# Barker Sequence for QPSK

I'm trying to implement a QPSK burst modulation and demodulation through a channel and I'm now considering the synchronization part.

I've read that Barker sequence were excellent option for this as their autocorellation looks like a dirac.

So far I know that they're composed of 1 and -1 and that the longest found is 13 characters long.

My question is the following:

Is there some adaptation of a Barker sequence for QPSK to make use of the complex representation or do you simply send a classic sequence using only 1 and -1 while you could use also i and -i?

• Polyphase Barker sequences have been studied (Google throws up multiple hits), but from a practical viewpoint, it is usually simpler to use binary Barker sequences on the I and Q channels. – Dilip Sarwate Jul 16 '13 at 13:08
• @DilipSarwate when you say binary Barker sequences on the I and Q channels you mean one on the I channel and one on the Q channel? – Leo Jul 16 '13 at 15:27
• Yes, that is what is I meant, and in fact, it is best to use the same binary Barker sequence on both channels so that you get BPSK during the synchronization phase. See, for example, a note on by Eric Jacobsen on comp.dsp which is also considering this topic right now. – Dilip Sarwate Jul 16 '13 at 19:11
• @DilipSarwate funny that you would mention the post on comp.dsp because I'm the one who posted it! Anyway thanks for all the usefull information. You should put it as an answer so I can accept it. – Leo Jul 16 '13 at 20:45