How GPS Works
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Questions and Answers

What is the primary function of Differential GPS?

  • To reduce the effect of multipath interference
  • To increase the number of satellites in view
  • To increase the signal strength of GPS signals
  • To improve the accuracy and correct bias errors at one location (correct)

    • What type of errors are corrected in Differential GPS?

  • Ionosphere and troposphere delays, receiver noise and multipath
  • Satellite clock and orbit errors, receiver noise and multipath
  • Multipath, receiver noise and atmospheric delays
  • Satellite clock differences, ephemeris errors and atmospheric delays (correct)

    • What is the main effect of increasing age or latency of corrections on DGPS?

  • Increase in accuracy
  • No effect on accuracy
  • Decrease in accuracy (correct)
  • Increase in satellite visibility

    • What is the typical error increase in DGPS per 100 km of separation distance?

    <p>0.5 m</p> Signup and view all the answers

    What is the main advantage of using Differential GPS?

    <p>Improved accuracy and correction of bias errors</p> Signup and view all the answers

    What is the typical maximum separation distance recommended for DGPS?

    <p>50 km</p> Signup and view all the answers

    What is the primary purpose of the GPS receiver obtaining signals from at least four satellites?

    <p>To determine the receiver's position in three-dimensional space</p> Signup and view all the answers

    What is the term for the measured propagation time delay between the satellite and the receiver?

    <p>Time of flight</p> Signup and view all the answers

    What is the purpose of the ephemeris data in GPS calculations?

    <p>To determine the satellite's position</p> Signup and view all the answers

    What is the term for the error in the measured range due to the receiver's clock bias?

    <p>Pseudo-range error</p> Signup and view all the answers

    What is the purpose of the fourth satellite in GPS calculations?

    <p>To synchronize the receiver's clock</p> Signup and view all the answers

    What is the frequency of the L1 carrier signal in GPS?

    <p>1.57542 GHz</p> Signup and view all the answers

    What is the purpose of the Coarse/Acquisition (C/A) code in GPS?

    <p>To provide free public access to GPS signals</p> Signup and view all the answers

    What is the term for the process of determining the satellite's position using ephemeris data?

    <p>Orbit determination</p> Signup and view all the answers

    What is the purpose of the GPS receiver's clock bias calculation?

    <p>To synchronize the receiver's clock with GPS time</p> Signup and view all the answers

    What is the term for the calculation of the receiver's position using ranging equations?

    <p>Navigation solution</p> Signup and view all the answers

    What is the primary factor that determines the Dilution of Precision (DOP) in GPS receiver calculations?

    <p>Number of satellites and their location</p> Signup and view all the answers

    What is the result of good geometric DOP in GPS receiver calculations?

    <p>Smaller error and good geometry</p> Signup and view all the answers

    What is the primary purpose of Differential GPS (DGPS) in precision GPS applications?

    <p>To provide sub-meter accuracy in GPS positioning</p> Signup and view all the answers

    What is the effect of bad visibility on GPS receiver calculations, even with good GDOP?

    <p>Results in poor GDOP</p> Signup and view all the answers

    What is the role of reference stations in Differential GPS (DGPS) applications?

    <p>To calculate and broadcast corrections for various errors</p> Signup and view all the answers

    What is the benefit of using multiple satellites in GPS receiver calculations?

    <p>Reduces DOP and improves geometry</p> Signup and view all the answers

    What is the effect of satellite geometry on GPS receiver calculations?

    <p>Reduces error and improves accuracy</p> Signup and view all the answers

    What is the purpose of the broadcast corrections in Differential GPS (DGPS) applications?

    <p>To provide real-time corrections for various errors</p> Signup and view all the answers

    Study Notes

    GPS System Overview

    • GPS receivers use radio signals from satellites to calculate their current position and speed/direction
    • The system requires a minimum of three satellites in view to provide a location solution

    How GPS Works

    • A GPS receiver measures the time delay between when a signal is sent and when it is received to calculate the distance from the satellite
    • The distance is calculated by multiplying the time delay by the speed of light
    • The receiver uses the intersection of three or more spheres (one for each satellite) to determine its location

    GPS Timing Solution

    • GPS satellites have highly accurate atomic clocks, which provide GPS time
    • Civilian GPS receivers have less accurate quartz clocks, which require synchronization with GPS time
    • The receiver clock bias is calculated using a fourth satellite signal, which provides a fourth equation to solve for the clock bias
    • The navigation solution provides the user's location in three-dimensional space (x, y, z)
    • The solution requires a minimum of four satellites in view to determine the user's location and clock bias

    GPS Signal Structure

    • GPS satellites transmit two carrier frequencies: L1 (1.57542 GHz) and L2 (1.22760 GHz)
    • Each satellite transmits two distinct spread spectrum codes: C/A (coarse/acquisition) and P (precise) codes

    Geometric Errors (DOP)

    • The accuracy of a GPS location is affected by the geometric configuration of the satellites in view
    • A good geometric configuration provides a low DOP (dilution of precision) factor, while a bad configuration results in a high DOP

    Differential GPS (DGPS)

    • DGPS provides sub-meter accuracy by using reference stations to calculate and broadcast corrections for various error sources
    • Corrections are used to correct pseudorange, satellite ephemeris, clock offsets, and propagation errors due to ionospheric and tropospheric effects

    Error Sources in GPS

    • Typical error sources in GPS include satellite clock errors, orbit errors, ionospheric and tropospheric delays, receiver noise, and multipath effects
    • DGPS can correct for most of these errors, except for multipath effects and receiver noise

    DGPS Errors

    • DGPS errors increase with the age of the corrections and the distance between the reference station and user
    • Errors can be minimized by using corrections within 10s and separation distances within 50 km

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    Description

    Learn how GPS or GNSS works, including how satellites transmit signals and how receivers calculate current position and speed. Discover how time and distance are used to determine location.

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