Closed-Form Receivers for Mimo Communications Assisted by Hybrid Sensing and Reflecting Ris

Recent research has focused on advanced architectures for reconfigurable intelligent surfaces (RIS) incorporating sensing capabilities. A notable development is the hybrid simultaneously sensing and reflecting RIS (HRIS), which integrates both sensing and reflecting meta-atoms. This design endows HRIS with signal processing abilities to tackle the channel estimation challenge. This work develops a closed-form semi-blind receiver pair for HRIS-assisted multiple-input multiple-output wireless communications, leveraging HRIS for joint symbol detection and channel estimation under a tensor space-time coding. By transmitting information symbols instead of pilots during the CE stage, our data-aided method reduces decoding delay while estimating symbols at a low computational cost. Simulation results show competitive performance in terms of normalized mean square error and symbol error rates compared to existing solutions, highlighting the effectiveness of enabling semi-blind estimation at both the HRIS and BS. Furthermore, data estimation directly at the HRIS opens new opportunities and use cases for HRIS/RISassisted communications.