This paper considers a RIS-assisted symbiotic communication system, where additional information is conveyed by the passive reconfigurable intelligent surface (RIS). In existing schemes, individual phase modulation is usually adopted at the RIS elements, which severely limits exploiting all extra multiplexing gains brought by the RIS. To address the issue, we propose a novel matrix decomposition algorithm that transforms the equivalent channel into a structured form while effectively suppressing the decomposition residual. Based on this, a novel transceiver architecture employing grouped annulus modulation (GAM) with a hexagonal-lattice-based constellation is developed, which is capable of achieving the full degrees of freedom (DoFs) when the decomposition algorithm performs as expected. Numerical results demonstrate that the proposed transceiver achieves much higher communication rates, thereby leading to higher spectral efficiency, compared to the conventional phase-only modulation scheme, while maintaining comparable error performance.

翻译：本文研究了一种RIS辅助的共生通信系统，其中被动式可重构智能表面（RIS）可传输额外信息。现有方案通常在RIS单元上采用独立相位调制，这严重限制了利用RIS带来的多址复用增益。为解决该问题，我们提出一种新型矩阵分解算法，可将等效信道转换为结构化形式，同时有效抑制分解残差。基于此，我们开发了一种采用六边形晶格星座图的分组环调制（GAM）收发机架构，当分解算法达到预期性能时，可实现全自由度。数值结果表明，与传统的纯相位调制方案相比，所提收发机在保持可比误差性能的同时，可实现更高的通信速率，从而获得更高的频谱效率。