Whan Woo Kim

The development of reactor coolant pump vibration monitoring and a diagnostic system in the nuclear power plant

Monitoring abnormalities within reactor coolant pumps due to vibration, we introduce a Wigner distribution (WD) to a vibration monitoring system for analyzing vibration signals, and develop an on-line diagnostic method using the neural network employing back propagation algorithm. A rotor kit is used to simulate the abnormal conditions in the pump such as bearing rubbing, shaft bending, misalignment, etc. The data collected from the kit are analyzed using both a conventional system based on the Fourier transform (FT) and the software developed with the WD in this study, and they are compared. The study shows that spectrum represented by WD makes it easy to analyze the vibration signals of a rotating machine and the developed diagnostic method will help the operators grasp the cause of vibrations.

A new ultrasonic technique for detection and sizing of small cracks in studs and bolts

If small cracks in stud bolts are not detected early enough, they can grow rapidly and cause catastrophic disasters in industrial facilities such as nuclear power plants. Their detection, despite its importance, is known to be a very difficult problem due to the complicated structures of the stud bolts. This study shows a method of detecting the existence and determining the size of a small crack in a root between two crests in the bolt threads using ultrasound. The Rayleigh wave propagating from the tip of a crack to the opening of the same crack is utilized. A delayed pulse, due to the Rayleigh wave, is detected between regularly spaced pulses from the threads, with the delay time being proportional to the size of the crack. Theoretical explanation is presented and experimental results demonstrating detection of cracks as small as 0.5 mm are shown.

An AGC design of mobile cellular systems

This paper studies an automatic gain control (AGC) algorithm used in mobile cellular systems. The AGC design includes the determination of the precision of quantizer and a circuit to keep the input power of quantizer constant to minimize the quantization noise generated from the analog-to-digital conversion process. The proposed algorithm illustrates the method to determine the required precision of quantizer and to set the design parameters of the AGC in a mobile cellular system. The validity of the proposed algorithm is verified by computer simulation.

Wireless Sensor Network Testbed for Real-Time Sensor Monitoring

Due to the proliferation of technologies and services related with wireless sensor network, various sensor network applications are being appeared on the stage and a lot of sensor network testing technologies are being studied. However, most of testing systems or testbeds have objective for test and evaluation of sensor network protocols. For testing sensors and evaluating signal processing algorithms, it is necessary to develop a testbed for those purposes and especially, for monitoring the high speed sensing data. This paper proposes and implements a wireless sensor network testbed for controlling sensors, getting and managing the real-time sensing data on the remote sites.

Performance analysis of a minimum selected cell-averaging CFAR detection

In this paper, a new cell-averaging constant false alarm rate (CA-CFAR) detector based on minimum selected cell in sub-reference windows (SRW) is proposed. It takes the minimum cells in sub-reference sliding windows for rejecting some strong interferences or alleviating the clutter-edge effect surrounding the test cell, and then it uses the general cell-averaging technique to detect the target. Under Swerling II target fluctuating model, the analytic expressions of PFA, PD and the average detection threshold (ADT) of the proposed CFAR detector are derived. By the performance comparison with other schemes through the simulation, it is found that the detection performance of minimum selected cell averaging (MSCA)-CFAR has a similar performance to that of OS-CFAR in nonhomogeneous background with strong interfering target.

An Efficient Downlink Automatic Gain Control Algorithm before Synchronization in WiBro AT (Access Terminal)

This paper proposes an efficient AGC scheme before mobile synchronization only using the existing hard-ware engine for AGC scheme after synchronization.

Hybrid Sensor Module and Data Processing Using Low-Power Wakeup in WSN

Due to the development and proliferation of ubiquitous technologies and services, various sensor network applications are being appeared on the stage. The needs for algorithms requiring complex signal processing with a high-performance processor such as digital signal processor are also increased. However, it is difficult to use such processor for the low-power sensor network operating with a battery because of power consumption. This paper proposes and implements hardware and software architecture of the hybrid-type sensor module composed of a low-power sensor module and a high-performance sensor module for the complicated signal processing in the wireless sensor node. Although this approach needs some additional hardware, it results in some improvements in operation time supporting complex algorithms for target detection in the sensor networks.

Window Energy Detection for Unmanned Surveillance with PIR Sensor

A PIR sensor is widely applied for motion sensing applications such as automated door control, camera triggering and automated on-off control of lamps. In particular, it is usually used to detect the existence of moving objects in an indoor environment. However, in outdoor, false alarms come about due to environmental changes and other sources. Therefore, it is difficult to provide consistent detecting performance outdoors. This paper presents an algorithm to reduce and minimize the false alarms and provide reliable quality to a surveillance system. We gathered PIR signals outdoors, analyzed collected data and extract target feature defined as the window energy. Using this feature, we made models of target and false alarms and proposed a target decision algorithm. We simulated real PIR signals to provide the performance of the proposed algorithm.

Keep-alive algorithm based periodic ranging code group for detecting abnormal SS in WiBro system

In this paper, we propose keep-alive algorithm based periodic ranging code group (PRCG), in which the periodic ranging code is divided into groups and the AP (access point) performs this algorithm when the periodic ranging code arrives at AP in WiBro (wireless broadband Internet) system. In order to increase the radio bandwidth resource efficiency in this system, we propose keep-alive algorithm for finding abnormal AT (access terminal). From the numerical results, our proposed PRCG algorithm can support more radio resource efficiency compared to message-driven keep-alive algorithm

BER performance of pilot-aided channel estimation in mobile-WiMAX in the presence of frame synchronization errors

In this paper, we analyzed the available frame synchronization error ranges through the uncoded BER (bit error rate) performance in the condition of 64-QAM digital modulation in Mobile-WiMAX system.