• The Journal of Korean Association of Computer Education
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• v.11 no.3
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• pp.81-89
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• 2008

The failure occurrence of resources in the grid computing is higher than in a tradition parallel computing. Since the failure of resources affects job execution fatally, fault tolerance service is essential in computational grids. And grid services are often expected to meet some minimum levels of quality of service (QoS) for desirable operation. However Globus toolkit does not provide fault tolerance service that supports fault detection service and management service and satisfies QoS requirement. Thus this paper proposes fault tolerance service to satisfy QoS requirement in computational grids. In order to provide fault tolerance service and satisfy QoS requirements, we expand the definition of failure, such as process failure, processor failure, and network failure. And we propose resource scheduling service, fault detection service and fault management service and show implement and experiment results.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.3B
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• pp.264-273
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• 2009

For IEEE 802.15.3 HR-WPAN, we propose the DABL algorithm that PNC can allocate the channel times to the DEV in super frame in order that system frame throughput is increased and the delay is decreased. In detail, the DABL algorithm allows to dynamically allocate channel time as well as to adaptively apply the modulation and coding scheme based on the link quality of the DEV. In addition, due to the facts that QoS is quite different depending on service types, we provide the DABL algorithm taking into account RT(Real Time) traffic and Non-RT traffic respectively. Finally, we show simulation results of the DABL algorithm compared to the conventional algorithm that the PNC equally allocates channel times to the DEV regardless of the link quality of the DEV.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.12
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• pp.67-74
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• 2004

AES is frequently used as a symmetric cryptography algorithm for the Internet. Wireless embedded systems increasingly use more conventional wired network protocols. Hence, it is important to have low-cost implementations of AES for thor The basic architecture of AES unrolls oかy one full cipher round which uses 20 S-boxes together with the key scheduler and the algorithm repeatedly executes it. To reduce the implementation cost further, the folded architecture which uses only eight S-box units was studied in the recent years. In this paper, we will study a low-cost AES implementation for wireless communication technology based on the folded architecture. We first improve the folded architecture to avoid the sixteen bytes of additional state memory. Then, we implemented a single byte architecture where only one S-box unit is used for data encryption and key scheduling. It takes 352 clocks to finish a complete encryption. We found that the maximum clock frequency of its FPGA implementation reaches about 40 MHz. It can achieve about 13 Mbps which is enough for 3G wireless communication technology.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.1-12
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• 2005

In wireless personal area networks(PANs), the successful design of channel time allocation algorithm is a key factor in guaranteeing the various quality of service(QoS) requirements for the stringent real-time constraints of multimedia services. In this paper we propose a dynamic channel time allocation algerian for providing delay guarantees to multimedia traffics such as MPEG streams in the IEEE 802.15.3 high-rate WPANs. The dynamic algorithm exploits the characteristics of MPEG stream, wherein the devices (DEVs) send their channel time requests only at the end of superframe boundaries. The algerian uses mini packets for feedback control in order to deliver dynamic parameters for channel time requests from the DEVs to the piconet coordinator (PNC). In this scheme, the duration of channel time allocated to a DEV during a superframe is changed dynamically depending on the MPEG frame type, traffic load and delay bound of the frame, etc. Performance of the proposed scheme is investigated by simulation. Our results show that compared to traditional scheme, the proposed scheme is very effective and has high performance while guaranteeing the delay bound.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.48 no.2
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• pp.1-8
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• 2011

An underwater robot S/W framework consists of various sub-modules such as sensory data processing module, thruster control module, cognition module and behavior control module. Performance of a robot is determined by not only the efficiency of algorithms used but also effectiveness of their implementations. One most important factor of the effective implementation is the efficiency of data sharing module, as it transmits signals and data between the sub-modules and thus is directly related to the cycles of sensing and control The ideal data sharing module enables immediate access to any data source irrespective of system configurations. In reality, however, there are lots of obstacles including limitation of processing capacity of source modules, delay over network, and scheduling latency of operating systems. The paper proposes a new data sharing architecture and programming models to effectively handle such obstacles in implementation of underwater S/W framework on a small scale distributed computing system.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.1
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• pp.39-45
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• 2008

High-Rate Wireless Personal Area Networks (HR-WPANs) in IEEE 802.15.3 standard use a TIme Devision Multiple Access (TDMA) protocol to support isochronous traffic. Isochronous traffic requires a delay-bounded service. However, the HR-WPAN standard suffers from long access delay and association delay. In this paper, we propose an enhanced MAC protocol for the delay-bounded traffic. This proposed protocol provides a way that a central node is able to collect traffic status on all member nodes. Furthermore, by utilizing the information, a scheduling algorithm is also proposed in order to synchronize the instant of a packet transmission with that of the packet arrival. With the proposed protocol and algorithm, the delay of access and association can be reduced. Performance analysis is carried out and the significant performance enhancement is observed.

• Journal of Korea Multimedia Society
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• v.1 no.1
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• pp.67-79
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• 1998

In this paper, we present the design and analyze the transmission rate of a control algorithm for the client buffer on the VOD systems. The design is based on the server's data transmission rate and clients' data consumption rate. The proposed algorithm stabilizes the client's buffer by reducing the oscillation phenomena of the buffer. And it uses the BCT (Buffer Check Time) to reduce the scheduling load of the client system. The client's data consumption rate and the buffer size are calculated on the basis of BCT. In case that the predicted buffer size operates in the overrun or starvation the buffer. As the load fluctuation of the network, the transmission rate control policy cannot stabilize the client's buffer alone. The media scaling policy, therefore, also performs its complementary part in stabilizing the client's buffer, and performance evaluation of the proposed algorithm is provided through simulation.

• Journal of Korea Multimedia Society
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• v.10 no.3
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• pp.348-357
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• 2007

One of the major issues in recent researches on wireless sensor networks is to reduce energy consumption of sensor nodes operating with limited battery power, in order to lengthen their lifespan. Among the researches, we are interested in the schemes in which a sensor node periodically turns on and off its radio and requires information on the time when its neighbors will wake up (or turn on). Clock synchronization is essential for wakeup scheduling in such schemes. This paper proposes three methods based on the asynchronous averaging algorithm for clock synchronization in sensor nodes which periodically wake up: (1) a fast clock synchronization method during an initial network construction period, (2) a periodic clock synchronization method for saving energy consumption, and (3) a decision method for switching the operation mode of sensor nodes between the two clock synchronization methods. Through simulation, we analyze maximum clock difference and the number of messages required for clock synchronization.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.7A
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• pp.844-851
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• 2004

Various types of error are caused due to many factors of various environment in air interface channel of wireless communications. In this case, the reliability of the channel is much lower than that of wired case. IEEE 802.15.3 high-rate WPAN, which operates in an ad hoc networking environment, is more susceptible to such errors. The problem has been investigated for wireless LANs, for example, as follows. If the queue size of a certain node is longer than that of other nodes, the node estimates that its channel state is bad and the resource of the node is decreased. However this method has a disadvantage that a central controller must always monitor the status. To avoid this disadvantage, in this paper, a new MAC protocol that the throughput of overall piconet is increased by LDS (Link-status Dependent Scheduling) is proposed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37B no.12
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• pp.1138-1147
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• 2012

IEEE standard 802.16, often referred to as WiMAX, is considered a "last mile" broadband wireless access alternative to conventional DSL and Cable Internet. One extension that is recently receiving great attention is the IEEE 802.16j Mobile Multihop Relay (MMR) amendment. The focus of this amendment is the development of simple and lower cost relay stations (RSs) that can enhance network coverage and capacity. We use our proposed simple scheduling scheme for serving the SSs in a fair manner and evaluate the performance of WiMAX networks with relays, especially we analyze the impact of interference between RSs on cell throughput Through simulations and numerical analysis, we make several fundamental observations about interference aware cost effective coverage extension in such networks.