LTE-U: on the way to 5G

Ericsson and Qualcomm are promoting their new technology, LTE-U. Is it any better that LTE-A? And what is this combinations of letters supposed to mean, after all?

Recently Ericsson and Qualcomm have begun promoting their state-of-art technology, LTE-U. Is it any better that LTE-A, which is increasingly available all over the world, including US, Europe, Russia, China and so on? And what are these combinations of letters supposed to mean anyway?

Let’s start with the name. The first abbreviation, LTE-A, stands for “LTE-Advanced”, or “advanced 4th gen mobile network.” Such networks have been rolling out all around the world. As for LTE-U, it is by no means some “LTE-Ultimate” or “LTE-Unbeatable,” as some may think. “U” stands for “Unlicensed” here. So, this mobile network technology relies on the use of the so-called “unlicensed” frequency spectrum.

Now, what does “unlicensed” mean? That’s quite simple: the majority of radio frequencies, including those used by mobile operators or radio stations, are licensed. Those frequencies are controlled by a government authority and can be used only by those to whom the license to transmit on this frequency was issued.

For low-capacity civil transmitters, unlicensed spectrum is used: anyone can use those frequencies to transmit the radio signal. This makes complete sense: imagine you had to obtain permission for each RC toy you purchased for your child! The main requirement for those operating in this “free” radio frequency spectrum is certain maximum limit of the transmission power in order not to disturb operation of other people’s appliances.

The concept of LTE-Unlicensed is based on the deployment of LTE networks using “free” frequency ranges. Of course, we are talking about low-power base stations designed for indoor use

For instance, 27 MHz range is used be RC toys, 433 MHz is for walkie-talkies, and 2.4 GHz and 5 GHz ranges are allocated for Wi-Fi routers. These ranges vary from country to country, which provokes certain compatibility issues.

The concept of LTE-Unlicensed is based on the deployment of LTE networks using “free” frequency ranges. Of course, we are talking about low-power base stations, i.e. femtocells and picocells designed for indoor use. The more free frequencies they are able to “aggregate,” which means to bring together several parallel transmission channels into one, the higher data rates would be.

One rogue thought would start to bug you immediately: why would we need Wi-Fi then? Well, no one is disposing of Wi-Fi; quite the opposite, the technology continues to serve its intended purpose, which is being the foundation of small local wireless networks.

Initially, this technology was used to build broadband access networks just because there was no other option. After all, Wi-Fi lacks several features, which are critical for reliable broadband wireless networks: it does not deploy state-of-art functions to manage network efficiency in case of high number of connections, does not enable secure authorization or other things like carrier aggregation, which is the process of uniting several frequency ranges into a single transmission channel.

LTE already has it all by design. Since the unlicensed spectrum consists of various bits and pieces residing in various frequency ranges, the ability to aggregate them all would enable higher bandwidth networks.

While 5G networks are nowhere near, Wi-Fi might serve the environment of choice to connect PCs, TVs, and other home appliances. Traffic-consuming devices, primarily smartphones and tablets, will belong to LTE-U world. Moreover, to integrate those into home networks, the Link Aggregation technology was designed. It brings together LTE and Wi-Fi frequencies, forming a cumulative frequency “pool”, available to devices and supporting both wireless technologies.

This approach will help to balance the traffic between different networks or utilize both networks at once to facilitate faster data rates. And, of course, it will enable a seamless network swap without interruption of current session. In other words, it looks like a free roaming within your home network.

LTE-U would be deployed quite similarly to existing 3G femtocells: a subscriber would need to purchase a specific femtocell and register it with his/her mobile operator.

From the provider’s point of view, an encrypted VPN channel would be deployed, creating two separate logical connectivity channels working through a single physical cable.

On a side note, LTE-U would not increase the speed of your home provider’s Internet connection. At the same time, mobile devices would use wireless connections more efficiently.

However, this is not ideal: LTE-U deployment presupposes service provider’s involvement, and those folks are not always proactivity champions. Many SPs used another trick to address the same challenge, i.e. offloading indoor connections, calling it Wi-Fi Offload.

In other words, they rolled out massive carrier Wi-Fi networks, enabled seamless offload and SIM card based authorization, launched voice-over-Wi-Fi services (Wi-Fi Calling), etc. They invested a great deal of money into that infrastructure and have to get return on their investment. When these investments are fully returned, 5G will have already been around for some time.

On the other hand, those operators who are still to tackle the problem of massive traffic growth, face quite a dilemma: they would need to either invest into Wi-Fi Offload or pioneer in LTE-U development, acknowledging the lack of support and the somewhat murky future of the newborn technology. We’ll live, we’ll see.