Wireless data networks are sprouting up like daisies. Wi-Fi hot spots have proliferated. Bluetooth personal-area networks are everywhere. And the push to make electric grids smarter is bringing with it a proliferation of ZigBee radios that use the airwaves to connect electric meters, lamps, light switches, thermostats, and appliances. So it might come as a surprise that yet another wireless-networking scheme, called Dash7, is entering the fray—and appears to be gaining traction. The International Organization for Standardization (ISO) first ratified the standard behind Dash7 in 2004, and it continues to be refined. Like Bluetooth and ZigBee, it's intended for low-power, low-bandwidth digital communications. But Dash7 hardware is designed to use even less power than other schemes, making it especially appropriate for such things as radio-frequency identification (RFID) tags, which must work for years without any external power source.
Whereas the familiar RFID tags used today for such things as door keys are passive devices (they draw their energy from the radio waves their readers emit), Dash7 tags are active, meaning that they make use of small batteries instead. So Dash7 readers don't have to transmit high RF power levels and consequently can be manufactured inexpensively—yet they can communicate with tags located hundreds of meters away or even farther when conditions are right.
Dash7 operates at around 433 megahertz, a globally available frequency also used, for example, in many keyless entry systems for automobiles. The corresponding wavelength is about 70 centimeters, which makes it difficult to design efficient antennas that are conveniently compact. Dash7 supporters say that the advantage of using a wavelength this long is that it can penetrate such obstacles as concrete walls and work in environments with large amounts of metallic clutter. This, the Dash7 advocates contend, is more of a problem for ZigBee, which employs 868 MHz, 915 MHz, or most popularly, 2.4 gigahertz, the last of which is also used for many Wi-Fi networks. Using "2.4 GHz is really nasty in environments with a lot of metal," says Pat Burns, vice president of marketing and licensing for Savi Technology, the Mountain View, Calif., company that first devised the Dash7 technology.
Jon Adams, Freescale Semiconductor's director of business development for wireless connectivity operations and a former vice chairman of the ZigBee Alliance, is, however, skeptical. "Wavelength is only part of the equation," he says, adding that if the only way for a radio signal to pass into or out of a room is through a window, a shorter wavelength may, in fact, work better. "I think some of what we're hearing about Dash7 is market positioning," he says.
The search for a market for Dash7 isn't new. Savi began developing this technology two decades ago, intending it initially as a way for parents to keep track of their kids during family outings. But that application proved a dud. According to Burns, advisors told Savi's founders, recent graduates of Stanford, "You guys have to do a reboot and find a different business model." So they shifted plans, and following the first Gulf War, they began selling active RFID tags to the U.S. Department of Defense for tracking shipments of war materials.