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COMPASS/BEIDOU 2B E2 Code Generators

 

Grace Gao, Alan Chen, Sherman Lo, and Per Enge

 

On April 13, the first Medium Earth Orbit (MEO) satellite of the Compass GNSS system was launched on April 13, 2007.  The satellite orbits at an altitude of 21,550 kilometers above the Earth. Conventionally designated Beidou 2B, it has been observed to transmits on 3 distinct frequencies: 1561.1MHz, 1268.52 MHz, 1207.14MHz.  The 1561.1 MHz signal (essentially the Galileo E2 band) is a BPSK(2) signal.  At Stanford University, we collected signals from the satellite on May 7, 2007 using the Stanford GNSS Monitor Station (SGMS).  The results were processed in a similar manner to the GIOVE-A code to determine the COMPASS code.

Figure 1. Spectrum of COMPASS E2 centered at 1561.1 MHz from data collected using the SGMS

 

Results:
  • The code is a linear code based on 11 stage Gold Codes
  • The CNES indicated that the E2 and E5B broadcast code should be the same [1]

E2 code: 2046 chips, 1ms, Gold code

Polynomial 1: X11+X10+X9+X8+X7+X+1 

Polynomial 2: X11+X9+X8+X5+X4+X3+X2+X+1

Initial state 1: [0 1 0 1 0 1 0 1 0 1 0 ]

Initial state 2: [0 0 0 0 0 0 0 1 1 1 1]

 

LINKS

COMPASS E6 Code, (TO BE CREATED LATER)

 

References

[1]. Thomas Grelier, Joel Dantepal, Antoine Delatour, Alain Ghion, and Lionel Ries, "Initial Observations and Analysis of the Compass MEO Satellite Signals", InsideGNSS June 2007

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