ZigBee overview UM0923
18/153 Doc ID 17261 Rev 1
3.1.1 General characteristics
ZigBee is intended as a cost-effective and low-power solution. It is targeted to a number of
markets including home automation, building automation, sensor networks, health care,
automated meter reading and personal health care monitoring. The general characteristics
for a ZigBee network are as follows:
● Low power - Devices can typically operated for several years on AA type batteries using
suitable duty cycles.
● Low data rate - The 2.4 GHz band supports a radio data rate of 250 Kbps. Actual
sustainable traffic through the network is lower than this theoretical radio capacity. As
such, ZigBee is better used for sampling and monitoring applications.
● Small and large networks - ZigBee networks vary from several devices to thousands of
devices communicating seamlessly. The networking layer is designed with several
different data transfer mechanisms (types of routing) to optimize the network operation
based on the expected use.
● Range - Typical devices provide sufficient range to cover a normal home and readily
available designs with power amplifiers extend the range substantially. A distributed
spread spectrum is used at the physical layer to be more immune to interference.
● Simple network installation, start up and operation - The ZigBee standard supports
several network topologies and the simple protocols for forming and joining networks
allow systems to self configure and fix routing problems as they occur.
3.1.2 IEEE 802.15.4
ZigBee networks are based on the IEEE 802.15.4 MAC and physical layer. The 802.15.4
standard operates at 250 Kbps in the 2.4 GHz band and 40/20 Kbps in the 900/868 MHz
bands. A number of chip companies provide solutions in the 2.4 GHz band with a smaller
number supporting the 900/868 MHz band. ZigBee adopted the 802.15.4 - 2003 version of
the standard. The IEEE has since issued a 2006 version of this standard that has not yet
been adopted by ZigBee.
The 802.15.4 standard provides some options within the MAC layer on beacon networks,
guaranteed time slots that are not used by ZigBee in any current stack profiles. As such,
these items are not normally included in the ZigBee software stack to save code space.
ZigBee also has specific changes to the 802.15.4 MAC that are documented in Annex D of
the ZigBee specification.
The 802.15.4 medium access control (MAC) layer is used for basic message handling and
congestion control. This MAC layer includes mechanisms for forming and joining a network,
a CSMA mechanism for devices to listen for a clear channel as well as a link layer retries
and acknowledgement of messages for reliable communications between adjacent devices.
These underlying mechanisms are built upon by the ZigBee network layer to provide reliable
end to end communications in the network. The 802.15.4 standard is available from
www.ieee.org
3.1.3 Hardware and Software elements
A ZigBee solution requires implementation of a ZigBee radio and associated
microprocessor (together in a single chip or separately), and implementation of an
application on top of a ZigBee stack.
Typically a developer can purchase a ZigBee radio and software as a bundled package
although there are some third party software stacks that have been developed. Typically