ECE 415 GPSprelim2 - CA code and P code are broadcast 90...

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ECE 415 GPS  Prelim 2 Notes Chapter 6 – GPS Observables GPS Signal Composed of two carriers called L1 and L2, and two modulator codes called CA code,  and P code. 3 Physical quantities can be observed from the GPS signal o Code Arrival time o Integrated Carrier phase (as it changes in an interval) o Frequency of signal-generally not used in determining the navigation solution Non-dispersive medium – radio wave frequency does not depend on the medium.  o Group Velocity = c speed of light Phase path = true range/lambda = # number of wavelengths between satellite and  receiver Measured phase by receiver  = integrated carrier frequency – LO frequency of receiver GPS signal frequency is designed to be constant Fundamental Frequency of all signals = 10.23 MHz Structure S = AG(t)D(t) cos(wl1t ) + AP(t)D(t) sin(wl1t)] o G – CA code modulator, P – precise code modulator
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Unformatted text preview: CA code and P code are broadcast 90 degrees out of phase Received signals will differ in frequency due to Doppler shift in frequency since both satellite and receiver are moving relative to each other. CA code is a fixed 1023 chips (fixed pattern of bits) Each satellite has its own CA code 1 chip = 1540 cycles of carrier signal 20 x 1023 PRN chips = 1 data bit CA code is 1 ms long, and thus repeats 1000 per second Subframes 1-3 contains all necessary information = ephemerides, GPS time, sat clock corrections Subframes 4-5 contain almanacs older or less accurate ephemerides 25 frames = 12.5 minutes are needed to transmit the full almanacs Data is modulated at 50 bps for the navigation message on L1...
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ECE 415 GPSprelim2 - CA code and P code are broadcast 90...

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