GPS performance indicators

　　1. Satellite track

　　There are 24 GPS satellites orbiting the earth in six orbits (groups of four), and generally no more than 12 satellites are on the same side of the earth, and most GPS receivers can track 8 to 12 satellites. At least 3 satellites are required to calculate LAT/LONG (2D) coordinates. Add one more to calculate 3-dimensional coordinates. For a given location, the GPS receiver knows which satellites are nearby at the time because it is constantly receiving updates from the satellites.

　　2. Parallel channel

　　Some consumer GPS devices have 2 to 5 parallel channels to receive satellite signals. Because up to 12 satellites may be visible (the average is 8), this means that the GPS receiver must visit each satellite in sequence to obtain information about each satellite.

　　Most GPS receivers on the market are of the 12-parallel channel type, which allows them to continuously track the information of each satellite. The advantages of 12-channel receivers include fast cold start and initialization of satellite information, and can have more information in forest areas. good reception. Generally 12 channel receivers do not need an external antenna, unless you are in an enclosed space, such as a cabin, a car.

　　3. Positioning time

　　This is the time it takes for your GPS receiver to determine your current location when you restart it. For a 12-channel receiver, if you are near the location of the last positioning, the positioning time is generally 3 to 5 minutes during a cold start and 15 to 30 seconds during a hot start, while for a 2-channel receiver, the cold start is mostly more than 15 minutes, 2 to 5 minutes during hot start.

　　4. Positioning accuracy

　　The horizontal position positioning accuracy of most GPS receivers is around 5m to 10m, but this is only when SA is not turned on.

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