ZigBee raises a buzz
The marketing person who decided that the consumer might be a tad confused by what exactly IEEE802.11a, b or g, or even 802.15 or 802.16 are, let alone what they can do for them, deserves their money. Re-labelling the wireless standards with snappy names such as Bluetooth, WiFi and WiMax has enabled (at least some) consumers to get to grips with relatively complex technology. “Bluetooth-enabled” and “WiFi-connectivity”—as seen in mobile and notebook ads—are phrases that are beginning to breed familiarity and trust.
So next up, instead of “802.15.4”, we have “ZigBee”. Promoted by five companies, Honeywell, Invensys, Mitsubishi, Motorola and Philips , the ZigBee protocol has been designed from the ground up to support very long life battery applications.
“Users can expect a multi-year battery life when using standard batteries in a typical monitoring application,” says the ZigBee Alliance (www.zigbee.org), which now numbers 30 participant companies including semiconductor manufacturers, wireless IP providers and OEMs.
Similar and different
Wireless standards in the IEEE802 family have much in common. Technically, they all use the license-free industrial, scientific and medical (ISM) frequency bands. Although nationally there can be several ISM bands, products targeted for global markets typically use the 2.4-GHz frequency. Most products use some method of frequency hopping in an attempt (not always successful) to avoid interference with others in the same location operating at the same frequency.
The primary differences are in speed, range, and as a consequence of these two, power consumption. WiMax (802.16) is designed for wireless broadband access, can reach 50 km and 70 Mbit/s (see Electronics News 14 August 2003 page 14). The WiFi family (802.11a, b and g), designed for wireless Ethernet applications, can reach 10’s of metres in range, and data rates from 5.5 Mbit/s to 11 Mbit/s for “a” and “b”, through to 54 Mbit/s for “g”. And Bluetooth, a subset of the 802.15 “wireless personal area network” (WPAN) standard, has a range up to 10 m or so (this can be extended at the expense of increased power consumption), and a data exchange rate of around 1 Mbit/s.
The power consumption requirements decrease as the data rate decreases so that, for example, efficient Bluetooth devices can run for a few hours solely on batteries.
Commercially, the various standards have followed a well trodden path from conception to the market. In today’s competitive environment, very few companies have the resources to create and promote a de-facto standard alone. And so it is with wireless RF technology. For example, Ericsson, the Swedish telecoms manufacturer which pioneered and promoted Bluetooth, encouraged a group of like-minded companies to form an alliance to develop the technology and push for a standard via the US-based IEEE (IEEE standards tend to be globally accepted). The main advantage of standards ratification for the Alliance was that apart from ensuring compatibility between their own products, other companies leapt on the moving bandwagon because they perceived the commercial risk of designing with the technology to be low. That has certainly proved to be the case for Bluetooth, which, after a slow start, is now entering the mainstream and generating decent revenues for the Alliance members and many others. (See Electronics News 14 August 2003 front cover.)
Having invested considerable resource and capital into their technologies it is perhaps no surprise that the various organizations tread warily when asked whether they are in competition. The official line is that Bluetooth and WiFi, in particular, are complementary. But not everyone is convinced. At present a convenient divide does seem to exist, but inevitably Bluetooth will get faster, and WiFi will demand less power until the divide between the technologies blurs.
Running for years on batteries
Despite these reservations, the ZigBee Alliance sees room for its technology and is busy carving a niche. ZigBee has just passed a significant milestone with IEEE ratification of 802.15.4. This specifies the physical (PHY) and media access control (MAC) layers for the technology, and defines three license-free frequency bands: 2.4 GHz (global), 915 MHz (Americas) and 868 MHz (Europe). 802.15.4 is claimed to be a “simple but powerful packet data protocol providing high reliability through message acknowledgement, error checking, prioritised communications, direct sequence spread spectrum and the ability to change frequencies to avoid interference”.
Strictly speaking 802.15.4 and ZigBee aren’t the same thing: “It may be helpful to think of IEEE 802.15.4 as the physical radio and ZigBee as the logical network and application software,” says the Alliance’s website. Further confusion could come from the fact that 802.15 is the WPAN standard that already encompasses elements of Bluetooth. So ZigBee is more a daughter of Bluetooth than a sister.
Nonetheless, ZigBee is clearly aimed at different applications to the other wireless protocols. “ZigBee is currently the only standards-based technology that addresses the needs of most remote monitoring and control applications,” says the Alliance. The organization is hoping to encourage the broad-based deployment of wireless networks that are able to run for years on standard batteries in a monitoring applications.
ZigBee’s addressing scheme supports 255 active nodes per “network coordinator”, and multiple network coordinators can be linked together to support large networks. With support for 16 channels in the 2.4-GHz band, and 255 nodes per network coordinator (compared with eight for Bluetooth), ZigBee can comprise over 4,000 unique nodes in a single network.
Low power dictates low data transfer rate. ZigBee is said to achieve raw data throughput rates of 250 kbit/s using 2.4 GHz (10 channels), 40 kbit/s at 915 MHz (6 channels) and 20 kbit/s at 868 MHz (single channel). Moreover, the ZigBee stack is small (at 28 kByte) compared to Bluetooth’s (at 250 kByte). Transmission distance is better than Bluetooth’s though, at 10 to 75 m, depending on power output and environmental characteristics.
The annoying potential for interference is bound to exist with all the 802 technologies crowding the 2.4-GHz band. WiFi and Bluetooth use various forms of frequency hopping to avoid interference when operating in the same sphere. ZigBee avoids too much additional cost by eschewing the others’ adaptive frequency hopping schemes, preferring to rely partially on the fact that its duty cycle is likely to be extremely low, with relatively few data packets, minimising the likelihood of operation when other devices are in range. The ZigBee sender is able to resend, however, if it doesn’t see the acknowledgement packet come back from the destination.
Putting ZigBee to work
ZigBee’s forté is to link hundreds of wireless-enabled sensors into a robust, very reliable network. Each node has its own power source which is designed to last for years without replacement or recharge. Example applications include home security, remote thermostats for air conditioners, universal remote controller for TV and radio, and industrial and building automation and control. As yet there are no chips available for purchase, although the ratification of 802.15.4 has galvanised development.
Motorola, for example, is now delivering hardware and software samples to several development partners in support of the specification. AMI Semiconductor (distributed by Arrow Electronics ) has demonstrated an operational transceiver designed to the standard, and two Taiwan-based chip design houses have announced that their Zigbee products will be launched towards the end of the year. Uniband Electronic, one of the companies, expects its Zigbee chips to debut by year-end, and says the devices should cost around US$2.50 ($3.83) per chipset, about half the current price of the Bluetooth equivalent. And ITE Tech, a spin-off from major chip foundry United Microelectronics, will also launch its Zigbee wireless chip this year.
Certainly the potential applications make this a lucrative market. Unfortunately, as a fledgling technology, that might just prove to be ZigBee’s undoing. Already it’s bigger sister, in the form of Ericsson’s specialist Bluetooth division, Ericsson Technology Licensing, is eyeing the sector. The company is considering developing a derivative of the Bluetooth standard that would compete directly in industrial control and automation applications. The proposal has set backers of wireless RF technologies at odds, with critics saying that Bluetooth chip suppliers are only trying to dip into a growing market with better margins than mobiles and PDAs.
No quick bucks
Unfortunately for those looking to make a quick buck, it will several years yet before anybody makes margins from Zigbee.
Bluetooth has taken six years to reach the stage where it is becoming accepted by the consumer. And in that time the price has dropped to the point where high volumes are the only way to make money.
That’s another well-trodden path that the Zigbee Alliance looks destined to follow.
29-Aug-2003