In OTDR, BOTDR, BOTDA and other distributed sensors the use of coding techniques becomes very popular. This improves the SNR of the system and better spatial resolution is satisfied because the the pulse width is decreased without affecting the SNR. My question is why the use of simplex codes and not Hamming codes. The same for RZ code. I need a helpful reference that explains the difference between these codes. Thanks
RZ codes are mandatory in Brillouin sensors, because the amplitude of the acoustic wave has to return to zero before an other pump pulse is coming. There is a compltete paper on that : http://infoscience.epfl.ch/record/182038/files/765332_1.pdf
Kind of coding: Simplex is simply... the simplest :-) That does not mean that other kind of codes are useless. In fact, I believe that Simplex codes are not so efficient as they should. Moreover for a code length L one has to launch L sequences to retrieve the local information at one frequency, unless you use cyclic codes. But you mean intensity coded schemes: you can alos play in frequency...
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