• Journal of the Korea Society of Computer and Information
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• v.17 no.1
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• pp.141-149
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• 2012

This paper proposes a resource management and allocation algorithm to guarantee QoS continuity of realtime multimedia services and to maximize the resource utilization in heterogeneous wireless networks simultaneously. This scheme reserves the appropriate resources to be used by real-time multimedia services and allocates those resources left unused due to decreased transmission rate of realtime services to non-realtime services. Those resources can be preempted by the need of realtime services later. Performances are analyzed by simulation.

• Journal of the Institute of Convergence Signal Processing
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• v.8 no.4
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• pp.244-248
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• 2007

In this paper, we propose a novel self-networking and replaceable structure method for the ubiquitous multimedia. As the contents in the ubiquitous multimedia should be realistic and continuously updated in the real-time manner, an efficient scheme of a self-networking and replaceable structure is necessary. In the proposed method, the contents itself connects to the server or corresponding devices and updates itself autonomously. Also, we can reduce the total amount of data transmission comparing to the cases where the whole contents should be downloaded. A Markov chain model is introduced for the proposed structure in order to perform the throughput analysis. The whole mechanism is implemented in the wireless handset and also, various applications of the scheme are discussed.

• Journal of KIISE:Computing Practices and Letters
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• v.9 no.4
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• pp.369-380
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• 2003

With the proliferation of a wireless support and the advances of mobile devices, there is a growing need of making it available for a wireless network as well. Low bandwidth of a wireless network is one of the major issues that should be considered for extending a synchronous collaboration system developed for a wired network to supuort a wireless network. We propose a priority-based view synchronization scheme, exploiting the relaxed synchronization. The proposed scheme leverages the fact that mobile users need not have the exactly same view as the users in a wired network since they usually have a limited screen size and thus focus only on part of a whole document. We evaluate the performance of a simple group editor with the propose scheme using ns -2. The performance results show that the proposed scheme keeps the message transmission delay low so that mobile users can have synchronous colloboration with wired users without signification delay. The proposed scheme is designed and implemented as a framework to support various kinds of realtime groupware applications, exploiting the existing groupware framework, Habanero. As a client program, we implemented a simple group text editor.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.11
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• pp.1434-1442
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• 2019

In this paper, the channel change was continuously measured for 24 hours from July 5, 2017 on the coast near Deokjeok-do, Incheon. The underwater channel has various channel environment characteristics as the change in the time axis and the change in the frequency axis occurs in real time, and the underwater communication performance decreases due to the multipath fading and the Doppler effect. Therefore, in this study, we performed the OFDM system performance analysis in the underwater channel environment by applying the repetitive transmission diversity scheme in the time and frequency domain to improve the communication performance in the real-world underwater communication environment. Using the collected data, we compared the channel environment in the time and frequency domain and analyzed the BER performance according to the pilot spacing and the number of repetitive transmissions in the time and frequency axis.

• Journal of Institute of Control, Robotics and Systems
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• v.13 no.7
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• pp.711-717
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• 2007

Location information will become increasingly important for future Pervasive Computing applications. Location tracking system of a moving device can be classified into two types of architectures: an active mobile architecture and a passive mobile architecture. In the former, a mobile device actively transmits signals for estimating distances to listeners. In the latter, a mobile device listens signals from beacons passively. Although the passive architecture such as Cricket location system is inexpensive, easy to set up, and safe, it is less precise than the active one. In this paper, we present a passive location system using Cricket Mote sensors which use RF and ultrasonic signals to estimate distances. In order to improve accuracy of the passive system, the transmission speed of ultrasound was compensated according to air temperature at the moment. Upper and lower bounds of a distance estimation were set up through measuring minimum and maximum distances that ultrasonic signal can reach to. Distance estimations beyond the upper and the lower bounds were filtered off as errors in our scheme. With collecting distance estimation data at various locations and comparing each distance estimation with real distance respectively, we proposed an equation to compensate the deviation at each point. Equations for proposed algorithm were derived to calculate relative coordinates of a moving device. At indoor and outdoor tests, average location error and average location tracking period were 3.5 cm and 0.5 second, respectively, which outperformed Cricket location system of MIT.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.12B
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• pp.2298-2319
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• 1999

In this paper, we propose a new moving mobile base station (MMBS) scheme for very low power and micro-size RMIMS (radio-interfaced micro information monitoring system) terminals. RMIMS terminals can be used in various application service areas such as pollution monitoring, environment surveillance, traffic monitoring, emergency monitoring (e.g., building, bridge, railroad breakdown), security monitoring (e.g., theft, alarm) and military application. For these applications based on wireless transmission technologies, sensor type RMIMS terminals must satisfy low cost and low power design (e.g., solar power, life limited battery) requirement. In RMIMS terminal design, this low power requirement limits transmission range of uplink or reverse link and means small cell size. Also these applications using RMIMS terminals may have a little bit non real-time traffic characteristic and low scattering density in service area.

• Journal of Korea Multimedia Society
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• v.3 no.5
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• pp.479-494
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• 2000

Although the proliferation of real-time multimedia services over the Internet might indicate its successfulness in dealing with heterogeneous environments, it is obvious, on the other hand, that the internet now has to cope with a flood of multimedia data which consumes most of network communication channels due to a great deal of video or audio streams. Therefore, for the purpose of an efficient and appropriate utilization of network resources, it requires to develop and deploy a new scalable transmission technique n consideration of respective network environment and individual clients computing power. Also, we can eliminate the waste effects of storage device and data transmission overhead in that the same video stream duplicated according to QoS. The purpose of this paper is to develop a technology that can adjust the amount of data transmitted as an MPEG video stream according to its given communication bandwidth, and technique that can reflect dynamic bandwidth while playing a video stream. For this purpose, we introduce a media scalable media decomposer working on server side, and a scalable media composer working o n a client side, and then propose a scalable transmission method and a media sender and a media receiver in consideration of dynamic QoS. Those methods proposed her can facilitate an effective use of network resources, and provide multimedia MPEG video services in real-time with respect to individual client computing environment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.22 no.12
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• pp.2653-2663
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• 1997

The successive and parallel interference cancellation schemes are two well-known types of multi-stage interference cancellation schemes using the conventional correlator receivers as a basic building block, which has been known to significantly improve the performance of DS/CDMA system in the multiple access communication. Performance comparison between these two schemes is made strictly based on the analytical and it has been shown that the successive interference cancellation (SIC) scheme is more resistant to fading than the parallel interference cancellation (PIC) scheme. We further investigate the performance of the successive IC scheme subject to the delay constraint, which may be imposed typically on most of service applications with a real-time transmission requirement, including speech and video applications. Our analysis demonstrates that the performance may be significantly improved by the groupwise successive interference cancellation (GSIC) scheme, which can be properly optimized to meet the given delay constraint.

• Journal of KIISE:Information Networking
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• v.33 no.2
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• pp.156-164
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• 2006

The SCTP (Stream Control Transmission Protocol) implementation with the DAR (Dynamic Address Reconfiguration) extension is called the mSCTP (Mobile SCTP) that is proposed recently for mobility support in transport layer. The mSCTP does not satisfy short handover latency for real-time applications and it has no specific handover decision mechanisms. In this paper, we propose fast handover schemes for mobile nodes that are moving into different subnet using pre-acquisition RA (Router Advertisement) and L3 trigger for improving handover performance. Furthermore, we introduce three specific methods which are RA cache, FMIPv6 (Fast Handovers for Mobile IPv6) and dual interface and how proposed scheme can be interoperated with handover process respectively. Finally, we show two experimental results which are the mSCTP and the mSCTP using FMIPv6 on Linux platforms. Experimental results show that handover performance is improved with reducing the time of receiving RA which takes most of total handover latency.

• The KIPS Transactions:PartC
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• v.16C no.3
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• pp.373-382
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• 2009

we present more efficient method of a medium access for real-time ubiquitous sensor networks. Proposed MAC protocol is like the randomized CSMA/CA protocol, but unlike previous legacy protocols, it does not use a time-varying contention window from which a node randomly picks a transmission slot. To reduce the latency for the delivery of event reports from sensor nodes, we carefully decide to select a fixed-size contention window with non-uniform probability distribution of transmitting in each slot. We show that the proposed method can offer up to several times latency reduction compared to legacy of IEEE 802.11 as the size of the sensor network scales up to 256 nodes using a widely-used network simulation package, NS-2. We finally show that proposed MAC scheme comes close to meet bounds on the best latency being achieved by a decentralized CSMA-based MAC protocol for real-time ubiquitous sensor networks which is sensitive to latency.