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How Bluetooth LE drives IoT designs

Posted: 19 Aug 2014 ?? ?Print Version ?Bookmark and Share

Keywords:Bluetooth Low Energy? Bluetooth Smart? Internet of Things? IoT? Zigbee?

The latest versions of Bluetooth are pointing to an interesting evolution of the technology. Bluetooth Low Energy (now called Bluetooth Smart) defines very low power modes for wireless links and is gaining traction in the portable market for point-to-point connections, but the latest additions to the specification are providing key advantages in medical, industrial and home markets as part of the Internet of Things (IoT).

With the increasing focus on wearable computing, the current version 4.0 of Bluetooth LE is enabling a wide range of new devices and form factors, from the Fitbit and Nike Fuelband fitness systems even to a 'smart' basketball. The 94Fifty Smart Sensor Basketball from InfoMotion Sports Technologies measures and diagnoses both the frequency and quality of key skills critical to build confidence, versatility, and success on the basketball court using the 4.0 version of Bluetooth Low Energy.

The key to these developments has been having Bluetooth on every almost smartphone, providing a ready-made interface at no extra cost, coupled with the availability of low cost, pre-certified modules that can be easily integrated into an existing design. Bluetooth 4.1, released in December 2013, takes this a step further, using that interface to control a network rather than just an individual device. This is a fundamental change in the way Bluetooth operates and opens up a wide range of new applications for the Internet of Things.

Powering a device from a small or rechargeable battery is key for the wearable market and it is also vital for the Internet of Things. Being able to run an embedded wireless link for several years from one battery is driving the adoption of Bluetooth Smart in IoT as well.

Figure: The L2CAP channel architecture for Bluetooth Smart 4.1 enables a network of devices to be controlled, opening up the Internet of Things.

Bluetooth LE uses the same 2.4GHz ISM band frequencies as the previous Classic Bluetooth but implements a simpler Gaussian frequency shift protocol to reduce the power consumption. It also uses smaller, 2MHz channels and direct-sequence spread spectrum (DSSS) modulation, giving it lower power and more robust connections. This helps with reducing any interference from other 2.4GHz networks such s Zigbee or WiFi or cellular data such as 3G and LTE. The 4.0 and 4.1 specifications use 40 of the 2MHz channels, giving a link bit rate of 1 Mbit/s and an application throughput of 270 kbit/s. However, this lower bit rate for applications is offset by reducing the latency to 6 ms from the 100 ms of the classic Bluetooth to enable more monitoring applications. The maximum transmit power is also reduced to 10 mW, reducing the range to under 50 m, which is more than sufficient for the short range wearable and home applications.

Version 4.1, allows devices to support multiple roles simultaneously so that a Bluetooth Smart Ready product can act as a hub and a peripheral at the same time. The coexistence with other wireless technologies, notably WiFi on the same 2.4GHz band, has been improved, and dedicated channels have been added, and it is these that specifically enable IoT applications.

This comes from a Logical Link Control and Adaptation Architecture (L2CAP) that supports the higher-level protocol multiplexing, packet segmentation and reassembly and quality of service information that is needed for IoT, using 64 KB packets. The architecture is based around channels where each end-point has a channel identifier (CID). The CID assignment is relative to a particular device and a device can assign CIDs independently from other devices, making it easy to add devices to a network.

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