Uplink performance remains a critical limitation in modern 5G networks, where UEs have to balance limited transmission power against propagation challenges. We conducted extensive measurements in the University of Notre Dame's football stadium, which has a seating capacity of 80,000 spectators, evaluating network behavior under both unloaded (pregame) and severely congested (game day) conditions, with a focus on uplink performance. Analyzing PHY-layer metrics captured via the Rohde & Schwarz QualiPoc, we show that high-frequency TDD bands in the uplink are severely bottlenecked in both the spectral and temporal domains. Despite transmitting near maximum 3GPP power limits, propagation loss inherent to high-frequency bands restricts UEs to low MCS indices and low PRB allocations, even in unloaded networks. This inability to achieve wideband allocation is further compounded by the significantly smaller number of uplink slots compared to downlink slots in TDD frames. Consequently, we observe a severe disparity between uplink and downlink: while high-frequency TDD bands carry the majority of downlink throughput, the network relies heavily on lower-frequency FDD bands for uplink. Additional measurements under favorable propagation conditions around a Verizon COW deployment located in the stadium parking lot also show that this limitation is not solely propagation-driven; rather, the duplexing scheme itself also plays a significant role. Even when TDD bands achieve higher or comparable MCS, FDD bands have a performance edge in the uplink due to the restrictive, downlink-heavy TDD architecture. These findings emphasize the indispensable role of low-frequency FDD spectrum in sustaining uplink capacity, providing insights that will help guide the design of next-generation wireless networks.

翻译：上行链路性能仍然是现代5G网络中的关键瓶颈，用户设备需要在有限的发射功率与传播挑战之间取得平衡。我们在圣母大学可容纳8万名观众的足球场进行了广泛测量，评估了网络在空闲（赛前）和严重拥塞（比赛日）条件下的行为，重点关注上行链路性能。通过分析由罗德与施瓦茨QualiPoc捕获的物理层指标，我们发现上行链路中的高频TDD频段在频谱和时域均存在严重瓶颈。尽管用户设备在接近3GPP最大功率限制下传输，高频频段固有的传播损耗仍将其限制在低MCS索引和低PRB分配，即使在空闲网络中也是如此。这种无法实现宽带分配的问题，进一步因TDD帧中上行时隙数量远少于下行时隙而加剧。因此，我们观察到上下行之间存在严重差异：高频TDD频段承载了大部分下行吞吐量，而网络则严重依赖较低频段的FDD频段进行上行传输。在体育场停车场Verizon COW部署点附近有利传播条件下的额外测量表明，这种限制并非仅由传播导致，双工方案本身也起到重要作用。即使TDD频段达到更高或可比的MCS，由于受限的下行主导型TDD架构，FDD频段在上行链路中仍具有性能优势。这些发现强调了低频FDD频谱在维持上行链路容量中不可或缺的作用，为下一代无线网络的设计提供了指导性见解。