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.

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