# Demodulation of direct sequence spread spectrum technique [closed]

I can't intuitively believe that a signal could be demodulated whose voltage is below the noise floor. Can some one explain me how this demodulation of direct sequence spread spectrum happens without mathematics ?

## closed as too broad by Marcus Müller, Dmitry Grigoryev, brhans, Voltage Spike, uint128_tApr 4 '17 at 18:57

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• This is an easily researchable question. VTC telecomabc.com/d/dsss.html – Voltage Spike Apr 4 '17 at 15:19
• "Please explain to me what is written in hundreds of textbooks." No, we can't write a textbook that is quicker to read then your textbook. Go read a textbook. – Marcus Müller Apr 4 '17 at 15:43
• without mathematics won't work, by the way. that's really asking for "how does this mathematical algorithm work? Explain without math!". This is digital communication. The things we do are always very math-y. – Marcus Müller Apr 4 '17 at 15:44

Take two such receivers and add the outputs together. Your signal becomes twice as big but your noise only becomes $\sqrt2$ bigger. Therefore your signal to noise increases by 3 dB. The noises are uncorrelated hence they only become 3 dB bigger whilst your signals are totally correlated hence they become twice as big.
Two receivers give a 3 dB increase in signal to noise ratio and adding more receivers and channels improves this figure but there is a law of diminishing returns because to achieve 6 dB improvement you need 4 receivers/channels etc. 1024 channels is $2^{10}$ hence a 30 dB improvement can be realised.