We consider the problem of \textit{rate loss} - a strict penalty suffered in achievable rates due to the lack of channel state information at the receiver (Rx) of a classical-quantum (CQ) channel. First, we identify non-commutative CQ channels and analytically prove a rate loss. Building on this, we next prove that coset-code-based strategies can strictly outperform conventional unstructured IID-code-based strategies for non-commutative 3-user CQ broadcast channels.

翻译：我们研究\textit{速率损失}问题——即在经典-量子（CQ）信道中，由于接收端（Rx）缺乏信道状态信息而导致的可达速率遭受严格惩罚。首先，我们识别出非对易CQ信道，并通过解析方法证明了速率损失的存在。在此基础上，我们进一步证明，对于非对易三用户CQ广播信道，基于陪集码的策略能够严格优于传统的非结构化独立同分布码策略。