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The improvement of GPS dual-frequency positioning for precision
Aug 06, 2018

      High bit rate can effectively improve accuracy L1 's code rate is low, each code takes up about ten times minus six square seconds. Of course, these signals are the speed of light transmission, that is, three times 10 of eight times, then time times the speed of light is probably nearly 300 meters. L5 's code rate is 10 times times the L1, each code takes up 10 times times less time than L1, and becomes 10 minus seven times. Then times the speed of light is about 30 meters. Of course, this is a satellite resolution, if more than one satellite at the same time, a lot of satellite irradiation range to take the intersection, then the L1 precision will be far less than 300 meters.


  And L5 more accurate. There are many high-rise buildings in the city, satellite signals after the reflection of these buildings become very messy, and the correct direct signal intertwined, we call multipath (many paths). These signals are transmitted at the speed of light, and even a small signal delay caused by a tiny reflection is a great distance from the speed of light multiplication.


  And these are the sources of error. L5 Letter number rate is high, the spectral density is easier to concentrate.


  Although the L5 will also reflect, the probability that the error signal after reflection and the correct direct signal superposition creates a new spectral density peak is relatively low, making it easier for the computing engine to find direct satellite signals. L5 High code rate so good, why not directly with L5? This is because the L1 low bit rate is more easily captured, we have to precision and can not sacrifice the location time.


  So L1 is also called a rough capture code, and after the signal is captured, L5 can participate in the calculation.


  Two frequencies to eliminate ionospheric errors If only the L1 signal, the phone will be received after the L1 is direct.


  In fact, L1 may have been refracted in the atmosphere, and refraction will lead to a certain delay, the atmosphere of this delay will cause a lot of errors, many scientists believe that the atmospheric error accounted for all the error of 60% weight. Different frequencies of the signal through the same medium refractive index is different. L5 are born and L1 different frequencies.


  The satellite also emits two frequencies of signals, and the phone receives a different time, giving the phone an opportunity to calculate the atmospheric error and eliminate it. GPS dual-frequency can only cancel ionospheric error, multipath error can not be eliminated (although the L5 signal multipath has improved), NLOS (not direct signal) can not be eliminated. However, the latter two are the main error sources in the mobile phone location in urban environment.


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