• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.25 no.6_1
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• pp.537-543
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• 2007

Since the GPS absolute positioning with pseudorange measurements can significantly be affected by the observation error, the time series analysis of the GPS receiver clock errors was performed in this study. From the estimated receiver clock errors, the time series model is generated, and constrained back in the absolute positioning process. One of the CORS (Continuously Operating Reference Stations) network is used to analyze the behavior of the receiver clock. The dominant part of the model is the linear trend during 24 hours, and the seasonal component is also estimated. After constraining the modeled receiver clock errors, the estimated position error compared to the published coordinates is improved from ${\pm}11.4\;m\;to\;{\pm}9.5\;m$ in 3D RMS.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.36 no.6
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• pp.621-628
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• 2018

More than four visible GPS (Global Positioning System) satellites are required to obtain absolute positioning. However, it is not easy to satisfy this condition when a rover is in such unfavorable condition as an urban area. As a consequence, clock-aided positioning has been used as an alternative method especially when the number of visible satellites is three providing that receive clock error information is available. In this study, LSC (Least-Squares Collocation) method is proposed to interpolate clock errors for clock-aided positioning after analyzing the characteristics of receiver clock errors. Numerical tests are performed by using GPS data collected at one of Korean CORS (Continuously Operating Reference Station) and a nearby GPS station. The receiver clock errors are obtained through the DGPS (Differential GPS) positioning technique and segmentation procedures are applied for efficient interpolation. Then, LSC is applied to predicted clock error at epoch which clock information is not available. The numerical test results are analyzed by examining the differences between the original and interpolated clock errors. The mean and standard deviation of the residuals are 0.24m and 0.49m, respectively. Therefore, it can be concluded that sufficient accuracy can be obtained by using the proposed method in this study.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.395-400
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• 2006

Among the various error sources in positioning and navigation, the paper focuses on the modeling and prediction of receiver clock bias and then tries to achieve positioning based on simulated and predicted clock bias. With the SA off, it is possible to model receiver clock bias more accurately. We selected several types of GNSS receivers for test using ARMA model. To facilitate prediction with short and limited sample pseudorange observations, AR and ARMA are compared, and the improved AR model is presented to model and predict receiver clock bias based on previous solutions. Our work extends to clock bias prediction and positioning based on predicted clock bias using only 3 satellites that is usually the case under urban canyon situation. In contrast to previous experiences, we find that a receiver clock bias can be well modeled using adopted ARMA model. Test has been done on various types of GNSS receivers to show the validation of developed model. To further develop this work, we compare solution conditions in terms of DOP values when point positioning is conducted using 3 satellites to simulate urban positioning environment. When condition allows, height component is derived from other ways and can be set as known values. Given this condition, location is possible using less than 2 GNSS satellites with fixed height. Solution condition is also discussed for this background using mode of constrained positioning. We finally suggest an effective predictive time span based on our test exploration under varied conditions.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.3
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• pp.225-231
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• 2011

The satellite clock anomalies, one of the abnormal signal factors of the GPS satellites, can have a significant impact on the GPS measurements. However, it can be difficult to detect the anomalies of the satellites clock before the range of the satellites clock error becomes bigger than the range of the other factors, due to the measurement including error of the orbit, ionosphere delay, troposphere delay, multipath and receiver clock. In order to perform quick and accurate detection by minimization of critical range in anomalies of the satellites clock, this paper suggested a solution to detect precise anomalies of the satellites clock after application of carrier smoothing filter from measurement by dual-frequency and adjustment of errors which can be occurred by other factor and the receiver clock errors. The performance of the proposed method was confirmed by comparing to the satellite clock biases which are provided by IGS.

• Proceedings of the IEEK Conference
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• 1999.11a
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• pp.899-902
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• 1999

In this paper, we designed a equalizer that moved the multipath of channel in 8-VSB transmission receiver. After doing the initial equalization with "LMS(Least Mean Square)"aigorithm. this equalizer used "Stop-and-Go" algorithm. Because of estimating SER(Symbol to Error Ratio) every a training sequence, this can positively cope with transformation of channel and because of using fast clock than symbol-clock(10.76 MHz), we are able to reduce a multiplier.

• Proceedings of the Korea Electromagnetic Engineering Society Conference
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• 2003.11a
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• pp.394-397
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• 2003

In this paper, we have proposed a clock recovery algorithm of OFDM/QPSK-DMR(Orthogonal Frequency Division Multiplexing/Quadrature Phase Shift Keying Modulation-Digital Microwave Radio)system using BL-PSF(Band Limited-Pulse Shaping Filter) and have analyzed the clock phase error variance performance of OFDM/QPSK and single carrier DMR systems. The existing OFDM/QPSK-DMR system using the windowing requires training sequence or CP(Cyclic Prefix) to synchronize a receiver clock frequency Because there is no training sequence or CP(Cyclic prefix) in our proposed DMR system, the proposed clock recovery algorithm is useful to the OFDM/QPSK-DMR system using BL-PSF, The simulation results confirm that the proposed clock recovery algorithm has the same clock phase error variance performance in a single carrier DMR system under AWGN(Additive White Gaussian Noise) environment.

• Journal of Advanced Navigation Technology
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• v.18 no.5
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• pp.429-436
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• 2014

This paper proposes three methods of the time synchronization for Pseudolite and GPS and analyzes pseudolite time synchronization error factors for software based performance evaluation on proposed time synchronization methods. Proposed three time synchronization methods are pseudolite time synchronization station construction method, method by using UTC(KRIS) clock source and GPS timing receiver based time synchronization method. Also, we analyze pseudolite time synchronization error factors such as errors of pseudolite clock and reference clock, time delay as clock transmission line, measurement error of time interval counter and error as clock synchronization algorithm to design simulation platform for performance evaluation of pseudolite time synchronization.

• Journal of Institute of Control, Robotics and Systems
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• v.7 no.6
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• pp.550-557
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• 2001

There are several applications and error analysis methods using GPS(Global Positioning System) In most analysis positioning and timing errors are represented as the multiplication of DOP(Dilution Of Precision) and measurement errors, which are affected by the receiver and measurement type. Therefore, lots of DOPs are defined and used to analyze and predict the performance of positioning and timing systems. In this paper, the relationships between these DOPs are investigated in detail, The relationships between GDOP(Geometric DOP), PDOP(Position DOP) and TDOP(Time DOP) in the absolute positioning are de-rived. Using these relationships, the affect of clock bias is analyzed. The relationships between RGDOP(Relative DOP) and PDOP are also derived in relative positioning where the single difference and double dif-ference techniques are used. From the results, it is expected that using the common clock will give better performance when the single difference technique is used while the effects of clock is eliminate when the double difference technique is used. Finally, the error analyses of dual frequency receivers show that the narrow lane measurements give more accurate results than wide line of or L1. L2 independent measurements.

• Journal of Satellite, Information and Communications
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• v.9 no.2
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• pp.119-125
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• 2014

In this paper, we developed the signal generator of GNSS navigation signals and analysis the performance of DCO(Digitally Clock Oscillator) compensation algorithm for cumulative distance error thorough simulation. In general, To generate a GNSS signal calculates the Doppler and Initial Pseudorange by using the location information of the receiver and the satellite. The GNSS signal generator generates a signal by determine the carrier and code output frequency using the Doppler information which is calculated as a function of time. The output frequency of the carrier and code would be used the DCO scheme. At this time, It extract the bit and code information on a for each sample by accumulating the DCO. an error of Pseudorange is generated by the cumulative error of the DCO. If Pseudorange error occurs, so that the influence to and operation of the receiver. Therefore, in this paper, we implemented the accumulated error compensation algorithm of the DCO to remove the accumulated error components DCO thereof, Pseudorange accumulated error is removed through the experiment, it was confirmed to be a high accuracy can be operated.

• Journal of the Optical Society of Korea
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• v.20 no.5
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• pp.623-627
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• 2016

A power-adjustable fully-integrated CMOS optical receiver with multi-rate clock-and-data recovery circuit is presented in standard 65-nm CMOS technology. With supply voltage scaling, key features of the optical receiver such as bandwidth, power efficiency, and optical sensitivity can be automatically optimized according to the bit rates. The prototype receiver has −23.7 dBm to −15.4 dBm of optical sensitivity for 10⁻⁹ bit error rate with constant conversion gain around all target bit rates from 1.62Gbps to 8.1 Gbps. Power efficiency is less than 9.3 pJ/bit over all operating ranges.