This work studies a covert communication scheme for an uplink multi-user scenario in which some users are opportunistically selected to help a covert user. In particular, the selected users emit interfering signals via an orthogonal resource dedicated to the covert user together with signals for their own communications using orthogonal resources allocated to the selected users, which helps the covert user hide the presence of the covert communication. For the covert communication scheme, we carry out extensive analysis and find system parameters in closed forms. The analytic derivation for the system parameters allow one to find the optimal combination of system parameters by performing a simple one-dimensional search. In addition, the analytic results elucidate relations among the system parameters. In particular, it will be proved that the optimal strategy for the non-covert users is an on-off scheme with equal transmit power. The theoretical results derived in this work are confirmed by comparing them with numerical results obtained with exhaustive searches. Finally, we demonstrate that the results of work can be utilized in versatile ways by demonstrating a design of covert communication with energy efficiency into account.

翻译：本文研究了一种上行多用户场景中的隐蔽通信方案，其中部分用户被机会性地选择来辅助隐蔽用户。具体而言，所选用户通过专用于隐蔽用户的正交资源发射干扰信号，同时利用分配给自身的正交资源进行自有通信，从而帮助隐蔽用户隐藏其通信行为的存在。针对该隐蔽通信方案，我们进行了详尽的分析，并以闭式形式确定了系统参数。系统参数的解析推导使得仅通过简单的一维搜索即可找到系统参数的最优组合。此外，解析结果揭示了系统参数之间的关联关系。特别地，我们证明了非隐蔽用户的最优策略是采用等发射功率的通断方案。通过将理论推导结果与穷举搜索获得的数值结果进行对比，验证了本文理论结论的有效性。最后，通过展示一种考虑能量效率的隐蔽通信设计方案，我们证明了本文研究成果的广泛可应用性。