• Journal of Information Technology Services
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• v.10 no.1
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• pp.117-133
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• 2011

In this paper, we present a frequency reassignment problem (FRP) arising from the reconfiguration of radio networks such as adding new base stations (BSs) and changing the number of frequencies assigned to BSs. For this problem, we develop an integer programming (IP) model that minimizes the sum of frequency reassignment cost and the cost for unsatisfied frequency demands, while avoiding interference among frequencies. To obtain tight lower bounds, we develop some valid inequalities and devise an objective function relaxation scheme. Also, we develop a simple but efficient heuristic procedure to solve large size problems. Computational results show that the developed valid inequalities are effective for improving lower bounds. Also, the proposed tabu search heuristic finds tight upper bounds with average optimality gap of 2.3%.

• Bulletin of the Korean Mathematical Society
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• v.50 no.5
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• pp.1725-1736
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• 2013

In this paper, we compute the images of homotopy groups of various classical Lie groups under the homomorphisms induced by the natural projections from those groups to irreducible symmetric spaces of classical type. We identify that those computations are certain lower bounds of Gottlieb groups of irreducible symmetric spaces. We use the lower bounds to compute some Gottlieb groups.

• Journal of applied mathematics & informatics
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• v.20 no.1_2
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• pp.1-16
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• 2006

The classical perturbation theory is extended to the weighted Kronecker product linear systems $W(A{\bigotimes}B)W\chi=h$. Upper bounds are derived for the normwise condition number.

• Communications for Statistical Applications and Methods
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• v.7 no.1
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• pp.257-268
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• 2000

As one of indirect ways to get an optimal answer for sensitive questions both lower and upper values are sometimes asked and collected. In this paper a statistical method is proposed to analyze this kind of data using graphics. This method could define each sample median and estimate an optimal value between lower and upper bounds. In particular we find that this method has similar explanations of an equilibrium price with demand and supply functions in Economics.

• Journal of Electrical Engineering and information Science
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• v.2 no.6
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• pp.56-63
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• 1997

Under most system assumptions, closed form solutions of performance measures for ATM switches with input queueing are not available. In this paper, we present expressions and bounds for the derivatives of cell loss probabilities with respect to the arrival rate evaluated at a zero arrival rate. These bounds are used to give an approximation by Taylor expansion, thereby providing an economical way to estimate cell loss probabilities in light traffic.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.2A
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• pp.138-143
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• 2006

We present upper bounds for the maximum-likelihood decoding performance of particular LDPC codes and turbo-like codes with particular interleavers. Previous research developed upper bounds for LDPC codes and turbo-like codes using ensemble codes or the uniformly interleaved assumption, which bound the performance averaged over all ensemble codes or all interleavers. Proposed upper bounds are based on the simple bound and estimated weight distributions including the exact several smallest distance terms because if either estimated weight distributions on their own or the exact several smallest distance terms only are used, an accurate bound can not be obtained.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.12C
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• pp.1150-1156
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• 2006

In this paper we derive some lower bounds on the linear complexity and upper bounds on the 1-error linear complexity over $F_p$ of M-ary Sidel'nikov sequences of period $p^m-1$ when $M\geq3$ and $p\equiv{\pm}1$ mod M. In particular, we exactly compute the 1-error linear complexity of ternary Sidel'nikov sequences when $p^m-1$ and $m\geq4$. Based on these bounds we present the asymptotic behavior of the normalized linear complexity and the normalized 1-error linear complexity with respect to the period.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.1
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• pp.193-214
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• 2017

In this paper, we study the problem of network utility maximization in a CSMA based multi-hop wireless network. Existing work in this aspect typically adopted continuous time Markov model for performance modelling, which fails to consider the channel conflict impact in actual CSMA networks. To maximize the utility of a CSMA based wireless network with channel conflict, in this paper, we first model its weighted network capacity (i.e., network capacity weighted by link queue length) and then propose a distributed link scheduling algorithm, called CSMA based Maximal-Weight Scheduling (C-MWS), to maximize the weighted network capacity. We derive the upper and lower bounds of network utility based on C-MWS. The derived bounds can help us to tune the C-MWS parameters for C-MWS to work in a distributed wireless network. Simulation results show that the joint optimization based on C-MWS can achieve near-optimal network utility when appropriate algorithm parameters are chosen and also show that the derived utility upper bound is very tight.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.1A
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• pp.43-47
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• 2000

In regions of low signal-to-noise ratio (SNR), performance analysis uses simulations of hybrid concatenated coding systems. However, for higher SNR regions beyond simulation capabilities, average upper bounds to bit error rate (BER) and word error rate (WER) are used. In [1], all weight enumerating functions are needed to obtain average bounds. In this paper, we use RSC as constituent codes, by using effective free distances instead of WEF, we derive average BER and WER bounds of hybrid concatenated convolutional codes (HCCC) and analyze the BER and WER over AWGN and Rayleigh/Rician fading channels.

• 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.