• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2008년도 춘계종합학술대회 A
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• pp.567-571
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• 2008

In this paper, an overview on the ordering sphere decoder (SD) class for space-time codes (STC) will be presented. In SDs, the ordering techniques are considered as promising methods for reducing complexity by exploiting a sorted list of candidates, thus decreasing the number of tested points. First, we will present the current state of art of SD with their advantages and disadvantages. Then, the overview of simply geometrical approaches for ordering is presented to address the question to overcome the disadvantages. The computer simulation results shown that, thanks to the aid of ordering, the ordering SDs can achieve optimal bit-error-rate (BER) performance while requiring the very low complexity, which is comparable to that of linear sub-optimal decoders.

• 한국산학기술학회논문지
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• 제3권2호
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• pp.120-125
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• 2002

본 논문은 전자상거래의 발전으로 인해 더욱 그 중요성이 부각되고 있는 중간창고(데포)에서의 발주시스템에 관한 연구이다. 제안 모델의 특징으로는 종래의 발주점 개념에서 발주범위라는 새로운 개념을 도입한 것이다. 제안 모델에서는 종래의 발주점 방식에서 고려하지 못 했던 다품종 발주와 발주시 적재효율을 고려한 수송조건 등을 포함하여 정식화하고 모델의 해법을 제안하고 있다. 또한 수치 예를 통하여 제안 모델의 유용성을 보여주고 있다.

• 대한산업공학회지
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• 제8권1호
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• pp.3-12
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• 1982

Three types of repair-ordering polices for the production facility with r-out-of-n configuration are considered. Policies are characterized by states of the system and two types of lead times ; regular lead time and expedited lead time. Optimum repair-ordering policy is determined by minimizing the cost rate for the system. Optimum policy consists of the type of policies and repair-ordering time. Variations of the optimum policies are observed with respect to variations of lead times and associated ordering costs and downtime cost, respectively.

• 한국경영과학회지
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• 제4권1호
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• pp.25-31
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• 1979

We consider the optimal ordering policy for a single-product two-stage inventory system where the main assumptions are as follows: (i) constant continuous demand only at stage 2, (ii) constant input (production) rate at stage 1, (iii) instantaneous delivery (transportation) from stage 1 to stage 2, (iv) backlogging is allowed only at stage 2, (v) an infinite planning horizon. Costs considered are ordering and linear holding costs at both stages, and linear shortage cost only at stages 2. By solving 9 different case problems, we have observed the general from of the optimal ordering policies for our model which minimizes the total cost per unit time. It is noticeable from this observation that the questionable but more often than not adopted assumption by many authors in determining the optimal potimal policy for multistage inventory systems, that the ordering (lot) sizes at each stage remain constant thruout the planning horizon, is not valid.

• 대한산업공학회지
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• 제3권1호
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• pp.39-47
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• 1977

Most of the current literature on inventory theory has been devoted to the study of single stage models. A class of inventory problems which is of great interest is the multistage inventory system which involves a series and hierarchical sequence of stations. This study analyzes some aspect of the series type and multi-stage inventory system, using the fixed cycle ordering which bas a modificatory control function in the system equations. The objective of this study is to clarify the dynamic behavior of the system. The author has derived the theoretical formulas of variation of ordering quantity and stock fluctuation of each stage due to power spectral density function. Influence of parameters such as, (1) intensity of autocorrelation of demand sequence ($\lambda$), (2) forecasting exponential smoothing factors of each stage (${\alpha}_1,\;{\alpha}_2,\;{\alpha}_3$) and (3) production control factor of the 3rd stage ($\gamma$), as operators of the system on the variation of ordering quantity and stock fluctuation of the system. is also clarified. As a result of this study, the relations between the variation of ordering quantity, stock fluctuation and the parameters of the system, have been found. The principles and the theorical analysis presented here will be applicable to more complex type of discrete control systems in constructing the specific condition of the system to minimize inventory variances.

• 산업경영시스템학회지
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• 제17권31호
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• pp.59-72
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• 1994

This paper deals with ordering policies of consumable goods which have large demand rates in a multi-level distribution system. The system we are concerned consists of one Central Distribution Center(CDC) and N non-identical Regional Distribution Centers(RDCs) which have different demand rates, minimum fillrates, leadtimes, etc. The customer demand on the RDC is stationary poisson and the RDCs demand on the CDC is superposition of Q-stage Erlang distributions. We approximate the RDCs and CDC demand distribution to nomal in order to enhance the efficiency of algorithm. The relevant costs include a fixed ordering cost and inventory holding cost, and backorder cost. The objective is to find a continuous-review ordering policy that minimizes the expected average costs under constraints of minimum fill rates of RDCs and maximum allowable mean delay of CDC. We developed an algorithm for determining the optimal ordering policies of the CDC and the RDCs. We verified and compared the performance of the algorithm through the simulation using the algorithm result as the input parameters.

• 한국경영과학회지
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• 제28권1호
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• pp.51-61
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• 2003

In the normal equations approach in which the ordering and factorization phases are separated, the factorization in the augmented system approach is computed dynamically. This means that in the augmented system the numerical factorization should be performed to obtain the non-zero structure of Cholesky factor L. This causes much time to set up the non-zero structure of Cholesky factor L. So, we present a method which can separate the ordering and numerical factorization in the augmented system. Experimental results show that the proposed method reduces the time for obtaining the non-zero structure of Cholesky factor L.

• Journal of Photoscience
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• 제5권4호
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• pp.153-155
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• 1998

The optical spectroscopic properties of the ordered perovskite structure A2BWO6 doped with Eu3+ have been studied. The experimental result about Eu3+ ordering in the system of A2BWO6 indicate the different structural conditions. Some influence of Eu3+ substitutioin on the different types of cation site have been investigated.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권3호
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• pp.494-507
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• 2011

In this paper, we propose two schemes to reduce the complexity of fixed-complexity sphere decoder (FSD) algorithm in the ordering and tree-search stages, respectively, while achieving quasi-ML performance. In the ordering stage, we propose a QR-decomposition-based FSD signal ordering based on the zero-forcing criterion (FSD-ZF-SQRD) that requires only a few number of additional complex flops compared to the unsorted QRD. Also, the proposed ordering algorithm is extended using the minimum mean square error (MMSE) criterion to achieve better performance. In the tree-search stage, we introduce a threshold-based complexity reduction approach for the FSD depending on the reliability of the signal with the largest noise amplification. Numerical results show that in 8 ${\times}$ 8 MIMO system, the proposed FSD-ZF-SQRD and FSD-MMSE-SQRD only require 19.5% and 26.3% of the computational efforts required by Hassibi's scheme, respectively. Moreover, a third threshold vector is outlined which can be used for high order modulation schemes. In 4 ${\times}$ 4 MIMO system using 16-QAM and 64-QAM, simulation results show that when the proposed threshold-based approach is employed, FSD requires only 62.86% and 53.67% of its full complexity, respectively.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제5권2호
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• pp.330-343
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• 2011

In this paper, we propose two schemes to reduce the complexity of fixed-complexity sphere decoder (FSD) algorithm in the ordering and tree-search stages, respectively, while achieving quasi-ML performance. In the ordering stage, we propose a QR-decomposition-based FSD signal ordering based on the zero-forcing criterion (FSD-ZF-SQRD) that requires only a few number of additional complex flops compared to the unsorted QRD. Also, the proposed ordering algorithm is extended using the minimum mean square error (MMSE) criterion to achieve better performance. In the tree-search stage, we introduce a threshold-based complexity reduction approach for the FSD depending on the reliability of the signal with the largest noise amplification. Numerical results show that in $8{\times}8$ MIMO system, the proposed FSD-ZF-SQRD and FSD-MMSE-SQRD only require 19.5% and 26.3% of the computational efforts required by Hassibi’s scheme, respectively. Moreover, a third threshold vector is outlined which can be used for high order modulation schemes. In $4{\times}4$ MIMO system using 16-QAM and 64-QAM, simulation results show that when the proposed threshold-based approach is employed, FSD requires only 62.86% and 53.67% of its full complexity, respectively.