Spreading CDMA via RIS: Multipath Separation, Estimation, and Combination

As a revolutionary technology for future wireless communications, reconfigurable intelligent surface (RIS), characterized by an efficient way of manipulating wireless signals, has been widely investigated in recent years toward enhancing signal quality, energy efficiency, throughput, and so on. However, in RIS-assisted Internet of Things (IoT), a new issue as multipath separation emerges, especially, when deploying multiple RISs to assist communication, since the devices may have limited signal processing capabilities. For alleviating this problem, we conceive a novel RIS-enabled code-division multiple access (CDMA) structure, where each RIS holds a specified time-varying coefficient to tag the channel. Moreover, multipath extraction is further considered, including a practical channel estimation approach along with theoretical derivations in terms of Cramer-Rao lower bound, mean-square error, as well as ergodic channel capacity. Simulation results corroborate the feasibility of the conceived RIS-CDMA structure and the effectiveness of the proposed multipath extraction approach.

Automated summary

The article introduces the reconfigurable intelligent surface (RIS) as a revolutionary technology for future wireless communications. It has been widely studied in recent years for enhancing signal quality, energy efficiency, and throughput. However, in RIS-assisted IoT, a new issue of multipath separation arises when deploying multiple RISs. To alleviate this problem, a novel RIS-enabled code-division multiple access (CDMA) structure is proposed, along with practical channel estimation and theoretical derivations. Simulation results confirm the feasibility of the conceived RIS-CDMA structure and the effectiveness of the proposed multipath extraction approach.