This paper establishes the fundamental limits of a two-user single-receiver system where communication from User 1 (but not from User 2) needs to be undetectable to an external warden. Our fundamental limits show a tradeoff between the highest rates (or square-root rates) that are simultaneously achievable for the two users. Moreover, coded time-sharing for both users is fundamentally required on most channels, which distinguishes this setup from the more classical setups with either only covert users or only non-covert users. Interestingly, the presence of a non-covert user can be beneficial for improving the covert capacity of the other user.

翻译：本文建立了双用户单接收器系统的基本极限，在该系统中，用户1（而非用户2）的通信需要对外部监控者不可检测。我们的基本极限揭示了两个用户同时可达到的最高速率（或平方根速率）之间存在权衡。此外，在大多数信道上，对两个用户进行编码时分复用是基本必要的，这使该设置区别于更经典的仅包含隐蔽用户或仅包含非隐蔽用户的场景。有趣的是，非隐蔽用户的存在可能有助于提升另一用户的隐蔽容量。