Suppose two users in a Direct Sequence-CDMA system have signatures (that is, seq

Question

Suppose two users in a Direct Sequence-CDMA system have signatures (that is,
sequences of chips) given by (1 -1 1 -1) and (1 1 -1 -1), respectively.

(a) Evaluate the correlation between the two signatures.

(b) Sketch the baseband signals for the two users when user 1 sends the bits 011, and
user 2 sends the bits 101. Add the signals for the first bit only, and show that the
output of the correlator for user 1 is -4, corresponding to a 0, and the output of the
correlator for user 2 is 4, corresponding to a 1.


(c) Suppose now that user 2 is assigned the signature (1 -1 1 1). Adding the signals as
in part (b), what is the output of the correlator for user 1 for the first bit? Explain the
effect of changing the signature in terms of the likelihood of making an error when
additional noise and interference is present.

Explanation / Answer

CDMA stands for code division multiple access. There are two varients of it. 1) DSSS. Direct sequence spread spectrum. Technology that is being utilized in 3G mobiles 2) FHSS. Frequency hoping spread spectrum. A technique that is utilized in Blue Tooth. the exact difference is that gsm has a sim card and the other doesn't (you are tied to the phone)

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