Sung-Woong Ra

A tree key graph design scheme for hierarchical multi-group access control

A tree key graph design scheme for hierarchical multi-group access control with low communication overhead is presented. A simulation result shows that the proposed scheme can reduce a communication overhead up to about 15.2% compared to the previously proposed scheme.

An analysis of isometry transforms in frequency domain for fast fractal encoding

A new fast fractal encoding algorithm, which minimizes the iterations of isometry transforms for each domain block, is proposed. The effects of isometry transforms are analyzed in the Walsh-Hadamard transform (WHT) domain, and the search for the minimum Euclidean-distance isometry transform to a range block starts with the one having the minimum feature distance. The search is then terminated with the test reports that the remaining isometry transforms have larger distances than current minimum distance. The second and third low frequency coefficients of WHT are used as the features of the image blocks. The simulation results confirmed that our algorithm produces a completely identical fractal code, including minimum distance isometry transform, to that of the conventional full search in reduced time.

A Development of Reflector for CAL/VAL of SAR Satellite

The payload can be classified as a passive and active type. Generally radar satellite to acquire specific information through various radar images will use the SAR (Synthetic Aperture Radar) as active type payload. the principal of SAR satellite is to receive the signal returned from certain objects and/or surfaces in order to construct an radar image. The data acquired from the satellite in its real orbit shall be needed to perform successful CAL/VAL (Calibration & Validation) because the SAR satellite have to receive the returned signal for SAR image construction. In order to do the above, the returned signal shall be related to ground targets. Especially ground target is the corner reflector (CR) for CAL/VAL. Generally the reflector has various types and shapes. Their selection can be dependent on characteristics and mission objectives of SAR satellite. In this paper, reflector focused on the optimal case and effective case has been studied and then the trihedral corner reflector under this study has been designed and its performance also analyzed.

The Analysis on the relation between the Compression Method and the Performance Enhancement of MSC(Multi-Spectral Camera) Image data

Multi-Spectral Camera(MSC) is a main payload on the KOMPSAT-2 satellite to perform the earth remote sensing. The MSC instrument has one(1) channel for panchromatic imaging and four(4) channel for multi-spectral imaging covering the spectral range from 450nm to 900nm using TDI CCD Focal Plane Array (FPA). The instrument images the earth using a push-broom motion with a swath width of 15 km and a ground sample distance (GSD) of 1 m over the entire field of view (FOV) at altitude 685 Km. The instrument is designed to have an on-orbit operation duty cycle of 20% over the mission lifetime of 3 years with the functions of programmable gain/ offset and on-board image data compression/ storage. The compression method on KOMPSAT-2 MSC was selected and used to match EOS input rate and PDTS output data rate on MSC image data chain. At once the MSC performance was carefully handled to minimize any degradation so that it was analyzed and restored in KGS(KOMPSAT Ground Station) during LEOP and Cal./Val.(Calibration and Validation) phase. In this paper, on-orbit image data chain in MSC and image data processing on KGS including general MSC description is briefly described. The influences on image performance between on-board compression algorithms and between performance restoration methods in ground station are analyzed, and the relation between both methods is to be analyzed and discussed.

Mission Planning and Control Analysis Algorithms for the Safe Flight of an Unmanned Aerial Vehicle

An unmanned aerial vehicle (UAV) is generally flied via a pre-planned flight path or real-time commands by an operator. To succeed in an assigned mission, analysis such as the line-of-sight analysis for communication between UAV and a ground data terminal should be performed. In this paper, various analysis algorithms which are performed by a ground control station in pre-flight and in-flight phases, are proposed for the safe flight of UAV. Note that the proposed algorithms can be applied to most UAV systems.

The design of MSC (multi-spectral camera) system operation

Multi-spectral camera (MSC) is a payload on the KOMPSAT-2 satellite to perform the Earth remote sensing. The instrument images the Earth using a push-broom motion with a swath width of 15 km and a ground sample distance (GSD) of 1 m over the entire field of view (FOV) at altitude 685 Km. The installment is designed to have an on-orbit operation duty cycle of 20% over the mission lifetime of 3 years with the functions of programmable gain/ offset and onboard image data compression/storage. The MSC instrument has one (1) channel for panchromatic imaging and four (4) channels for multi-spectral imaging covering the spectral range from 450 nm to 900 nm using TDI CCD Focal Plane Array (FPA). In this work, the architecture and function of MSC hardware including electrical interface and the operation concept which have been established based on the mission requirements are described. The design and the preparation of MSC system operation are analyzed and discussed.

Scene-adaptive bit rate control strategy

An effective bit rate control scheme is one of the most important issues in the video coding algorithm for the transmission of high quality images through the band limited channel. An MPEG2 three step rate control algorithm is well suited for high compression of normal pictures maintaining good quality. But it is well known that the MPEG2 rate control algorithm can not handle scene change efficiently. In this paper, we present a simple rate control algorithm which is capable of handling scene changed pictures efficiently. The algorithm assigns more bits to scene changed pictures and fewer bits to previous pictures maintaining the total bit rate. We also propose a method that can estimate the complexity of a picture using the activity of the picture. The estimated complexity is usefully used as a rate control parameter in coding of scene changed picture. Simulation results show that proposed algorithm enhance the visual qualities after scene change.

Robust Least Squares Motion Deblurring Using Inertial Sensor for Strapdown Image IR Sensors

This paper proposes a new robust motion deblurring filter using the inertial sensor measurements for strapdown image IR applications. With taking the PSF measurement error into account, the motion blurred image is modeled by the linear uncertain state space equation with the noise corrupted measurement matrix and the stochastic parameter uncertainty. This motivates us to solve the motion deblurring problem based on the recently developed robust least squares estimation theory. In order to suppress the ringing effect on the deblurred image, the robust least squares estimator is slightly modified by adoping the ridge-regression concept. Through the computer simulations using the actual IR scenes, it is demonstrated that the proposed algorithm shows superior and reliable motion deblurring performance even in the presence of time-varying motion artifact.

Robustness and Actuator Bandwidth of MRP-Based Sliding Mode Control for Spacecraft Attitude Control Problems

Nonlinear sliding surface design in variable structure systems for spacecraft attitude control problems is studied. A robustness analysis is performed for regular form of system, and calculation of actuator bandwidth is presented by reviewing sliding surface dynamics. To achieve non-singular attitude description and minimal parameterization, spacecraft attitude control problems are considered based on modified Rodrigues parameters (MRP). It is shown that the derived controller ensures the sliding motion in pre-determined region irrespective of unmodeled effects and disturbances.

An Active Entitlement Key Management for Conditional Access System on Digital TV Broadcasting Network

Conditional access system (CAS) performs entitlement management to make only legitimate subscribers watch pay-services. Generally, CAS uses passive entitlement management to fulfil that entitlement control, and various schemes are existed for that. Among them, Tu introduced two schemes in F.K. Tu et al., (1999), which are the simple scheme and complete scheme of four levels hierarchy. The advantage of the simple scheme of four levels hierarchy is a small key generation and encryption load for a CAS, but it is not good for the dynamic entitlement management. On the other hand, the complete scheme of four levels hierarchy is good for the dynamic entitlement management, but key generation and encryption load for CAS is considerable when it is compared to the simple scheme. In this circumstance, we proposed a novel scheme, which is an active entitlement key management. The proposed scheme not only performs the dynamic entitlement management very efficiently, but also generates and encrypts keys with a small load for CAS, which is just the same as the load of the simple scheme