Taekook Kim

Hybrid storage-based caching strategy for content delivery network services

This study proposes a novel caching scheme for content delivery network services. In general, video content users often watch the first part of video clips and then switch to other content. Therefore, a caching scheme is proposed, in which the first part of the frequently referenced content is stored on a solid state drive (SSD) while the remaining video content is stored on a hard disk drive (HDD),. The proposed hybrid (SSD/HDD) caching scheme offers several benefits, such as an improved average data output capacity due to the high average data rate and average hit capacity of the SSD. That is, performance can be significantly improved at a low extra cost with the cache server of a content delivery network (CDN).

View pattern-based adaptive streaming strategy for mobile content delivery services

This study contributes towards a new streaming strategy for mobile multimedia content such as audio/video delivered to mobile access devices. In general, users often watch the first part of a video clip and then switch to some other content. In this regard, this paper presents a view pattern-based adaptive streaming (abbreviated VPAS) strategy for mobile content delivery services that considers mobile network environments characterized by limited available bandwidth. VPAS offers a distinction by requesting smaller data chunk sizes in the remaining parts of the video content, which are not as frequently referenced as the first parts. VPAS offers several benefits, including the less wasting of network resources and less network traffic.

System integration using embedded web server and wireless communication

As the buildings become intelligent with the development of information communication, many facilities have appeared. Usually, each facility performed independent functions, but with the development of the internet, the facilities integrate with each other and perform various new abilities. At present, in order to offer linked service by integrating, PC servers are being used. However, the use of a PC server is expensive, consumes a lot of electricity and needs a lot of room. Therefore, this paper proposes the Embedded Web Server, which can substitute the existing PC server and control devices through the Web. Also, we propose integration through wireless communication, which can solve problems like complicating wiring and space restriction.

A Novel 3D Indoor Localization Scheme Using Virtual Access Point

The global positioning system (GPS) is a popular choice for accurate location sensing and is often used in navigation systems. However, GPS fails to operate inside buildings because satellite signals are blocked. Thus, GPS cannot be used for localization indoors. Moreover, it is difficult to distinguish between the different floors. Research to overcome this problem using the ultrawideband (UWB), radio frequency identification (RFID), and infrared ray (IR) has been conducted. These methods, however, have drawbacks, such as the need for an additional communication module and database. Wireless local area network (WLAN) access point (AP) is widely installed at various locations, and using these WLAN APs can be a viable alternative. The proposed system in this paper indicates the location information in the service set identifier (SSID) of virtual AP. Therefore, merely by scanning the WLAN signals, mobile users can detect their location indoors.

Real-time white spectrum recognition for cognitive radio networks over TV white spaces

A key technical challenge in TV white spaces is the efficient spectrum usage without interfering with primary users. This paper considers available spectrum discovery scheme using in-band sensing signal to support super Wi-Fi services effectively. The proposed scheme in this paper adopts non-contiguous orthogonal frequency-division multiplexing (NC-OFDM) to utilize the fragmented channel in TV white space due to microphones while this channel cannot be used in IEEE 802.11af. The proposed solution is a novel available spectrum discovery scheme by exploiting the advantages of a sensing signaling. The proposed method achieves considerable improvement in throughput and delay time. The proposed method can use more subcarriers for transmission by applying NC-OFDM in contrast with the conventional IEEE 802.11af standard. Moreover, the increased number of wireless microphones (WMs) hardly affects the throughput of the proposed method because our proposal only excludes some subcarriers used by WMs. Additionally, the proposed method can cut discovery time down to under 10 ms because it can find available channels in real time by exchanging sensing signal without interference to the WM.

Categorization-based video streaming for traffic mitigation in content delivery services

This paper presents a categorization-based video streaming approach (CVS) to mitigate the Internet traffic in content delivery services. The CVS uses the statistical information related to the users’ view patterns (i.e., the average view duration in accordance with the playback time of the content) to adjust the request period of content chunks. Therefore, it can reduce the amount of Internet traffic by reducing unnecessary chunk requests and content chunks. The operation of the CVS is based on the average view duration provided by the content provider (CP). However, even if the CP does not provide the average view duration of the content, the CVS can properly predict the average view duration by using the content categorization and adjust the request period of content chunks. The simulation results show that the CVS achieves better performance in terms of the average waste ratio of network resources, the amount of network traffic, and the number of chunk requests.

Scalable wireless-optical broadband access network using reconfigurable optical backhaul and gateway selection method

We propose a scalable optical-wireless access network that is composed of reconfigurable passive optical network and wireless mesh network architectures, which is to flexibly adapt to a large scale of traffic variation in the mobile networks. The reconfigurable PON is equipped with dynamic bandwidth reallocation capability by the arrayed waveguide grating, so that it can provide improved bandwidth efficiency and graceful scalability. Furthermore, a selection method of optical-wireless integrated gateway is included to balance the network load between the two architectures. The proposed network can enhance the network capacity and decrease the congestion probability of optical-wireless access network.

Implementation of Embedded Web Server and XML Web Services for Intelligent Building System

The existing building control and automation systems which have been applied to buildings are provided by many different vendors and each vendor has its own proprietary protocol. There are many problems in system integration since those building control and automation systems belong to each vendor. Also, the problems of cost and space increase, due to the usage of personal computers as the control servers of DDC(Direct Digital Control) in each facility. Those problems mentioned above can be effectively resolved by using XML Web Services and Embedded Web Server. Embedded Web Server and XML Web Services are technologies emerging out of the IT industries and there are many researches to apply them into many fields. In this paper, Embedded Web Server and XML Web Services are proposed to be used in building control and automation system to resolve problems in building system integration.