In this paper, we examine the energy consumption of a user equipment (UE) when it transmits a finite-sized data packet. The receiving base station (BS) controls a reconfigurable intelligent surface (RIS) that can be utilized to improve the channel conditions, if additional pilot signals are transmitted to configure the RIS. We derive a formula for the energy consumption taking both the pilot and data transmission powers into account. By dividing the RIS into subarrays consisting of multiple RIS elements using the same reflection coefficient, the pilot overhead can be tuned to minimize the energy consumption while maintaining parts of the aperture gain. Our analytical results show that there exists an energy-minimizing subarray size. For small data blocks and when the channel conditions between the BS and UE are favorable compared to the path to the RIS, the energy consumption is minimized using large subarrays. When the channel conditions to the RIS are better and the data blocks are large, it is preferable to use fewer elements per subarray and potentially configure the elements individually.

翻译：在本文中，我们研究了用户设备（UE）传输有限大小的数据包时的能量消耗。接收基站（BS）控制可重构智能表面（RIS），如果传输额外的导频信号以配置RIS，则可以利用其改善信道条件。我们导出了一个考虑导频和数据传输功率的能量消耗公式。通过将RIS划分为子阵，其中每个子阵由多个具有相同反射系数的RIS元素组成，可以调整导频开销以最小化能量消耗，同时保持部分入射增益。我们的分析结果表明，存在能量最小化子阵大小。对于小数据块且与BS和UE之间的信道条件相比较有利的路径，使用大型子阵可以最小化能量消耗。当与RIS之间的信道条件更好且数据块较大时，则更倾向于使用较少的元素进行配置。