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since usually in spread spectrum systems the length of PN sequence is very long, it is not economically efficient to correlate recieved signal with the whole PN sequence to detect your desired(which you know it's PNseq) user. so they invent new codes that exhibit such charactristics so you can do the detection with smaller length correlators....
I want to know how we can corrolate a little number of PN code to find peak (in acquisition)? because in 1023 length code the FPGA dosent have enough space to make this corrolation (or multiplication).
shift 1 by 1 and corrolate is dificult if the code has 1023 lentghes.
please continue the ...
I want more and more.
how we can invent such smaller code.please send more information about it.
1-excuse me, last time i was not quiet sure and also what i'm saying now is just my understandings and may not be quiet right. for example i'm not quiet sure about the possiblity of doing the correlation with smaller length correlators.
2-I took a look at my reference and it said :"rapid synchronization of long codes often requiers an estimate of the correlation between recieving code and the despreading one be made in less than a full code period. thus this correlation estimate is based on a partial period...". THIS is the purpose of partial correlation. I dont think that it is a replacement for desired user detection by complete autocorrelation. clearly, partial correlation function is depends upon it's size(the length of correlation window) and it's begining time and it shows the number of agreements (between recieved and despreading code) minus disagreements. think about it....if we use partial correlator as a "desired user code detector" instead of complete correlator, then how can we determine the difference between two DIFFERENT codes that accidentally have the same first 128 bits but differ in remaining bits?! you see, it is not ENOUGH and we need the complete correlator anyhow.
3-As a FPGA designer, may i ask you why do you think "in 1023 length code the FPGA doesnt has enough space to make this corrolation"?!!!!
assuming that you have a 1024 length code. i think it is 1024 bits and it costs you only 1024 flipflops for a shiftregister plus you need some thousands of XORs to do the correlation and it counts NOTHING in any of FPGAs!(I wonder why did you say multiplications! when you are working with bits of data you should use XORs for correlation).
4- My reference is "spread spectrum communiations" by "Ziemer", chapter 3 is about codes and their characteristics. but i think you should search the net for FPGA implementation of spread spectrum reciever...
I would like to addsomething according to my readings.
Partial correlation some times happened due to multuirate system. means that when different users allocated with different code lengths according to their data type (voice, data, multi...) then in the receiver side, the a full correlation will be done between users with same code length and a partial correlation will be done between users with different length. this is in case of synchronization.
on the other hand, the partial correlation may occure between 2 users with same data rate but without synchronization, then the receiver will try to detect the transmitted signal based on the overlabing between the transmitted code and the stored one on the receiver.