In this paper, a novel transmissive reconfigurable intelligent surface (RIS) enabled uplink communication system with orthogonal frequency division multiple access (OFDMA) is investigated. Specifically, a non-conventional receiver architecture equipped with a single receiving horn antenna and a transmissive RIS is first proposed, and a far-near field channel model based on planar waves and spherical waves is also given. Then, in order to maximize the system sum-rate of uplink communications, we formulate a joint optimization problem over subcarrier allocation, power allocation and RIS transmissive coefficient design while taking account of user quality-of-service (QoS) constraint. Due to the coupling of optimization variables, the optimization problem is non-convex, so it is challenging to solve it directly. In order to tackle this problem, the alternating optimization (AO) algorithm is utilized to decouple the optimization variables and divide the problem into two sub-problems to solve. First, the problem of joint subcarrier allocation and power allocation is solved via the Lagrangian dual decomposition method. Then, the RIS transmissive coefficient design scheme can be obtained by applying difference-of-convex (DC) programming, successive convex approximation (SCA) and penalty function methods. Finally, the two sub-problems are iterated alternately until convergence is achieved. Numerical results verify that the proposed algorithm has good convergence performance and can improve sum-rate of the proposed system compared with other benchmark algorithms.

翻译：本文研究了一种新型透射式可重构智能表面（RIS）赋能的正交频分多址（OFDMA）上行通信系统。具体而言，首先提出了一种采用单接收喇叭天线与透射型RIS的非传统接收机架构，并给出了基于平面波与球面波的远近场信道模型。然后，为最大化上行通信的系统总速率，在考虑用户服务质量（QoS）约束的前提下，构建了关于子载波分配、功率分配及RIS透射系数设计的联合优化问题。由于优化变量耦合，该问题为非凸问题，直接求解具有挑战性。为解决该问题，采用交替优化（AO）算法解耦优化变量，将原问题划分为两个子问题求解。首先，通过拉格朗日对偶分解方法解决联合子载波分配与功率分配问题；其次，利用凸差（DC）规划、逐次凸近似（SCA）及惩罚函数方法获得RIS透射系数设计方案。最后，对两个子问题进行交替迭代直至收敛。数值结果验证了所提算法具有良好的收敛性能，且相较于其他基准算法能有效提升系统总速率。