GPS positioning accuracy

　　GPS positioning accuracy can be inspected under static and dynamic conditions, and the dynamic positioning effect is better than the static positioning. The nominal positioning parameters of the GPS module refer to those measured in a fully open sky with good satellite signals. Therefore, it is difficult to achieve the nominal positioning time and positioning accuracy in conventional testing. There are two common methods to describe horizontal positioning accuracy: one is "horizontal positioning accuracy", and the other is "horizontal positioning accuracy"? M CEP, namely circle probability error, means that 50% probability of the measured point is located at a circle center with the real coordinate as the center, and the probability of the measured point is 50%? M is within the circle of radius; Second is? M 2DRMS, i.e. twice the average root mean square error of water, means that there is about 95.5% probability that the measured point is located at a circle center with the real coordinate as the center? M is within the circle of radius.

　　The positioning accuracy of the GPS module depends on many aspects, such as the satellite clock error and orbit error from the GPS system, the number and geometric distribution of visible GPS satellites, solar radiation, atmosphere, multipath effect, etc. In addition, the same GPS module will generate different positioning errors due to antenna and feeder quality, antenna position and direction, test time period, open sky range and direction, weather, PCB design, etc. Even if different GPS modules of the same manufacturer and model are tested simultaneously with antenna diversity, the static drift will be different.

　　The GPS module is often used as the time reference in practical applications, supplemented by the RTC inside the module, which can obtain very high precision time reference, providing great convenience for product design. As for GPS velocity measurement, it is only an expanded application of simple calculation based on longitude and latitude.

　　The common antenna of GPS is a ceramic flat antenna, which has low cost, an external active amplifier circuit, a single direction of receiving signal, and a high gain ratio, so it is widely used. However, its disadvantage is that it is large in size and prone to frequency drift caused by temperature. If the ceramic area is smaller, the receiving gain will be affected; If it is thinned, the receiving bandwidth of the receiving antenna will be affected, and it will also be affected by the active amplification part. The size with good use effect is 25 × twenty-five × 4mm3。 The ceramic antenna has the best effect when it is placed vertically upwards in actual use.

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