• Journal of the Institute of Electronics Engineers of Korea TC
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• 제44권5호
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• pp.7-15
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• 2007

In wireless communication networks, single-radio single-channel architecture degrades throughput and end-to-end delay due to half-duplex transmission of wireless node and route intra interference. Also, In contention-based MAC (Medium Access Control) architecture, channel contention reduces throughput and packet collision enlarges end-to-end delay. In this paper, we use multi-radio multi-channel architecture which will make wireless node to operate in full duplex mode, and exclude route intra interference. Based on this architecture, we propose a new link metric, ccf which reflects the characteristics of a contention-based wireless link, and propose a routing path metric MCCR considering channel switching delay and route intra interference. MCCR is compared with MCR by simulation, the performance of a route established by MCCR outperforms the performance of a route by MCR in terms of throughput and end-to-end delay.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권1호
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• pp.146-170
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• 2017

Joint channel assignment and routing is a well-known problem in multi-radio wireless mesh networks for which optimal configurations is required to optimize the overall throughput and fairness. However, other objectives need to be considered in order to provide a high quality service to network users when it deployed with high traffic dynamic. In this paper, we propose a re-configuration optimization model that optimizes the network throughput in addition to reducing the disruption to the mesh clients' traffic due to the re-configuration process. In this multi-objective optimization model, four objective functions are proposed to be minimized namely maximum link-channel utilization, network average contention, channel re-assignment cost, and re-routing cost. The latter two objectives focus on reducing the re-configuration overhead. This is to reduce the amount of disrupted traffic due to the channel switching and path re-routing resulted from applying the new configuration. In order to adapt to traffic dynamics in the network which might be caused by many factors i.e. users' mobility, a centralized heuristic re-configuration algorithm called State-Aware Joint Routing and Channel Assignment (SA-JRCA) is proposed in this research based on our re-configuration model. The proposed algorithm re-assigns channels to radios and re-configures flows' routes with aim of achieving a tradeoff between maximizing the network throughput and minimizing the re-configuration overhead. The ns-2 simulator is used as simulation tool and various metrics are evaluated. These metrics include channel-link utilization, channel re-assignment cost, re-routing cost, throughput, and delay. Simulation results show the good performance of SA-JRCA in term of packet delivery ratio, aggregated throughput and re-configuration overhead. It also shows higher stability to the traffic variation in comparison with other compared algorithms which suffer from performance degradation when high traffic dynamics is applied.

• Journal of the Korean Institute of Educational Facilities
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• 제19권2호
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• pp.41-50
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• 2012

This study aims to analyze chlidcare philosophy and the architectural characteristics of communal childcare cooperative nurseries(parent cooperative childcare facilities), and also to examine their mutual relationship. The communal childcare cooperative is an ideal childcare method to break away from employee-supported childcare system and cooperatively solve childcare problems in the family community system. The child-rearing philosophy of the communal childcare can bring spontaneous and creative development amidst 'daily life' and 'play' by switching from knowledge and skill-oriented education and puts an emphasis on physical environments in child's growth. The features of architecture related the childcare philosophy derived from this study are as follows: the way of participation and self-help, the extension of spatial scope and focuses on outside space, architecture of house-like residence rather than educational facility, spatial 'overlapping' focusing on transitional space and multi-purpose space rather than spatial partitions, the pursuit of creativity through play is realized in the incompletion and unspecification of space evolving over time.

• Proceedings of the IEEK Conference
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• 대한전자공학회 2005년도 추계종합학술대회
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• pp.147-150
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• 2005

Low actuation voltage and no contact stiction are the important factors to apply MEMS RF switches to mobile devices. Conventional electrostatic MEMS RF switches require several tens of voltages for actuation. In this paper we propose PAS MEMS RF switch which adopt PZT actuators and seesaw cantilevers to meet the above requirements. The fundamental structures of PAS MEMS switch were designed, optimized, and fabricated. Through the developed processes PAS SPDT MEMS RF switches were successfully fabricated on 4" wafers and they showed good electrical properties. The driving voltage was less than 5 volts. And the insertion loss was -0.5dB and the isolation was 35dB at 5GHz. The switching speed was about 5kHz. So these MEMS RF switches can be applicable to mobile communication devices or wireless multi-media devices at lower than 6GHz.

• Journal of Power Electronics
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• 제17권2호
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• pp.551-560
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• 2017

The present study proposes an angle droop controller for converter interfaced (dispatchable) distributed generation (DG) resources in the islanded mode of operation. Due to the necessity of proper real and reactive power sharing between different types of resources in microgrids and the ability of systems to respond properly to abnormal conditions (sudden load changes, load uncertainty, load current disturbances, transient conditions, etc.), it is necessary to produce appropriate references for all of the mentioned above conditions. The proposed control strategy utilizes a current controller in addition to an angle droop controller in the discrete time domain to generate appropriate responses under transient conditions. Furthermore, to reduce the harmonics caused by switching at converters' output, a LCL filter is used. In addition, a comparison is done on the effects that LCL filters and L filters have on the performance of DG units. The performance of the proposed control strategy is demonstrated for multi islanded grids with various types of loads and conditions through simulation studies in the DigSilent Power Factory software environment.

• Journal of Power Electronics
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• 제15권5호
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• pp.1380-1391
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• 2015

This paper provides a loss analysis and comparison of high power semiconductor devices in 5MW Permanent Magnet Synchronous Generator (PMSG) Medium Voltage (MV) Wind Turbine Systems (WTSs). High power semiconductor devices of the press-pack type IGCT, module type IGBT, press-pack type IGBT, and press-pack type IEGT of both 4.5kV and 6.5kV are considered in this paper. Benchmarking is performed based on the back-to-back type 3-level Neutral Point Clamped Voltage Source Converters (3L-NPC VSCs) supplied from a grid voltage of 4160V. The feasible number of semiconductor devices in parallel is designed through a loss analysis considering both the conduction and switching losses under the operating conditions of 5MW PMSG wind turbines, particularly for application in offshore wind farms. This paper investigates the loss analysis and thermal performance of 5MW 3L-NPC wind power inverters under the operating conditions of various power factors. The loss analysis and thermal analysis are confirmed through PLECS Blockset simulations with Matlab Simulink. The comparison results show that the press-pack type IGCT has the highest efficiency including the snubber loss factor.

• Journal of Power Electronics
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• 제15권5호
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• pp.1329-1337
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• 2015

By placing distributed generation power sources beside a big nonlinear load, these sources can be used as a power quality enhancer, while injecting some active power to the network. In this paper, a new scheme to use the distributed generation power source in both operation modes is presented. In this scheme, a fuzzy controller is added to adjust the optimal set point of inverter between compensating mode and maximum active power injection mode, which works based on the harmonic content of the nonlinear load. As the high order current harmonics can be easily rejected using passive filters, the DG is used to compensate the low order harmonics of the load current. Multilevel transformerless cascade inverters are preferred in such utilization, as they have more flexibility in current/voltage waveform. The proposed scheme is simulated in MATLAB/SIMULINK to evaluate the circuit performance. Then, a 1kw single phase prototype of the circuit is used for experimental evaluation of the paper. Both simulative and experimental results prove that such a circuit can inject a well-controlled current with desired harmonics and THD, while having a smaller switching frequency and better efficiency, related to previous 3-phase inverter schemes in the literature.

• ETRI Journal
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• 제36권2호
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• pp.214-223
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• 2014

A fully-integrated penta-band reconfigurable power amplifier (PA) is developed for handset Tx applications. The output structure of the proposed PA is composed of the fixed output matching network, power and frequency reconfigurable networks, and post-PA distribution switches. In this work, a new reconfiguration technique is proposed for a specific band requiring power and frequency reconfiguration simultaneously. The design parameters for the proposed reconfiguration are newly derived and applied to the PA. To reduce the module size, the switches of reconfigurable output networks and post-PA switches are integrated into a single IC using a $0.18{\mu}m$ silicon-on-insulator CMOS process, and a compact size of $5mm{\times}5mm$ is thus achieved. The fabricated W-CDMA PA module shows adjacent channel leakage ratios better than -39 dBc up to the rated linear power and power-added efficiencies of higher than around 38% at the maximum linear output power over all the bands. Efficiency degradation is limited to 2.5% to 3% compared to the single-band reference PA.

• Journal of KIISE:Computing Practices and Letters
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• 제16권12호
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• pp.1249-1253
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• 2010

As personal computers have been recently improved in performance, the multi tasking of running several applications at the same time has been generalized. Since only one task space is provided for performing such tasks on Windows operating system, a number of computer users feel inconvenient. In this paper, we propose a 3D Virtual Desktop System which can show a process of switching task spaces in 3D motion using DirectX. The proposed system can provide a computer user with more task spaces and the intuitive UI(User Interlace) such as Compiz of Linux.

• Journal of Power Electronics
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• 제11권2호
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• pp.132-139
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• 2011

The selective harmonic elimination pulse width modulation (SHEPWM) switching strategy has been applied to multilevel inverters to remove low harmonics. Naturally, the related equations do not have feasible solutions for some operating points associated with the modulation index (M). However, with these infeasible points, minimizing instead of eliminating harmonics is performed. Thus, harmful harmonics such as the $5^{th}$ harmonic still remains in the output waveform. Therefore, it is proposed in this paper to ignore solving the equation associated with the highest order harmonics. A reduction in the eliminated harmonics results in an increase in the degrees of freedom. As a result, the lower order harmonics are eliminated in more operating points. A 9-level inverter is chosen as a case study. The genetic algorithm (GA) for optimization purposes is used. Simulation results verify the proposed method.