Introduction to BLE (Bluetooth low energy)

January 22nd 2016

Created in 1994, Bluetooth technology was conceived as a wireless alternative to data cables by exchanging data using radio transmissions. The name Bluetooth came from a tenth century Danish King, Harold Bluetooth. One of the most popular applications for Bluetooth historically has been wireless audio—headsets and hands-free connectivity in cars to wireless speakers and headphones that stream music from your phone or tablet. This uses a version of Bluetooth called BR/EDR (bit rate/enhanced data rate) that is optimized for sending a steady stream of high quality data in a power efficient way. 

 

With the advent of Bluetooth Smart (BLE or low energy) for short-range communication, developers are now able to create small sensors that run off tiny coin-cell batteries for months, and in some cases, years. Many of these Bluetooth sensors use so little energy that developers are starting to find ways to use scavenged energy, like solar and kinetic.

 

BR/EDR and Bluetooth Smart are fundamentally different. Bluetooth Smart is not only low energy but, even more importantly, built on an entirely new development framework using Generic Attributes, or GATT. GATT is extremely flexible from a developer’s perspective and can be used for just about any scenario.  As a result, Bluetooth Smart not only connects devices together in an ultra-power efficient way, but also directly connects devices to applications on your smartphone, PC or tablet.

 

The BLE protocol stack is composed of two main parts: the controller and the host. The controller comprises the Physical Layer and the Link Layer, and is typically implemented as a small System-on-Chip (SOC) with an integrated radio. The host runs on an application processor and includes upper layer functionality, i.e., the Logical Link Control and Adaptation Protocol (L2CAP), the Attribute Protocol (ATT), the Generic Attribute Profile (GATT), the Security Manager Protocol (SMP) and the Generic Access Profile (GAP). Communication between the host and the controller is standardized as the Host Controller Interface (HCI). 

 

The latest Bluetooth specification uses a service-based architecture based on the attribute protocol (ATT). All communication in low energy takes place over the Generic Attribute Profile (GATT). An application or another profile uses the GATT profile so a client and server can interact in a structured way.

 

 

The latest Bluetooth specification uses a service-based architecture based on the attribute protocol (ATT). All communication in low energy takes place over the Generic Attribute Profile (GATT). An application or another profile uses the GATT profile so a client and server can interact in a structured way.

The server contains a number of attributes, and the GATT Profile defines how to use the Attribute Protocol to discover, read, write and obtain indications. These features support a service-based architecture. The services are used as defined in the profile specifications. GATT enables you to expose service and characteristics defined in the profile specification. The GATT profile is also part of the core and defined in the core specification.

 

A device that only implements BLE (which is referred to as a single-mode device) cannot communicate with a device that only implements classic Bluetooth. It is expected that many devices will implement both the classic Bluetooth and the BLE protocol stacks. These devices are called dual-mode devices.

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