Frequency Domain Turbo Equalization for Multicode DS-CDMA in Frequency Selective Fading Channel

The higher data rate of mobile communications has been required for various multimedia services. In DS-CDMA system, one of the solutions to increase the throughput is to use multicode. However, multipath channel destroys the orthogonality of spreading codes, which causes the intercode interference (ICI). ICI gives severe effect on multicode DS-CDMA for BER performance. Conventionally, multicode DS-CDMA system uses the Rake receiver with turbo code, which cannot overcome error floor caused by ICI. In this paper, we propose frequency domain turbo equalization based on minimum mean squared error (FDTE-MMSE) for multicode DS-CDMA in frequency selective channel and evaluate its BER performance by computer simulation. The simulation results show that FDTE-MMSE gives much better performance than the Rake receiver with turbo code in multipath length L > 1.