Non-orthogonal multiple access (NOMA) was recently regarded as a potential technique for next generation wireless networks. Recent works on relay selection for cooperative NOMA systems have mainly addressed the best relay selection to forward its received signals to terminal nodes. Nonetheless, in practical scenarios, the best relay may be unavailable due to non-ideal conditions such as scheduling and overload constraints or possibly due to channel feedback delay. Therefore, there is compelling need to consider a more practical solution, in which the best available relay is selected. In this article, we examine the error rate performance for simultaneous wireless information and power transfer (SWIPT)-enabled NOMA, while considering the selection of the $m$ th best available relay. In particular, we present an exact pairwise error probability (PEP) expression to obtain a bit error rate (BER) upper bound. The asymptotic PEP is investigated to evaluate the achievable diversity order for NOMA users. Finally, simulation results are provided to verify the accuracy of the derived PEP expressions and to give more insights into the system performance.

中文翻译：

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启用S​​WIPT的合作式NOMA与 米最佳继电器选择

非正交多址（NOMA）最近被视为下一代无线网络的潜在技术。有关合作NOMA系统的中继选择的最新工作主要解决了最佳中继选择，以将其接收到的信号转发到终端节点。但是，在实际情况下，由于诸如调度和过载约束之类的非理想条件，或者可能由于信道反馈延迟，可能无法获得最佳中继。因此，迫切需要考虑一种更实际的解决方案，在该解决方案中选择最佳的可用继电器。在本文中，我们研究了同时启用无线信息和功率传输（SWIPT）的NOMA的误码率性能，同时考虑了选择 $ m $ 最好的继电器。特别是，我们提出了精确的成对错误概率（PEP）表达式，以获得误码率（BER）上限。研究了渐近PEP，以评估NOMA用户可获得的分集阶数。最后，提供了仿真结果以验证派生的PEP表达式的准确性，并提供有关系统性能的更多见解。