Gijeong Kim

Spectral characteristics of steady quiet-time EMIC waves observed at geosynchronous orbit

We have studied the spectral properties of quiet-time electromagnetic ion cyclotron (EMIC) waves following a steady quiet condition, which is defined with Kp values 1 during 12h, using GOES 10, 11, and 12 magnetometer data for solar minimum years 2007-2008. We identified 6584 steady quiet-time EMIC wave samples using a semiautomated procedure. Approximately 82% of the samples were observed in the morning-to-early afternoon sector (0700-1500 magnetic local time) with a maximum occurrence near noon, and their peak frequencies were mostly in the He band. We found that the occurrence rate of steady quiet-time EMIC waves is higher than that of EMIC waves for all or quiet geomagnetic conditions (Dst > 0nT or AE < 100nT) reported in previous studies by a factor of 2 or more. The frequency ratio f(peak) (samples peak frequency)/ fH+ (the local proton gyrofrequency) of the He-band waves (approximate to 0.11-0.16) under steady quiet conditions is lower than that (approximate to 0.14-0.24) in previous studies. These results may be due to the fact that the plasmasphere expanded more frequently to the geosynchronous region under extremely quiet geomagnetic conditions in 2007-2008 than the periods selected in previous studies. The amplitude and frequency of He-band EMIC waves for nonlinear wave growth are examined as changing cold plasma density at geosynchronous orbit. We confirm that the spectral properties of observed EMIC waves are in good agreement with the nonlinear theory.

Occurrence of EMIC waves and plasmaspheric plasmas derived from THEMIS observations in the outer magnetosphere: Revisit

We have statistically studied the relationship between electromagnetic ion cyclotron (EMIC) waves and cold plasmaspheric plasma (Nsp) in the L range of 6-12 using the Time History of Events and Macroscale Interactions during Substorms (THEMIS) data for 2008-2011. The important observational results are as follows: (1) Under quiet geomagnetic conditions (Kp≤ 1), the maximum occurrence rate of the hydrogen (H) band EMIC waves appears in the early morning sector (0600-0900 MLT) at the outermost region (L = 10-12). (2) Under moderate and disturbed conditions (Kp≥ 2), the H-band occurrence rate is higher in the morning-to-early afternoon sector for L> 10. (3) The high occurrence region of helium (He) band waves for Kp≤ 1 varies from L = 7 to 12 in radial distances along the local time (i.e., at L∼ 7 near noon and at L = 8-12 near late afternoon). (4) The He-band waves for Kp≥ 2 are mainly localized between 1200 and 1800 MLT with a peak around 1500-1600 MLT at L = 8-10. (5) Nsp is much higher for the He-band intervals than for the H-band intervals by a factor of 10 or more. The He-band high occurrence appears at a steep Nsp gradient region. (6) The morning-afternoon asymmetry of the normalized frequency seen both in H-band and He-band is similar to the asymmetric distribution of Nsp along the local time. These observations indicate that the cold plasma density plays a significant role in determining the spectral properties of EMIC waves. We discuss whether a morning-afternoon asymmetry of the EMIC wave properties can be explained by the spatial distribution of cold plasmaspheric plasma.

Multi-RAT mobile node architecture for efficient handover using software defined network

Owing to an increase in mobile devices and the advent of the Internet of Things (IoT), mobile traffic has increased exponentially. Consequently, a wide range of research on handover has been conducted to provide mobile device users with stable network quality. Most research on handover uses a network-dependent method that establishes a new protocol or a method that can refine handover time; however, these methods are difficult to apply because they necessitate network-level changes or they are unable to reduce the fundamental delay that occurs in handover, respectively. This paper suggests a simple and powerful handover scheme based on Multi-Radio Access Technology (Multi-RAT) as well as a method to efficiently use Multi-RAT when handover is not required. This method uses a Multi-RAT terminal equipped with a motion sensor. If a terminal motion exists, the active link and standby link of the mobile node enhance handover performance through data transfer and sensing, respectively. If the node is stationary, its transfer throughput is increased through Carrier Aggregation (CA). In this study, we build a testbed to enable handover based on the aforementioned mechanism and assess the performance of the proposed method through an experiment.

An SDN based fully distributed NAT traversal scheme for IoT global connectivity

Existing NAT solves to IP address exhaustion problem binding private IP address and public IP address, and NAT traversal such as hole punching scheme enables to communicate End-to-End devices located in different private networks. However, such technologies are centralized the workload at NAT gateway and increase transmission delay caused by packet modification per packet. In this paper, we propose an SDN based fully distributed NAT traversal scheme, which can distribute the workload of NAT processing to devices and reduce transmission delay by packet switching instead of packet modification. Furthermore, we describe SDN based IoT connectivity management architecture for supporting IoT global connectivity and enhanced real-time and security.

Seamless QoE Support for Mobile Cloud Services Using IEEE802.21 MIH and the GENI Future Internet Framework

Mobile cloud service is the most important traffic generator today, and high data rate services in this area are increasing. The Virtual Desktop Infrastructure (VDI) is a circuit-like service that is widely deployed owing to its security merits and the resource constraints of mobile devices. However, VDI requires a high and guaranteed virtually constant wireless data rate. Thus, we focus on the problems that have to be resolved in order for IEEE802.21 Media Independent Handover (MIH) to support a guaranteed wireless data rate and also enable it to offer optimized and maximized data rate support for mobile cloud services. We also consider a virtual machine (VM) migration scheme that is tightly coupled to mobile networks and can minimize the users service delay and reduce the bandwidth requirements of the wired network. We then present a consistent control framework by extending the Global Environment for Network Innovations (GENI) control framework to provide a single integrated control framework for cloud computing and Future Internet compatibility. Finally, we develop an experimental testbed using a mobile cloud computing environment and evaluate the performance of the proposed scheme. We show that the proposed method can enhance the Quality of Experience (QoE) of mobile cloud computing services with increased data rate support and a single consistent control framework that is compatible with the GENI-based Future Internet architecture. The results of evaluations conducted indicate that our proposed method provides 24%–41% better data rate compared to conventional methods.

Consensus-based information synchronization for content-centric networks

In this paper, we studied for the synchronization of CCNx that is one of the Content Centric Network (CCN) projects by using Hazelcast. CCN is considered as a way to solve the explosive growth of Internet traffic. Hazelcast is an open source In-Memory Data Grid. Hazelcast, that one of the consensus-based in-memory data grid, has the strength to speed, high-availability, and secure. To effectively use the CCN, we developed programs that actual synchronize information. The program can synchronize information by CCNx with Hazelcast. We predict, in a vast network, that will be faster than original CCNx. In this result, we can use efficiently and high-availably CCNx.

A proxy server by-passing scheme for the chained HTTP proxy networks

The use of the proxy server is being extended steadily in order to provide various web services and improve the quality of web service. However, passing many proxy servers may degrade the quality of web service, because of increasing HTTP message processing time. In this paper, we propose a scheme that bypasses many proxy servers constituting proxy chain. Furthermore, we perform network simulation and confirm that the proposed scheme offers better performance in terms of page loading time, the number of messages, the amount of messages generated in the network than the conventional HTTP message forwarding scheme in a proxy chain.