Indexed modulation (IM) is an evolving technique that has become popular due to its ability of parallel data communication over distinct combinations of transmission entities. In this article, we first provide a comprehensive survey of IM-enabled multiple access (MA) techniques, emphasizing the shortcomings of existing non-indexed MA schemes. Theoretical comparisons are presented to show how the notion of indexing eliminates the limitations of non-indexed solutions. We also discuss the benefits that the utilization of a reconfigurable intelligent surface (RIS) can offer when deployed as an indexing entity. In particular, we propose an RIS-indexed multiple access (RIMA) transmission scheme that utilizes dynamic phase tuning to embed multi-user information over a single carrier. The performance of the proposed RIMA is assessed in light of simulation results that confirm its performance gains. The article further includes a list of relevant open technical issues and research directions.

翻译：指数化调制(IM)是一种不断发展的技术,由于它相对于不同传输实体的组合具有平行数据通信能力,这种技术已经变得十分流行。在本条中,我们首先对基于IM的多重存取(MA)技术进行全面调查,强调现有非指数化的MA系统的缺点。提出理论比较是为了表明指数化概念如何消除非指数化解决办法的局限性。我们还讨论了在作为指数化实体部署时利用可重新配置的智能表面(RIS)所能带来的好处。特别是,我们建议采用RIS指数化的多重存取(RIMA)传输计划,利用动态阶段调控将多用户信息嵌入单一承运人。拟议中的RIMA的绩效是根据证实其绩效收益的模拟结果进行评估的。该条还包含一个相关的公开技术问题和研究方向清单。