The technology behind Gigabit LTE

The name alone tells you the basics. Gigabit LTE is a mobile broadband standard where the theoretical maximum download speed reaches a rate of one gigabit of data per second. That’s 1,000Mbits/sec, fast enough to download a 1GB movie in eight seconds.

It’s very, very fast, far quicker than any home broadband currently available to consumers in the UK. In fact 1,000Mbits/sec outstrips the write speeds of some hard drives! Even after considering how the realities of a congested network will eat away at this speed, we’re still looking at the internet on your phone being quicker than that of most home broadband services, with average user speeds often exceeding 100 to 200Mbits/sec.

What makes Gigabit LTE possible?

Gigabit LTE sounds like a technology of the future, but the hardware making it possible is already here. The Qualcomm® Snapdragon™ Gigabit LTE modem can deliver these speeds, and you’ll find it in several phones, including the Sony Xperia XZ Premium.

Gigabit LTE is made possible not by a single technology that magically unlocks this speed, but a whole series of improving standards that work together. Buyers may know when their new phones switched from 3G to 4G, but few know of the quiet innovation in the background that has seen mobile internet hardware speed up year-by-year.

It’s understandable, because the jargon of mobile internet can seem impenetrable. We’re going to break each Gigabit-enabling standard down to take the teeth out of the terminology. There are four main factors to examine. Ready?

CA (carrier aggregation)

The wireless communication needed for LTE, and all mobile internet, happens over specific frequency bands. You can think of these like different parts of the frequency dial of an FM radio, if you’re old enough to remember when people still used such things.

Three bands are currently used for 4G in the UK, 800MHz, 1800MHz and 2600MHz. Phone networks bid to the government for the exclusive use of chunks of these bands for their 4G networks, and end up with ‘blocks’ of the wireless spectrum over which they can transmit their services.

EE, for example, uses two 5MHz-wide blocks in the 800MHz band and two 45MHz blocks in the 1800MHz band for its 4G.

Carrier aggregation lets a phone receive data on multiple bands or blocks at the same time. It’s like a data motorway. Carrier aggregation adds lanes to the motorway, letting more traffic pass and helping to avoid jams. And you end up with faster, more reliable downloads.

Aggregation is an important part of LTE Advanced, one term used to encompass these speedier technologies, even if most people still think of it as simple “4G” or “LTE”.

Vodafone and EE have used dual carrier aggregation in the UK since 2014. EE launched the first triple carrier aggregation in late 2016, and it has been spreading across UK hot spots since then.

The Qualcomm Snapdragon Gigabit LTE Modem already supports 4x carrier aggregation, so is well equipped to make the best use of this piece of the puzzle.

4×4 MIMO

While 4×4 MIMO may sound intimidating, it’s one of the easiest parts of LTE Advanced to understand. This means a phone has four antennas rather than the usual two.

These four antennas communicate with four corresponding transmitter antennas on the cell tower, doubling the available streams of communication. Not only is this an important part of getting enough data streaming to reach Gigabit-class speeds, 4×4 MIMO can also be used to boost performance in areas not yet upgraded with Gigabit LTE infrastructure.

Essentially the phone has more ‘ears’ with which it can listen for mobile signal, which is extremely handy in an area with poor signal. Even cities like London have black spots, especially indoors.

256-QAM

So far we’ve looked at ways Gigabit LTE technologies add more ‘pipes’ of data between your network provider and your phone. 256-QAM is what fattens up these pipes, letting them transmit more data with the same wedge of spectrum.

QAM stands for Quadrature Amplitude Modulation, and relates to the complexity of the language used to send LTE data. To fully understand it you have to dig pretty deep into the behaviour of carrier waves.

In order to save the effort and avoid sounding like a chapter from a degree-level engineering text, using 256-QAM is a little like having command of a giant vocabulary that is 33% larger than others’. Knowing more terms lets you relay complicated ideas using fewer words, each able to deliver greater meaning. Big words aren’t just for showing off.

For a little more detail, the higher the QAM figure, the more variations of amplitude and phase there can be in the signal. This is what makes the ‘language’ more complicated.

The Snapdragon Gigabit LTE Modem uses 256-QAM for downloads and the level below, 64 QAM, for uploads.

LTE in Unlicensed Spectrum

One of the most recent LTE developments is LTE-U, and its close counterpart, LAA, which seeks to deal with one of mobile internet’s big problems, that there’s only so much wireless spectrum to play with. The U of LTE-U stands for unlicensed, meaning it’s mobile internet delivered over the free-for-all 5GHz wireless band rather than the bands providers have ‘bought’ for exclusive 3G/4G use.

 

It helps take the strain off those dedicated 4G bands, which are both extremely limited and extremely expensive to get hold of. In total, £2.3 billion was paid for chunks of the UK 800MHz band alone back in 2013.

The common worry of using the 5GHz band is that it’s what 802.11ac Wi-Fi home broadband routers and Wi-Fi hotspots use, so it could tread on their signals.

Qualcomm has come up with an answer, though. There are several ways to get LTE working in unlicensed spectrum, and LAA (Licensed Assisted Access) is one of the most important. Using LAA, the unlicensed spectrum is used to bolster signal in the normal licensed band, using the same carrier aggregation principle we discussed above. It implements something called LBT to make sure it doesn’t push existing Wi-Fi over and trample on it.

LBT stands for Listen Before Talk, and it checks for clear 5GHz channels to avoid congestion. Qualcomm calls this part of its “fair coexistence” practices, and it’s an important step in avoiding an LTE versus Wi-Fi civil war.

What’s next?

The Snapdragon Gigabit LTE modem is the modem you’ll find in today’s top-end phones. However, Qualcomm isn’t sitting back on its laurels.

The next Snapdragon Gigabit LTE modem has already been announced, adding room for 5x carrier aggregation to boost the max download bandwidth to 1.2Gbits/sec. Like the years between important wedding anniversaries, that doesn’t earn it a new title beyond Gigabit LTE. However, it shows how quickly the technology is developing and that Qualcomm is committed to pushing that development further.

Find out how Qualcomm is driving the Gigabit LTE revolution.