What is LTE and how does it work?

The mobile communications industry is always evolving and we have already seen the fifth generation (5G) of mobile networks. However, the technology that started the streamlining process for mobile communication technologies is LTE which is a predecessor of 5G. 4G, is the next evolutionary step after the third generation 3G mobile networks. While with 3G, we saw two key technologies, UMTS (Universal Mobile Telecommunications Systems) and CDMA2000, that could enable 3G; with 4G, we have a more streamlined approach. LTE is the primary technology that provides a 4G migration path to UMTS and CDMA2000 based 3G networks. Even though WiMAX (Worldwide Interoperability for Microwave Access) is also capable of addressing the 4G network requirements, LTE has been the primary path for most 4G deployments around the globe. As shown in the screenshot below, the LTE technology can be seen on our mobile phones as symbols like LTE, LTE+, 4G or 4G+. This post aims to explain what LTE technology is and how it works.

Screenshots showing the 4G and 4G+ symbols on mobile phones.
Screenshots showing the 4G and 4G+ symbols on mobile phones.

LTE is a 4G technology that allows 3G UMTS and CDMA2000 to migrate to 4G to offer high-speed mobile data. LTE uses the network resources efficiently to reduce latency and deliver peak data rates of up to 300 Mbps. LTE will co-exist with 5G and its advanced versions can offer peak speeds of 1-3 Gbps.

LTE, LTE+, 4G, 4G+

4G is an umbrella terminology that is enabled by the various releases of the LTE technology. LTE, LTE-Advanced and LTE-Advanced Pro are all fourth-generation, 4G, mobile cellular technologies. LTE networks were first introduced in 2009 as per the specifications in release 8 of 3GPP (Third Generation Partnership Project). Since then, the LTE technology has seen consistent enhancements, and it will continue to evolve alongside the fifth generation of mobile networks. LTE+ is just a symbol we see on our mobile phones that represents LTE-Advanced and LTE-Advanced Pro. LTE-Advanced was specified in 3GPP release 10, whereas LTE-Advanced Pro was specified in release 13. The fifth generation of mobile networks is enabled by a different technology, called NR or New Radio, as specified in 3GPP releases 15 and 16. The non-standalone variant or mode of 5G networks (NSA) relies on the core part of the LTE network to offer its services, but it uses NR radio technology.

Mapping of 1G, 2G, 3G, 4G and 5G with their enabling technologies

How does LTE work?

While LTE is the leading technology that enables 4G, it is not the only one that can allow mobile operators to move to 4G. There is another technology called WiMax (Worldwide Interoperability for Microwave Access) that also provides a path for the 4G upgrade. However, LTE has been the primary technology used worldwide for 4G because it allows operators both on GSM/UMTS and cdmaOne/CDMA2000 to migrate. As a result, LTE can be seen as a step towards streamlining the mobile network evolution. It makes efficient use of the network resources, reduces the latency in data transfer, and also reduces the overall network complexity. If you look at the high-level network diagram below, you may notice that the radio network in 4G is a bit leaner as compared to that in the 3G UMTS network. GSM and UMTS networks have BSC (Base Station Controller) and RNC (Radio Network Controller) respectively to provide the radio network control function, but in 4G, this responsibility sits with the 4G base station eNodeB.

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The data speed you get with LTE depends on which flavour of LTE your mobile operator offers and how they have deployed it. There can be multiple deployment combinations with variations to channel bandwidth and modulation techniques. When an LTE deployment uses a 20 MHz channel with 64 QAM (Quadrature amplitude modulation), the network can offer speeds of up to 300 Mbps in the downlink and 75 Mbps in the uplink. The downlink helps with the downloads and the uplink helps with the uploads.

In 2G and 3G networks, the conventional voice calls are only possible through the circuit-switched part of the network. LTE networks have Voice over LTE (VoLTE) capability to provide voice calls through the packet-switched part of the network. However, there is a circuit-switched fall-back option that mobile operators often use for voice calls. You may also check out our dedicated post on VoLTE to find out how to access it. Unlike GSM and UMTS networks, LTE uses separate multiple-access technologies for the uplink and the downlink. It uses Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink. More about OFDMA in this dedicated post.

How fast is LTE?

On cell phones, including iPhone, Android, Windows or any other SIM-enabled devices, the fourth-generation mobile cellular technology is displayed by LTE, LTE+ or 4G and 4G+. If your cell phone shows the LTE or 4G symbol, it means the basic LTE network is serving your phone. However, if your phone shows 4G+ or LTE+, it means you are served by LTE-Advanced or LTE-Advanced Pro networks. The theoretical maximum download speeds of LTE, LTE-Advanced and LTE-Advanced Pro networks are up to 300Mbps, 1Gbps and 3Gbps. The table below provides a summary of the peak LTE speeds.

4G TechnologyPeak Data Rates (Downlink)
LTE (Original release)Up to 300 Mbps
LTE AdvancedUp to 1 Gbs
LTE Advanced ProUp to 3 Gbps

In real life, factors like the distance between the user and the base station, the number of users the base station is serving and obstacles like buildings etc. impact the achievable data rates. Just because your phone is showing a full 4G signal (signal bar) doesn’t guarantee super high 4G speeds. In busy hours, you may experience slower speeds even if you are getting a full signal. As a result, the average speeds are considerably lower and mainly in tens of Mbps. In Reading UK, we conducted some tests in July 2020 using SIM cards from two leading mobile operators. The average download speeds were around 17 Mbps with LTE and around 66 Mbps with LTE Advanced. Have a look at this post to check out the detailed test results for upload and download speeds. In addition to high-speed internet on the mobile phone, 4G LTE technology allows basic mobile services, including voice calls, text messaging (SMS), picture messaging (MMS) etc.

Just like its earlier 3G counterpart, 4G SIMs also exist in both voice/text & data as well as data-only formats. The former can be used in smartphones while the latter in mobile broadband dongles, tablets or any other mobile device. If you live in an area with decent 4G coverage, you can potentially use LTE as an alternative to fixed broadband service.

What about 5G?

The need for higher data speed has been one of the key drivers for the evolution of mobile communications standards. While LTE may seem perfect for most of our use cases today, the fifth-generation networks (5G) will take things to a whole new level. 5G uses New Radio (NR) technology and can provide much higher speeds, much lower latency and also supports a large number of devices. LTE plays a key role in the deployment and evolution of 5G networks also. The initial 5G networks use a model where the radio part of the network is based on the New Radio (NR) technology, but the core part of the network utilises the existing 4G core network which is the Evolved Packet Core or EPC. This model is called the non-standalone model (NSA), which is not an end-to-end 5G network. The full end-to-end 5G networks under the umbrella of standalone mode (SA) use the cloud-native 5G Core Network or 5GCN. In this way, there is a physical relationship between the LTE core network and the 5G radio network as part of the non-standalone deployment model where a user gets connected to both 5G and 4G networks at the same time to benefit from higher data rates. 5G NR and 4G LTE will co-exist for a long time to deliver on many existing and future use cases. The full demand for 5G networks will evolve over time as we become more and more digital. The lower latency of 5G and the support for a large number of devices make it ideal for many market verticals e.g. manufacturing. For the general public, the most obvious benefit will be the super high data speeds they may get in locations with decent 5G coverage. 4G and 5G will co-exist for a very long time which means it will only make things better for the customers.

Conclusion

LTE or 4G LTE stands for Long Term Evolution, and it is a fourth-generation mobile communications technology standard that enables 4G cellular services. It makes efficient use of the network resources, reduces the latency in data transfer, and also reduces the overall network complexity. LTE was introduced in 2009 to migrate 3G UMTS and CDMA2000 networks to 4G, and it has seen enhancements in the form of LTE-Advanced, and LTE-Advanced Pro. 4G networks can provide peak (theoretical) download speeds of up to 300 Mbps with LTE, 1Gbps with LTE-Advanced and 3Gbps with LTE-Advanced Pro.

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need some extra support, especially when preparing for a new job, studying a new topic, or maybe just buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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