The ZigBee and Z-Wave short-range wireless technologies are used for remote monitoring and control. However, their specifications and applications are different. Both technologies are ideal for home-area networks (HANs), which are becoming more widespread in the U.S. Here is a comparison of these two widely used wireless technologies (see the table.
Based on the IEEE’s 802.15.4 personal-area network (PAN) radio standard, ZigBee is an open wireless standard fro, the ZigBee Alliance. The IEEE 802.15.4 standard provides layer 1 (physical layer, or PHY) and layer 2 (media access controller, or MAC) of the network, while the ZigBee stack software provides the network and applications layers.
ZigBee was established in the late 1990s as an alternative to Wi-Fi and Bluetooth for some applications. The IEEE 802.15.4 standard was completed in 2003 and updated in 2006. The ZigBee Alliance was established in 2004 to maintain the standard, continue its development, and provide interoperability testing.
As a wireless mesh networking technology, ZigBee can be used in direct communications, but most applications are based on a star or tree topology mesh network. A master coordinator node controls other connected nodes. If a node cannot communicate with another node, the two may communicate by way of links to other nodes within range acting as repeaters. ZigBee can support up to 65k nodes.
ZigBee devices operate in the unlicensed industrial, scientific, and medical (ISM) bands. The most popular configuration is in the 2.4-GHz band, where the standard defines sixteen 5-MHz channels of operation. Maximum data rate is 250 kbits/s using offset quadrature phase shift keying (OQPSK). Optional specifications provide for operation at 915 MHz (in the U.S.) with 40 kbits/s using binary phase shift keying (BPSK) modulation. A European version uses 868 MHz with 20 kbits/s.
ZigBee’s typical power of 1 mW or 0 dBm limits the free space range to about 10 meters, although longer ranges are possible depending on conditions. A big issue is co-existence with Wi-Fi and Bluetooth, which use the same band. Most transceivers have some co-existence mechanism to minimize interference. The available 16 channels typically allow the radio to find a frequency with minimum interference.
The ZigBee Alliance is a consortium of companies and other organizations supporting the development of the standard and promoting its use. There are more than 220 members. The Alliance performs testing to certify that all products comply with the standard.
One of the great benefits of ZigBee is its flexibility. It was designed so specific application software known as profiles could be developed and deployed. Profiles connect to the ZigBee stack and make it faster and easier for manufacturers to create wireless products for very specific applications. Available profiles include home automation, smart energy, telecommunications, health care, remote control (RF4CE, or radio frequency for consumer electronics), building automation, and retail services.
Ember’s EM351 and EM357 single-chip ZigBee devices include an 802.15.4 radio transceiver and an embedded 32-bit ARM cortex M3 processor. The EM351 has 128 kbytes of flash memory, and the EM357 has 192 kbytes of flash. Both have 12 kbytes of RAM and integral AES 128 encryption. Interfaces include UART, serial peripheral interface (SPI), two-wire interface (TWI), and an analog-to-digital converter (ADC). There are also 24 general-purpose I/Os (GPIOs). Ember supplies a complete development kit that includes hardware modules and all software (Fig. 1).
Meanwhile, iControl offers a ZigBee home monitor and control panel (Fig. 2). Ember and iControl have teamed up to help broadband service providers and home security companies to continue the trend toward interactive security, monitoring, and home management services. The iControl OpenHome Software Platform pairs its open, technology-agnostic software infrastructure with an all-in-one touchscreen, combining an alarm system, communications gateway, and home automation platform into one device. Ember’s ZigBee platform provides the two-way wireless networking infrastructure for the entire system.
Before it was acquired by Sigma Designs in 2008, Zensys developed Z-Wave as a proprietary wireless standard. Sigma Designs makes ICs and other products for power-line communications (PLC) as well as wireless. The standard is not open like many wireless standards, but it is available to Zensys/Sigma Design customers. Recently, the International Telecommunications Union (ITU) included the Z-Wave PHY and MAC layers as an option in its new G.9959 standard, which defines a set of guidelines for sub-1-GHz narrowband wireless devices.
The Z-Wave wireless mesh networking technology enables any node to talk to other adjacent nodes directly or indirectly through available relays. A master controller node controls any additional nodes. The nodes communicate directly with one another if they’re within range. If two nodes that want to communicate aren’t within range, they can link with another node that both can access and exchange information. A Z-Wave network can have up to 232 nodes. Multiple controllers can be set up to partition a network as required for different functions.
Z-Wave uses the Part 15 unlicensed ISM band. It operates at 908.42 MHz in the U.S. and Canada but uses other frequencies in other countries depending on their regulations. The modulation is Gaussian frequency shift keying (FSK). Available data rates include 9600 bits/s and 40 kbits/s. Output power is 1 mW or 0 dBm. As with any wireless technology, the range of transmission depends on the environment. In free space conditions, a range of up to 30 meters is possible. The through-wall range is considerably less, of course.
The Sigma Designs ZM3102 module is designed to be built into other products for monitor and control functions. In addition to the wireless transceiver, it has an onboard CPU with 32 kbytes of flash and 2 kbytes of SRAM. Also, it features a 12-bit ADC with four analog inputs. Interfaces include GPIO, SPI, UART, and pulse-width modulation (PWM). A triac controller is also provided. The module operates from 2.1 to 3.6 V dc and has very low power consumption. Typical transmit duty cycle is only 0.1%, meaning the device is usually in a sleep mode.
The more powerful ZM4101 and ZM4102 operate over a wider frequency range (Fig. 3). The 8051 CPU has 64 kbytes of one-time programmable (OTP) memory, 16 kbytes of SRAM, and 64 kbytes of nonvolatile RAM (NVRAM). The interfaces include USB and a 128-key matrix scanner. The modules also feature a four-channel LED controller. Data rate is boosted to 100 kbits/s, and AES 128 security is included as well.
Z-Wave is primarily focused on monitoring and control functions in the home and small commercial facilities. It is widely used for lighting control, security, and climate control. Other uses include smoke detectors, door locks, security sensors, appliances, and remote controls. Z-Wave is additionally used in some smart electric meters to provide consumption data for home HVAC monitors and controls.
The Z-Wave Alliance, consortium of more than 160 companies that design and sell wireless home control products based on the Z-Wave standard, plays a major role in the Z-Wave system. Currently, more than 575 interoperable products are available in 22 countries.
ZigBee and Z-Wave target the same general applications. Of the two, ZigBee is by far the more versatile since it can be configured for virtually any short-range wireless task. Profiles are readily available to minimize development time for common applications. On the other hand the protocol is far more complex, resulting in longer development times. Z-Wave uses a far simpler protocol, so development can be faster and simpler.
Z-Wave chips are available from only one source, Sigma Designs. They sell only to OEMs, ODM, and other major clients. More than 500 consumer home control products are available in stores like Home Depot and Lowes, but many don’t state that Z-Wave is used.
ZigBee chips are available from Ember, Freescale, Microchip Technology, and Texas Instruments. Complete, ready to use ZigBee modules are also available from multiple sources like Atmel, CEL, Digi, Jennic, Lemos, and RFM.
For a given power level of 0 dBm, Z-Wave’s range is greater than ZigBee simply because the lower operating frequency supports it with pure physics (Friis formula). That also translates into a more reliable connection in some applications.
ZigBee uses the widely populated 2.4-GHz ISM band, which it must share with Wi-Fi, Bluetooth, and other radios that can produce interference. Most ZigBee devices have co-existence features that help mitigate interference, yet the potential is greater in the 2.4-GHz band than the 908.42-MHz channel of Z-Wave.
- Sigma Designs
- Z-Wave Alliance
- ZigBee Alliance
- “ZigBee Versus Z-Wave Battle Continues,” Mark E. Hazen