Introduction to GNSS and GPS Accuracy
GNSS, or Global Navigation Satellite Systems, form the base of any GPS (Global Positioning System) navigation. In short, the GNSS offer information on the positioning of any object through a network of satellites. It offers an earth-based electronic receiver (referred to as a GPS Device hereafter) with signals (information) that helps the latter determine its location in terms of longitude, latitude, and height (the three basic angles offered by GNSS satellites) within a certain radius. The fourth angle (factor) is related to error correction in GPS devices using the precise time of signal reception and/or signal origination.
For example, if you are driving while using a GPS device, you need the fourth angle to know the exact time when your device received the signals, as you would have moved further by the time your device calculates the other three (longitude, latitude, and height) angles. If the fourth angle, the time of reception, is not taken into account, the information on your GPS device is a few meters back depending upon your speed (mph). Thus, the time of reception of GNSS signals or GNSS information plays an important role in enhancing the accuracy of GPS devices.
Although there are a few GNSS systems that are used by several GPS devices, the NAVSTAR Global Positioning System is the only one that is functioning fully at the moment. This is why most GPS devices rely on NAVSTAR for enhanced accuracy of GPS devices. Among other GNSS are GLONASS (Russia), Galileo (Europe), COMPASS (China), and IRNSS (India). However, these are still to be converted into GNSS with full functionality. (The last three are still in the deployment stage and are coined next-generation GNSS.)
GNSS in Short - GNSS offers information at regular intervals in form of analog signals about the longitude, latitude, and height of the GPS device so that the latter can calculate its position. The GPS device should have the feature whereby it can calculate the exact time when it received the GNSS signals. This helps in calculations that provide you with information about your location with minimum error coefficient. To ease this, GNSS also sends out time-stamps to the receptor.
FOOTNOTE: The military GPS systems take care that they do not miss out even on fractions of millimeters for enhanced accuracy of GPS devices. For stationary GPS, the reception time can be ignored. If your GPS device is connected to a central server, the time taken to transmit the information from the earth-based server to your machine should also be considered for further accuracy of GPS devices.
With this information in mind, we will be checking time-stamps in the coming section.