The application of non-orthogonal multiple access (NOMA) to downlink multi-user multiple-input single-output systems involves the design of a beamforming strategy in which the spatial dimension provided by each beam is shared among several users performing NOMA. This approach requires the management of both inter-cluster and intra-cluster interference. Moreover, the beamforming design is subject to instantaneous knowledge of the channel state information at the transmitter (CSIT). We propose a novel transmission scheme that combines blind interference alignment and NOMA. The proposed scheme fully cancels the inter-cluster interference for all users without the need for instantaneous CSIT, which is limited to the knowledge of the large scale effects of the channel in order to implement NOMA within each cluster. Considering user pairing, i.e., each cluster is composed of two users, we derive a method for determining the NOMA power coefficients that maximize the sum-rate, the user fairness or satisfy first the rate of a specific user by simply solving a polynomial function. Furthermore, we propose an alternative methodology based on some approximations in order to provide sub-optimal closed-form expressions of these NOMA power coefficients. Simulation results show that the proposed scheme outperforms conventional MISO-NOMA taking into consideration the costs of providing CSIT.

中文翻译：

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用于下行链路 MU-MISO 系统的半盲干扰对齐 NOMA

非正交多址 (NOMA) 在下行链路多用户多输入单输出系统中的应用涉及波束成形策略的设计，其中每个波束提供的空间维度在执行 NOMA 的多个用户之间共享。这种方法需要管理集群间和集群内的干扰。此外，波束成形设计受制于对发射机 (CSIT) 处的信道状态信息的即时了解。我们提出了一种结合盲干扰对齐和 NOMA 的新型传输方案。所提出的方案完全消除了所有用户的簇间干扰，而无需瞬时 CSIT，这仅限于了解信道的大规模效应，以便在每个簇内实现 NOMA。考虑用户配对，即 每个集群由两个用户组成，我们推导出了一种确定 NOMA 功率系数的方法，该方法可以通过简单地求解多项式函数来最大化和速率、用户公平性或首先满足特定用户的速率。此外，我们提出了一种基于一些近似值的替代方法，以提供这些 NOMA 功率系数的次优封闭形式表达式。仿真结果表明，考虑到提供 CSIT 的成本，所提出的方案优于传统的 MISO-NOMA。我们提出了一种基于一些近似值的替代方法，以提供这些 NOMA 功率系数的次优封闭形式表达式。仿真结果表明，考虑到提供 CSIT 的成本，所提出的方案优于传统的 MISO-NOMA。我们提出了一种基于一些近似值的替代方法，以提供这些 NOMA 功率系数的次优封闭形式表达式。仿真结果表明，考虑到提供 CSIT 的成本，所提出的方案优于传统的 MISO-NOMA。