Making Sense of Sprint’s Announcement of 3-Way Carrier Aggregation on LG G5

There seems to be quite a bit of confusion around advanced LTE capabilities of many popular commercial smartphones. Many smartphones are powered by Qualcomm’s Snapdragon 810/808 with X10 modem, or Snapdragon 820 with X12 modem, paired with Qualcomm’s WTR3925 transceiver. This combo enables a multitude of advanced LTE features, but it’s ultimately up to the phone manufacturers to deliver the full network capability to their products.

The X12 modem found in the Snapdragon 820 powered devices is capable of achieving speeds of up to 600Mbps on the downlink (Cat 12), and 150Mbps on the uplink (Cat 13). However, in order for a Snapdragon 820 powered smartphone to achieve 600Mbps on the downlink, the OEM needs to enable Three Channel Carrier Aggregation (3CCA), as well as 256QAM capability.

We know that U.S. bound Snapdragon 820 carrier branded smartphones don’t have 256QAM capability enabled out of the box, which means that 3CCA can theoretically bring us up to 450Mbps on the downlink. What’s often forgotten is that in order for the X12 modem to fully achieve Three-Way Inter-Band (non-contiguous) Carrier Aggregation, the WTR3925 transceiver needs to be paired with an additional WTR4905 “companion” transceiver chip. Major OEMs Samsung and HTC, and also smaller ones such as Xiaomi, LeEco, Asus, have been shipping their 2016 flagship products with this configuration. The standout here for a major OEM is LG with their G5 which only has a single WTR3925 transceiver, capable of only aggregating two non-contiguous, inter-band component carriers.

Going back to our prior article about the state of LTE networks in NYC to provide an example, Verizon could widen their FDD LTE channels to dedicate 20MHz of PCS spectrum, aggregate it with the existing 20MHz of AWS spectrum, and Cat 6 devices like LG G5 with a single transceiver solution will be able to fully achieve downlink rates of up to 300Mbps out of 40MHz of spectrum. However, try to add the additional 10 MHz of 700 MHz Upper C Block into the above mix, and the Cat 6 devices like LG G5 wouldn’t be able to keep up without an additional hardware, a  WTR4905 companion transceiver.

Given this, we’ve reached out to Qualcomm to help us understand Sprint’s announcement of 3-way carrier aggregation lab test, particularly highlighting the LG G5.

It actually turns out that a single WTR3925 transceiver can support Three Channel Carrier Aggregation and up to 60MHz of spectrum, if at least two out of three component carriers are contiguous. Considering that only Sprint holds 60+MHz of contiguous spectrum in many markets, and their existing TDD LTE 2.5GHz deployments are intra-band contiguous, devices with a single WTR3925 transceiver like LG G5 indeed are capable of aggregating three contiguous 20MHz TDD LTE component carriers.

Furthermore, this explains why last year’s Snapdragon 810/808 powered devices also with the WTR3925 transceiver, such as the HTC M9, are listed in Sprint’s announcement as well. Additionally, this opens up a possibility for 3CCA TDD LTE capability on Nexus 6P and Nexus 5X, and we certainly intend to test that theory in the future.

For years we’ve been hearing about Sprint’s “treasure trove” of 2.5GHz spectrum, but only in the last five months or so has Sprint dropped press releases of lab test detailing the benefits of 3CCA on three different smartphones.  These tests have so far turned out to be nothing more than a showcase of smartphone capabilities in the lab which prove the OEM readiness. On the other hand, we are still waiting for Sprint to fully exploit the treasure trove of spectrum in the field.

Sprint has a unique opportunity here. A move from TDD LTE Configuration 1 (max DL~82Mbps) to Configuration 2 (max DL~112Mbps), combined with 3-Way Carrier Aggregation (max DL~330Mbps peak), 256QAM (max DL~430Mbps), and then mix-in ongoing Small Cell strategy, Sprint is positioned to deliver massive capacity to consumers. No other operator comes close to the amount of fallow spectrum Sprint sits on, but in order to differentiate from the rest of the pack, Sprint actually needs to start delivering that capacity to consumers at scale, and they need to act fast. Other operators are already gearing up to deploy massive swaths of mmWave spectrum, and it would be such a letdown if the severe lack of funding and execution prevents Sprint from becoming a major force in the U.S. wireless marketplace that we all have been waiting for.