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How despreading in DSSS is achieved?

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fanshuo

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hi all,
I am not very familiar with DSSS.
I want to know how despreading is achieved? by simply multiplication with the corresponding PN ? or It depends on how the signal is spreaded?

Because I found that the spreading in 802.15.4 is achieved by mapping not multplication. I do no know how despreading will be achieved?

thanks!
 

mhamed

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how to despread?

Speading will be acheived by multiplying a key c(t) ,which behave such a psudo noise, to your original signal s(t). c(t) is consists of -1 and 1. so at the receiver side when you multiply the received signal by c(t), you will have c(t)^2 s(t). the first term is always 1.
Zigbee (IEEE802.15.4) use BPSK as its modulation. in this case the transmitted signal is c(t) or -c(t). so in receiver you only need to discover if it is c(t) or -c(t) (e.g. by considering the first bit only). Is it clear?
 
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islamianb4u

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Re: how to despread?

Please Read this book you can download it from TLFebook website

Springer.Principles.of.Spread.Spectrum.Communication.Systems.eBook-TLFeBOOK
 

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