• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1507-1514
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• 2015

Non-orthogonal multiple access (NOMA) is a promising candidate for 5G networks. NOMA achieves superior spectral efficiency than conventional orthogonal multiple access (OMA), as in NOMA multiple users uses the same time and frequency resources. Multiple-input-multiple-output (MIMO) is one another promising technique that can enhance system performance. In this paper we present a spectral and energy efficient multiple antenna based NOMA scheme, known as spatially modulated NOMA. In the proposed scheme the cell edge users are multiplexed in spatial domain, which means the information to cell edge users is conveyed using the transmit antenna indices. In NOMA the performance of cell edge users are deeply effected as it treats signals of others as noise. The proposed scheme achieves superior spectral efficiency than the conventional NOMA. The number of decoding steps involved in decoding NOMA signal reduces by one as cell edge user is multiplexed in spatial domain. The proposed scheme is more energy efficient as compare to conventional NOMA. All of the three gains high spectral, energy efficiency and one step reduction in decoding comes at cost of multiple transmit antennas at base station.

• Geophysics and Geophysical Exploration
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• v.10 no.1
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• pp.69-76
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• 2007

High-frequency electromagnetic (EM) wave propagation associated with borehole ground-penetrating radar (GPR) is a complicated phenomenon. To improve the understanding of the governing physical processes, we employ a finite-difference time-domain solution of Maxwell's equations in cylindrical coordinates. This approach allows us to model the full EM wavefield associated with crosshole GPR surveys. Furthermore, the use of cylindrical coordinates is computationally efficient, correctly emulates the three-dimensional geometrical spreading characteristics of the wavefield, and is an effective way to discretise explicitly small-diameter boreholes. Numerical experiments show that the existence of a water-filled borehole can give rise to a strong waveguide effect which affects the transmitted waveform, and that excitation of this waveguide effect depends on the diameter of the borehole and the length of the antenna.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.3A
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• pp.327-334
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• 2008

Conventional on-channel-repeaters (OCRs) have a crucial problem that the power of a re-transmitted signal is highly limited by a feedback signal due to antenna coupling. The power limitation problem in OCRs has been solved by incorporating a demodulation-type feedback canceller which eliminates unwanted feedback signals by estimating a feedback channel. In applying the demodulation-type feedback canceller to T-DMB repeaters, there is a troublesome problem of unfrequent known pilot symbols, resulting in poor convergence performance of channel estimation. To solve this problem and enhance the accuracy of estimation, we propose a partitioning method of the Phase Reference Symbol (PRS) transformed in time domain. Since filter coefficients are updated every one partitioned subgroup, the number of updates is increased by the number of partitioned subgroups and thus the convergence speed is enhanced. The improved performance of feedback-channel estimation is directly connected with the feedback-cancellation performance. Simulation result shows that the feedback canceller incorporating the proposed partitioning method has a good performance in terms of residual feedback power.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.12
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• pp.1106-1114
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• 2012

In order to provide high data rate and real time services under maritime environment, link-level performance of ship ad-hoc network (SANET) based on 3GPP LTE and IEEE 802.11p (WAVE) specifications are investigated and discussed in this paper. The measured maritime channel, whose delay spread is longer than the length of guard interval (GI) of both 3GPP LTE and IEEE 802.11p specifications, is adopted for the link-level simulations. For the purpose of eliminating inter-symbol interference (ISI) due to insufficient GI length, double antenna pattern (DAP) scheme and advanced time-domain decision-feedback equalizer (DFE) are proposed for LTE and WAVE systems, respectively. The proposed DFE removes the ISI in a same manner as the residual inter-symbol interference cancellation (RISIC) algorithm, but the inter-carrier interference (ICI) is reduced via cyclicity removal instead of cyclicity restoration used in the RISIC algorithm. Compared with existing schemes, our proposed DFE is a robust technique to overcome the severe ISI channel which has a comparatively large delay spread. Based on simulation results, not only comparisons between systems are discussed, but also some reformative suggestions are given.

• Journal of Sensor Science and Technology
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• v.27 no.5
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• pp.317-327
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• 2018

Terahertz (THz) time-domain spectroscopy(TDS), imaging techniques, and related systems have become mature technologies, widely used in many universities and research laboratories. However, the development of creative technologies still requires improved THz application systems. A few key points are discussed, including the innovative advances of mode-locking energy-emitting semiconductor lasers and better photoconductive semiconductor quantum structures. To realize a compact, low cost, and high performance THz system, it is essential that THz spectroscopy and imaging technologies are better characterized by semiconductor and nano-devices, both static and time-resolved. We introduce the THz spectroscopy and imaging systems, the OSCAT(Optical Sampling by laser CAvity Tuning) system and the ASOPS(ASynchronous Optical Sampling) system, are constructed by our research team. We report on the THz images obtained from their use.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.28 no.11
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• pp.902-915
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• 2017

In recent years, mobile devices have become increasingly multi-functional and high performance, resulting in a dramatical increase in processing speed. On the other hand, the size of device is reduced, circuits inside the device are more easily exposed to electromagnetic interference radiated from antenna or adjacent circuits, degrading the system performance. To prevent this, it is necessary to design the device considering the electromagnetic characteristics with EM simulation at the design stage of product. However, the EM simulation takes a long analysis time and require high-level system resources for fast analysis. In this paper, an equivalent circuit modeling method for a round wire is proposed using a PEEC method and the electromagnetic coupling from a dipole antenna to a transmission line is analyzed in frequency domain. And compared with the result of electromagnetic simulator. As a result, PEEC method shows good agreement with those of electromagnetic simulation, in a much more short time.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.8
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• pp.884-890
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• 2003

In order to reduce the specific absorption rate(SAR) in a human head exposed to electromagnetic fields radiated by a cellular phone, we have analyzed an electromagnetic wave absorber attached to the handset. A manufactured electromagnetic wave absorber was composed of Mn - Zn, which had complex relative permittivity of 7.30-j0.05 and permeability of 2.20-i1.55. The SAR value from the electromagnetic wave absorber attachment was calculated by using the nonuniform finite difference time domain(FDTD) algorithm and measured by phantom model at 835 MHz. The SAR reduction due to the electromagnetic wave absorber are about 18 % at 835 MHz. The V.S.W.R and radiation pattern of antenna are good agreement with the normal antenna. The gain reduction due to the electromagnetic wave absorber are only 0.3 dB at 835 MHz. But the sensitivity of cellular phone generally improves about 1 dB.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.10 no.2
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• pp.277-290
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• 1999

A simulation using the finite-difference time-domain method to analyze the electromagnetic interactions between a cellular phone and the human body was conducted, and a synthesis of a bone-equivalent material to make a human head phantom was performed. A test model of the cellular phone was fabricated to measure its reflection coefficient and radiation pattern in the free space. Various effects of the human body on the characteristics of the phone, such as input impedance, reflection coefficient, radiation pattern, and radiation efficiency are analyzed as the distance between the head and the phone antenna varies. When the phone was operated close to the head, the resonant frequency of the antenna decreased by up to 12%. With the output power of 0.6W, as long as the distance was larger than 30mm, the 1-g averaged peak SAR was below the ANSI/IEEE safety guideline, 1.6 W/kg. To synthesize the bone-equivalent material, an epoxy with hardener and a graphite powder were used as basis ingredients, and a small amount of a conducting epoxy was added to control the conductivity of the material. A material having a relative permittivity of 18.04 and a conductivity of 0.347, which are close to those of the bone at 850 MHz, was synthesized.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.11C
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• pp.948-956
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• 2010

Griffiths and Jim has proposed a beamforming structure called GSC algorithm, in which antenna elements are grouped into main-channel and sub-channel, and sidelobe is reduced by applying adaptive LMS algorithm. This paper proposes WLMS-GSC algorithm where the Haar and Daubechies wavelet filters are used to process array antenna output, instead of using subtractor filter. We analyze characteristics of the proposed WLMS-GSC algorithm. The WLMS-GSC has characteristic of reducing the computational requirement one-half compared to the LMS-GSC algorithm. In addition, we obtain MSE characteristics and adaptive beampattern of WLMS-GSC algorithm, and compared with the performance of LMS-GSC algorithm. The simulation results show that the WLMS-GSC algorithm proposed in this paper gives better or almost the same performance, compared to the LMS-GSC algorithm. In addition, the newly proposed structure has advantage of low computational requirements.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.46 no.4
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• pp.1-7
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• 2009

In this paper, the author presents the MIMO(Multi-Input Multi-Output) receiver algorithm with the capability of inter-cell or inter-sector interference cancellation over multi-antenna OFDM(Orthogonal Frequency Division Multiplexing) systems. As contrast with the previous research dealing with the filtering scheme at the time domain, the proposed algorithm is presented as the pre-filtering scheme which can be applicable to the frequency domain. Note that the proposed one can be implemented only by pilot symbols which are used in the channel estimation. In addition, it is analytically confirmed that the proposed scheme can be applied for either MIMO( C-SM(Collaborative-Spatial Multiplexing)) interference or SIMO(Single-Input Multi-Out) interference. The proposed receiver algorithm is verified by simulations over UL-PUSC SR off in IEEE 802.16e standard. From simulation results, it is confirmed that the proposed one can be applicable regardless of the kind of interference. Furthermore, it is verified that the performance is guaranteed even under Ole severe effect of interference and the improvement of system throughput is guaranteed.