In this letter, we study the multi-user multiple-input single-output (MU-MISO) transmission assisted by a reconfigurable intelligent surface (RIS). Specifically, for an arbitrary precoder employed at the base station (BS), by exploiting the concept of constructive interference (CI), we aim to design the phase shifts at the RIS such that the direct-link signals and the reflected signals can add constructively at each user side. An optimization problem is formulated to minimize the symbol error rate, where we also allow the on-off switch for the reflecting elements at the RIS. By relaxing the constant-envelope (CE) constraints, we arrive at a convex problem that can readily be solved, and a direct normalization is subsequently applied to satisfy the CE constraints. Moreover, we propose a greedy algorithm to further improve the system performance. Numerical results validate the effectiveness of the proposed scheme and demonstrate its superior performance compared to conventional schemes.

中文翻译：

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具有直接链接的可重构智能表面辅助多用户通信的干扰利用预编码

在这封信中，我们研究了由可重构智能表面 (RIS) 辅助的多用户多输入单输出 (MU-MISO) 传输。具体来说，对于基站 (BS) 使用的任意预编码器，通过利用建设性干扰 (CI) 的概念，我们旨在设计 RIS 的相移，以便直接链路信号和反射信号可以建设性地相加在每个用户端。优化问题被公式化以最小化符号错误率，我们还允许在 RIS 处对反射元件进行通断切换。通过放宽恒定包络 (CE) 约束，我们得出了一个可以轻松解决的凸问题，然后应用直接归一化来满足 CE 约束。此外，我们提出了一种贪心算法来进一步提高系统性能。