Kisong Lee

Cooperative Resource Allocation for Guaranteeing Intercell Fairness in Femtocell Networks

In this letter, we focus on intercell fairness in OFDM femtocell networks. Serious degradation of any cell cannot ensure fairness for entire network, thus, intercell fairness is important for the satisfaction of all users. In order to improve intercell fairness, we devise a cooperative resource-allocation algorithm, which is an enhanced modified iterative water-filling (EMIWF). The proposed algorithm takes account into cell capacity and traffic load at the same time in power allocation. So, each femto base station allocates power in order to reduce the interference that it causes to a femtocell which experiences severe capacity degradation or has heavy traffic load. Through intensive simulations, we show that the EMIWF enhances intercell fairness with negligible degradation in view of system capacity.

Diversity Analysis of Multiple Transmitters in Wireless Power Transfer System

Nonradiative wireless power transfer is a popular technology that transfers energy over medium range via strongly coupled magnetic resonance. We investigated the effect of transmit diversity on power transfer efficiency under multiple transmitters. We derived closed-form equations for the power transfer efficiency and the optimal load from both coupled mode theory and equivalent circuit model analyses. We also showed that the analytical results obtained from the two types of analysis are basically the same, so they can be expressed as an equivalent equation that consists of a quality factor and coupling coefficient. In addition, we performed simulations using the Ansoft High Frequency Structure Simulator and the Agilent Advanced Design System to demonstrate the accuracy of our analysis. The results show that a multiple-transmitter wireless power-transfer system can improve power transfer efficiency over all regions in both an angular aligned scenario and an angular misaligned scenario, due to the diversity in the transfer of power.

Collaborative Resource Allocation for Self-Healing in Self-Organizing Networks

The main objectives of a self-organizing network (SON) technology are autonomous network deployment, network performance optimization and real-time adaptation to environmental changes. There are three functionalities in SON, such as self-configuration, self-optimization and self-healing. In this paper, we focus on the self-healing issue with respect to abrupt network faults. In order to solve this problem, we design a healing channel (HC) and propose a collaborative resource allocation (CRA) algorithm based on a modified iterative water-filling (MIWF) algorithm. Through intensive simulations, we show that CRA efficiently supports users in disabled femtocell base stations (FBS) with the little degradation in system capacity.

Effect of DA-9701, a novel prokinetic agent, on stress-induced delayed gastric emptying and hormonal changes in rats

Background  DA‐9701 is a novel prokinetic agent formulated with Pharbitis Semen and Corydalis Tuber. This study aimed to evaluate the effect of DA‐9701 on stress‐induced delay in gastric emptying and changes in plasma adrenocorticotropic hormone and ghrelin levels in rats.

Analysis of Wireless Power Transfer for Adjustable Power Distribution among Multiple Receivers

In a multiple-receiver wireless power transfer system, most of the power tends to be transferred to a receiver close to a transmitter. Therefore, it is highly desirable to find a way of providing the required amount of power to each receiver, as well as to improve the overall power transfer efficiency. In this letter, we investigate an impedance matching method of providing adjustable power distribution among receivers while preserving a high overall power transfer efficiency using coupled mode theory and circuit model. We also derive an optimal matching condition and the upper bound of the overall power transfer efficiency, in order to assess the performance of the proposed method. Finally, we perform circuit-level simulations to validate the accuracy of our analysis and the effectiveness of the proposed method.

CoBRA: Cooperative Beamforming-Based Resource Allocation for Self-Healing in SON-Based Indoor Mobile Communication System

For the purpose of automating network management, self-organizing network (SON) technology is currently being investigated. There are three important issues in SON: self-configuration, self-optimization, and self-healing. This paper focuses on self-healing, in order to resolve the problem of unexpected network faults and improve network throughput simultaneously. To deal with this problem, we propose a healing channel selection and a cooperative beamforming-based iterative resource allocation algorithms. We utilize the cooperative beamforming in the healing channel based on phase pre-adjustment, and this cooperative beamforming can be performed without power cooperation between distributed nodes. Moreover, we derive the sub-optimality and convergence of the proposed algorithm in weak interference condition by using contraction mapping. Finally, simulation results demonstrate that the proposed algorithm improves average cell capacity and user fairness while repairing network failure effectively.

Cooperation based resource allocation for improving inter-cell fairness in femtocell systems

In this paper, we focus on the guarantee of inter-cell fairness in OFDM femtocell systems. To solve this problem, we formulate an optimization problem to maximize the summation of logarithmic cell capacity. Based on analytic results, we propose an enhanced modified iterative water-filling algorithm which improves inter-cell fairness compared to a modified iterative water-filling algorithm. The key feature of the proposed algorithm is that each cell performs power allocation to minimize the interference that it causes to a heavy traffic cell to ensure the inter-cell fairness. We verify the effectiveness of the proposed algorithm with respect to fairness improvement and the little degradation of sum capacity by intensive simulations.

Energy-Efficient Resource Allocation for Simultaneous Information and Energy Transfer With Imperfect Channel Estimation

Energy harvesting (EH) from background radio-frequency signals has recently started to be considered as a promising means of mitigating energy deficiencies in wireless sensors that have limited battery power. In this paper, to deal with the problem of energy shortage, we consider EH and energy efficiency, which is the ratio of the amount of data transferred to the energy dissipated within the system, at the same time. We formulate a nonconvex optimization problem for determining the training interval for channel estimation, user scheduling, and power allocation strategies to maximize the energy efficiency and transform the problem into a tractable convex problem. Based on the convexity of the problem, we propose an energy-efficient resource allocation strategy using an iterative method and provide the convergence of the proposed algorithm based on nonlinear fractional programming. The simulation results show that the proposed algorithm operates in an energy-efficient way, thereby achieving maximum energy efficiency while ensuring the data rate and harvested energy requirements.

Maximizing the Capacity of Magnetic Induction Communication for Embedded Sensor Networks in Strongly and Loosely Coupled Regions

We attempt to maximize the capacity of magnetic induction communication in strongly and loosely coupled regions. In a strongly coupled region, we investigate frequency splitting, which disturbs the resonance of transmitter and receiver coils. We find a splitting coupling point, which is the value just before frequency splitting occurs, and propose an adaptive frequency-tracking scheme for finding an optimal frequency. The proposed scheme compensates for the degradation of capacity and so guarantees large capacity even at regions where frequency splitting occurs. Next, in a loosely coupled region, we derive an optimal quality factor for maximizing capacity in a two-coil system. As the distance between coils increases, strong resonance is needed to overcome the serious attenuation of signal strength. As a result, the optimal quality factor should be increased. In addition, we find an optimal quality factor for a relay system in order to guarantee reliable communication at long distance. In addition, an optimal- Q scheme that adjusts the optimal quality factor according to a given distance can achieve near-optimal capacity. Finally, through simulations using the Agilent Advanced Design System, we demonstrate the accuracy of our analytic results and the effectiveness of the proposed schemes.

Resource allocation considering fault management in indoor Mobile-WiMAX system

We propose a fault-management channel (FMC) to address the problem of indoor-RAS (radio access station) faults and analyze it by using an optimization method. To reduce the complexity of the optimization problem, we also propose a suboptimal algorithm that is based on the FMC: an equal power allocation algorithm (EPA). Our main contributions are as follows: 1) proposing a solution for indoor-RAS faults; and 2) presenting an efficient suboptimal algorithm (EPA) for the improvement of fairness. Through intensive simulations, we evaluate the performance of our proposed algorithm with respect to fairness, spectral efficiency, and a new proposed metric that considers spectral efficiency and fairness together.