28 I D D Is the ZigBee wireless standard, promoted by an alliance of 25 firms, a big threat to Bluetooth? B~ Chris Evans-Pughe WIRELESS STANDARDS seem to he breeding. Perhaps as soon as you get two of them nicely settled in an unlicensed hit of spectrum it‘s inevitable. Late last year, ZigBee arrived in the 2.4GHz band, joining the now well-established Bluetooth and Wi-Fi. ZigBee looks rather like Bluetooth but is simpler, has a lower data rate and spends most of its time snoozing. This characteristic means that a node on a ZigBee network should be able to run for six months to two years on just two AA batteries, claim backers. However, there are questions about ZigBee’s viability The target of building automation as the main application makes technical sense but it is a field notoriously slow at adopting new technologies. Those with long memories may remember from ten years back how LonWorks control networks were going to revolutionise our homes and yet we are still waiting. In other proposed applications, ZigBee seems to tread on Bluetooth’s toes hut the technical and price advantages are marginal and unsubstantiated: there are no finished ZigBee chips and low prices necessitate very high volumes. The ZigBee promoters got together three years ago because, Bluetooth wasn’t suitable for building automation and industrial control. “These applications needed lower cost, better latency and [lower] power consumption than Bluetooth could give,” explains Nick Horne, group leader of the radio communications products group at Cambridge Consultants Ltd. (CCL), one of the 25 ZigBee Alliance members. Proprietary wireless control systems already exist for building automation, X-10 for instance, but they have fairly limited use. The theory behind the ZigBee effort is that such a price-sensitive field requires the economies of scale of a global standard for it to take off in a big way The hope is that at just $2 a throw, ZigBee chips will open up the market for remote wireless control of light fittings, heating, ventilation and security systems in commercial and residential buildings. A x .- EARLY PROMOTION I Philips, Motorola, Honeywell, Invensys and Mitsubishi Electric started promoting ZigBee when they formed the ZigBee Alliance in October 2002. This was once .- they had secured the physical layer (PHY) and media B access control (MAC) under the IEEE 802.15.4 WAN & [IN COULD B[E 50 ~[IG~[E[E [[D[E~[IC[ES [F[Iv[E YEARS’ u[IM[E, uw[E[w[E WOME AND EVEWUMALLV AS MANV AD U58 - 2 (Wireless Personal Area Network) standard.typical commercial application might be a control system for changing the ceiling light patterns in a large conference room. A ZigBee radio module on each of the light fittings would eliminate the spaghetti of control wiring usually needed to run to and from the central control panel to each light. Remote meter reading and medical sensors are also on the ZigBee list of target applications as they would benefit from low power consumption and standardisation. Longer-term aims are for ZigBee to colonise Bluetooth territory -consumer electronics, PC peripherals and even toys. “We believe it fits a gap between wireless LAN and point-to-point data links,” says Michael Eckhardt, Philips Semiconductors’s ZigBee product marketing manager. Bluetooth players are not convinced. “ZigBee is a dandy technology for controlling home appliances that are not transferring a lot of data and that are mainly asleep. But Bluetooth can also go to sleep. You can get months of use out of a Bluetooth wireless mouse,” comments Eric Janson, Cambridge Silicon Radio’s (CSR) vice-president for worldwide marketing. “And the cost claims also hear close examination.” Bluetooth is already under $5 in cellphone volumes although no one is saying that out loud. THE ZIG-ZAG COMMUNICATIONS DANCE Philips is a bigpromoter of ZigBee. The technology has been living under various guises at Philips for four years. It started life as HomeRF Lite (a sub-spec of the defunct HomeRF, which has now been ousted by Wi-Fi). Since then, it‘s had name changes to RF Lite, Firefly, RF EasyLink and finally. last summer, it became ZigBee. The whimsical name comes from the ZigBee Principle, the zig-zag dance bees do to tell their colony mates the location, distance and direction of new food sources. However none of ZigBee’s previous incarnations have taken off; all were aimed at the same + I. 29 IEE Review I Maah 2003"UMESE APPLUCAUUQWS NEEDED LOWER CQOU, BEUUER LAUEWCV AND LOWER POWER CQNSUMPUUOW UMAN BLUEUQQUM COIUIUD CAMBRIDGE CONSULTANTS GOWE"- NICK HORNE, GROUP LEADER, applications: home automation, input devices etc. Today, the alliance members believe that the market is now suitably tuned into wireless technology, through the success of Bluetooth and Wi-Fi, to take to ZigBee and understand its advantages. The ZigBee standard can operate in the 2.4GHz band or the 868MHz and 915MHz ISM (industrial, scientific and medical) bands used in Europe and the US respectively It sits below Bluetooth in terms of data rate: 250kbps at 2.4GHz (compared to Bluetooth's 1Mbps) and 20-40kbps in the lower frequency bands. The operational range is 10-75m, compared to 1Om for Bluetooth (without a power amplifier). One other important difference between ZigBee and Bluetooth is in how their protocols work. ZigBee's uses a basic master-slave configuration suited to static star networks of many infrequently used devices that talk via small data packets. This aspect suits ZigBee to building automation and the control of multiple lights, security sensors and so on. Bluetooth's protocol is more complex because it's geared towards handling voice, images and file transfers in ad hoc networks. Bluetooth devices can work peer-to-peer and support scatternets of multiple smaller non-synchronised networks (piconets). The protocol, however, only allows up to eight slave nodes in a basic master-slave piconet set-up. ZigBee allows up to 254 nodes. Masters can talk to each other and the number of31 .~ admits Philips’s Eckhardt, “hut they will be inherently lower cost once they hit ”OF VOIUI LOOK AU UWE SPEED UNAU UWESE UNDUSUWUED ACCEPU UWUS SUUFi, OU CAi UARE maturity,” Developers believe that it is the smaller AGES” -ERIC JANSON,
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