From Space to Earth and Inside your GPS - How GPS Systems Work?
Before talking about the working of GPS gadgets that you carry for different purposes such as tracking, navigation, or mapping, we need to know about the signals that help your GPS devices calculate the information. You know that there are several satellites in the space that continuously transmit signals that help your GPS devices to display required information.
The GPS satellites are not individual satellites orbiting the earth but are a set of four or more satellites known as a GNSS (Global Navigation Satellite Systems). The aim of GNSS is to supply data at regular intervals to the GPS ground stations and GPS devices. The data from GNSS helps in fixing the position of the GPS device. As the satellites use radio waves to send the GPS data, the data is subject to problems like any other device reliant on radio waves. For example, your cellphone service provider also employs radio waves to transmit data. You must have noticed that you cannot receive the cellphone signals properly in remote areas, noisy places, and in closed areas. Similarly, GPS signals too are degraded as they travel from the space to your GPS set. Plenty of factors contribute to GPS signal degradation. These include objects that do allow radio waves to pass through, weather, and more.
To get around with this problem, GNSS sends signals at two frequencies along with time stamps for the signals so that the GPS ground stations can relate the signals to help your GPS device compute the data with maximum accuracy. Still, there are times when your GPS device cannot receive the GPS signals - resulting in GPS Blackouts.
Also, the frequencies for military are different from those for civilian uses. This means that GNSS transmits GPS data at two levels: L2 for military purposes and L1 for civilian uses. The L2 signals for military use high encryption so that normal devices cannot decrypt the signals.
As the GPS signals travel miles to reach your GPS device, they may become weak and distorted due to atmospheric disturbances, urban blockages, and other factors. If the signals become weak, your GPS device will give you incorrect results. The GPS devices need minimum signal strength to offer you accurate readings. Please read our article on How GPS Satellite Detection Sensitivity Affects GPS Accuracy to understand how the GPS devices function once the GPS receiver obtains the signals.
Plenty of methods exist that help to increase the accuracy of GPS when the signals are weak. One of such methods formerly used in aviation is now being used in normal GPS systems too. Known as WAAS (Wide Area Augmentation System), the method helps increase the accuracy of your GPS devices.
The above tries to explain GPS systems and how they work. If you have doubts or if you wish to add anything on how GPS systems work, please feel free to use the comments section.