• Journal of Broadcast Engineering
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• v.21 no.1
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• pp.113-116
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• 2016

Cognitive radio network technology is that secondary (unlicensed) users use the spectrum of primary (licensed) users without interfering primary communication. In this paper, we propose multiple access scheme for a cognitive radio network, where multiple secondary users access spectrum of one primary user. We consider two types of multiple access scheme, one is p-persistent and one is non-persistent, and apply these two schemes in the secondary network. For each multiple access scheme, total throughput of secondary network is derived and verified by Monte Carlo simulation. Simulation results show that maximum total throughput of the secondary network is achieved when channel access probability or the number of maximum waiting frames is chosen appropriately.

• Journal of KIISE:Information Networking
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• v.30 no.2
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• pp.244-251
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• 2003

As the Internet and wireless mobile communication is being widespread, the WAP (Wireless Application Protocol) that merges these two technologies has emerged. Also, the research of the WAP gateway that enables efficient processing of multiple user demands concurrently and prompt response to requests from various wireless devices has been performed in many working groups. The WAP stack is the most fundamental technology among these researches. In this paper, we implement the WAP container utilizing the JAVA's multithreading and applying to the connection pooling technique to manage the available resource in the container efficiently. Also, we design and implement the WTP(Wireless Transaction Protocol) layer and the UDP(User Datagram Protocol) layer based on the priority Policy. Our design and implementation showed the shorter waiting time than that of the existing FCFS(First-Come, First-Served) system in the transaction layer and its efficiency was proved through simulation.

• Journal of Information Technology Applications and Management
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• v.25 no.3
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• pp.17-28
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• 2018

In this paper, an activity-oriented usability model is proposed. The usability model contains two types of characteristics: special-type characteristics of usability and sub-characteristics of usability. Workability, study-ability, and playability are, but do not exhaust, examples of special-type characteristic of usability. They correspond to working, studying, and playing using the software product, respectively. They represent the goal of using and can overlap each other. They are usability too by themselves. Navigate-ability, data-prepare-ability, data-input-ability, response-wait-ability, output-examine-ability, and output-utilize-ability are typical examples of sub-characteristics of usability. They correspond to navigating, preparing data, inputting data, waiting response, examining output, and utilizing the output data, respectively. They are not usability by themselves. They constitute usability together as a group. Assessing is the fundamental and indispensable aspect of quality. Without assessing, the concept of quality has little practical value. Satisfaction, effectiveness, and efficiency are the most typical sub-characteristics of usability in existing quality models, which correspond to the evaluation criteria of usability. In the activity-oriented usability model, however, only the user's satisfaction is included: Satisfaction is regarded as the operational definition of usability in the user's view. As the result, usability can be interpreted as the 'goodness for using, which is evaluated by the user. 'Three fundamental principles regarding software quality models are proposed too in this paper: Principles of Parsimony, Cohesiveness, and Inheritance. Discussions illustrate well that typical existing usability models violate these basic principles. Many authors have tried to define general usability models which can be applied to most kinds of software. The dream of the general and universal usability model, however, may be an illusion. The activity-oriented usability model is expected to serve as a prototype from which specialized usability models can be derived.

• Journal of the Korea Society of Computer and Information
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• v.14 no.9
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• pp.67-74
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• 2009

The presence informations of users of Instant Messaging System In SIP(Session Initiation Protocol) environment are obtained by presence server, and message waiting indication event package is used to provide various message informations stored in the message server. In this paper, I have proposed a new method in which Extended CPL(Call Processing Language) has been applied to presence service to provide various functions to the users. A user of Instant Messaging System subscribes presence information and CPL scripts which describe his requirements, and presence server executes CPL scripts when instant messaging service is subscribed and notifies presence informations. Several CPL operation tags are added, and therefore various services which combine presence service and call processing can be provided in this system. Furthermore a new method has been proposed in which message server and presence server correlate in Instant Messaging System. When changes of message status informations occur, message server send these informations to the presence server, and presence server provides both presence informations and message status informations in extended format. As this method can be a substitute for message waiting indication event package, the system operating efficiency can be increased. The performance of this proposed system is evaluated by experiments.

• The KIPS Transactions:PartA
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• v.9A no.2
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• pp.137-146
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• 2002

In VOD server, in order to guarantee playback of continuous media, such as video, without hiccups for multiusers, the server has to manage its buffer sophisticatedly by prefeching a part of the data into the buffer As the continuous media data buffered by one user can be used again by the others, the number of disk accesses is reduced and then the latency time far the users is also reduced. In this paper, we propose a new buffer management technique for continuous media in VOD server. Our basic algorithm partitions the buffer into groups and then a group of buffer which has the lowest utilization is chosen and partitioned again for a new user. The basic algorithm is extended for supporting multiple streams and clip data and for providing VCR functions. Our proposed technique is able to increase in the number of concurrent users as increasing the utilization of the buffer and to minimize the average waiting time for multiuser accesses as the bandwidth of storage is slowly reached to the limit. In the simulation study for comparing the performance of our technique with that of the existing techniques, we show that the average waiting time is reduced mere than 50% and the number of concurrent users increases by 1 ∼5% as compared with those of the exiting techniques.

• Journal of KIISE:Computer Systems and Theory
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• v.28 no.12
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• pp.660-673
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• 2001

In Video-on-Demand (VoD) servers, disk throughput is an important system design parameter because it is directly related to the number of user requests that can be served simultaneously. In this paper, we propose an efficient periodic request grouping scheme for disk array-based VoD servers that reduces the disk seek time, thus improving the disk throughput of VoD disk arrays. To reduce the disk seek time, the proposed scheme groups the periodic requests that access data blocks stored in adjacent regions into one, and arranges these groups in a pre-determined order (e.g., in left-symmetric or right-symmetric fashion). Our simulation result shows that the proposed scheme reduces the average disk bandwidth required by a single video stream and can serve more user requests than existing schemes. For a data block size of 192KB, the number of simultaneously served user requests is increased by 8% while the average waiting time for a user request is decreased by 20%. We also propose an adaptation technique that conforms the proposed scheme to the user preference changes for video streams.

• Journal of Biomedical Engineering Research
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• v.14 no.4
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• pp.321-326
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• 1993

Recently, microcomputer technology has been developed rapidly and it provides not only graphic user interface that can be fraendly accessable but also large storage capacity to han- dle much hospital information. Almost all the order communication system for hospital has been developed under the concept of host and terminal environment since last 20 years. However, host-terminal system has not been successful in korea simply because most of physicians prescibe for rrlany patients a day(sometimes more than 150 patients a day). Also, under the host-terminal environment, programs are not friendly implemented for users. Since March 1991, we had developed order communication system for out-patients(named YONSEI-PC) using personal computer(PC) and local area network(LAN) . Since September 1992, we has applied succesfully in the Yonsei Cardiovascular Center, Sevrance Hospital, Yonsei University College of Medicine. This system consisted with Server and Clients which is communicated through LAN(Ethernet). The system also use the Host computer(IBM 9221 170) as a data bank and communicates to the Server with emulation card(3270 emulator, Interlink Inc., Korea) . After introducing this system, it enables patients to receive drugs witllin 20 minutes after prescription of 300-400 patients per day and it seemed to be effective system not to reduce waiting time for the patients but also to remove charge-troubling(due to His-entry of prescription) . This system also seems to be effective in terms of office automatism for hospital management. However users, usually physitions, required more friendly and easy system to operate and we thought that the most important one to successfully introduce order communication computer system in the hospital is user interface.

• Journal of the Korean Society for information Management
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• v.25 no.2
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• pp.115-125
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• 2008

The Purpose of this study was to discover the factors which motivate academic library users to use chat reference service and which demotivate academic library users to use chat reference service. To achieve the study purposes, this study conducted interview with the selected participants (Information Studies graduate students at Florida State University(FSU)) through email in April and May 2007. This study found that 1) convenience, 2) anonymity, and 3) inexpensiveness of the service served as incentives(motivators) for chat reference service consumers to use the service. On the other hand, chat reference service consumers mentioned the following factors as obstacles (demotivators) for using the service: 1) waiting time, 2) accessibility, 3) interface design, and 4) difficulties with expressing themselves in a virtual space.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.3
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• pp.599-606
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• 2016

Many people feel uncomfortable when fitness center is crowded with people in all at the same time. So we propose exercise machines reservation system for resolving the problem that people feel uncomfortable in fitness center. In this paper, we design and implement the exercise machines reservation system that allows for users to reserve fitness equipments by using a NFC-based smart band. A user can reserve exercise machine using some reservation device. he or she will receive notifications through the smart band about when and which machine she or he will have to use. The user can do exercise with a recommended program, and can use any equipments conveniently even in a peak time because no one is waiting. Also, a manager can save cost through the efficient facility management and provide customized member management. Additionally, manager don't need to purchase other exercise machines or computers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.10A
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• pp.1517-1531
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• 1999

The Internet is recently evolving into the directions which is capable of incorporating stream-type services such as voice and video services. However, the existing Internet can only support a best-effort delivery model and thus it is difficult to satisfy these requirements as well as to provide the QoS beyond a certain degree. Accordingly, it is imperative to develop QoS based routing algorithm in order to allow the routing by the user's QoS demand and to be applied into wide area networks. In this thesis, we presented new routing algorithms and made performance evaluations. The proposed algorithms allow the routing by the user’s QoS demand level in order to provide the diverse Internet application services based on ATM network environment that is expected to play a role as an infrastructure of high-speed communication network. They also have a feature of shortening the waiting time for address analysis and have a quality-proven characteristics with enhanced network scalability.