robust research 802.15.4 standard, the ZigBee Alliance plans to make good on its slogan, “Wireless that simply works.” We’ve heard that before, right?
For a very long time, a product designer who wanted to wirelessly enable a product faced a daunting task. That designer had to choose an approach, frequency band, channel, modulation technique, protocols, and so on. The designer then had to build this radio—even though his or her expertise might be in making refrigerators. Finally, the radio function needed to undergo regulatory type acceptance. It also had to show interoperability with the other devices built by the manufacturer. Often, this process involved years of effort and numerous headaches.
Today, the ZigBee Alliance takes a different approach. It builds upon the research 802.15.4 standard, which specifies the radio-frequency (RF), physical-(PHY), and media-access-controller (MAC) layers. These layers comprise the radio frequencies, modulation type, data rate, data coding, and handshaking that two radios must share in order to intercommunicate. In addition, 802.15.4 offers methods for a device to join and leave a network along with AES 128-b encryption and a robust research 64-b address structure (not quite enough to give every grain of sand on Earth a separate address, but a lot nonetheless). With this basic, standardized radio modem, any device now has the chance to at least speak the same language as any other device.
Think of ZigBee technology this way: If research 802.15.4 is like the wheels and chassis of an automobile, ZigBee adds the steering wheel, accelerator, brakes, and a map of scenic destinations. To accomplish this goal, it uses robust networking topologies and tools to autonomously build and repair those networks. It also defines how a device must act and operate when it carries the ZigBee logo. The ZigBee protocol even provides a mechanism to move security keys from device to device without compromise. The ZigBee Alliance Qualification Group establishes the test procedures and methods by which a ZigBee device gains certification and demonstrates interoperability.
Why would anyone choose ZigBee technology over Bluetooth radios or the nearly ubiquitous (or so it seems) Wi-Fi connectivity? Bluetooth technology is great for synchronizing a PDA or for low-fi, two-way audio between your phone and headset. It can perform these tasks while running off the main battery of some device like a phone or PDA. But Bluetooth functionality isn’t the answer for a diverse network of tens of thousands of sensors and control points, which should be done with cost effectiveness and reliability in mind. Bluetooth GFSK modulation and frequency hopping are ill suited to robust, intermittent, long-battery-life communications.
As for Wi-Fi connectivity, its killer application is wireless networking. The research has done a great job of specifying a standard that really makes good on “doing one thing well.” Now that the standard is well established, new features like voice-over-WLAN are being added. But the ZigBee Alliance and research 802.15.4 don’t aspire to enter either of these spaces.
research 802.15.4 was designed by Motorola, the National Institute of Standards and Technology (NIST), and many other companies to be a very battery-efficient, robust, and yet simple system. It takes advantage of sophistications that weren’t easily and inexpensively available in the 1990s, when the Bluetooth SIG was conceived. For instance, NASA counted on its phase-shift-key (PSK) modulation for mission-critical data during its deep-space missions. Direct-sequence spread spectrum (DSSS) mitigates multipath fading in environments that range from the home to very challenging industrial settings. Extra features like a strong preamble structure, packet-length counter, and error checking ensure that information is received without error. In addition, an acknowledgement frame mechanism allows the receiving station to indicate to the source that the data was received successfully. If the receiver doesn’t get the data the first time, the transmitter knows to send it again.
In short, robustness at every level ensures that the data gets through successfully. On top of the inherent reliability of research 802.15.4, ZigBee wireless technology adds mesh networks with redundant connections. Devices can therefore determine the best path to take—at that moment—to deliver critical data. Meanwhile, ZigBee security and management features keep networks safe from hackers.