This standard has been defined by the ZigBee Alliance, an industrial consortium of companies led by Texas Instruments, Philips, Freescale and ST among others. Zigbee allows sending data, usually information from sensors and/or control commands for actuators, through multihop wireless mesh networks, which allows a great coverage area (due to message forwarding by the repeater nodes) with redundant links (if a route is down, information is sent over another path), making Zigbee a robust network suitable for critical environments.

The standard encompasses monitoring and control applications in various markets: building automation, home automation, healthcare, smart grid... In order to make this possible, Zigbee defines a series of profiles at application level that specify the commands to control the various Zigbee devices.

Products & Services

TST has been intensely working with Zigbee technology. For this reason TST has been selected as EDP partner by Digi, one of the world leaders in Zigbee technology. TST offers you its TSmarT platform, a complete wireless communications platform with a fully integrated Zigbee radio module. Additionally TST develops a customized software application ready to execute in TSmarT and integrates the sensors needed for your application.

Projects

Using its TSmarT platform with the Zigbee radio module, TST has designed a lighting control application at Santander harbor to manage the electric towers. At Bilbao’s harbor, TST has developed a remote control application of the traffic lights at railway crossings.

Technology

Zigbee specifies application, transport and network layers over IEEE 802.15.4 protocol. Therefore lower layers (physical and MAC/LLC) follow the dictates of 802.15.4. Thus Zigbee uses license free ISM frequency bands (868 MHz in Europe, 915 MHz in America and/or 2,4 GHz worldwide available). The gross bitrate in the air reaches 250 kbps, which equals to 62.5 kbaud because the modulation scheme establishes a spread factor of 4 (each logical bit is codified with 4 physical bits or chips). Frequency bands below 1 GHz have a single frequency channel available, but at 2.4 GHz there are 16 channels in which transmission is possible, allowing the peaceful coexistence between Zigbee, Wi-Fi, Bluetooth and another wireless standards in the same frequency band.

The medium access mechanism is CSMA/CA in non-beacon networks, also known as Listen Before Talk. Nodes send their information anytime, but checking first if the channel is free. Nodes that behave as repeater or router (FFD, Full Functional Devices) can’t sleep, they must be permanently listening for packets coming from simple devices (RFD, Reduced Functional Devices). For this reason repeaters need power supply, meanwhile RFD can work with batteries many years. At network level Zigbee supports mesh, star, tree and hybrid topologies. The typical routing algorithm is AODV, which establishes routes on demand.