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：索引调制（IM）是一种新兴技术，因其能通过不同传输实体组合实现并行数据通信而广受欢迎。本文首先对基于IM的多址接入（MA）技术进行了全面综述，重点阐述了现有非索引MA方案的不足。通过理论比较展示了索引概念如何消除非索引解决方案的局限性，并讨论了将可重构智能表面（RIS）作为索引实体部署时的优势。特别地，我们提出了一种RIS索引多址接入（RIMA）传输方案，该方案利用动态相位调谐在单一载波上嵌入多用户信息。仿真结果验证了所提RIMA方案的性能增益。文章最后列出了相关开放技术问题与研究方向。