The upper mid-band - roughly from 7 to 24 GHz - has attracted considerable recent interest for new cellular services. This frequency range has vastly more spectrum than the highly congested bands below 7 GHz while offering more favorable propagation and coverage than the millimeter wave (mmWave) frequencies. The upper mid-band can thus provide a powerful and complementary frequency range to balance coverage and capacity. Realizing the full potential of these bands, however, will require fundamental changes to the design of cellular systems. Most importantly, spectrum will likely need to be shared with incumbents including communication satellites, military RADAR, and radio astronomy. Also, the upper mid-band is simply a vast frequency range. Due to this wide bandwidth, combined with the directional nature of transmission and intermittent occupancy of incumbents, cellular systems will need to be agile to sense and intelligently use large spatial and frequency degrees of freedom. This paper attempts to provide an initial assessment of the feasibility and potential gains of wideband cellular systems operating in the upper mid-band. The study includes: (1) a system study to assess potential gains of multi-band systems in a representative dense urban environment and illustrate the value of wide band system with dynamic frequency selectivity; (2) an evaluation of potential cross interference between satellites and terrestrial cellular services and interference nulling to reduce that interference; and (3) design and evaluation of a compact multi-band antenna array structure. Leveraging these preliminary results, we identify potential future research directions to realize next-generation systems in these frequencies.

翻译：中上频段——大致在7至24 GHz范围内——近期因可支撑新型蜂窝服务而备受关注。相较于已高度拥挤的7 GHz以下频段，该频率范围拥有更广阔的频谱资源，同时比毫米波频段具备更优的传播特性与覆盖能力。因此，中上频段可作为平衡覆盖与容量的强有力补充频段。然而，要充分发挥这些频段的潜力，需对蜂窝系统设计进行根本性改革。其中最重要的挑战在于频谱需与包括通信卫星、军用雷达及射电天文在内的既有业务共享。此外，中上频段本身跨度极为宽广。由于这种宽带宽特性、传输的方向性特征以及既有业务的间歇性占用，蜂窝系统必须具备灵活感知空间与频率自由度、并实现智能化利用的敏捷能力。本文旨在对中上频段宽带蜂窝系统的可行性与潜在增益进行初步评估。研究内容包括：(1) 系统级分析，评估代表性密集城市环境中多频段系统的潜在增益，并论证具备动态频率选择性的宽带系统价值；(2) 评估卫星与地面蜂窝服务间的潜在交叉干扰，并研究零陷波束赋形技术以降低该干扰；(3) 设计并评估紧凑型多频段天线阵列结构。基于上述初步结果，我们识别出未来在这些频段实现下一代系统的潜在研究方向。