However, the biggest benefit of LTE-Advanced is expected to be carrier aggregation. This part of the standard lets service providers combine multiple small blocks of spectrum into one block that's large enough to deliver a strong LTE service. They'll even be able to tie together frequencies that are in widely different bands, taking advantage of already licensed spectrum that otherwise might have gone unused or underutilized.
Clearwire, the WiMax wholesale operator that plans to launch an LTE-Advanced network next year, plans to use carrier aggregation to combine two 20MHz spectrum blocks into a single block with 40MHz, said John Saw, Clearwire's chief technology officer. That will outstrip the 20MHz that both Verizon and AT&T are using for LTE in most markets. However, any carrier aggregation move has to use spectrum combinations that are certified by the 3GPP so device makers will have a specification to work with, Saw said.
Another technology that can help service providers use their spectrum more efficiently is TDD-LTE (time-division duplexing LTE). Most operators are building their networks with FDD (frequency-division duplexing) systems, which use two paired bands of spectrum, one for upstream and one for downstream traffic. Some are required to do so by regulators. TDD-LTE, on the other hand, uses one block of spectrum for traffic in both directions and segregates them by the amount of time they can take on the network. That better suits real traffic patterns and gives the operator more flexibility in how to use its spectrum, according to Clearwire, which uses TDD-LTE.
"TDD allows me to tailor my spectrum resources to where my customers' behavior is," Clearwire's Saw said. This system can also make it easier to combine multiple chunks of spectrum, because each chunk doesn't have to be paired with another, he said.
Making better use of all spectrum
Some experts say it's time to throw out the whole notion of allocating certain frequencies exclusively to commercial mobile services, or to any exclusive use. Instead, they advocate mobile operators sharing spectrum with current users, such as government agencies.
In a report issued earlier this year, the U.S. President's Council of Advisors on Science and Technology recommended that the secretary of commerce identify 1,000MHz of frequencies where commercial and federal users could coexist. "This study finds that today's apparent shortage of spectrum is in fact an illusion brought about because of the way spectrum is managed," the report said.