• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.5
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• pp.117-123
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• 2003

One of the most important elements in satellite attitude control is sensor technology. Generally, inertial sensors introduce drift and noise which cause continuous errors. Absolute reference is needed to eliminate the problem of the inertial sensors. Star trackers are used primarily for such a purpose. There has been relatively less research effort or ground feasibility test experience on star trackers in the domestic side despite the importance of the associated technologies. In this paper, we re-introduce the basic concept of a star tracker and present the S/W simulator for the star tracker. The star simulator may be used ground test of a star tracker for the basic functioning test or the whole spacecraft test with the star tracker assembled.

• Journal of The Korean Astronomical Society
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• v.37 no.3
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• pp.119-129
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• 2004

A new method has been developed to solve the star cluster membership problem. It is based on synthetic photometry employing the Black Body concept as stellar radiation simulator. Synthetic color-magnitude diagram is constructed showing the main sequence band and the positions of binary star systems of combinations of various components through different photometric tracks. The method has been applied to the Hyades. The cluster membership problem has been re-appraised for the cluster (both single and binary) stars. For the binary members, the components' spectral types have been derived by the method. The results obtained agree very well with those found in literature, The method is simpler than the others and can be developed to undertake other cases as multiple star systems.

• Journal of Space Technology and Applications
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• v.4 no.3
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• pp.232-243
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• 2024

In order to perform various missions in space, including planetary exploration, estimating the position of a satellite in orbit is a very important factor because it is directly related to the success rate of mission performance. As a study for autonomous satellite navigation, this study estimated the satellite's attitude and real time orbital position using a star sensor algorithm with two star trackers and earth sensor. To implement the star sensor algorithm, a simulator was constructed and the position error of the satellite estimated through the technique presented in the paper was analyzed. Due to lens distortion and errors in the center point finding algorithm, the average attitude estimation error was at the level of 2.6 rad in the roll direction. And the position error was confirmed by attitude error, so average error in altitude direction was 516 m. It is expected that the proposed satellite attitude and position estimation technique will contribute to analyzing star sensor performance and improving position estimation accuracy.

• Current Optics and Photonics
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• v.1 no.2
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• pp.107-112
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• 2017

An adaptive optics system can be simulated or analyzed to predict its closed-loop performance. However, this type of prediction based on various assumptions can occasionally produce outcomes which are far from actual experience. Thus, every adaptive optics system is desired to be tested in a closed loop on an optical test bench before its application to a telescope. In the close-loop test bench, we need an atmospheric simulator that simulates atmospheric disturbances, mostly in phase, in terms of spatial and temporal behavior. We report the development of an atmospheric turbulence simulator consisting of two point sources, a commercially available deformable mirror with a $12{\times}12$ actuator array, and two random phase plates. The simulator generates an atmospherically distorted single or binary star with varying stellar magnitudes and angular separations. We conduct a simulation of a binary star by optically combining two point sources mounted on independent precision stages. The light intensity of each source (an LED with a pin hole) is adjustable to the corresponding stellar magnitude, while its angular separation is precisely adjusted by moving the corresponding stage. First, the atmospheric phase disturbance at a single instance, i.e., a phase screen, is generated via a computer simulation based on the thin-layer Kolmogorov atmospheric model and its temporal evolution is predicted based on the frozen flow hypothesis. The deformable mirror is then continuously best-fitted to the time-sequenced phase screens based on the least square method. Similarly, we also implement another simulation by rotating two random phase plates which were manufactured to have atmospheric-disturbance-like residual aberrations. This later method is limited in its ability to simulate atmospheric disturbances, but it is easy and inexpensive to implement. With these two methods, individually or in unison, we can simulate typical atmospheric disturbances observed at the Bohyun Observatory in South Korea, which corresponds to an area from 7 to 15 cm with regard to the Fried parameter at a telescope pupil plane of 500 nm.

• International Journal of Computer Science & Network Security
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• v.23 no.8
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• pp.85-90
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• 2023

The Ant Colony System (ACS) is a variant of Ant colony optimization algorithm which is well-known in Traveling Salesman Problem. This paper proposed a hybrid method based on genetic algorithm (GA) and ant colony system (ACS), called GACS, to solve traffic routing problem. In the GACS, we use genetic algorithm to optimize the ACS parameters that aims to attain the shortest trips and time through new functions to help the ants to update global and local pheromones. Our experiments are performed by the GACS framework which is developed from VANETsim with the ability of real map loading from open street map project, and updating traffic light in real-time. The obtained results show that our framework acquired higher performance than A-Star and classical ACS algorithms in terms of length of the best global tour and the time for trip.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.4
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• pp.247-256
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• 2013

According to the complete standard document for PHY/MAC layer of visible light communication through the IEEE 802.15.7 WG on Sept. 2011, visible light communication lays a good foundation for developing a variety of application services. Thus, visible light communication moves to the advanced research period for developing application services, but most of applications are limited only to PtP service model. However, PtMP communication environment for VLC is required to accommodate more various applications. In this paper, we analyze an effect of key parameters on network performance in the star topology based visible personal area network system. We implement a simulator with considering attributes of PHY and MAC layer which are defined by IEEE 802.15.7 standard documents, and analyze the VLC performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.12
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• pp.1286-1299
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• 1991

In this paper we present a multiple capture model for common spreading code CDMA packet radio systems with star topology. Basic equations for the collision free, header detection. and multiple capture probabilities are derived at the central receiver. Link performances. including the average number of packet captures, allowable number of simultaneous transmission, and system throughput are theoretically evaluated for a hybrid system. combining envelope header detection and differential data detection, Using the Block Oriented Systems Simulator(BOSS), simulations were carried out for the central receivers with envelope or differential geader detection, It is shown that for a threshold approx-imation to the probability of data packet success, the mulyiple capture model significantly improves system throughput.

• Journal of Environmental Impact Assessment
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• v.30 no.1
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• pp.13-23
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• 2021

In this study, we performed a Random Walker analysis to predict the Major Movement Paths of otters. The scope of the research was a simulation analysis with a radius of 7.5 km set as the final range centered on the Ansim-wetland in Daegu City, and a field survey was used to verify the model. The number of virtual otters was set to 1,000, the number of moving steps was set to 1,000 steps per grid, and simulations were performed on a total of 841 grids. As a result of the analysis, an average of 147.6 objects arrived at the boundary point under the condition of an interval of 50 m. As a result of the simulation verification, 8 points (13.1%) were found in the area where the movement probability was very high, and 9 points (14.8%) were found in the area where the movement probability was high. On the other hand, in areas with low movement paths probabilities, there were 8 points (13.1%) in low areas and 4 points (6.6%) in very low areas. Simulation verification results In areas with high otter values, the actual otter format probability was particularly high. In addition, as a result of investigating the correlation with the otter appearance point according to the unit area of the evaluation star of the movement probability, it seems that 6.8 traces were found per unit area in the area where the movement probability is the highest. In areas where the probability of movement is low, analysis was performed at 0.1 points. On the side where otters use the major movement paths of the river area, the normal level was exceeded, and as a result, in the area, 23 (63.9%), many form traces were found, along the major movement paths of the simulation. It turned out that the actual otter inhabits. The EN-Simulator analysis can predict how spatial properties affect the likelihood of major movement paths selection, and the analytical values are used to utilize additional habitats within the major movement paths. It is judged that it can be used as basic data such as to grasp the danger area of road kill in advance and prevent it.

• Journal of the Korea Society for Simulation
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• v.17 no.3
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• pp.35-44
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• 2008

Facility location problem is an important subject in many areas of modern business environment. In this paper, we deal with uncapacitated and multi-period facility location problem where the object is a maximization of total profit within predetermined cost. We assume that all demand have to be met. Particularly, we represent various types of customer based on four well-known urban spatial structures to represent a spread of customers. Those are concentric zone model, sector model, multiple nuclei model and star model respectively. We apply to the genetic algorithm to simulate a large scaled problem and develop simulator. We analyze both optimal numbers and locations of facilities for each urban structure. Furthermore, we examine the appropriate time to further expansion of the facilities in the planning horizon. The experimental results show that the developed algorithm can be applied effectively to the facility location problem in the various types of urban area.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.760-764
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• 2015

Wireless sensors, installed on machinery, and Time Division Multiple Access (TDMA) transmission make an ideal system for monitoring machine conditions in industrial plants because there is no need for electronic wiring. However, there has not yet been a successful field application of such a system, capable of continuously transmitting data at sample rates greater than 100 Hz. In this research, a TDMA network protocol capable of acquiring data from multiple sensors at sample rates greater than 100 Hz was developed for field application. The protocol was implemented in a single cluster-star topology network, and the system was evaluated based on the node number and transmission distance. Network simulator 2 (ns-2) was used for a real field simulation. Non-TDMA and TDMA protocol cases were compared using four sensor nodes. In the cases of 20-s and 40-s transmission times, there was little difference between the reception rates of the non-TDMA and TDMA systems. However, the difference was much greater when using a 60-s transmission time.