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long PN sequence' usage in CDMA

Started by Laron September 9, 2009
Hi all,
     there always said long PN sequence(period 2^n-1) got a small
cross-correlation  property as -1/(2^n-1). But in practice, one symbol
could only be spread by a small amount(128 etc) but not 2^n-1, so how can
we guarantee the cross correlation property -1/(2^n-1)? Thanks.


B. R.
Laron
On Tue, 08 Sep 2009 22:37:01 -0500, Laron wrote:

> Hi all, > there always said long PN sequence(period 2^n-1) got a small > cross-correlation property as -1/(2^n-1). But in practice, one symbol > could only be spread by a small amount(128 etc) but not 2^n-1, so how > can we guarantee the cross correlation property -1/(2^n-1)? Thanks.
You can't. The level of noise from other transmitter's PN-modulated traffic can be high, which is why there are layers of synchronous demodulation and error correction after the first despreading. -- http://www.wescottdesign.com