ZigBee
ZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on the IEEE 802.15.4-2003 standard for wireless personal area networks (WPANs), such as wireless headphones connecting with cell phones via short-range radio. The technology defined by the ZigBee specification is intended to be simpler and less expensive than other WPANs, such as Bluetooth. ZigBee is targeted at radio-frequency (RF) applications that require a low data rate, long battery life, and secure networking.
The ZigBee Alliance is a group of companies which maintain and publish the ZigBee standard.
Overview
ZigBee is a low-cost, low-power, wireless mesh networking proprietary standard. The low cost allows the technology to be widely deployed in wireless control and monitoring applications, the low power-usage allows longer life with smaller batteries, and the mesh networking provides high reliability and larger range.
The ZigBee Alliance, the standards body which defines ZigBee, also publishes application profiles that allow multiple OEM vendors to create interoperable products. The current list of application profiles either published or in the works are:
* Home Automation
* ZigBee Smart Energy
* Commercial Building Automation
* Telecommunication Applications
* Personal, Home, and Hospital Care
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 the ZigBee Alliance. Most recently, the ZigBee 2007 specification was posted on 30 October 2007. The first ZigBee Application Profile, Home Automation, was announced 2 November 2007.
For non-commercial purposes, the ZigBee specification is available free to the general public. An entry level membership in the ZigBee Alliance, called Adopter, costs US$3500 annually and provides access to the as-yet unpublished specifications and permission to create products for market using the specifications.
ZigBee operates in the industrial, scientific and medical (ISM) radio bands; 868 MHz in Europe, 915 MHz in the USA and Australia, and 2.4 GHz in most jurisdictions worldwide. The technology is intended to be simpler and less expensive than other WPANs such as Bluetooth. ZigBee chip vendors typically sell integrated radios and microcontrollers with between 60K and 128K flash memory, such as the Freescale MC13213, the Ember EM250 and the Texas Instruments CC2430. Radios are also available stand-alone to be used with any processor or microcontroller. Generally, the chip vendors also offer the ZigBee software stack, although independent ones are also available.
"In the U.S., as of 2006, the retail price of a Zigbee-compliant transceiver is approaching $1, and the price for one radio, processor, and memory package is about $3." Comparatively, the price of consumer-grade Bluetooth chips is now under $3.. In other countries the prices are higher. For example in the UK, (March 2009) the one-off cost to a hobbyist for a barebones ZigBee surface-mount transceiver IC varies from £5 to £9, with pre-assembled modules around £10 more (excluding aerials).
Because Zigbee can activate (go from sleep to active mode) in 15 msec 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. Because Zigbees can sleep most of the time, average power consumption can be very low, resulting in long battery life.
The first stack release is now called Zigbee 2004. The second stack release is called Zigbee 2006, and mainly replaces the MSG/KVP structure used in 2004 with a "cluster library". The 2004 stack is now more or less obsolete.
Zigbee 2007, now the current stack release, contains two stack profiles, stack profile 1 (simply called ZigBee), for home and light commercial use, and stack profile 2 (called ZigBee Pro). ZigBee Pro offers more features, such as multi-casting, many-to-one routing and high security with Symmetric-Key Key Exchange (SKKE), while ZigBee (stack profile 1) offers a smaller footprint in RAM and flash. Both offer full mesh networking and work with all ZigBee application profiles.
ZigBee 2007 is fully backward compatible with ZigBee 2006 devices: A ZigBee 2007 device may join and operate on a ZigBee 2006 network and vice versa. Due to differences in routing options, ZigBee Pro devices must become non-routing ZigBee End-Devices (ZEDs) on a ZigBee 2006 or ZigBee 2007 network, the same as ZigBee 2006 or ZigBee 2007 devices must become ZEDs on a ZigBee Pro network. The applications running on those devices work the same, regardless of the stack profile beneath them.
Uses
ZigBee protocols are intended for use in embedded applications requiring low data rates and low power consumption. ZigBee's current focus is to define a general-purpose, inexpensive, self-organizing mesh network that can be used for industrial control, embedded sensing, medical data collection, smoke and intruder warning, building automation, home automation, etc. The resulting network will use very small amounts of power — individual devices must have a battery life of at least two years to pass ZigBee certification[8].
Typical application areas include
* Home Entertainment and Control — Smart lighting, advanced temperature control, safety and security, movies and music
* Home Awareness — Water sensors, power sensors, smoke and fire detectors, smart appliances and access sensors
* Mobile Services — m-payment, m-monitoring and control, m-security and access control, m-healthcare and tele-assist
* Commercial Building — Energy monitoring, HVAC, lighting, access control
* Industrial Plant — Process control, asset management, environmental management, energy management, industrial device control
Device types
There are three different types of ZigBee devices:
* ZigBee coordinator (ZC): The most capable device, 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, including acting 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. A ZED requires the least amount of memory, and therefore can be less expensive to manufacture than a ZR or ZC.
Software and hardware
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 though 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. Thus, radios are tested to the ISO 17025 standard with guidance given by Clause 6 of the 802.15.4-2006 Standard. Most vendors plan to integrate the radio and microcontroller onto a single chip.
ZigBee and ZigBee PRO technologies
All ZigBee technology devices implement a layered stack architecture. The ZigBee stack uses the IEEE 802.15.4 Physical (PHY) and Medium Access Control (MAC) Layers. In addition to the IEEE layers, the ZigBee Alliance has defined a set of standardized layers that sit on top of the IEEE layers and together these layers make up the ZigBee technology stack architecture.
The lower layers (including PHY/MAC, Network and Security layers) make up the ZigBee stack. On top of this there is an Application layer which will be specific to the particular "Profile" being implemented. The Profile contains the protocol that is specific to the application ZigBee is being used to implement.
Two types of ZigBee technology have been defined. These are ZigBee and ZigBee PRO. The differences between the types relate to network architecture and available security, however they have been design to allow a mixture of types within one network under certain network configurations. For further information relating to the two types of ZigBee technology click on the following link ZigBee & ZigBee PRO
Global Approvals
In addition to the regulatory Radio, Safety and EMC requirements that apply to ZigBee devices, the ZigBee Alliance has put in place a certification process that must be satisfied prior to using the ZigBee name or logo.
For further information on gaining market access to specific markets, just follow the relevant link:
* European
* North America
* South and Central America
* Africa
* Asia
* Australasia
* Middle East
The ZigBee Advantage
The ZigBee protocol was designed to carry data through the hostile RF environments that routinely exist in commercial and industrial applications.
ZigBee protocol features:
* Low duty cycle - Provides long battery life
* Low latency
* Support for multiple network topologies: Static, dynamic, star and mesh
* Direct Sequence Spread Spectrum (DSSS)
* Up to 65,000 nodes on a network
* 128-bit AES encryption – Provides secure connections between devices
* Collision avoidance
* Link quality indication
* Clear channel assessment
* Retries and acknowledgements
* Support for guaranteed time slots and packet freshness
