• Journal of Communications and Networks
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• v.12 no.5
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• pp.475-479
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• 2010

The clipping value, defined as the log-likelihood ratio (LLR) in the case wherein all the list of candidates have the same binary value, is investigated, and an effective method to estimate it is presented for iterative tree search detection. The basic principle behind the method is that the clipping value of a channel bit is equal to the LLR of the maximum probability of correct decision of the bit to the corresponding probability of erroneous decision. In conjunction with multilevel bit mappings, the clipping value can be calculated with the parameters of the number of transmit antennas, $N_t$; number of bits per constellation point, $M_c$; and variance of the channel noise, $\sigma^2$, per real dimension in the Rayleigh fading channel. Analyses and simulations show that the bit error performance of the proposed method is better than that of the conventional fixed-value method.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7C
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• pp.954-961
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• 2004

In this paper, we propose a STF(Space-Time-Frequency) coded OFDM(Orthogonal Frequency Division Multiplexing) transmission scheme as an attractive solution for high bit rate data transmission in a multipath fading environment. The STF-OFDM transmission scheme that we propose in this paper is a simple transmission cheme for achieving frequency diversity gain with low complexity. Using preceding in frequency domain, we obtain frequency diversity gain and improve the SER performance of conventional ST-OFDM. The preceding scheme proposed in this paper is a very simple method that can be encoded and decoded with low complexity.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.44-52
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• 2001

This paper considers a modeling and identification for the MIMO magnetic bearing system. To obtain the nominal plant transfer functions, we have experimented on the frequency response by a closed-loop identification method because the system is unstable essentially. We suggest a method of curve-fitting for obtaining the transfer function from the frequency responses by using the system's modeling structure and two controllers which are different from each other. From the frequency response results, we found the effects of coupling by opposing controllers. And using this effects and the system's modeling structure, we could obtain the transfer functions of which have the same modularized denominators.

• Journal of Power System Engineering
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• v.5 no.4
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• pp.53-60
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• 2001

This paper considers a modeling for the MIMO magnetic bearing system. The rotor is flexible and has a complex shape. To obtain the nominal plant transfer functions, we perform a numerical analysis by using the finite element method(F.E.M.) for the rotor's dynamics, and make a nominal model by reducing the modes from the results. And, we have experimented on the frequency response by a closed-loop identification method, and compared it with the simulation's result on the closed-loop control system.

• ETRI Journal
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• v.37 no.6
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• pp.1055-1064
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• 2015

We demonstrate a next-generation high-capacity mobile fronthaul based on radio over fiber (RoF) technology, which links between a digital unit and a radio unit supporting two frequency assignments and $2{\times}2$ multiple input, multiple output antennas. To confirm the technical feasibility of a mobile fronthaul, we experimentally investigate its down- and uplink end-to-end performances including the optical and radio frequency (RF) signal path. Frequency-dependent performance deviations, error vector magnitude variations, overall system performance variations caused by optical to electrical conversion, and intermediate frequency to RF conversions are examined. Experimental verifications on multiple LTE uplink signals are performed for the first time. We also demonstrate several commercial mobile Internet services, YouTube video streaming, and file transfers using off-the-shelf mobile devices, through a mobile fronthaul based on RoF.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.1C
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• pp.1-8
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• 2009

Cooperative diversity is a novel technique to improve diversity gains, capacity gains, and energy saving. This technique involves multiple terminals sharing resources in order to build a virtual antenna array in a distributed fashion. In this paper, we propose a multi-user cooperative diversity protocol called Relay-assisted Multiple Access Channel(R-MAC) that allows multiple source terminals to transmit their signals simultaneously and the relay terminal forwards the aggregated signal received from the source terminals to the destination terminal. The proposed protocol converts the distributed antenna channels into an effective MIMO channel by exploiting a relay, increasing both diversity gain and system throughput. We investigate the performance of the proposed protocol in terms of outage probability and diversity-multiplexing tradeoff where we assume block fading channel environment. Our simulation results show that the proposed protocol outperforms direct transmission in the high spectral efficiency regime where the conventional cooperative diversity protocols cannot outperform direct transmission.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.1
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• pp.62-69
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• 2011

A novel QEGT codebook index searching algorithm for long tenn evolution (LTE) system is proposed. The proposed algorithm divides the Q precoding vectors into M groups, and selects the optimal precoding vector from the selected group at the receiver. This algorithm reduced the calculation for searching the optimal precoding vector index compared to the previous algorithms. The index searching algorithm is implemented for TI's TMS320C6713 DSP board. When the number of transmit antenna is 4, the number of clock cycles is reduced to 25%.

• Korean Chemical Engineering Research
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• v.46 no.3
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• pp.486-491
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• 2008

This paper describes a model identification method that has been applied to a commercial 12-inch RTP (rapid thermal processing) equipment with an ultimate aim to develop a high-performance advanced controller. Seven thermocouples are attached on the wafer surface and twelve tungsten-halogen lamp groups are used to heat up the wafer. To obtain a MIMO balanced state space model, multiple SIMO (single-input multiple-output) identification with highorder ARX models have been conducted and the resulting models have been combined, transformed and reduced to a MIMO balanced state space model through a balanced truncation technique. The identification experiments were designed to minimize the wafer warpage and an output linearization block has been proposed for compensation of the nonlinearity from the radiation-dominant heat transfer. As a result from the identification at around 600, 700, and $800^{\circ}C$, respectively, it was found that $y=T(K)^2$ and the state dimension of 80-100 are most desirable. With this choice the root-mean-square value of the one-step-ahead temperature prediction error was found to be in the range of 0.125-0.135 K.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.9C
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• pp.820-825
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• 2007

Super-orthogonal space-time trellis code (SOTTC) uses the expanded set of the orthogonal space-time block code to obtain coding gain and diversity gain without loss of transmit rate. In SOSTTCs, signal set expansions are performed by rotating the first column of the code matrix. The rotating phases used previously were selected to avoid the signal constellation expansion rather than the performance improvement. In this paper, we make a design criterion to select the proper rotating phase to improve the performance of SOSTTCs for fast Rayleigh fading channels. In addition, we design improved SOSTTCs by using the proper rotating phase. Simulation results are also provided to confirm our SOSTTCs are superior to the previous SOSTTCs in the view of BER performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.4C
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• pp.418-424
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• 2007

This paper proposes a scheme to track channel response in OFDM systems with null sub-carriers. The proposed channel tracking scheme estimates the channel response first in the frequency domain by using the decision directed data. The time domain channel estimation is then performed to remove additive white Gaussian noise (AWGN) components further. Due to the channel estimation in the frequency domain, no inverse matrix calculation is required in the time domain channel estimation. Computational reduction in the proposed method is about 93%, compared with the conventional time domain channel estimation method. Mean square error (MSE) and bit error rate (BER) performances are evaluated by using computer simulation. The proposed method shows the same performance as that of the conventional time domain channel estimation even though the significant computational reduction.