The government may have auction fever, but companies are betting the 2.4 GHz band won’t be disturbed, and it will continue to be a free industrial, scientific and medical band.
Radiating in the dead middle of the 2.4 GHz to 2.5 GHz band, at 2.45 GHz, are 80 million microwave ovens, in homes throughout the nation.
With that obvious interference, the Federal Communications Commission admits it can’t charge for the spectrum. Businesses can use the frequency free of charge on the understanding that “you can suffer interference but cause none,” said Tom Stanley, chief engineer of the FCC’s Wireless Telecommunications Bureau.
Companies operating devices at 2.4 GHz have found that spread spectrum best tolerates the noise and, in some instances, can even repair the signal.
“Spread spectrum users are the perfect candidates for this ISM band,” Stanley said.
That may be why new, innovative equipment and service ideas are popping up for 2.4 GHz. For instance, New York-based Madah-Com Inc. deployed its Waves service at three events at the Atlanta Olympics. The voice signal from the announcer’s booth was transmitted to large, horn speakers using digital spread spectrum at 2.4 GHz. The system included a short lease base station and transceivers. The equipment is built in a plant in Israel and exported to the United States, which is the company’s primary market.
“The Waves system is an extremely robust communication network,” said Daniel Haimov, Madah-Com’s executive vice president of engineering. Haimov received an award from the Israeli government in 1980 for exceptional technical achievements in security and the development of frequency hopping technology.
Madah-Com also has deployed Waves in the main aircraft factory of McDonnell Douglas in St. Louis. McDonnell is using the technology for wireless signs and public address systems to meet requirements of the Americans with Disabilities Act.
Madah-Com said it chose 2.4 GHz instead of the 900 MHz ISM band because it saw “everyone else going that way.” The 900 MHz ISM band is used for cordless phones and some in-building wireless systems.
Madah-Com selected frequency hopping instead of direct sequence technology because frequency hopping can accommodate more independent users, more addresses, and is less prone to interference, said Dr. Alan Avidan, executive vice president of Madah-Com.
“With frequency hopping, you can have an adaptive system that learns the environment, avoids interference and continually adopts,” Avidan said.
There is some concern that highly-reliable communication links aren’t possible at 2.4 GHz because of the interference, said Subramanian Vasudevan of U S West Advanced Technologies in a document about mitigating interference.
“An understanding of the detailed structure of such interference leads instead to optimism about the possibility of using interference cancellation techniques to mitigate its impact on wideband spread-spectrum communication systems operating in this ISM band,” Vasudevan said.
