ZigBee EQUIPMENT

       If you are like most people, interested in technology and home automation you probably have been hearing more about ZigBee lately, but you probably are not exactly sure what ZigBee is and how it relates to home automation, and home energy monitoring. This article is intended to provide some background information on ZigBee and to dispel some of the false information that has been circulating about the technology. Maybe most of all it's meant to illustrate how ZigBee will impact the field of home automation, energy monitoring, and even personnel health care monitoring. While ZigBee has generally been flying under the radar, I feel that this technology is likely the most important and exiting technology to impact home automation since X-10.

WHAT IS Zigbee?


  Alliance of over 100 active member companies involved in development of wireless specification for sensors & control equipment
  IEEE 802.15.4 State-of-the-art PHY and MAC layer Standard
  Zigbee Protocol stack finalized in December of 2004
 Low data rate, low power, low cost solution
 Data Rates of 250kbps when operating at 2.4 GHz
 40 kbps when operating at 915 MHz, and 20kbps
 when operating at 868 MHz
 Range ~50m range (5-500m depending on environment
       Before we get started discussing ZigBee, let’s first discuss another wireless technology, Wi-Fi, so we can compare the evolution of this technology to ZigBee. In the mid-90’s, before Wi-Fi existed, several companies were selling wireless products that performed the function of what Wi-Fi does today, basically substituting a wireless connection for an Ethernet cable. At the time, a typical access point and client device together cost about $700, and since each manufacturer used a proprietary protocol over wireless, each company’s client would only communicate to that company’s client. Seeing this as a problem, the IEEE (Institute of Electronic and Electrical Engineers) got together with companies that made these products at the time, and after much debate and compromise, produced the 802.11b standard for wireless LANs in October 1999. Within a year, a handful of companies were making 802.11b devices, many more were making 802.11b chips, and you could purchase a wireless access point/client for under $250. Soon after, a non-profit group composed of member companies was formed to perform interoperability testing between devices from different companies. That group later went on to be called the Wi-Fi Alliance. Fast-forward ten years to present, and the shelf at Fry’s or Best Buy contains Wi-Fi products as far as the eye can see. Ninety nine percent of laptops made today have Wi-Fi as do 20% of cell phones. In-Stat forecasts over 450 million Wi-Fi devices will be shipped this year. This is what a technology standard can do in a several-year period.
       Now lets move on to home automation and ZigBee. Home Automation arguably started in 1975 with X-10, but while it was a fantastic technology for the time and is still used today, the technology was limited, and admittedly, the number of home automation enthusiasts’ back then was also limited. Still enough people were interested in home automation that several companies thought there was enough market for “follow-on” products like UPB, Z-Wave, RadioRA, INSTEON, ALC and others. All are great products, all proprietary, and all designed by one company (and possibly licensed to others) to perform a specific task for the purpose of selling a product and making money. In terms of evolution, all are at the equivalent time of wireless LAN before the 802.11b standard was approved.
The Technology
       So what is ZigBee and how does it fit into all this? ZigBee is a wireless standard and technology whose goal it is to provide low-speed connectivity (250Kbps max.) with a range of 150 feet and running from a single battery for several years. ZigBee also incorporates mesh technology so range can be extended, and over 64,000 devices can be incorporated into a network. ZigBee operates at 2.400–2.484 GHz, 902-928 MHz and 868.0–868.6 MHz. Overall, ZigBee is a much broader technology than Wi-Fi, since ZigBee can be a simple radio, a mesh transport network, and/or it can specify how applications communicate. Wi-Fi is just a transport of TCP/IP.
Like Shrek and an onion, ZigBee is composed of layers. At the lowest layer is the 802.15.4 physical radio that allows two ZigBee devices to connect via a radio link. These ZigBee radios can be made cheaply for only a few dollars, and currently Freescale and TI are major manufacturers of these radios. Normally one radio speaking to another isn’t very useful in and of itself, but with ZigBee there is a an application that will be very important, the replacement of infrared in remotes and TVs and audio equipment. This remote standard is called RF4CE and has advanced to the point where many large manufacturers are supporting it, including Philips, Sony, and Samsung. High-end equipment will be shipping with ZigBee soon, and lower-priced equipment will follow in a few years. Here is a press release from Sony announcing it: http://www.sony.net/SonyInfo/News/Press/200903/09-0304E/index.html
The next layers up with ZigBee are the MAC and networking layers that specify how devices interoperate with each other using a self-forming mesh network. This is the ZigBee you’ve likely heard about, a mesh network of wireless devices all communicating. This standard is called the ZigBee Feature Set or the ZigBee Pro Feature Set, and a few companies have made products that based on this. Remember, this layer only gets data from any node to any other node, but it doesn’t specify what the data means, in other words, it doesn’t specify how to turn on a light. More on this below.

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