Z-Wave
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Z-Wave is the interoperable wireless communication protocol developed by Danish company Zensys and the Z-Wave Alliance.[1][2] It is designed for low-power and low-bandwidth appliances, such as home automation and sensor networks.
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[edit] Use cases
Someone might be interested in Z-Wave-enabled devices for their home automation needs if they want to do one of the following:
- Control lighting remotely. This includes dimming of both incandescent and magnetic lighting.
- Control blinds, drapes, or projection screens
- Control or monitor a thermostat from a distance.
- Control "scenes". A scene can set the level of several light switches at the same time. For example, a "Start a movie" scene might turn off the lights throughout the first floor except in the living room, dim those lights to 20%, and close the blinds in the living room.
- Trigger scenes using external events such as the garage door opening, motion detected by a motion detector, or the time of day.
[edit] Z-Wave vs. X10
Z-Wave is, in some sense, a better X10 (industry standard). Where X10 sent signals over power lines and offered an optional RF adapter, Z-wave is completely RF based. Z-wave systems respond much more quickly than X10-based systems, and offer native acknowledgment to ensure that messages are not lost without generating an error. X10 systems took approximately one second to send a command. Z-wave can send a command and receive an acknowledgment in about 50 ms. Most nodes in a Z-Wave system are also repeaters. Thus a controller does not need to be within the transmission range of the device it is trying to address if a series of hops will get the message there.
Also, Z-Wave has substantially better security than X-10. Each controller has a 32 bit home code. When that controller is used to create a network, that home code is assigned into each device and controller as it is added to the network. Comparing this to X-10, which has 16 house codes (or 4 bits, versus 32 in Z-wave). Z-Wave devices hear message for other home codes, but will not relay or respond to them. A skilled attacker could certainly forge messages for a house code, but this will never happen accidentally.
[edit] Setting up a network of devices
To start using a network of z-wave devices a person will need at least one controller and one controllable device. A controller cannot control a device until it is "added" to the network. Usually this amounts to pressing a key sequence on the controller and a button on the device to pair them. Every controller is different in terms of how it subsequently controls the device after that. This setup sequence is far from intuitive on some controllers and is perhaps the Achilles heel of the whole system in terms of usability. However, this process only needs to be done once. This process is repeated for each device in the system. Because the controller is learning the signal strength between the devices during this process, it is important that the devices themselves be in their final location before they are added to the system. Also, it's important to properly remove a node from the system using a "removal" process if a node is going to be removed. It is generally not recommended to simply unplug it or move its location.
[edit] Controlling your network of devices
Most users will start with a portable controller to setup their network in the first place. Two such controllers are the Intermatic HA07 and the Leviton RZCPG. The controller used to create the network is the primary controller. That controller can copy the node network to other controllers. Note that this process will unfortunately have to be repeated each time a new node is added. Using this process, someone can add multi-device remote controls such as some of Logitech's Harmony remotes or USB or serial interface controllers for their PC. A variety of computer software can control multiple devices, including HomeSeer and ThinkEssentials.
[edit] Proprietary Interface
The computer controllers that interface to Z-wave systems speak a standardized serial protocol. Unfortunately, that protocol is proprietary to zen-sys. So if it's necessary to interface the software to z-wave, a person would need to sign an NDA and buy a developers kit (at approximately US $10,000, available from Digikey in the US). C# and VB programmers can also buy ControlThink's Z-Wave PC SDK (which is $70) which does not require an NDA. On the positive side, this makes many of the USB sticks for controlling z-wave networks interchangeable. On the downside, if someone wanted to do something interesting from a software perspective, they may not be able to do so.
[edit] Interoperability
While there are some downsides to the proprietary nature of the technology, there's a very big upside: interoperability. Z-wave labelled devices interoperate very well. Consumers can buy a controller from brand A, a USB stick from brand B, and light switches from brand C. They'll all work together. Some vendors do have proprietary extensions that allow enhanced functionality between devices of the same brand. But basic interoperability is assured when the z-wave logo is seen on the device.
[edit] Z-Wave Alliance
The Z-Wave Alliance is a consortium of more than one hundred independent manufacturers who have agreed to build wireless home control products based on the Z-Wave standard. Principal members include Danfoss, Intel, Intermatic, Leviton, Monster Cable, Universal Electronics, Wayne-Dalton, Z-Wave and Zensys.
[edit] Radio specifications
Bandwidth: 9,600 bit/s or 40 Kbit/s, fully interoperable
Range: Approximately 100 feet (or 30 meters) assuming "open air" conditions, with reduced range indoors depending on building materials, etc.
Frequency band: The Z-Wave Radio uses the 900 MHz ISM band: 908.42MHz (USA); 868.42MHz (Europe); 919.82MHz (Hong Kong); 921.42MHz (Australia/New Zealand).
[edit] Radio specifics
In Europe, the 868 MHz band has a 1% duty cycle limitation, meaning that a Z-wave unit can only transmit 1% of the time. This limitation is not present in the US 908 MHz band, but US legislation imposes a 1 mW transmission power limit (as opposed to 25 mW in Europe). Z-wave units can be in power-save mode and only be active 0.1% of the time, thus reducing power consumption dramatically.
[edit] Topology and routing
Z-wave uses an intelligent Mesh network topology and has no master node. A message from node A to node C can be successfully delivered even if the two nodes are not within range providing that a third node B can communicate with nodes A and C. If the preferred route is unavailable, the message originator will attempt other routes until a path is found to the "C" node. Therefore a Z-wave network can span much further than the radio range of a single unit. In order for Z-wave units to be able to route unsolicited messages, they cannot be in sleep mode. Therefore, most battery-operated devices will opt not to be repeater units. A Z-wave network can consist of up to 232 units with the option of bridging networks if more units are required.
[edit] Application areas
Z-Wave is widely used RF technology for remote control devices. Z-Wave technology with low power consumption, 2-way RF, mesh networking technology and battery-to-battery support is well suited for sensors and control units.
Z-Wave mesh networking technology routes 2-way command signals from one Z-Wave device to another around obstacles or radio dead spots that might occur.
[edit] See also
- Insteon - dual-mesh technology from SmartLabs
- ZigBee - standards-based protocol based on IEEE 802.15.4.
- EnOcean - an alternative to Zigbee, mostly for battery-less switches.
[edit] References
- ^ Products & Technology. zen-sys.com. Retrieved on 2008-03-18.
- ^ Zensys Launches Ground Breaking Fourth Generation Z-Wave Chips. z-wavealliance.org. Retrieved on 2008-03-18.
