• Journal of the Korean Institute of Telematics and Electronics D
• /
• v.36D no.4
• /
• pp.34-41
• /
• 1999

Unlike the traditional radar system, Synthetic Aperture Radar(SAR) system is capable of imaging a target scene to ceertain degree of cross-range resolution. And this resolution is mainly depends on the size of aperture synthesized. Thus, a good system model and inversion scheme should be developed to actually give effect of synthesizing aperture size, which in turn gives better cross range resolution of reconstructed target scene. Among several inversion schemes for SAR imaging, we used an inversion scheme called wavefront reconstruction which has no approximation in wave propagation analysis, and tried to verify whether the collected data with synthesized aperture actually give the same support as that with physical aperture in the same size. To do this, we performed a signal subspace comparison of two imaging models with physical and synthesized arrays, respectively. Theoretical comparisons and numerical analysis using Gram-Schmidt procedures have been performed. The results showed that the synthesized array data fully span the physical array data with the same system geometry. This result strongly supports the previously proposed inversion scheme valuable in high resolution radar imaging.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.32 no.3
• /
• pp.233-244
• /
• 2014

Precise Point Positioning (PPP) is an increasingly recognized precisely the GPS/GNSS positioning technique. In order to improve the accuracy of PPP, the error sources in PPP measurements should be reduced as much as possible and the ambiguities should be correctly resolved. The correct ambiguity resolution requires a careful control of residual errors that are normally categorized into random and systematic errors. To understand effects from two categorized errors on the PPP ambiguity resolution, those two GPS datasets are simulated by generating in locations in South Korea (denoted as SUWN) and Hong Kong (PolyU). Both simulation cases are studied for each dataset; the first case is that all the satellites are affected by systematic and random errors, and the second case is that only a few satellites are affected. In the first case with random errors only, when the magnitude of random errors is increased, L1 ambiguities have a much higher chance to be incorrectly fixed. However, the size of ambiguity error is not exactly proportional to the magnitude of random error. Satellite geometry has more impacts on the L1 ambiguity resolution than the magnitude of random errors. In the first case when all the satellites have both random and systematic errors, the accuracy of fixed ambiguities is considerably affected by the systematic error. A pseudorange systematic error of 5 cm is the much more detrimental to ambiguity resolutions than carrier phase systematic error of 2 mm. In the $2^{nd}$ case when only a portion of satellites have systematic and random errors, the L1 ambiguity resolution in PPP can be still corrected. The number of allowable satellites varies from stations to stations, depending on the geometry of satellites. Through extensive simulation tests under different schemes, this paper sheds light on how the PPP ambiguity resolution (more precisely L1 ambiguity resolution) is affected by the characteristics of the residual errors in PPP observations. The numerical examples recall the PPP data analysts that how accurate the error correction models must achieve in order to get all the ambiguities resolved correctly.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.2
• /
• pp.94-100
• /
• 2007

An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with a modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures and large-scale instability waves.

• The Transactions of the Korea Information Processing Society
• /
• v.6 no.1
• /
• pp.115-122
• /
• 1999

This paper presents a key distribution scheme based on the Yacobi scheme that does not use the secret key provided by key distribution center, but uses instead a random number generated y the user. The scheme is independent of the exposure of the secret key. this paper also presented the key distribution schemes based on the Diffie-Hellman (DH) and ID (identity). The schemes based on the solving of the discrete logarithm and prime resolution into factors are better on the expose of secret key. The proposed scheme based on the DH was applied to VSAT satellite communications and simulated on PC using Montgomery algorithm for modular and MD5 (Message Digest) for hashing function.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
• /
• v.30 no.2
• /
• pp.189-197
• /
• 2012

This research attempted to find possibilities of the practical use utilizing geospatial methods for the balanced promotion of sustainable coastal development and preservation through a case study of Jekyll Island, one of Georgia's barrier islands. In response, this research provided ways for practical use in sustainable development and preservation plans. First this research thoroughly investigated the 1996 master plan of Jekyll Island and tried to recalculate developed and undeveloped areas. Second, new estimations for developed areas were investigated through field survey. Third, this research proposed the use of the satellite images with different levels of spatial resolutions and tested different classification schemes to find possibilities for practical use. For these purposes, first, we classified developed and undeveloped features by manual digitization using an aerial photo image with 0.5m spatial resolution. Second, a Landsat 7 ETM+ and a QuickBird satellite images with mid- and high-levels of spatial resolutions were applied to identify developed and undeveloped areas using both the National Land Cover Data (NLCD) and the Coastal Change Analysis Program (CCAP) classification schemes. Also, GEOBIA (Geographic Object-Based Image Analysis) was conducted to accurately identify developed and undeveloped areas.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2007.04a
• /
• pp.329-334
• /
• 2007

An axisymmetric supersonic jet screech in the Mach number range from 1.07 to 1.2 is numerically simulated. The axisymmetric mode is the dominant screech mode for an axisymmetric jet. The Reynolds-averaged Navier-Stokes equations in the conjunction with modified Spalart-Allmaras turbulence model are employed. A high resolution finite volume essentially non-oscillatory(ENO) schemes are used along with nonreflecting characteristic boundary conditions that are crucial to screech tone computations to accurately capture the sound waves, shock-cell structures, unsteady shock motions and large-scale instability waves.

• ETRI Journal
• /
• v.38 no.5
• /
• pp.922-933
• /
• 2016

IP header compression schemes offer a valuable measure for bandwidth preservation. Such schemes have been practically implemented in infrastructure-based IP networks for point-to-point links. However, minimal research and practical implementation efforts have been conducted in the direction of an IP header compression strategy that can meet the peculiar requirements of multi-hop ad hoc wireless networks. In this paper, we present a practically implemented multi-hop IP header compression scheme using the Robust Header Compression (ROHC) protocol suite. The scheme runs on a novel identifier (ID) based networking architecture, known as an ID-based ad hoc network (IDHOCNET). IDHOCNET additionally solves a number of bottlenecks of pure IP-based ad hoc networks that have emerged owing to IP address auto-configuration service, distributed naming and name resolution, and the role of an IP address as an identifier at the application layer. The proposed scheme was tested on a multi-hop test bed. The results show that the implemented scheme has better gain and requires only O (1) ROHC contexts.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.30 no.4
• /
• pp.143-152
• /
• 2018

Numerical convergence and stability of TVD schemes have been applied in the FUNWAVE-TVD model were compared. The fourth order accurate MUSCL-TVD scheme using minmod limiter suggested by Yamamoto and Daiguji (1993), the fourth order accurate MUSCL-TVD scheme using van-Leer limiter suggested by Erduran et al. (2005) and the second order accurate MUSCL-TVD scheme using van-Leer limiter in Zhou et al. (2001) were compared. Comparisons of the numerical scheme were conducted with experimental data of Vincent and Briggs irregular wave experiments. In comparison with the fourth order accurate scheme using van-Leer limiter, the fourth order accurate scheme using minmod limiter is less dissipative but required lower CFL condition for stable numerical solution. On the other hand, the scheme using van-Leer limiter required smaller resolution spatial grid due to numerical dissipation, but relatively higher CFL condition can be used compared to the scheme using minmod limiter. In the breaking wave experiments which were conducted using high resolution spatial grid to reduce numerical dissipation, the characteristic of the schemes can be clearly observed. Numerical instabilities and blow-up of the numerical solutions were found in the irregular wave breaking simulation with the scheme using minmod limiter. However, the simulation can be completed with the scheme using van-Leer limiter, but required low CFL condition. Good agreements with the observed data were also observed in the results using van-Leer limiter.

• Proceedings of the IEEK Conference
• /
• 2003.07a
• /
• pp.57-60
• /
• 2003

IEEE 802.16 Wireless MAN standard specifies the air interface of fixed point-to-multipoint broadband wireless access systems providing multiple service. Among the service classes supported by the wireless MAN, the BE class is ranked on the lowest position in priority and is usually deployed by multicast and broadcast polling MAC scheme. In provisioning such BE service, the delay performance is influenced by a number of components including restrictions on resource request per SS, the number of request opportunities in upward frame, scheduling requests at BS, and contention resolution method. As candidate components of MAC function for BE service, we propose single and multiple request schemes (for controling the number of requests per SS), exhaustive and limited request schemes (for regulating the amount of grant per request) and FCFS, H-SMF, pure SMF, SS-wise Round Robin, and pure Round Robin (for scheduling requests at BS). Then, we construct MAC schemes by combining the above components and evaluate the delay performance exhibited by each MAC scheme using a simulation method. From numerical results, we investigate the effect of MAC components on average delay and delay variation and observe the dissonance on collision reduction in a resource - limited environment.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.1
• /
• pp.65-73
• /
• 2004

In this paper, we propose a tunnel establishment scheme using Next Hop Resolution Protocol over mobile IP networks, which consist of LAN-based IP networks and ATM-based IP networks. As a basic idea, we use the shortest path algorithm to establish a short-cut tunnel between HA and FA. Also, we classify methods for establishing a short-cut tunnel into four cases considering the locations of HA, FA, CN and MN. To confirm the advantages of our schemes, which deliver packets using short-cut tunnel in optimized path method over mobile IP networks, we performed mathematical analysis and simulation, compared proposed schemes with existing IP routing method in terms of transmission delay between CN and MN. The simulation results show that our scheme have superior performance to that of existing IP routing mechanism, because the store-and-forward delay which occurred in IP routing mechanism is considerably reduced in short-cut tunnel over ATM networks.