Intelligent reflecting surfaces (IRSs) were introduced to enhance the performance of wireless communication systems. However, from a service provider's viewpoint, a concern with the use of an IRS is its effect on out-of-band (OOB) quality of service. Specifically, if two operators, say X and Y, provide services in a given geographical area using non-overlapping frequency bands, and if operator X uses an IRS to enhance the spectral efficiency (SE) of its users, does it degrade the performance of users served by operator Y? We answer this question by analyzing the average and instantaneous performances of the OOB operator considering both sub-6 GHz and mmWave bands, accounting for their corresponding channel characteristics. Specifically, we derive the ergodic sum-spectral efficiency achieved by the operators under round-robin scheduling. We also derive the outage probability and analyze the change in the SNR witnessed by an OOB user in the presence of the IRS using stochastic dominance theory. Surprisingly, even though the IRS is randomly configured from operator Y's point of view, the OOB operator still benefits from the presence of the IRS, witnessing a performance enhancement for free, in both sub-6 GHz and mmWave bands. This is because the IRS introduces additional paths between the transmitter and receiver, increasing the overall signal power arriving at the receiver and providing diversity benefits. We numerically illustrate our findings and conclude that an IRS is always beneficial to every operator, even when the IRS is deployed and controlled by only one operator to serve its own users.

翻译：智能反射面（IRS）被引入用于提升无线通信系统的性能。然而，从服务提供商的角度来看，使用IRS的一个关切在于其对带外（OOB）服务质量的影响。具体而言，若两个运营商（例如X和Y）在同一地理区域使用非重叠频段提供服务，且运营商X利用IRS提升其用户的频谱效率（SE），这是否会降低运营商Y所服务用户的性能？我们通过分析考虑sub-6 GHz与毫米波频段及其相应信道特性下OOB运营商的平均性能与瞬时性能来回答这一问题。具体而言，我们推导了运营商在轮询调度下实现的遍历和频谱效率。同时，我们利用随机占优理论推导了中断概率，并分析了在IRS存在下OOB用户所经历信噪比的变化。令人惊讶的是，尽管从运营商Y的角度来看IRS是随机配置的，但OOB运营商仍能从IRS的存在中受益，在sub-6 GHz与毫米波频段均免费获得了性能提升。这是因为IRS在发射机与接收机之间引入了额外路径，增加了到达接收机的总信号功率，并提供了分集增益。我们通过数值仿真验证了上述发现，并得出结论：即使IRS仅由单一运营商部署并控制以服务其自身用户，该IRS始终对每个运营商均有益。