Space-time coding for single-carrier block-spread CDMA cellular downlink

The combination of space-time block coding (STBC) and direct-sequence code division multiple access (DS-CDMA) has the potential to increase the performance of multiple users in a cellular environment. However, if not carefully designed, the resulting communication scheme suffers from increased multi-user interference (MUI), which dramatically deteriorates the performance. To tackle this MUI problem in the downlink, we combine two specific CDMA and STBC techniques, namely single-carrier block-spread (SCBS) CDMA and time-reversal (TR) STBC. The resulting transceiver allows for deterministic maximum likelihood (ML) user separation through low-complexity code-matched filtering as well as deterministic transmit stream separation through linear processing. These properties guarantee maximum diversity gains of N_TN_R(L+1) for every user in the system, irrespective of the system load, where N_T is the number of transmit antennas, N_R the number of receive antennas and L the order of the underlying multipath channels. Moreover, it turns out that a low-complexity linear receiver based on frequency-domain equalization comes close to extracting the full diversity in reduced as well as full load settings.