• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.2
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• pp.178-182
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• 2011

A FSK receiver RF block has been developed for Dubaisat-1 Low Earth Orbit satellite. The receiver has Doppler tracking function which compensate frequency shift on uplink channel for commanding the satellite. It consist of LNA, downconverter and IF module. The IF module has Doppler tracking circuitry which sweep and lock on to input signal. It satisfies the requirement of the Dubaisat-1 in mass, power consumption, tracking speed and BER performance.

• Journal of Satellite, Information and Communications
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• v.5 no.1
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• pp.54-57
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• 2010

The navigation system like GPS which is core technology is based on Code Division Multiple Access(CDMA) techniques. To receive satellite signal smoothly in CDMA, received signals have to synchronize with spread code. In this paper, we focus on the code tracking methods among synchronization techniques. The conventional delay lock loop(DLL) is unsuitable for multi-path channel. We will introduce how it overcomes distortion by multi-path. We will propose method that separates out multi-path signals and tracks the each path signals. And we will confirm performance of proposed method using Spirent simulator.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.2 no.4
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• pp.17-27
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• 2003

This paper presents the channel estimation method with STBC applied to IEEE802.11a. Tenacious channel estimation method for OFDM system, that generally uses STTC, has been presented once and massive amount of calculation was needed However, regarding this paper, the amount of calculation can be reduced by using Curve Fitting, and channel tracking performance improvement can be achieved Based on the estimation method, computer simulation was done for the performance analysis and delay spread Doppler frequency and many other group sizes and numbers were considered As a result of the testing, we found out that Doppler frequency deviation effects equally as frequency offset. Also compared to the existing technique, channel estimated performance confirmed that have 0.9dB SNR improvement than old method.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.9 no.6
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• pp.746-760
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• 1998

In this paper, an adaptive RSSD(reduced-state sequence detection) receiver is proposed for the purpose of reducing the complexity and decision delay of the adaptive MLSD(maximum-likelihood sequence detection) receiver in the mobile satellite channel. The RSSD receiver reconstructs the trellis with a reduced number of states. The performance degradation due to the reduced states is compensated by modifying the branch metric calculation which uses the symbols in each path memory to estimate the residual ISI(intersymbol interference) terms. The structure of the proposed adaptive RSSD is a modified RSSD utilizing a per-survivor processing as well as the symbol-aided method and a channel estimation using the tentative data sequences. The complexity and performance of the proposed adaptive RSSD are controlled by the number of system states and ISI cancelers and the inserting period of the known symbols. In spite of a suboptimal alternative receiver compared to the adaptive MLSD receiver, the proposed adaptive RSSD receiver is able to reduce the complexity significantly and track the time-varying channel fast and reliably.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.12
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• pp.1383-1389
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• 2011

The current study focuses on the consistent analysis of heat transfer in multichannel volumetric solar receivers used for concentrating solar power. Changes in the properties of the absorbing material and channel dimensions are considered in an optical model based on the Monte Carlo ray-tracing method and in a one-dimensional heat transfer model that includes conduction, convection, and radiation. The optical model results show that most of the solar radiation energy is absorbed within a very small channel length of around 15 mm because of the large length-to-radius ratio. Classification of radiation losses reveals that at low absorptivity, increased reflection losses cause reduction of the receiver efficiency, notwithstanding the decrease in the emission loss. As the average temperature increases because of the large channel radius or small mass flow rate, both emission and reflection losses increase but the effect of emission losses prevails.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2298-2306
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• 2014

In this paper, we propose an open loop power control algorithm to control transmission power of the On-The-Move(OTM) Satcom terminal in GEO satellite communication environment. The proposed algorithm identifies the current channel state restricted by an obstacle or an antenna depointing loss based on the received beacon signal strength. On the basis of the determined signal attenuation causes, the OTM Satcom terminal turns off the RF output when an antenna tracking is failed. If the OTM Satcom terminal experiences a channel blockage by an obstacle, the terminal spreads the transmit data to increase data reception probability. To evaluate the performance of the proposed algorithm, we compare an adjacent satellite interference level and an outage probability. The results show the performance of the proposed algorithm is better than that of the conventional algorithm.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.4
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• pp.705-712
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• 2018

The radiation characteristics of a phased array antenna is changed according to the beam steering angle. The monopulse tracking system calculates the prediction angle using the radiation characteristics of antenna. Therefore, the monopulse ratio curve is changed according to the beam steering angle for the monopulse tracking system using a phase array antenna, and the tracking accuracy goes down. In the case of a single-channel monopulse system, the monopulse rate curve is controlled by the configuration variables of the system. In this paper, a simplified formula was presented for adaptive control of monopulse system configuration variables on beam steering angle. The presented formula can induce a uniform monopulse ratio curve for the beam steering angle as well as the phased array antenna design parameters.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.8
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• pp.759-764
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• 2004

This paper proposes a method that estimates MIMO channel characteristics analytically using a 3D ray tracing propagation model. We calculate the discrete spatial correlation between sub-channels by considering phase differences of paths, and using this, estimate the mean capacity upper bound of MIMO channel by Jensen's inequality. This analysis model is a deterministic model that do not approach stochastically through measurement nor approach statistically through Monte-Carlo simulations, so this model has high efficiency for time and cost. And based on the electromagnetic theory, this model may analyze quantitatively the parameters which can affect the channel capacity - antenna pattern, polarization mutual coupling, antenna structure and etc. This model may be used for the development of an optimal antenna structure for MIMO systems.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.11C
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• pp.1108-1115
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• 2005

In this paper, we propose a practical iterative channel estimation and decoding method for an LDPC-coded frequency hopping OFDMA system in the uplink of a packet-based cellular system. In the method, the channel gain and noise variance are iteratively estimated with both pilot symbols and LDPC decoder outputs to provide more reliable decoding metrics in intercell interference (ICI) environments. In addition, the channel correlation coefficient is also estimated to select proper filter coefficients according to the channel variation rate. Through simulations under the various channel conditions and different receiver configurations, it is shown that the proposed iterative receiver improves the performance without boosting the pilot power and mitigates the adverse effects of the non-uniform ICI.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.6
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• pp.581-588
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• 1997

Time-variant mobile radio fading channels distort amplitude, frequency and phase of a transmitted signal. On channels that have time-variant spectral nulls, the conventional equalizers which have low convergence speed and high sensitiveness to phase distortion yields very poor error rate performance. In this paper, the performance of a combined structure with the data-recycling algorithm and fractionally spaced equalizer (FSE) has been investigated on time-variant mobile radio fading channels through computer simulations and compared to other kinds of equalizers. The results show that the data-recycling FSE has excellent capabilities for tracking rapidly time-variant mobile channels and effective compensation for phase distortion.