We have seen that the entire system of GPS is dependent on a network of 24 satellites orbiting the earth. While research and development work is still going on to develop more and more accurate systems, it would be a good idea to understand what the external sources of error are.
What's a GPS signal?
There are two frequencies of low power radio signals that GPS satellites transmit. These are called L1 and L2. The L1 frequency at 1575.42 MHz in the UHF band is what comes into play for civilian applications. These signals can pass through clouds, glass, plastic and such light objects, but cannot go through more solid objects like buildings and mountains.
Every GPS signal packs three bits of information- these are the pseudorandom code, ephemeris data and almanac data. The pseudorandom code is the identification code of the individual satellite. The ephemeris data identifies the location of each GPS satellite at any particular time of the day. Each satellite transmits this data for the GPS receivers as well as for the other satellites in the network. The almanac data has information about the status of the satellite as well as current date and time. The almanac part of the signal is essential for determining the position.
Possible Causes of Error
Apart from the inaccuracy of the clock in the GPS receiver, there can be other factors that affect the quality of the GPS signal and cause calculation errors. These are:
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