"Aside from 4×4 MIMO, the new iPhone XS and XS Max also gain support for QAM and LAA, which are other radio technologies that will help improve speed and range on the new phones."
4x4 instead of 2x2 in the 8/8 Plus/X, and LTE advanced.
From Qualcomm's explanation:
"4X4 MIMO uses four antennas on the cell tower to transmit data to four antennas in your Gigabit LTE device, instead of the typical two antennas used in the vast majority of LTE devices. In good signal conditions, this can up to double your speed. In the highway analogy, it is akin to building additional decks for cars to travel on, on top of the existing lanes. Gigabit LTE devices with 4x4 MIMO technology have an additional and important benefit: In weak signal conditions, the extra antennas act as additional “ears” that boost the signal received from the tower, resulting in up to 70% faster speeds."
"Just like carrier aggregation, LTE-U/LAA technology builds new lanes on the data highway between the cell site and your device to improve download speeds. But unlike traditional LTE technology, LTE-U/LAA technology uses freely available unlicensed spectrum, and they are sent from a “small cell” (a miniaturized cell site in a compact box) instead of a big tower. This makes small cells especially helpful in relieving congestion in areas like airports, busy city centers and malls, as they can be placed conveniently where they are needed most."
"256-QAM is a digital signal modulation technology that encodes eight bits of information into every LTE signal sent from the tower to your device, instead of the typical six bits with 64-QAM. That results in up to 33% faster download speeds. It also means that you need fewer resources from the tower to complete your downloads, since more data is being sent to you in every signal. In the highway analogy, it would be akin to stuffing 33% more packages into each delivery truck, reducing the number of trucks on the road and improving speeds for everyone."
