1. Signal Strength

• Power of the Signal: The strength of the GPS signal as it arrives at the receiver is critical for accurate positioning. Weaker signals (due to distance, obstructions, or interference) can result in poor positioning accuracy or even signal loss.
• Multipath Errors: When GPS signals bounce off nearby objects (such as buildings, trees, or the ground), the signal arrives at the receiver at slightly different times. This can cause multipath errors, reducing the accuracy of the GPS fix.
  • Further understanding towards the 'Signal Multipath and Reflections':
    • Multipath Propagation: This occurs when GPS signals reflect off nearby surfaces (buildings, rocks, vehicles, etc.) and take a longer path to the receiver. This can cause errors in calculating the position because the signal arrives at slightly different times from the reflected signal.
    • Urban Canyon Effect: In urban areas with tall buildings, GPS signals can bounce off surfaces and cause multipath errors. This is why GPS accuracy in cities can often be worse than in open areas.

2. Sky Visibility

• Clear Line of Sight: GPS receivers need a clear line of sight to multiple satellites to provide an accurate position. Obstructions like tall buildings, dense foliage, or mountains can block the signals from satellites, leading to degraded signal quality.
• Number of Satellites Visible: The more satellites a GPS receiver can "see" (i.e., the more it can communicate with), the better the accuracy. Typically, having signals from at least four satellites is required for a 3D position (latitude, longitude, and altitude).

3. Satellite Geometry

• Satellite Positioning: The arrangement of the GPS satellites in the sky influences the quality of the GPS fix. If the satellites are clustered too closely together (poor geometry), the receiver may struggle to calculate an accurate position. Ideally, satellites should be spread out across the sky to improve accuracy.
• Dilution of Precision (DOP): This refers to the effect of satellite geometry on positional accuracy. A high DOP (indicating poor geometry) can lead to less accurate positioning, while a low DOP (indicating good geometry) means higher accuracy.
  • 'DOP' is a general term based on the geometry of the satellites in the sky. Yarbo uses 'HeadingDop' to represent the 'HDOP'. Which actually means the 'Horizontal Dilution of Precision'. It is a measure of the accuracy of a GPS receiver's horizontal position (latitude and longitude) based on the geometry of the satellites used to calculate the position.

4. Atmospheric Conditions

• Ionosphere: The ionosphere, a layer of charged particles in Earth's upper atmosphere, can slow down GPS signals, especially during solar activity. This can cause delays in signal arrival and result in positioning errors.
• Troposphere: The troposphere, the lower layer of the atmosphere, also affects GPS signals. Variations in temperature, pressure, and humidity can cause signal delays, which can degrade the accuracy of GPS positioning.
• Solar Activity: Solar flares and geomagnetic storms can interfere with GPS signals, leading to signal degradation or temporary outages.
  • It happened once in early 2024 and actually affected Yarbo's performance.

5. Receiver Quality

• Antenna Design: The quality of the GPS receiver’s antenna plays a significant role in signal reception. A high-quality antenna with good gain and directional sensitivity can improve the GPS signal reception and reduce the effects of multipath errors.
• Receiver Sensitivity: The sensitivity of the GPS receiver itself determines how weak a signal it can detect. Modern GPS receivers are generally more sensitive and can handle weaker signals, but older or lower-quality receivers may struggle in poor signal conditions.

6. Interference

• Radio Frequency Interference (RFI): External sources of electromagnetic interference, such as nearby radios, cell phones, power lines, or electronic devices, can disrupt GPS signals. This can cause the GPS receiver to lose lock or experience inaccuracies.
• Jamming: Intentional GPS jamming (which is illegal in most countries) can block or distort GPS signals, making it impossible for receivers to maintain a reliable fix.
• Noise: Electronic noise from nearby devices can interfere with the GPS signal, affecting its quality and reliability.

7. Satellite Health and Maintenance

• Satellite Signal Integrity: GPS satellites are monitored by ground stations to ensure they are functioning properly. If a satellite is malfunctioning or has been decommissioned, it may provide inaccurate or unreliable signals.
• Satellite Upgrades and Replacements: Occasionally, older satellites may be replaced or upgraded to newer models to ensure better signal quality and accuracy.

8. Ephemeris and Almanac Data

• Ephemeris Data: This data includes information about the position and trajectory of each satellite. If the ephemeris data is outdated or inaccurate, it can affect the accuracy of the GPS position.
• Almanac Data: This is a less detailed dataset that contains information about the general location of all GPS satellites in orbit. If the almanac data is old or corrupted, it can take longer for the GPS receiver to acquire satellites when it first starts up.

9. Signal Processing Algorithms

• Filter and Correction Algorithms: GPS receivers often use algorithms like Kalman filters or pseudo-range correction techniques to improve the accuracy of the position solution. The effectiveness of these algorithms can have a significant impact on the final GPS signal quality.
  • We have not applied these filters and corrections yet. The RTK antenna provider did not mention anything about this.
• Differential GPS (DGPS): DGPS improves accuracy by using ground-based reference stations to send corrections to GPS receivers. This can significantly reduce errors in positioning.