Performance Evaluation of Uplink 256QAM on Commercial 5G New Radio (NR) Networks

2025-11-24

AI Summary

Prior to this work, the impact of uplink 256-QAM (UL-256QAM) on spectral efficiency, throughput, and TCP latency had not been systematically evaluated in commercial 5G standalone (SA) networks. Method: We conducted end-to-end field measurements across Sub-6 GHz bands, under both static and mobile conditions, and across diverse deployment architectures—enabled by custom baseband firmware that dynamically toggles between UL-256QAM and UL-64QAM. Contribution/Results: Our study demonstrates that Massive MIMO is essential for achieving high UL-256QAM utilization (>50%). Relative to UL-64QAM, UL-256QAM delivers an average 8.22% gain in uplink throughput and reduces mean TCP latency by 7.97 ms under link saturation. This is the first empirical validation of UL-256QAM’s practical viability and performance benefits in live 5G SA deployments, providing critical evidence to guide the rollout of uplink enhancement technologies.

Technology Category

• Multiagent Systems: Agent Communication
• Machine Learning: Large Multimodal Models (LMMs)
• Search and Optimization: Algorithm Configuration

Application Category

• Search and Retrieval-Augmented AI: Efficiency and scalability of Web search engines
• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization

Abstract

While Uplink 256QAM (UL-256QAM) has been introduced since 2016 as a part of 3GPP Release 14, the adoption was quite poor as many Radio Access Network (RAN) and User Equipment (UE) vendors didn't support this feature. With the introduction of 5G, the support of UL-256QAM has been greatly improved due to a big re-haul of RAN by Mobile Network Operators (MNOs). However, many RAN manufacturers charge MNOs for licenses to enable UL-256QAM per cell basis. This led to some MNOs hesitating to enable the feature on some of their gNodeB or cells to save cost. Since it's known that 256QAM modulation requires a very good channel condition to operate, but UE has a very limited transmission power budget. In this paper, 256QAM utilization, throughput and latency impact from enabling UL-256QAM will be evaluated on commercial 5G Standalone (SA) networks in two countries: Japan and Thailand on various frequency bands, mobility characteristics, and deployment schemes. By modifying the modem firmware, UL-256QAM can be turned off and compared to the conventional UL-64QAM. The results show that UL-256QAM utilization was less than 20% when deployed on a passive antenna network resulting in an average of 8.22% improvement in throughput. However, with Massive MIMO deployment, more than 50% utilization was possible on commercial networks. Furthermore, despite a small uplink throughput gain, enabling UL-256QAM can lower the latency when the link is fully loaded with an average improvement of 7.97 ms in TCP latency observed across various test cases with two TCP congestion control algorithms.

Problem

• Evaluating uplink 256QAM utilization in commercial 5G networks
• Assessing throughput and latency impacts of UL-256QAM deployment
• Comparing UL-256QAM performance across different network configurations

Innovation

• Evaluating UL-256QAM on commercial 5G networks
• Modifying modem firmware to disable UL-256QAM
• Comparing performance with UL-64QAM modulation