LONDON—Today, I got to play around with Europe's (and probably the world's) fastest LTE network: when I opened up Speedtest.net, depending on how many people were standing in the room, my download speed was between 350 and 400Mbps, my upload speed was around 45Mbps, and my ping latency was just 20ms.

Funny enough, beyond Speedtest.net, it is actually quite hard to use 400Mbps of bandwidth. When I loaded up a 4K video from YouTube, I only used around 40Mbps, or 10 percent, of my wireless uber-pipe. Ars Technica certainly loaded very quickly indeed. As it stands today, there are very few websites or services that will let you pull data down at 400Mbps, or where being able to download at 400Mbps even makes much sense. If we've learned anything from the last few decades of telecoms and networking, however, it's that Internet usage will always expand until every last inch of available bandwidth is consumed. So while 400Mbps might seem a little bit over the top today, in five years you'll probably wonder how you ever survived with anything less.

For some background, I had a 400Mbps LTE connection at my disposal because I had been invited to Wembley Stadium in London to try out the first deployment of Category 9 LTE in the UK. It was a "live" deployment in that it used commercially available hardware, but it was still very much a tech demo—the Cat 9 base station only covered a small portion of the stadium, and there were only a handful of devices in the world configured to connect to this specific LTE network. The LTE network was operated by EE (one of the UK's big four wireless carriers), the LTE base station was made by Huawei, and the mobile device that I used was a smartphone powered by the Qualcomm Snapdragon 810 SoC.

Category 9 LTE, part of 3GPP Release 11, allows for a max theoretical downlink speed of 452.2Mbps and uplink of 51Mbps. In previous tests, EE, Huawei, and Qualcomm have achieved download speeds of 410Mbps. Today, due to interference and attenuation caused by some fleshy bags of meat that happened to be in the same room as me, the downlink speed was a little lower. In a real-world deployment, where you're more than a few meters away from the base station, you'll probably get upwards of 150Mbps.

Much like Category 6 LTE, Category 9 allows for carrier aggregation. In this case, EE uses three different carriers—a 20MHz block at 1800MHz, 20MHz at 2.6GHz, and a further 15MHz band elsewhere at 2.6GHz—working in perfect harmony to achieve max throughput. If one of the carriers isn't available (the second block of 15MHz at 2.6GHz will likely only be available in built-up urban areas, for example), your mobile device will fall back to a lower category. Carrier aggregation is very important in markets where mobile carriers have multiple blocks of non-contiguous spectrum (i.e. just about everywhere in Europe and the US). Instead of providing a bunch of separate services on each band, each with mediocre throughput, mobile operators can combine a few of them to offer a single, aggregated channel that is both faster and higher quality.

While it was very exciting to have 400Mbps of mobile bandwidth at my disposal, it's important to note that massive download speeds are only part of the reason that mobile carriers are moving to deploy higher categories of LTE Advanced. With wireless networks, the bottleneck is rarely the base station's backplane or the backhaul connection to the carrier's core network. With tri-band Category 9 LTE, those 400 megabits are split across every user who is currently sharing the same air interface—i.e. every device currently connected to that base station. If 100 users are concurrently connected to the same cell (which would be unusually high), they would still get a respectable 4Mbps down. That's why current 3G and 4G deployments can feel very slow; you're probably sharing a fairly small amount of bandwidth with dozens of other people.

The first commercial LTE network with tri-band carrier aggregation recently went live in South Korea, but it has a max speed of "only" 300Mbps. EE doesn't have a specific timeline for the commercial rollout of 400Mbps Category 9 LTE in the UK, but late 2015 or early 2016 is likely. In the US, we're not aware of any major carrier currently testing or preparing to deploy tri-band Category 9 LTE.