Movable antenna (MA) is a promising technology to improve wireless communication performance by varying the antenna position in a given finite area at the transceivers to create more favorable channel conditions. In this paper, we investigate the MA-enhanced multiple-access channel (MAC) for the uplink transmission from multiple users each equipped with a single MA to a base station (BS) with a fixed-position antenna (FPA) array. A field-response based channel model is used to characterize the multi-path channel between the antenna array of the BS and each user's MA with a flexible position. To evaluate the MAC performance gain provided by MAs, we formulate an optimization problem for minimizing the total transmit power of users, subject to a minimum-achievable-rate requirement for each user, where the positions of MAs and the transmit powers of users, as well as the receive combining matrix at the BS are jointly optimized. To solve this non-convex optimization problem involving intricately coupled variables, we develop two algorithms based on zero-forcing (ZF) and minimum mean square error (MMSE) combining methods, respectively. Specifically, for each algorithm, the combining matrix of the BS and the total transmit power of users are expressed as a function of the MAs' position vectors, which are then optimized by using the gradient descent method in an iterative manner. It is shown that the proposed ZF-based and MMSE-based algorithms can converge to high-quality suboptimal solutions with low computational complexities. Simulation results demonstrate that the proposed solutions for MA-enhanced multiple access systems can significantly decrease the total transmit power of users as compared to conventional FPA systems under both perfect and imperfect field-response information.

翻译：可移动天线（MA）是一种通过改变收发器给定有限区域内天线位置以创造更有利信道条件来提升无线通信性能的 promising 技术。本文研究了MA增强的多址接入信道（MAC），用于多个用户（各配备单根MA）到固定位置天线（FPA）阵列基站（BS）的上行传输。采用基于场响应的信道模型来表征BS天线阵列与各用户MA（位置灵活）之间的多径信道。为评估MA带来的MAC性能增益，我们构建了一个优化问题，在满足各用户最小可达速率要求的条件下最小化用户总发射功率，其中联合优化了MA的位置、用户发射功率及BS的接收合并矩阵。针对这一涉及复杂耦合变量的非凸优化问题，我们分别基于迫零（ZF）和最小均方误差（MMSE）合并方法开发了两种算法。具体而言，对于每种算法，BS的合并矩阵和用户总发射功率均表示为MA位置向量的函数，随后通过梯度下降法迭代优化该函数。研究表明，所提出的基于ZF和基于MMSE的算法能够以低计算复杂度收敛到高质量次优解。仿真结果表明，与传统的FPA系统相比，所提出的MA增强多址接入系统解决方案在完美和非完美场响应信息条件下均能显著降低用户总发射功率。