The concept of Z-Wave technology is that it uses a low-power RF radio circuitry which is embedded into home electronics devices and systems.
Z-Wave technology is aimed at a number of wireless home automation areas including lighting, residential access control, entertainment systems and all forms of household appliances. Z-Wave can be used within a network (Home Area Network, HAN), and can therefore be used to set up all areas of home automation, possibly controlled by a single controller.
With many more home devices becoming remotely controlled, Z-Wave technology is seen as having a large market opportunity, especially with the talk about the Internet of Things, IoT becoming more widespread.
Z-Wave modules are available from a variety of sources relatively cheaply and therefore they provide an excellent format for home automation.
The International Telecommunications Union, ITU has included the Z-Wave PHY and MAC layers as an option in its G.9959 standard. This defines a set of guidelines for sub-1-GHz narrowband wireless devices.
To support and promote Z-Wave technology, and organisation known as the Z-Wave Alliance was founded.
This is a consortium of manufacturers who have products int his sector. By having a common standard, the market share is increased as users are able to select products from different manufacturers to more exactly suit their needs.
The Alliance also provides certification of products, thereby enabling standards to be maintained and user to select products they know will operate alongside each other.
Z-Wave technology basics
Z-Wave uses a mesh network topology and accordingly any non battery powered device acts as a signal repeater, enabling reliable connections from one node to the next. Battery powered devices do not act as repeaters as this would result in high levels of battery drain.
The mesh network approach means that, the more devices in the network, the more resilient it becomes.
the frequencies used for Z-Wave are below that of the normal 2.4 GHz Wi-Fi band and this enables better penetration of walls and other items found in all homes, but in addition to this, the mesh network means that data to be transferred can intelligently routed by the network to get around obstacles and thereby obtaining robust whole-home coverage.
Z-Wave typically has a range of about 100 metres or 328 feet in open air. However walls and other items in the home will considerably reduce this and therefore it is recommended that the maximum device spacing Z-Wave network is around 10 metres of 30 feet. Anything closer will provide better communications.
The Z-Wave signal can hop roughly 600 feet, and Z-Wave networks can be linked together for even larger deployments. Each Z-Wave network can support up to 232 Z-Wave devices allowing the flexibility to provide sufficient devices for a complete automated home.
Z-Wave RF interface
The Z-Wave technology uses a simple RF interface to ensure that encode and decode functions are able to be achieved with a minimum level of processing, and hence power consumption. It also ensures that the RF signal can be transmitted with the maximum efficiency.
Some of the key parameters of the Z-Wave RF interface are summarised in the table below.
|Z-Wave Technology Summary|
|Data rate||9.6 or 40 kbit/s; speeds are fully interoperable.|
|Modulation scheme||GFSK Manchester channel encoding|
|Approximate max range||Around 30 m in almost line of site situations. Reduce range is expected within buildings.|
|Frequency bands||868.42 MHz SRD Band (Europe)|
900 MHz ISM band: 908.42 MHz (United States)
916 MHz (Israel)
919.82 MHz (Hong Kong)
921.42 MHz (Australian/New Zealand)
|Duty cycle||In Europe, the 868 MHz band has a 1% duty cycle limitation|
|Power save||Z-Wave units are only be active 0.1% of the time to reduce power consumption|
Z-Wave Network layer
The Z-Wave network layer is the area of the protocol stack that controls the data exchange between the different devices, sending data over the RF or radio layer.
The network layer consists of three layers:
- Media Access Layer: Referred to as the MAC, this layer controls the basic usage of the wireless hardware. It does this in a manner that is not visible to the end user.
- Transport Layer: The transport layer within the Z-Wave technology protocol stack controls message transfer between two wireless nodes and ensures error free transmission.
- Routing Layer: The routing layer manages the Z-Wave wireless mesh capabilities. It enables the various nodes to link together and route messages from one node to another if one node is out of range of another..
In order to have a hierarchy within a wireless network, various types of Z-Wave device are specified:
- Controller: As the name implies, these devices are those that control other Z-Wave devices. Controller devices are factory programmed with what is termed a Home ID. This cannot be changed by the user.
- Slave: Slave devices are those that are controlled by controllers. Slave devices do not have a pre-programmed Home ID, but instead they take the Home ID assigned to them by the Z-Wave network controller.
- Routing slave: This form of Z-Wave slave is one that knows its neighbours and has partial knowledge of routing table. It can reply to the node from which it has received the message. It can also send unsolicited messages to a number of predefined nodes to which it has routes.
In order to cater for a wide variety of applications, the assignment of IDs is regulated and allows for a variety of scenarios. A primary controller has the function of including other nodes into the network. It does this by assigning them its own Home ID. If a node accepts the Home ID of the primary controller this slave node then becomes part of the network. The primary controller also assigns an individual Node ID to each new device that is added to the network - this is called Inclusion.
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