• Journal of information and communication convergence engineering
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• v.4 no.1
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• pp.5-9
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• 2006

In this paper, a low-complexity ML decoder based on QR decomposition, called LCMLDec decoder, is proposed for the V-BLAST with 2 transmit antennas. Then, it is combined with other suboptimal interference nulling and cancelling decoders originated form QR decomposition such as sorted QR or MMSE-SQRD decoder to generate efficient decoders that significantly improve the performance of the V-BLAST with more than 2 transmit antennas, at the expense of a small increase in complexity. Simulation results are provided to demonstrate the performances and complexities of the proposed decoders.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.2311-2313
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• 2000

In this paper, we consider $H^{\infty}$ optimal Kalman filter problems for linear weakly coupled stochastic systems. We introduce a decomposition for the systems of the Hamiltonian form, which plays an important role of exclusion of ill-condition by ${\varepsilon}$-effect and the parallel computation possibility. It is shown that the algebraic Riccati equation of the weakly coupled $H^{\infty}$ optimal Kalman filter problem is decoupled into completely independent reduced-order, well-defined, two suboptimal Kalman filters.

• ETRI Journal
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• v.37 no.5
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• pp.906-916
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• 2015

High-speed I/O channels require adaptive techniques to optimize the settings for filter tap weights at decision feedback equalization (DFE) read channels to compensate for channel inter-symbol interference (ISI) and crosstalk from multiple adjacent channels. Both ISI and crosstalk tend to vary with channel length, process, and temperature variations. Individually optimizing parameters such as those just mentioned leads to suboptimal solutions. We propose a joint optimization technique for crosstalk cancellation (XTC) at DFE to compensate for both ISI and XTC in high-speed I/O channels. The technique is used to compensate for between 15.7 dB and 19.7 dB of channel loss combined with a variety of crosstalk strengths from $60mV_{p-p}$ to $180mV_{p-p}$ adaptively, where the transmit non-return-to-zero signal amplitude is a constant $500mV_{p-p}$.

• ETRI Journal
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• v.38 no.5
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• pp.934-940
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• 2016

In this paper, secure multicasting with the help of cooperative decode-and-forward relays is considered for the case in which a source securely sends a common message to multiple destinations in the presence of a single eavesdropper. We show that the secrecy rate maximization problem in the secure multicasting scenario under an overall power constraint can be solved using semidefinite programing with semidefinite relaxation and a bisection technique. Further, a suboptimal approach using zero-forcing beamforming and linear programming based power allocation is also proposed. Numerical results illustrate the secrecy rates achieved by the proposed schemes under secure multicasting scenarios.

• Journal of Ginseng Research
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• v.7 no.1
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• pp.74-79
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• 1983

Effect of soil moisture on content and partition of mineral nutients in panax ginseng (2 years old) was investigated. Similarity was found between N and p, Ca and Mg, K and Fe. Mn and Zn were quite different each other and from others. Nutrient partition was affected more by nutrient content than by dry matter. Under suboptimal moisture condition partition to shoot was inhibited in order of Mg, Zn, Ca, Mg, N and P while accelerated in odor of Fe. K and Mn. Under supraoptimal moisture condition Partition to shoot was inhibited in order of Zn, Fe, K, and Ca, while accelerated in order of Mg, N, Mn and p.

• ETRI Journal
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• v.38 no.1
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• pp.62-69
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• 2016

In this paper, we propose two novel user selection algorithms for multiuser multiple-input and multiple-output downlink wireless systems, in which both a base station (BS) and mobile stations (MSs) are equipped with multiple antennas. Linear transmit beamforming at the BS and receive combining at the MSs are used to avoid interference between users and find a better sum-rate capacity performance. An optimal technique for selecting users would entail an exhaustive search, which in practice becomes computationally complex for a realistic number of users. Suboptimal algorithms with low complexity are proposed for a coordinated beamforming scheme. Simulation results show that the performance of the proposed algorithms is better than that provided by previous algorithms and is very close to an optimal approach with reduced complexity.

• ETRI Journal
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• v.36 no.4
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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.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.3
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• pp.218-223
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• 2012

Maintenance and improvement of the graph connectivity is very important for decentralized multi-agent systems. Although the CBBA (Consensus-Based Bundle Algorithm) guarantees suboptimal performance and bounded convergence time, it is only valid for connected graphs. In this study, we apply a decentralized estimation procedure that allows each agent to track the algebraic connectivity of a time-varying graph. Based on this estimation, we design a decentralized gradient controller to maintain the graph connectivity while agents are traveling to perform assigned tasks. Simulation result for fully-actuated first-order agents that move in a 2-D plane are presented.

• East Asian mathematical journal
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• v.32 no.1
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• pp.101-115
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• 2016

In this paper, we consider a semi-discrete mixed discontinuous Galerkin method with an interior penalty to approximate the solution of parabolic problems. We define an auxiliary projection to analyze the error estimate and obtain optimal error estimates in $L^{\infty}(L^2)$ for the primary variable u, optimal error estimates in $L^2(L^2)$ for ut, and suboptimal error estimates in $L^{\infty}(L^2)$ for the flux variable ${\sigma}$.

• Smart Structures and Systems
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• v.10 no.6
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• pp.573-591
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• 2012

In this study, a procedure to design an optimal LCVA that maximizes the equivalent damping ratio added to the primary structure subjected to along-wind excitation is proposed. That design procedure does not only consider the natural frequency and damping ratio of the LCVA, but also the proportion of the U-shaped liquid, which is closely related to the participation ratio of the liquid mass in inertial force. In addition, constraints to ensure the U-shape of the liquid are considered in the design process, so that suboptimal solutions that violate the optimal tuning law partly are adopted as a candidate of the optimal LCVA. The proposed design procedure of the LCVA is applied to the control of the 76-story benchmark building, and the optimal proportions of the liquid shape under various design conditions are compared.