Interleaving for outer convolutional codes in DS-CDMA systems

In DS CDMA systems the probability of error for each user depends on the crosscorrelation between the spreading sequences and on the received energies of all users. Thus even Maximum Likelihood joint detection might in general have a large loss compared to one user transmission. Choosing the individual error correcting codes of all users in a suitable way reduces this loss for given crosscorrelation values. This may be achieved by interleaving the convolutional codes used. It is theoretically shown for a certain kind of interleaving and a moderate codelength that almost the complete innuence of the interuser interference can be eliminated for large signal to noise ratios. Hence the performance of a coded DS CDMA system comes close to transmission without interuser interference. Simulations connrm the analysis.