Bluetooth Low Energy

Bluetooth Low Energy (Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart) is a wireless personal area network technology designed and marketed by the Bluetooth Special Interest Group (Bluetooth SIG) aimed at novel applications in the healthcare, fitness, beacons, security, and home entertainment industries. It is independent of classic Bluetooth and has no compatibility, but Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) and LE can coexist. The original specification was developed by Nokia in 2006 under the name Wibree, which was integrated into Bluetooth 4.0 in December 2009 as Bluetooth Low Energy.

Compared to Classic Bluetooth, Bluetooth Low Energy 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 macOS, Linux, Windows 8, Windows 10 and Windows 11, natively support Bluetooth Low Energy.

Compatibility

Bluetooth Low Energy is distinct from the previous (often called "classic") Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) protocol, but the two protocols can both be supported by one device: the Bluetooth 4.0 specification permits devices to implement either or both of the LE and BR/EDR systems.

Bluetooth Low Energy uses the same 2.4 GHz radio frequencies as classic Bluetooth, which allows dual-mode devices to share a single radio antenna, but uses a simpler modulation system.

Branding

In 2011, the Bluetooth SIG announced the Bluetooth Smart logo so as to clarify compatibility between the new low energy devices and other Bluetooth devices.

* Bluetooth Smart Ready indicates a dual-mode device compatible with both classic and low energy peripherals.
* Bluetooth Smart indicates a low energy-only device which requires either a Smart Ready or another Smart device in order to function.

With the May 2016 Bluetooth SIG branding information, the Bluetooth SIG began phasing out the Bluetooth Smart and Bluetooth Smart Ready logos and word marks and reverted to using the Bluetooth logo and word mark in a new blue color.

Target market

The Bluetooth SIG identifies a number of markets for low-energy technology, particularly in the smart home, health, sport, and fitness sectors. Cited advantages include:
* low power requirements, operating for “months or years” on a button cell.
* small size and low cost.
* compatibility with a large installed base of mobile phones, tablets, and computers.

History

In 2001, researchers at Nokia determined various scenarios that contemporary wireless technologies did not address. The company began developing a wireless technology adapted from the Bluetooth standard which would provide lower power usage and cost while minimizing its differences from Bluetooth technology. The results were published in 2004 using the name Bluetooth Low End Extension.

After further development with partners, in particular Logitech and within the European project MIMOSA, and actively promoted and supported by STMicroelectronics since its early stage, the technology was released to the public in October 2006 with the brand name Wibree. After negotiations with Bluetooth SIG members, an agreement was reached in June 2007 to include Wibree in a future Bluetooth specification as a Bluetooth ultra low power technology.

The technology was marketed as Bluetooth Smart and integration into version 4.0 of the Core Specification was completed in early 2010. The first smartphone to implement the 4.0 specification was the iPhone 4S, released in October 2011. A number of other manufacturers released Bluetooth Low Energy Ready devices in 2012.

The Bluetooth SIG officially unveiled Bluetooth 5 on 16 June 2016 during a media event in London. One change on the marketing side is that the point number was dropped, so it is now just called Bluetooth 5 (and not Bluetooth 5.0 or 5.0 LE like for Bluetooth 4.0). This decision was made to “simplify marketing, and communicate user benefits more effectively”. On the technical side, Bluetooth 5 will quadruple the range by using increased transmit power or coded physical layer, double the speed by using optional half of the symbol time compared to Bluetooth 4.x, and provide an eight-fold increase in data broadcasting capacity by increasing the advertising data length of low energy Bluetooth transmissions compared to Bluetooth 4.x, which could be important for IoT applications where nodes are connected throughout a whole house. An 'advertising packet' in Bluetooth parlance is the information that is exchanged between two devices ''before'' pairing, i.e. when they are not connected. For example, advertising packets is what let you see the name of a Bluetooth device before you can pair it. Bluetooth 5 will increase the data length of this advertising packet. The length of this packet in Bluetooth 4.x was 31 bytes (for broadcast topology).

The Bluetooth SIG released Mesh Profile and Mesh Model specifications officially on 18 July 2017. Mesh specification enables using Bluetooth Low Energy for many-to-many device communications for home automation, sensor networks and other applications.

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. Manufacturers are expected to implement the appropriate specifications for their device in order to ensure compatibility. A device may contain implementations of multiple profiles.

The majority of current low energy application profiles are based on the Generic Attribute Profile (GATT), a general specification for sending and receiving short pieces of data, known as attributes, over a low energy link. The Bluetooth mesh profile is an exception to this rule, being based on the General Access Profile (GAP).

Mesh profiles

Bluetooth mesh profiles use Bluetooth Low Energy to communicate with other Bluetooth Low Energy devices in the network. Each device can pass the information forward to other Bluetooth Low Energy devices creating a “mesh” effect. For example, switching off an entire building of lights from a single smartphone.

* MESH ( Mesh Profile) — for base mesh networking.
* MMDL ( Mesh models) — for application layer definitions. Term “model” is used in mesh specifications instead of “profile” to avoid ambiguities.

Health care profiles

There are many profiles for Bluetooth Low Energy devices in healthcare applications. The Continua Health Alliance consortium promotes these in cooperation with the Bluetooth SIG.

* BLP (Blood Pressure Profile) — for blood pressure measurement.
* HTP (Health Thermometer Profile) — for medical temperature measurement devices.
* GLP (Glucose Profile) — for blood glucose monitors.
* CGMP (Continuous Glucose Monitor Profile)

Sports and fitness profiles

Profiles for sporting and fitness accessories include:
* BCS (Body Composition Service)
* CSCP (Cycling Speed and Cadence Profile) — for sensors attached to a bicycle or exercise bike to measure cadence and wheel speed.
* CPP (Cycling Power Profile)
* HRP (Heart Rate Profile) — for devices which measure heart rate
* LNP (Location and Navigation Profile)
* RSCP (Running Speed and Cadence Profile)
* WSP (Weight Scale Profile)

Internet connectivity

* IPSP (Internet Protocol Support Profile)

Generic sensors

* ESP (Environmental Sensing Profile)
* UDS (User Data Service)

HID connectivity

* HOGP ( HID over GATT Profile) allowing Bluetooth LE-enabled Wireless mice, keyboards and other devices offering long-lasting battery life.

Proximity sensing

“Electronic leash” applications are well suited to the long battery life possible for 'always-on' devices. Manufacturers of iBeacon devices implement the appropriate specifications for their device to make use of proximity sensing capabilities supported by Apple’s iOS devices.

Relevant application profiles include:
* FMP — the “find me” profile — allows one device to issue an alert on a second misplaced device.
* PXP — the proximity profile — allows a proximity monitor to detect whether a proximity reporter is within a close range. Physical proximity can be estimated using the radio receiver's RSSI value, although this does not have absolute calibration of distances. Typically, an alarm may be sounded when the distance between the devices exceeds a set threshold.

Alerts and time profiles

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

Battery

* The Battery Service exposes the Battery State and Battery Level of a single battery or set of batteries in a device.

Audio

Announced in January 2020, LE Audio allows the protocol to carry sound and add features such as one set of headphones connecting to multiple audio sources or multiple headphones connecting to one source and also adds support for hearing aids. It introduces LC3 as its default codec. Compared with standard Bluetooth audio it offers longer battery life.

Specifications on the implementation of Basic Audio Profile and Coordinated Set Identification was released in 2021, and the Common Audio Profile and Service in March 2022.

Contact tracing and notification

In December 2020, the Bluetooth SIG released a draft specification for a wearable exposure notification service. This service will allow exposure notification services on wearable devices to communicate with and be controlled by client devices such as smartphones.

Implementation

Chip

Starting in late 2009, Bluetooth Low Energy integrated circuits were announced by a number of manufacturers. These ICs commonly use software radio so updates to the specification can be accommodated through a firmware upgrade.

Hardware

Current mobile devices are commonly released with hardware and software support for both classic Bluetooth and Bluetooth Low Energy.

Operating systems

* iOS 5 and later
* Windows Phone 8.1
* Windows 8 and later (Windows 7 requires drivers from Bluetooth radio manufacturer supporting BLE as it has no built-in generic BLE drivers )
* Android 4.3 and later. Android 6 or later requires location permission to connect to LBE.
* BlackBerry OS 10
* Linux 3.4 and later through BlueZ 5.0
* Unison OS 5.2
* macOS 10.10
* Zephyr OS

Technical details

Radio interface

Bluetooth Low Energy technology operates in the same spectrum range (the 2.400–2.4835 GHz ISM band) as classic Bluetooth technology, but uses a different set of channels. Instead of the classic Bluetooth 79 1-MHz channels, Bluetooth Low Energy 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 1 Mbit/s (with an option of 2 Mbit/s in Bluetooth 5), and the maximum transmit power is 10 mW (100 mW in Bluetooth 5). Further details are given in Volume 6 Part A (Physical Layer Specification) of th
Bluetooth Core Specification V4.0

Bluetooth Low Energy 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 an FHSS scheme, Bluetooth Low Energy is classified as a system using digital modulation techniques or a direct-sequence spread spectrum.

More technical details may be obtained from official specification as published by the Bluetooth SIG. Note that power consumption is not part of the Bluetooth specification.

Advertising and discovery

BLE devices are detected through a procedure based on broadcasting advertising packets. This is done using 3 separate channels (frequencies), in order to reduce interference. The advertising device sends a packet on at least one of these three channels, with a repetition period called the advertising interval. For reducing the chance of multiple consecutive collisions, a random delay of up to 10 milliseconds is added to each advertising interval. The scanner listens to the channel for a duration called the scan window, which is periodically repeated every scan interval.

The discovery latency is therefore determined by a probabilistic process and depends on the three parameters (viz., the advertising interval, the scan interval and the scan window). The discovery scheme of BLE adopts a periodic-interval based technique, for which upper bounds on the discovery latency can be inferred for most parametrizations. While the discovery latencies of BLE can be approximated by models for purely periodic interval-based protocols, the random delay added to each advertising interval and the three-channel discovery can cause deviations from these predictions, or potentially lead to unbounded latencies for certain parametrizations.

Security

Software model

All Bluetooth Low Energy devices use the Generic Attribute Profile (GATT). The application programming interface offered by a Bluetooth Low Energy aware operating system will typically be based around GATT concepts. 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. Descriptors are optional – each characteristic can have any number of descriptors.

Some service and characteristic values are used for administrative purposes – for instance, the model name and serial number can be read as standard characteristics within the ''Generic Access'' service. Services may also include other services as sub-functions; the main functions of the device are so-called ''primary'' services, and the auxiliary functions they refer to are ''secondary'' services.

Identifiers

Services, characteristics, and descriptors are collectively referred to as ''attributes'', and identified by UUIDs. Any implementer may pick a random or pseudorandom UUID for proprietary