What is LTE? Everything you need to know

Social media, video streaming and even online gaming, you name it, our smartphones are better connected than ever and we’re consuming more and more data as a result. 4G LTE is the current generation of wireless technology making all of this a reality, and at much faster speeds than the older 3G and 2G standards.

In this article, we’ll be taking a look at some of the technical aspects of how LTE works and the hardware associated with it, along with the benefits and how it all relates to the smartphone in your pocket.

How 4G LTE works

The most notable differences from LTE’s predecessors is the change in frequency and bandwidth usage. There are a wide number of 4G LTE bands defined by the standard, the usage of which will vary depending on your country and even your specific carrier’s technology.

These frequencies are split into Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) types. FDD spectrum requires pair bands, one for uplink and one for downlink. TDD uses a single band as uplink and downlink on the same frequency, but these are time separated instead. There are 31 pairs of LTE bands that operate between 452MHz and 3600MHz and an additional 12 TDD bands between 703MHz and 3800MHz. Higher frequencies allow for faster transmission in built up areas, while lower frequencies offer additional coverage distance, but more limited bandwidth. These bands typically offer between 10 and 20MHz of bandwidth for data transfer, although they are also commonly split up into smaller 1.4, 3 and 5MHz chunks too.

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FDD is the LTE variation that is regularly seen in North American, European, and some Asian markets. TDD has been implemented in China and India as the wider bandwidth allows for more users per Mhz. This is why you should always be careful to double check LTE bands and carrier compatibility when importing phones from other countries.

LTE uses two different radio links for downlink and uplink, that is, from tower to device, and vice versa. For the downlink, LTE uses an OFDMA (orthogonal frequency division multiple access), which requires MIMO. MIMO, which stands for Multiple Input, Multiple Output, uses two or more antennas to reduce latency significantly and boost speeds within a given channel. Standard LTE can accommodate up to a 4×4 arrangement (the first digit is the number of transmit antennas, and the second, the number of receive antennas).

For the uplink (from device to tower), LTE uses a SC-FDMA (single carrier frequency division multiple access) signal. SC-FDMA is better for uplink because it has a better peak-to-average power ratio.

Speeds and LTE-A

With that jargon out of the way, the major benefit for consumers with 4G LTE is faster download speeds. Although the quality and speed for your connection will clearly vary based on the number of users and the strength of the signal, most LTE networks provide between 10 and 20 Mbps download speeds, according to the latest OpenSignal research. The fastest 4G LTE countries boasts up to 50Mbps download speeds, although in reality these top out somewhere around 35Mbps.

For comparison, older 3G networks can vary quite widely in their actual results. HSPA networks can peak at around 14Mbps download and 6Mbps upload, but rarely come close to this. Typically, a good LTE network is at least 3 to 5 times faster than the best 3G coverage.

QualcommLTE theoretical speeds can peak at 100 Mbps download and around 50 Mbps upload. If we are to achieve higher speeds, we need to increase the amount of available bandwidth. LTE-Advanced introduces 8×8 MIMO in the Downlink and 4×4 in the Uplink, which allows for multiple carrier bands to be aggregated together, to improve signal strength and bandwidth. Each LTE band has a bandwidth of either 1.4, 3, 5, 10, 15 or 20 MHz, giving us a maximum bandwidth of 100MHz with five combined, although this will vary depending on the bandwidth available in your particular area.

Theoretically, these provide a maximum download speed of approximately 3.3Gbps and 1.5 Gbps upload. However, the hardware modem found inside your smartphone probably isn’t quite that fast and network coverage certainly isn’t good enough to meet that criteria yet.

From the perspective of a network carrier, the network architecture for LTE is greatly simplified from its predecessors because LTE is an Internet Protocol (IP) based packet-switched network only. The early trade-off was that these networks didn’t have the capability to handle voice calls and text messages natively, but the introduction of VoIP and LTE-A services has begun bringing these features to customers.

The tech inside your phone

As you have probably figured out, 4G LTE has been an evolving standard and it continues to change as we move towards a future with 5G technology. As such, the hardware inside our smartphones has changed over the years to keep pace with faster LTE networks.

To keep things relatively simple, user equipment is split into a number of different categories, each designed to offer a set of features and speeds based on a specification release. This is often the number that you’ll see listed on a smartphone specification sheet. Release 10 introduced the speed and MIMO improvements that come with LTE-Advanced, but there are a number of newer Release 12 categories on the way too. Here’s a comparison of how some of them break down.

	Max Download	Max Upload	MIMO Config.	Release #
Category 4	150Mbps	51Mbps	2	8
Category 6	300Mbps	51Mbps	2 or 4	10
Category 9	450Mbps	51Mbps	2 or 4	11
Cateogy 10	450Mbps	102Mbps	2 or 4	12
Cateogy 12	600Mbps	102Mbps	2 or 4	12
Cateogy 15	3.9Gbps	1.5Gbps	8	12

While not necessary, mobile SoC manufacturers often bundle 4G LTE modems alongside their processing components into the main chip, as it is such an essential technology. This helps save on development time and costs. For example, Qualcomm’s Snapdragon 810 features a the company’s own Cat 9 X10 LTE modem, while the Snapdragon 820 comes with a faster X12 modem with Category 12 support, both with 3 band carrier aggregation.

MediaTek’s top-end Helio X20 features a LTE-A Cat 6 modem, as does the Samsung built Exynos 7420 found inside its Galaxy S6 range of smartphones. While supporting higher speeds is clearly better, remember that most LTE networks aren’t close to pushing these peak speeds yet, so there’s no rush to be right on the cutting edge of modem technology in order to enjoy faster data speeds.

The road to 5G

The roll-out of fast 4G LTE networks isn’t over yet, there are still many more customers to bring online and infrastructure to improve across the globe. Even legacy technologies are set to stick around for a good while yet. 4G adoption is expected to grow from around 7 billion connections in 2015 to almost 9 billion by 2020.

However, that hasn’t stopped us looking forward to the future and the even faster 5G connection standard is already under development. 5G networks will be required to offer sub-1ms latency and downlink speeds greater than 1Gbps in the real world, not just theoretical maximums. The 5G standard is also being designed to accommodate a huge number of smaller IoT connected devices, while simultaneously attempting to address concerns over growing energy consumption.

We’re still a way off from consumer deployment of 5G, but the testing of networks capable of meeting these targets have already begun in South Korea and US carrier Verzion has its own tests planned for later this year.