Multiuser spreading codes retaining orthogonality through unknown time- and frequency-selective fading

Suppression of Multi-User Interference (MUI) and mitigation of timeand frequency-selective effects constitute major challenges in the design of third-generation wireless mobile systems. Relying on block spreading and judiciously chosen time-frequency guard intervals, we propose a multi-user transceiver that eliminates MUI deterministically and guarantees symbol detectability in the presence of unknown timeand frequency-selective fading. Blind channel estimation is also investigated. Simulation results demonstrate the validity of the theoretical results and show improved performance of the proposed transceiver over a multi-user time-frequency RAKE receiver.