The success of Z-Wave

With the improvement of the quality of life, the demand for home automation is also increasing. This demand facilitates the research and development of varieties of home automation technologies such as Z-wave, Zigbee, Insteon, X10 and so on. A New emerging industry is forming. Plenty of home automation products have been sold in the market. The fact, that different technologies are often not compatible with each other, also means if one of those technologies has particular advantages, it will be possible for it to reach the mass-market and become the common standard in this industry. In my blog the attention has been put on Z-wave technology. To evaluate the success of Z-Wave standard, I am going to analyze it based on two aspects: market and technology.

Home Automation Market

As mentioned in previous section, in order to have a mass-market for home automation, some issues should be addressed, including cost, energy, installation complexity and functionality.

Different from other technologies, Z-wave is clearly targeted at home control application. Its single application determines that Z-wave chip needs simple structure and less memory. Therefore, the cost of Z-wave chip is rather low compared to the others. Home control application also requires the transmission of tiny amounts of data. With very short transmit times and efficient design, Z-Wave nodes can easily be powered from a battery, with a long lifetime.

Z-Wave based systems are easy to install and use, and allow products from all members to interoperate seamlessly between multiple home control applications and multiple vendors.

Z-wave technology

Z-wave protocol supports mesh network structure which is able to covers large area. More advantages of mesh network are its “self configureing” and “self healing” functions as mentioned in previous section. Its protocol pattern insures the success of data transmission via ACK frame. To secure the data transmission and keep hackers out of the building, the security model has been embedded in the new generation of Z-wave chip.

Among all the advantages of Z-wave standard, its features of low cost and low energy are the most attractive, compared to other standard. However, on the other side it also implies low data transmission rate, which limits the applications of Z-wave standard. For industrial environment requiring large data transmission, Z-wave standard is not a good choice. However, I think that its advantages such as the convenience, low cost and low energy waste will make Z-wave successful in the home automation market.

Standardization of Z-Wave

A standard can be defined generally as a construct that results from reasoned, collective choice and enables agreement on solution of recurrent problems. A standard can be viewed as striking a balance between the requirements of users, the technological possibilities and associated costs of producers, and constraints imposed by goverment for the benefit of society in general.

More functionally, an industry standard is a set of specifications to which all elements of products, processes, formats, or procedures under its jurisdiction must conform. The process of standarization is the pursuit of this conformity.

As a standard, it must have four basic functions: Quality/Reliability, Information standards, Compatibility/Interoperability, Variety Reduction. I am going to analyze Z-wave standard based on these four basic function.



Quality/Reliability
Standards are developed to specify acceptable product or service performance along one or more demensions such as functional levels, performance variation, service lifetime, efficiency, safety and environmental impact.

Many RF technologies communicate across the public bands. Consequently, the public band are crowed with interference, resulting in poor reliabilty for most RF technologies. Z-Wave minimizes these "noise and distortion" problems by using transmission mechanisms such as 2-way acknowledgement, condensed frame formats and random back-off algorithms, ensuring highly reliable communication between all the devices in the network



Information Standards
Standards help provide evaluated scientific and engineering information in the form of publications, electronic data bases, terminology, and test and measurement methods for describing quantifying, and evaluting product attributes.

All the information about Z-Wave technology is open to the users, including product information, publications, evaluation of Z-wave technolgy and so on. The related information could be found in the websites:
http://www.zen-sys.com
http://www.z-wavealliance.org
http://www.zwaveworld.com



Compatibility/Interoperability
Standards specify properties that a product must have in order to work with complementary products within a product or service system.

In Z-Wave, interoperability is guaranteed by use of the appropriate Device Class Specification and by the Z-Wave Certification Program. The Device Class Specification governs standardization on command and device level for all home control products. The work is carried out in the Z-Wave Alliance ensuring that all relevant market inputs from Z-Wave partners are injected into the Device Classes. The certification program ensures that all products, which carry the Z-Wave logo, have gone through the certification process.



Variety Reduction
Standards limit a product to a certain range or number of characteristics such as size or quality levels.

All the products carried Z-wave logo work in the same frequency bands and are applied in the mesh network. They have the same protocol stack and frame structure. Before puting in market, the products must go through the Z-Wave certification and the Device Class Specification to ensure the achievement of requirments and quality.



Z-Wave is not an open standard. The industry leading device specifications of Z-Wave will be made available royalty free based on a reasonable and non-discriminatory (RAND)-Z model. With RAND-Z Zynsys promises to license the technology at no charge. But the implementers still have to get the licenser's permission to implement. So while the licenser may not make money off the deal they can still stop any products they don't like or do more subtle things like drag out the licensing process. To accelerate the adoption of Z-Wave standard, Z-Alliance and its members strive to develop and open Z-Wave technology further. The figure following shows the standardization process of Z-Wave.




Figure from :http://www.z-wavealliance.org

Battles between the standards for wireless sensor network

Wireless Sensor Network (WSN) is one of the most popular applications in the area of wireless technology. However there is no uniform standard yet since it is an emerging application. Today, many research centres and organizations all over the world are working on the developement of this technology and differents standards have been introduced. They are ZigBee, Z-Wave, Bluetooth, Wibree, 6loWPAN and so on. Among those technical standards, ZigBee and Z-Wave are the maturest, competing to become a standard for WSN. I have already described Z-Wave standard in the previous articles. Next let's look at ZigBee technology and analyze theirs advantage and disadvantage.

ZigBee is a low-cost, low-power, wireless mesh networking standard, using low-power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). ZigBee is defined by the ZigBee Alliance.

Both Zig Bee alliance and Z-Wave include long lists of well-known corporations. Both technologies are battery-operated and, therefore, consume very little power. Each employs mesh networking, which enables daisy-chaining nodes throughout a premises and the utilization of multiple communications paths. Although the range of a node is a maximum of 30 meters, mesh networking makes the range essentially limitless in high-density applications where there are many nodes.

Z-Wave is clearly targeted at home control applications. Those include not just traditional home control applications, such as lighting, HVAC, drapes, windows shades, garage doors and integration with alarm panels, but also entertainment control and digital home healthcare devices.

In contrast, ZigBee does not have a clear target market but instead broadly addresses practically all applications: toys, body network devices, PC peripherals, home control, large-scale building controls, industrial sensor networks, logistics, RFID and even homeland security and military-battlefield applications. The challenge for ZigBee is that those target segments have vastly differing requirements.

Mesh networking is a suitable vehicle to extend the reach of wireless communication to cover entire homes. But since both ZigBee and Z-Wave operate in license-exempt frequency bands, interference could destroy robustness and reliability.

For ZigBee, this risk is especially large, since the vast majority of IEEE802.15.4 solutions offered today use the 2.4-GHz band exclusively. Wireless LANs use the same band and typically operate at between 100 and 1,000 times the transmitter power. Further, more and more WLAN users operate directed antennas that are available in mass retail. With the use of WLANs for bandwidth-hungry applications (such as HDTV video) growing, and with 802.11n increasing WLAN use in consumer electronic applications, the risk for interference rises.

The leadership of the ZigBee Alliance publicly denies that a problem exists and points to the interference risk at 915 MHz, where hardly any high-volume data devices exist for home use. But simulations performed by the task group that developed IEEE 802.15.4-2006 clearly show that WLAN heavily interferes with ZigBee. Measurements by OEMs have confirmed these simulations. The ISA SP100 group, citing the interference problems, has rejected the idea of using 15.4 as defined and used in ZigBee today.

In fact, several OEMs have left ZigBee and joined Z-Wave. Large initiatives, including a $150 million project at Telepathx, have abandoned ZigBee after measuring interference, and the U.S. Army FCS Mobile Node Test at White Sands, N.M., reported harmful interference between WLAN and ZigBee.

In comparision with Z-Wave, ZigBee pays a higher price. The reason is not just for its "committee"-inflated complexity and proliferation of options, but also for the more-complex 15.4 DSSS/O-QPSK PHY and the very feature-rich MAC protocol layers. Its solutions are more than twice the size of the Z-Wave memory and chip. The level of complexity of Z-Wave is comparable to the lowest-cost two-way wireless solutions in the market. Further developments in semiconductor technology will not significantly alter that ratio. This gives Z-Wave a sustainable cost benefit over ZigBee and has contributed to the volume leadership Z-Wave enjoys in wireless home control.

Z-Wave security model

The original version of Z-Wave used a security algorithm called triple Data Encryption Algorithm (DES) with 56-bit key, which is a cipher developed by IBM and then selected as an official standard for the United States in 1976. However, Later on Z-Wave gave up this security layer. According to John Walters, Z-Wave Alliance vice president, "The Z-Wave 100 series single chips had triple DES, but not a single customer used it", said Walters. "When we were developing the 200 series we asked our customers about security and everyone said it was not need it."

People get worried about the security issues of Z-Wave without the security layer. John Adams, voice chair of the ZigBee Alliance "is okay for hobby-type tools. But once home automation becomes the way we expert thing to be, then Z-Wave's lack of security becomes a horrible impediment." He then mentioned that since there is no encryption for the Z-Wave messages, someone could set up a sniffer and watch any message and see the addresses of source and destination;he can then becomes that device and spoof a message.

Having realized this issue, Zensys announced the launch of its fourth generation Z-Wave single chip on January 7, 2008. The new generation chip supports 128-bit security encryption called Advanced Encryption Standard (AES), which is a cipher selected by the United States as an official standard. AES is much more reliable than DES. Recently DES has been superseded by the AES.

Z-Wave network overview

Wireless mesh networking technology is applied in the Z-Wave. Mesh networking means that all the nodes can participate in routing data and nodes connect to each other via multiple hops . Mesh network is a "self configuring" network; a new node can be added automatically into network without needing any adjustments. It is also a "self healing" network, since the network automatically finds the fastest and most reliable paths to send data, even if nodes are blocked or lose their signal. Mesh network supports Non-Line-of-Sight (NLoS) network configurations where wireless signals are intermittently blocked, because the data is able to get around obstacles and reach the destination via other nodes.


The picture gives an example for routing method in the z-wave mesh network. The user in living room want to control the lamp A in the dining room. However the straight transmission is blocked by reflection from the oven in the kitchen. Z-Wave automatically selects an alternative signal route and ensure the command is carried out.

From:http://www.z-wavealliance.com

The Z-Wave network contains two kinds of nodes: controller nodes and slave nodes. Controller nodes are responsible for sending out the commands to other nodes. The routing table is recorded in the controller nodes and kept updated constantly. The primary controller has the capability to include or exclude nodes in the network. The examples of controllers are remotes controllers and internet gateways. Slave nodes reply on and execute the commands. They both can be used for routing data.

Each Z-Wave network has a unique identifier called Home ID to seperate itself from others. The Home ID is a 32 bit unique identifier that is pre programmed in all controller nodes. Each node also has its own unique 8 bits Node ID assigned by the controller.

Z-Wave protocol stack overview

From: http://www.zen-sys.com

Z-Wave started as a proprietary wireless protocol oriented to the residential control anutomation market. Z-Wave protocol is a low bandwidth half duplex protocol intended to offer reliable wireless communication in a low cost control network in the house. The protocol is not designed to transfer large amounts of data or to transfer any kind of streaming.

The protocol consists of 4 layer as figure shows, the MAC layer, the Transfer layer, the Routing layer and the application layer.

The MAC layer controls the radio frequency medium. The data stream is manchester coded and use FSK modulation. A standard collision-avoidance method is applied in this layer which prevents nodes from starting to transmit while other nodes are transmitting. If media is busy, the transmission is delayed by a random number of milliseconds.

The Transfer layer controls the transfer of data between two nodes including retransmission, checksum check and acknowledgements. This layer contains 4 basic frame formats, which are singlecast frame, multicast frame, broadcast frame and transfer acknowledge frame. Different types of frames are identified in the frame header. If frame is successfully received, ACK frame is sent back to the source node. However, multicast and broadcast frames don't get ACK so these types of frames cannot be used for reliable communication. The solution is to send a singlecast frame to each destination node following multicast and broadcast frame.

The routing layer controls the routing of frames from one node to another in the network. The Z-Wave network contains two kinds of nodes: controller node and slave node, which will be described later. Both controllers and slaves can participate in routing of frames in case they're always listening and have a fixed position. The layer is responsible for routing a frame and ensuring that the frame is repeated from node to node. In the case of the controller device, the routing layer is also responsible for scanning the network topology and maintaining a routing table.

The application layer is responsible for decoding and executing commands in a Z-Wave network.

Z/IP Program: As a big step to broaden adoption

As an accelerator for the adoption of Z-Wave wireless home-control technology, the Z/IP program drives convergence of Z-Wave and TCP/IP. As with all previous Z-Wave protocol advances, Z/IP remains backwards compatible with existing Z-Wave products while adding compliant TCP/IP services to Z-Wave nodes and allows the use of Z-Wave device and command classes in TCP/IP networks.

Compatibility with the Internet Protocol’s Transmission Control Protocol (TCP/IP) enables remote access to a Z-Wave home-control system in a standardized way from the Web browser of any PC or cellphone without loading special software applications onto them, said Zensys marketing EVP Lew Brown. Compatibility also simplifies the integration of Z-Wave systems into increasingly popular IP-based control systems, he said.

"Using TCP/IP transmission will help to accelerate the adoption of applications for multiple uses of Z-Wave around the home, as well as interoperability among multiple vendors," added Martin Manniche, a senior director at Cisco’s Linksys division. Cisco is an investor in Zensys.

With a converged Z-Wave/IP standard, "all Z-Wave network nodes would be addressable from any browser in the world, and all devices in the home would be on a single IP network," a spokeswoman continued. The advanced standard “will remain backwards compatible with existing Z-Wave products while adding compliant TCP/IP services to Z-Wave nodes,” she noted.

In the future, we can use Z-Wave/IP technology to select remotely Z-Wave devices in the home to stream Internet content from the Web, Brown noted. That capability will become more important as Zensys transitions from its current-generation technology, which delivers control commands wirelessly at up to 40kbps, to a 200kbps version in chips meant for the U.S. market, he noted. Z-Wave started out as a 9.6kbps technology.