• Proceedings of the Korean Information Science Society Conference
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• 2004.10a
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• pp.529-531
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• 2004

Just-Just-in-Time 컴파일러를 이용하여 자바의 성능을 향상시키려면 여러 문제들을 극복하여야 한다. 이 문제 중 중요한 부분을 차지하는 것이 null check 코드와 array bound check코드를 어떻게 최적화하느냐는 것이다. Static한 컴파일 환경에서는 이미 많은 연구가 진행되어 매우 강력한 성능을 가지는 알고리즘이 알려져 있으나 이를 컴파일 시간이 수행시간의 일부인 Just-in-Time 컴파일 환경에 적응하기에는 컴파일 오버헤드가 너무 커서 적절하지 않다. 현재 Just-in-Time 컴파일러들은 가볍고 단순한 알고리즘을 적용하지만 중복된 array bounds check를 충분히 제거하지 못하거나 아니면 강력하지만 flow-insensitive한 SSA form을 기반으로 해야 하는 알고리즘을 사용하고 있다. SSA form의 적용은 SSA form으로의 변환과 되돌림에 의한 overhead로 가볍고 빠른 컴파일러를 지향하는 Just-in-Time 컴파일러에 부합되지 않는다. 본 논문은 변수간의 대소관계를 표현하는 그래프를 array bounds check 알고리즘에 적용해 충분한 power를 내면서도 flow-sensitive한 환경에서 동작하는 알고리즘을 제안한다.

• Journal of KIISE:Software and Applications
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• v.32 no.12
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• pp.1283-1291
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• 2005

One of the problems in boosting Java performance using a Just-in-Time (JIT) compiler is removing redundant array bound checks. In conventional static compilers, many powerful algorithms have been developed, yet they are not directly applicable to JIT compilation where the compilation time is part of the whole running time. In the current JIT compilers, we tan use either a naive algorithm that is not powerful enough or an aggressive algorithm which requires the transformation into a static single assignment (SSA) form of programs (and back to the original form after optimization), thus causing too much overhead not appropriate for JIT compilation This paper proposes a new algorithm based on an inequality graph which can eliminate array bounds check codes aggressively without resorting to the SSA form. When we actually perform this type of optimization, there are many constraints in code motion caused by the precise exception rule in Java specification, which would cause the algorithm to miss many opportunities for eliminating away bound checks. We also propose a new method to overcome these constraints.

• Journal of Communications and Networks
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• v.1 no.3
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• pp.182-188
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• 1999

The optimal joint maximum-likelihood sequence estima-for using an array of antennas is derived for synchronous direct sequence-code division multiple access (DS-CDMA) system. Each user employs a rate 1/n convolutional code for channel coding for the additive white Gaussian noise (AWGN) channel. The array re-ceiver structure is composed of beamformers in the users' direc-tions followed by a bank of matched filters. The decoder is imple-mented using a Viterbi algorithm whose states depend on the num-ber of users and the constraint length of the convolutional code. The asymptotic array multiuser coding gain(AAMCG)is defined to encompass the asymptotic multiuser coding gain and the spatial information on users' locations in the system. We derive the upper and lower bounds of the AAMCG. As an example, the upper and lower bounds of AAMCG are obtained for the two user case where each user employes the maximum free distance convolutional code with rate 1/2. The enar-far resistance property is also investigated considering the number of antenna elements and user separations in the space.

• Bulletin of the Korean Mathematical Society
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• v.43 no.2
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• pp.443-459
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• 2006

The prey-predator system with a single cross-diffusion pressure is known to possess a local solution with the maximal existence time $T\;{\leq}\;{\infty}$. By obtaining the bounds of $W\array_2^1$-norms of the local solution independent of T we establish the global existence of the solution. And the long-time behaviors of the global solution are analyzed when the diffusion rates $d_1\;and\;d_2$ are sufficiently large.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.28 no.4
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• pp.919-928
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• 2018

Out-Of-Bounds (OOB) is one of the most powerful vulnerabilities in heap memory. The OOB vulnerability allows an attacker to exploit unauthorized access to confidential information by tricking the length of the array and reading or writing memory of that length. In this paper, we propose a method to automatically detect OOB vulnerabilities in heap memory using dynamic symbol execution and shadow memory table. First, a shadow memory table is constructed by hooking heap memory allocation and release function. Then, when a memory access occurs, it is judged whether OOB can occur by referencing the shadow memory, and a test case for causing a crash is automatically generated if there is a possibility of occurrence. Using the proposed method, if a weak block search is successful, it is possible to generate a test case that induces an OOB. In addition, unlike traditional dynamic symbol execution, exploitation of vulnerabilities is possible without setting clear target points.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.30 no.2
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• pp.169-172
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• 2019

Frequency-modulated continuous wave(FMCW) radars with array antennas are widely used because of their light weight and relatively high resolution. A usual approach for the joint range and angle estimation of a target using an array FMCW radar is to create a range-angle matrix with the deramped received signal, and subsequently apply two-dimensional(2D) frequency estimation methods such as 2D fast Fourier transform on the range-angle matrix. However, such frequency estimation approaches cause bias errors since the frequencies in the range-angle matrix are not independent. Therefore, we propose a new maximum likelihood-based algorithm for joint range and angle estimation of targets using array FMCW radar, and demonstrate that the proposed algorithm achieves the Cram?r-Rao bounds, both for range as well as angle estimation.

• Proceedings of the IEEK Conference
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• 2004.06a
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• pp.139-142
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• 2004

X-band Waveguide slot way antenna is developed for heliborne MTD radar applications. The antenna is composed of multi-layer waveguide structures. Each of them has it's own functions, such as, radiation, power/phase distribution, coupling, etc. Broad-wall offset slots are used for radiators, inclined slots on broad-wall for power distribution to radiating(branch) waveguide, some kind of coaxial probe structures for in-phase coupling and H-plane T-junction power dividers. Antenna is realized by precision machining and careful assembly. It is tested and measured by 3m${\times}$l.7m planar near-field probe, which is set-up in MTG. Far-field calculations have good agreement in tolerable bounds. Special but necessary process such as brazing, will increase the accuracy and performance. Results show promising possibilities of future applications for real systems.

• Journal of Korea Multimedia Society
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• v.11 no.12
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• pp.1697-1705
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• 2008

Several studies made for wireless mesh networks aim to optimize the capacity for wireless networks. Aside from protocol improvements, researches were also done on the physical layer particularly on modulation techniques and antenna efficiency schemes. This paper is concerned with the capacity improvements derived from using spatial diversity with smart adaptive array antennas. The use of spatial diversity, which has been widely proposed for use in cellular networks in order to lessen frequency re-use, can be used in mesh networks both to minimize co-channel interference (CCI) and enable multiple transmissions. This paper aims to study the capacity region and bounds in using smart antennas for single-channel multi-radio systems in relation to the number of spatial diversity or sectors as defined by the beam angle $\beta$.

• Proceedings of the Korea Information Processing Society Conference
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• 2004.05a
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• pp.309-312
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• 2004

임베디드 시스템은 특별한 목적을 수행하기 위해 컴퓨터 하드웨어와 소프트웨어를 결합시킨 것이다. 임베디드 시스템은 일반 데스크탑보다 작은 규모의 하드웨어에서 운영된다. 임베디드 시스템은 파워, 공간, 메모리 등의 여러 가지 환경적 요소에 제약을 받는다. 그리고 임베디드 시스템은 실시간으로 동작하기 때문에 임베디드 시스템에서 소프트웨어의 실패는 일반 데스크탑에서보다 훨씬 심각한 문제를 발생시킨다. 따라서 임베디드 시스템은 주어진 자원을 효율적으로 사용하여야 하고 임베디드 시스템의 실패율을 낮춰야만 한다. 치명적인 문제를 발생시킬 수 있는 임베디드 시스템의 실패의 원인 중 하나가 메모리에 관련한 문제이다. 임베디드 시스템 특정상 메모리 문제는 크게 하드웨어 기반의 메모리 문제와 소프트웨어 기반의 메모리 문제로 분류된다. 소프트웨어 기반의 메모리에 관련한 문제는 Memory Leak, Freeing Free Memory, Freeing Unallocated Memory, Memory Allocation Failed, Late Detect Array Bounds Write, Late Detect Freed Memory Write 등과 같은 것들이 있다. 본 논문에서는 임베디드 시스템의 메모리 관련에 대한 문제점을 파악하고 관련 툴을 연구하여 그 문제점들을 효율적으로 해결할 수 있는 기법을 점증적으로 연구하고자 한다.

• The KIPS Transactions:PartC
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• v.8C no.6
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• pp.693-702
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• 2001

One of the major characteristics of C language is that it allows us to use pointer type variables to access any area of virtual address space. So, we can read/write/execute from/to virtual memory area not controlled delicately by operating system. We can access such memory area by using format string and it can be a vulnerability of C language from the point of secure programming. In this paper, we analyze in detail the process of security attack based on format string and then exploit a new virus style attack which is stepwise and durable with some actual scenarios to warn the severity of it, and grope for some preliminary responding actions.