December 10, 1971, 6:00 a.m.: A young Arogyaswami Joseph Paulraj is roused from his hostel room at IIT Delhi and taken to Bombay, where he inspects the sonar systems on other Indian ships. The Navy asks him if he can work to improve the sonar. Paulraj agrees.

Back at IIT Delhi, Paulraj began work on the new project. “We developed a new sonar using some of the old core system, and this dramatically improved the sonar performance. The new model was manufactured and fitted in many Navy ships from 1975 onwards,” says Paulraj.

Though the Indian Navy was delighted with the new model, it wanted the world’s top sonar for its fleet. Unfortunately, the world’s best - U.S.-made - sonar was not available to India. Paulraj and a few others managed to convince the Navy that an advanced sonar system could be built indigenously. It wasn’t easy, recalls Paulraj. “We had little track record to back up such dreams. And I was pretty green too,” he says now. Nevertheless, the Navy obliged and soon the APSOH (Advanced Panoramic Sonar Hull mounted) was rolling. Today, the APSOH (and its variants - HUMVAD, HUMSA) are the backbone sonar systems of the Indian fleet.

Stanford
For over a decade, Paulraj, now a professor at Stanford, has been absorbed in developing a new technology that could make wireless broadband a reality. His goal is to expand the bandwidth of today’s constrained wireless spectrum.

The challenge is to provide them access at multi-megabit data speeds. With spectrum in short supply, carriers are looking at all sorts of techniques to squeeze more traffic through their existing spectrum.

MIMO
Paulraj’s technology promises to squeeze up to eight times more capacity from the existing spectrum. His group at Stanford is recognized for its work in space-time signal processing and for developing a technology known as MIMO (multiple input, multiple output). As the name suggests, MIMO uses multiple antennas to both transmit and receive radio signals. “The idea of using [a] modified antenna to improve wireless communication cropped up while having my hair cut,” says Paulraj.

How do MIMO systems utilize spectrum efficiently? In a 2x2 MIMO system, user data is split into two bit streams, which are then modulated in the same frequency channel. The modulated signals are transmitted simultaneously over two antennas. The receiver processes the separate data flows and puts them back together. This spatial multiplexing technique proportionally boosts the carrying capacity or the data-transmission speed by a factor equal to the number of transmitting antennas. In this case, since two antennas are used, the data-transmission speed is doubled.

MIMO has become a major research area at many universities around the globe, with an estimated 200 Ph.D researchers currently working on the technology, not counting industry efforts.

Iospan
“Broadband wireless access for fixed and mobile users is a promising market,” says Paulraj, “The key challenges for wireless are high quality, and data rates comparable to wired access.”

To commercialize his research, Paulraj went on sabbatical in 1998 and founded Iospan Wireless.

Known as AirBurst, Iospan’s technology is designed to allow service providers to quickly deploy broadband wireless services. The company recently finished a successful field trial that recorded peak individual downlink rates of more than13.6 Mbps over Iospan’s 2 MHz channelization, equating more than 40 Mbps on a typical 6 MHz channel. With a base-station antenna of 100 feet, as opposed to the 50-foot-high antenna used in the trials, Iospan’s AirBurst technology could successfully deliver these speeds at distances of up to 10 miles. “These speeds and distances translate into drastically reduced infrastructure costs for the service provider and multi-megabit data rates for the individual subscriber,” says Paulraj, who says trials in India are on the way.

Though Paulraj has resumed his academic activity at Stanford, he continues to serve on the board of Iospan and as its CTO. “I knew that I [couldn’t] be the central person in the company. From day one, I concentrated on building a strong management team. My role was more a mentor and technology lead person.”
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