• The Journal of the Korea institute of electronic communication sciences
• /
• v.7 no.1
• /
• pp.135-139
• /
• 2012

A majority of 4G Mobile communication manufacturers have launched separated-type base stations composed of DU (digital unit) and RU (ratio unit). DUs are usually installed in the central office, while RUs with antennas are installed on the top of building or pole. Therefore, the allowable distance between DU and RU is very important for cell planning. In this paper, we analyze the allowable distance between DU and RU induced by closed-loop MIMO (mulitple input multiple output) technology in 4G FDD (frequency division duplexing) mobile communication systems. In conclusion, the distance limit between DU and RU is dependent on the frequency of the wireless communication, and the allowable distance is about 11 km when assuming the operating frequency is 2 GHz.

• Proceedings of the IEEK Conference
• /
• 1998.10a
• /
• pp.67-70
• /
• 1998

In this paper, an interference analyzer for communication and/or broadcasting services is developed and presented based on Monte Carlo technique, which is now under study in the International Telecommunication Union(ITU). Monte Carlo technology is a statistical approach which functions by considering many trials. For each simulation trial, a scenario is built up using a number of different random variables, such as signal and interference strengths, transmitting and receiving antenna heights, antenna gains, etc.. Furthermore, this paper shows and application example of the analyzer to examine interference influence of the PCS(IS-95) base stations affecting to the IMT-2000 FDD base station, depending on serveral service environments like rural, suburban, and urban areas. The wave propagation model used in this simulation is the modified Hata model, which is known to the suitable to Korean environments.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
• /
• 2000.11a
• /
• pp.25-28
• /
• 2000

본 논문에서는 국제전기통신연합(ITU의 전파통신분야(ITU-R)에서 간섭분석기의 표준으로 채택한 몬테카를로 기법에 기초한 간섭분석기를 개발한 후, 개발된 간섭분석기를 이용하여 서로 같은 주파수대역에 있는 IMT-2000(FDD)기지국과 IMT-2000(TDD) 기지국 상호간의 간섭영향 분석을 수행하였다. 개발된 몬테카를로 간섭분석기는 한국 지형에 적합하도록 전파모델에 있어 수정된 하타모델을 이용하였으며 국내 서비스 환경을 고려한 간섭 시나리오를 설정하여 모의실험을 수행하였다. 모의실험을 통하여 IMT-2000의 파라미터들의 적합성과 함께 동일 주파수 대역에 있는 두 시스템을 같은 셀내에서 공유가능함을 확인하였다.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.29 no.11 s.242
• /
• pp.1220-1228
• /
• 2005

Fault detection and diagnostic (FDD) systems have the potential to reduce equipment downtime, service costs, and utility costs. In this study, model based algorithm and fuzzy algorithm were used to detect and diagnose various fault at System multi-air conditioner. various fault include the Refrigerant Low charging, Fouling of Indoor Heat Exchanger, Fouling of Outdoor Heat Exchanger A experimental verification was conducted in the 6HP System multi-air conditioner on an 8-floor building. Test results showed diagnosis result about 78 $\~$ 90$\%$ for given faults. This Study lays the foundation fur future work on develope the real-time fault detection and diagnosis system for the System multi-air conditioner.

• ETRI Journal
• /
• v.33 no.4
• /
• pp.633-636
• /
• 2011

In this letter, we propose an overlaid hybrid division duplex (HDD) concept for cellular systems which divides a cell into inner and outer regions and utilizes the merits of both time division duplex (TDD) and frequency division duplex (FDD). The proposed system can take advantage of both TDD and FDD without handover between two duplex schemes. Moreover, it is shown that the proposed HDD system outperforms the conventional TDD or FDD system with mobile relay stations when the synchronization issue is considered in orthogonal frequency division multiple access systems. Thus, the proposed overlaid HDD can be considered as a new framework for future cellular systems.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.16 no.4
• /
• pp.137-144
• /
• 2008

This study deals with on-line fault detection and diagnosis(FDD) for heat exchangers of a variable speed refrigeration system(VSRS) based on current information. The current residual which is the difference between real detected current from current sensors and estimated current from no fault model was utilized to diagnose faults of the heat exchangers. Comparing to the conventional FDD of constant refrigeration system based on temperature and pressure information, the suggested FDD method shows better robustness to the VSRS which has a feedback control loop. Moreover the suggested method can be expected more precise and faster diagnosis of faults about heat exchangers. Throughout some experiments, the validity of the method was verified.

• Progress in Medical Physics
• /
• v.22 no.4
• /
• pp.163-171
• /
• 2011

The purpose of this study was to investigate the effect of various technical parameters for the dose optimization in pediatric chest radiological examinations by evaluating effective dose and effective detective quantum efficiency (eDQE) including the scatter radiation from the object, the blur caused by the focal spot, geometric magnification and detector characteristics. For the tube voltages ranging from 40 to 90 kVp in 10 kVp increments at the FDD of 100, 110, 120, 150, 180 cm, the eDQE was evaluated at the same effective dose. The results showed that the eDQE was largest at 60 kVp when compares the eDQE at different tube voltage. Especially, the eDQE was considerably higher without the use of an anti-scatter grid on equivalent effective dose. This indicates that the reducing the scatter radiation did not compensate for the loss of absorbed effective photons in the grid. When the grid is not used the eDQE increased with increasing FDD because of the greater effective modulation transfer function (eMTF). However, most of major hospitals in Korea employed a short FDD of 100 cm with an anti-scatter grid for the chest radiological examination of a 15 month old infant. As a result, the entrance surface air kerma (ESAK) values for the hospitals of this survey exceeded the Korean DRL (diagnostic reference level) of $100{\mu}Gy$. Therefore, appropriate technical parameters should be established to perform pediatric chest examinations on children of different ages. The results of this study may serve as a baseline to establish detailed reference level of pediatric dose for different ages.

• Maxillofacial Plastic and Reconstructive Surgery
• /
• v.15 no.1
• /
• pp.63-79
• /
• 1993

To repair bony defects with tansplanted bone in the body, fresh autogenous bone is undoubtly, the most effective bone graft for clinical applications. But the demineralized bone has the matrix-induced bone formation which was suggested by Urist in 1965. Many authors assisted that demineralized bone powder induces phenotypic conversion of mesenchymal cells into osteoblasts, with high-density bone formation. The process of inducing differentiated cells becomes osteogenic properties. The purpose of this study was to evaluate the osteoinductive capacity of allogenic freeze-dried demineralized bone block (FDD, $7{\times}7mm$) and to compare FDD with the same sue of deep-frozen allogenic bone(DF), fresh autogenous bone (A) after implantation. The histological and ultrastructural features of tissue responses were examined after 1, 2, 4, 6, 8 weeks implantation of each experimental groups in the operative site of the New Zealand white rabbits. The results were as follows : 1. Inflammatory cell infiltration generally has appeared at 1 week, but reduced at 4 weeks in each group, but most severe in DF group. 2. Osteoblastic activity has increased for 4 weeks, but decreased at 6 weeks in each group and there was no significant difference among experimental groups. 3. New bone formation has begun at 1week, least activations in A groups, and showed the revesal line of bone formation among each group at 6 to 8 weeks. 4. Bone resorption has appeared at 1 week, but disappeared at 4 weeks in both A and DF groups, but more severe in DF than A groups. 5. In ultrastructural changs, the DF group have showed the most remarkable osteoclastic activities among experimental groups. 6. Osteoid or tangled collagen fibrils near the implanted sites were replaced by more mature, lamellated bony trabeculae during bone remodeling. There was little difference among each experimental groups. 7. During the convertion osteoblasts to osteocytes which embedded within the bone matrix, there was organ-less-poor cytoplasm, increased nuclear chromatin, abundant rough endothelial reticulum (RER) in each groups. From the above the findings, the DF group shored more bone resorption and foreign body reaction than FDD and A groups, and FDD group showed more new bone formation or osteoblastic activity than DF and A groups in early stage. There was no significant difference of cellular activities among the FDD DF, and A groups according to the time.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.31 no.11A
• /
• pp.1076-1084
• /
• 2006

In this paper, we first review a concept of hybrid division duplexing (HDD) scheme, which has been proposed as a new type of duplexing scheme useful for a next generation mobile communication system and its implementation issues, including the unified radio resource management for HDD scheme. The HDD scheme maintains the advantages of both TDD and FDD at the same time while providing a useful structure to control the inter-cell interference, caused by an asymmetric traffic load of multimedia services over uplink and downlink in the TDD scheme. Employing two frequency bands, one for TDD scheme and the other for FDD scheme, uplink is operating under the TDD scheme only, while downlink is operating under the TDD or FDD scheme, depending on the location of mobile station. In the HDD scheme, therefore, it must determine a type of duplexing scheme to employ in the downlink and futhermore, a ratio of uplink and downlink duration to meet a given traffic load of asymmetric service, which requires some unified radio resource management for handling the subsequent inter-cell interference. In this paper, we propose a distributed adaptive control approach as a means of unified radio resource management for a HDD system that maximizes the overall system efficiency by fully utilizing the resource in TDD band, while minimizing the inter-cell interference.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.11
• /
• pp.594-603
• /
• 2018

Recently, according to the development of measurement techniques, it has become possible to take complicated and time-consuming field measurements in a simple and convenient manner. In this background, this study estimated the tension of cables under ambient vibration using minimized measurement and signal processing. The VBDM using video-only by low-cost equipment was used as a minimized measurement. An estimation of the natural frequency using the mirror frequency concept was also proposed to solve the shortage of frequency band in this case. Furthermore, the FDD method was adopted for a natural frequency estimation in the ambient vibration related to field application. Experimental studies using a cable-stayed bridge model were carried out to examine the properties of the mirror frequency and the applicability of FDD with the proposed minimized system. The results showed that FDD for ambient vibration also works properly in an estimation of the natural frequency using the minimized system. In addition, the mirror frequency concept can allow a high natural frequency estimation even in a distorted signal by low-speed recording, which can overcome the limit of the minimized system. Overall, the proposed minimized system can be effective for the tension estimations of a cable under ambient vibration.