LTE-Advanced: what it is and isn’t, and why that matters

1Executive Summary

This week the International Telecommunication Union approved the LTE-Advanced standard, which led to several stories proclaiming the arrival of “5G.” At GigaOM, we are pretty excited about the second coming of LTE, too. It will bring huge gains in speeds, capacity and network efficiency and may even lead to a big drop in the cost of mobile data. LTE-Advanced will make wireless connections more akin to wireline broadband, which can have profound effects across the tech sector. But we also think that our technically savvy readers should be a little skeptical and take some of the more radical claims about LTE-Advanced with a grain of salt.

The LTE-Advanced networks that Sprint, AT&T and Clearwire will deploy in 2013 won’t be the 1 Gbps monstrosities that the standard calls for. Rather, they will be works in progress — iterative networks that will gradually grow faster and more efficient as operators get more spectrum and gain access to more-powerful technologies. Ultimately, those networks will be limited by the usual issues that plague every operator: money, access to spectrum, handset capabilities and battery life.

As I wrote in my GigaOM post, it is apt to think of LTE-Advanced as a menu of technologies. Operators will select the technology or technique that looks tastiest at the time and implement it in their current LTE networks. Then, when they get hungry for more speed, capacity or efficiency, they will return to their vendors for another meal. For a detailed list of all of LTE-Advanced’s components, check out Stacey’s post on the 10 things you need to know about the technology. In this post I will explain some of the most significant parts of the standards and how they will be implemented by U.S. operators, but I will also go into the technology’s limitations.

LTE-Advanced step 1: aggregation

The LTE-Advanced that AT&T, Sprint and Clearwire talk about launching next year is really a single component of the standard: carrier aggregation. Today LTE networks can only support a maximum bandwidth of 20 MHz on both the uplink and downlink, but the more megahertz you pack into a channel, the faster speeds you can support. Carrier aggregation will simply allow operators to stack those uplink and downlink channels — collectively known as a carrier — on top of one another to create stupendously fast links to devices. T-Mobile is already using this technique in its HSPA+ network to offer 42 Mbps speeds.

While the standards call for networks that will eventually support 1 Gbps speeds, that is more of a theoretical aspiration than a realistic goal for most operators. To reach those speeds, operators will need to aggregate 100 MHz of spectrum into a single downlink, along with another separate 100 MHz channel to get a 200 Mbps downlink. To put that in perspective, Verizon’s LTE network uses 20 MHz today. To achieve the full capability of LTE-Advanced it would need to devote 10 times that amount of bandwidth to LTE, but Verizon currently only owns licenses for 118 MHz across its largest markets. Even if Verizon were to double its spectrum holdings — which it is working on — it would still have to shut down all of its 2G and 3G and repurpose their frequencies for 4G.

Bottom line: It is going to take a long time before operators can milk the full capabilities of LTE-Advanced.

Step 2: lots of antennas

If you think spectrum is tricky, then let’s talk antennas. LTE-Advanced will support up to eight antennas in a device using a technique called MIMO that divides the air link into separate parallel transmission paths. Think of it running multiple networks over the same spectrum, which isn’t entirely accurate but gives you the general drift. Today’s LTE devices only have two antennas, so quadrupling that number will give your device a sizable capacity boost and a more persistent connection. But MIMO antennas can’t be packed on top of one another like sardines. If they aren’t properly spaced apart, the network fails to recognize them as individual transmitters, nullifying their advantage. Unless you want to carry a device the size of a Volkswagon in your pocket, you won’t be getting an eight-antenna device anytime soon, if ever.

While we’re on the subject of Volkswagons, cars may wind up being the ideal candidates to reap the full benefits of MIMO and LTE-Advanced. Unlike our phones, cars have alternators, which can supply the enormous power demands eight antennas would require. Wondering why your new Motorola Razr is going dead after a few hours? Well, its two MIMO antennas mean the phone is maintaining two constant links to the network. That Razr is basically running the equivalent of two cell phones on a single battery. Battery efficiency will have to improve immensely before handset makers can even think about eight, or even four, MIMO antennas to mobile devices.

Step 3: the really cool stuff

Finally, there are a lot of really mind-blowing network technologies in LTE-Advanced that won’t be obvious to consumers, though they will see the benefits in the form of more-consistent broadband speeds, more-persistent signal strength and — hopefully — cheaper data pricing. Coordinated multipoint will allow a single device to connect to multiple towers and cells. Relays within cells will grab your phone’s transmission out of the air, amplify it and pass it on to the tower, Self-organizing and self-healing network technologies will turn static networks into organic systems that change their shape and evolve, creating cell sites that follow subscribers through the network. Small cell and heterogeneous networks (het net) technologies will allow operators to build huge capacity overlays into the network, ultimately driving down the cost of delivering a megabyte of data.

Like I said, we will start seeing the beginning of the LTE-Advanced revolution next year, when AT&T and possibly Sprint start spanning disparate spectrum blocks with carrier aggregation technology. I wouldn’t, however, expect the impact on the customer to be that big. For instance, Sprint will be using aggregation to tie two 5 MHz by 5 MHz carriers together, which will give it an LTE network exactly the size of Verizon’s current one. That is hardly going to stretch the boundaries of mobile broadband. But don’t lose hope. LTE-Advanced may launch quietly, but it will eventually crescendo into a symphony.

I would like to address one last point: Is LTE-Advanced really 5G? The only people to use that term so far are marketers and the gullible journalists who listen to them (Broadcom is already applying 5G to Wi-Fi). In fact, 3G, 4G and 5G have all become meaningless. If you want to get technical, though, LTE-Advanced — at least its initial implementation — wouldn’t even be considered 4G by the standards bodies’ definitions. A 4G network must be theoretically capable of supporting a stationary downlink of 1 Gbps, which will be impossible for most of the world’s operators to achieve. So the technical definitions are just as useless as the marketing definitions for distinguishing among the generations of network technology, unless you are willing to concede we will exist in a world of perpetual 3G. We will keep using 4G for now, but in general I like the more inclusive and less loaded term “mobile broadband.”

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