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）已将公民宽带无线电服务（CBRS）频段（3.55-3.7 GHz）开放用于商业无线用途，采用基于三层分层架构的共享模式。其中联邦现役用户为最高优先级的第一级用户，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）模式下运行，无需支付许可费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并未为最低优先级的GAA用户提供相互保护，且要求其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用户间的次级干扰可能性随之增加——尤其当SAS架构不允许在面临干扰时进行动态信道切换时。本文首次对部署在印第安纳州南本德市的商用CBRS网络开展大规模测量活动，分别量化了竞争性GAA设备引起的同频干扰（CCI）与C波段5G引起的邻频干扰（ACI）。我们（i）识别出特定CCI场景，并通过基于周边频段分配研究调整频率配置来优化性能；（ii）量化C波段（3.7 GHz）5G对CBRS吞吐量的ACI影响。结论表明：（i）SAS对GAA用户的CCI与ACI管理存在不足；（ii）GAA的合理频率分配需先分析其他GAA用户的干扰情况，再进行动态信道选择；（iii）高功率5G部署占用紧邻频段会制约CBRS性能。