Intelligent reflecting surfaces (IRSs) were introduced to enhance the performance of wireless systems. However, from a cellular service provider's view, a concern with the use of an IRS is its effect on out-of-band (OOB) quality of service. Specifically, given two operators, say X and Y, providing services in a geographical area using non-overlapping frequency bands, if operator-X uses an IRS to optimally enhance the throughput of its users, does the IRS degrade the performance of operator-Y? We answer this by deriving the ergodic sum spectral efficiency (SE) of both operators under round-robin scheduling. We also derive the complementary cumulative distribution function of the change in effective channel at an OOB user with and without the IRS, which provides deeper insights into OOB performance. Surprisingly, we find that even though the IRS is randomly configured from operator-Y's view, the OOB operator still benefits from the IRS, witnessing a performance enhancement for free. This happens because the IRS introduces additional paths between the nodes, increasing the signal power at the receiver and providing diversity benefits. We verify our findings numerically and conclude that an IRS is beneficial to every operator, even when the IRS is deployed to optimally serve only one operator.

翻译：智能反射表面（IRS）被引入以提升无线系统性能。然而，从蜂窝服务运营商的角度来看，使用IRS的一个担忧是其对带外（OOB）服务质量的影响。具体而言，假设运营商X和Y在同一地理区域使用非重叠频段提供服务，若运营商X利用IRS最优地提升其用户吞吐量，IRS是否会降低运营商Y的性能？我们通过推导两种运营商在轮询调度下的遍历和频谱效率（SE）来回答这一问题。同时，我们推导了有无IRS时OOB用户有效信道变化的互补累积分布函数，这为理解OOB性能提供了更深入的见解。令人惊讶的是，我们发现即使从运营商Y的角度看IRS配置是随机的，OOB运营商仍能从IRS中获益，免费获得性能增强。这是因为IRS在节点间引入了额外路径，增加了接收端的信号功率，并提供了分集增益。我们通过数值验证了研究结果，并得出结论：即使IRS仅部署为最优服务单一运营商，其对所有运营商均有益处。