In this technical note, we present a new theoretical result for multi-cell non-orthogonal multiple access (NOMA). For multi-cell scenarios, a so-called load-coupling model has been proposed earlier to characterize the presence of mutual interference for NOMA, and the optimization process relies on the use of fixed-point iterations across cells. One difficulty here is that the order of decoding for successive interference cancellation (SIC) in NOMA is generally not known a priori. This is because the decoding order in one cell depends on interference, which, in turn, is governed by resource usage in other cells, and vice versa. To achieve convergence, previous works have used workarounds that pose restrictions to NOMA, such that the SIC decoding order remains throughout the fixed-point iterations. As a comment to the previous works, we derive and prove the following result: The convergence is guaranteed, even if the order changes over the iterations. The result not only waives the need of previous workarounds, but also implies that a wide class of optimization problems for multi-cell NOMA is tractable, as long as that for single cell is.

中文翻译：

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负载耦合的多小区NOMA用户分组解码顺序及功率优化注意事项


在本技术报告中，我们提出了多小区非正交多址（NOMA）的新理论结果。对于多小区场景，早期已经提出了所谓的负载耦合模型来表征NOMA相互干扰的存在，并且优化过程依赖于跨小区定点迭代的使用。这里的一个困难是 NOMA 中连续干扰消除 (SIC) 的解码顺序通常是事先未知的。这是因为一个小区中的解码顺序取决于干扰，而干扰又受其他小区中的资源使用情况的控制，反之亦然。为了实现收敛，之前的工作使用了对 NOMA 施加限制的解决方法，使得 SIC 解码顺序在整个定点迭代中保持不变。作为对先前工作的评论，我们得出并证明了以下结果：即使迭代中顺序发生变化，也能保证收敛。结果不仅不需要以前的解决方法，而且还意味着多单元 NOMA 的各种优化问题都是易于处理的，就像单单元的优化问题一样。