The gain of UL 256QAM compared to UL 64QAM
– UL 256QAM transfers 8 bits per symbol, While UL 64QAM transfers 6 bits per symbol. This means that UL 256QAM can provide up to 33% gain in the maximum UL Speed
Do both 4G and 5G support UL 256 QAM?
– Yes, Both 4G and 5G support UL 256QAM; however, the penetration of TDD & FDD UL 256QAM capable Devices is much less compared to 5G, and from practical experience, the requirement to get UL 256QAM activated is much more difficult in 4G compared to 5G. which gives more advantage to 5G in the UL compared to 4G.
How to verify 4G & 5G UL 256QAM functionality from Field/L3 messages:
For 4G Part:
UL 256QAM requires that UEs meet all of the following conditions:
1- For MR-DC UEs, The value ul-256QAM-r15 in the UE capability message is supported.
2- For other UEs: The value of ul-256QAM-r14 or ul-256QAM-perCC-InfoList-r14 in the UE capability message is supported.
For 5G Part:
1- pusch-256QAM should be included in the UE Capability message, as shown in the figure below.
2- During Field testing, Check that 256QAM mcs-table is delivered in the RRC Reconfiguration message(This should be applicable for both 4G & 5G)
Note: From Practical experience, UL 256QAM FDD was very recently introduced, and very few devices supported the feature, as I remember starting from iPhone 14. If anyone has more information about the release supporting FDD UL 256QAM. Please share it in the comments.
