Qualcomm’s X20 LTE modem supports speeds up to 1.2 Gbps
Last year around Mobile World Congress, Qualcomm announced the Snapdragon X16, billed as the company's first "gigabit" LTE modem. Most of you still don't have an X16 in your phones, though that will change in the next few months with the imminent arrival of the Snapdragon 835 processor and the flagship phones that use it. But Qualcomm has already moved on to the next thing, namely its new Snapdragon X20 modem—this chip bumps the maximum theoretical download speed from the X16's 1.0Gbps to 1.2Gbps, but more importantly it makes those gigabit speeds easier to actually hit.
The X20 hits those (at this point, still mostly theoretical) gigabit speeds by using many of the same tricks as the X16. Carrier aggregation and 4×4 MIMO antennas allow up to 12 streams of data to be received using between three and five 20MHz chunks of spectrum, up from 10 streams across three or four 20MHz chunks of spectrum in the X16. Use of 256-QAM instead of 64-QAM allows up to 100Mbps of data to be sent in each stream, adding up to 1.2Gbps of total bandwidth (a good, basic explainer of QAM, or Quadrature Amplitude Modulation, can be found here).
The big difference for the X20 is that wireless operators can use more combinations of licensed and unlicensed LTE spectrum to actually hit gigabit speeds. The graphic above shows all of the combinations of licensed (yellow) and unlicensed (red) spectrum that can be mixed and matched to reach 1.0 or 1.2Gbps. In theory, operators could offer gigabit LTE speeds using just 10MHz of licensed spectrum, a feature enabled by the modem's 5x carrier aggregation.
Again, these speeds will be difficult to come by in reality. Unlicensed spectrum (sometimes referred to as either LTE-U or LAA, as above) uses some of the same bands as Wi-Fi networks use, which can subject these streams to additional interference. And like Wi-Fi, unlicensed LTE also has a shorter range than the licensed spectrum does. If phones can cobble together a bunch of bandwidth from a bunch of different sources, that ultimately will help with both download speeds and network congestion; you should just continue to treat these maximum theoretical bandwidth figures as thoroughly theoretical.
The X20's bandwidth remains frozen at 150Mbps, the same as the X16 and X12 modems before it. Qualcomm tells us it is still enough to keep up with demand from both users and wireless network operators.
The X20 is built on Samsung's 10nm FinFET manufacturing process and is sampling to phone makers now; availability in consumer devices is expected "in the first half of 2018." As with the X16, though, you may not actually encounter the X20 until Qualcomm integrates it into one of its Snapdragon SoCs. Qualcomm wouldn't say when to expect a new Snapdragon 800-series chip with an X20 modem built in, but if the company keeps to its current schedule we should start to hear news about it later this year.
Finally, while Qualcomm is still ahead of its competition here, other companies are still playing catch-up. Most significantly, Intel announced a new XMM 7560 modem today (PDF) that promises gigabit LTE speeds and many of the same technologies as the X16 and X20: 5x carrier aggregation on the downlink, 256-QAM, four MIMO antennas, use of LAA to boost speeds, and download speeds "exceeding" 1Gbps. Intel also supports 3x carrier aggregation on the uplink, promising speeds of up to 225Mbps. Intel's modems aren't as good as Qualcomm's, but the company scored a major victory last year when some of its modems began shipping in some models of Apple's iPhone 7.
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