated continuous-wave) altitude simulator which generates propagation delay signals according to target distances to test the radar altimeter. To improve the conventional RF method for creating delay signals, the simulator is designed by the RF-optics-RF method using optical delay lines. In addition, it is designed to simulate the Doppler shift and jamming that may occur in actual flight environment. In order to evaluate the performance of the developed simulator, the integration tests have been conducted with the radar altimeter. Through the test, we successfully verified the performance of the simulator.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.22 no.2
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• pp.311-318
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• 2021

Underwater, signals are transmitted by sound waves. Sound waves are transmitted through a multipath, either directly or through reflection, due to the variety of underwater environmental characteristics. In such diverse and complex underwater environments, tests must be conducted to determine the extent of the hazard from the survivability and pitfalls of submarines by measuring the underwater radiated noise. Usually, the sound source level measurement of underwater radiated noise should be made within the closest point (CPA: Closest Point of Approach) ± a few meters between the measurement sensor and the submarine. In this study, FDOA and TDOA methods were proposed to estimate the underwater source range. A simulation based on the underwater channel model confirmed the performance of the proposed method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.9
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• pp.1734-1741
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• 2007

In this paper, the Hybrid SC/MRC-2/4 method in which bit synchronization and phase synchronization were not required was applied to the orthogonal MC DS-CDMA system in which each normalized subcarrier interval and processing gain had the same value, respectively, and the direct sequence spread code of each subcarrier was orthogonal. In the broadband wireless system in which multi-carrier transmission was used, a Doppler frequency shift occurred, which was caused by the difference between the highest subcarrier frequency md the lowest subcarrier frequency. In order to complement phase error caused by the shift, the orthogonal MC DS-CDMA system was analyzed so that the receiving signal could be perfectly synchronized by adjusting the PLL gain suitable for the entire system. As a result of simulations, as the PLL gain was increased, the change in the intervals was close to the case of perfect synchronization however, it became less when the PLL gain reached more than a certain value. Therefore, by selecting a proper PLL gain suitable for the system the orthogonal MC DS-CDMA can be designed in which the Hybrid SC/MRC method is applied.

• Journal of Advanced Navigation Technology
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• v.27 no.4
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• pp.410-416
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• 2023

Unlike geostationary satellite communication systems, low-earth orbit(LEO) satellite communication systems move at relatively high speeds, and the angle with the ground device is not fixed and varies over a wide range. The propagation channel condition between satellites and ground nodes cannot be assumed line of sight(LOS) anymore. This paper analyzes the low-orbit multi-path fading satellite channel model that can occur in LEO satellite communication systems and Doppler frequency transition caused by high-speed maneuvering of LEO satellites and presents effective equalization techniques for OFDM and SC-FDE transmission methods suitable for multi-path frequency selective fading satellite channel models. In addition, this paper compares and analyzes the performance of OFDM and SC-FDE transmission methods in multipath fading LEO satellite channel environment using the proposed equalization techniques through simulations. Simulation results showed that SC-FDE outpeformed OFDM.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.10
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• pp.28-33
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• 2009

In this paper, we propose the receiver algorithms suitable for the VHF (Very High Frequency) digital link mode-2(VDL Mode-2) system. Unlike conventional digital communication systems using the root raised cosine filter as a transmit and receive filter, raised cosine filter is used as a transmit filter in the VDL Mode-2 system. Hence, it is crucial to design and implement the optimum lowpass receive filter by considering inter-symbol interference and noise performance. On the other hand, due to the short preamble pattern, it is crucial to develop an efficient packet detection algorithm for reliable communication link for the VDL Mode-2 system. Also, frequency offset due to the carrier frequency difference between transmitter and receiver and doppler frequency shift must be estimated and compensated for reliable communication. In this paper, the optimum receive filter, packet detection and frequency offset compensation algorithms are proposed and the performance of the VDL system employing the proposed algorithms are evaluated.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.6C
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• pp.530-538
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• 2010

In this paper, estimation methods of cell searching and DoA (Direction of Arrival) for mobile relay stations with a uniform linear array are proposed. The proposed methods can improve the performance of cell searching and DoA estimation by removing the effect of STOs when there exist symbol timing offsets (STOs) between the signals received from adjacent base stations,. Also, the proposed methods can improve the performance of DoA estimation significantly when there exists Doppler frequency shift caused by movement of the mobile relay station. The performances and computational complexities of the proposed cell searching and DoA methods are evaluated by computer simulation under Mobile WiMAX environments.