How despreading in DSSS is achieved?

[fanshuo]

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!

 

[fanshuo]

how to despread?

anybody?

 

[mhamed]

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?

 

[islamianb4u]

Re: how to despread?

Please Read this book you can download it from TLFebook website

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