Joint Tx/iterative Rx FDE for broadband direct-sequence code division multiple access

Direct-sequence code division multiple access (DS-CDMA) is a promising uplink access technology for broadband cellular mobile communication systems. In this paper, we propose a joint transmit (Tx)/iterative receive (Rx) frequency-domain equalization (FDE) for DS-CDMA. In the proposed scheme, simple one-tap FDE at the transmitter and iterative one-tap FDE at the receiver are jointly performed using the common knowledge of channel state information (CSI). Before transmitting the signal, the transmitter predicts the degree of residual inter-chip interference (ICI) power after the iterations of Rx FDE to determine the Tx FDE weight while the receiver performs the iterative Rx FDE. In practice, it is almost impossible to share the perfect knowledge of CSI. In this paper, a Gaussian approximation of channel estimation (CE) errors is introduced. We theoretically derive a set of Tx and iterative Rx FDE weights based on the minimum mean square error (MMSE) criterion in the presence of the CE error. We show by computer simulation that the proposed scheme provides better bit error rate (BER) performance than the conventional scheme which uses iterative Rx FDE only (i.e., without Tx FDE) even in the presence of CE error.