• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.10
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• pp.1990-1998
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• 2017

The success of naval operation prioritizes the implementation of a robust communication network that delivers accurate and prompt communications to one another. The satellite, which is the main communication network of the military, is required to construct a preliminary communication network because of the enemy radio disturbance and weak point of fixed antenna. The military operational communication network has been in transition from voice-centered wireless communication network to text message-based communication network. In this paper we suggest an enhanced communication method built on Roll Call, the main communication method of ROK Navy operating tactical data link called Link-11. Simulation results display that the proposed method reduces the transmission time per unit frame by 4.3 times compared to the Roll Call and 6.3 times compared with the Round Robin & Broadcasting; it is also proved that the higher the direct reception rate, the shorter the transmission time required by 1.6 times maximum.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2C
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• pp.210-218
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• 2010

In order to improve the efficiency of frequency bandwidth, various modulation methods such as QAM and PSK have been widely used, and their variation APSK(Amplitude Phase Shift Keying) type modulation methods were proposed and are being used in some satellite communication systems. In this paper, a new constellation method named as $4L^2$-APSK is proposed, which places symbol points circularly as the existing APSK constellations do, but has different number of points and different distance between adjacent points on each layer. An equation for error probability in AWGN channel is also induced for $4L^2$-APSK. In addition, a new Gaussian noise channel is proposed in which noise variances are in the amplitude and in the phase and the two are not equal, and a method of obtaining error probabilities in this channel is also suggested. The equations for error probabilities are verified by computer simulations, and error probabilities of $4L^2$-APSK and QAM are analyzed and compared in the AWGN channel and the proposed noise channel, respectively.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.685-692
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• 2008

In this paper, we propose a timing recovery loop for Inmarsat mini-m system downlink receiver. Inmarsat mini-m system requires a timing recovery loop which is robust in frequency offset and has fast acquisition because Inmarsat mini-m system specification requires frequency tolerance is required of ${\pm}924$ Hz (signal bandwidth: 2.4 kHz) and acquisition time of UW (Unique Word) signal duration (15ms).Therefore, we propose a timing recovery loop which is suitable for Inmarsat mini-m system. The proposed timing recovery loop adopted noncoherent UW detector and differential ELD which applied differential UW signal for stability and fast acquisition in frequency offset environment. Simulation results show that the proposed timing recovery loop has stable operation and fast acquisition in frequency offset environment for the system.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.10
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• pp.97-104
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• 2003

This paper addresses EMC test results for the EQM Communications & Broadcasting Satellite(CBS) Ka-band Payload System. The aim of the EMC test is to verify that the payload system has no effect on the other system and is not affected by the external field. The compliance of EMC system requirements was verified by the analysis and measurement of the emission level from the payload system. The variation of performance by noise injection was measured to inspect the susceptibility of the payload system. The analysis and test results also showed that the electromagnetic interference has no serious effect on the overall payload system performance. It is confirmed that the EQM CBS Ka-band payload system can be operable in the space environment from the EMC performance's viewpoint. It is also obtained that better performance can be acquired by improving waveguide design and integration method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.4C
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• pp.417-425
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• 2006

This Paper Proposes a method of building a panoramic video from several videos captured from adjacent cameras. The panoramic image which constructed from adjacent and overlapped images is used for photogrammetry, satellite photo or many computer graphic applications. The perspective transformation, which is estimated from the appropriate corresponding pairs of images, can be used to construct the panoramic image without unwarranted distortion and its quality is decided by how to find the features needed for transform estimation. We used the corner points for the corresponding features, and morphological structures were utilized for fast and robust corner detection. We used the criterion of the corner strength, which guarantees the robust detection of the corner in most situations. For the transformation, 8 parameters were estimated from perspective equations which use matched points of adjacent images, and bilinear color blending was used to construct a soapless panoramic video. The experiments showed that the proposed method yields fast results with good quality under various conditions.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7B
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• pp.695-705
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• 2002

In this paper, we propose a simple open loop transmit diversity (TD) scheme for the wideband code division multiple access (W-CDMA) systems in Rician multipath fading channels such as rural area or satellite channels where line-of-sight (LOS) paths are in presence. The proposed scheme does not require any pre-processing of transmit data, resulting in simpler structure as compared to conventional closed loop transmit adaptive array (TxAA) and open loop space-time transmit diversity (STTD). We analytically derive the probability density function of signal-to-noise ratio at the Rake receiver output and the uncoded bit error rate performance of the proposed scheme. Extensive simulation is Performed to verify the analytical performance of the proposed scheme under typical Rician multipath fading channel environments. Moreover, comparative results with the conventional TxAA and STTD are also provided. Simulation results show that the proposed scheme shows slightly better performance than the conventional open loop STTD under the channels with very weak LOS components, however, it significantly outperforms the STTD under the channels with dominant LOS components, and achieves a close performance of ideal closed loop TxAA.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.27 no.7B
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• pp.719-726
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• 2002

In WRC-2000, Resolution 734 was adopted to study the use of high altitude platform station(HAPS) operating in the bands above 30GHz. Therefore, frequency sharing feasibility between a new HAPS systems and an existing terrestrial fixed-service(FS) system should be analyzed primarily. In this paper, interference effects from the HAPS system into the radio-relay station are analyzed in terms of two cases; one is the interference distribution from the power-flux density(PFD) of HAPS airships, and the other the interference power from the ground stations. In conclusion, the new PFD criteria different from the exiting satellite system should be required, and the coordinated distance between the HAPS nadir and the radio-relay station should be 60km ∼ 253km for P$\sub$HG/ = -50dBW/MHz of transmitting power spectral density to share the new HAPS system into the existing FS system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.7
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• pp.1433-1440
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• 2015

In this paper, we propose an unambiguous correlation function to improve tracking performance for binary offset carrier (BOC) signals. Specifically, we divide a BOC sub-carrier into multiple rectangular pulses, and analyze that the BOC autocorrelation function is made up of the sum of several partial correlation functions. Then, we obtain two sub-correlation functions by combining two partial correlation functions and propose a novel unambiguous correlation function with no side-peak which can be regulated its width based on the combination of the sub-correlation functions and partial correlation functions. From numerical results, it is confirmed that the proposed correlation function provides a tracking performance improvement over the conventional correlation functions in terms of the tracking error standard deviation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.42 no.4
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• pp.739-746
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• 2017

Orthogonal frequency division multiplexing(OFDM) systems have many advantages. However, OFDM systems are much affected by a nonlinear distortion because those systems have a high peak to average power ratio(PAPR) value. A selected mapping technology was suggested to reduce a PAPR value. The technology does not have data loss but receivers need side information to know modified phase sequence. Therefore, side information causes decreased a transmission efficiency. In this paper, we suggest a blind SLM receiver using a cross correlation technology. This receiver does not require side information. The proposed blind SLM receiver calculates sums of cross-correlation between transmitted pilot signals multiplied by each phase sequence and received pilot signals. So, this receiver detects side information which has a maximum sum cross-correlation value. We compared our proposed SLM receiver to a conventional blind SLM receiver through bit error rate(BER) and side information error rate(SIER) performances. Simulation results show that the proposed SLM receiver has improved BER and SIER performances than the conventional SLM receiver.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.11 no.1
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• pp.26-36
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• 2000

A circularly polarized $12\times12$ array with application in the satellite communications is designed at 10 GHz. The radiator is an aperture-coupled ring patch, which is suitable of large arrays. The element spacing of the array is chosen to be $0.7\lambda_0$to maintain the main beam in the broadside direction. The array is a sequential array constructed on a series-parallel feed network to obtain high gain and low axial ratio. Measurement results for the array, acquired by experiments in the compact range of POSTECH, showed a directivity of 27.88 dB, a high gain of 25.55 dB, an efficiency of 60%, an axial ratio of 1.74 dB, and a side-lobe level of -13 dB. The bandwidth of the array was 43% when the VSWR was 2, and the bandwidth of the axial ratio was 16%.