• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• 제27권3호
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• pp.261-268
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• 2016

In this paper, dual-polarized monopulse cassegrain antenna for W-band millimeter-wave seeker was proposed and the performances were verified by the measured results of the fabricated antenna. Dual-polarized monopulse Cassegrain antenna consists of main/subreflector, dual-polarized feed horn and monopulse comparator. The proposed feed horn has $2{\times}2$ array square waveguide feeding structure to make monopulse signals and it was designed using 90 degree rotational symmetric structure to receive dual-polarized signals. At the sum and difference channel, the measured vertical and horizontal polarization radiation pattern were similar. Measurement gains are 35.1 dBi for v-pol. and 35.6 dBi for h-pol. at the center frequency with 0.5dBi difference between each polarization and the side lobe level is below -21.6 dB.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제34권9C호
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• pp.887-895
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• 2009

This paper proposes a cooperative power allocation with the use of partial channel information (e.g., the average signal-to-noise ratio (SNR) and transmit correlation) in multi-cell dual-hop multi-input single-output (MISO) relay systems. In a dual-hop MISO relay channel, it is desirable to allocate the transmit power between dual-hop links to maximize the end-to-end capacity. We consider the maximization of the end-to-end capacity of a dual-hop MISO relay channel under sum-power constraint. The proposed scheme adaptively allocates the transmit power considering the average channel gain of the target relay and the transmit correlation of the desired and inter-relay interference channel from adjacent relays. It is shown by means of upper-bound analysis that the end-to-end capacity can be maximized by making the angle difference of the principal eigenvectors of the desired and inter-relay interference channel orthogonal in highly-correlated channel environments. Finally, the performance of the proposed scheme is verified by computer simulation.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제10권3호
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• pp.479-485
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• 2006

The double gate(DG) MOSFET is a promising candidate to further extend the CMOS scaling and provide better control of short channel effect(SCE). DGMOSFETs, having ultra thin undoped Si channel for SCEs control, ale being validated for sub-20nm scaling. A novel analytical transport model for the subthreshold mode of DGMOSFETs is proposed in this paper. The model enables analysis of short channel effect such as the subthreshold swing(SS), the threshold voltage roil-off$({\Delta}V_{th})$ and the drain induced barrier lowering(DIBL). The proposed model includes the effects of thermionic emission and quantum tunneling of carriers through the source-drain barrier. An approximative solution of the 2D Poisson equation is used for the distribution of electric potential, and Wentzel-Kramers-Brillouin approximation is used for the tunneling probability. The new model is used to investigate the subthreshold characteristics of a double gate MOSFET having the gate length in the nanometer range $(5-20{\sim}nm)$ with ultra thin gate oxide and channel thickness. The model is verified by comparing the subthreshold swing and the threshold voltage roll-off with 2D numerical simulations. The proposed model is used to design contours for gate length, channel thickness, and gate oxide thickness.

• Korean Journal of Optics and Photonics
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• 제34권1호
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• pp.1-12
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• 2023

In this study, we propose a hybrid phase-control algorithm for multi-channel coherent beam combining (CBC) system by combining the covariant matrix adaption evolution strategy (CMA-ES) and stochastic parallel gradient descent (SPGD) algorithms and analyze its operational performance. The proposed hybrid CMA-ES/SPGD algorithm is a sequential process which initially runs the CMA-ES algorithm until the combined final output intensity reaches a preset interim value, and then switches to running the SPGD algorithm to the end of the whole process. For ideal 7-channel and 19-channel all-fiber-based CBC systems, we have found that the mean convergence time can be reduced by about 10% in comparison with the case when the SPGD algorithm is implemented alone. Furthermore, we analyzed a more realistic situation in which some additional phase noise was introduced in the same CBC system. As a result, it is shown that the proposed algorithm reduces the mean convergence time by about 17% for a 7-channel CBC system and 16-27% for a 19-channel system compared to the existing SPGD alone algorithm. We expect that for implementing a CBC system in a real outdoor environment where phase noise cannot be ignored, the hybrid CMA-ES/SPGD algorithm proposed in this study will be exploited very usefully.

• The Journal of Korean Institute of Communications and Information Sciences
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• 제38A권5호
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• pp.401-408
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• 2013

Dual-layer differential codebook using 8-PSK (phase shift keying) constellation as its codeword elements, is proposed for Long term evolution (LTE) and/or LTE-Advanced systems. Due to the temporal correlation of the adjacent channel matrices, the consecutive precoding matrices are likely to be similar. This approach quantize only the differential information of the channel instead of the whole channel subspace, which virtually increase the codebook size to realize more accurate quantization of the channel. Especially, the proposed codebook has the same properties of LTE release-8 codebook that is, constant modulus, complexity reduction, and nested property. The mobile station can be designed by using less expensive non-linear amplifier utilizing constant modulus property. Computer simulations show that the capacity of the proposed dual-layer codebook performs almost 1.2dB better than those of any other non-differential codebooks with the same amount of feedback information.

• Journal of the Institute of Electronics Engineers of Korea SD
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• 제38권9호
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• pp.652-662
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• 2001

A WDM/SCM multiple access protocol suitable for optical double star networks is proposed. A node-grouping scheme is employed in the protocol, which is accomplished by connecting some nodes through passive star sub-hubs forming a group. The resulting multiple groups in a network are then connected through a central passive star hub resulting in a passive double star network. Each group is pre-assigned a WDM channel as its home channel, and SCM channels are used to identify the packet reception at each node. [n the proposed protocol, the average packet delay is remarkably reduced since the frame consists of the number of groups rather than the number of network nodes. Furthermore, additional reduction of the average packet delay is achieved by limiting the propagation paths of control packets to the roundtrip between source nodes and sub-hub using a double star network. It is shown in the performance evaluations using analytic and simulation model that the proposed protocol has the advantages of the higher channel utilization and excellent network throughput and average packet delay characteristic.

• Journal of the Korean Institute of Telematics and Electronics S
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• 제36S권9호
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• pp.9-17
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• 1999

In this paper, we present a mathematical modeling and perform a performance analysis of double-dwell serial search algorithm, which has a search window concept, for pilot channel in DS-CDMA(Direct Sequence Code Division Multiple Access). We derive a code detection function, a false alarm function, a code miss function, and a mean code acquisition time for the performance analysis. We calculate the mean code acquisition time of the mathematical model in IS-95 forward link and compare it with that of the conventional search methods. The performance of the code acquisition system is also evaluated to investigate the effect of dwell times and search window size. The JTC channel model, which is a PCS channel model in North America, is used for the analysis. The numerical result shows that the mean code acquisition time of the double-dwell serial search algorithm with a search window is reduced by about 17%~25% than those of the conventional ones.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제18권12호
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• pp.2939-2945
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• 2014

This paper has analyzed the change of threshold voltage for oxide structure of symmetric and asymmetric double gate(DG) MOSFET. The asymmetric DGMOSFET can be fabricated with different top and bottom gate oxide thickness, while the symmetric DGMOSFET has the same top and bottom gate oxide thickness. Therefore optimum threshold voltage is considered for top and bottom gate oxide thickness of asymmetric DGMOSFET, compared with the threshold voltage of symmetric DGMOSFET. To obtain the threshold voltage, the analytical potential distribution is derived from Possion's equation, and Gaussian distribution function is used as doping profile. We investigate for bottom gate voltage, channel length and thickness, and doping concentration how top and bottom gate oxide thickness influences on threshold voltage using this threshold voltage model. As a result, threshold voltage is greatly changed for oxide thickness, and we know the changing trend greatly differs with bottom gate voltage, channel length and thickness, and doping concentration.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제16권5호
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• pp.982-988
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• 2012

This paper has presented the relation of scaling theory and threshold voltage of double gate(DG) MOSFET. In the case of conventional MOSFET, current and switching frequency have been analyzed based on scaling theory. To observe the possibility of application of scaling theory for threshold voltage of DGMOSFET, the change of threshold voltage has been observed and analyzed according to scaling theory. The analytical potential distribution of Poisson equation has been used, and this model has been already verified. To solve Poisson equation, charge distribution such as Gaussian function has been used. As a result, it has been observed that threshold voltage is grealty changed according to scaling factor and change rate of threshold voltages is traced for scaling of doping concentration in channel. This paper has explained for the best modified scaling theory reflected the influence of two gates as using weighting factor when scaling theory has been applied for channel length and channel thickness.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제19권11호
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• pp.2643-2648
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• 2015

This paper analyzes the phenomenon of drain induced barrier lowering(DIBL) for doping profiles in channel of asymmetric double gate(DG) MOSFET. The DIBL, the important short channel effect, is described as lowering of source barrier height by drain voltage. The analytical potential distribution is derived from Poisson's equation to analyze the DIBL, and the DIBL is observed according to the change of doping profile to influence on potential distribution. As a results, the DIBL is significantly influenced by projected range and standard projected deviation, the variables of channel doping profiles. The change of DIBL shows greatly in the range of high doping concentration such as $10^{18}/cm^3$. The DIBL increases with decrease of channel length and increase of channel thickness, and with increase of bottom gate voltage and top/bottom gate oxide film thickness.