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：本文研究了用户设备（UE）在传输有限长度数据包时的能耗问题。接收基站（BS）控制着一个可重构智能表面（RIS），该表面可通过发射额外导频信号进行配置以改善信道条件。我们推导了同时考虑导频与数据传输功率的能耗公式。通过将RIS划分为多个共享相同反射系数的子阵列（每个子阵列包含多个RIS单元），可调节导频开销以在保持部分孔径增益的同时最小化能耗。分析结果表明，存在一个能耗最优的子阵列尺寸。当数据块较小时，且BS与UE之间的信道条件优于通向RIS的信道时，采用大尺寸子阵列可使能耗最小化；当通向RIS的信道条件更优且数据块较大时，宜采用每子阵列包含较少单元的方式，并可能需要对各单元进行单独配置。