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Wireless tech increases spectrum utilization

Posted: 01 Aug 2011 ?? ?Print Version ?Bookmark and Share

Keywords:DIDO? wireless technology? spectrum utilization?

A new wireless technology claims to deliver more than ten-fold increases in spectrum utilization compared to today's cellular systems.

Steve Perlman, chief executive of Rearden Companies and one of the inventors of the technology, said, "We have only scratched the surface of the potential of this technology."

According to the white paper about the wireless technology, the Digital Input, Distributed Output (DIDO) method can radically extend the range while decreasing the power consumption and silicon complexity of radios.

"We believe there are not only far more applications in communications, but we believe that the unprecedented control and capacity that we have with radio signals will lead to a wide range of applications in other fields, such as medicine, imaging, manufacturing and alternative energy," Perlman said.

Steve Perlman

Perlman: We have only scratched the surface of the potential of this technology.

The technique uses a data center as an intermediary for all wireless communications. The servers apparently compute waveforms specific to each wireless client's data request.

Each client receives a unique waveform with just that user's data. DIDO does this by synthesizing a private channel for each user, which is why each user gets 100 percent of the data rate of the spectrum, regardless of how many users share the spectrum, Perlman said.

Rearden has tested the technique with 10 radios, each using the full data rate available for a given slice of spectrum in a site near Austin, Texas.

"We know we can get to one-hundred fold what today's cellular systems provide, and we are optimistic we can get to a thousand-fold," says Perlman at Columbia University where he first publically described DIDO. "We don't know what the limit is (because) this is all green-field research," he added.

The average power is easily one-tenth that of cellular, which in many cases its one one-hundredth, Perlman said.

In a fully deployed DIDO system, the antennas are far closer to the user on average than in a cellular system where, for example, many users are on the fringes of the system, he explained. Also, DIDO doesn't transmit much power where there are no users, so this is far less wasted RF energy, he added.

In terms of silicon complexity a DIDO access point radio can be as simple as an A/D, D/A and an amplifier, said Perlman. All it is doing is digitizing and transmitting, or receiving and digitizing a digital waveform. He says it does no processing at all.

A DIDO user radio has a little more to it because it is a portable radio, but it is closer to a walkie-talkie than a 3G radio in complexity, Perlman says.

Path to market unclear
Perlman has filed multiple patents on the technology, at least two of which have been issued. One application published a year ago provides a wealth of detail about the math behind the approach.

"The patent reveals this to be a distributed MIMO approach," says Jan Rabaey, a professor at the University of California, Berkeley who heads a wireless research center. "There has been a large amount of activity in this space over the past couple of years," says Rabaey.

"To be honest, I do not see that much new in this patent that was not known," Rabaey adds. "Actually, LTE-Advanced does use similar approaches," he says.

Rearden has tested the frequency-agnostic DIDO concept at a range of frequencies from 1MHz to 1GHz. The FCC declined to provide Rearden an experimental spectrum use license for its work, so most of the tests were conducted using amateur radio bands in the 450MHz range.

DIDO promises high rates of propagation based on a high signal-to-noise ratio with signals extending as far as 30 miles in Rearden's tests to date. The tests used only Wi-Fi-like access points, rather than relatively expensive cellular towers and base stations.

The technique also can deliver latency in the sub-millisecond range compared to 40ms for 4G wireless and about 15 for a wired DSL line, Perlman said. "It's a whole different way to think about propagating radiation," he adds.

It's not clear how Perlman will commercialize DIDO. To date, both venture capitalists and FCC officials have rejected the approach. "We have had the door slammed in our faces many times," says Perlman.

The company may attempt to license the technology broadly and let others bring it to market in a variety of areas. For cellular systems, "I imagine [DIDO] coming in as an overbuilt, where maybe phones have both (DIDO and conventional radios)," Perlman said.

The approach could be a boon to cellular carriers dealing with a flood of mobile data from smartphones and a relative scarcity of spectrum. However, it requires they build new networks and adopt new handsetsa huge undertaking.

Perlman is known for his most recent venture, OnLive, a cloud-based gaming system. He also pioneered a fresh approach to animated affects with his startup Mova and helped develop QuickTime during his tenure at Apple.

- Rick Merritt
??EE Times





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