Dr. Hossein Eslambolchi
May, 2012
The IEEE 802.15.4 wireless standard and the associated ZigBee Alliance is enables low-power, low-complexity networking interfaces that operate over a range of about 30 meters.
Key Points
- The ZigBee Alliance promotes application profiles running over IEEE 802.15.4 radios.
- The standard is targeted for home and building automation and controls, consumer electronics, PC peripherals, medical monitoring, and toys.
- Primary benefits are simplicity, long battery life, networking capability, reliability and low cost.
- First products are expected in 2003, with large scale product deployment in 2004.
- The technology seems well targeted and practical.
Introduction:
Zigbee is often compared with Bluetooth, but while Bluetooth is now directed more towards voice and headset applications, ZigBee is optimized for the following conditions:
- The network is static;
- There are many devices;
- It is infrequently used;
- Applications are timing-critical; and
- Data packets are small.
A primary objective of the ZigBee Alliance is to enable ultra-low power connectivity for battery powered household appliances like light switches, smoke detectors, thermostats, kitchen equipment, and TV and audio remote controls. Designs aspire to two years of use with ordinary batteries. Eventually, consumers may deploy ZigBee systems in a single-chip, “antenna-to-application” implementation.
The IEEE 802.15.4 specification describes the physical and media access control layers (ISO Layers 1 and 2) of the technology, while the ZigBee Alliance promotes a standard logical network and application software.
The low-data-rate market is currently estimated at 150 M units per year. With standardization, the ZigBee Alliance hopes to triple the size of the market.
Technology Issues
Capabilities
The ZigBee Alliance promotes a wireless technology standard for commercial applications. Primary market drivers are simplicity, long battery life, networking capability, reliability and low cost. Examples of applications include:
- Wireless home security
- Remote thermostats for air conditioners
- Remote lighting, drape controllers
- Call buttons for the elderly and disabled
- Universal remote controllers for TV and radio
- Wireless keyboard, mouse and game pads
- Wireless smoke and CO detectors
- Industrial and building automation and control (lighting, etc.)
Mesh network configurations use a decentralized, multi-hop architecture. Mesh networks provide more robust performance under adverse conditions, but incur penalties in additional complexity and power consumption.
IEEE 802.15.4 Standard
Like the more familiar IEEE 802.11 working group, the IEEE 802.15 Task Group 4 (TG4) is part of the IEEE Standards organization. IEEE 802.15.4 is chartered to investigate a low-data-rate solution with multi-month to multi-year battery life and very low complexity, and focuses on the Physical (PHY) and Media Access Control (MAC) ISO layers. It is intended to operate in an unlicensed, international frequency band. The current draft of the group (Draft D18) was approved in May 2003. The draft specifies the following radio features:
- Data rates of 250 kbps, 40 kbps, and 20 kbps
- 16-bit short and 64-bit IEEE addressing
- Support for critical latency devices, such as joysticks
- CSMA-CA channel access
- Automatic network establishment by the coordinator
- Full handshake protocol for transfer reliability
- Power management to ensure low power consumption
- 16 channels in the 2.4 GHz ISM band, 10 channels in the 915 MHz band, and one channel in the 868 MHz band
Zigbee Industry Alliance
The ZigBee Alliance was founded in 2002. Consisting of more than 50 members, its mission is “to enable reliable, cost-effective, low-power, wirelessly networked, monitoring and control products based on an open global standard.”
The goals of the ZigBee Alliance are clearly described in a June 2003 briefing. Efforts are targeted at home and building automation and controls, consumer electronics, PC peripherals, medical monitoring, and toys. They support an industry standard through application profiles running over IEEE 802.15.4 radios. The Alliance provides interoperability and certification testing.
Technical Details
A comparison of three popular wireless standards is shown below.
| Nominal Values for | ZigBee | Bluetooth | Wi-Fi (802.11b) |
| Range | 30 meters10 to 70 meters (application dependent) | 10 meters | 100 meters |
| Wake-up time | ~30 msec | ~3 seconds | ~3 seconds (est.)[1] |
| Spectrum | 2.4 GHz (worldwide)915 MHz (Americas)
868 MHz (Europe) |
2.4 GHz (worldwide) | 2.4 GHz (worldwide) |
| Modulation | DSSS[2] | FHSS[3] | DSSS (commonly) |
| Max Transmit Power | 0.5 mW[1] (-3 dBm) | 100 mW | 100 mW (typical) |
| # of Devices per network | 255 | 8 | dozens to hundreds[2] |
| Program size | 28 Kbytes | 250 Kbytes | n.a.[3] |
| Throughput | 250 kbps | 1 Mbps | 11 Mbps |
| Peak Information Rate | ~128 kbps | ~720 kbps | ~6 Mbps |
Some consider Bluetooth comparable to ZigBee; however, Bluetooth has failed to live up to expectations. Some believe this failure is due to a constantly shifting emphasis on exactly what applications it is trying to address. In comparison, the ZigBee technology has maintained its focus. It does only a few, simple things, but it does them well.
Implications for Service Providers
The ZigBee Alliance is primarily aimed at to enabling ultra-low power connectivity for battery powered household appliances like light switches, smoke detectors, thermostats, kitchen equipment, and TV and audio remote controls. Owing to the exceedingly low-power transmitters used, it is unlikely these devices could interfere with communication links sharing the same spectrum, like Bluetooth. However, communication devices could conceivably interfere with ZigBee appliances, although the ZigBee-sending device is able to resend if an acknowledgement is not returned. Such interference issues are receiving ongoing attention from most wireless standards groups. Note that ZigBee is intended to coexist peacefully with 802.11.
I believe service providers should promote the use of a residential gateway device — a broadband “point-of-presence” in each household. ZigBee technology might be useful in providing low-cost connectivity with networked appliances. This is already happening in IPTV solutions but adding Zigbee will increase and potentially provide significant revenue for service providers.
References
The ZigBee Alliance (www.zigbee.org)
Appliance Manufacturer, Smart Appliances, Microcontrollers & ICs, 30-Jun-2003
