Kitae Kim

An Incremental Frequency Reuse Scheme for an OFDMA Cellular System and Its Performance

We propose an incremental frequency reuse (IFR) scheme that reuses effectively the radio spectrum through systematic segment allocation over a cluster of adjoining cells. It divides the entire frequency spectrum into several spectrum segments. Based on the above segmentation, a set of cell- specific segment allocation sequences is designed for universal frequency reuse. Here, each sequence defines its own base segment and allocation order. The designed sequences are then assigned to respective cells over the cell cluster. In this scheme, the base segments over the cell cluster are mutually non-overlapped and collectively exhausted, and the added segments are interfered with from surrounding cells, but only in an incremental and coordinated manner. Hence, the proposed scheme can provide better reuse efficiency over the conventional ones such as the classical universal frequency reuse scheme and the soft frequency reuse (SFR) scheme. In addition, the simple and flexible IFR scheme can be easily configured as most existing reuse schemes only by redefining the set of segment allocation sequences. A system-level simulator for an orthogonal frequency division multiple access (OFDMA) cellular system covering surrounding cells up to 3rd-tier has been implemented. Simulation results show that the IFR scheme provides quite better reuse efficiency as compared to the classical universal reuse scheme and the SFR scheme, especially at the cell-edge region.

A Universal Frequency Reuse System in a Mobile Cellular Environment

We propose a universal frequency reuse (UFR) system that can reuse effectively a given frequency resource in a mobile cellular environment. The key concept is to control mutual interferences among neighboring cells in a systematic manner. The system first assigns the whole frequency resource to all cells, so that the whole resource could be reused without any restrictions in all the cells as in the cellular systems with frequency reuse factor of 1. Then, it defines a cell-specific resource allocation rule for each cell, so as to control mutual interferences among neighboring cells in a cooperative way. In our case, the resource allocation rules are designed so that they can avoid maximally inter-cell interference (ICI) when the loading factor is less than a threshold loading factor, while exceeding the threshold, ICI would be averaged over the whole frequency resource. Hence, the proposed system can maintain ICI always at the minimum level, in turn expecting greater spectrum reuse efficiency. Finally, we perform extensive computer simulations in order to verify the effectiveness of the proposed reuse system, assuming an OFDMA-based cellular system. From simulation results, we show that the UFR system provides quite better spectrum reuse efficiency, regardless of omni-cell and 3-sector cell systems.

Cognitive Ad-hoc Networks under a Cellular Network with an Interference Temperature Limit

We propose an efficient deployment scenario for cognitive ad-hoc networking under a cellular network with a pre-defined interference temperature limit (ITL). Using this scenario, a cellular radio spectrum can be reused efficiently without disturbing the existing cellular network. It uses a relaxed ITL concept in which the pre-defined ITL is satisfied at the target receiver only instead of all around the cellular service coverage. In this scenario, a cognitive radio (CR)-enabled secondary user (also, called as a cognitive ad-hoc user), equipped with the cellular signal strength monitoring device measures the pathloss from the nearest cellular base station (CBS) (also, called as the target CBS) in a cellular downlink channel. Then, using the measured pathloss, each secondary user computes its allowable maximum transmit power level (AMTPL) for a cellular uplink channel. In this scenario, secondary users farther from the target CBS can transmit more power than nearer users can do, thus making the cellular uplink resource reused more efficiently. Therefore, the proposed scenario can reduce the routing overhead and associated delay, and the infrastructure cost because this secondary user power flexibility can decrease the number of required nodes for cognitive ad-hoc networking, or can increase the utilization efficiency of the cellular radio spectrum.

Performance Analysis of OFDMA Cellular Systems Using a Multi-Cell Resource Management Scheme

In this paper, we analyze the performance of OFDMA downlink cellular systems using a novel multi-cell resource management scheme. Both omni-cell and 3-sector cellular systems are considered here. We first develop inter-cell interference models and then analyze the spectral efficiency and the service outage probability based on the interference models. The proposed scheme first divides the entire system bandwidth into K identical reuse-bands corresponding to frequency reuse factor (FRF) K. They are assigned to a desired cell and K-1 neighboring cells, respectively, and are reused in remaining outer cells. In the proposed scheme, if the pre-assigned resource in the center cell is exhausted, the center cell encroaches one of the preferred reuse-bands assigned to K-1 neighboring cells according to an initial resource assignment rule. As the proposed scheme controls effectively the ICI level according to the use of additional supplementary reuse-bands, an increased spectral efficiency or loading factor is obtained. In a multi-cell cellular system, since the ICI level depends severely on the cell deployment pattern and the loading unevenness among neighboring cells, the suitability and the degree of performance improvement of the proposed scheme were derived through extensive simulations in various system environments. From an ICI mitigation point of view, simulation results show that the proposed scheme performs best for OFDMA-based cellular systems, regardless of sectorization types

Multi-Cell Coordinated Radio Resource Management Scheme Using a Cell-Specific Sequence in OFDMA Cellular Systems

In this paper, we propose a multi-cell coordinated radio resource management scheme in OFDMA cellular systems, in which each cell has its own sequence for allocating radio subchannels. We first divide a given radio resource into a set of subchannels in each cell. Here, we assume an identical set of subchannels in all cells considered. Then, we choose a set of cell-specific subchannel allocation sequences, so that they can avoid maximally inter-cell interference (ICI) and also minimize the probability of major collisions from neighbor cells in a mobile cellular environment. Finally, each cell allocates a subset of pre-defined subchannels to a requested user. In addition, prior to resource scheduling, each base station (BS) determines the total number of subchannels requested by all users in the cell, and allocates subchannels corresponding to the requested number according to its own cell-specific sequence. Through simulation results, we show that the proposed scheme can achieve a greater spectral efficiency or much higher loading under system outages as compared to the conventional schemes. We consider both the omni-cell and 3-sector cell

An improved incremental frequency reuse scheme employing maximally orthogonal fundamental segments

We propose an efficient segment assignment strategy for the incremental frequency reuse (IFR) scheme [1], in which each cell within a cluster of adjoining cells has its own fundamental segment orthogonal to a maximal extent to those of other cells within the cluster, in order to control effectively inter-cell interference (ICI). First, the IFR scheme with maximally orthogonal fundamental segments (MOFS) (hereafter, called as the IFR-MOFS scheme) divides the entire radio spectrum into multiple segments, in which all the cells within the cluster follow the same segmentation rule. Then, it designates a unique MOFS for each cell, distinct from those of other cells within the cluster. Finally, a set of corresponding segment assignment sequences is defined to mitigate ICI within the cluster greatly through systematic segment allocation among adjoining cells. A system-level simulator for an orthogonal frequency division multiple access (OFDMA) cellular system covering surrounding cells up to 3rd-tier has been implemented. Simulation results show that the IFR-MOFS scheme provides quite bett er the cell-edge performance as well as the overall cell capacity a s compared with the original IFR scheme [1], the soft frequency reuse (SFR) scheme, and the classical universal frequency reuse (UFR) scheme.

Development of Load Profile Monitoring System Based on Cloud Computing in Automotive

ABSTRACT Purpose: For improving result of estimated remaining useful life in Prognostics and Health Management (PHM), a system which is able to consider a lot of environment and load data is required.Method: A load profile monitoring system was presented based on cloud computing for gathering and process-ing raw data which is included environment and load data. Result: Users can access results of load profile information on the In ternet. The developed system provides information which consists of distribution of load data, basic statistics, etc.Conclusion: We developed the load profile monitoring system for considering much environment and load data. This system has advantages such as improving accessibility through smart device, reducing cost, and covering various conditions.Key Words: Prognostics and Health Management. Load Profile Monitoring. Cloud Computing. Big Data. Automotive ● Received 19 November 2015, 1st revised 3 December 2015, accepted 14 December 2015Corresponding Author(chongman@mju.ac.kr)ⓒ 2015, The Korean Society for Quality ManagementThis is an Open Access article distributed under the terms of t he Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits u nrestricted non-Commercial use, distribution, and re-production in any medium, provided the original work is properl y cited.※ 이 논문은 2014년도 정부(미래창조과학부)의 재원으로 한국연구재단의 지원을 받아 수행된 기초연구사업임 (NO. 2012R1A1A1015120)

Assessment of the reliability of the solder joints of the ultra-fine-pitch FCBGA

In this study, reliability assessment of the IMC layer of the ultra-fine-pitch FC-BGA(Flip-Chip Ball Grid Array) is conducted. The samples are prepared to reveal the differences in the adhesion forces of the IMC layer by dissimilarly establishing each plating thickness for surface finish(Ni/Pd/Au). The hardness and thickness of a P-rich Ni layer, which is known as the weakest section in ENPIG surface, are measured using the nano-indentation and TEM analysis. The degree of adhesion of the IMC layer under each experimental condition is evaluated and the metal plate shear test is performed for verification. The results showed significant correlations between the hardness and thickness of the IMC later and the high fraction defectives of the brittle fractures whose IMC layer had low hardness.

Coordinated inter-cell resource allocation approach for better frequency reuse in OFDMA cellular systems

We propose a coordinated inter-cell resource allocation (CICRA) approach that can reuse efficiently the radio spectrum through inter-cell interference (ICI) management over a cluster of adjoining cells in some coordinated manner. In this, the entire radio spectrum is assigned to all the cells within the cell cluster. We use a set of coordinated cell-specific resource allocation sequences in order to manage ICI. The set of sequences should be designed and assigned in a coordinated manner over all cells within the cell cluster, so that ICI from nearer interfering cells could be preferentially avoided and the average ICI level according to the loading factor (LF) could be monotonic and minimally incremented. By the virtue of such ICI-managing mechanism, the CICRA approach can govern efficiently the average ICI level only through individual resource allocation without intervention among cells. In this paper, we would apply the CICRA approach to orthogonal frequency division multiple access (OFDMA) cellular systems. A system-level simulator for an OFDMA cellular system covering surrounding cells up to 3rdtier has been implemented. Simulation results show that the proposed CICRA approach can improve noticeably the system performance in terms of both the outage probability and spectral efficiency as compared with the classical UFR scheme and the soft frequency reuse (SFR) scheme over the entire LF range.