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 (DSCDMA) 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 TimeReversal (TR) STBC. The resulting transceiver allows for deterministic Maximum Likelihood (ML) user separation through lowcomplexity code-matched filtering as well as deterministic transmit stream separation through linear processing. These properties guarantee maximum diversity gains of NT NR(L + 1) for every user in the system, irrespective of the system load, where NT is the number of transmit antennas, NR the number of receive antennas and L the order of the underlying multi-path 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.