ZigBee is another member of Wireless Networking Standard which is implemented for monitoring and control applications, with a low data rate, low cost, low energy usage, and global use, with broad applicability to consumer products, commercial, industrial and government markets. It is based on the IEEE (Institute of Electrical and Electronics Engineers) 802.15.4 specification for low data rates technology that allows devices to communicate with one another with very low power consumption and allowing the devices to run on simple batteries for several years. Zigbee also targeting various forms of automation, as the low data rate communication is ideal for sensors and monitors. This technology was from and patent to ZigBee Alliance, is a group of companies who maintain and publish ZigBee standards.
The goal of the ZigBee Alliance was to provide the consumer with ultimate flexibility, mobility, and ease of use by building wireless intelligence & capabilities into routine devices. ZigBee technology will be embedded in a wide range of products and applications across consumer, commercial, industrial and government markets worldwide.
For the first time, companies will have a standards-based wireless platform optimised for the unique needs of remote monitoring and control applications including simplicity, reliability, low-cost and low-power. Technology defined by ZigBee specification was intended to be simpler and less expensive than other WPANs (Wireless Personal Area Networks) like Bluetooth. ZigBee was targeted on radio-frequency (RF) applications that require a low data rate, long battery life and secure networking.
ZigBee was designed to transmit slowly. It has a data rate of 250kbps (kilobits per second), pitiful compared with WiFi, that is hitting throughput of 20Mbps or more. Since ZigBee transmits slowly, it doesn’t need much power and basically uses digital radios to allow devices to communicate with one another.
Network with ZigBee
A network coordinator is a device that sets up the network, is aware of all the nodes within its network, and manages both the information about each node as well as the information that is being transmitted/received within the network. Every ZigBee network must contain a network coordinator. Other Full Function Devices (FFD’s) may be found in the network, and these devices support all of the 802.15.4 functions. They can serve as network coordinators, network routers, or as devices that interact with the physical world. The final device found in these networks is the Reduced Function Device (RFD), which only serve as devices that interact with the physical world.
The relationship between IEEE 802.15.4 and ZigBee is similar to that between IEEE 802.11 and the Wi-Fi Alliance. The ZigBee 1.0 specification was ratified on 14 December 2004 and is available to members of ZigBee Alliance. The first ZigBee Application Profile, Home Automation, was announced on November 2nd, 2007. Since ZigBee can activate (go from sleep to active mode) within 15msec or less, the latency can be very low and devices can be very responsive — particularly compared to Bluetooth wake-up delays, which are typically around three seconds.
ZigBee Pro offers more features, such as multi-casting, many-to-one routing and high security with Symmetric-Key Key Exchange (SKKE).
ZigBee-style networks became enhanced in 1998’s, when many manufacturers realized that both WiFi & Bluetooth & other wireless technologies were going to be unsuitable for many applications and devices. Many engineers saw a need for self-organizing digital radio networks. IEEE 802.15.4 standard was completed in May 2003 and in the summer of 2003, Philips Semiconductors, a major mesh network supporter, ceased the investment. Philips Lighting has however, continued Philips’ participation and Philips remains a promoter member on the ZigBee Alliance Board of Directors.
In October 2004, ZigBee Alliance announced that the memberships have doubled in the preceding year and had grown to more than 100 member companies in 22 countries. By April 2005, membership had grown-up to more than 150 companies and by December 2005, membership had passed 200 companies.
Name of the brand, “ZigBee” is originated with reference to the behaviour of honey bees after return to the beehive.
The first packaged ZigBee system was made by Freescale, featured a switch that operated from the other side of a huge hall. “We are getting to the world of James Bond gadgets,” said Jon Adams, director of radio technology at Freescale and one of the ZigBee founders.
ZigBee In Action
ZigBee designed for wireless control and sensors. Mostly ZigBee operates in Personal Area Networks (PAN’s) and device-to-device networks. Control of lights, switches, thermostats, appliances, etc. In most large network instances, the network will be a cluster of clusters. It can also form a mesh or a single cluster. The current profiles derived from the ZigBee protocols support beacon and non-beacon enabled networks.
In non-beacon-enabled networks (those whose beacon order is 15), an unslotted CSMA/CA channel access mechanism is used. In this type of network, ZigBee Routers typically have their receivers continuously active, requiring a more robust power supply. However, this allows for heterogeneous networks in which some devices receive continuously, while others only transmit when an external stimulus is detected.
In beacon-enabled networks, the special network nodes called ZigBee Routers transmit periodic beacons to confirm their presence to other network nodes. Nodes may sleep between beacons, thus lowering their duty cycle and extending their battery life. Beacon intervals may range from 15.36 milliseconds to 15.36 ms * 214 = 251.65824 seconds at 250 kbit/s, from 24 milliseconds to 24 ms * 214 = 393.216 seconds at 40 kbit/s and from 48 milliseconds to 48 ms * 214 = 786.432 seconds at 20 kbit/s. However, low duty cycle operation with long beacon intervals requires precise timing, which can conflict with the need for low product cost.
The software is designed to be easy to develop on small, inexpensive microprocessors. The radio design used by ZigBee has been carefully optimized for low cost in large scale production. It has few analog stages and uses digital circuits wherever possible. Even the radios themselves are inexpensive, the ZigBee Qualification Process involves a full validation of the requirements of the physical layer. This amount of concern about the Physical Layer has multiple benefits, since all radios derived from that semiconductor mask-set would enjoy the same RF characteristics. On the other hand, an uncertified physical layer that malfunctions could cripple the battery lifespan of other devices on a ZigBee network. Where other protocols can mask poor sensitivity or other esoteric problems in a fade compensation response, ZigBee radios have very tight engineering constraints: they are both power and bandwidth constrained.
There are 3 different types of ZigBee devices available in the marketplace.
- ZigBee coordinator (ZC): The coordinator forms the root of the network tree and might bridge to other networks. There is exactly one ZigBee coordinator in each network since it is the device that started the network originally. It is able to store information about the network and acts as the Trust Centre & repository for security keys.
- ZigBee Router (ZR): As well as running an application function, a router can act as an intermediate router, passing on data from other devices.
- ZigBee End Device (ZED): Contains just enough functionality to talk to the parent node (either the coordinator or a router); it cannot relay data from other devices. This relationship allows the node to be asleep a significant amount of the time thereby giving long battery life. ZED requires the least amount of memory, therefore, can be less expensive to manufacture, than ZR or ZC.