Combined performance of joint detection with FEC coding for CDMA mobile communication systems

We determine the combined performance of linear joint detection schemes with FEC coding, and specifically turbo-codes, as proposed for the UMTS third generation mobile communication system. We consider zero-forcing (ZF) decorrelation and minimum mean square error (MMSE) detection, and compare them with the conventional matched filter. Thus we obtain a bound based on the Shannon (1949) bound, and also estimate performance with turbo-codes of various rates with interleaver length 1024. In each case we find the required bit energy to noise density ratio on the channel in terms of the cell spectral efficiency, assuming perfect power control. The results show that there is in general, and especially in the case of ZF, a non-zero optimum code rate. At the Shannon bound there is little to choose between MMSE joint detection and the matched filter, but with turbo-codes joint detection gives a significant improvement.