Everyone gets excited everytime a feature comes out especially those that claims to improve the subscriber experience in terms of throughput by a factor of 50%-100%. Question is: Under the same radio conditions can 256QAM deliver on its promise?
First, it’s definitely handset capability dependent. The phones that support such capability would be, at the minimum, the Galaxy S8 - and all the succeeding high-end batches. Practically we’re looking at less than 1% of all the LTE capable mobile handsets out there - well, at least as of this writing. Probably it is for another set of devices at home in the future. But it certainly gives the hype - at least for now. But for curious RF Engineers out there, have a look at the following figure and realize that it is still the task of securing a good radio access interface quality which will quarantee that 256QAM will actually work for the subscribers. CQI=10 is the top of mind target across the board!.
Figure above shows the default and the alt-cqi table (used for 256QAM) compared side-by-side under the same radio conditions. It could be observed that 256QAM implementation assigns larger transport blocks to deliver higher speed - and that is all that it does… period.