Will ZigBee wireless technology have an effect on Bluetooth? Once envisioned as the solution to all personal-area wireless connectivity, the reality of rapidly growing multimedia file sizes, connectivity needs and reliability have proven to be challenges for Bluetooth as it attempts to redefine itself away from a solid niche market of wireless headsets for cellular phones. The Bluetooth Special Interest Group has continued to address the significant interoperability and setup issues it has faced, maintaining its own value between two formidable and successful standards, with ZigBee networking penetrating into the simple, low-rate connectivity applications, and Wi-Fi nibbling away at its high-rate aspirations.
In the high-data-rate realm, Wi-Fi has emerged as the victor in the enterprise and residential space. Once a little-known technology laying low on the radar, Wi-Fi simply focused on reliably doing wireless Ethernet and at a reasonable price. The roadmap for future enhancements for Wi-Fi seems unlimited, ensuring its utility for the next decade. Its success has allowed Wi-Fi to insinuate itself into the handset world, where it is beginning to provide high-rate wireless connectivity for handsets in a hot-spot environment for both Voice over Internet Protocol and data applications. But even with the high-rate, improved security and other important extensions, Wi-Fi is based on analog radio technology that is too power hungry and slow to serve future needs for consumers in keeping their personal universes organized and synchronized.
Below Bluetooth’s knees lays the low data rate, previously unsexy space of sensors, control widgets and simple wireless networking. Long ignored by most everyone, the space has been courted and won by IEEE’s robust and well-thought-out wireless standard 802.15.4 and the ZigBee wireless technology developed by the ZigBee Alliance.
ZigBee has brought the necessary features to the sensors/control design table. ZigBee technology is based on the strong, open 802.15.4 standard, released by the IEEE in 2003 and now supported with a broad array of single-chip transceivers from a plethora of semiconductor companies. The standard is a valuable insight into the importance of open, standards-based technologies. This IEEE body worked to define not only the needs for the sensors/control space but then crafted a standard that met those needs and provided room for growth. 802.15.4 employs BPSK and O-QPSK modulation, a more robust and reliable modulation than the GFSK employed by Bluetooth technology, with a simple packet structure that ensures that information sent from one device to another arrives without error. Direct-sequence coding spreads the information over a broad channel, reducing multipath issues without adding the complexities of maintaining synchronization in a frequency-hopping system. 802.15.4 made this and other important choices to focus on amorphous networks that changed characteristics and topology over time and variations in propagation.
ZigBee networking brings native mesh networking to a simple protocol like 802.15.4. Therefore, ZigBee networks have the capability to self form and self heal, with the ability for tens of thousands of devices to actively participate in a local sensor/control network, allowing each sensor node to last from months to years to decades on a couple of inexpensive alkaline batteries. Bluetooth technology’s need for continuous maintenance of frequency and timing synchronization, required to hold down latency, means that Bluetooth can at best last days to weeks on that same set of batteries, and the added costs of keeping in synchronization more than a few nodes is a power and complexity burden that cripples most simple sensor/control networks.
ZigBee technology adds the reliable and simple mesh networking, which means that one radio can talk to a distant radio by routing messages that “hop” through intermediate nodes. This meshing capability also allows nodes to establish multiple RF routes between network nodes, ensuring that the data generated by a sensor or the control information destined for a load controller gets to its destination in a timely manner, with reliability like the wired network it replaced. ZigBee networks have multiple dimensions of optimization depending on a user’s needs: battery life, latency, network topology, the ability for the entire network to run on batteries, etc. Each of these features can be aligned to what the user’s immediate need is for network functionality.
ZigBee mesh-networking technology is developed specifically to serve the needs of the low-rate sensor/control space, providing excellent robustness and strong network flexibility as well as battery life of years when needed. Bluetooth technology’s present and future aligns ideally with its vision of supporting the small, personal, ad-hoc peer-to-peer networking between audio devices right now and potentially high-rate multimedia in the future. RCR
Jon Adams is director of technology strategy at Freescale Semiconductor Inc., a ZigBee solutions provider. Adams is representing the ZigBee Alliance.
