This paper studies joint beamforming problems for an intelligent reflecting surface (IRS)-aided multi-cell multiple-input single-output (MISO) system, and the goal is to maximize the sum rate by jointly optimizing the transmit beamforming vectors at BSs and the reflective beamforming vector at the IRS, subject to the individual maximum transmit power constraints at BSs, and the reflection constraints at the IRS. Due to the formulated optimization problem is highly non-convex, we propose an alternating optimization (AO) algorithm based on successive convex approximation (SCA) such that the transmit and reflective beamforming vectors can be optimized alternately. We further consider the SINR balancing beamforming design scheme by maximizing the minimum SINR among all users to enhance the fairness among users, in which the transmit and reflective beamforming vectors are optimized in an alternating manner. The transmit beamforming vectors are optimized by the second-order-cone programming (SOCP) based on bisection method and the reflective beamforming vector is updated based on the technique of semidefinite relaxation (SDR). Simulation results show that the two proposed algorithms considerably outperform the benchmark zero-forcing (ZF) scheme. Moreover, the AO algorithm based on SCA has good communication performance than the other two schemes. And the AO algorithm based on bisection search guarantees the fairness for all users.

中文翻译：

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IRS 辅助多小区 MISO 系统的联合波束成形：和速率最大化和 SINR 平衡

本文研究了智能反射面 (IRS) 辅助的多小区多输入单输出 (MISO) 系统的联合波束成形问题，目标是通过联合优化 BS 和基站的发射波束成形向量来最大化总和速率。 IRS 处的反射波束成形矢量，受制于 BS 处的各个最大发射功率约束以及 IRS 处的反射约束。由于公式化的优化问题是高度非凸的，我们提出了一种基于逐次凸逼近（SCA）的交替优化（AO）算法，可以交替优化发射和反射波束形成向量。我们进一步考虑SINR平衡波束成形设计方案，通过最大化所有用户之间的最小SINR来增强用户之间的公平性，其中发射和反射波束形成矢量以交替方式进行优化。基于二分法的二阶锥规划（SOCP）优化发射波束形成向量，基于半定松弛（SDR）技术更新反射波束形成向量。仿真结果表明，所提出的两种算法大大优于基准迫零（ZF）方案。而且，基于SCA的AO算法比其他两种方案具有更好的通信性能。而基于二分搜索的AO算法保证了对所有用户的公平性。基于二分法的二阶锥规划（SOCP）优化发射波束形成向量，基于半定松弛（SDR）技术更新反射波束形成向量。仿真结果表明，所提出的两种算法大大优于基准迫零（ZF）方案。而且，基于SCA的AO算法比其他两种方案具有更好的通信性能。而基于二分搜索的AO算法保证了对所有用户的公平性。基于二分法的二阶锥规划（SOCP）优化发射波束形成向量，基于半定松弛（SDR）技术更新反射波束形成向量。仿真结果表明，所提出的两种算法大大优于基准迫零（ZF）方案。而且，基于SCA的AO算法比其他两种方案具有更好的通信性能。而基于二分搜索的AO算法保证了对所有用户的公平性。