Is there a race for the wireless home control market?

Bernd Grohmann


EE Times

Both Z-Wave and ZigBee are low-power wireless control technologies that provide mesh networking in ******-exempt frequency bands--and that's about all they have in common. Nonetheless, they are often seen as competitors.

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. Unlike earlier technologies, Z-Wave is not limited to the hobbyist or enthusiast markets, nor to use in multimillion dollar homes, but is intended for the mass-market consumer. OEMs and installers also use Z-Wave products in light commercial applications.

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.

Z-Wave hardly overlaps with any other established wireless communication standard and is clearly complementary to Wi-Fi/IEEE 802.11 and Bluetooth. In contrast, ZigBee strongly overlaps with those and other established and emerging technologies, forcing it to compete on multiple fronts.

Z-Wave products are largely end-user products. Today, more than 170 Z-Wave-certified products are listed on the Z-Wave Alliance Web site. ZigBee lists both platforms and products on its Web site, but a closer look shows that four out of the six products listed on the ZigBee site are really development platforms or modules. In such cases, the application still needs to be added, and thus interoperability cannot be promised.

As is the case in many committee-driven standardization attempts, ZigBee suffers from the proliferation of people and organizations attempting to find their own perspectives reflected in the standard. Very often, consensus can only be reached by permitting multiple proposed alternatives as equal options. Implementing all options in low-cost, small-memory-footprint devices is not possible. Therefore, ZigBee started to assemble sets of options into software protocol stack profiles. But even those stack profiles do not unambiguously define all aspects required to achieve interoperability.

What's more, application device classes are defined and available in Z-Wave for practically every home control application. ZigBee, however, has not yet published a single completed application profile for home control.

Evolution of specifications

Multiple generations of Z-Wave have evolved over the years, mostly initiated by new requirements and incremental opportunities. Z-Wave has a strong track record of proactively driving innovation that is relevant to the consumer. What is important for both the consumer and manufacturers is that the newest product is based on Z-Wave version 5.0 and is still interoperable and backward-compatible with the first generation of Z-Wave products that came to market years ago.

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 ******-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.
The ZigBee Alliance has reportedly been working on a channel-switching solution for the past year. But OEMs have already commented negatively about the solution, which is targeted for the fall, since it enables switching only once per day; always operates the entire ZigBee network on one channel, even if different neighbors on different sides use different channels; and has a considerable delay during the channel switch in which the ZigBee cannot be used at all.

Z-Wave doesn't have those problems, since it operates in the 915-MHz band (in the 868-MHz band in Europe), which results in a longer transmission range and better penetration of walls and other objects than use of the 2.4-GHz band does.

ZigBee pays a high price 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 strongly benefits from the Z-Wave Alliance, an industry consortium of manufacturers of Z-Wave products and Z-Wave platform technology, as well as channel partners and service providers. ZigBee has a comparably strong following in the ZigBee Alliance. But the biggest difference is that instead of product divisions, more often corporate research groups are represented.

Dominating standard

It is often argued that ZigBee will succeed in setting the dominating standard for the home because the ZigBee specification is created in an open-consortium, working-group-driven process, but further review debunks this argument. In fact, by a wide margin, most technology standards in the home are first created by individual entities, grown in the market and then opened further.

Over the past few months, it has become increasingly clear that chip vendors understand the challenges and the relatively low probability of success for ZigBee. ZigBee chip vendor CEOs are setting a yearend-2008 deadline for ZigBee to fix the problems and openly describe alternative paths.

Freescale's announcement around its recent entertainment Control Platform (ECP) initiative, meanwhile, clearly cuts into ZigBee territory. Other vendors, such as Ember, have endorsed and developed ZigBee stacks but have failed to sell and promote their proprietary stacks. And Texas Instruments of late has emphasized Wibree and its associated market much more than ZigBee and home control.

The fact that Z-Wave chips are currently available from Zensys only is usually stated as a key objection to the implementation of Z-Wave in large strategic initiatives. But that has not stopped Z-Wave from creating substantial market momentum and industry support. The Danish Electricity Saving Fund, for example, has launched a large energy-saving initiative and has selected Z-Wave as its technology base.

In May, Zensys announced a licensing program for the Z-Wave technology and its single-chip designs. It has signed its first far-reaching technology ****** agreement with one of the top 10 global semiconductor manufacturers.

There are now more than 160 members in the Z-Wave Alliance, and more than 170 products are in the market.

Bernd Grohmann (BGR@zen-sys.com) is a senior director at Zensys responsible for product marketing. Prior to Zensys, Grohmann built and led the Communication Technology Centre at Danfoss A/S, where he was also served as a working group vice chair of the ZigBee Alliance. He has more than 17 years of high-technology experience including Andersen Consulting's Communication & High Tech Practice; Retix; and startup NetCS, which he founded and later merged with Isocor.

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