Bluetooth LE

Bluetooth low energy, Bluetooth LE, or BLE, marketed as Bluetooth Smart, is a wireless personal area network technology aimed at novel applications in the healthcare, fitness, security, and home entertainment industries. Compared to "Classic" Bluetooth, BLE is intended to provide considerably reduced power consumption and cost while maintaining a similar communication range.

Mobile operating systems including iOS, Android, Windows Phone and BlackBerry, as well as OS X and Windows 8, natively support Bluetooth low energy. The Bluetooth SIG predicts more than 90 percent of Bluetooth-enabled smartphones will support the low energy standard by 2018.

Bluetooth low energy is not backward-compatible with the previous, often called Classic, Bluetooth protocol. The Bluetooth 4.0 specification permits devices to implement either or both of the LE and Classic systems. Those that implement both are known as Bluetooth 4.0 dual-mode devices.

Technical Details

Bluetooth low energy technology operates in the same spectrum range (the 2.400 GHz-2.4835 GHz ISM band) as Classic Bluetooth technology, but uses a different set of channels. Instead of Bluetooth's 79 1-MHz channels, Bluetooth low energy technology has 40 2-MHz channels. Within a channel, data is transmitted using Gaussian frequency shift modulation, similar to Classic Bluetooth's Basic Rate scheme. The bit rate is 1Mbit/s, and the maximum transmit power is 10 mW.

Bluetooth low energy technology uses frequency hopping to counteract narrowband interference problems. Classic Bluetooth also uses frequency hopping but the details are different; as a result, while both FCC and ETSI classify Bluetooth technology as a Frequency-hopping spread spectrum scheme, Bluetooth low energy technology is classified as a system using digital modulation techniques or a direct-sequence spread spectrum.

Software model

All Bluetooth low energy devices use the Generic Attribute Profile (GATT). GATT has the following terminology:

·         Client - A device that initiates GATT commands and requests, and accepts responses, for example a computer or smartphone.

·         Server - A device that receives GATT commands and requests, and returns responses, for example a temperature sensor.

·         Characteristic - A data value transferred between client and server, for example the current battery voltage.

·         Service - A collection of related characteristics, which operate together to perform a particular function. For instance, the Health Thermometer service includes characteristics for a temperature measurement value, and a time interval between measurements.

·         Descriptor - A descriptor provides additional information about a characteristic. For instance, a temperature value characteristic may have an indication of its units (e.g. Celsius), and the maximum and minimum values which the sensor can measure.

Services, characteristics, and descriptors are collectively referred to as attributes and identified by UUIDs (Universally unique identifiers).

The GATT protocol provides a number of commands for the client to discover information about the server. These include:

·         Discover UUIDs for all primary services
·         Find a service with a given UUID
·         Find secondary services for a given primary service
·         Discover all characteristics for a given service
·         Find characteristics matching a given UUID
·         Read all descriptors for a particular characteristic

 Applications:

Borrowing from the original Bluetooth specification, the Bluetooth SIG defines several profiles — specifications for how a device works in a particular application — for low energy devices.

All current low energy application profiles are based on the generic attribute profile or GATT.

·         Health care profiles

o   HTP — for medical temperature measurement devices

o   GLP — for blood glucose monitors

o   BLP — for blood pressure measurement

·         Sports and fitness profiles

o   HRP — for devices which measure heart rate

o   CSCP — for sensors attached to a bicycle or exercise bike to measure cadence and wheel speed

o   RSCP — running speed and cadence profile

o   CPP — cycling power profile

o   LNP — location and navigation profile

·         Proximity sensing

o   FMP — the "find me" profile — allows one device to issue an alert on a second misplaced device.

o   PXP — the proximity profile — allows a proximity monitor to detect whether a proximity reporter is within a close range.

·         Alerts and time profiles

o   The phone alert status profile and alert notification profile allow a client device to receive notifications such as incoming call alerts from another device.

o   The time profile allows current time and time zone information on a client device to be set from a server device, such as between a wristwatch and a mobile phone's network time.