Also, both companies are using spectrum that was previously used for UHF television channels, a prime piece of the airwaves.

It can cover wide areas easily and penetrate deep into buildings. (Clearwire’s WiMax network uses a frequency that has shorter range and more difficulty penetrating buildings.)

Future upgrades can further boost the speed of mobile wireless broadband networks. But at some point, they will run out of room for improvement. There’s a theoretical limit for how much information a certain slice of the airwaves can carry. When that happens, there will still be two ways to add capacity to mobile wireless broadband.

The government can assign more spectrum, perhaps by taking it from TV stations. But spectrum, too, will run out. The carriers can add more cell towers, but that’s expensive and difficult. They can’t put cell towers everywhere they’d like.

Given these limiting factors, mobile wireless broadband isn’t likely to ever replace wireline connections for home and school broadband access, except possibly in rural areas where it’s expensive to draw cables for high-speed connections to homes and schools.

Another reason Verizon has been aggressive about LTE is that its 3G network uses a technology that isn’t upgradable to higher speeds, as AT&T’s and T-Mobile’s are. That’s left it with a burning need for the next network technology.

Verizon Wireless is a joint venture of Verizon Communications Inc. and Vodafone Group PLC of Britain. Motorola Mobility Inc. was formed this week as Motorola Inc. split into two parts. The Mobility unit consists of Motorola’s cell-phone business.


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