Is there a 'Nyquist Criteria' for the minimum samples per chip that are needed for a correlator? I've heard 2, but will 1 work? What are the implications of having less than the minimum (in the context of radar and communications)?
$\begingroup$
$\endgroup$
2
asked May 22, 2014 at 22:32
-
$\begingroup$ What exactly is this samples per chip quantity you're taking about? What is a chip? $\endgroup$– PhononCommented May 23, 2014 at 0:15
-
1$\begingroup$ @Phonon I believe that he is referring to DSSS chips. $\endgroup$– Jim ClayCommented May 23, 2014 at 0:30
Add a comment
|
2 Answers
$\begingroup$
$\endgroup$
Actually much less than 1 sample/chip will work for DSSS. Doing so erodes the spreading gain and makes chip level detection impractical, but it works. The undersampled spreading sequence simply acts as a vector (subspace) for the undersampled signal. Matched filtering is still matched filtering -- as long as you are still sampled well above the symbol (not chip) rate.
$\begingroup$
$\endgroup$
It is not a good idea to do 1 sample/chip because if you happen to have the samples at the chip transitions then demodulation will go poorly. Also, if you have much carrier offset you will likely lose and/or alias part of the signal.
