• Journal of Korean Society of Transportation
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• v.24 no.3 s.89
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• pp.17-27
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• 2006

Car following model is a theory that examines changes of condition and interrelationship of acceleration deceleration. headway, velocity and so on closely based on the hypothesis that the Posterior vehicle always follows the preceding vehicle. Car following mode) which is one of the research fields of microscopic traffic flow was first introduced in 1950s and was in active progress in 1960s. However, due to the limitation of data gathering the research depression was prominent for quite a while and then soon was able to tune back on track with development in global positioning system using satellite and generalization of computer use. Recently, there has been many research studies using reception materials of global Positioning system(GPS). Introducing GPS technology to traffic has made real time tracking of a vehicle position possible. Position information is sequential in terms of time and simultaneous measurement of several vehicles in continuous driving is also practicable. Above research was focused on judging whether it is feasible to overcome the following model research by adopting the GPS reception device that was restrictively proceeded due to the limitation of data gathering. For practical judgment, we measured the accuracy and confidence level of the GPS reception devices material by carrying out a practical experiment. Car following model is also being applied in simulations of traffic flow analysis, but due to the difficulty of estimating parameters the basis of the above result. it is our goal to produce an accurate calibration of car following model's parameters that is suitable in this domestic actuality.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1134-1141
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• 1999

In this paper, we implement an optical code division multiple access(OCDMA) system and analyze the performance of the implemented system. In the implemented system, a transmitter encodes input data into optical pulses by using laser diode, and spreads the encoded pulses in an encoder which consists of 4 stage delay lines. The decoder which is the same structure as that of encoder delays and combines the spreaded pulses, and thus recovers the original data. At first, we discuss the auto- and cross-correlations of OCDMA signals under both environments of single user and multi-users, and then verify the simulation results with experimental results. We also evaluate the effect of a number of stages of delay line and code length on the system performance through computer simulations. As experimental results we can see that if the decoder have the same configuration as that of encoder, the peak auto-correlation characteristics can be achieved, and thus we can recover the original data from received data. As simulation results we can see that although bit error rate decreases as code length decreases or the number of stage of delay line increases, it is difficult to implement the system because the pulse width becomes narrow. From the results, we can apply CDMA technologies to optical communication networks.

• Journal of KIISE
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• v.44 no.1
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• pp.1-12
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• 2017

The continuously growing internet service requirements has resulted in a multitier system structure consisting of web server and database (DB) server. In this multitier structure, the existing intrusion detection system (IDS) detects known attacks by matching misused traffic patterns or signatures. However, malicious change to the contents at DB server through hypertext transfer protocol (HTTP) requests at the DB server cannot be detected by the IDS at the DB server's end, since the DB server processes structured query language (SQL) without knowing the associated HTTP, while the web server cannot identify the response associated with the attacker's SQL query. To detect these types of attacks, the malicious user is tracked using knowledge on interaction between HTTP request and SQL query. However, this is a practical challenge because system's source code analysis and its application logic needs to be understood completely. In this study, we proposed a scheme to find the HTTP request associated with a given SQL query using only system log files. We first generated an HTTP request-SQL query map from system log files alone. Subsequently, the HTTP request associated with a given SQL query was identified among a set of HTTP requests using this map. Computer simulations indicated that the proposed scheme finds the HTTP request associated with a given SQL query with 94% accuracy.

• The KIPS Transactions:PartC
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• v.12C no.4 s.100
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• pp.571-580
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• 2005

In fast long-distance networks, TCP's congestion control algorithm has the problem of utilizing bandwidth effectively. Several window-based congestion control protocols for high-speed and large delay networks have been proposed to solve this problem. These protocols deliberate mainly three properties : scalability, TCP-friendliness, and RTT-fairness. These protocols, however, cannot satisfy above three properties at the same time because of the trade-off among them This paper presents a new window-based congestion control algorithm, called EM (Exponential Increase/ Multiplicative Decrease), that simultaneously supports all four properties including fast convergence, which is another important constraint for fast long-distance networks; it can support scalability by increasing congestion window exponentially proportional to the time elapsed since a packet loss; it can support RTT-fairness and TCP-friendliness by considering RTT in its response function; it can support last fair-share convergence by increasing congestion window inversely proportional to the congestion window just before packet loss. We evaluate the performance of EIMD and other algorithms by extensive computer simulations.

• KIPS Transactions on Computer and Communication Systems
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• v.2 no.9
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• pp.381-392
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• 2013

During the last decade, the multitude of advances attained in terminal computers, along with the introduction of mobile hand-held devices, and the deployment of high speed networks have led to a recent surge of interest in Quality of Service (QoS) for video applications. The main difficulty is that mobile devices experience disparate channel conditions, which results in different rates and patterns of packet loss. One way of making more efficient use of network resources in video services over wireless channels with heterogeneous characteristics to heterogeneous types of mobile device is to use a scalable video coding (SVC). An SVC divides a video stream into a base layer and a single or multiple enhancement layers. We have to ensure that the base layer of the video stream is successfully received and decoded by the subscribers, because it provides the basis for the subsequent decoding of the enhancement layer(s). At the same time, a system should be designed so that the enhancement layer(s) can be successfully decoded by as many users as possible, so that the average QoS is as high as possible. To accommodate these characteristics, we propose an efficient transmission scheme which incorporates SVC-aware dual-channel repetition to improve the perceived quality of services. We repeat the base-layer data over two channels, with different characteristics, to exploit transmission diversity. On the other hand, those channels are utilized to increase the data rate of enhancement layer data. This arrangement reduces service disruption under poor channel conditions by protecting the data that is more important to video decoding. Simulations show that our scheme safeguards the important packets and improves perceived video quality at a mobile device.

• Journal of KIISE:Information Networking
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• v.28 no.3
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• pp.406-416
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• 2001

Single path routing schemes using dynamic routing metric amy find out the dynamic network status and recompute paths to keep the traffic from the highly loaded regions of the network. This type of routing approach, however, may lead to a routing oscillation, and further, it cannot exploit multi-paths that may frequently exist in the real network. We propose a multipath routing scheme with dynamic load balancing, called MP-DLB, which is capable of reducing the overhead incurred by the multipath routing with dynamic load balancing approach while taking advantage of the high routing performance provided by the approach. According to the analysis of Internet packet traces which show that a high percentage of network traffic is destined for a small number of networks, MP-DLB applies the multipath routing with dynamic load balancing only to a limited subset of all the destinations in the network. For the rest of the destinations, it applies traditional single path routing scheme. This approach may reduce overall routing overheads by limiting the number of destinations to apply the more complicated routing scheme while it can keep the routing performance high by providing efficient routing for the most significant traffic in the routing performance. A series of simulations are done to analyze the performance of MP-DLB. The simulation results show that MP-DLB may effectively cope with the congestion and achieve high routing performance by distributing traffic streams that are generated from varying sources and heading toward a specific hot destination over multi-paths.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.9 no.1
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• pp.93-99
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• 2008

In this paper, we propose new modulation schemes using the conventional CACB modulation with constant amplitude property. Also the proposed modulation schemes supports high transmission data rate by increasing the spectral efficiency. In order to obtain the high spectral efficiency, the $Q^2$PSK and CA-$Q^2$PSK are used. We explain the simplest combining modulation scheme of CACB and $Q^2$PSK (i.e., CACB-$Q^2$PSK). However, this modulation scheme cannot support the constant amplitude property. Hence the first CACB-CA-$Q^2$PSK (or CACB-CA-$Q^2$PSK I) modulation scheme is proposed for the constant amplitude property. In the modulation scheme, the redundant constant amplitude encoding (spectral efficiency decrease) is required. Therefore, the second CACB-CA-$Q^2$PSK (or CACB-CA-$Q^2$PSK II) modulation scheme is proposed retaining the constant amplitude and the spectral efficiency. Computer simulations show that the proposed CACB-CA-$Q^2$PSK II is the efficient modulation scheme.

• Journal of Broadcast Engineering
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• v.12 no.2
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• pp.148-158
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• 2007

Recently, IEEE 802.15.4a(low-rate UWB) technique has been paid much attention to the LR-UWB communication system for WPAN. However, there are various interferences such as MPI(Multi Path Interference) or IPI(Inter Piconet Interference) in IEEE 802.15.4a wireless channel. In order to cancel various interferences occurred to WPAN environment, in this paper, we propose a UWB wireless communication system with high QoS(Quality of Service) which is a chaotic-OOK(On-Off Keying) system using unipolar ZCD(Zero Correlation Duration) spreading code in physical layer level. Furthermore, we analyze its performance via simulations and verify the availability of proposed system with prototype implementation.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.5 no.1
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• pp.91-99
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• 2007

It was intended in this study to investigate the effects of various parameters on the chemical reaction or mass transfer yield in a tubular-type nuclear waste treatment equipment. Since such equipments, as a tubular reactor, multistage solvent extractor, and adsorption column, accompany chemical reaction or mass transfer along the fluid-flowing direction, mathematical modeling for each equipment was carried out first. Then their behaviors of the chemical reaction or mass transfer were predicted through computer simulations. The inherent major parameters for each equipment were chosen and their sensitivities. affecting the reaction or mass transfer yield were analyzed. For the tubular reactor, the effects of axial diffusion coefficient and reaction rate constant on the reaction yield were investigated. As for the multistage solvent extractor, the backmixing of continuous phase and the distribution coefficient between fluid and solvent were considered as the major parameters affecting the extraction yield as well as concentration profiles throughout the axial direction of the extractor. For the adsorption column, the equilibrium constant between fluid and adsorbent surface, and the overall mass transfer coefficient between the two phases were taken as the major factors that affect the adsorption rate.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.10 no.3
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• pp.213-219
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• 2017

Recently, the Internet Protocol Television (IPTV) services have become very common, enabling various Internet-based services as well as watching TV. In the IPTV system, a Set-Top box (STB) plays a key role as a network terminal device that transmits and receives realtime multimedia contents. In addition, the IPTV networks are usually supported by broadband optical fiber-base network such as fiber-to-the-home (FTTH), However, a general IPTV STB is regarded as one of the local area network (LAN)-attached devices while sharing the bandwidth of the LAN (e.g., Ethernet). In order to overcome the limited bandwidth utilization by fully facilitating the broadband bandwidth (e.g., 1 Gbps) of the optical fiber-based network, we propose a new FC (Fiber Channel)-embedded IPTV STB which can be directly attached to the optical fiber network. Then, we verify that the impacts of the proposed FC-embedded IPTV STB by organizing the the FC-AL (Fiber Channel-Arbitration Loop) network equipped with the FC-embedded IPTV We measures the average Start-up Delay, Average Reject Ratio and the Number of Concurrent Users through extensive simulations to investigate the performances of the suggested FC-AL-based IPTV network. Surprisingly, the IPTV network architecture with the proposed FC-embedded IPTV STBs has an excellent average start-up delay of less than 10 msec, an acceptable average reject ratio of less than 3 % as well as a linear increase of the number of concurrent users when extending the architecture. This reveals that the proposed FC embedded STB has a superior impacts on the performance of the entire IPTV network by effectively utilizing the broadband bandwidth of the fiber optic-based network.