This paper investigates the secure transmission in hybrid automatic repeat request (HARQ)-assisted non-orthogonal multiple access (NOMA) networks, where a security-required (SR) user is paired with an opportunity-served (OS) user to perform NOMA. Different from the previous works where NOMA and HARQ are separately considered for secure transmissions, in this paper, both NOMA and HARQ are utilized to enhance the security of the SR user. We derive the closed-form expressions for connection outage probability (COP), secrecy outage probability (SOP), reliable and secure transmission probability (RSP) and effective secrecy throughput (EST) of the SR user in both maximum ratio combining (MRC) and selection combining (SC) schemes. The security-reliability trade-off (SRT) results of the SR user in both MRC and SC schemes are also provided. Analysis and simulation results show that HARQ improves secrecy performance in MRC and SC schemes in terms of RSP, especially in low transmit power region. Besides, since every retransmission is utilized in the MRC scheme, it strictly outperforms the SC scheme in terms of the SRT metric. However, the SC scheme has the potential to achieve higher EST than the MRC scheme by optimizing the transmit power or the power allocation factor. Significantly, the quality of service (QoS) of the OS user can be guaranteed by pairing an SR user who is far away from the transmitter and the secrecy performance of the SR user can be enhanced by pairing an OS user.

中文翻译：

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HARQ辅助的非正交多址网络中的安全传输

本文研究了混合自动重发请求（HARQ）辅助的非正交多路访问（NOMA）网络中的安全传输，其中安全要求（SR）用户与机会服务（OS）用户配对以执行NOMA。与以前的工作中分别考虑将NOMA和HARQ用于安全传输的工作不同，本文将NOMA和HARQ都用于增强SR用户的安全性。我们得出最大比率组合（MRC）和（SRC）和SR用户的连接中断概率（COP），保密中断概率（SOP），可靠和安全的传输概率（RSP）和有效保密吞吐量（EST）的闭式表达式。选择组合（SC）方案。还提供了MRC和SC方案中SR用户的安全可靠性折衷（SRT）结果。分析和仿真结果表明，HARQ在RSP方面提高了MRC和SC方案的保密性能，尤其是在低发射功率区域。此外，由于在MRC方案中利用了每次重传，因此就SRT度量而言，它严格胜过SC方案。但是，通过优化发射功率或功率分配因子，SC方案具有比MRC方案更高的EST的潜力。重要的是，可以通过配对远离发射器的SR用户来保证OS用户的服务质量（QoS），并且可以通过配对OS用户来提高SR用户的保密性能。由于MRC方案中利用了每个重传，因此就SRT度量而言，它严格胜过SC方案。但是，通过优化发射功率或功率分配因子，SC方案具有比MRC方案更高的EST的潜力。重要的是，可以通过配对远离发射器的SR用户来保证OS用户的服务质量（QoS），并且可以通过配对OS用户来提高SR用户的保密性能。由于MRC方案中利用了每个重传，因此就SRT度量而言，它严格胜过SC方案。但是，通过优化发射功率或功率分配因子，SC方案具有比MRC方案更高的EST的潜力。重要的是，可以通过配对远离发射器的SR用户来保证OS用户的服务质量（QoS），并且可以通过配对OS用户来提高SR用户的保密性能。