Xiao, ZhenyuLiu, GuangyaoMao, TianqiLiu, RuiqiZhang, WeiXia, Xiang-GenHanzo, Lajos2024-02-072024-02-072023-11-06Z. Xiao et al., "Twin-Layer RIS-Aided Differential Index Modulation Dispensing With Channel Estimation," in IEEE Transactions on Vehicular Technology, doi: 10.1109/TVT.2023.3330256.1939-9359https://udspace.udel.edu/handle/19716/33957© 2015 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This article was originally published in IEEE Transactions on Vehicular Technology. The version of record is available at: https://doi.org/10.1109/TVT.2023.3330256. This article will be embargoed until 11/06/2025.In this correspondence, we propose a twin-layer hierarchical differential index modulation scheme for a reconfigurable intelligent surface (RIS)-aided transmitter architecture, termed as HD-RIS-IM. More specifically, the RIS array is partitioned into perfectly tiling sub-arrays. Each sub-array is mapped across multiple time slots, where each RIS element is activated only once at a particular time slot. These sub-arrays represented by sub- matrices are then used for constructing a block-based permutation matrix for data transmission. With the aid of this hierarchical structure, additional information can be conveyed by the specific order of the sub-arrays that are activated. Furthermore, extra bits are also embedded in the particular order of the RIS elements that are activated within each sub-array. By exploiting all the distinct permutations of the activated matrices, a differential modulation scheme is proposed for the RIS-aided transmitter, which maintains an M -ary phase shift keying (MPSK) and facilitates CSI-free demodulation. Furthermore, at the receiver, we propose a low-complexity distributed maximum likelihood (ML) detector, which significantly reduces the detection complexity. Our simulation results demonstrate the performance benefits of the proposed HD-RIS-IM scheme.en-USindex modulation (IM)reconfigurable intelligent surface (RIS)differential modulationmetasurface (MTS)intelligent reflecting surface (IRS)Article