Large deviations for CDMA with interference cancellation

For a code division multiple access (CDMA) model we compare the bit error probability (BEP) without interference cancellation, with the BEP after interference cancellation. Using large deviation theory we calculate for both cases the exponential rates, defined as the limit of log(BEP)/n, for the processing gain n→∞. We show that the exponential rate with interference cancellation is larger than without interference cancellation, which demonstrates that the BEP, after interference cancellation is considerably smaller than before interference cancellation. Furthermore, we give the second order asymptotics of the BEP with interference cancellation for the case with 3 or more users. Finally, we compute the second order asymptotics of the BEP after interference cancellation for the case of 3 users