ZigBee is an open global standard providing wireless networking based on the IEEE 802.15.4 standard and taking full advantage of a powerful physical radio this standard specifies.

The term "ZigBee" originates from honeybees' method of communicating newfound food sources. This silent-but-powerful communication system is known as the "ZigBee Principle." By dancing in a zig-zag pattern, the bee is able to share critical information, such as the location, distance, and direction of a newly discovered food source to its fellow hive members.

A ZigBee based sensor network has emerged as a good alternative for industrial, commercial and home automation markets, where harsh RF conditions exist. ZigBee was created as a cost-effective, standards-based wireless networking solution that supports low data-rates, low-power consumption, security, and reliability. It is the only standards-based technology that addresses the unique needs of remote monitoring, control and sensor network applications.

ZigBee sensor networks require far less throughput but offer even greater flexibility than competitive network types. Thus, ZigBee networks are well suited to applications requiring low data rate transmissions. Asset tags need only send brief transmissions of approximately 100 bytes. Lower throughput results in lower complexity, longer battery life, and lower cost. Additionally, with ZigBee sensor networks, RF frequencies are allocated which maintain separation from Wi-Fi and other traffic, preventing the battle for bandwidth that may affect mission-critical applications when converging RFID with Wi-Fi.

Complementary Networks Can Co-Exist

There are many proprietary wireless systems that function like ZigBee; inexpensive, very-low current draining solutions that address a multitude of problems without requiring high data rates. These proprietary systems were designed because there were no standards that met their requirements. These legacy systems are now creating significant interoperability problems with each other and with newer technologies.

Complementary wireless networks can co-exist in order to minimize overall costs, make the best use of available bandwidth, and to partition the use of the available RF spectrum to prevent interference and over-utilization. With the use of clear channel assessment practices, wireless communication protocols such as 802.11 or 802.15.4 (upon which ZigBee is based) include collision avoidance techniques to prevent interference.

The 2.4 GHz band is used worldwide and has 16 channels and a maximum over-the-air data rate of 250 Kbps. Lower frequency bands are also specified. The 902–928 MHz band serves the Americas and much of the Pacific Rim, with 10 channels and a burst rate of 40 Kbps. European applications use one channel in the 868–870 MHz band, which provides 20 Kbps burst rate. This rich assortment of frequencies lets applications with the appropriate hardware configuration adjust in real time to local interference and/or propagation conditions. Once on a specific channel, the 802.15.4 radio relies on a number of mechanisms to ensure reliable data transmission, including binary phase shift keying (BPSK) in the 868/915 MHz bands and offset quadrature phase shift keying (O-QPSK) at 2.4 GHz.

Transmission Power

Transmission power density is regulated by the FCC based on research data studying the effects of RF energy on biological systems like the human body. When implementing new applications, providing reliable communication (as required by the specific application) with transmission power as low as possible should always be considered and is of particular concern in healthcare settings. ZigBee 802.15.4 networks communicate at 1 mW of radiated RF power, compared to 100 mW for nodes within Wi-Fi networks, and 1 watt for mobile phones. These transmission power requirements illustrate sequentially lower overall power consumption of ZigBee 802.15.4 based on matching the transmission needs of Wi-Fi.

Power Consumption and Battery Life

Power consumption and battery life of the actual asset tags are key considerations in choosing the type of network to deploy. In RTLS for example, low power ZigBee sensor networks provide a cost-effective communications medium that is sufficient for communicating sensor data and requires no maintenance. These networks can be designed to communicate small amounts of data very infrequently, with most asset data residing on the server, indexed by unique ID's associated with the tagged asset. The low transmission power of 802.15.4 ZigBee networks results in both overall lower power consumption and longer battery life.

Standard 802.11 Wi-Fi networks require significant power due to their higher data rates and the associated higher complexity. Many devices connected to Wi-Fi networks are AC-powered and have large, high-capacity batteries to offset these power requirements, such as laptops and VoIP phones that are easily recharged.

Low data rate wireless sensor networks consume less power to operate simply because they don't have the same data rate requirements. In addition, the nodes within these networks can be electronically simpler and cheaper. They are designed to provide for a large number of nodes, and for nodes, which can run on a single battery for several years without re-charging or changing the battery.

ZigBee RF Mesh Network

ZigBee devices have the ability to form an RF mesh network between nodes. Each node is self routing and able to connect to other nodes as needed. ZigBee sensor networks leverage this mesh network to route data among the sensors themselves to collection points or to bridges onto the LAN. The network of sensors communicates wirelessly with each other along with wireless communication from the battery-powered tags to the sensors. As the diagram below shows, this type of ad-hoc network formation is much like the internet itself, and provides tremendous flexibility and fault tolerance.

For applications requiring widespread communication like RTLS, ZigBee sensors are deployed with sufficient density to "cover" a building (or possibly some subset of a building). This coverage must provide a sufficient density of network nodes for routing data, even at low transmission power. The sensors themselves provide the backbone for wirelessly collecting sensor data.