How 4G Works

The Mobile Broadband Battlefield

Everywhere you go, you see those brash, frenetic ads for both smartphones and wireless broadband. In this bloodthirsty, cutthroat industry, carriers are desperate to lure subscribers. To win more subscribers, carriers try to build the fastest networks with the greatest geographical and population coverage.

To build those networks, they need spectrum. Other than capital for building infrastructure, spectrum is the single most vital resource for carriers. It is, in business parlance, what's called a constraining resource.

Spectrum is the range of radio frequencies that government agencies auction to carriers, and in each area there's only so much spectrum to go around. Carriers go to battle with each other for that limited spectrum. Those with spectrum access can provide the best reception for their customers, and thus haul in more subscribers and revenue.

Spectrum is extravagantly expensive. For example, in a bid to expand its 4G network, AT&T paid nearly $2 billion for a block of 700 MHz spectrum that covers roughly 300 million people in the United States [source: Apple Insider].

With older technologies, carriers needed a contiguous block of spectrum in order to provide service. Advanced air interfaces, such as LTE, can use a lot of different frequencies, such as 700 MHz, 900 MHz, 1.7 GHz, 2.1 GHz and dozens more. Not all frequencies are equal, though.

Lower frequencies such as 700MHz are the most desirable, because they settle, much like a dense fog, and they're capable of penetrating obstructions like buildings. By contrast, higher frequencies work in a line-of-sight fashion and they're more easily scattered by random objects and other interference. Thus, carriers that want to provide the more reliable and speedy service lust after spectrum in lower frequencies.

Once a carrier has the spectrum, it can begin upgrading subnets of its networks, piece by piece. The hardware that's replaced generally isn't the cell tower equipment that you see by the highway or on tall buildings. Instead, engineers start by replacing routers and servers to new versions that will scale up easily as more capacity is required in the future.

And the future is always, always on the minds of wireless experts. Keep reading for glimpses into the next era of cell communications, beyond even today's freaky-fast 4G.