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Hard Limiting

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FundamentalsFundamentals
Title Hard Limiting
Author(s) J.A Ávila Rodríguez, University FAF Munich, Germany.
Level Advanced
Year of Publication 2011

During the design of the GPS M-Code different multiplexing options were considered to achieve a constant envelope [P.A. Dafesh et al., 2006][1]. Together with the majority voting, hard-limiting of the C/A Code, P(Y) Code and M-Code signals was another considered option.

The hard-limiting approach basically forces the non-constant envelope of the sum of C/A Code and M-Code on one phase and P(Y) on the orthogonal phase (assuming we want to place the M-Code on the same phase as the C/A Code) to be constant by limiting the variation of the amplitude to its minimum value. The problem though is that the C/A Code and M-Code suffer from significant power losses and distortions. Indeed, the total efficiency of the hard-limiting modulation is roughly of 83 % as shown in [P.A. Dafesh et al., 2006] [1], what corresponds to approximately 0.8 dB of overall combining losses. Moreover, the power split between the different signals is not easy to achieve.


References

  1. ^ a b [P.A. Dafesh et al., 2006] P.A. Dafesh, Nguyen, M. Tien, Quadrature product sub-carrier modulation system, Patent US 7120198, Granted 10 October 2006.


Credits

The information presented in this NAVIPEDIA’s article is an extract of the PhD work performed by Dr. Jose Ángel Ávila Rodríguez in the FAF University of Munich as part of his Doctoral Thesis “On Generalized Signal Waveforms for Satellite Navigation” presented in June 2008, Munich (Germany)