• Aerospace Engineering and Technology
• /
• v.6 no.1
• /
• pp.45-54
• /
• 2007

In this study, the function of TIS-B(Traffic Information Service-Broadcasting), Runway incursion prevention, conflict warning, way-point assignment were evaluated using ground-to-ground surveillance test bed of KARI which was based on ADS-B(Automatic Dependant Surveillance-Broadcasting) concept. VDL(VHF Data Link) based on STDMA protocol was used as a data link, and an UAT(Universal Access Transceiver) was included to get the TIS-B information, and four ground vehicles and two aircraft were included as rover units. The main purpose of this test bed was to realize the ADS-B concept for the application of ground surveillance and to evaluate its performance.

• Journal of Communications and Networks
• /
• v.4 no.3
• /
• pp.161-169
• /
• 2002

Ad hoc wireless networks involving large populations of scattered communication nodes will play a key role in the development of low power, high capacity, interactive, multimedia communication networks. Such networks must support arbitrary network connections and provide coverage anywhere and anytime. This paper partitions such arbitrarily connected network architectures into three distinct groups, identifies the associated dual network architectures and counts the number of network architectures assuming there exist N network nodes. Connectivity between network nodes is characterized as a random event. Defining the link availability P as the probability that two arbitrary network nodes in an ad hoc network are directly connected, the network connection probability $ \integral_n$(p) that any two network nodes will be directly or indirectly connected is derived. The network connection probability $ \integral_n$(p) is evaluated and graphically demonstrated as a function of p and N. It is shown that ad hoc wireless networks containing a large number of network nodes possesses the same network connectivity performance as does a fixed network, i.e., for p>0, $lim_{N\to\infty} Integral_n(p)$ = 1. Furthermore, by cooperating with fixed networks, the ad hoc network connection probability is used to derive the global network connection probability for hybrid networks. These probabilities serve to characterize network connectivity performance for users of wireless ad hoc and hybrid networks, e.g., IEEE 802.11, IEEE 802.15, IEEE 1394-95, ETSI BRAN HIPERLAN, Bluetooth, wireless ATM and the world wide web (WWW).

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.45 no.2
• /
• pp.114-123
• /
• 2017

Little Intelligent Nanosatellite of KAIST(LINK) is a 2U-size CubeSat which is developed by Aerospace Systems & Control Lab.(ASCL) of KAIST as a part of the international cooperation project QB50. The objective of the QB50 project is to carry out atmospheric research within the lower thermosphere and ionosphere and CubeSats are planned to be deployed at the International Space Station(ISS) from the first quarter of 2017. To implement this objective, a flight model(FM) of LINK has been successfully developed and the design and performance of the satellite have been verified by performing environment and function tests in accordance with acceptance requirement level. This paper describes the development of flight model and the results of vibration and thermal vacuum test.

• Journal of Digital Convergence
• /
• v.18 no.10
• /
• pp.225-232
• /
• 2020

The underlaying communication scheme in 5G cellular network is a very promising resource sharing scheme, and it is an effective scheme for improving service performance of 5G and reducing communication load between a cellular link and a device to device (D2D) link. This paper proposes the algorithm to minimize the resource interference that occurs when performing 5G-based multi-class service on gNB(gNodeB) and the cooperative priority-based resource allocation scheduling scheme (CPRAS) to maximize 5G communication service according to the analyzed control conditions of interference. The proposed CPRAS optimizes communication resources for each device, and it optimizes resource allocation according to the service request required for 5G communication and the current state of the network. In addition, the proposed scheme provides a function to guarantee giga-class service by minimizing resource interference between a cellular link and a D2D link in gNB. The simulation results show that the proposed scheme is better system performance than the Pure cellular and Force cellular schemes. In particular, the higher the priority and the higher the cooperative relationship between UE(User Equipment), the proposed scheme shows the more effective control of the resource interference.

• Journal of Communications and Networks
• /
• v.18 no.1
• /
• pp.65-74
• /
• 2016

Ship ad-hoc network (SANET) extends the coverage of the maritime communication among ships with the reduced cost. To fulfill the growing demands of real-time services, the SANET requires an efficient clock time synchronization algorithm which has not been carefully investigated under the ad-hoc maritime environment. This is mainly because the conventional algorithms only suggest to decrease the beacon collision probability that diminishes the clock drift among the units. However, the SANET is a very large-scale network in terms of geographic scope, e.g., with 100 km coverage. The key factor to affect the synchronization performance is the signal propagation delay, which has not being carefully considered in the existing algorithms. Therefore, it requires a robust multi-hop synchronization algorithm to support the communication among hundreds of the ships under the maritime environment. The proposed algorithm has to face and overcome several challenges, i.e., physical clock, e.g., coordinated universal time (UTC)/global positioning system (GPS) unavailable due to the atrocious weather, network link stability, and large propagation delay in the SANET. In this paper, we propose a logical clock synchronization algorithm with multi-hop function for the SANET, namely multi-hop clock synchronization for SANET (MCSS). It works in an ad-hoc manner in case of no UTC/GPS being available, and the multi-hop function makes sure the link stability of the network. For the proposed MCSS, the synchronization time reference nodes (STRNs) are efficiently selected by considering the propagation delay, and the beacon collision can be decreased by the combination of adaptive timing synchronization procedure (ATSP) with the proposed STRN selection procedure. Based on the simulation results, we finalize the multi-hop frame structure of the SANET by considering the clock synchronization, where the physical layer parameters are contrived to meet the requirements of target applications.

• Journal of Advanced Navigation Technology
• /
• v.20 no.2
• /
• pp.161-166
• /
• 2016

In high capacity and long haul optical communication systems, signal distortion is induced by chromatic dispersion and nonlinear effects of optical fibers. Dispersion management (DM) combining with mid-spans spectral inversion (MSSI) is one of the various techniques for overcoming this drawback. The most simple configuration of DM link is obtained by uniformly distributing the lengths of single mode fiber (SMF) and residual dispersion per span (RDPS) over whole fiber spans consisted of optical link. In this paper, the system performances in the uniformly distributed DM link combined with MSSI are assessed as a function of the number of fiber spans, because the system performances in this configuration are used as the significant performance criterion in other link configurations, such as the artificial distribution or the random distribution of SMF lengths and RDPS.

• Structural Engineering and Mechanics
• /
• v.47 no.6
• /
• pp.881-898
• /
• 2013

This paper describes analytical investigation into a new dual function system including a couple of shear links which are connected in series using chevron bracing capable to correlate its performance with magnitude of earthquakes. In this proposed system, called Chevron Knee-Vertical Link Beam braced system (CK-VLB), the inherent hysteretic damping of vertical link beam placed above chevron bracing is exclusively utilized to dissipate the energy of moderate earthquakes through web plastic shear distortion while the rest of the structural elements are in elastic range. Under strong earthquakes, plastic deformation of VLB will be halted via restraining it by Stopper Device (SD) and further imposed displacement subsequently causes yielding of the knee elements located at the bottom of chevron bracing to significantly increase the energy dissipation capacity level. In this paper first by studying the knee yielding mode, a suitable shape and angle for diagonal-knee bracing is proposed. Then finite elements models are developed. Monotonic and cyclic analyses have been conducted to compare dissipation capacities on three individual models of passive systems (CK-VLB, knee braced system and SPS system) by General-purpose finite element program ABAQUS in which a bilinear kinematic hardening model is incorporated to trace the material nonlinearity. Also quasi-static cyclic loading based on the guidelines presented in ATC-24 has been imposed to different models of CK-VLB with changing of vertical link beam section in order to find prime effectiveness on structural frames. Results show that CK-VLB system exhibits stable behavior and is capable of dissipating a significant amount of energy in two separate levels of lateral forces due to different probable earthquakes.

• Proceedings of the KIEE Conference
• /
• 1994.07a
• /
• pp.435-437
• /
• 1994

Cramped resonant DC link inverter is analyzed by widely available software such as SPICE. In this paper, the model of ACRDCL which is based on converter switch function rather than actual circuit configuration is used. Power circuit is modeled by functional transfer function and the controller is based on the macro-model. Computer memory and runtime are based reduced compared to micro-model. Overall performance including control strategy and harmonic characteristics in the steady state can be analyzed easily.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 1995.10a
• /
• pp.1009-1012
• /
• 1995

This paper presents an example of the development of motor drives for machine tools. Machine tools need motor drives with high control precision and performance. We developed a motor drive system that meets these requirements. The converter, the one component of drive system, adopts modular structure and high DC-link voltage. The drive which consists rest part of drive system is developed based on TMS320C32 DSP and state-of-the-art circuit technology. In this paper each developed parts are described in terms of its structure, specification and features.

• Proceedings of the Korean Operations and Management Science Society Conference
• /
• 1995.04a
• /
• pp.787-796
• /
• 1995

A man model is a useful design tool for the evaluation of man machine systems and products. An arm reach trajectory prediction for such a model will be specifically useful to present human activities and, consequently, could increase the accuracy and reality of the evaluation. In this study, a three-dimensional reach trajectory prediction model was developed using an inverse kinematics technique. The upper body was modeled as a four link open kinematic chain with seven degrees of freedom. The Resolved Motion Method used for the robot kinematics problem was used to predict the joint movements. The cost function of the perceived discomfort developed using the central composite design was also used as a performance function. This model predicts the posture by moving the joints to minimize the discomfort on the constraint of the end effector velocity directed to a target point. The results of the pairwise t-test showed that all the joint coordinates except the shoulder joint's showed statistically no differences at .alpha. = 0.01. The reach trajectory prediction model developed in this study was found to accurately simulate human arm reach trajectory and the model will help understand the human arm reach movement.