# Discrete-time model of 2-user CDMA system, recovered information at receiver using polarity detection?

I have discrete-time model of 2-user CDMA system with: $b_1=-1, b_2=+1, \alpha_1, \alpha_2, s_1, s_2$ and $n$ white noise.

What are the recovered infromation bits for user 1 and user 2 respectively if polarity detection is used? If the optimum MLE is used, what are the recovered infromation bits?

I tried to solve but stucked with polarity.

• I could do it: $b_1=s_1^T(b_1∗α_1∗s_1+b_2∗α_2∗s_2+n)$ ; $b_2=s_2^T(b_1∗α_1∗s_1+b_2∗α_2∗s_2+n)$
– Ab.
Nov 8 '11 at 13:01
• You're going to need to add some more details of your problem. It may be obvious to you, but definitions of the variables in your question would be helpful. Nov 8 '11 at 13:40
• In many cases, the MLE is the polarity method. There would be a difference this were a coded system or a system with intersymbol interference (ISI) and you were using something like maximum-likelihood sequence estimation, but as Jason R says, you need to give some more details, or be satisfied with the answer that you gave (which incidentally probably needs a sgn to get $+1$ or $-1$ from the real numbers that you compute) Nov 8 '11 at 15:20