• Aerospace Engineering and Technology
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• v.1 no.1
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• pp.135-140
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• 2002

The position and trajectory of in-flight rocket are important informations to determine the flight safety of rocket. In general tracking system, radar and transponder are used to acquire position information. Rocket position and trajectory can be determined by using RF communication between ground station and in-flight rocket and antenna position data. Onboard transponder system is composed of RF receiving part, RF transmitting one, decoder and single TX/ RX antenna. Therefore circulator is necessary for minimizing RF signal interference. In this paper, the radar transponder system was developed to track the trajectory and position of KSR-Ⅲ by using radar.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.1
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• pp.44-49
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• 2001

In this paper, we propose a new technique to compensate for the VCO nonlinearity using only the returned beat signal whose spectrum contains the internal reflections and the targets simultaneously. In the case of a distance measurement system using single antenna, the reflections from the circulator and the antenna are much larger than the return signal from target. The beat signal by these reflections is at much lower frequency than that of the target, and the VCO nonlinearity can be compensated for using these signals. Indoor experiments were carried out and the results show marked improvement in the shape of range profile and the range resolution.

• The KIPS Transactions:PartC
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• v.13C no.7 s.110
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• pp.865-872
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• 2006

Cooperative communications (CC) have received a great deal of attention recently as an efficient way to obtain the spatial diversity without physical arrays. Thus, space-time block codes (STBC) which are well-known for use in co-located multi-antenna systems can be still utilized for single-antenna users in a distributed fashion. In this paper, we propose a cooperative signaling structure using the $\frac{3}{4}$-rate STBC and derive closed-form BER expression which takes the effect of network geometry and transmit power constraint into account. A variety of simulated and numerical results demonstrated the cooperation considerably outperforms the direct transmission when partners are located in appropriate positions.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.16 no.9
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• pp.6269-6273
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• 2015

Performance of the Alamouti algorithm based M-ary $2{\times}N$ OSTBC(Orthogonal Space Time Block Coded) MIMO(Multi Input Multi Output) system has been simulated varying two main parameters - the number of constellation(M), and the number of receiving antennas(N). Computer simulation has also been carried out using Matlab software for performance comparison between $2{\times}N$ MIMO and MRC(Maximal Ratio Combining) diversity antenna system to evaluate the degree of enhancement achieved through the use of Alamouti $2{\times}N$ MIMO. Under 10 dB EbNo QPSK scenario, $2{\times}1$ MIMO brought 4.2 dB BER improvement over single antenna system and $2{\times}2$ MIMO resulted in 7.4 dB BER improvement over $1{\times}2$ MRC.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.6
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• pp.2204-2224
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• 2021

This paper studies secure wireless transmission from a multi-antenna transmitter to a single-antenna intended receiver overheard by multiple eavesdroppers with considering the imperfect channel state information (CSI) of wiretap channel. To enhance security of communication link, the artificial noise (AN) is generated at transmitter. We first design the robust joint optimal beamforming of secret signal and AN to minimize transmit power with constraints of security quality of service (QoS), i.e., minimum allowable signal-to-interference-and-noise ratio (SINR) at receiver and maximum tolerable SINR at eavesdroppers. The formulated design problem is shown to be nonconvex and we transfer it into linear matrix inequalities (LMIs). The semidefinite relaxation (SDR) technique is used and the approximated method is proved to solve the original problem exactly. To verify the robustness and tightness of proposed beamforming, we also provide a method to calculate the worst-case SINR at eavesdroppers for a designed transmit scheme using semidefinite programming (SDP). Additionally, the secrecy rate maximization is explored for fixed total transmit power. To tackle the nonconvexity of original formulation, we develop an iterative approach employing sequential parametric convex approximation (SPCA). The simulation results illustrate that the proposed robust transmit schemes can effectively improve the transmit performance.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.38 no.3
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• pp.249-255
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• 2002

This paper describes on the extraction of ship's real-time movement information using a combination full-function ARPA radar and ECS system that displays radar images and an electronic chart together on a single PC screen. The radar target extractor(RTX) board, developed by Marine Electronics Corporation of Korea, receives radar video, trigger, antenna bearing pulse and heading pulse signals from a radar unit and processes these signals to extract target information. The target data extracted from each pulse repetition interval in DSPs of RTX that installed in 16 bit ISA slot of a IBM PC compatible computer is formatted into a series of radar target messages. These messages are then transmitted to the host PC and displayed on a single screen. The position data of target in range and azimuth direction are stored and used for determining the center of the distributed target by arithmetic averaging after the detection of the target end. In this system, the electronic chart or radar screens can be displayed separately or simulaneously and in radar mode all information of radar targets can be recorded and replayed In spite of a PC based radar system, all essential information required for safe and efficient navigation of ship can be provided.

• Journal of the Korean Geotechnical Society
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• v.33 no.11
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• pp.21-34
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• 2017

The ground penetrating radar (GPR) signal can be measured with different amplitudes according to the directivity, so the directivity of the antenna should be considered. The objective of this study is to investigate the directivity of antenna by analyzing the reflection characteristics of electromagnetic waves radiated from the antenna, and to evaluate effective range of angle that can inspect an abnormal area according to the directivity of antenna. For the measurement of the directivity, a circular metal bar is used as reflector and the signals are measured by changing the angle and the distance between reflector and antenna in the E- and H-plane. The boundary distance between the near field and the far field is determined by analyzing the amplitudes of reflected signals, and two points with different distances from each of near and far fields are designated to analyze radiation patterns in near and far fields. As a result of radiation pattern measurement, in the near field, minor lobes are observed at angle section at more than $50^{\circ}$ in both E- and H-plane. Therefore, antenna has the directivity for the direction of main lobe and minor lobes in near field. In the far field, antenna has the directivity for a single direction of main lobe because minor lobes are not observed. The amplitude of the signal reflected from the near field is unstable, but it can be distinguished from noise. Therefore, in the near field, the ground anomaly can be detected with high reliability. On the other hand, the amplitude of the signal reflected from the far field is stable, but it is hard to distinguish between reflected signal and noise because of the excessive loss of electromagnetic wave. The analyses of directivity in the near and the far fields performed in this study may be effectively used to improve the reliability of the analyses of abnormal area.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.423-429
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• 2019

Recently, a variety of methods for the performance improvement of ultra-high speed wideband wireless transmission systems have been suggested. This paper proposes a space-frequency (SF) block coded single side band (SSB) single carrier (SC)-frequency division multiple access (FDMA) transmission system. In the proposed SSB SC-FDMA system, SF block code is implemented with the complex conjugates, which are formed from discrete Fourier transform (DFT) spreading of pulse amplitude modulation (PAM) signals. As a result, transmit diversity gain can be obtained in the proposed SF block coded SSB SC-FDMA system without any significant increase of the system computational complexity. The simulation result shows that the signal-to-noise power ratio (SNR) performance of the proposed SF block coded SSB SC-FDMA system is approximately 4 dB better than the SNR performance of the conventional SSB SC-FDMA system with single transmit antenna at a symbol error rate (SER) of $10^{-2}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.895-904
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• 2007

This paper proposes a robust sub-optimal smart antenna in Code Division Multiple Access (CDMA) basestation. It makes use of the property of the Least Mean Square (LMS) algorithm and the Conjugate Gradient Method (CGM) algorithm for beamforming processes. The weight update takes place at symbol level which follows the PN correlators of receiver module under the assumption that the post correlation desired signal power is far larger than the power of each of the interfering signals. The proposed algorithm is simple and has as low computational load as five times of the number of antenna elements(O(5N)) as a whole per each snapshot. The output Signal to Interference plus Noise Ratio (SINR) of the proposed smart antenna system when the weight vector reaches the steady state has been examined. It has been observed in computer simulations that proposed beamforming algorithm improves the SINR significantly compared to the single antenna case. The convergence property of the weight vector has also been investigated to show that the proposed hybrid algorithm performs better than CGM and LMS during the initial stage of the weight update iteration. The Bit Error Rate (BER) characteristics of the proposed array has also been shown as the processor input Signal to Noise Ratio (SNR) varies.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.6
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• pp.43-49
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• 2014

In this paper, we consider the performance evaluation of space time block code (STBC)) with coordinate interleaved orthogonal design (CIOD) over time selective channel. In case of quasi static channel, STBC-CIOD satisfies full rate and full diversity (FRFD) property with the single symbol decoding. However in the time selective channel, the symbol interference degrades the system performance when we employ the single symbol decoding. We derive the union bound of the symbol error probability by evaluating the pairwise error probability in the first order Markov channel. We also present simulation results of STBC-CIOD with QPSK.