• Journal of the Institute of Electronics Engineers of Korea SD
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• v.41 no.8
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• pp.105-113
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• 2004

MRAM uses magneto-resistance material as a storage element, which stores cell data as a polarization of spin in a free magnetic layer. This magneto-resistance material has hysteresis, asteroid curve at the thermal variation, and R-V characteristics for switching the data. Therefore, a macro-model which can reproduce these characteristics is required for MRAM simulation. We propose a macro-model of TMR (Tunneling Magneto Resistance) that can reproduce all of these characteristics on HSPICE. Also we propose a novel sensing scheme, which generates reference resistance having the medium value, ( $R_{H}$+ $R_{L}$)/2, for a wide range of applied voltage and present simulation results based on the HSPICE macro-model of MTJ that we have developed.d.d.

• Proceedings of the IEEK Conference
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• 2006.06a
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• pp.525-526
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• 2006

A macro model for Savtchenko switching mode MRAM (toggling MRAM) cells which can be utilized to develop the core architecture and the peripheral circuitry is proposed, and a writing scheme suitable to the toggling characteristic is developed. The sensing and writing operations of the toggling MRAM adopting the macro model are verified by Spectre simulations.

• Proceedings of the IEEK Conference
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• 2003.07b
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• pp.863-866
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• 2003

Recently, there has been growing interests in the magneto-resistive random access memory (MRAM) because of its great potential as a future nonvolatile memory. In this paper, a CMOS macro-model for MRAM cell based on a twin cell structure is proposed. The READ and WRITE operations of the MTJ cell can be emulated by adopting data latch and switch blocks. The behavior of the circuit is confirmed by HSPICE simulations in a 0.35-${\mu}{\textrm}{m}$ CMOS process. We expect the macro model can be utilized to develope the core architecture and the peripheral circuitry. It can also be used for the characterization and the direction of the real MTJ cells.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.9
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• pp.1596-1612
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• 2011

Coordinated Multi-Point (CoMP) transmission / reception is being studied in Long Term Evolution-Advanced (LTE-A) for future evolution of the $3^{rd}$ Generation Partnership Project (3GPP) LTE. Support of soft handover is essential for improving the performance of cell edge users. CoMP provides a natural framework for enabling soft handover in the LTE system. This paper evaluates the soft handover gain in LTE-A downlink. Mathematical analysis of signal to interference plus noise ratio (SINR) gain and the handover margins for soft handover and hard handover are derived. CoMP system model is developed and an inter-cell and intra-cell interference model is derived, taking into account the pathloss, shadowing, cell loading, and traffic activity. Reference signal received power (RSRP) is used to define the triggers and the measurements for soft handover. Our results indicate that parameter choices such as handover margin and the CoMP set size impact CoMP performance gain.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.4
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• pp.1481-1500
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• 2016

Device-to-Device (D2D) communication underlaying macro-small cell networks, as one of the promising technologies in the era of 5G, is able to improve spectral efficiency and increase system capacity. In this paper, we model the cross- and co-tier D2D communications in two-tier macro-small cell networks. To avoid the complicated interference for cross-tier D2D, we propose a mode selection scheme with a dedicated resource sharing strategy. For co-tier D2D, we formulate a joint optimization problem of power control and resource reuse with the aim of maximizing the overall outage capacity. To solve this non-convex optimization problem, we devise a heuristic algorithm to obtain a suboptimal solution and reduce the computational complexity. System-level simulations demonstrate the effectiveness of the proposed method, which can provide enhanced system performance and guarantee the quality-of-service (QoS) of all devices in two-tier macro-small cell networks. In addition, our study reveals the high potential of introducing cross- and co-tier D2D in small cell networks: i) cross-tier D2D obtains better performance at low and medium small cell densities than co-tier D2D, and ii) co-tier D2D achieves a steady performance improvement with the increase of small cell density.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2243-2257
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• 2019

A heterogeneous cellular network (HCN) is useful to increase the spectral and energy efficiency of wireless networks and to reduce the traffic load from the macro cell. The performance of the secondary user equipment (SUE) is affected by interference from the eNodeB (eNB) in a macro cell. To decrease the interference between the macro cell and the small cell, allocating resources properly is essential to an HCN. This study considers the scenario of a software-defined heterogeneous cellular network and performs the resource allocation process. First, we show the system model of HCN and formulate the optimization problem. The optimization problem is a complex process including power and frequency resource allocation, which imposes an extremely high complexity to the HCN. Therefore, a hierarchical resource allocation scheme is proposed, which including subchannel selection and a particle swarm optimization (PSO)-based power allocation algorithm. Simulation results show that the proposed hierarchical scheme is effective in improving the system capacity and energy efficiency.

• Journal of Advanced Navigation Technology
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• v.15 no.2
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• pp.307-312
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• 2011

In the macro/femto cellular networks, the portion of channels assigned to each cell is a critical factor which sets the stability and the performance of the whole system. To grasp the concrete influence that the channel split portion have on the system, we present the queueing model for IP based macro/femto cellular networks, and find the stability conditions. Additionally we provide the strategy to decide the portion of channels allocated to each cell. Through the experiments, we prove that the proposed strategies operate feasibly in various network environments, and on the basis of these results we discuss the efficient system structure plan.

• Proceedings of the Korean Magnestics Society Conference
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• 2003.12a
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• pp.222-222
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• 2003

• Computers and Concrete
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• v.27 no.4
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• pp.385-393
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• 2021

Reinforcement corrosion is the main cause of the durability failure of reinforced concrete (RC) structure. In this paper, a three-dimensional (3D) numerical model of macro-cell corrosion is established to reveal the corrosion mechanisms of steel reinforcement in RC structure. Modified Direct Iteration Method (MDIM) is employed to solve the system of partial differential equations for reinforcement corrosion. Through the sensitivity analysis of electrochemical parameters, it is found that the average corrosion current density is more sensitive to the change of cathodic Tafel slope and anodic equilibrium potential, compared with the other electrochemical parameters. Furthermore, both the anode-to-cathode (A/C) ratio and the anodic length have significant influences on the average corrosion current density, especially when A/C ratio is less than 0.5 and anodic length is less than 35 mm. More importantly, it is demonstrated that the corrosion rate of semi-circumferential corrosion is much larger than that of circumferential corrosion for the same A/C ratio value. The simulation results can give a unique insight into understanding the detailed electrochemical corrosion processes of steel reinforcement in RC structure for application in service life prediction of RC structures in actual civil engineer.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.11
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• pp.1387-1401
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• 2016

When a closed access policy in which only an authorized user is allowed to access to a given base station (BS) has been employed in heterogeneous cellular networks, a macro-cell user is used to experience strong cross-tier interference from its adjacent small-cell BSs to which the user is not allowed to access. To mitigate this problem, it has been proposed that a small-cell BS employs a beamforming vector which is orthogonal to the channel of the victim user. However, this technique requires considerable mutual exchange of information among the macro-cell BS, the macro-cell user, and the small-cell BS. In this paper, we propose a cognitive beamforming scheme, in which a small-cell BS employs the beamforming orthogonal to the victim users' channel without any explicit mutual information exchange. Particularly, the small-cell BS finds small- and macro-cell users experiencing the co-tier and cross-tier interferences from it, respectively. Then, it employs a beamforming which is orthogonal to the victim users' channels to mitigate the co-tier and cross-tier interferences. Using the system-level simulation, we demonstrate that the proposed scheme effectively mitigates the cross-tier interference problem.