Abstract
Reconfigurable intelligent surface (RIS)-assisted wireless communications have been widely investigated toward enhanced signal quality, energy efficiency as well as throughput. The issue of multipath separation and identification via multiple RISs, which, however, remains to be further investigated, is of paramount importance. For alleviating this problem, we conceive a novel RIS-assisted spreading and code division multiple access (CDMA) structure, where each RIS holds a time-varying reflection coefficient sequence for spreading, in order to tag the channel and distinguish each other with the idea of CDMA. Moreover, practical channel estimation and multipath identification are considered, and the ergodic channel capacity is also derived when the receiver employs maximum ratio combining. Simulation results corroborate the feasibility of the proposed RIS-CDMA structure and the effectiveness of the developed channel estimation and multipath combination approaches.
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