Bluetooth® wireless technology has received a lot of attention for wireless connectivity.
Now it's ZigBee's turn. ZigBee™ is the name of an alliance of companies formed around IEEE's recently approved (May 2003) 802.15.4 specification for low data rates in the Industrial, Scientific and Medical (ISM) radio bands. The ZigBee protocol promises to provide longer battery life (months or even years on a single battery charge) and to be a lower-cost alternative to Bluetooth for wireless sensing and control applications.
The ZigBee alliance—which includes such companies as Invensys, Honeywell, Mitsubishi Electric, Motorola, and Philips—takes its name from the zig-zag path of bees that form mesh networks between flowers. ZigBee proponents believe mesh networking is the key to unattended wireless systems in the home, business, or industry. Mesh networking, they say, provides redundancy required for unattended system operation and is essential for the reliability of the ZigBee network.
The IEEE 802.15.4 wireless standard was developed specifically for remote monitoring and control. Since it has been ratified, engineers can start considering a standards-based alternative to proprietary wireless sensing.
"802.15.4 is the first standard I am aware of that expressly focuses on low cost and low power and fairly modest bit rates," says Robert Poor, a technical editor for the 802.15.4 standards specification, and chief technology officer and co-founder of Ember Corporation. Ember was established to provide embedded wireless networking solutions and is one of the participants in the ZigBee Alliance. The 802.15.4 bit rates are specifically limited to 250Kbps compared to 1Mbps for Bluetooth.
The standard defines transmission and reception on the physical radio channel (PHY), and the channel access, PAN (personal area network) maintenance, and reliable data transport (MAC). ZigBee defines the topology management, MAC management, routing, discovery protocol, and security management, and includes the 802.15.4 portions.
To meet global regulatory requirements, ZigBee is designed to work in either the 868-through-928 MHz band to cope with regional differences, or 2.4 GHz ISM band typically available worldwide.
"Where we see the market really taking off is in the home," says Kirsten West, founder of West Technology Research Solutions, a market research and consulting company focused on emerging technologies. "There is a lot of activity occurring now in China for wireless for home automation, and ZigBee is going to be the answer." In a report published on ZigBee opportunities, West predicts that in the future it will be common to find as many as 50 ZigBee chips in the house.
The motivation for wireless connectivity in Asia/Far East is conservation. For example, washing machines cannot be run after 8:00 pm, so when owners are not at home, they must activate the appliance remotely by cell phone so the washing cycle is completed before the required deadline. Mesh networking aids such unattended system operation. The star topology used in cell phones and wireless LANs has a central control point that requires physical movement to improve connectivity. Mesh networking allows alternative paths to routing data to the target device and this process is transparent to the user. To provide low cost, the system requirements for ZigBee are much less than Bluetooth and other wireless protocols. Also, ZigBee's bandwidth is lower than Bluetooth, but the range is greater and the number of nodes is much greater. The larger node capability means that a large number of nodes can be initially established in a network or added (up to 255) as technology and system requirements change. Bluetooth is limited to eight nodes per network. Many of the potential ZigBee applications, such as networked lighting in office buildings, would require dozens and even several dozens of nodes.
Available Hardware and Design Tools
The keys to designing end products are integrated circuits, software, and design and deployment tools. Some of these ICs, software, and tools are in production and others are in pre-production or sampling/evaluation mode. The availability and choices of hardware and design tools simplify the development and reduce the risk of implementing wireless networks. With ZigBee, the risk is reduced because the hardware is not proprietary to a single supplier but is standards-based. OEMs interested in designing wireless sensing or wireless control can already evaluate the potential of ZigBee.
Ember and ChipCon co-designed and introduced an integrated circuit—ChipCon's CC2420 and Ember's EM2420—that are both 802.15.4-compliant and termed ZigBee-ready (the ZigBee protocol has not been finalized). Ember's EM2420 includes the software stack that allows the user to make the radio into a self-organizing network.
Ember's evaluation kit is comprised of a dozen wireless nodes that can be simply placed at various locations in a facility. By attaching any one of the nodes into the serial port of a PC, an engineer can immediately monitor the network connectivity and perform tests such as pinging, test route, and pairing (making application layer associations between node A and node B). They also have a developer's kit that is a dozen wireless nodes on a breakout board with an Ethernet back channel to upload firmware and develop code for a protocol stack and load the code into the wireless node.
"At this point in time this is an early adapters' market for ZigBee," says George Karayannis, vice president of sales and marketing, Helicomm. Helicomm offers ZigBee-Ready Starter Bundles, based on their IPWiNS software platform and ZMD's RFIC silicon products. The bundles allow OEMs to quickly prototype wireless mesh networking in their environment with their sensors. This provides customers who want to be early adapters with a migration path to ZigBee. Even though the ZigBee 1.0 spec will not be completely ratified until late 2004, you will see a lot of OEMs starting to design in both 15.4 and ZigBee, says Karayannis. It looks like residential lighting control could be among the first applications.
Another semiconductor supplier sampling an RF data modem designed for the 2.4 GHz 802.15.4 and ZigBee standards is Motorola. Their RF modem can be mated to an 8-bit MCU with the 802.15.4 MAC and variety of sensors including CMOS pressure, smoke detector IC and accelerometers that they also manufacture. Motorola plans on offering platform solutions, reference designs, and software to support the ZigBee standard.
Ember ChipCon, Helicomm, Motorola, and other companies demonstrated their ability to meet the 802.15.4 standard, the foundation for ZigBee, at the ZigBee Alliance Open House held on November 19, in San Jose, CA.
The Stackup: The protocol stack for IEEE
802.15.4 and ZigBee uses a cost-effective. 8-bit microcontroller to
provide the silicon hardware and run the software. The full stack is less
than 32 kbytes, while a simple node-only stack can be as small as 4
With companies such as Honeywell, Invensys, Mitsubishi Electric, Samsung, ABB, Danfoss, Eaton, Oki, Omron, Silicon Wave, and other equipment manufacturers as either promoters or participants in the ZigBee Alliance, several new ZigBee wireless sensing products can be expected in the near future. Until the ZigBee protocol is finalized, these products must be considered ZigBee-ready.
For example, Danfoss A/S, a member of the alliance, has 802.15.4/ZigBee technology in house today. According to Bernd Grohmann, manager of Danfoss' Communication Technology Centre, "The strengths of the underlying IEEE802.15.4 technology, performance of first chip implementations, focus, and direction of the ZigBee work, and the overall momentum within and around the ZigBee Alliance have convinced us to expect ZigBee to be one of the key wireless technologies in our future." Danfoss is continuing to work with WLAN and Bluetooth technologies in areas where they are appropriate. The company recognizes the potential of ZigBee for new sensor and control applications and is well beyond the evaluation phase in several of Danfoss' key products, which include refrigeration and air conditioning, heating, and industrial automation.
ZigBee Alliance promoter Ember has a customer that makes data loggers to manage cold-chain information. A wireless data logger can be placed in the shipping crate of temperature-sensitive produce or pharmaceutical products. The wireless data logger allows measurements to be made and transmitted to a receiver (one of the repeater nodes) at the customer's dock without requiring the truck to be unloaded, especially if the shipment would eventually be rejected due to unacceptable temperature exposure. This savings in time provides a substantial cost savings to customers. This product was in pilot production in late 2003.
Welcome wagon: as the newest kid on the
wireless block, ZigBee was developed to address different applications
than existing wireless standards.
Today, embedded wireless networking software is 100 percent proprietary. With the industry experts working to develop the ZigBee network layer and protocol stack and the lessons learned from Bluetooth as their experience factor, Alliance members believe that the risk involved in initiating a design based on the 802.15.4 standard is minimal, even though the ZigBee protocol is not finalized and approved. Helicomm's Karayannis says, "In the worst case scenario, ZigBee would fail to catch on broadly, in which case the ZigBee network layer would be available as yet another proprietary solution, but one built by experts from across the industry."
Some ZigBee supporters, such as Jose Gutierrez, program manager for the ZigBee specification and principal engineer in Eaton Corporation's Innovation Center, fear that adding last-minute features to ZigBee to make it more complex will imply additional cost, more difficult testing and debugging, higher implementation risks, and higher power consumption. Existing alliance members are working hard to avoid those changes. A draft specification was ready for review by Alliance members in early 2004 with final review target for Q3, 2004. Gutierrez feels confident that wireless sensing based on the 802.15.4 standard is ready to be evaluated for its potential.
Sky's the Limit: ZigBee's market growth
can easily exceeed 500 million units by 2008 if the specification is
approved on time and efforts to promote the benefits of 802.15.4 and
ZigBee are successful.
In a ZigBee presentation at the 2004 Consumer Electronics Show in Las Vegas the cost of the 802.15.4 bill of materials was shown as half that of a Bluetooth node. That kind of cost reduction should generate some serious interest, especially once the ZigBee standard is approved. As Helicomm's Karayannis notes, "You have about a 9- to-12-month window to catch your competitors off guard."