International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Quartz crystal is an important electronic element in the field of communication systems, computer systems, etc. It is important to precisely measure the frequency of quartz crystal unit for manufacturing. The Pi-network transmission system recommended by International Electrotechnical Commission (IEC) is generally acknowledged as a measurement technique. However it needs a precise frequency source. The frequency source must be calibrated within a regular period in the process of manufacturing. Frequency counters, time internal counters, phase comparisons, which are the most common frequency calibrations, are introduced in the paper. Nowadays GPS has also become the primary system for frequency calibration. GPS receivers provide 1 PPS (Pulse Per Second) with accuracy < 100 nanoseconds to UTC under normal conditions. Motorola UT Oncore timing GPS with time accuracy < 50ns (1 sigma) uses time RAIM algorithm to ensure the validity and reliability of measurements. The comparison between the precise 1PPS and local reference is implemented. And the phase differences are logged and read by computer. According to the values, the frequency output of DDS is coordinated. In order to reduce the phase ambiguity, local reference is divided before comparison. The calibration can be implemented at any time by GPS. Block diagrams of calibration are presented in this paper.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / Several test programs have reported degraded Global Positioning System (GPS) performance when L-band (1435-1535 MHz) telemetry is used while other test programs have had acceptable GPS performance with L-band telemetry. Most test programs seem to have minimal problems with S-band telemetry interfering with GPS performance if a bandpass filter is used between the GPS antenna and the low noise amplifier (LNA). This paper will present measured data on GPS performance with L- and S-band telemetry and explain what must be done to minimize interference to GPS. The paper will present both GPS signal-to-noise ratio (S/N) values as well as measured spectra from telemetry transmitters. System design guidelines for compatible operation will be presented.

ITC/USA 2005 Conference Proceedings / The Forty-First Annual International Telemetering Conference and Technical Exhibition / October 24-27, 2005 / Riviera Hotel & Convention Center, Las Vegas, Nevada / Background and advantages of GPS based Remote Sensing are introduced, characteristics of forward scattered GPS signal such as polarization change, cross-correlation power variation, code delay due to the wave travel distance difference between direct and scattered signal, and cross-correlation power expansion due to sea surface roughness are discussed in detail. Working principle of the self-developed delay-mapping receiver is also presented. First data collection campaign is done at Inshore of BOHAI ocean with the delay-mapping receiver mounted on an airplane. Results show that the reflected signals has much variation than the direct signals, the code delay of the reflected signals varies as the receiver height and satellite elevation angle changes and expansion of the cross-correlation due to the wind driven surface was also demonstrated.

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Approved for public release; distribution is unlimited / Measurements of a 1230-km baseline were made during an eight-week period in the fall of 1987 using Trimble 4000SX single-frequency, five channel Global Positioning System (GPS) receivers. Twenty-eight days of carrier phase data were processed using correlated triple differences with fixed satellite orbits, the broadcast ephemerides, a modified Hopfield tropospheric model, and without ionospheric correction to determine the accuracies and precisions of the slope distance and baseline components. The data were processed in ever increasing observing sessions to determine the optimized observation periods required to achieve various orders of geodetic accuracies. The accuracies of the slope distances were better than 1.0 ppm for any observing period. The day-to-day repeatabilities of the slope distance measurements were better than 1.0 ppm (2) sigma after 20 minutes of observations. Accuracies and repeat-abilities (2 sigma) of the baseline components were better than 10.0 ppm after 20 minutes of observations. The correlated triple difference results were on the order of previous GPS surveys that used higher resolution differencing or external timing aids. Discussions include the effect of ephemeris, tropospheric and ionospheric errors, and dilution of precision. Observation periods and mean slope distance errors were reduced when observations started close to and included the infinite peak of the Position Dilution of Precision (PDOP). The smallest variances were associated with observations about the infinite PDOP peak / http://archive.org/details/optimizedobserva00bouc / Lieutenant, United States Navy

Thesis (S.M. in Transportation)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 101-103). / The pervasive location-based technologies, such as GPS and cell phone, help us find the pattern of geographical information of human behavior and also help dig opportunities in real world. In transportation field, they help people better understand the transportation behavior and at the same time collect necessary information for us. One important aspect of its application is how people choose the route given the existing urban network. However, dealing with the excessive amount of data and the modeling of route choice behavior are two major challenges in the route choice analysis.This thesis discusses the general process in the route choice analysis, from GPS data processing, map matching to the generation of route choice sets. Besides, the Path-Size logit model is implemented to address the modeling issue. In this thesis, I develop a new effective method, which I called Point-Based Local Search Map Matching, to match the consecutive GPS data to the network data. Also, I develop a new model, which I called Random Weight Choice Set Generation Model to deal with the choice set generation problem in the route choice analysis. The data comes from two major sources. One is the Boston car GPS data. It tells when and where a specific car is. The other is the Boston urban network data, which contains all types of roads in GIS format. / by Anyang Hou. / S.M.in Transportation

The principal objectives of this research are: to investigate the performance of different fingerprint-based WiFi Indoor Positioning Systems (IPS), analyse historical long-term data signals, detection of signal change points and outliers; then present an enhanced method that generates temporal based fingerprints. The proposed method consists of analysing signal strength profiles over time and detecting points at which the profile behaviour changes. This methodology can be used to dynamically adjust the fingerprint based on environmental factors, and with this select the relevant Wireless Access Points (WAPs) to be used for fingerprinting. The use of an Exponentially Weighted Moving Average (EWMA) Control Chart is investigated for this purpose. A long-term analysis of the WiFi scenery is presented and used as a test-bed for evaluation of state-of-the-art fingerprinting techniques. Data was collected and analysed over a period of 18 months, with over 840 different WAPs detected in over 77,000 observations covering 47 different locations of varying characteristics. A fully functional IPS has been developed and the design and implementation is described in this thesis. The system allows the scanning and recording of WiFi signals in order to define the generation of temporal fingerprints that can create radio-maps, which then allow indoor positioning to occur. This thesis presents the theory behind the concept and develops the technology to create a testable implementation. Experiments and their evaluation are also included. Based on the timestamp experiments the proposed system shows there is still room level accuracy, with a reduction in radio-map size.

Ground deformation due to volcanic magma intrusion is recognised as an important precursor of eruptive activity at a volcano. The Global Positioning System (GPS) is ideally suited for this application by being able to measure three-dimensional coordinate changes of the monitoring points over time. Due to the highly disturbed ionosphere in equatorial regions, particularly during times of maximum solar activity, a deformation monitoring network consisting entirely of single-frequency GPS receivers cannot deliver baseline solutions at the desired accuracy level. In this thesis, a mixed-mode GPS network approach is proposed in order to optimise the existing continuous single-frequency deformation monitoring system on the Papandayan volcano in West Java, Indonesia. A sparse network of dual-frequency GPS receivers surrounding the deformation zone is used to generate empirical 'correction terms' in order to model the regional ionosphere. These corrections are then applied to the single-frequency data of the inner network to improve the accuracy of the results by modelling the residual atmospheric biases that would otherwise be neglected. This thesis reviews the characteristics of existing continuously operating GPS deformation monitoring networks. The UNSW-designed mixed-mode GPS-based volcano deformation monitoring system and the adopted data processing strategy are described, and details of the system's deployment in an inhospitable volcanic environment are given. A method to optimise the number of observations for deformation monitoring networks where the deforming body itself blocks out part of the sky, and thereby significantly reduces the number of GPS satellites being tracked, is presented. The ionosphere and its effects on GPS signals, with special consideration for the situation in equatorial regions, are characterised. The nature of the empirically-derived 'correction terms' is investigated by using several data sets collected over different baseline lengths, at various geographical locations, and under different ionospheric conditions. Data from a range of GPS networks of various sizes, located at different geomagnetic latitudes, including data collected on Gunung Papandayan, were processed to test the feasibility of the proposed mixed-mode deformation monitoring network approach. It was found that GPS baseline results can be improved by up to 50% in the midlatitude region when the 'correction terms' are applied, although the performance of the system degrades in close proximity to the geomagnetic equator during a solar maximum.