This research study explores the Global Positioning System (GPS), its history, and the process of discovery needed to create the most accurate GPS possible, as well as the contemporary applications of GPS technology. Starting with the first satellite in space, GPS has been a work in progress. Originally pursued by the military for improvements to military tactics, GPS has become integrated into the everyday lives of millions of people around the world. How GPS determines location is a dichotomy, with simplistic theory and complex application. Many factors go into GPS to provide a consistent, accurate location. The orbital planes the satellites are placed in provide 24/7 coverage globally, the L-band frequencies used were chosen specifically for the characteristics they possess, and the multiple atomic clocks installed on each satellite provide incredible accuracy down to the nanoseconds, which is quintessential in GPS accuracy. The applications in GPS are far reaching and more applications are continually being discovered. With as far as GPS technology has progressed, there are still several factors that degrade the signal and are a challenge to overcome. Many of these challenges can be corrected efficiently, however, others, such as scintillation and total electron content variability in the ionosphere, create major hurdles to overcome. Luckily, there are many programs that aid in the correction process of these hurdles. The History of GPS According to R. Saunders’ article ​A Short History of GPS Development,​ The Global Positioning System (GPS) has a long history of trial and error and refinement and improvement. It’s purpose has shifted from being a military strategic asset to commonplace among the general public with its use in traveling, farming, and even banking. The beginning of GPS, introduced with a simple idea, can be traced back to the Soviet Union in the late 1950’s. In 1957, the Soviet Union made history with successfully launching the first satellite in space. To track the satellite Sputnik, Physicists and Scientists at John Hopkins University’s Applied Physics Laboratory listened to the beeps Sputnik’s signals produced. They noticed that the beeps had a Doppler Effect or Doppler Shift as the satellite passed by. Much like the sound a siren makes as a fire truck approaches, then as it passes, the sound of the siren seems different. The change in timing between the beeps let the scientist know Sputnik’s location. This led to the idea of reversing that process, to give a location on the Earth. Using radio frequencies to determine location in a two dimensional plane had been around since WWII, but using satellites would push this technology into the three dimensional realm. The United States Navy, Army, and Air Force all began developing their own GPS satellites in the 1960’s, but this was no small task. In the early 1960’s, the Navy launched its first Transit Satellite. The failure of this satellite, however, was due to

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The Global Positioning System

High-rate GPS has been widely used to construct displacement waveforms and to invert for source parameters of earthquakes. Almost all works on internal and external evaluation of high-rate GPS accuracy are based on GPS relative positioning. We build an experimental platform to externally evaluate the accuracy of 50-Hz PPP displacement waveforms. Since the shake table allows motion in any of six degrees of freedom, we install an inertial measurement unit (IMU) to measure the attitude of the platform and transform the IMU displacements into the GPS coordinate system. The experimental results have shown that high-rate PPP can produce absolute horizontal displacement waveforms at the accuracy of 2–4 mm and absolute vertical displacement waveforms at the sub-centimeter level of accuracy within a short period of time. The significance of the experiments indicates that high-rate PPP is capable of detecting absolute seismic displacement waveforms at the same high accuracy as GPS relative positioning techniques, but requires no fixed datum station. We have also found a small scaling error of IMU and a small time offset of misalignment between high-rate PPP and IMU displacement waveforms by comparing the amplitudes of and cross-correlating both the displacement waveforms.

High-rate precise point positioning (PPP) to measure seismic wave motions: an experimental comparison of GPS PPP with inertial measurement units

This technical note is concerned with the nonlinear state smoothing problem in the case that the measurements are randomly delayed by one sampling time. Under Gaussian domain, two general Gaussian approximation (GA) and Gaussian mixture approximation (GMA) smoothers are proposed in minimum mean square error (MMSE) sense. The smoothing implementation is transformed into computing some special posterior covariances, which triggers the development of the new unscented Kalman smoother (UKS) by applying unscented transformation (UT). Simulation results demonstrate the superior performance of the proposed GA-UKS and GMA-UKS algorithms.

Gaussian Smoothers for Nonlinear Systems With One-Step Randomly Delayed Measurements

High-rate precise point positioning (PPP) to measure seismic wave motions: An experimental comparison of GPS PPP with inertial measurement units

The demand for more sophisticated Location-Based Services (LBS) in terms of applications variety and accuracy is tripling every year since the emergence of the smartphone a few years ago. Equally, smartphone manufacturers are mounting several wireless communication and localization technologies, inertial sensors as well as powerful processing capability, to cater to such LBS applications. A hybrid of wireless technologies is needed to provide seamless localization solutions and to improve accuracy, to reduce time to fix, and to reduce power consumption. The review of localization techniques/technologies of this emerging field is therefore important. This article reviews the recent research-oriented and commercial localization solutions on smartphones. The focus of this article is on the implementation challenges associated with utilizing these positioning solutions on Android-based smartphones. Furthermore, the taxonomy of smartphone-location techniques is highlighted with a special focus on the detail of each technique and its hybridization. The article compares the indoor localization techniques based on accuracy, utilized wireless technology, overhead, and localization technique used. The pursuit of achieving ubiquitous localization outdoors and indoors for critical LBS applications such as security and safety shall dominate future research efforts.

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Seamless Outdoors-Indoors Localization Solutions on Smartphones: Implementation and Challenges

A unified approach to the ultra-tightly coupled GPS/INS Integrated navigation system is proposed. It is shown that other methods of ultra-tightly coupled GPS/INS integrated navigation systems are included in the proposed framework, and some implementation issues are discussed. In order to show the validity of the proposed approach, position accuracy and anti-jamming capabilities of three methods of ultra-tightly-coupled GPS/INS integration system, included in the proposed framework, were compared. The comparisons were carried out through computer simulations and post-processing of data from a GNSS hardware simulator. The results show that the proposed approach works well and gives accurate navigation output with anti-jamming capability.

Unified approach to ultra-tightly-coupled GPS/INS integrated navigation system

Demands on the indoor positioning capability is being increased. The assisted GPS (AGPS) needs the enhanced correlator scheme and the assistance information to acquire the weak GPS signal with strength below -150dBm within 2 ~ 3 seconds. This paper designs the AGPS receiver with an efficient digital correlator scheme that is able to reduce the squaring loss for weak signal acquisition. In order to evaluate the performance of the correlator scheme, this paper shows the success rates of signal acquisition under various environments. Finally, the performance of the designed receiver is analyzed with positioning accuracy and TTFF using assistance information from CDMA network of the cell phone

Design of an Assisted GPS Receiver and its Performance Analysis

A relationship between the sensor placement and the PDOP (Position Dilution of Precision) is derived in the TDOA-based localization system. And the geometric condition of the sensor placement is analyzed in order to get a minimum PDOP based on the derived relationship. Through computer simulations, effect of the sensor placement on the PDOP is observed.

Position DOP Analysis for Sensor Placement in the TDOA-based Localization System

Disclosed is a localization method of multiple based on a TDOA method, including calculating TDOA measurements step S 100 of arranging multiple sensors, and calculating TDOA measurement values while a reference sensor is changed, in turn; locating multiple jammers using all TDOA measurements step S 200 of calculating estimated location solutions of the multiple jammers; a finding a searching quadrant step S 300 of finding a quadrant having the highest density of the estimated location solutions; a setting a searching range and detecting searching cell step S 400 of deciding a searching range, and searching the searching cell; and determining estimated positions of the multiple jammers step S 500 of deciding the number of the jammers, and calculating location solutions of the multiple jammers. Therefore, the present invention can accurately localize the multiple jammers.

Localization method of multiple jammers based on TDOA method

The software GPS receivers based on the SDR technology provide the ability to easily adapt the other signal processing algorithms without changing or modifying the hardware of the GPS receiver. However, it is difficult to implement the software GPS receivers using a commercial processor because of the heavy computational burden for processing the GPS signals in real-time. This paper proposes an efficient GPS signal processing scheme to reduce the computational burden for processing the GPS signals in the software GPS receiver, which uses a fundamental notion compressing the replica signals and the encoded look-up table method to generate correlation values between GPS signals and replica signals. In this paper, it is explained that the computational burden of the proposed scheme is much smaller than that of the typical GPS signal processing scheme. Finally, the processing time of the proposed scheme is compared with that of the typical scheme, and the improvement in the aspect of the computational burden is also shown.

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Deok Won Lim

Papers

Unified approach to ultra-tightly-coupled GPS/INS integrated navigation system

Design of an Assisted GPS Receiver and its Performance Analysis

Position DOP Analysis for Sensor Placement in the TDOA-based Localization System

Localization method of multiple jammers based on TDOA method

An Efficient Signal Processing Scheme Using Signal Compression for Software GPS Receivers