In conventional backscatter communication (BackCom) systems, time division multiple access (TDMA) and frequency division multiple access (FDMA) are generally adopted for multiuser backscattering due to their simplicity in implementation. However, as the number of backscatter devices (BDs) proliferates, there will be a high overhead under the traditional centralized control techniques, and the inter-user coordination is unaffordable for the passive BDs, which are of scarce concern in existing works and remain unsolved. To this end, in this paper, we propose a slotted ALOHA-based random access for BackCom systems, in which each BD is randomly chosen and is allowed to coexist with one active device for hybrid multiple access. To excavate and evaluate the performance, a resource allocation problem for max-min transmission rate is formulated, where transmit antenna selection, receive beamforming design, reflection coefficient adjustment, power control, and access probability determination are jointly considered. To deal with this intractable problem, we first transform the objective function with the max-min form into an equivalent linear one, and then decompose the resulting problem into three sub-problems. Next, a block coordinate descent (BCD)-based greedy algorithm with a penalty function, successive convex approximation, and linear programming are designed to obtain sub-optimal solutions for tractable analysis. Simulation results demonstrate that the proposed algorithm outperforms benchmark algorithms in terms of transmission rate and fairness.

翻译：在传统反向散射通信（BackCom）系统中，由于实现简单，时分多址（TDMA）和频分多址（FDMA）通常用于多用户反向散射。然而，随着反向散射设备（BD）数量的激增，传统集中式控制技术将带来高昂开销，且被动反向散射设备难以承受用户间协调成本。现有研究对此问题关注不足，尚未形成有效解决方案。为此，本文提出一种基于时隙ALOHA的随机接入方案用于BackCom系统，其中每个BD被随机选择并与一个主动设备共存，实现混合多址接入。为挖掘和评估系统性能，本文构建了以最大化最小传输速率为目标的资源分配问题，联合考虑发射天线选择、接收波束赋形设计、反射系数调整、功率控制及接入概率确定。为应对该棘手问题，首先将最大最小形式的目标函数转化为等价线性形式，进而将原问题分解为三个子问题。随后，设计基于块坐标下降（BCD）的贪心算法，结合惩罚函数、逐次凸近似和线性规划，获得易于分析的次优解。仿真结果表明，所提算法在传输速率和公平性方面均优于基准算法。