Demoing improvements to mobile phone networks is difficult. Where an individual vendor such as Intel or AMD can show off an improved CPU architecture mostly by themselves, it takes a lot of cooperation between companies to show off advanced mobile data initiatives.
This is just what Sprint, Qualcomm, and Motorola teamed up to do last week at the Smoothie King Center in New Orleans, Louisiana.
The first part of the story revolves around Sprint’s unique placement in the US mobile network market. While network operators such as Verizon, ATT, and T-Mobile in the US currently operate their LTE networks on low and mid-band LTE frequencies, the vast majority of Sprint's allocated frequency into the high-band range of 2.5GHz. The reason that Sprint has this spectrum is from their short-lived rollout of WiMax technology with Clear.
High-band frequencies can provide several advantages when deploying technologies enabling Gigabit-class LTE and on the road to 5G.
First, the antenna size needed in the 2.5GHz range is substantially smaller than the antenna size for a more common LTE frequency like 1900MHz. This means that when looking to deploy cellular sites utilizing technologies like 4X4 MIMO antenna arrays, Sprint can make smaller cell sites and be more nimble by placing them in areas where they are seeing substantial network load.
Additionally, the concept of contiguous spectrum is important for high-bandwidth mobile internet deployments. With an availability of more than 160MHz of spectrum in the 2.5GHz range in the top 100 markets of the US, Sprint has placed a high emphasis on rolling out Carrier Aggregation to as many customers as possible. While is possible to do Carrier Aggregation with Inter-band non-contiguous spectrum (bands in different frequency ranges), it requires multiple transceivers on the handset site, increasing end cost and power draw of the device. This is why is a great benefit for Sprint to have so much contiguous spectrum available.
However, there are tradeoffs with using such a high frequency like 2.5GHz, namely transmission distance. It is much more difficult for higher frequency radio waves to travel as far.
The industry's answer to this problem is called High Performance User Equipment (HPUE). HPUE is a specification recently ratified by the 3GPP, which allows certified handsets to operate their radios at a higher power in order to increase transmission distance. It's worth noting that HPUE only increases the uplink connection, as it is was the limiting factor with current 2.5GHz LTE rollouts.
If you’ve ever shopped for an unlocked smartphone, you might be familiar with the idea of LTE Bands. These Band designations break down broad categories of spectrum like 1900MHz or 2500MHz into smaller chunks.
Carrier Aggregation is a feature of LTE-Advanced, which allows a user’s handset (with supported hardware) to connect to multiple bands at the same time. By being connected to multiple LTE bands at the same time, users can achieve higher throughput and more importantly, the overall capacity of the LTE network increases so that more users can be served at the same time.
In the case of Sprint, they currently have deployed three-channel carrier aggregation (3xCA) to over 100 US markets with their current "LTE Plus" rollout. Sprint is depending on this wide rollout of 3-channel CA to be the backbone of their Gigabit-class LTE network.
Carrier Aggregation is an important part of the Gigabit LTE story, there are 2 other very important technologies enabling this technology – 256-QAM and 4X4 MIMO.
Quadrature Amplification Modulation (QAM) is a very complicated subject and will require more detail than I can go into here. Essentially, 256-QAM allows for significantly more complex modulation of radio waves, which means more data can be transmitted at once.
Just like your home wireless internet connection, mobile broadband networks depend highly on the concept of MIMO antennas. MIMO utilizes multiple antennas at once to talk to the same base station.
In the case of Gigabit-class LTE, Sprint was demoing 4X4 MIMO, courtesy of a yet-to-be-unveiled Motorola smartphone. The first handset to feature four 2.5GHz antennas and the Qualcomm Snapdragon 835 SoC featuring the X16 modem, it is currently the only phone capable of delivering gigabit-class LTE speeds on Sprint's future network, but we were promised other handsets coming soon after Motorola's option.
All of this combined to form a very impressive demo at the Smoothie King Center. While fans were filing into the arena for a New Orleans Pelicans NBA game, Sprint was demonstrating simultaneous speed tests running on three of the unnamed Motorola phones.
With just one of the phones running we saw Speedtest.net results around 500Mbps, and with all 3 handsets using the network at the same time, we were able to see a total of almost 600Mbps combined speed, all in a real-world environment! This was the first demo of Gigabit-class LTE on an actual handset, the Telstra event that Morry went to earlier this year was demonstrating using a higher-powered mobile hotspot device.
And that is an important thing to realize with Gigabit-class LTE. While it may be easy for carriers to market the pure throughput of a single handset in a lab, that isn't a realistic expectation. The real advantage of Gigabit-class LTE to users will be the ability for mobile phone networks to handle more people at higher speeds. It might be difficult to utilize 600Mbps on your phone, but I'm sure we can all commiserate with slow transfer speeds in crowded areas.
This certainly won't be the last we hear about Gigabit-class LTE and I'm looking forward to hearing about the other US carrier's plans to enable high mobile data speeds and network capacity!