What is ZigBee? It simply is an interesting wireless protocol for communication between devices.
ZIGBEE KEY CONCEPTS
A legitimate question is: “Do we really need another wireless protocol?”. The answer can be found analyzing the reasons that brought to the creation of ZigBee by the ZigBee Alliance. ZigBee was born with a mission to define a complete, open, global standard for reliable, cost-effective, low-power, wirelessly networked products addressing monitoring and control. In particular, the focus was on:
- Large networks (a large number of devices and a large coverage area) that could form autonomously, and operate very reliably and securely for years without operator intervention.
- Very long battery life (years of use from a pair of AA cells), very low infrastructure cost (low device and setup costs), very low complexity, and small size.
- A relatively low data rate.
- A standardized protocol, allowing multiple-vendor, interoperable products for the global market.
The key aspects of ZigBee are here summarized.
Wireless communication is inherently unreliable. ZigBee is based on IEEE 802.15.4, which defines the short-range wireless communications. It uses what is called Offset-Quadrature Phase-Shift Keying (O-QPSK) and Direct Sequence Spread Spectrum (DSSS), a combination of technologies that provide excellent performance in low signal-to-noise ratio environments. To handle the communication between the different nodes, ZigBee uses the Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA).
ZigBee is based on a stack of protocols that do not require a lot of computing power. For this reason (and because it does not need to reach high data rates) it can be implemented on very cheap chips. It is also based on technologies in the public domain (such as AES-128 and AODV) that do not require patent fees.
The most interesting quality of ZigBee is the ability to operate for years with simple batteries (such as AA). Besides the use of low-end hardware and inexpensive in terms of consumption, this goal is achieved thanks to the possibility of sleep: a node does not need to be in constant contact with the network. For example, a temperature sensor can wake up once a minute to read the temperature and communicate it to a receiving node, remaining inactive the rest of the time. A button instead may be activated only when pressed by a user, for communicating the event.
To secure communications, ZigBee uses the AES-128. The main reasons that led to its adoption are as follows:
- It is a trusted and recognized standard
- It does not need a license to use
- It is implementable on 8-bit processorsZigBee provides both encryption and authentication.
OPEN GLOBAL STANDARD
ZigBee uses the IEEE 802.15.4 MAC and physical layers. The ZigBee specifications were developed by the ZigBee Alliance, a group of over 250 companies located throughout the world, and ensure complete interoperability between devices made by different manufacturers. In addition, the standard specifications are freely available and can be implemented by anyone.
One of the most interesting aspects in ZigBee is its ability to create a mesh network, which is a network with the following characteristics:
- A communication range that can be extended my multi-hopping: a node can communicate with nodes out of its range using intermediate nodes for packet delivering
- Ad-hoc creation of the network, of which we do not need to know the spatial disposition nor the devices that will join it in the future
- Automatic routes discovery and fault-tolerance, by the use of AODV, that permit to change the routing paths dynamically
With these characteristics we can obtain reliability, adaptation and large communication range, thus disposing of low communication power.