Bell Labs Scientists Shatter Limit On Fixed Wireless Transmission

This innovation, known as BLAST, may allow so-called "fixed" wireless technology to rival the capabilities of today's wired networks, while also providing faster and more cost-effective deployment. One potential application would be for businesses, where wires no longer would be necessary to transmit data between desktop computers, notebook computers and hand-held devices. Another possible use would be providing phone service to remote and rural areas, where wireless networks would connect homes and businesses to copper-wired public telephone service providers.

"Technologies that provide a 10-fold improvement in wireless capacity come along once a decade," said Bell Labs President Dan Stanzione. "This is a very significant scientific development with long-term potential impact on our wireless business."

The BLAST technology is not well suited for mobile wireless applications, such as hand-held and car-based cellular phones, because multiple antennas -- both transmitting and receiving -- are needed. In addition, tracking signal changes in mobile applications would increase the computational complexity.

The inspiration for BLAST (Bell Labs Layered Space-Time) can be traced to a challenge from Rich Gitlin, chief technical officer and Data Networking Technology Vice President in Lucent's Data Networking Systems business unit. Gitlin asked the researchers to take a fresh look at a 50-year-old mathematical theory developed at Bell Labs, which is the theoretical foundation of today's high-speed communications systems. The end result was cramming roughly 10 to 20 times more information on the same frequency band by developing new signal processing techniques.

"The breakthrough results prove the feasibility of a technology which leapfrogs what we assumed about the limitations of radio communications," said Jim Brewington, president of Lucent's Wireless Networks Group. "While there is still a great deal of applied research required before we apply this discovery, we are very excited about its potential implications for our future wireless systems."

The BLAST technology essentially exploits a concept that other researchers believed was impossible. The prevailing view was that each wireless transmission needed to occupy a separate frequency, similar to the way in which FM radio stations within a geographical area are allocated separate frequencies. Otherwise, the interference is too overwhelming for quality communications.

The BLAST researchers, however, theorized it is possible to have several transmissions occupying the same frequency band. Each transmission uses its own transmitting antenna. Then, on the receiving end, multiple antennas again are used, along with innovative signal processing, to separate the mutually interfering transmissions from each other. Thus, the capacity of a given frequency band increases proportionally to the number of antennas.

The BLAST prototype, built to test this theory, uses an array of eight transmit and 12 receive antennas. During its first weeks of operation, it achieved unprecedented wireless capacities of at least 10 times the capacity of today's fixed wireless loop systems, which are used to provide phone service in rural and remote areas.

"This new technology represents an opportunity for future wireless systems of extraordinary communications efficiency," said Bell Labs researcher Reinaldo Valenzuela, who headed the BLAST research team. "This experiment, which was designed to illustrate the basic principle, represents only a first step of using the new technology to achieve higher capacities."

The advanced signal-processing techniques used in BLAST were first developed by researcher Gerard Foschini from a novel interpretation of the fundamental capacity formulas of Claude Shannon's Information Theory, first published in 1948. While Shannon's theory dealt with point-to-point communications, the theory used in BLAST relies on "volume-to -volume" communications, which effectively gives Information Theory a third, or spatial, dimension, besides frequency and time. This added dimension, said Foschini, is important because "when and where noise and interference turn out to be severe, each bit (of data) is well prepared to weather such impairments."

Remarkably, the initial BLAST experiment designed by researchers Glenn Golden and Peter Wolniansky did not use the technology of error correction coding to correct signal errors, nor did the transmitter have prior knowledge of which signal components would propagate easily and which would be severely impaired.

Also, BLAST research by Michael Gans includes determining the optimal placement and number of transmitting and receiving antennas. If, for instance, the distance between antennas on each end were further reduced, the number of potential applications, such as mobile communications, might increase. In addition, researchers are trying to boost capacity even further and exploring how to enhance BLAST for all wireless formats.

More technical information about BLAST is available at http://www.bell-labs.com/news/1998/september. Additional information about the BLAST research project is available at http://www.bell-labs.com/projects/blast. For technical information on the BLAST architecture, see Gerard J. Foschini, "Layered Space-Time Architecture for Wireless Communication in a Fading Environment when Using Multiple Antennas," Bell Labs Technical Journal, Volume 1, Number 2 Autumn 1996, pp 41-59 (or: http://www.lucent.com/ideas2/perspectives/bltj/autumn_96/paper04/main.html. For more information on Claude Shannon's Information Theory, see http://www.lucent.com/informationtheory.

Lucent Technologies (LU) designs, builds, and delivers a wide range of public and private networks, communications systems and software, consumer and business telephone systems and microelectronics components. Bell Labs is the research and development arm of the company. For more information about Lucent Technologies, headquartered at Murray Hill, N.J., visit our website at http://www.lucent.com.