• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.7
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• pp.550-559
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• 2017

In order to maintain communication while the vehicle is moving, satellite azimuth angle and elevation angle correction are needed in real time. The elevation angle correction affects the system G/T according to the variation of the external noise temperature flowing into the antenna. G/T is expressed as a ratio of power gain G to noise temperature T and is an important performance function required for antenna gain design. This paper aims to G/T analysis considering elevation angle change and the establishment of an antenna design procedure. For this purpose, the relationship between elevation angle and brightness temperature including rain attenuation was analyzed according to recommendation ITU-R P.372 radio noise. Next, an antenna was designed based on the analysis results and design procedure was verified by G/T measurement. Through this experiment, G/T according to elevation angle was confirmed, and the minimum antenna gain analysis and design procedure required in the system could be established.

• 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.

• 전자공학회논문지 IE
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• v.45 no.4
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• pp.54-59
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• 2008

In this paper, circularly polarized patch antenna with 2-stage LNA for the reception of S-DMB is presented. It used teflon didelectric substrate of ${\in}_r$=2.2 and the size is $40{\times}40{\times}15\;[mm]$. Experimental results of fabricated antenna show that bandwidths of input return loss and axial ratio are about 22 [MHz] and 25 [MHz]. Input return loss, output return loss, gain, and noise figure of the fabricated 2-stage LNA are $S_{11}$=-14 [dB], $S_{22}$=-18 [dB], $S_{21}$=26.8 [dB], and NF=1.14 [dB] respectively. The fabricated active type antenna has total gain of 30.4 [dB] at 2.642 [GHz].

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.5
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• pp.38-47
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• 2008

The most commonly used location recognition system is the GPS-based approach. However, the GPS is inefficient for an indoor or urban area where high buildings shield the satellite signals. To overcome this problem, this paper propose the indoor positioning method using wavelet and neural network. The basic idea of proposed method is estimated the location using the received signal strength from wireless APs installed in the indoor environment. Because of the received signal strength of wireless radio signal is fluctuated by the environment factors, a feature that is strength of signal noise and error and express the time and frequency domain is need. Therefore, this paper is used the wavelet coefficient as the feature. And the neural network is used for estimate the location. The experiment results indicate 94.6% an location recognition rate.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5B
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• pp.797-808
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• 2000

This paper presents the bit error rate(BER) upper bounds for trellis coded asymmetric 8PSK(TC-A8PSK) system using the Ka-band satellite in the rain fading environment. The probability density function(PDF) for the rain fading random variable can be theoretically derived by assuming that the rain attenuation can be approximated to a long-normal distribution and the rain fading parameters are calculated by using the rain precipitation data from the Crane global model. Furthermore, we analyze the BER upper bounds of TC-A8PSK system according to the number of states in the trellis diagram and the availability of channel state information(CSI). In the past, Divsalar and Simon[9] has analyzed the BER upper bounds of 2-state TCM system in Rician fading channels however this paper is the first to analyze the BER upper bounds of TCM system in the rain fading channels. Finally, we summarize the dominant six factors which are closely related to the BER upper bounds of TC-A8PSK satellite system in the rain fading channel as follows: 1) frequency band, 2) rain intensity, 3) elevation angle, 4) signal to noise ratio, 5) asymmetric angle, and 6) availability of CSI.

• Korean Journal of Remote Sensing
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• v.28 no.5
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• pp.561-571
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• 2012

The MTF(Modulation Transfer Function) is one of quality assesment factors to evaluate the performance of satellite images. Image restoration is needed for MTF compensation, but it is an ill-posed problem and doesn't have a certain solution. Lots of filters were suggested to solve this problem, such as Inverse Filter(IF), Pseudo Inverse Filter(PIF) and Wiener Filter(WF). The most commonly used filter is a WF, but it has a limitation on distinguishing signal and noise. The L-curve-based Modified Wiener Filter(MWF) is a solution technique using a Tikhonov regularization method. The L-curve is used for estimating an optimal regularization parameter. The image restoration was performed with Dubaisat-1 images for PIF, WF, and MWF. It is found that the image restored with MWF results in more improved MTF by 20.93% and 10.85% than PIF and WF, respectively.

• Journal of Satellite, Information and Communications
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• v.12 no.4
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• pp.141-145
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• 2017

Spectrum sensing is a critical functionality of Cognitive Radio(CR) systems and the CR systems can be applied to RF energy harvesting systems to improve an energy harvesting rate. There are number of spectrum sensing techniques. One of techniques is energy detection. Energy detection is the simplest detection method and is the most commonly used. But, energy detection has a hidden terminal problem in real wireless communication, because of secondary user (SU) can be affected by frequency fading and shadowing. Cooperative spectrum sensing can solve this problem using spatial diversity of SUs. But it has a problem of increasing data by processing multiple secondary. So, we propose the system model using adaptive spectrum sensing algorithm and system model is simulated. This algorithm chooses sensing method between single energy sensing and cooperative energy according to the received signal's Signal to Noise Ratio (SNR) from Primary User (PU). The simulation result shows that adaptive spectrum sensing has an efficiency and improvement in CR systems.

• Journal of Satellite, Information and Communications
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• v.8 no.4
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• pp.37-42
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• 2013

In this paper, we propose a compensation method of a non-ideal antenna array and a computationally efficient estimation method of the direction of arrival (DOA) for the antenna array. For DOA estimation, an antenna array is essential. By using the phase difference between the output signals of antennas, we can derive the DOA. In practice, however, mutual coupling between the elements of an antenna array change the beam pattern of each element and degrade the performance of DOA estimation. In the proposed method, we first estimate the DOA for the mid-subarray of the array, where all elements undergo relatively same coupling effect. We use the estimation of signal parameters via rotational invariance techniques (ESPRIT) algorithm to estimate the DOA. Then, we expand the array based on the estimated DOA by compensating the coupling effect. Simulation results show that the proposed method is effective when jamming to noise power ratio (JNR)is relative low.

• Journal of Satellite, Information and Communications
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• v.12 no.1
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• pp.64-71
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• 2017

In this paper, Kalman filter and RRWA algorithm are used to estimate the accurate target in IR-UWB (Impulse-Radio Ultra Wideband) radar system, which enables accurate location recognition of indoors and outdoors with low cost and low power consumption. In the signal reflected by the target, unnecessary signals exist in addition to the target signal. We have tried to remove unnecessary signals and to derive accurate target signals and improve performance. The location of the targets is estimated in real time with one transmitting antenna and one receiving antenna. The Kalman filter was used to remove the background noise and the RRWA algorithm was used to remove the reflected signal. In this paper, we think that it will be useful to study the accurate distance estimation and tracking in future target estimation.

• Journal of Satellite, Information and Communications
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• v.11 no.4
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• pp.58-62
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• 2016

In this paper, we propose a pre-processing scheme for improving indoor positioning accuracy in impulsive noise channel environments. The impulsive noise can be generated by multi-path fading effects by complicated indoor structures or interference environments, which causes an increase in demodulation error probability. The proposed pre-processing scheme is performed before a triangulation method to calculate user's position, and providing reliable input data demodulated from a received signal to the triangulation method. Therefore, we studied and proposed an adaptive threshold function for mitigation of the impulsive noise based on wavelet denoising. Through results of computer simulations for the proposed scheme, we confirmed that Bit Error Rate and Signal-to-Noise Ratio performance is improved compared to conventional schemes.