• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.4
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• pp.2058-2074
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• 2017

Dense Heterogeneous Cellular Networks(HCNs) offer a promising approach to meet the target of 1000x increase in aggregate data rates in 5G wireless communication systems. However how to best utilize the available radio resources at densely deployed small cells remains an open problem as those small cells are typically unplanned. In this paper we focus on balancing loads across macro cells and small cells by offloading users to small cells, as well as dynamically switching off underutilized small cells. We propose a joint user association and base station(BS) sleep mangement(UA-BSM) scheme that proactively offloads users to a fraction of the densely deployed small cells. We propose a heuristic algorithm that iteratively solves the user association problem and puts BSs with low loads into sleep. An interference relation matrix(IRM) is constructed to help us identify the candidate BSs that can be put into sleep. User associations are then aggregated to selected small cells that remain active. Simulation results show that our proposed approach achieves load balancing across macro and small cells and reduces the number of active BSs. Numerical results show user signal to interference ratio(SINR) can be improved by small cell sleep control.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.16 no.11 s.102
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• pp.1123-1130
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• 2005

In this paper, we propose an improved side information processing scheme which is important in the sub-block phase weighting(SPW) method for the peak-to-average power ratio(PAPR) reduction. SPW method is to divide the input OFDM subchannels into several subblocks and to multiply phase weighting with each subblocks, properly for the reduction of the peak power. SPW method is similar to the conventional PTS method when the number of sub-carriers, signal modulation format and the number of subblocks are the same. However, unlike the conventional PTS(Partial Transmit Sequence) and SLM(Selected Mapping) method using many stages of IFFT(Inverse Fast Fourier Transform), SPW method only needs one IFFT. Although PAPR can be reduced by SPW method, complex computation burden still remains. In this paper the flipping algorithm and the full iteration algorithm are used f3r the phase control method. Through the computer simulation, we analyze and discuss the properties and the performance of the suggested method.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.776-781
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• 2005

In this paper, using received channel information, we analyze performance in MIMO multiuser system in low-to-medium mobile speed by selecting each user's constellations, powers, and transmit antennas. Given a target of symbol error, we determine each user's constellations, powers, selected tranprobability smit antennas such that the required signal-to-noise(SNR) is minimized for MMSE, V-BLAST receiver according to each user's information and channel estimation information. When we do power control with antenna selection technique through uplink channels of MIMO system in low-to-medium mobile speed, we analyze system performance with wireless channel information from Base-Station(BS) to Users. By simulation, it has been shown that the proposed antenna selection scheme for transmitting data offer better performance improvement than all transmit antennas for transmitting data.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.11
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• pp.141-149
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• 2013

IETF 6LoWPAN standard technique has been studied in IoT environment to support the IPv6 packet communication. 6LoWPAN protocol for transmission of packets mainly in the AODV routing protocol and a variety of extended techniques have been investigated. In particular, consisting of nodes with limited resources in a network error occurs when the 6LoWPAN reliable data transfer and fast routing method is needed. To this end, in this paper, we propose resilient routing protocol and extension of IETF LOAD algorithm, for optimal recovery path, More specifically, the optimal recovery path setup algorithm, signal flow, and detailed protocols for the verification of the reliability of packet transmission mathematical model is presented. The proposed protocol techniques to analyze the performance of the NS-3 performance through the simulation results that is end-to-end delay, throughput, packet delivery fraction and control packet overhead demonstrated excellence in comparison with existing LOAD.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.9
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• pp.1635-1641
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• 2017

In this paper, a trellis-coded 3-dimensional (3-D) orthogonal frequency division multiplexing (OFDM) system is presented and its performance is analyzed. Here, a set-partitioning technique for trellis coding with respect to a 3-D signal constellation is also presented. We show theoretically that the proposed system, which exploits a trellis coding scheme with recursive systematic convolutional codes (RSC) of code rate R = 1/3 and 2/3, can improve symbol error rate (SER) up to 7.8 dB as compared with the uncoded OFDM system in an additive white Gaussian noise (AWGN) channel. Computer simulation confirms that the theoretical analysis of the proposed system is very accurate. It is, therefore, considered that the proposed trellis-coded 3-D OFDM system is well suited for the high quality digital transmission system without increase in the available bandwidth.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.188-198
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• 2010

Recently, as the demand of the environmental-friendly energy storage system such as an electric double-layer condenser increases, that of the bidirectional charger/discharger for the systems also increases. However, when charging/discharging mode-change occurs, the charger/discharger employing a bi-directional DC-DC converter with a commercialized analog controller has a complex circuit scheme, and a poor transient response. On the other hand, if a single digital controller is used for the bi-directional mode, the system performances can be improved by application of an advanced power-processing algorithm. In the paper, an environmental-friendly power storage systems including an Electric Double Layer Capacitor(EDLC) banks were developed with a bi-directional buck-boost converter and a digital signal processor (TMS320F28335). A simulation test-bed was realized and tested by MATLAB Simulink, and the hardware experiment was performed which shows that the dynamic response was improved such as the simulation results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.4
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• pp.714-725
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• 1997

This paper proposes an image compression method using the wavelet transform and bit-plane coding of wavelet coefficients. The hierarchical application of wavelet transform to an image produces one low resoluation(the subband with lowest frequency) image and several high frequency subbands. In the proposed method, the low resolution image is compressed by a lossless method at 8 bits per each coefficient. However, the high frequency subbands are decomposed into 8 bit planes. With an adptive block coding method, the decomposed bit planes are effectively compressed using localized edge information in each bit plane. In addition, the propsoed method can control bit rates by selectively eliminating lessimportant subbands of low significant bit planes. Experimental results show that the proposed scheme has better performance in the peak signal to noise ratio (PSNR) and compression rate than conventional image coding methods using the wavelet transform and vector quantization.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.6
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• pp.64-73
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• 1997

RPWM(Random Pulse Width Modulation) techniques have been attracting an interest as an excellent reduction method of acoustic noise on the inverter drive system. Using randomly changed switching fre-quency of the inverter, the power spectrum of the electromagnetic acoustic noise can be spread out into the wide-band area. The wide band noise is much more comfortable and less annoying than the narrow-band one. This paper describes an implementationof the triangular carrier frequency modultde RPWM inverter drive system The poweer soedtrum of the noise emittde from the induction motro was measured in the anechoic chamber. The analysis of the sources for the acoustic noise and the effects of the noise reduction are confirmed by the ceasured dpectra of the noise. Real-time RPWM along with the speed control was achieved by high speed DSP(Digital Signal Processor ) TmS320C31, By changing the center frequency and the bandwidth of the carrier, theis real-time RPWM scheme can be used as an efficient switching frequency band acoustic noise reduction method for the inverter system with variant load conditions.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.9
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• pp.2131-2139
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• 2014

In this paper, a binary-coded physical-layer network coding (PNC) is considered when high-order modulation techniques are used at source nodes in wireless communication environments. In the conventional PNC schemes, tight power control and phase compensation are required at a relay node. However, they may not be feasible in practical wireless communication environments. Thus, we do not assume the pre-equalization in this paper, and we only utilize the channel state information at receiver (CSIR). We propose a signal detection method for the binary-coded PNC with high-order modulation, such as QPSK and 16QAM, at the source nodes, while the conventional scheme only consider the BPSK at source nodes. We also analyze the bit-error performance of the proposed technique in both uncoded and coded cases.

• Journal of the Institute of Convergence Signal Processing
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• v.9 no.4
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• pp.304-312
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• 2008

Orthogonal codes like Walsh and Golay codes may have large correlation value when they are not synchronized, hence they are seldom used in asynchronous CDMA systems. Wysocki[1] showed that by multiplying the original Walsh-Hadamard matrix with an orthogonal transformation matrix the resultant matrix sustains orthogonality between row vectors and their cross-correlation can be reduced. Soberly and Wysocki[2] proposed similar scheme on Golay codes. This implies that using the proper orthogonal transformation cross-correlation of Walsh and Golay codes can be reduced, and the transformed codes can be used for user separation in the CDAM reverse link. In this paper we discuss cross-correlation related parameters which affect the performance of an asynchronous CDMA link, and we investigate the correlation properties of the transformed codes. When we designed orthogonal transformation matrices for Walsh and Golay codes, we minimized the maximum value of aperiodic cross-correlation of the codes ($ACC_{max}$) or the mean square value of the aperiodic cross-correlation($R_{cc}$) with preserving the orthogonality of the modified codes. We also evaluate the asynchronous CDMA system that uses the transformed Walsh and Golay codes.