The Federal Communications Commission (FCC) in the U.S. has made the Citizens Broadband Radio Service (CBRS) band (3.55 - 3.7 GHz) available for commercial wireless usage under a shared approach using a three-tier hierarchical architecture, where the federal incumbent is the highest priority Tier 1 user, Priority Access License (PAL) holders, who have paid for licenses, are Tier 2 users and Tier 3 users operate under General Authorized Access (GAA), without license fees or protection from higher priority users. The Spectrum Access System (SAS) ensures that higher priority users are protected from interference from lower priority users. However, the lowest priority GAA users are not given any protection from each other by the SAS and are expected to not cause any harmful interference to Tier 1 and Tier 2 users. As the deployments of GAA devices grow, the potential for secondary interference between GAA users increases, especially since the SAS architecture does not allow dynamic channel switching when faced with interference. In this paper, we present a first-of-its-kind extensive measurement campaign of a commercial CBRS network deployed in the city of South Bend, IN, that quantifies both co-channel interference (CCI) and adjacent channel interference (ACI) caused by competing GAA devices and C-band 5G, respectively. We (i) identify a particular CCI scenario and improve performance by changing the frequency allocation based on our study of other allocations in the vicinity and (ii) quantify ACI from 5G in C-band (3.7 GHz) on CBRS throughput. We conclude that (i) CCI and ACI for GAA users is not handled well by the SAS, (ii) proper frequency allocation for GAA requires additional analysis of interference from other GAA users followed by dynamical channel selection, and (iii) utilization of immediate adjacent channels by high power 5G deployments limits the performance of CBRS.

翻译：美国联邦通信委员会（FCC）已开放市民宽带无线电服务（CBRS）频段（3.55-3.7 GHz），采用三层分级架构的共享方案用于商业无线应用。其中，联邦现役用户为最高优先级的第一级用户；已付费获得许可的优先接入许可证（PAL）持有者为第二级用户；第三级用户则在通用授权接入（GAA）机制下运行，无需许可费用且不受高优先级用户保护。频谱接入系统（SAS）确保高优先级用户免受低优先级用户干扰，但SAS并不为最低优先级的GAA用户提供相互保护，且要求GAA用户不得对第一级和第二级用户造成有害干扰。随着GAA设备部署规模扩大，GAA用户间的次级干扰风险随之增加，尤其是SAS架构在面临干扰时无法实现动态信道切换。本文首次对部署于印第安纳州南本德市的商业CBRS网络开展了大规模测量研究，量化了竞争性GAA设备引发的同频干扰（CCI）以及C波段5G系统造成的邻频干扰（ACI）。我们（i）识别出特定CCI场景，基于对邻近频段分配的调研优化频率分配后提升了性能；（ii）量化了C波段（3.7 GHz）5G系统对CBRS吞吐量的ACI影响。研究结论表明：（i）SAS未能有效处理GAA用户的CCI与ACI问题；（ii）GAA合理频率分配需额外分析其他GAA用户的干扰并执行动态信道选择；（iii）高功率5G系统占用紧邻信道会制约CBRS性能。