• Proceedings of the IEEK Conference
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• 2001.06a
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• pp.117-120
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• 2001

In this paper, we propose a robust trellis coded modulation for a correlated Rayleigh fading channel. This method use only one transmit antenna, which can achieve superior performance compared to Space-Time Trellis Coded Modulation (STTC) over a wide channel correlation range among transmit antennas. The code is designed to have the largest Euclidean distance between faded signals at the receiver. Computer simulations are performed to evaluate the frame error rate (FER) performance and to compare the proposed code with the conventional one.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.11A
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• pp.1092-1100
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• 2006

In this paper, we propose a full rate quasi-orthogonal space-time-frequency block coded orthogonal frequency division multiplexing(QOSTF-OFDM) that can achieve full symbol rate with four transmit antennas. Sincr: the proposed QOSTF-OFDM can not achieve full diversity, we use diversity advantage collection with zero forcing (DAC-ZF) decoder to compensate the diversity loss at receive side. At the same frequency efficiency, compared with linear orthogonal space-time codes which can not achieve full rate with four transmit antennas over complex constellations, low level modulation can be employed by proposed scheme due to its full rate, i.e., modulation advantage can be achieved. Due to modulation advantage and collected diversify advantage, the proposed scheme exhibits better BER performance than other orthogonal schemes.

• The Journal of the Korea Contents Association
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• v.8 no.4
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• pp.55-62
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• 2008

Adaptive modulation and Coding(AMC) scheme is promising technique to support the demands for high data rates and wideband proposed for 4G mobile communication system standards. In this paper, adaptive modulation and coding(AMC) based on OFDM system is analyzed through simulation for single user case and compared with SISO-OFDM and SFBC(Space frequency block coding)-OFDM. The performance analysis in terms of capacity for downlink system environments with different values of constellation size under multipath fading channel is done. The adaptive modulation and coding technique is based on perfect estimation channel. It has been observed that SFBC(Space-frequency block coding)-OFDM system gives better performance in terms of capacity.

• Journal of Korea Society of Industrial Information Systems
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• v.27 no.5
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• pp.25-36
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• 2022

This paper proposes a random sign reversal technique in space frequency block code for single carrier modulation. The traditional space time and frequency block coding technique may be confronted with radio environments openly, severe radio hijacking problems are to be overcome. In order to avoid such an open radio issue, random coded data protection technique for space-time block code was proposed, but this algorithm can change channel combination per an Orthogonal Frequency Division Multiplexing block. This kind of slow switching increases the probability that nearby receivers will detect the transmitted data. This paper proposes a fast switching algorithm per data symbols' basis which is a random sign reversal technique in space frequency block code for Single Carrier Modulation. It is shown in simulation that the proposed one has a superior performance in comparison with the performance of the receiver which do not know the random timing sequence of sign reversal.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.411-416
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• 2003

In this paper, We analysed performance of adaptive modulation system with STTD. Transmission error of system is increased by ISI according to delay wave in wireless channel environment. Therefore, We analysed performance that it is applied adaptive modulation system with STTD to reduce ISI's effect. As a results, Data transmission of high speedㆍhigh quality could know possible by applying adaptive modulation system with STTD. Because of selected high modulation mode in low SNR.

• Journal of Power Electronics
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• v.10 no.5
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• pp.468-476
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• 2010

This paper proposes and develops a new direct voltage control (DVC) approach. This method is designed to be applied in various applications for AC drives fed with a three-phase voltage source inverter (VSI) working with a constant switching time interval as in the standard direct torque control (DTC) scheme. Based on a very strong min(max) criterion dedicated to selecting the inverter voltage vector, the developed DVC scheme allows the generation of accurate voltage forms of waves. The DVC algorithm is implemented on a dSPACE DS1104 controller board and then compared with the space vector pulse width modulation technique (SVPWM) in an open loop AC drive circuit. To demonstrate the efficiency of the developed algorithm in real time and in closed loop AC drive applications, a scalar control scheme for induction motors is successfully implemented and experimentally studied. Practical results prove the excellent performance of the proposed control approach.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.739-741
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• 1993

This paper deals with the Improvement of inverter output waveform with space vector modulation using the DSP-chip. The proposed scheme can be considered as a alternative of the conventional, subharmonic method. This scheme features a maximum output voltage that is 15% greater. The number of switchings is also 30% less than the one obtained by subharmonic modulation method(SHM) A performance function(PF) which is the time integral function of the inverter output voltage is introduced in this paper. An optimal PWM pattern is obtained by minimizing the distortion factor of performance function. The experiment was carried out with an TMS320C25.

• Journal of Astronomy and Space Sciences
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• v.37 no.4
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• pp.219-228
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• 2020

A CubeSat platform has become a popular choice due to inexpensive commercial off-the-shelf (COTS) components and low launch cost. However, it requires more power-efficient and higher-data rate downlink capability for space applications related to remote sensing. In addition, the platform is limited by the size, weight and power (SWaP) constraints as well as the regulatory issue of licensing the radio frequency (RF) spectrum. The requirements and limitations have put optical communications on promising alternatives to RF communications for a CubeSat platform, owing to the power efficiency and high data rate as well as the license free spectrum. In this study, we analyzed the performance of optical downlink communications compatible with CubeSat platforms in terms of data rate, bit error rate (BER) and outage probability. Mathematical models of BER and outage probability were derived based on not only the log-normal model of atmospheric turbulence but also a transmitter with a finite extinction ratio. Given the fixed slot width, the optimal guard time and modulation orders were chosen to achieve the target data rate. And the two performance metrics, BER and outage data rate, were analyzed and discussed with respect to beam divergence angle, scintillation index and zenith angle.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.4A
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• pp.426-433
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• 2008

In this paper, we present a method to improve the performance of the four transmit antenna quasi-orthogonal space-time block code (STBC) in the coded system. For the four transmit antenna case, the quasi-orthogonal STBC consists of two symbol groups which are orthogonal to each other, but intra group symbols are not. In uncoded system with the matched filter detection, constellation rotation can improve the performance. However, in coded systems, its gain is absorbed by the coding gain especially for lower rate code. We propose an iterative decoding method to improve the performance of quasi-orthogonal codes in coded systems. With conventional quasi-orthogonal STBC detection, the joint ML detection can be improved by iterative processing between the demapper and the decoder. Simulation results shows that the performance improvement is about 2dB at 1% frame error rate.

• Annual Conference of KIPS
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• 2005.05a
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• pp.1477-1480
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• 2005

AOC-SS (Advanced Orthogonal Code-Spread Spectrum) modulation [1] is a flexible scheme to obtain a multi-rate transmission but PAPR (Peak-to-Average Power Ratio) increases in proportion to the number of AOCs and thus, the mapping technique is proposed to solve this problem. Moreover, by combining with space-time coding (STC), AOC-SS is capable of resistance to multi-path fading. The simulation programs have been performed to verify the validity of the suggested scheme.