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Wibree

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Wibree

Bluetooth low energy (or Bluetooth LE, or BLE, marketed as Bluetooth Smart) is a wireless computer network technology which is aimed at novel applications in the healthcare, fitness, security, and home entertainment industries.[1] Compared to "Classic" Bluetooth, BLE is intended to provide considerably reduced power consumption and lower cost, while maintaining a similar communication range (see table below).

Bluetooth LE was originally introduced under the name Wibree by Nokia in 2006,[2] but it was merged into the main Bluetooth standard in 2010, when the Bluetooth Core Specification Version 4.0 was adopted.

Positioning

Compatibility

The Bluetooth low energy protocol is not backward compatible with the previous (often called 'Classic') Bluetooth protocol. The

Bluetooth LE uses the same 2.4 GHz ISM band radio frequencies as Classic Bluetooth, which allows dual-mode devices to share a single radio antenna. LE does, however, use a simpler modulation system.

Bluetooth Smart branding

In 2011, the Bluetooth Special Interest Group announced the Bluetooth SMART logo scheme, intended to clarify compatibility between LE devices.[4]

  • Bluetooth Smart Ready indicates a dual-mode device,typically a laptop or smartphone, whose hardware is compatible with both Classic and LE Bluetooth peripherals.
  • Bluetooth Smart indicates an LE-only device, typically a battery-operated sensor, which requires either a SMART Ready or another SMART device in order to function.

Target market

The Bluetooth SIG identifies a number of markets for Low Energy technology, particularly in the 'Health & Wellness' and 'Sport & Fitness' sectors.[5] The claimed advantages are:

  • 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

One of the major adopters of the Bluetooth low energy protocol stack is the Continua Health Alliance targeting vital monitoring in healthcare.

History

In around 2001, researchers at Nokia determined that there were various scenarios that contemporary wireless technologies did not address.[6] The company started the development of a wireless technology adapted from the Bluetooth standard which would provide lower power usage and price while minimizing difference between Bluetooth technology and the new technology. The results were published in 2004 using the name Bluetooth Low End Extension.[7]

After further development with partners, e.g., within

Integration of Bluetooth low energy technology with version 4.0 of the Core Specification was completed in early 2010.[11] The first device to implement v4.0 spec was the iPhone 4S which came out in October 2011, with a number of other manufacturers bringing out v4.0 devices in 2012.[12]

Applications

The Bluetooth SIG defines many profiles for Low Energy devices: a profile is a specification for how a device works in a particular application. Manufacturers are expected to implement the appropriate specification(s) for their device in order to ensure compatibility. Bluetooth 4.0 provides low power consumption with higher baud rates.

The GATT profile is a general specification for sending and receiving short pieces of data known as 'attributes' over an LE link. All current Low Energy application profiles are based on GATT.[13]

Note that individual devices may implement more than one profile - e.g. one unit could contain both a heart rate monitor and a temperature sensor.

Health care profiles

There are many profiles for Bluetooth LE devices in healthcare applications. The Continua Health Alliance is a consortium which promotes these, in cooperation with the Bluetooth SIG.

Amongst these profiles are:

  • HTP, the Health Thermometer Profile, for medical temperature measurement devices
  • GLP, the Glucose Profile, for blood glucose monitors
  • BLP, the Blood pressure profile

Sports and fitness profiles

Profiles for sporting and fitness accessories include:

  • HRP, the Heart Rate Profile, for devices which measures heart rate
  • CSCP, the Cycling Speed and Cadence Profile - allows a sensor attached to a bicycle or exercise bike to measure the cadence and wheel speed.
  • RSCP, the Running speed and cadence profile
  • CPP, the Cycling power profile
  • LNP, the Location and navigation profile

Proximity sensing

"Electronic leash" applications are well-suited to the long battery life possible for 'always-on' devices.[14]

Relevant application profiles include:

  • FMP, the Find Me Profile. Allows a button pressed on one device (e.g. a wristwatch) to cause an alert signal to be shown on another device (e.g. a phone). These devices are referred to as the 'Find Me Locator' and 'Find Me Target', respectively[15]
  • PXP, the Proximity Profile allows one device (the Proximity Monitor) to detect whether another device (the Proximity Reporter) is within a close physical 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 (PASP) and Alert notification profile (ANP) allows a client device (e.g. a wristwatch) to receive notifications from another device (e.g. a phone). This allows the client device to signal to a user that a phone is receiving an incoming call or email message.

The Time Profile (TIP) allows the time (and time zone information) on a 'client' device to be set from a 'server' device. Typically, this is used to allow the current time on a wristwatch to be synchronized to network time as received by a smart phone.

Implementation

Chip

Bluetooth LE integrated circuit implementations were announced by a number of manufacturers (Broadcom,[16] Texas Instruments,[17] CSR[18] and Nordic Semiconductor[19]), starting in late 2009. Commonly, these implementations use software radio, so that updates to the specification can be accommodated through a device firmware upgrade.

Hardware

Windows Phone

Android

  • Samsung (Galaxy S3, Galaxy S4, Galaxy S4 Mini, Note 2 and Note 3)[21]
  • LG (Nexus 4, Nexus 5, Optimus G, 4X, G2 and up)

Apple

  • iPhone 4s and later
  • iPad 3 and later
  • iPod Touch 5
  • iPad mini (from its introduction)

Operating systems

  • iOS 5 and later
  • Windows Phone 8
  • Android 4.3 and later [22]

Technical details

Radio interface

Bluetooth low energy technology operates in the same spectrum range (the 2.400 GHz-2.4835 GHz Bluetooth Core Specification V4.0.

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

Technical Specification Classic Bluetooth technology Bluetooth low energy technology
Distance/Range 100 m (330 ft) 50 m (160 ft)
Over the air data rate 1–3 Mbit/s 1 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
Total time to send data (det.battery life) 100 ms 3 ms , <3 ms[23]
Voice capable Yes No
Network topology Scatternet Star-bus
Power consumption 1 as the reference 0.01 to 0.5 (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, automotive, PCs, security, proximity, healthcare, sports & fitness, etc. Mobile phones, gaming, PCs, watches, sports and fitness, healthcare, security & proximity, automotive, home electronics, automation, 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.

Software model

All Bluetooth Low Energy devices use the Generic Attribute Profile (GATT). The application programming interface offered by a Bluetooth LE-aware operating system will typically be based around GATT concepts.[24] 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 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.

Further reading

GATT is described in full in Volume 3, Part G of the Bluetooth 4.0 Core Specification.

See also

References

External links

  • HowStuffWorks (How Wibree Works)
  • Bluetooth low energy profiles explained (not working)
  • Getting startedzh:藍牙#低耗電藍牙
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