Bluetooth Gets Smarter with Bluetooth Low Energy
By Pete Rembiszewski, Principal Prod Dev Engineer
There has been a lot of talk recently about Bluetooth 4.0, Bluetooth Low Energy (BLE), and Bluetooth Smart or Smart Ready. The question is what are they, why are they important, and what do we need to understand when creating applications or devices using each of them.
Bluetooth 4.0 is the latest release of the Bluetooth specification. This includes previous versions of Bluetooth 1.0 to 3.0, which is now called Bluetooth Classic and Bluetooth +HS, which allows transfer of data of some Bluetooth devices via Wi-Fi. It also includes BLE or Bluetooth Smart, which is a specification focusing on the efficient transfer of data. Yes, it can all get a little confusing, but lets focus on BLE or Smart, an advancement in the technology that focuses specifically on the efficient transfer of data via wireless connectivity.
Bluetooth Low Energy vs. Bluetooth Classic
BLE has actually been around for over a decade and is not new technology. We have our friends over at Nokia to thank for the original specification, known as Wibree. For those who don’t know, Wibree entered the public eye back in 2006, but it had been in the works within Nokia’s labs for about 5 years prior. Fortunately, instead of being positioned as a rival technology to Bluetooth, it ultimately became part of the specification back in 2008. The specification’s focus was to improve the amount of energy that Bluetooth devices actually used.
Bluetooth Classic was great for its ability to easily pair and stream data via a persistent connection between enabled devices, but there has always been a major issue with battery life. We have all had to deal with Bluetooth devices slowly draining the battery from the headset or from the mobile phone over time. At best, we had to recharge our battery once a week, or every few days – even when the device was on standby for most of the time. At worst, we may have to recharge our battery every few hours when using a headset to make calls or listen to music.
The typical latency for a Bluetooth Classic package is about 100ms, which is not too bad when sending a lot of data, but what if you were sending packages that were measured in number of bytes in size? BLE solves this by lowering the throughput a little bit, but drastically improves the latency to around 10ms. This means for applications that require quick sending of data (sensors, remote controls, equipment), many small messages can be sent at a fraction of the time and energy that is required by Bluetooth Classic. This means better responsiveness and longer battery life.
When coupled with a tiny CPU and a coin cell battery, a device enabled with BLE can have a battery life that is no longer measured in days, but is measured in months or years. The possibilities of what such a form factor can enable are almost endless. I have personal experience with my Garmin Vivofit activity monitor, which runs ontwo coin cell batteries. I never have to take it off or charge it. Of course, I will need to replace the battery after a year, but as someone who still wears a watch (the one with gears and springs and not the ones that have cameras and make phone calls), I am totally used to that. This makes the idea of placing a mobile sensor that needs to have the battery replaced once a year a possibility (similar to smoke detectors in our houses).
Benefits of Bluetooth Low Energy
BLE allows connectivity between two devices; one device acts as a scanner and listens for other BLE devices that act as an advertiser. When a scanning device finds another device that it knows or can utilize, it can interact with that device or simply capture the data being sent. These interactions can happen multiple times a second (number of times can be adjusted to affect battery life and responsiveness of the applications) with the fraction of overhead that comes with Bluetooth Classic.
The nice thing about BLE is that it is designed to either sit alongside Bluetooth Classic or sit by itself on the device. It uses the 2.4GHz band to transmit data. This is the same band used by Wi-Fi, game controllers, home phones, and of course, Bluetooth Classic. Since Bluetooth LE uses the same hardware as Bluetooth Classic, it can be added to any device that has Bluetooth Classic for a fraction of the cost of to the existing hardware. Both iOS and Android currently support BLE, although Android can only scan for other devices.
In a future blogs, I will dig a little deeper into some BLE implementation such as iBeacons. For more information, please check out the Bluetooth Special Interest Group. If there are any topics concerning mobile devices or development you want to cover a little deeper, please leave your comments below!