Comprehensive Analysis of Cellular Uplink Performance in a Dense Stadium Deployment

TL;DR

This study analyzes uplink performance limitations in dense stadium 5G deployments, highlighting the critical role of low-frequency FDD spectrum and duplexing schemes in ensuring uplink capacity.

Contribution

It provides an extensive measurement-based analysis of uplink bottlenecks in high-density environments, emphasizing the impact of duplexing schemes and spectrum choices.

Findings

High-frequency TDD bands are severely bottlenecked in spectral and temporal domains.

Propagation loss and duplexing scheme significantly restrict uplink performance.

Low-frequency FDD spectrum is essential for maintaining uplink capacity in dense deployments.

Abstract

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.