What happened to the promise of a connected world?
A review of wireless embedded control.

The ZigBee® specification turned three in December. ZigBee has come a long way since it was ratified in 2004, becoming more mature, better defined, and more focused. This milestone provides an interesting opportunity to reflect on the state of Wireless Embedded Control (WiEC) technologies that promised to seamlessly connect the world with millions of transceivers. Promoters of the competing WiEC technologies have promised many things to design engineers over the past few years, and the question should be asked: Have they delivered?

 

WiEC technology

First, a definition of what qualifies as a WiEC technology should be given: At the transceiver level, they are low power radios that typically have a range between 10m and 50m, with data rates under 4Mbps, and operating in any of several Industrial, Scientific, and Medical (ISM) frequency bands. Network protocols are used to control communication between the wireless nodes, ranging from simple point-to-point topologies for Machine-to-Machine (M2M) communication; through to star topologies for basic Wireless Sensor Networks (WSN); and advanced self-healing mesh networks, where all nodes are able to communicate with each other.

 

The promises of WiEC

Any design engineer who has spent sufficient time in the embedded space is likely to be familiar with the promises of WiEC technologies. These varied in their boldness and scope, but some key terms were used by all WiEC technology promoters: low power, low cost, high reliability, high security, ease of design-in, and ease of use. Along with the technical promises came bold forecasts of rapid returns on investment – the vendors would sell hundreds of millions of units, customers would realise increased efficiencies and lower costs, and the world would be covered with small, low-power transceivers that connect everything to everything else.

 

Promises Vs. Reality

Unfortunately, a few years into the hype, no single wireless technology has delivered on all those promises. As so often happens in engineering, compromises have to be made - can one technology be equally suited to controlling the lights in a home and controlling a safety valve in a factory? Although promoters of some WiEC technologies did make that very promise, perhaps they over-promised. Perhaps the silicon and stack vendors under-delivered. Perhaps engineers should have not believed that any single technology could solve all problems.

 

Why the mismatch?

There are several discernable reasons for the failure to deliver. The first is that some target performance goals are fundamentally opposed to others.

Consider low cost versus high reliability. Engineering a low-cost solution requires a holistic approach to reducing expenses. This might, for example, include reducing silicon size. To reduce silicon size it is necessary to make compromises in the transceiver architecture, thereby trading die size for reliability. The next cost-cutting step might be to trim the network stack in order to minimise the amount of code space needed in the processor running the RF transceiver. Slimming down the network stack would probably mean that intelligent features like complete node-to-node routing and network self-healing have to go in return for reduced silicon area.

Comparing low cost and high reliability provides only one example of the many concessions that have to be made when designing a wireless system, but it effectively illustrates the challenge.

 

The market contenders

Although there was no evidence to support the possibility of a grand unifying wireless technology, the initial response was the proliferation of a WiEC technologies promising to deliver just that.

The list is a veritable collection of trademarks, brands, and clever marketing: ZigBee, ANT, Z-Wave, INSTEON, Wavenis, ISA SP-100, WirelessHART, and a host of proprietary RF technologies from companies like Cypress, Nordic, TI, and Freescale and more.

The consequence is a market that is highly fragmented. Customers have a multitude of WiEC technologies to choose from, but no clear winner has emerged. Lack of adoption is feeding uncertainty, and uncertainty leads back to lack of adoption.

The good news is that this kind of pressure is exactly what is needed to create the technological equivalent of natural selection. The market is now observing a growing maturity from WiEC technologies. The hype is slowly dying down, and is being replaced with rational, measured thinking based on sound engineering. By better understanding target markets and end applications, suppliers and promoters are fine-tuning their focus and their offerings.

Take ZigBee for example, the mesh technology that promised to be in everything from low-cost consumer applications to mission-critical systems. More recently, the ZigBee Alliance has been focusing on a few select applications that play to the strengths of ZigBee, including Automated Metering Infrastructure (AMI) and commercial building automation. There is less talk now about consumer applications (where low cost needs make ZigBee less competitive than other technologies) and process automation (where higher reliability and stronger security are needed). The recent addition of the ZigBee PRO feature set addresses the real-world applications faced by its customers over the past two years, although compatibility between the evolving versions remains a challenge for some suppliers and customers.

The inability of ZigBee to address the industrial process-automation market has resulted in some spin-off technologies. Designers have realised that the RF-transceiver technology underlying ZigBee, defined by IEEE 802.15.4, may be the right transceiver if paired with a networking protocol better targeted at challenges specific to process automation. This has yielded, among others, WirelessHART, promoted by the HART Communication Foundation (HCF). The wired version of HART technology has an installed base of over 20 million units, and the wireless version aims to capitalise on that existing deployment. Members of the HCF, such as Emerson Process Management and Endress+Hauser, have fine-tuned the technology to solve problems with which they are intimately familiar. In theory, WirelessHART has all the right components to succeed in the market, although it remains to be seen how the first products, due for release in 2008, are going to perform in real-world conditions.

That is not to say that every supplier of process-automation equipment is backing WirelessHART. Honeywell Process Solutions is pushing its own proprietary OneWireless technology instead, with a promise to adopt the measures outlined in the ISA’s SP-100 specification once that is finalised.

An interesting trend to note is the migration of suppliers and customers to the IEEE 802.15.4 specification. It appears that 15.4 is a good transceiver and MAC technology for several applications, if the network protocol running on top is fine-tuned to each application. Some of these protocols are being standardised among alliances, whereas others are building their own proprietary protocols on top of a standard transceiver technology. However, the fact that many silicon vendors offer IEEE 802.15.4-compliant solutions, will eventually mean lower costs and higher performance as the competition heats up.

 

Widespread WiEC

Moving away from industrial wireless applications to consumer applications, one WiEC technology that has had a sense of purpose from its inception is Z-Wave. Z-Wave is a proprietary technology being promoted by its creator, Zensys Inc, which leads the Z-Wave Alliance of adopters. Despite being a single-supplier technology for several years, the specification has recently been opened up to other silicon vendors and Z-Wave has created a modest ecosystem of adopters by targeting home automation, and nothing else. The Z-Wave Alliance pitched the technology as a lower-cost, simpler alternative to ZigBee that still provides mesh-networking capability. Focusing on the home automation market enabled Zensys to focus on low cost, ease of use, and compatibility between equipment from multiple vendors. It is not, however, the most sophisticated wireless technology, and its exceedingly simple architecture may prevent it from being implemented in applications more complex than turning a light on or off. Similar to Z-Wave is another technology called INSTEON, which targets the same market, and has a comparable network of vendors.

Even with relatively simple WiEC technologies like Z-Wave and INSTEON, wide-spread adoption by consumers has been largely absent. The key reasons from an end-user perspective are cost and ease-of-use. For example, a regular light switch costs under $2. A ZWave enabled wireless light switch costs around $40 and, of course, it must have a wireless light source with which to communicate, adding another $40 or so. The price difference is tremendous for consumers, and the benefit is not compelling enough to justify the added expense. Furthermore, installing a wireless system is still quite challenging, requiring optimal placement and configuration. This is why ZigBee, Z-Wave and INSTEON remain in the domain of the custom-installer market, where well-off consumers spend thousands of dollars to have specialised companies come and outfit their homes with these wireless solutions. Consequently, these technologies still ship in low volumes, and healthy profits are nowhere to be found.

 

A conclusion on the connected world

When asked, a marketing manager at a major lighting-control company was of the opinion that in order to achieve shipping volumes in the millions, each node would need to cost under $5, and consumers would need to be able to install it unassisted. It is clear that this goal is still far away, however, it is not beyond reach. So even though the promise of millions of small WiEC transceivers connecting the world remains unfulfilled today, it is only a matter of time before ubiquitous connectivity becomes a reality. Businesses need it and consumers expect it. It will, however, take a better understanding of the different markets, target applications, and underlying motivations to finally achieve that goal.

 

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