Chip-interleaved Multi-rate CDMA with 2-dimensional OVSF Spreading

Chip interleaving technique has been proposed for DS-CDMA to eliminate the multiple-access interference (MAI). In this paper, we develop this technique to provide the single- or multicarrier CDMA with flexible low-to-high bit rate transmission by jointly using 2-dimensional (2D) OVSF spreading and chip interleaving for quasi-synchronous uplink transmissions in time- and frequency-selective fading channels. Through appropriate design of 2D spreading code assignment, not only the maximum time- and frequency-domain diversity can be achieved but also users are equipped with multi-rate services. The complexity of receivers is greatly reduced since single-user frequency-domain equalization (FDE) based on the MMSE criterion can be applied for signal detection. Computer simulation results show that the multi-rate transmission is possible for the 2D OVSF spread/chip-interleaved CDMA uplink and the bit error rate (BER) performance with turbo coding is very robust against Doppler spread