• ETRI Journal
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• 제43권6호
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• pp.978-990
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• 2021

This article presents techniques for improved estimation of symbol timing offset (STO) and carrier frequency offset (CFO) for dual-polarization (DP) orthogonal frequency division multiplex (DP-OFDM) systems. Recently, quaternion multiple-input multiple-output OFDM has been proposed for high spectral efficiency communication systems, which can flexibly explore different types of diversities such as space, time, frequency, and polarization. This article focuses on synchronization techniques for DP-OFDM systems using a cyclic prefix, where the application of quaternion algebra leads to new improved estimators. Simulations performed for DP system methods show faster reduction of STO estimator variance with a double-slope line in the logvariance line versus signal-to-noise ratio (SNR) plot compared with singlepolarization (SP) counterparts, and simulations for CFO estimates show a 3-dB gain of DP over SP estimates for same SNR values defined, respectively, for quaternion-valued or complex-valued signals. Cramer-Rao bounds for STO and CFO are derived for the synchronization methods, correlating with the observed gains of DP over SP OFDM systems.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제13권1호
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• pp.41-53
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• 2009

A primal-dual interior point method(IPM) not only is the most efficient method for a computational point of view but also has polynomial complexity. Most of polynomialtime interior point methods(IPMs) are based on the logarithmic barrier functions. Peng et al.([14, 15]) and Roos et al.([3]-[9]) proposed new variants of IPMs based on kernel functions which are called self-regular and eligible functions, respectively. In this paper we define a new kernel function and propose a new IPM based on this kernel function which has $O(n^{\frac{2}{3}}log\frac{n}{\epsilon})$ and $O(\sqrt{n}log\frac{n}{\epsilon})$ iteration bounds for large-update and small-update methods, respectively.

• Journal of Positioning, Navigation, and Timing
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• 제11권1호
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• pp.35-44
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• 2022

In this paper, a dual foot (DF)-PDR system is proposed for the fusion of integration (IA)-based PDR systems independently applied on both shoes. The horizontal positions of the two shoes estimated from each PDR system are fused based on a particle filter. The proposed method bounds the position error even if the walking time increases without an additional sensor. The distribution of particles is a non-Gaussian distribution to express the lateral error due to systematic drift. Assuming that the shoe position is the pedestrian position, the multi-modal position distribution can be fused into one using the Gaussian sum. The fused pedestrian position is used as a measurement of each particle filter so that the position error is corrected. As a result, experimental results show that position of pedestrians can be effectively estimated by using only the inertial sensors attached to both shoes.

• Journal of applied mathematics & informatics
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• 제30권1_2호
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• pp.127-133
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• 2012

We establish the polynomial convergence of a new class of path-following methods for SDLCP whose search directions belong to the class of directions introduced by Monteiro [3]. We show that the polynomial iteration-complexity bounds of the well known algorithms for linear programming, namely the short-step path-following algorithm of Kojima et al. and Monteiro and Alder, carry over to the context of SDLCP.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제13권3호
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• pp.189-202
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• 2009

In this paper we propose new primal-dual interior point algorithms for $P_*(\kappa)$ linear complementarity problems based on a new class of kernel functions which contains the kernel function in [8] as a special case. We show that the iteration bounds are $O((1+2\kappa)n^{\frac{9}{14}}\;log\;\frac{n{\mu}^0}{\epsilon}$) for large-update and $O((1+2\kappa)\sqrt{n}log\frac{n{\mu}^0}{\epsilon}$) for small-update methods, respectively. This iteration complexity for large-update methods improves the iteration complexity with a factor $n^{\frac{5}{14}}$ when compared with the method based on the classical logarithmic kernel function. For small-update, the iteration complexity is the best known bound for such methods.

• 대한조선학회지
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• 제23권2호
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• pp.27-32
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• 1986

This paper describes an application of the adaptive finite element computations to a free surface flow problem in a canal. A-posteriori error estimates for the adaptive finite element computations are based on the dual extremum principles. Previously the dual extremum principles were applied to compute the upper and lower bounds of the added mass of two-dimensional cylinders in a canal[1,2]. However, the present method improves the convergence of the computed results by utilizing the local error estimates and by applying the adaptive meshes in the finite element computations. In a test result using triangular elements it is shown that the numerical error in the adaptive finite elements reduces quadratically compared with that in a uniform mesh subdivision.

• ETRI Journal
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• 제36권4호
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• pp.625-634
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• 2014

This paper studies a dual-hop multiple-access relay network where two independent source nodes transmit information to a common destination node with the aid of multiple single-antenna amplify-and-forward relays. Each relay node is subject to an individual power constraint. We focus on the design of distributed beamforming schemes for the relays to support the transmission rate requirements of the two sources. To this end, we first characterize the achievable rate region for this network via solving a sequence of corner point optimization problems proposed in this paper. We also develop several low-complexity suboptimal schemes in closed form. Two inner bounds of the achievable rate region are theoretically shown to be approximately optimal in two special scenarios. Finally, numerical results demonstrate the effectiveness of our proposed approaches.

• 한국산학기술학회논문지
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• 제16권7호
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• pp.4918-4924
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• 2015

본 논문은 비가시선 채널 환경에서 이중 편파 안테나를 이용하여 두 명의 사용자에게 데이터를 전송하는 시스템의 전송 용량 향상 방안을 고려한다. 이것을 위해 이 시스템의 멀티캐스트 및 유니캐스트 평균 채널 용량의 상한 분석을 수행하여 평균 채널 용량을 최대화하는 복소 교차 편파 식별도의 조절 조건을 제안한다. 또한 최대 평균 채널 용량에 근접한 성능을 달성하면서 동시에 시스템 복잡도를 줄일 수 있는 복소 교차 편파 식별도 조절 조건 역시 제시한다. 마지막으로 시뮬레이션 기반 성능 검증을 통해 제안한 조절 조건을 이용하는 시스템이 현존하는 복소 교차 편파 식별도 조절 조건을 포함한 다양한 다른 조절 조건을 채용하는 시스템 보다 높은 주파수 이용 효율을 획득할 수 있음을 보인다.

• 한국컴퓨터정보학회논문지
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• 제20권12호
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• pp.45-52
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• 2015

We propose a hybrid prefix caching scheme to enable high speed IP address lookup. All prefixes loaded in a prefix cache should not be overlapped in address range for correct IP lookup. So, every non-leaf prefix needs to be expanded not so as to be overlapped. The shorter expanded prefix is more preferable because it can cover wider address range just as an single entry in a prefix cache. We exploits advantages of two dynamic prefix expansion techniques, bounded prefix expansion technique and bitmap-based prefix expansion technique. The proposed scheme uses dual bound values whereas just one bound value is used in bounded prefix expansion. Our elaborated technique make the dual bound values be associated with several subtries flexibly using bitmap information, rather than with fixed subtries. We evaluate the performance of the proposed scheme in terms of the average length of the expanded prefixes and cache miss ratio. The experiment results show the proposed scheme has lower cache miss ratio than other previous schemes including both bounded prefix expansion and bitmap-based expansion irrespective of the cache size.

• Management Science and Financial Engineering
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• 제14권2호
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• pp.67-87
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• 2008

Data envelopment analysis (DEA) has proven to be a useful tool for assessing efficiency or productivity of organizations which is of vital practical importance in managerial decision making. While DEA assumes exact input and output data, the development of imprecise DEA (IDEA) broadens the scope of applications to efficiency evaluations involving imprecise information which implies various forms of ordinal and bounded data possibly or often occurring in practice. The primary purpose of this article is to characterize the variable efficiency in IDEA. Since DEA describes a pair of primal and dual models, also called envelopment and multiplier models, we can basically consider two IDEA models: One incorporates imprecise data into envelopment model and the other includes the same imprecise data in multiplier model. The issues of rising importance are thus the relationships between the two models and how to solve them. The groundwork we will make includes a duality study which makes it possible to characterize the efficiency solutions from the two models. This also relates to why we take into account the variable efficiency and its bounds in IDEA that some of the published IDEA studies have made. We also present computational aspects of the efficiency bounds and how to interpret the efficiency solutions.