• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.2
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• pp.69-76
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• 2014

Multiple-input and multiple-output (MIMO) technique is used in many communication fields in order to increase the channel capacity. However, this MIMO system has difficulty of miniaturization of antenna size due to the multiple RF chains Also, multiple RF chain raises some problems which increase power consumption at RF circuit and degrade the system performance due to the interference between RF chains. Because of these reasons, beamspace MIMO (BS-MIMO) technique with only single RF chain was proposed for MIMO transmission. This BS-MIMO system basically uses electronically steerable parasitic array radiator (ESPAR) antenna. Existing ESPAR antenna has a 5-element structure. So, it is possible to do only $3{\times}3$ MIMO transmission. Therefore, in order to extend BS-MIMO dimension, extension of ESPAR antenna structure is essential. In this paper, we show that BS-MIMO dimension can be increased according to the extension of structure of the ESPAR antenna, as in the conventional MIMO techniques. For example, we show that it is possible to design the $7{\times}7$ BS-MIMO transmissions with the 13-element ESPAR antenna. Also, when the number of parasitic elements of ESPAR antenna increases by two elements, MIMO dimension is expanded by 1.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.07a
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• pp.532-535
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• 2000

We have fabricated a sensor system for on-line monitoring the oxygen permeability and diffusivity of six different polymer films using the miniaturized 6 cathode(Ag)-single anode(Ag/AgCl) type hexagonal oxygen electrode. This system consists of multiple input front-end electronics, signal conditioning circuit using the embedded microcontroller 80C196KC, PC interface circuit and PC with the OS for microcontroller and the operating program for this system. The digital low-[ass filter was programmed and the simulated filter characteristics were enough to eliminate the noise from sensor signal. According to the experimental results, the linearity coefficients of the output voltage to oxygen partial pressure for each sensor electrode of six cathode type oxygen sensor are 0.998, 0.997, 0.998, 0.997, 0.997, 0.997 respectively, and the response times are all within 4 minutes.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.7
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• pp.2365-2382
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• 2014

While single-user spatial multiplexing multiple-input multiple-output (SU-MIMO) allows spatially multiplexed data streams to be transmitted to one node at a time, multi-user spatial multiplexing MIMO (MU-MIMO) enables the simultaneous transmission to multiple nodes. However, if the transmission time required to send packets to each node varies considerably, MU-MIMO may fail to utilize the available MIMO capacity to its full potential. The transmission time typically depends upon two factors: the link quality of the selected channel and the data length (packet size). To utilize the cumulative capacity of multiple channels in MIMO applications, the assignment of channels to each node should be controlled according to the measured channel quality or the transmission queue status of the node.A MAC protocol design that can switch between MU-MIMO and multiple SU-MIMO transmissions by considering the channel quality and queue status information prior to the actual data transmission (i.e., by exchanging control packets between transmitter and receiver pairs) could address such issues in a simple but in attractive way. In this study, we propose a new MAC protocol that is capable of performing such switching and thereby improve the system performance of very high throughput WLANs. The detailed performance analysis demonstrates that greater benefits can be obtained using the proposed scheme, as compared to conventional MU-MIMO transmission schemes.

• Journal of Power Electronics
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• v.16 no.4
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• pp.1483-1493
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• 2016

Multiple parallel inverters have multiple resonant frequencies that are influenced by many factors. This often results in stability and power quality problems. This paper develops a multiple input multiple output model of grid-connected inverter systems using a closed-loop transfer function. The influence factors of the resonant characteristics are analyzed with the developed model. The analysis results show that the resonant frequency is closely related to the number, type and composition ratio of the parallel inverters. To suppress resonance, a scheme based on virtual impedance is presented, where the virtual impedance is emulated in the vicinity of the resonance frequency. The proposed scheme needs one inverter with virtual impedance control, which reduces the design complexity of the other inverter controllers. Simulation and experimental tests are carried out on two single phase converter-based setups. The results validate the correctness of the model, the analytical results and the resonant suppressing scheme.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.12 no.8
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• pp.4006-4020
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• 2018

In recent years, one of the most remarkable 5G technologies is massive multiple-input and multiple-output (MIMO) system which increases spectral efficiency by deploying a large number of transmit-antennas (eg. tens or hundreds transmit-antennas) at base station (BS). However, conventional massive MIMO system using single-polarized (SP) transmit-antennas increases the size of the transmit-array proportionally as the number of transmit-antennas increases. Hence, size reduction of large-scale transmit-array is one of the major concerns of massive MIMO system. To reduce the size of the transmit-array at BS, dual-polarized (DP) transmit-antenna can be the solution to halve the size of the transmit-array since one collocated DP transmit-antenna deploys vertical and horizontal transmit-antennas compared to SP transmit-antennas. Moreover, proposed DP massive MIMO system increases the spectral efficiency by not only in the space domain but also in the polarization domain whereas the conventional SP massive MIMO system increases the spectral efficiency by space domain only. In this paper, the comparative performance of DP and SP massive MIMO systems is analyzed by space division multiple access (SDMA) and space-polarization division multiple access (SPDMA) respectively. To analyze the performance of DP and SP massive MIMO systems, DP and SP spatial channel models (SCMs) are proposed which consider depolarized propagation channels between transmitter and receiver. The simulation results show that the performance of proposed 32 transmitter (Tx) DP massive MIMO system improves the spectral efficiency by about 91% for a large number of user equipments (UEs) compare to 32Tx SP massive MIMO system for identical size of the transmit-array.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.30 no.1C
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• pp.82-91
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• 2005

This paper introduces an efficient affine projection algorithm(APA) using iterative hyperplane projection. Among various fast converging adaptation algorithms, APA has been preferred to be employed for various applications due to its inherent effectiveness against the rank deficient problem. However, the amount of complexity of the conventional APA could not be negligible because of the accomplishment of sample matrix inversion(SMI). Moreover, the 'shifting invariance property' usually exploited in single channel case does not hold for the application of space-time decision-directed equalizer(STDE) deployed in single-input-multi-output(SIMO) systems. Thus, it is impossible to utilize the fast adaptation schemes such as fast transversal filter(FlF) having low-complexity. To accomplish such tasks, this paper introduces the low-complexity APA by employing hyperplane projection algorithm, which shows the excellent tracking capability as well as the fast convergence. In order to confirm th validity of the proposed method, its performance is evaluated under wireless SIMO channel in respect to bit error rate(BER) behavior and computational complexity.

• The Journal of the Acoustical Society of Korea
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• v.35 no.2
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• pp.118-124
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• 2016

In this paper, contribution analysis method using a partial coherence function is dealt with in the case of underwater radiation noise. When performing the contribution analysis using a partial coherence function, it is important to select the order of system input. But in the case of frequency correlated systems, it is very difficult to properly select the order of system input. In order to solve this problem, the contribution analysis is performed by subdividing the area of contribution using multiple coherence function. And the new contribution analysis method is presented by using the relationship between the contribution characteristic matrix and multiple coherence function. In order to validate the new method, calculation is performed about multi-input / single-output model which is composed of sine waves. The result of calculation shows that it is possible to derive the exact contribution values.

• Journal of electromagnetic engineering and science
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• v.4 no.4
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• pp.183-189
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• 2004

In this paper, the Eigen-RAKE receiver in wideband direct sequence code-division multiple access(DS-CDMA) systems with downlink smart antenna is analyzed for different spreading bandwidths(1.25 MHz, 5 MHz, 10 MHz) and different channel environments(macro, micro). The realistic spatio-temporal wideband multipath channel is assumed, one of which is standardized multiple-input single-output(MISO) radio channel model for WCDMA link-level simulations proposed by $3^{rd}$ generation partnership project(3GPP) contributions. We assumed spatial scattering phenomenon in which many unresolvable path signals within a limited range of spatial angle simultaneously contribute to the signals received at the receiver. Several multipaths within one chip are distinguished into each one and the first multipath components are selected as the desired signal and the others are considered self-interference. Downlink DS-CDMA system with eigenbeamformer using wider bandwidth present better performance than that using narrow bandwidth system by employing Eigen-RAKE receiver of many number of branches. It is shown that the downlink eigenbeamformer is more effective in typical urban macro cellular environments when using Eigen-RAKE receiver.

• ETRI Journal
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• v.40 no.3
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• pp.309-317
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• 2018

Single carrier-frequency-division multiple access (SC-FDMA) has been adopted as the uplink transmission standard in fourth-generation cellular networks to facilitate power efficiency transmission in mobile stations. Because multiuser multiple-input multiple-output (MU-MIMO) is a promising technology employed to fully exploit the channel capacity in mobile radio networks, this study investigates the uplink transmission of MU-MIMO SC-FDMA systems with orthogonal space-frequency block codes (SFBCs). It is preferable to minimize the length of the cyclic prefix (CP). In this study, the chained turbo equalization technique with chained turbo estimation is employed in the designed receiver. Chained turbo estimation employs a short training sequence to improve the spectrum efficiency without compromising the estimation accuracy. In this paper, we propose a novel and spectrally efficient iterative joint-channel estimation, multiuser detection, and turbo equalization for an MU-MIMO SC-FDMA system without CP-insertion and with short TR. Some simulation examples are presented for the uplink scenario to demonstrate the effectiveness of the proposed scheme.

• Journal of Broadcast Engineering
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• v.24 no.4
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• pp.613-622
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• 2019

A differential codebook design method using wireless channel's temporal correlation is proposed over closed loop multiple-input single-output (MISO) system. The single layer codewords in a codebook are selected among a set of phase elements. In the conventional codeword selection rule, codewords are assumed to be on a spherical cap and sine formula was used. In this paper, however, a new method using Pythagoras formula is employed to simplify computational complexity. Also, an adaptive differential codebook selection is adopted to enhance performance. Monte-Carlo simulations demonstrate that the proposed codebook is superior to the conventional ones.