Bluetooth Low Energy

Bluetooth Low Energy (Bluetooth LE, colloquially BLE, formerly marketed as Bluetooth Smart[1]) 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,[2] security, and home entertainment industries.[3] 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 and Windows 10, natively support Bluetooth Low Energy. The Bluetooth SIG predicts that by 2018 more than 90% of Bluetooth-enabled smartphones will support Bluetooth Low Energy.[4]

Compatibility

Bluetooth Low Energy is not backward-compatible with the previous (often called "classic") Bluetooth Basic Rate/Enhanced Data Rate (BR/EDR) protocol. 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. LE does, however, use a simpler modulation system.

Branding

The previously used Bluetooth Smart logo

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.[5]

  • Bluetooth Smart Ready indicates a dual-mode device compatible with both classic and low energy peripherals.[6]
  • 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 has reverted to using the Bluetooth logo and word mark.[7] The logo uses 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.[8] 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

The now-defunct Wibree logo

In 2001, researchers at Nokia determined various scenarios that contemporary wireless technologies did not address.[9] 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.[10]

After further development with partners in particular Logitech and within the European project MIMOSA,[lower-alpha 1] actively promoted and supported also by STMicroelectronics since its early stage,[lower-alpha 2] the technology was released to the public in October 2006 with the brand name Wibree.[13] 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.[14][15]

The technology was marketed as Bluetooth Smart and integration into version 4.0 of the Core Specification was completed in early 2010.[16] The first smartphone to implement the 4.0 specification was the iPhone 4S, released in October 2011.[17] 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 they dropped the point number, so it now just called Bluetooth 5 (and not Bluetooth 5.0 or 5.0 LE like for Bluetooth 4.0). This decision was made allegedly to "simplifying marketing, and communicating user benefits more effectively".[18] 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.[19]

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.[20]

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.

Majority of current low energy application profiles is 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.[21] Bluetooth mesh profile is the exception to this rule as it is based on General Access Profile (GAP).[22]

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.[23]

  • 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.[24] Manufacturers of iBeacon devices implement the appropriate specifications for their device to make use of proximity sensing capabilities supported by Apple's iOS devices.[25]

Relevant application profiles include:

  • FMP — the "find me" profile — allows one device to issue an alert on a second misplaced device.[26]
  • 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.

Implementation

Chip

Starting in late 2009, Bluetooth Low Energy integrated circuit implementations were announced by a number of manufacturers. Implementations 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 the Bluetooth Low Energy.

Operating systems

  • iOS 5 and later[27]
  • Windows Phone 8.1[28]
  • Windows 8 and later[29]
  • Android 4.3 and later[30]
  • BlackBerry 10[31]
  • Linux 3.4 and later through BlueZ 5.0[32]
  • Unison OS 5.2 [33]

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 the 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.[34]

Technical specification Bluetooth Basic Rate/Enhanced Data Rate technology Bluetooth Low Energy technology
Distance/range (theoretical max.) 100 m (330 ft) >100 m (>330 ft)
Over the air data rate 1–3 Mbit/s 125 kbit/s – 1 Mbit/s – 2 Mbit/s
Application throughput 0.7–2.1 Mbit/s 0.27 Mbit/s
Active slaves 7 Not defined; implementation dependent
Security 56/128-bit and application layer user defined 128-bit AES with Counter Mode CBC-MAC and application layer user defined
Robustness Adaptive fast frequency hopping, FEC, fast ACK Adaptive frequency hopping, Lazy Acknowledgement, 24-bit CRC, 32-bit Message Integrity Check
Latency (from a non-connected state) Typically 100 ms 6 ms
Minimum total time to send data (det. battery life) 0.625 ms 3 ms [35]
Voice capable Yes No
Network topology Scatternet Scatternet
Power consumption 1 W as the reference 0.01–0.50 W (depending on use case)
Peak current consumption <30 mA <15 mA
Service discovery Yes Yes
Profile concept Yes Yes
Primary use cases Mobile phones, gaming, headsets, stereo audio streaming, smart homes, wearables, automotive, PCs, security, proximity, healthcare, sports & fitness, etc. Mobile phones, gaming, smart homes, wearables, automotive, PCs, security, proximity, healthcare, sports & fitness, Industrial, etc.

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[36] 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.[37]

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.[38] 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 uses, but the Bluetooth SIG have reserved a range of UUIDs (of the form xxxxxxxx-0000-1000-8000-00805F9B34FB [39]) for standard attributes. For efficiency, these identifiers are represented as 16-bit or 32-bit values in the protocol, rather than the 128 bits required for a full UUID. For example, the Device Information service has the short code 0x180A, rather than 0000180A-0000-1000-... . The full list is kept in the Bluetooth Assigned Numbers document online.

GATT operations

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

Commands are also provided to read (data transfer from server to client) and write (from client to server) the values of characteristics:

  • A value may be read either by specifying the characteristic's UUID, or by a handle value (which is returned by the information discovery commands above).
  • Write operations always identify the characteristic by handle, but have a choice of whether or not a response from the server is required.
  • 'Long read' and 'Long write' operations can be used when the length of the characteristic's data exceeds the MTU of the radio link.

Finally, GATT offers notifications and indications. The client may request a notification for a particular characteristic from the server. The server can then send the value to the client whenever it becomes available. For instance, a temperature sensor server may notify its client every time it takes a measurement. This avoids the need for the client to poll the server, which would require the server's radio circuitry to be constantly operational.

An indication is similar to a notification, except that it requires a response from the client, as confirmation that it has received the message.

Battery impact

Bluetooth Low Energy chipset power consumption profiles with different configuration parameters, as per The Hitchhikers Guide to iBeacon Hardware by Aislelabs.[40]

Bluetooth Low Energy is designed to enable devices with low power consumption. Several chipmakers including Cambridge Silicon Radio, Dialog Semiconductor, Nordic Semiconductor, STMicroelectronics, Cypress Semiconductor, Silicon Labs and Texas Instruments have introduced their Bluetooth Low Energy optimized chipsets over the last few years. Devices with peripheral and central roles have different power requirements. A study by beacon software company, Aislelabs, reported that peripherals, such as proximity beacons, usually function for 1–2 years with a 1,000mAh coin cell battery.[41] This is possible because of power efficiency of Bluetooth Low Energy protocol which only transmits small packets as compared to Bluetooth Classic which is also suitable for audio and high bandwidth data.

In contrast, a continuous scan for the same beacons in central role can consume 1,000 mAh in a few hours. Android and iOS devices also have very different battery impact depending on type of scans and number of Bluetooth Low Energy devices in the vicinity.[42] With the newer chipsets and advances in software, both Android and iOS phones now have negligible power consumption in real-life Bluetooth Low Energy use scenarios.[43]

See also

Notes

  1. ↑ MIMOSA stands for Microsystems platform for mobile services and applications,[11] and is the name of one of the projects funded by the European Framework Programmes for Research and Technological Development
  2. ↑ STMicroelectronics went on to release a processor to support implementation of the standard[12]

References

  1. ↑ "Bluetooth Smart or Version 4.0+ of the Bluetooth specification". bluetooth.com.
  2. ↑ beacons
  3. ↑ "bluetooth.com: Bluetooth Smart". bluetooth.com.
  4. ↑ "Mobile Telephony Market". Bluetooth Special Interest Group. Retrieved 16 January 2014.
  5. ↑ "Bluetooth SIG Extends Bluetooth Brand, Introduces Bluetooth Smart Marks" (Press release). Bluetooth SIG. 24 October 2011. Archived from the original on 3 February 2015. Retrieved 2016-01-31.
  6. ↑ "Bluetooth Smart Marks FAQ". Bluetooth SIG. Archived from the original on 24 July 2015. Retrieved 2016-01-31.
  7. ↑ "Brand Your Product - Bluetooth Technology Website". www.bluetooth.com.
  8. ↑ "Bluetooth Technology Website". www.bluetooth.com.
  9. ↑ Genuth, Iddo (16 November 2006). "Nokia's Wibree and the Wireless Zoo". The Future of Things. Archived from the original on 2012-11-08.
  10. ↑ Honkanen, M.; Lappetelainen, A.; Kivekas, K. (2004). Low end extension for Bluetooth. 2004 IEEE Radio and Wireless Conference 19–22 September 2004. IEEE. pp. 199–202. Retrieved 2018-04-27.
  11. ↑ "Mimosa WebSite: Home". MIMOSA FP6 project. Archived from the original on 2016-08-04. Retrieved 2016-08-18.
  12. ↑ "BlueNRG-MS – Bluetooth Low Energy Network Processor supporting Bluetooth 4.1 core specification – STMicroelectronics". Retrieved 2016-08-18.
  13. ↑ "Bluetooth rival unveiled by Nokia". BBC News. 4 October 2006. Retrieved 2018-04-27.
  14. ↑ "Wibree forum merges with Bluetooth SIG" (PDF) (Press release). Nokia. 12 June 2007. Archived from the original (PDF) on 2007-06-16.
  15. ↑ Reynolds, Melanie (12 June 2007). "Wibree becomes ULP Bluetooth". ElectronicsWeekly.com. Reed Business Information Limited. Archived from the original on 2008-09-07. Retrieved 2008-09-09.
  16. ↑ Pollicino, Joe (25 October 2011). "Bluetooth SIG unveils Smart Marks, explains v4.0 compatibility with unnecessary complexity". Engadget. Oath Tech Network AOL Tech. Retrieved 2018-04-17.
  17. ↑ O'Brien, Terrence (12 October 2011). "iPhone 4S claims title of first Bluetooth 4.0 smartphone, ready to stream data from your cat". Engadget. Retrieved 2014-02-09.
  18. ↑ "Bluetooth 5 Promises Four times the Range, Twice the Speed of Bluetooth 4.0 LE Transmissions". www.cnx-software.com. Retrieved 2017-11-08.
  19. ↑ "Bluetooth® 5 Quadruples Range, Doubles Speed, Increases Data Broadcasting Capacity by 800% | Bluetooth Technology Website". www.bluetooth.com. Retrieved 2017-11-08.
  20. ↑ "Bluetooth SIG Announces Mesh Networking Capability | Bluetooth Technology Website". www.bluetooth.com. Retrieved 2017-07-20.
  21. ↑ Bluetooth SIG Adopted specifications
  22. ↑ bluetooth. "Bluetooth Mesh and the IOT". www.bluetooth.com.
  23. ↑ "Smart Building - Bluetooth Technology Website". www.bluetooth.com.
  24. ↑ "Casio Bluetooth Low Energy Watch communicates with smartphones". M2M / IoT hints and tips. 2011-03-07. Retrieved 2017-11-08.
  25. ↑ "Inside iOS 7: iBeacons enhance apps' location awareness via Bluetooth LE". AppleInsider. Retrieved 2017-11-08.
  26. ↑ "Find Me Profile specification". bluetooth.org.
  27. ↑ "iOS 5.0". Apple. Retrieved 2 June 2018.
  28. ↑ Brynte (2014-05-04). "Windows Phone 8.1 for Developers–Introducing Bluetooth LE". MSDN Blogs. Retrieved 2014-05-18.
  29. ↑ wdg-dev-content. "Windows.Devices.Bluetooth Namespace - UWP app developer". msdn.microsoft.com.
  30. ↑ "Bluetooth low energy overview - Android Developers". Android Developers.
  31. ↑ "BlackBerry Press Room - Official News, Events & Product Releases". press.blackberry.com.
  32. ↑ Gustavo Padovan (2013-02-22). "The big changes of BlueZ 5". As the MGMT interface is the only one to support the new Bluetooth Low Energy devices, BlueZ developers decided to drop support for the old interface once MGMT was completed. As a result, you need to be running Linux Kernel 3.4 or newer to use BlueZ 5.
  33. ↑ "Wireless Protocols - WiFi, Bluetooth, BT, BTLE, GPS, GPRS, 6loWPAN, Zigbee, RoweBots Bluetooth Stack - RoweBots". rowebots.com.
  34. ↑ Bluetooth Special Interest Group "Bluetooth Low Energy Regulatory Aspects", April 2011
  35. ↑ "Bluetooth Low Energy Technology - Technical Information". Bluetooth SIG. Archived from the original on 2014-02-14.
  36. ↑ "PI-LatencyComp - Neighbor Discovery in BLE-Like protocols". CodeOcean. doi:10.24433/co.fec70c60-c265-4eea-9e37-8f7222ec5c92.
  37. ↑ Kindt, P. H.; Saur, M.; Balszun, M.; Chakraborty, S. (2017). "Neighbor Discovery Latency in BLE-Like Protocols". IEEE Transactions on Mobile Computing. PP (99): 1–1. doi:10.1109/tmc.2017.2737008. ISSN 1536-1233.
  38. ↑ See for example Apple's Core Bluetooth framework
  39. ↑ See sec 2.5.1 of the Bluetooth 4.0 Core Specification
  40. ↑ "The Hitchhikers Guide to iBeacon Hardware: A Comprehensive Report by Aislelabs". Aislelabs. 2014-10-03. Retrieved 2014-10-07.
  41. ↑ "How to find the best beacon hardware for everything from stores to cities". GigaOM. 2014-10-04. Retrieved 2014-10-11.
  42. ↑ "In terms of battery life, Android devices are more optimized for iBeacons than iPhones". GigaOM. 2014-08-14. Retrieved 2014-10-07.
  43. ↑ "iBeacon Battery Drain on Apple vs Android: A Technical Report – Aislelabs". Aislelabs. 2014-08-14. Retrieved 2014-08-18.

Further reading

  • "Specifications - Bluetooth Technology Website". www.bluetooth.org. "Bluetooth 4.0 Core Specification" – GATT is described in full in Volume 3, Part G
  • Official website
  • Gomez, Carles; Oller, Joaquim; Paradells, Josep (29 August 2012). "Overview and Evaluation of Bluetooth Low Energy: An Emerging Low-Power Wireless Technology". Sensors. 12 (12): 11734–11753. doi:10.3390/s120911734. ISSN 1424-8220.
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