• Journal of Mechanical Science and Technology
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• v.16 no.12
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• pp.1604-1612
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• 2002

Rollers in the continuous process systems are ones of key components that determine the quality of web products. The condition of rollers (e.g. eccentricity, runout) should be consistently monitored in order to maintain the process conditions (e.g. tension, edge position) within a required specification. In this paper, a new diagnosis algorithm is suggested to detect the defective rollers based on the frequency analysis of web tension signals. The kernel of this technique is to use the characteristic features (RMS, Peak value, Power spectral density) of tension signals which allow the identification of the faulty rollers and the diagnosis of the degree of fault in the rollers. The characteristic features could be used to train an artificial neural network which could classify roller conditions into three groups (normal, warning, and faulty conditions) The simulation and experimental results showed that the suggested diagnosis algorithm can be successfully used to identify the defective rollers as well as to diagnose the degree of the defect of those rollers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.7
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• pp.559-565
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• 2014

In this paper, we propose an unambiguous correlation function for time-multiplexed binary offset carrier (TMBOC) signal tracking. Specifically, considering that the TMBOC modulation transmits two kinds of sine-phased BOC signals in time domain alternatively, we generate sub-correlation functions for each of the BOC signals by using split sine-phased BOC signals, and then, obtain a correlation function with no side-peak by recombining the sub-correlation functions. From numerical results, we confirm that the proposed correlation function offers an improved tracking error standard deviation performance than the TMBOC autocorrelation function.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 1999.05a
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• pp.78-81
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• 1999

The position and time errors of a conventional L1-band GPS receiver (1575.42MHz) are known to be about 100 m and 70 ns, respectively. These errors are mainly due to the propagation delay of GPS satellite signals through ionosphere. Various L1/L2 dual-band GPS receivers are normally used to compensate for those position and time errors by detecting an accurate propagation delay. These receivers detect the propagation delay difference between the L1 and L2 signals based on the fact that the propagation delay through ionosphere is dependent on frequency and, from which, calculate an accurate propagation delay of the GPS signals through ionosphere. In this paper, we analyzed the architecture of a L1/L2 dual-band CPS receiver by high-level simulations with Synopsys's COSSAP Tool.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.3
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• pp.183-189
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• 2020

In emergency rescue situations, the localization accuracy of the rescue requestor is a very important factor in determining the success or failure of the rescue. Indoors where Global Navigation Satellite System (GNSS) is not operated, there is no choice but to use Wi-Fi or LTE signals. However, the performance of the current emergency rescue system utilizing those RF signals is exceedingly low. In this study, the effectiveness of the surface correlation technology using the accumulated signal pattern of RF signals was verified in relation to the emergency localization technology. To validate the proposed system, we configured and tested an emergency rescue scenario in multi-floors building. When the emergency rescue was requested, it was confirmed that the initial localization error was large owing to the short length of the accumulated signal pattern. However, the localization error decreased over time, which eventually led to the accurate location information being delivered to the rescuer.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.2
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• pp.131-136
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• 2006

Commercial uses of GPS have been growing rapidly with applications for aircraft, ship, and land vehicle navigation as well as for surveying and time keeping. The next generation GPS and Japanese QZS (Quasi Zenith Satellite) will provide three different civil signals. Galileo will also provide several types of civil signals. The availability of the third civil frequency has obvious advantages to instantaneous carrier phase accuracy and ambiguity resolution for centimeter level measurements. This paper discusses the effects of additional new civil signals for the high accuracy positioning in urban areas based on simulation using practical raw data. As for constellation, only GPS and GPS+QZS are considered. For positioning, a short distance baseline is assumed in order to disregard atmosphere effects. In this simulation, mask angle and signal conditions were fixed and ambiguity success rates were compared between different triple frequency combination scenarios. The coefficient of reflection was set randomly from 0.05 to 0.5 and the multipath delay was also set randomly from 5-100 m. Visible satellites and signal strength were determined by raw data collected in Tokyo by car. These simulation results have confirmed that the availability of high accuracy positioning will increase in all scenarios if we use GPS+QZS with triple frequencies.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.5
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• pp.616-624
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• 2019

In order to understand flying aircraft, satellite, missile, etc, a telemetry ground system is used to receive, record, and process the transmitted radio signal from vehicles. In some cases, a line-of-sight communication is not possible along to the trajectory of vehicles, and multipath fading result in a shade area of communication. A number of telemetry ground systems are installed to overcome this limitation, and acquire the transmitted signal seamlessly. The telemetry signals received by multiple independent ground systems have independent probability of errors since they experienced their own communication channels. In other words, we can exploit the independent error characteristics of received signals by processing them in a hybrid method. The optimum hybrid post-process method is proposed in this study, and applied to process telemetry signals acquired from flight tests.

• Journal of Positioning, Navigation, and Timing
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• v.10 no.2
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• pp.153-158
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• 2021

In order to mitigate the vulnerability of the satellite navigation system against radio frequency interference, South Korea has been developing advanced terrestrial navigation system (eLoran) technology since 2016. The eLoran system synchronizes the transmission time of the pulse used in the existing Loran-C system with UTC and transmits correction information that can improve the position error. The eLoran system is known to reduce the position error of about 460 m of the existing Loran-C system to 20 m, and for this, the transmitter must be able to transmit eLoran signals according to more stringent standards. For this reason, an international standard that further developed the Loran-C signal standard established by US Coast Guard was established by Society of Automotive Engineers (SAE) International. In this paper, based on the analysis of the SAE9990 document, the international standard for eLoran transmission signals, a standard inspection process was produced to check whether the eLoran transmitter is transmitting signals in accordance with the standard.

• Journal of Positioning, Navigation, and Timing
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• v.9 no.4
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• pp.327-336
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• 2020

This study presents signal availability of inter-operable global navigation satellite system (multi-GNSS) combined with future Korean Positioning System (KPS), specifically at geosynchronous orbit (GSO). The orbit of KPS, which is currently under conceptual feasibility study, is first introduced, and the grid points for evaluating space service volume (SSV) at GSO are generated. The signal observabilities are evaluated geometrically between those grid points and KPS/GNSS satellites. Then, analyzed are the visibility averaged over time/space and outage time to not access one or four signals. The reduction of maximum outage time induced by KPS are presented with different maximum off-boresight angles depending on L1/E1/B1 and L5/L3/E5a/B2 frequencies. Our numerical analysis shows that the SSV of multi-GNSS combined with KPS provides up to 7 additional signals and could provide continuous observation time (zero outage time) of more than four GNSS or KPS signals for 3.20-14.83% of SSV grid points at GSO. Especially at GSO above North/South America and Atlantic region, the introduction of KPS reduces the outage duration by up to 63 minutes with L1/E1/B1 frequency.

• IEMEK Journal of Embedded Systems and Applications
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• v.17 no.4
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• pp.239-247
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• 2022

The existing studies on the localization in the GNSS (Global Navigation Satellite System) denied environment usually exploit low-cost MEMS IMU (Micro Electro Mechanical Systems Inertial Measurement Unit) sensors to replace the GNSS signals. However, the navigation system still requires GNSS signals for the normal environment. This paper presents an integrated GNSS/INS (Inertial Navigation System) navigation system which combines GNSS and multiple IMU sensors using extended Kalman filter in partially GNSS-denied environments. The position and velocity of the INS and GNSS are used as the inputs to the integrated navigation system. The Mahalanobis distance is used for novelty detection to detect the outlier of GNSS measurements. When the abnormality is detected in GNSS signals, GNSS data is excluded from the fusion process. The performance of the proposed method is evaluated using MATLAB/Simulink. The simulation results show that the proposed algorithm can achieve a higher degree of positioning accuracy in the partially GNSS-denied environment.

• Journal of Positioning, Navigation, and Timing
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• v.11 no.1
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• pp.1-9
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• 2022

Global Navigation Satellite System (GNSS) provides location information using signals from multiple satellites. However, a spoofing attack that forges signals or retransmits delayed signals may cause errors in the location information. To prevent such attacks, authentication protocols considering the navigation message structure of each GNSS can be used. In this paper, we analyze the authentication protocols of Global Positioning System (GPS), Galileo, and BeiDou, and compare the performance of Navigation Message Authentication (NMA) of the above systems, using several performance indicators. According to our analysis, authentication protocols are similar in terms of performing NMA and using Elliptic Curve Digital Signature Algorithm (ECDSA). On the other hand, they are different in several ways, for example, whether to perform Spreading Code Authentication (SCA), whether to use digital certificates and whether to use Timed Efficient Stream Loss-tolerant Authentication (TESLA). According to our quantitative analysis, the authentication protocol of Galileo has the shortest time between authentications and time to first authenticated fix. We also show that the larger the sum of the navigation message bits and authentication bits, the more severely affected are the time between authentications and the time to first authenticated fix.