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Smart antennas and the radio renaissance

STANFORD -- Marconi would be amazed.

A hundred years after the Italian inventor demonstrated that radio waves can carry information, his "wireless" technology has become the basis for an emerging digital communication system that eventually will allow people to use a single device to exchange high-quality voice, video and data messages anywhere, anytime.

Stanford's "smart antenna" research group, headed by Professor Arogyaswami J. Paulraj of Stanford's Information Systems Laboratory, plays a key role in this research - developing technology to replace the single antennas that are used now in radio and cellular phone systems with arrays of multiple antennas that are connected to advanced signal processors. The group works on several aspects of this technology, but specializes in developing algorithms - the signal processing procedures needed to realize the technology's potential.

"Smart antennas have the potential for significantly improving coverage, signal quality and capacity in most types of wireless networks," Paulraj said.

He predicts that smart antenna technology could save $3 billion for the cellular phone industry over a decade. The technology also could play a role in eliminating the need for multiple telephones, and could contribute to a revolution in battlefield communications.

Better cell phones

A major focus of Paulraj's group, which includes 12 graduate students and visiting researchers, is applying smart antenna technology to commercial cellular phone systems. Base stations enhanced with smart antenna technology can handle a higher volume of calls, cover a larger area, and provide higher voice quality than conventional base stations. Much of the group's work is targeted at upgrading existing base stations while maintaining their compatibility with existing cellular phones.

The group receives support from a number of cellular equipment manufacturers and service providers, including Ericsson, Qualcomm, Nortel, Hughes and AirTouch. Last summer, representatives from nearly 50 companies attended an annual forum on the group's research.

In addition to their work on cellular phones, the group participates in several major government contracts, including:

  • A consortium working on a wireless multimedia communications network for the battlefield of the future, using a $2.4 million, five-year research grant from the U.S. Army. Consortium members include Rockwell Collins Avionics and Radio, Watkins-Johnson, and Hughes Network Systems.
  • A joint effort with Hughes Network Systems, Hughes Research Labs and E-Systems to assemble a high-speed digital battlefield network using commercial off-the-shelf hardware. The $8.6 million project is designed to provide soldiers with continuously updated information about battlefield conditions, such as the locations of hostile forces or land mines.

Conventional versus smart antenna systems

The simple antenna systems used in current wireless networks, such as those used for cellular phones, send and receive radio waves in all directions. Such systems cannot separate the desired signal from interfering signals on the same channel. Simple antennas also have difficulty dealing with "multipath" signals that scatter off buildings and hills. When a cell phone is in a fast-moving vehicle, the strength of multipath signals can fluctuate rapidly.

Paulraj says that smart antenna systems can alleviate these problems. By processing the signals from several antennas, smart antenna technology can distinguish between desired and undesired signals, even when they are on the same channel. A smart antenna also can combine antenna outputs, such as multipath signals, to improve signal quality. By listening only in directions from which a desired signal arrives, smart antennas can detect weaker signals than can conventional antennas.

The directional ability of smart antennas also can improve transmission. Beaming power in the direction of the receiver takes less power and produces less interference at other receivers on the same channel.

Battlefield communications

The U.S. military is experimenting with smart antenna technology to reduce power consumption on high-speed multimedia battlefield networks.

"These days an army marches on its batteries," Paulraj said. During the Gulf War, the Army had to bring in jet transports full of batteries to meet the demand. Smart antennas can reduce battery drain substantially, Paulraj said, because they can transmit radio energy only in the required direction. That capability also can make it more difficult for enemy troops to intercept radio signals, and it can make "spoofing" - the generation of disguised messages by enemy troops - more difficult.

Instead of backpack radios with whip antennas and radio handsets, soldiers will rely on "patch" antennas - small discs sewed into their backpacks - and on lightweight video displays that will allow them to exchange real-time maps and pictures, as well as voices and messages.

Almost a year into the contract, the Stanford researchers already have managed to solve one critical problem. They have developed an algorithm that allows individual cell phones to receive more than one radio link on the same channel if the signals come from different directions, without resorting to "training signals" that reduce effective transmission rates.

Battlefield situation awareness project

Stanford's contract with the Advanced Research Projects Agency, which will begin in May, is designed to put together a "battlefield situation awareness" network by combining smart antennas with existing commercial technology. It is part of the Department of Defense's technology reinvestment program.

"Today, a military one-man radio typically costs about $6,500," Paulraj said. "A commercial wireless digital phone costs about $450 and is in many ways more powerful. The purpose of the project is to narrow that gap and help deliver state-of-the-art communications technology for the Army at 25 to 30 percent of current costs."

The two-year project will set up a demonstration network that could have application in war zones such as Bosnia, where thousands of uncharted land mines are a constant threat. The system will collect and rapidly disseminate information about the locations of land mines to the troops. Soldiers using "ruggedized" commercial cell phones will report the positions of the mines that they detect. Commercial cellular base stations, enhanced with smart antenna systems, will link such data through the commercial VSAT satellite system to a central database located outside the battlefield.

The information from all incoming reports will be incorporated into an area map, and the updated map then will be uplinked to a commercial broadcast satellite similar to the one that currently beams Home Shopping and ESPN directly to homes. The satellite system then will broadcast the information to all the soldiers in the field.

An all-purpose phone

Paulraj foresees a time when wireless services will have the same quality and speed as the curre