Make way for ZigBee

ZigBee is a funny name that may soon be on everyone's lips. Aimed at providing low-speed wireless communications for industrial and embedded systems, the ZigBee protocol is based on the wireless personal area network (WPAN) radio standard defined in IEEE 802.15.4.

The WPAN radio standard was defined a year ago, but the ZigBee protocol specification is only now being finalized and is targeted for release by the end of 2004. When it is ready, test engineers may need to come up to speed quickly on ZigBee test.

The physical layer of ZigBee provides for data rates of 20, 40, and 250 kbps working in one of several radio bands. There are 16 channels in the 2.4-GHz ISM band, 10 channels in the 915-MHz ISM band, and one channel in the 868-MHz band used in Europe. Key radio specs include:

• transmit power: ¡Ý0.5 mW,
• transmit center frequency tolerance: ¡À40 ppm, and
• receiver sensitivity for a packet error rate: <1% (¨C85 dBm in the 2.4-GHz band and ¨C92 dBm in the other bands).

The standard also calls for different data modulation schemes depending on the operating frequency. In the 2.4-GHz band, data modulation uses O-QPSK with 16 symbols. Higher frequencies use BPSK.

Unlike the IEEE specification, which calls for a frequency hopping spread spectrum (FHSS), ZigBee uses a direct sequence spread spectrum (DSSS). This cuts the data rate for ZigBee by a factor of two to four, but it lowers the cost of implementation. It also helps reduce power consumption and extend battery life.

Bob Heile, chairman of the ZigBee Alliance (www.zigbee.org), says that low cost and long battery life (2 to 20 years) are the key attributes that the Alliance is trying to ensure in the specification, and lower performance is not a problem. While other wireless standards are aimed at high-speed data and multimedia applications, ZigBee targets simple monitoring and control functions. "This class of applications typically has a low data rate requirement and uses equipment of limited complexity," says Heile. It is also typical for such devices to be installed in inconvenient locations, he adds, hence the need for extraordinarily long battery life.

The radio will not be the main challenge for test engineers, however; the networking function will be. A

Tools such as the Steeple protocol sniffer will become essential when the ZigBee wireless networking standard gains acceptance. Courtesy of CompXs.

Fortunately, some analysis tools are already available, even though the specification is not yet finalized. Companies such as CompXS (Santa Clara, CA) have begun releasing protocol "sniffers" that will analyze data traffic over the network, helping engineers troubleshoot and validate their products. Standard RF test tools will be able to handle the radio layer.

The ZigBee Alliance will also provide conformance test suites once the specification is finalized, says Heile. The tests are available now to Alliance members and will become available to OEMs interested in developing ZigBee products once the specification is released later this year. In addition, conformance testing services will be available through TUV America and National Technical Systems, both members of the ZigBee Alliance.

Market watchers expect that many OEMs will be interested in ZigBee. Analyst Chris Lopez at market research firm AMI Research (Oyster Bay, NY) expects that nearly a million ZigBee units will ship in 2005, climbing to 6 million in 2006. Industrial and business applications will launch the technology, Lopez expects, with home automation providing a major growth opportunity later on.