Novel Transmission Schemes for Multicell Downlink MC/DS-CDMA Systems Employing Time- and Frequency-Domain Spreading

This contribution investigates the achievable error performance of transmitter preprocessing in the downlink multicell multicarrier direct-sequence code-division multiple-access (MMC/DS-CDMA) systems employing both time (T)-domain and frequency (F)-domain spreading. Three types of multiuser transmitter preprocessing (MUTP) schemes are studied and compared, when assuming communications over frequency-selective Rayleigh fading channels. The first one is a single-cell minimum mean-square error MUTP (SMMSE-MUTP1), which only aims at suppressing the intracell interference (IntraCI). The second one is also a single-cell MMSE-MUTP (SMMSE-MUTP2), which tries to suppress both the IntraCI and intercell interference (InterCI). The final one is the multicell cooperative MMSE-MUTP (CMMSE-MUTP), which exploits the multicell diversity (or macro-diversity) for interference suppression and performance enhancement. Furthermore, power-allocation in these schemes is considered. Our studies show that the CMMSE-MUTP is capable of achieving the best error performance among the three schemes considered. However, it demands an extremely high complexity, as it requires information exchange among the base-stations (BSs) with the aid of a backhaul system. By contrast, when the number of mobile terminals (MTs) supported by each cell is not very high, the SMMSE-MUTP2, which does not require any intercell cooperation, can effectively mitigate both the IntraCI and the InterCI.