Title: Integrating Intelligent Reflecting Surface into Base Station: Architecture, Channel Model, and Passive Reflection Design Show Chinese title

Title: 将智能反射表面集成到基站中：架构、信道模型和被动反射设计

Abstract: Existing works on IRS have mainly considered IRS being deployed in the environment to dynamically control the wireless channels between the BS and its served users. In contrast, we propose in this paper a new integrated IRS BS architecture by deploying IRSs inside the BS antenna radome. Since the distance between the integrated IRSs and BS antenna array is practically small, the path loss among them is significantly reduced and the real time control of the IRS reflection by the BS becomes easier to implement. However, the resultant near field channel model also becomes drastically different. Thus, we propose an element wise channel model for IRS to characterize the channel vector between each single antenna user and the antenna array of the BS, which includes the direct (without any IRS reflection) as well as the single and double IRS-reflection channel components. Then, we formulate a problem to optimize the reflection coefficients of all IRS reflecting elements for maximizing the uplink sum rate of the users. By considering two typical cases with/without perfect CSI at the BS, the formulated problem is solved efficiently by adopting the successive refinement method and iterative random phase algorithm (IRPA), respectively. Numerical results validate the substantial capacity gain of the integrated IRS BS architecture over the conventional multi antenna BS without integrated IRS. Moreover, the proposed algorithms significantly outperform other benchmark schemes in terms of sum rate, and the IRPA without CSI can approach the performance upper bound with perfect CSI as the training overhead increases. Show Chinese abstract

Abstract: 现有关于IRS的研究主要考虑将IRS部署在环境中，以动态控制基站和其服务用户之间的无线信道。 相比之下，本文提出了一种新的集成IRS基站架构，通过将IRS部署在基站天线罩内。 由于集成IRS与基站天线阵列之间的距离实际较小，它们之间的路径损耗显著降低，基站对IRS反射的实时控制也更容易实现。 然而，产生的近场信道模型也变得截然不同。 因此，我们提出了一种元素级的信道模型用于IRS，以表征每个单天线用户与基站天线阵列之间的信道向量，该模型包括直接（没有任何IRS反射）以及单次和双次 IRS反射信道分量。 然后，我们制定一个优化问题，以最大化用户的上行链路总速率，优化所有IRS反射元件的反射系数。 通过考虑两种典型情况，即基站具有/不具有完美CSI，分别采用逐步细化方法和迭代随机相位算法（IRPA）高效地解决该问题。 数值结果验证了集成IRS基站架构相对于没有集成IRS的传统多天线基站的显著容量增益。 此外，所提出的算法在总速率方面显著优于其他基准方案，且无需CSI的IRPA随着训练开销的增加可以接近具有完美CSI的性能上限。