异构蜂窝网络（heterogeneous cellular network, HCN）是一种具有发展前景的结构，可以提供无缝无线覆盖并提高网络容量。然而，密集化的多层网络结构引入了过多的层内和层间干扰，使HCN容易受到窃听攻击。本文提出了一种基于频谱动态控制（dynamic spectrum control, DSC）的传输方案，用于加强HCN的网络安全并提高网络容量。该DSC辅助传输方案利用了分组加密的密码学思想，通过执行迭代和正交的序列变换生成代表传输决定的序列族。基于这些序列族，多位用户可以动态地占用不同频隙进行数据传输。此外，本文还分析了数据传输的碰撞概率，从而得出可靠传输概率和保密概率的解析表达式。然后，在给定可靠传输概率和安全传输概率的要求下，进一步得出了网络容量的上下限。仿真结果表明，本研究提出的DSC辅助方案在安全性能方面能够优于基准方案。最后，本文评估并讨论了DSC辅助方案中的关键因素对网络容量和安全性的影响。

Heterogeneous cellular networks (HCNs) are envisioned as a promising architecture to provide seamless wireless coverage and increase network capacity. However, the densified multi-tier network architecture introduces excessive intra- and cross-tier interference and makes HCNs vulnerable to eavesdropping attacks. In this article, a dynamic spectrum control (DSC)-assisted transmission scheme is proposed for HCNs to strengthen network security and increase the network capacity. Specifically, the proposed DSC-assisted transmission scheme leverages the idea of block cryptography to generate sequence families, which represent the transmission decisions, by performing iterative and orthogonal sequence transformations. Based on the sequence families, multiple users can dynamically occupy different frequency slots for data transmission simultaneously. In addition, the collision probability of the data transmission is analyzed, which results in closed-form expressions of the reliable transmission probability and the secrecy probability. Then, the upper and lower bounds of network capacity are further derived with given requirements on the reliable and secure transmission probabilities. Simulation results demonstrate that the proposed DSC-assisted scheme can outperform the benchmark scheme in terms of security performance. Finally, the impacts of key factors in the proposed DSC-assisted scheme on the network capacity and security are evaluated and discussed.