• The Journal of Korea Institute of Information, Electronics, and Communication Technology
• /
• v.11 no.3
• /
• pp.259-269
• /
• 2018

Multipath TCP (MPTCP) can be expected to provide improved network performance because it transmits data through multiple paths. However, Bufferbloat, which unexpectedly occurs in the transmission path, degrades not only the performance of the corresponding path but also the performance of other paths, so that the performance is worse than that of a single TCP. In this paper, we propose the transmission status monitoring method at the sender's MPTCP level and also HoL packets retransmission algorithm in order to solve the Bufferbloat problem. The proposed algorithm enables Bufferbloat detection by the sender side independently, and it can resolve the HoL blocking problem by identifying the HoL packet in the proposed transmission status monitoring buffer and retransmitting it to the normal path. Simulation results based on NS-3 show that the proposed algorithm achieves the improved throughput performance up to 22.8% compared to the existing MPTCP, and the average number of queued packets in the sender and receiver's buffers is decreased to 44.3% and 9.2%, respectively.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.43 no.8 s.350
• /
• pp.84-90
• /
• 2006

With the widespread of the wireless Internet and wireless LAN, different wireless technologies such as 3G cellular networks and WLAN will cooperate to support more users and applications with higher data rate over wider areas. When a mobile node moves around in the hybrid networks, it needs to perform seamless vertical handoffs between different wireless networks to provide high performance data transmission. When an application with TCP connection in a mobile node performs a vertical handoff, TCP performance is degraded due to packet losses even though it maintains the previous TCP state information during handoff, because 3G and WLAN have different available bandwidth. In this paper, we propose a new congestion control algorithm for vertical handoff to improve the TCP performance by measuring the rough end-to-end available bandwidth and calculating the slow-start threshold. By ns-2 simulation, we show that the proposed algorithm enhances the TCP performance during vertical handoffs compared to the previous algorithms.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2009.11a
• /
• pp.55-55
• /
• 2009

Silicon Carbide (SiC) is a material with a wide bandgap (3.26eV), a high critical electric field (~2.3MV/cm), a and a high bulk electron mobility (${\sim}900cm^2/Vs$). These electronic properties allow high breakdown voltage, high frequency, and high temperature operation compared to Silicon devices. Although various SiC DMOSFET structures have been reported so far for optimizing performances. the effect of channel dimension on the switching performance of SiC DMOSFETs has not been extensively examined. In this paper, we report the effect of the interface states ($Q_s$) on the transient characteristics of SiC DMOSFETs. The key design parameters for SiC DMOSFETs have been optimized and a physics-based two-dimensional (2-D) mixed device and circuit simulator by Silvaco Inc. has been used to understand the relationship with the switching characteristics. To investigate transient characteristic of the device, mixed-mode simulation has been performed, where the solution of the basic transport equations for the 2-D device structures is directly embedded into the solution procedure for the circuit equations. The result is a low-loss transient characteristic at low $Q_s$. Based on the simulation results, the DMOSFETs exhibit the turn-on time of 10ns at short channel and 9ns at without the interface charges. By reducing $SiO_2/SiC$ interface charge, power losses and switching time also decreases, primarily due to the lowered channel mobilities. As high density interface states can result in increased carrier trapping, or recombination centers or scattering sites. Therefore, the quality of $SiO_2/SiC$ interfaces is important for both static and transient properties of SiC MOSFET devices.

• Journal of Korea Water Resources Association
• /
• v.53 no.3
• /
• pp.155-166
• /
• 2020

In this study, we applied the Radar-AWS Rainrates (RAR), weather radar-based quantitative precipitation estimations (QPEs), to the Yongdam study watershed in order to perform the flood runoff simulation and calculate the inflow of the dam during flood events using hydrologic model. Since the Yongdam study watershed is a representative area of the mountainous terrain in South Korea and has a relatively large number of monitoring stations (water level/flow) and data compared to other dam watershed, an accurate analysis of the time and space variability of radar rainfall in the mountainous dam watershed can be examined in the flood modeling. HEC-HMS, which is a relatively simple model for adopting spatially distributed rainfall, was applied to the hydrological simulations using HEC-GeoHMS and ModClark method with a total of eight independent flood events that occurred during the last five years (2014 to 2018). In addition, two NCL and Python script programs are developed to process the radar-based precipitation data for the use of hydrological modeling. The results demonstrate that the RAR QPEs shows rather underestimate trends in larger values for validation against gauged observations (R² 0.86), but is an adequate input to apply flood runoff simulation efficiently for a dam watershed, showing relatively good model performance (E_NS 0.86, R² 0.87, and PBIAS 7.49%) with less requirements for the calibration of transform and routing parameters than the spatially averaged model simulations in HEC-HMS.

• The Journal of The Korea Institute of Intelligent Transport Systems
• /
• v.17 no.4
• /
• pp.168-180
• /
• 2018

Due to the spread of mobile devices and the introduction of high-quality services, mobile traffic is expected to increase sharply and overload of cellular networks is expected. D2D communication is a way to reduce the load and evolve to 5th generation. Since D2D communication directly communicates between the terminals, it can reduce the overload of the cellular network and improve energy efficiency, data rate and network performance. This paper proposes a D2D handover scheme for D2D communication in cellular networks. The cellular network is a 3GPP EPS, and the proposed D2D handover method improves the existing EPS handover process considering compatibility between existing EPS and D2D communication. We also demonstrate the superiority of the proposed handover scheme using the network simulator ns-3. Simulation results show that the proposed handover scheme is superior to existing handover methods in terms of CUE variation, packet transmission delay time, and throughput.

• Journal of IKEEE
• /
• v.9 no.1 s.16
• /
• pp.1-6
• /
• 2005

This paper proposes a high performance multiplier using CMOS multiple-valued logic circuits. The multiplier based on the Modified Baugh-Wooley algorithm is designed with current-mode CMOS quaternary logic circuits. The multiplier is functionally partitioned into the following major sections: partial product generator block(binary-quaternary logic conversion block), current-mode quaternary logic full-adder block, and quaternary-binary logic conversion block. The proposed multiplier has 4.5ns of propagation delay and 6.1mW of power consumption. This multiplier can easily adapted to the binary system by the encoder and the decoder. This circuit is designed with 0.35um standard CMOS process at 3.3V supply voltage and 5uA unit current. The validity and effectiveness are verified through the HSPICE simulation.

• Proceedings of the KIEE Conference
• /
• 2006.10c
• /
• pp.482-484
• /
• 2006

This paper describes fast-hopping frequency synthesizers for multi-band OFDM(MB-OFDM) ultra-wide band(UWB) systems. Three different structures in generating 3 center frequencies(3432MHz, 3960MHz, 4488MHz) are designed and compared. The first structure generates 3 center frequencies using only one PLL operating at 4224MHz. The second uses three PLLs operating at corresponding center frequencies. The third employes two PLLs operating at 3960MHz and 528MHz. Simulation results using a 0.18um RF CMOS process parameters show that the third structure exhibit the best characteristics. The band switching time of the proposed synthesizer is less than 1.3ns and the spur is less than -36dBc. The synthesizer consumes 22mA from a 1.8V supply.

• Journal of the military operations research society of Korea
• /
• v.33 no.2
• /
• pp.115-127
• /
• 2007

The army developed the ATCIS(Army Tactical Command Information System) for the battlefield information system with share the command control information through the realtime. The using the public key and the encryption equipment in the ATCIS is enough to the confidentiality, integrity. but, it is vulnerable about the availability with the zero day attack. In this paper, we implement the worm propagation simulation on the ATCIS infrastructure through the modelling on the ATCIS operation environment. We propose the countermeasures based on the results from the simulation.

• Journal of the Korea Society for Simulation
• /
• v.12 no.3
• /
• pp.55-68
• /
• 2003

As mobile IP has been suggested only to support mobility of mobile station(MS) by which it dose nothing but guarantee MS's new connection to the network, it is for nothing in Quality of Service(QoS) after handoff of MS. QoS is very important factor in mobile IP network to provide multimedia applications and real-time services in mobile environment, and it is closely related to handoff delay Therefore as a main issue in mobile IP research area, handoff delay problem is actively studied to guarantee and promote QoS. In this paper, in order to resolve such a problem, we suggest Simple Network Management Network(SNMP) information-based routing that adds keyword management method to information-based routing in active network, and then propose QoS controlled handoff by SNMP information-based routing. After setting up routing convergence time, modeling of suggested method and existing handoff method is followed in order to evaluate the simulations that are carried out with NS-2. The result of simulation show the improvement of handoff delay, and consequently it turns off the QoS has been improved considerably.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.52 no.1
• /
• pp.40-47
• /
• 2015

We propose a method to provide a selective VoD service during live streaming sessions. In the proposed method, each peer joined the live streaming session receives video stream packets with P2P manner and stores the packets to provide a VoD service. To mitigate the overhead of each peer node to store the video stream packets, the proposed scheme categorizes peers into three different groups based on their link types. To increase data gathering speed and reduce the network load, we also proposes the P2P transmission scheme within the same AP network for the peers with Wi-Fi link. To evaluate the performance of the proposed method, we implement computer simulator using NS-3. Simulation results show that the proposed method reduces the overhead about 66% and increases the P2P data gathering speed about 50% compared to the conventional schemes.