023mcps data 50bps 1023mcps p code eecs 455 univ of

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Unformatted text preview: P Code EECS 455 (Univ. of Michigan) − 2Pp sin(2π f1 t ) Fall 2012 October 16, 2012 6 / 62 Lecture Notes 12 GPS Transmitter (L2 band) 50bps Data 10.23Mcps 2Pp cos(2π f2 t ) P Code EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 7 / 62 Lecture Notes 12 C/A Gold Code Generator 1 2 3 4 5 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 8 / 62 Lecture Notes 12 C/A code (Gold Code) Generator Notes Initial state of shift registers is the all one state. Addition is done mod 2 (exclusive or). The taps of the lower shift register (shown dotted) are different for different satellites. The sequence has a period of 1023 chips. Period of sequence is 1 ms. Sequence of 0’s and 1’s mapped to +1 and -1 (0 → 1, 1 → −1) before modulation. Data bit duration is 20ms (50bps) which means the Gold code repeats 20 times per data bit duration. EECS 455 (Univ. of Michigan) Fall 2012 October 16, 2012 9 / 62 Lecture Notes 12 Gold Code Generator Notes Satellite 1 2 3 4 . . . Connections 2⊕4 3⊕7 4⊕8 5⊕9 . . . EECS 455 (Univ. of Michigan) First 10 chips (octal) 1440 1620 1710 1744 . . . Fall 2012 First 10 chips (binary) 1 100 100 000 1 110 010 000 1 111 001 000 1 111 100 100 . . . October 16, 2012 10 / 62 Lecture Notes 12 Gold Code Waveform 2 1.5 Satellite Code 1 1 0.5 0 −0.5 −1 −1.5 −2 0 0.2 0.4 0.6 time (s) 1 1.2 −3 x 10 1 Satellite Code 1 1.5 1 0.8 2 1.5 Satellite Code 1 2 0.5 0 −0.5 Repeat 0.5 0 −0.5 −1 −1 −1.5 −1.5 −2 0 0.5 1 1.5 2 time (s) EECS 455 (Univ. of Michigan) 2.5 3 3.5 −2 0.98 4 −5 x 10 Fall 2012 0.985 0.99 0.995 1 1.005 time (s) 1.01 1.015 1.02 −3 x 10 October 16, 2012 11 / 62 Lecture Notes 12 GPS C/A Link Analysis Transmitted power (C/A code) is Pt =479W (26.8dBW). Frequency 1575.42 MHz, wavelength λ = .1904m. Range d = 2 × 107 m. Path loss (λ/(4π d ))2 = 182.4dB. Atmospheric attenuation: 2 dB. Received signal power (P ): -157.6 dBW. Received signal power density (P /W ): -220.6 dBW/Hz. Noise power spectral densi...
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