Content area
Full Text
ZigBee is becoming a major player in the low-data-rate embedded communications arena. Yet that doesn't make designing this embedded technology a simple process. | By Andy Wheeler
With the ratification of the ZigBee wireless networking standard, companies are integrating complete wireless SoCs on semiconductors smaller than a shirt button, enabling systems designers to embed low-cost, low-power sensor and control capabilities to everyday devices. Today, ZigBee-compliant networks are already being built into home monitoring and control products such as smoke detectors, so that the unit in the basement can wirelessly notify the occupants on the third floor in case of trouble, or even dial the homeowner's telephone. Paintings in art galleries each have their own networked disturbance sensor, discretely informing the guards if any painting has been touched. Room air conditioning units for hotels can be controlled remotely - and their efficiency monitored from a central location - saving hotel owners thousands of dollars every week. And ZigBee-enabled utility meters can potentially save public utility companies millions of dollars by eliminating the need to manually read meters at homeowners' premises.
But although the ZigBee v1.0 specification has finally been ratified, the protocol is not a one-size-fits-all blueprint for companies wishing to tap into this promising market. At its most basic level, ZigBee simply ensures interoperability with other standard-compliant products. The deeper application, architectural and platform issues that designers must carefully weigh are as wide-ranging as the potential ZigBee applications themselves.
ZigBee-compliant embedded networks have several characteristics that set them apart from conventional wireless local area networks such as IEEE 802.11. A node in a ZigBee network has the following:
Low power - Many applications must run unattended for years using battery power. Commercially available ZigBee system nodes consume approximately 50 mW when active and less than a microwatt in sleep mode. With a battery source of three watthours, such systems will last two and half days if active 100% of the time; but with a duty cycle of 0.1 %, the same system will last more than six years without a battery change.
Relatively low data rates - An average light switch communicates about four bits per day, or 46 microbaud. In many applications, high data rates are not a requirement. The ZigBee v1.0 specification...