What’s in a Megahertz: How spectrum impacts our 4G experience

If you’ve read any of OpenSignal’s reports, you’ll notice that we often point out the type and amount of spectrum mobile operators use. While those particulars might seem like arcane technical details, spectrum can tell you a lot about how powerful a network’s connections are or how far its signals can reach. We felt a primer on spectrum’s role in the mobile network might be useful.

Spectrum, which is measured in megahertz, is the fundamental building block for every generation of mobile networking from analogue networks to 4G. But after the 4G revolution kicked off with the advent of LTE, spectrum has become particularly important for creating powerful mobile data networks. You can think of spectral frequencies as lanes on a highway. Just as a highway with more lanes can handle more cars, a network with more spectrum can handle more connections or more mobile traffic. The total traffic a network can carry at any given moment is known as its capacity, and networks with higher capacity generally support higher speeds. But just like highways, networks are shared infrastructure. If there are too many users on them vying for capacity, everyone is forced to slow down. That’s one of the major trade-offs in mobile networking.

Frequencies are like lanes on a highway. Even networks with lots of capacity will get congested if there are lots of users. (Photo by Flickr user Thomanication)

Frequencies are like lanes on a highway. Even networks with lots of capacity will get congested if there are lots of users. (Photo by Flickr user Thomanication)

For instance, let’s say we have an LTE cell tower with 100 Mbps of total capacity. Theoretically that tower could supply a single user with a fat 100 Mbps connection or it could divide that capacity among 10 users, simultaneously providing each of them a 10 Mbps connection. If you double the number of users to 20, those connection speeds drop to 5 Mbps and so forth. But suppose we double the amount of spectrum used by our cell tower? We’d wind up doubling our capacity, and suddenly we could supply those 20 users each with a 10 Mbps connection.

Operators constantly engage in a balancing act between speed and capacity as the more users they have on their networks the more they compete for resources. If their networks become too congested, they often look for more spectrum to increase their capacity, which not only allows them to support more users but improve the performance of everybody’s 4G connection. If no spectrum is available for the taking, they still have options. They can add capacity into the network by building more cell towers, which essentially allows them to use the same spectrum in more locations. That’s why we’re starting to hear more about the concept of “small cells” lately. By creating ever denser clusters of cells, operators can cram more users onto their networks in high-demand areas without sacrificing connection speeds.

Those are the basics of how spectrum impacts networks, but I should point out that not all spectrum is created equal. There are a few other things you’ll need to know about the frequencies powering our mobile networks:

  • Lower is better: You often hear operators touting the low-frequency spectrum they’re using, and they have reason to brag. Lower frequencies, such as those in the 700 MHz or 800 MHz bands, propagate further. That means signals travel greater distances in rural areas and they punch deeper into buildings in urban areas. Low frequencies don’t offer any more capacity than higher band frequencies — a megahertz of 700 MHz spectrum supports the same amount of data as a megahertz of 2600 MHz spectrum — but operators use lower frequencies to improve their network coverage and provide a more consistent 4G experience.
  • LTE-Advanced: An operator’s spectrum holdings are usually all over the frequency chart, but you can only deploy an LTE network over a single frequency band. The result is most operators have built two, three, sometimes four separate LTE networks. Using LTE-Advanced techniques, operators can tie those networks together, allowing devices to connect to multiple 4G frequencies simultaneously. This not only creates a unified network but can tremendously boost the maximum speed at which a device can connect to that network.
  • Technology is often a limitation: An operator may have gobs and gobs of spectrum, but in many cases the network or handset technology isn’t yet available for them to fully access it.

The type, amount and quality of spectrum an operator owns clearly has a big say in how its 4G networks will perform, and we’re seeing all kinds of different spectrum scenarios play out around the world. In Europe and East Asia, LTE-Advanced is already having a big impact, driving average download speeds in many countries well beyond 20 Mbps, as measured in OpenSignal’s February State of LTE report.

But we’re also seeing the more subtle effects of spectrum’s impact in different parts of the world. New 4G networks in South America and Eastern Europe are debuting with some impressively fast speeds, even though the operators building them have limited spectrum portfolios. Their networks, however, are still lightly loaded with users. As those networks get more congested with subscribers, speeds will slow down. That’s the problem some of LTE’s earliest adopters are now facing. In the U.S., Japan and Sweden operators have a lot of spectrum but they also have a lot of users vying for that capacity. Consequently all three of those countries have fallen far down the global ranking charts in 4G speed.

Some operators have used new spectrum to address specific weaknesses in their networks. 3 in the U.K. and T-Mobile in the U.S. both recently began building new LTE networks in low-band frequencies for the express purpose of boosting their coverage. Meanwhile technology has proven a hindrance to Telstra’s ambitions in Australia. It’s deployed the LTE-Advanced networks that tie together 100 MHz of 4G airwaves, but none of its customers can access the full power of that network since Telstra is still waiting for handset technology to catch up.

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