In this paper, we consider an orthogonal frequency division multiplexing (OFDM) based heterogeneous cellular network consisting of a macro cell and a small cell, where a macro-cell base station (MBS) and a small-cell base station (SBS) communicate with respective macro-cell user (MU) and small-cell user (SU) with the existence of a common eavesdropper across different OFDM subcarriers. In order to make full use of the mutual interference between MBS and SBS against eavesdropping, an artificially designed signal is emitted at MBS to cancel out the interference received at MU as well as to interfere with the common eavesdropper at each subcarriers. For the purpose of further improving the secrecy performance, a sum secrecy rate (SSR) of OFDM-based heterogeneous cellular networks is maximized by optimizing the power allocation between MBS and SBS across different OFDM subcarriers when the eavesdropper owns the global instantaneous channel state information (ICSI), thus called ICSI based SSR maximization (ICSI-SSRM). As for the case when the ICSI of wiretap channels is unknown, we propose a statistical CSI based SSR maximization (SCSI-SSRM) scheme, where the statistical characteristics of channels from MBS and SBS to eavesdropper are employed to optimally allocate powers of MBS and SBS across different subcarriers under the constraint of MBS's total transmit power. The formulated ICSI-SSRM and SCSI-SSRM problems are all non-convex due to form of the difference between two-convex (D.C.) functions. Thus, we utilize the D.C. approximation approach to respectively convert original optimization problems into convex problems. Moreover, iterative optimal power allocation algorithms for ICSI-SSRM and SCSI-SSRM schemes are also presented to obtain their respective SSR values. Simulation results illustrate that the ICSI-SSRM and SCSI-SSRM algorithms can converge to their optimal values, which confirms the correctness and validation of the proposed algorithms. In addition, numerical results are also given to show that the ICSI-SSRM and SCSI-SSRM schemes outperform conventional power allocation methods in terms of their SSR performance.

中文翻译：

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基于 OFDM 的异构蜂窝网络中智能干扰利用的功率分配辅助物理层安全

在本文中，我们考虑了一个基于正交频分复用 (OFDM) 的异构蜂窝网络，它由一个宏小区和一个小小区组成，其中宏小区基站 (MBS) 和小小区基站 (SBS) 与各自的宏小区用户 (MU) 和小小区用户 (SU) 存在跨不同 OFDM 子载波的公共窃听器。为了充分利用MBS和SBS之间的相互干扰来防止窃听，在MBS处发射人为设计的信号，以抵消MU处接收到的干扰，并在每个子载波上干扰公共窃听者。为进一步提高保密性能，当窃听者拥有全局瞬时信道状态信息（ICSI）时，通过优化 MBS 和 SBS 之间跨不同 OFDM 子载波的功率分配来最大化基于 OFDM 的异构蜂窝网络的总保密率（SSR），因此称为基于 ICSI 的 SSR 最大化（ ICSI-SSRM）。对于窃听信道的ICSI未知的情况，我们提出了一种基于统计CSI的SSR最大化（SCSI-SSRM）方案，其中利用从MBS和SBS到窃听者信道的统计特性来优化分配MBS和SBS的功率在 MBS 总发射功率的约束下跨不同子载波。由于两凸（DC）函数之间的差异形式，公式化的 ICSI-SSRM 和 SCSI-SSRM 问题都是非凸的。因此，我们利用 DC 分别将原始优化问题转化为凸问题的近似方法。此外，还提出了 ICSI-SSRM 和 SCSI-SSRM 方案的迭代最优功率分配算法，以获得它们各自的 SSR 值。仿真结果表明ICSI-SSRM和SCSI-SSRM算法可以收敛到它们的最优值，这证实了所提出算法的正确性和有效性。此外，还给出了数值结果，表明 ICSI-SSRM 和 SCSI-SSRM 方案在其 SSR 性能方面优于传统的功率分配方法。仿真结果表明ICSI-SSRM和SCSI-SSRM算法可以收敛到它们的最优值，这证实了所提出算法的正确性和有效性。此外，还给出了数值结果，表明 ICSI-SSRM 和 SCSI-SSRM 方案在其 SSR 性能方面优于传统的功率分配方法。仿真结果表明ICSI-SSRM和SCSI-SSRM算法可以收敛到它们的最优值，这证实了所提出算法的正确性和有效性。此外，还给出了数值结果，表明 ICSI-SSRM 和 SCSI-SSRM 方案在 SSR 性能方面优于传统的功率分配方法。