• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.18 no.1
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• pp.47-58
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• 2018

The heterogeneous cellular network (HCN) is most significant as a key technology for future fifth generation (5G) wireless networks. The heterogeneous network considered consists of randomly macrocell base stations (MBSs) overlaid with femtocell base stations (BSs). The stochastic geometry has been shown to be a very powerful tool to model, analyze, and design networks with random topologies such as wireless ad hoc, sensor networks, and multi- tier cellular networks. The HCNs can be energy-efficiently designed by deploying various BSs belonging to different networks, which has drawn significant attention to one of the technologies for future 5G wireless networks. In this paper, we propose switching off/on systems enabling the BSs in the cellular networks to efficiently consume the power by introducing active/sleep modes, which is able to reduce the interference and power consumption in the MBSs and FBSs on an individual basis as well as improve the energy efficiency of the cellular networks. We formulate the minimization of the power onsumption for the MBSs and FBSs as well as an optimization problem to maximize the energy efficiency subject to throughput outage constraints, which can be solved the Karush Kuhn Tucker (KKT) conditions according to the femto tier BS density. We also formulate and compare the coverage probability and the energy efficiency in HCNs scenarios with and without coordinated multi-point (CoMP) to avoid coverage holes.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.11
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• pp.12-20
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• 2013

Even though extensive research results have been applied to wireless cellular systems to improve their capacity and coverage, severe performance degradation experienced in cell boundary areas still remains as a major limiting factor to prohibit further improvement of user equipment (UE) throughput. In the Long Term Evolution-Advanced (LTE-A) standard of the Third Generation Partnership Project (3GPP), Some advanced techniques have been introduced to overcome this "cell-edge problem", including coordinated multipoint transmission and reception (CoMP) and inter-cell interference coordination (ICIC). In this paper, we propose yet another strategy to improve the performance of low-tier UEs by using the concept of multiple beam direction patterns (BDPs). Such multiple BDPs can be implemented using multi-layer antenna arrays stacked vertically at base station (BS) sites to transmit signals in different main beam directions. In comparison to conventional three-sector antennas with a fixed beam pattern, the proposed methods makes signal transmission in a rotational fashion to significantly enhance the reception quality of UEs located near sector (or cell) edge areas, preventing the situation where certain UEs are marginally covered by the BS for the whole transmission time. Performance evaluation results show that the proposed scheme outperforms the conventional three-sector transmission by 171% in low 5% UEs in terms of the UE throughput.

• The KIPS Transactions:PartC
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• v.9C no.3
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• pp.385-398
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• 2002

To accommodate the increasing number of mobile terminals in the limited radio spectrum, wireless systems have been designed as micro/picocellular architectures for a higher capacity. This reduced coverage area of a cell has caused a higher rate of hand-off events, and the hand-off technology for efficient process becomes a necessity to provide a stable service. Population-based Bandwidth Reservation(PBR) Scheme is proposed to provide prioritized handling for hand-off calls by dynamically adjusting the amount of reserved bandwidth of a cell according to the amount of cellular traffic in its neighboring cells. We analyze the performance of the PBR scheme according to the changes of a fractional parameter, f, which is the ratio of request reservation to the total amount of bandwidth units required for hand-off calls that will occur for the next period. The vague of this parameter, f should be determined based on QoS(Quality of Service) requirement. To meet the requirement the value of Parameter(f) must be able to be adjusted dynamically according to the changing traffic conditions. The best value of f can be determined by a function of the average speed of mobile stations, average call duration, cell size, and so on. This paper considers the average call duration and the cell size according to the speed of mobile stations. Although some difference exists as per speed, in the range of 0.4 $\leq$ f $\leq$ 0.6, Blocking Probability, Dropping Probability and Utilization show the best values.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.427-427
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• 2016

Organic-inorganic hybrid perovskite have attracted significant attention as a new revolutionary light absorber for photovoltaic device due to its remarkable characteristics such as long charge diffusion lengths (100-1000nm), low recombination rate, and high extinction coefficient. Recently, power conversion efficiency of perovskite solar cell is above 20% that is approached to crystalline silicon solar cells. Planar heterojunction perovskite solar cells have simple device structure and can be fabricated low temperature process due to absence of mesoporous scaffold that should be annealed over 500 oC. However, in the planar structure, controlling perovskite film qualities such as crystallinity and coverage is important for high performances. Those controlling methods in one-step deposition have been reported such as adding additive, solvent-engineering, using anti-solvent, for pin-hole free perovskite layer to reduce shunting paths connecting between electron transport layer and hole transport layer. Here, we studied the effect of alkali metal halide to control the fabrication process of perovskite film. During the morphology determination step, alkali metal halides can affect film morphologies by intercalating with PbI2 layer and reducing $CH3NH3PbI3{\cdot}DMF$ intermediate phase resulting in needle shape morphology. As types of alkali metal ions, the diverse grain sizes of film were observed due to different crystallization rate depending on the size of alkali metal ions. The pin-hole free perovskite film was obtained with this method, and the resulting perovskite solar cells showed higher performance as > 10% of power conversion efficiency in large size perovskite solar cell as $5{\times}5cm$. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma optical emission spectrometry (ICP-OES) are analyzed to prove the mechanism of perovskite film formation with alkali metal halides.

• 한국생물공학회:학술대회논문집
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• 2003.04a
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• pp.302-305
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• 2003

It is difficult to obtain sufficient healthy skin for coverage of a wide area of skin wound. In the skin, an additional population of living epithelial cells is located in the outer root sheath (ORS) of hair $follicles.^{1),2)}$ ORS cells should be a good source of epithelium because they are easily obtainable and patients do not have to suffer from scar formation at donor sites. We modified ordinary primary culture technique for the purpose of solving such problem that epithelial cells have a low propagation and easy aging during culture periods. First of all, we improved primary cultivation methods. In the ordinary primary culture, average yield of human ORS cells was $2\;{\times}\;10^3$ cells/follicle by direct incubation with trypsin (0.1%)/EDTA (0.02%) solution for 15 min at $37^{\circ}C$ but we could obtain about $6.5\;{\times}\;10^3$ cells/follicle by two step enzyme digestion method with dispase (1.2 U/ml) and trypsin (0.1%)/EDTA (0.02%) solution. So we could achieve three times higher primary cultured ORS cell yield. Secondly, we could obtain total $2\;{\times}\;10^7$ cells in serum free medium and even more total $6\;{\times}\;10^7$ cells in modified E-medium with mitomycin C-treated feeder cells during 17 days. Using the cultured ORS cells, and we could make bioartificial skin equivalent in vitro and concluded that ORS cells were progenitor cells for skin epithelial cell.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.1
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• pp.26-33
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• 2013

Femto-cells are low power/cost, micro-base stations and are main components in heterogeneous networks. However, some of technical issues arise when femto-cells are initially installed. One approach to resolve the problems is to control the transmission (TX) power autonomously via SON(Self-Organized Network) scheme. By controlling the femto-cell TX power, the system throughput performance can be improved or the system overhead is highly reduced. Generally, the TX power for maximizing the system throughput and that for reduced system overhead may not be identical. Therefore, we propose a TX power control scheme by which we can improve the system throughput and reduce the system overhead, simultaneously. When we apply the proposed method, the simulation results show that the system overhead can be reduced by up to 41% compared to the performance of the method which maximizes throughput performance only, and the throughput performance can be improved by up to 63% compared to that of the method which only optimizes the coverage area.

• Bulletin of the Korean Chemical Society
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• v.32 no.2
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• pp.599-604
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• 2011

In typical proteomic analysis, trypsin digestion is one of the most time-consuming steps. Conventional proteomic sample preparation methods use an overnight trypsin digestion method. In this study, we compared high-pressure cycling technology (PCT) during enzyme digestion for proteome analysis to the conventional method. We examined the effect of PCT on enzyme activity at temperatures of 25, 37, and $50^{\circ}C$. Although a fast digestion (1 h) was used for the standard protein mixture analysis, the PCT-assisted method with urea showed better results for protein sequence coverage and the number of peptides identified compared with the conventional method. There was no significant difference between temperatures for PCT-assisted digestion; however, we selected PCT-assisted digestion with urea at $25^{\circ}C$ as an optimized method for fast enzyme digestion, based on peptide carbamylation at these conditions. The optimized method was used for stem cell proteome analysis. We identified 233, 264 and 137 proteins using the conventional method with urea at $37^{\circ}C$ for 16h, the PCT-assisted digestion with urea at $25^{\circ}C$ for 1 h, and the non-PCT-assisted digestion with urea at $25^{\circ}C$ for 1 h, respectively. A comparison of these results suggests that PCT enhanced the enzyme digestion by permitting better access to cleavage sites on the proteins.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3370-3392
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• 2017

Next Generation Beyond 4G/5G systems will rely on the deployment of small cells over conventional macrocells for achieving high spectral efficiency and improved coverage performance, especially for indoor and hotspot environments. In such heterogeneous networks, the expected performance gains can only be derived with the use of efficient interference coordination schemes, such as Fractional Frequency Reuse (FFR), which is very attractive for its simplicity and effectiveness. In this work, femtocells are deployed according to a spatial Poisson Point Process (PPP) over hexagonally shaped, 6-sector macro base stations (MeNBs) in an uncoordinated manner, operating in hybrid mode. A newly introduced intermediary region prevents cross-tier, cross-boundary interference and improves user equipment (UE) performance at the boundary of cell center and cell edge. With tools of stochastic geometry, an analytical framework for the signal-to-interference-plus-noise-ratio (SINR) distribution is developed to evaluate the performance of all UEs in different spatial locations, with consideration to both co-tier and cross-tier interference. Using the SINR distribution framework, average network throughput per tier is derived together with a newly proposed harmonic mean, which ensures fairness in resource allocation amongst all UEs. Finally, the FFR network parameters are optimized for maximizing average network throughput, and the harmonic mean using a fair resource assignment constraint. Numerical results verify the proposed analytical framework, and provide insights into design trade-offs between maximizing throughput and user fairness by appropriately adjusting the spatial partitioning thresholds, the spectrum allocation factor, and the femtocell density.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.10a
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• pp.357-360
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• 2008

Vital sign monitoring system using IEEE 502.IS.4 based wireless sensor network(WSN) is designed and developed on mobile environment and sensor node platform. WSN and CDMA are integrated to create a wide coverage to support various environments like inside and outside. We developed query processor to use selective any devices(ECG, Blood pressure and sugar module) and control of the self-organizing network of sensor nodes in a wireless sensor network. Vital sign from wireless medical any devices are analysed in cell phone first for real time signal analyses and the abnormal vital signs are sent and save to hospital server for detail signal processing. wireless signal traffic in wireless sensor network environment or data communication inside the cell phone is reduced.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37 no.1B
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• pp.31-38
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• 2012

In this paper, we propose a method to improve cell edge users' performance in HetNet (heterogeneous network) systems by cooperatively transmitting signals using remote radio heads (RRHs) located near coverage boundaries, referred to as edge RRHs. The proposed method locates the edge RRHs in specific locations of the cell boundary and provides an efficient operational strategy by adjusting the duty cycle of the edge RRHs and base stations. The effectiveness of the method is demonstrated by experimental performance based on the system model parameters of the CoMP (coordinated multi-point transmission and reception) scenario, which is discussed in LTE-Advanced (Long Term Evolution - Advanced) standard contributions. When compared with conventional methods, utilization of edge RRHs is especially advantageous for the performance improvement of lower percentile users in terms of average throughput and effectively improves the fairness among users.