Measuring GPS Signal Strength – An Overview
GPS devices rely on the data received through the radio signals sent by GNSS. A GNSS can be defined as a network of satellites orbiting the earth that send data regarding the altitude, longitude, and latitude of the GPS receiver. At the moment, there are around 31 satellites catering to the worldwide GPS systems. Based on the data sent by these satellites, your GPS device computes your location and helps you with navigation, tracking something, or mapping an area. Apart from these basic uses, the GPS systems provide other important information used by military and other high level government agencies.
There are several methods to measure GPS signal strength. However, as the data sent by GNSS is through radio signals, the most common methods used by civilians are the ones related to telecommunications, including the Received Signal Strength Indication (RSSI, based on the IEEE 802.11 protocol). In addition, different GPS manufacturers use their own GPS algorithms to create code for calculating GPS signal strength.
It is a known fact that radio signals cannot maintain their strength for longer distances. Hence, the signals are sent with enough strength to reach the Earth's surface. The NAVSTAR (US controlled GNSS) system employs phase modulation to superimpose data on the radio signals for better reception by the GPS receiver. The manufacturers employ different algorithms to retrieve the data from the radio signals for offering the desired data. Thus, the measure of GPS signal strength is strongly vendor dependant.
The next section discusses the factors and obstructions encountered to measure GPS signal strength. It also offers a quick look at the RSSI measurements.