GPS analyzes the composition and principle of satellite signals
In GPS high-frequency unit design using high-frequency, low-noise amplifiers, in order to attenuate the GPS antenna thermal noise and the first few levels of unit circuitry on the performance of the receiver; in GPS using the antenna principle of GPS when satellites to achieve navigation and positioning, the user's receiver's main task is to extract the pseudo-random noise code and data code in the satellite signal to further address the position, velocity and time (PVT) of the receiver carrier and other navigation information. Therefore, the GPS receiver is the key to user equipment.
The current practical application of GPS receiver circuit is generally composed of antenna unit, RF unit, communication This paper analyzes the unit and solves the four parts of the unit and the four parts of the GPS satellite signal composition based on the RF front-end GP principle and application in 2010.
First, the GPS composition satellite signals
GPS satellite signal using typical code division multiple access (CDMA) synthesis modulation technology, its complete signal mainly includes carrier, pseudo-random code and data code. Signal carrier L band, the two carrier center frequency are recorded as L1 and L2. reference satellite signal clock frequency f0 is 10.23MHz, the signal carrier L center frequency of 1f0 154 times the frequency, that is:
fL1=154×f0=1575.42MHz (1)
Its wavelength λ1=19.03cm; signal carrier L2 center frequency is 120 times frequency of f0, i.e.:
fL2=120&TImes;f0=1227.60MHz (2)
Second, GPS antenna principle analysis
Its wavelength λ2 = 24.42cm. the frequency difference between the two carriers is 347.82MHz, about 28.3% of the carrier frequency of L2 is easy to measure or eliminate the navigation signal GPS when the satellite propagation to the receiver, the ionosphere effect caused by the transmission delay error. Pseudo-random noise code (PRN) that is, ranging code is mainly fine ranging code (P code) and coarse ranging code (C/A code) two kinds of P code code code rate of 10.23MHz, C/A code code rate of 1.023MHz. data code is the GPS satellites in the form of binary to the user's receiver to send navigation and positioning data, also known as the navigation message or D code mainly includes the satellite calendar, the satellite clock corrections, ionospheric Delay correction, work status information C / A code is converted to capture P total message consists of 1500 bits, divided into 5 sub-frames, each sub-frame 6 s within the launch of 10 words, each word 30, a total of 300, so the baud rate of the data code is 50bps.
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