Bluetooth has long been one of those technologies we take for granted—it’s in all our wireless headsets and increasingly in hands-free audio in our cars. But until the emergence of Bluetooth Low Energy it had trouble breaking out of the ‘headset ghetto’ beyond migrating to wireless mice and keyboards. That’s now rapidly changing, thanks to the emergence of “Bluetooth Smart” and “Bluetooth Smart Ready” devices.
Bluetooth is a connection-oriented protocol designed for continuous, relatively high-speed data streaming—making it well suited to wireless headphones, its original and still main market. Operating at its Basic Rate (BR) Bluetooth enables connections at up to 720 kbps. Bluetooth 2.0 (2004) added an extended data rate (EDR) of 3 Mbps; and Bluetooth 3.0 (2009) added a high-speed (HS) rate of 24 Mbps. The focus has long been on higher and higher speed, which works against low power consumption.
Bluetooth Low Energy was designed from the beginning to be an ultra-low power (ULP) protocol to service short range wireless devices that may need to run for months or even years on a single coin cell battery. Introduced in Bluetooth Version 4.0 (2010), Bluetooth Low Energy uses a simple stack that enables asynchronous communication with low power devices such as wireless sensors that send low volumes of data at infrequent intervals. Connections can be established quickly and released as soon as the data exchange is complete, minimizing PA on time and thus power consumption.
Like Classic Bluetooth, Bluetooth Low Energy utilizes adaptive frequency hopping to minimize interference with co-located radios. However Bluetooth Low Energy uses three fixed advertising channels, only one of which (Channel 1) is subject to possible interference from neighboring Wi-Fi devices. When a connection is requested, these same advertising channels serve to connect the devices, which then proceed to use the data channels for communication. The initiating device becomes the master—initiating connection events and determining the timing, channels, and parameters of the data exchange—and the other the slave.
One of the ways Bluetooth Low Energy manages to minimize power consumption is by switching the radio on for only very brief periods of time. Bluetooth Low Energy radios only need to scan three advertising channels to search for other devices—which they can do in 0.6-1.2 ms—while Classic Bluetooth radios must constantly scan 32 channels, which requires 22.5 ms each time. This trick alone enables low-energy devices to consume 10 to 20 times less power than Classic Bluetooth ones.
In order to be backward compatible with billions of legacy Bluetooth devices Bluetooth 4.0 introduced two types of devices:
- Single-mode chips running the compact Bluetooth Low Energy protocol stack
- Dual-mode chips that can communicate with “Classic Bluetooth” devices as well as single-mode chips in ultra-low power devices
Dual-mode chips will enable new PCs and cell phones, for example, to communicate with a wide range of medical, industrial, and consumer applications. This added capability comes at very little extra cost but opens up a lot of possibilities for machine-to-machine (M2M) communications. In the medical field, for example, smart phones will be able to connect to a wide range of wireless sensors in blood pressure monitors, blood glucose meters, even shirt-pocket EKG machines and alert your doctor should an abnormality occur.
In order to differentiate new Bluetooth 4.0 chips—at least in consumers’ minds—the Bluetooth SIG refers to single-mode Bluetooth Low Energy enabled products as “Bluetooth Smart” devices. Single-mode Bluetooth BR/EDR chips will continue to be called simply Bluetooth devices. New dual-mode chips—running both Bluetooth Low Energy and Classic Bluetooth BR/EDR protocol stacks—are now called “Bluetooth Smart Ready” devices.
Personally I think both labels were badly thought out. Bluetooth Smart—in contrast to what, the legacy Bluetooth Stupid? And Bluetooth Smart Ready—ready for what? Ready to be smart? What’s wrong with Bluetooth Low Energy and Dual Mode? OK, I see the problem with Bluetooth Low Energy, as it would highlight that Classic Bluetooth isn’t that low power; but everything is getting lower power, and it’s already officially called Bluetooth Low Energy. And Bluetooth Dual Mode couldn’t be any clearer. But the horse is already out of the barn, so best to disregard my grumbling and learn the appropriate terminology.
The rush is now on to Get Smart. The first Bluetooth Smart Ready smartphone was the Apple iPhone 4S, introduced in 2011. Since then all iPhones, iPads, and MacBooks have been Bluetooth Smart Ready hubs, able to connect to Classic Bluetooth as well as Bluetooth Low Energy—excuse me, Bluetooth Smart—devices. Windows 8 and Windows RT both support Bluetooth Smart Ready chips, as do Apple’s OS X Mountain Lion operating system for PCs and iOS for mobile devices.
Bluetooth devices are getting smarter and lower power, and the increasing operating system support for them all but guarantees that Bluetooth Low Energy devices will continue to proliferate. Moore’s law may be slowing down, but the wireless revolution is only speeding up.