Author Topic: Technical description  (Read 1176 times)

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Technical description
« on: 2013-12-03 13:02:52 »
How does Bluetooth work? 

For starters: There is a pretty good explanation of Bluetooth and its inner workings on: Howstuffworks (

The following profiles are defined and adopted by the Bluetooth SIG (Special Interest Group):

Advanced Audio Distribution Profile ( (A2DP (
This profile defines how high quality audio (stereo ( or mono ( can be streamed ( from one device to another over a Bluetooth connection. For example, music can be streamed from a mobile phone to a wireless headset or car audio or from a laptop/desktop to a wireless headset.

A2DP was initially used in conjunction with an intermediate Bluetooth transceiver that connects to a standard audio output jack, encodes the incoming audio to a Bluetooth-friendly format, and sends the signal wirelessly to Bluetooth headphones that decode and play the audio. Bluetooth headphones, especially the more advanced models, often come with a microphone and support for the Headset (HSP (,Hands-Free (HFP ( and Audio/Video Remote Control (AVRCP ( profiles.
A2DP is designed to transfer a uni-directional 2-channel stereo audio stream, like music from an MP3 player, to a headset or car radio.

Hands-Free Profile ( (HFP (

Currently in version 1.5, this is commonly used to allow car hands-free kits to communicate with mobile phones in the car. It uses SCO ( (Synchronous connection oriented ( carry a monaural audio channel with continuously variable slope delta modulation or pulse-code modulation, and with logarithmic a-law or μ-law quantization.
The Bluetooth car kits allow users with Bluetooth-equipped cell phones to make use of some of the phone's features, such as making calls, while the phone itself can be left in the user's pocket or hand bag. Companies like Nokia, Johnson Controls, Peiker acustic, RAYTEL, Parrot and Motorola manufacture Bluetooth hands-free car kits for well-known brand car manufacturers.

Most bluetooth headsets implement both Hands-Free Profile and Headset Profile, because of the extra features in HFP for use with a mobile phone, such as last number redial, call waiting and voice dialing.

Headset Profile ( (HSP (

This is the most commonly used profile, providing support for the popular Bluetooth Headsets to be used with mobile phones. It relies on SCO for audio encoded in 64 kbit/s CVSD (Continuously variable slope delta modulation ( or PCM (Pulse-code modulation ( and a subset of AT commands from GSM 07.07 for minimal controls including the ability to ring, answer a call, hang up and adjust the volume.
« Last Edit: 2013-12-03 14:27:47 by STeinar »
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