Full-duplex radios could reuse channels, saving mobile spectrum

IDG News Service - As mobile network and device makers explore many paths to using wireless spectrum more efficiently, one possible solution is still hard to achieve: Sending and receiving data on the same frequency at the same time, in the same space.

There are multiple efforts going on to reuse spectrum for mobile data. Equipment vendors are working out how to have traditional "macro" base stations and smaller cells serve the same neighborhood, with automatic coordination. There are also efforts to let mobile operators and government agencies share the same spectrum while staying out of each other's way. Each of these has its own challenges.

But when it comes to a particular base station transmitting and receiving signals on the same channel at the same time, it can't be done on current 3G or 4G mobile networks, according to researchers at the University of California, Riverside. Today's networks send and then receive, or do each on a different frequency. In fact, most mobile broadband networks are built around two separate "paired" blocks of spectrum, one for "upstream" signals coming from devices to the network and one for "downstream" traffic going the other way.

The Riverside researchers think they are close to solving this limitation in a way that would only slightly increase the cost of a cellular base station. Their so-called full-duplex radio could be technically ready by the end of next year, according to Ping Liang, a member of the Riverside team.

He and Professor Yingbo Hua are leading a project funded partly by a grant from the U.S. Department of Defense. Liang said a major vendor of mobile equipment, whom he can't name, is actively pursuing full-duplex and is interested the team's work. The technology might also be applied to Wi-Fi, he said.

Doubling efficiency?

By sending and receiving data at the same time on the same frequency, a full-duplex radio theoretically could double the efficiency of a wireless network. If a mobile operator could do that, it could offer users the same speed and capacity using just half the spectrum, saving billions on auctions for spectrum licenses. More likely, that carrier could take the same amount of spectrum it has now and make it last years longer, serving growing numbers of users and higher data demands without having to take over more frequencies.

In reality, the benefit to most applications would be less, because few uses of mobile involve subscribers sending the same amount of data they receive. But it could still make a difference, and network operators are expected to look for any advantage they can get over the next few years when it comes to efficient use of spectrum.