Delay-Time/Code Division Multi-Access for Uplink Transmission in a Frequency-Selective Fading Channel

The downlink Bit Error Rate (BER) performance of Direct Sequence-Code Division Multi-Access (DS-CDMA) in a frequency-selective fading channel can be significantly improved by the use of Frequency-Domain Equalization (FDE) based on Minimum Mean Square Error (MMSE) criterion. In the uplink case, however, the presence of Multi-Access Interference (MAI) significantly degrades the BER performance even if MMSE-FDE is used. In this paper, the authors propose a new hybrid multi-access technique called Delay-Time/Code Division Multi-Access (DT/CDMA) for the uplink transmission, which can mitigate the MAI while achieving the frequency diversity gain, and evaluate the achievable BER performance by computer simulation.