Information AboutZigbee |
| CATEGORIES ABOUT ZIGBEE | |
| wireless-stub | |
| wireless networking | |
| ieee 802 | |
| domotics | |
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ZigBee is the name of a specification for a suite of high level communication protocols using small, low-power Digital Radio s based on the IEEE 802.15.4 Standard for Wireless Personal Area Network s (WPANs). ZigBee is targeted at RF applications that require a low data rate, long battery life, and secure networking. OVERVIEW The relationship between IEEE 802.15.4-2003 and ZigBee is similar to that between IEEE 802.11 and the Wi-Fi Alliance . The ZigBee 1.0 specification was ratified on December 14 , 2004 and is available to members of the ZigBee Alliance. An entry level membership, called Adopter, in the ZigBee Alliance costs US$ 3500 annually and provides access to the specifications and permission to create products for market using the specifications. For non-commercial purposes, the ZigBee specification is available to the general public at the [http://www.zigbee.org/en/spec_download/download_request.asp ZigBee Specification Download Request]. Most recently, the ZigBee 2006 specification was posted in December 2006. ZigBee operates in the industrial, scientific and medical ( ISM ) radio bands; 868 MHz in Europe, 915 MHz in the USA and 2.4 GHz in most jurisdictions worldwide. The Technology is intended to be Simpler and Cheaper than other WPANs such as Bluetooth . The most capable ZigBee node type is said to require only about 10% of the software of a typical Bluetooth or Wireless Internet node, while the simplest nodes are about 2%. However, actual code sizes are much higher, closer to 50% of Bluetooth code size. ZigBee chip vendors have announced 128 kilobyte devices. As Of 2006 , the retail price of a Zigbee-compliant transceiver is approaching $1, and the price for one radio, processor, memory package is about $3.1 Comparatively, before Bluetooth was launched (1998) it had a projected price, in high volumes, of $4 - $6; the price of consumer-grade Bluetooth chips is now under $3.2 First stack release is now called "Zigbee 2004". The 2nd stack release (today, 26 June 2007, the current public one) is called 2006, and mainly replaces the MSG/KVP structure used in 2004 with a "cluster library". The 2004 stack is now more or less obsolete. The ZigBee Alliance has started work on ZigBee 2007, looking to extend the ZigBee 2006 specification capabilities, the main enhancements are optimising certain network level functionality (such as data aggregation). There're also some new application profiles like Automatic Meter Reading, Commercial building automation and home automation based on the "cluster library principe". Zigbee 2007 is sometimes called "Pro", but Pro is a stack profile, which defines certain stack settings and mandatory features. ZigBee 2007 at the network level is not backwards compatible with ZigBee 2004/2006, although a ZigBee 2004/2006 RFD node can join a 2007 network and vice versa. It's not possible to mix 2004/2006 routers with 2007 routers/coordinator. USES ZigBee protocols are intended for use in embedded applications requiring low Data Rate s 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 , Domotics , etc. The resulting network will use very small amounts of power so individual devices might run for a year or two using the originally installed battery. DEVICE TYPES There are three different types of ZigBee device:
PROTOCOLS The protocols build on recent algorithmic research ( Ad-hoc On-demand Distance Vector , NeuRFon ) to automatically construct a low-speed ad-hoc network of nodes. 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. The typical example of a heterogeneous network is a Wireless Light Switch : the ZigBee node at the lamp may receive constantly, since it's connected to the mains supply, while a battery-powered light switch would remain asleep until the switch is thrown. The switch then wakes up, sends a command to the lamp, receives an acknowledgment, and returns to sleep. In such a network the lamp node will be at least a ZigBee Router, if not the ZigBee Coordinator; the switch node is typically a ZigBee End Device.
In general, the ZigBee protocols minimize the time the radio is on so as to reduce power use. In beaconing networks, nodes only need to be active while a beacon is being transmitted. In non-beacon enabled networks, power consumption is decidedly asymmetrical: some devices are always active, while any others present spend most of their time sleeping.
The radios use Direct-sequence Spread Spectrum coding, which is managed by the digital stream into the modulator. BPSK is used in the 868 and 915 MHz bands, and orthogonal QPSK that transmits two bits per symbol is used in the 2.4 GHz band. The raw, over-the-air data rate is 250 Kbit / S per Channel in the 2.4 GHz band, 40 kbit/s per channel in the 915 MHz band, and 20 kbit/s in the 868 MHz band. Transmission range is between 10 and 75 Meter s (33~246 Feet ), although it is heavily dependent on the particular environment. The maximum output power of the radios is generally 0 DBm (1 mW). The basic channel access mode specified by IEEE 802.15.4-2003 is "carrier sense, multiple access/collision avoidance" ( CSMA/CA ). That is, the nodes talk in the same way that people converse; they briefly check to see that no one is talking before they start. There are three notable exceptions to the use of CSMA. Beacons are sent on a fixed timing schedule, and do not use CSMA. Message acknowledgements also do not use CSMA. Finally, devices in Beacon Oriented networks that have low latency real-time requirements may also use Guaranteed Time Slots (GTS) which by definition do not use CSMA. SOFTWARE AND HARDWARE The software is designed to be easy to develop on small, cheap 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 Circuit s wherever possible. Even though the radios themselves are cheap, 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 802.15.4-2003 Standard. Most vendors plan to integrate the radio and microcontroller onto a single chip. (Some interesting links: {Link without Title} {Link without Title} look for the USB Dongle) HISTORY
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