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Bluetooth
Bluetooth is an industrial specification for wireless personal area networks (PANs), also known as IEEE 802.15.1. Bluetooth provides a way to connect and exchange information between devices like personal digital assistants (PDAs), mobile phones, laptops, PCs, printers, digital cameras and video game consoles such as the Nintendo Wii and Sony PlayStation 3 via a secure, globally unlicensed short range radio frequency.
The name Bluetooth is derived from the cognomen of a 10th century king of Denmark, Harald Bluetooth. According to the inventors of the Bluetooth technology, Harald engaged in diplomacy which led warring parties to negotiate with each other, making Bluetooth a fitting name for their technology, which allows different devices to talk to each other.
Introduction
Bluetooth is a radio standard and communications protocol primarily designed for low power consumption, with a short range (power class dependent: 1 meter, 10 meters, 100 meters) based around low-cost transceiver microchips in each device. ad Bluetooth lets these devices communicate with each other when they are in range. The devices use a radio communications system, so they do not have to be in line of sight of each other, and can even be in other rooms, so long as the received power is high enough. As a result of different antenna designs, transmission path attenuations, and other variables, observed ranges are variable; however, transmission power levels must fall into one of three classes:
| Class |
Maximum Permitted Power
|
Maximum Permitted Power
|
Range
(approximate) |
| Class 1 |
100 mW |
20 dBm |
~100 meters |
| Class 2 |
2.5 mW |
4 dBm |
~10 meters |
| Class 3 |
1 mW |
0 dBm |
~1 meter |
Bluetooth Application
- Wireless control of and communication between a cell phone and a hands free headset or car kit. This is the most popular use.
- Wireless networking between PCs in a confined space and where little bandwidth is required.
- Wireless communications with PC input and output devices, the most common being the mouse, keyboard and printer.
- Transfer of files between devices via OBEX.
- Transfer of contact details, calendar appointments, and reminders between devices via OBEX.
- Replacement of traditional wired serial communications in test equipment, GPS receivers and medical equipment.
- For remote controls where infrared was traditionally used.
- Sending small advertisements from Bluetooth enabled advertising hoardings to other, discoverable, Bluetooth devices.
- Wireless control of a games console, Nintendo's Wii and Sony's PlayStation 3 will both use Bluetooth technology for their wireless controllers.
- Sending commands and software to the LEGO Mindstorms NXT instead of infra red.
Specification and features
The Bluetooth specification was first developed by Ericsson (now Sony Ericsson and Ericsson Mobile Platforms), and was later formalized by the Bluetooth Special Interest Group (SIG). The SIG was formally announced on May 20, 1999. Today it has over 1800 companies worldwide. It was established by Sony Ericsson, IBM, Intel, Toshiba and Nokia, and later joined by many other companies as Associate or Adopter members. Bluetooth is also known as IEEE 802.15.1.
Bluetooth 1.0 and 1.0B
Versions 1.0 and 1.0 B had numerous problems and the various manufacturers had great difficulties in making their products interoperable. 1.0 and 1.0B also had mandatory Bluetooth Hardware Device Address (BD_ADDR) transmission in the handshaking process, rendering anonymity impossible at a protocol level, which was a major setback for services planned to be used in Bluetooth environments, such as Consumerium.
Bluetooth 1.1
- many errata found in the 1.0B specifications were fixed.
- added support for non-encrypted channels.
- Received Signal Strength Indicator (RSSI)
Bluetooth 1.2
This version is backwards compatible with 1.1 and the major enhancements include
- Adaptive Frequency-hopping spread spectrum (AFH), which improves resistance to radio frequency interference by avoiding the use of crowded frequencies in the hopping sequence
- Higher transmission speeds in practice
- extended Synchronous Connections (eSCO), which improves voice quality of audio links by allowing retransmissions of corrupted packets.
- Host Controller Interface (HCI) support for 3-wire UART
- HCI access to timing information for Bluetooth applications
Bluetooth 2.0
This version is backwards compatible with 1.x. The main enhancement is the introduction of Enhanced Data Rate (EDR) of 3.0 MBps. This has the following effects (Bluetooth SIG, 2004):
- 3 times faster transmission speed (up to 10 times in certain cases).
- Lower power consumption through a reduced duty cycle.
- Simplification of multi-link scenarios due to more available bandwidth.
- Further improved BER (bit error rate) performance.
Future of Bluetooth
The next version of Bluetooth, currently code named Lisbon, includes a number of features to increase security, usability and value of Bluetooth. The following features are defined:
- Atomic Encryption Change - allows encrypted links to change their encryption keys periodically, increasing security, and also allowing role switches on an encrypted link.
- Extended Inquiry Response - provides more information during the inquiry procedure to allow better filtering of devices before connection. This information includes the name of the device, and a list of services, with other information.
- Sniff Subrating - reducing the power consumption when devices are in the sniff low power mode, especially on links with asymmetric data flows. Human interface devices (HID) are expected to benefit the most with mice and keyboards increasing the battery life from 3 to 10 times those currently used.
- QoS Improvements - these will enable audio and video data to be transmitted at a higher quality, especially when best effort traffic is being transmitted in the same piconet.
- Simple Pairing - this improvement will radically improve the pairing experience for Bluetooth devices, while at the same time increasing the use and strength of security. It is expected that this feature will significantly increase the use of Bluetooth.
Bluetooth technology already plays a part in the rising Voice over IP (VOIP) scene, with Bluetooth headsets being used as wireless extensions to the PC audio system. As VOIP becomes more popular, and more suitable for general home or office users than wired phone lines, Bluetooth may be used in Cordless handsets, with a base station connected to the Internet link.
The version of Bluetooth after Lisbon, code-named Seattle, has many of the same features, but is most notable for plans to adopt Ultra-wideband radio technology. This will allow Bluetooth use over UWB radio, enabling very fast data transfers, synchronizations and file pushes, while building on the very low power idle modes of Bluetooth. The combination of a radio using little power when no data is transmitted, and a high data rate radio used to transmit bulk data, could be the start of software radios. Bluetooth, given its worldwide regulatory approval, low power operation, and robust data transmission capabilities, provides an excellent signalling channel to enable the soft radio concept.
On 28 March 2006, the Bluetooth Special Interest Group (SIG) announced its selection of the WiMedia Alliance Multi-Band Orthogonal Frequency Division Multiplexing (MB-OFDM) version of Ultra-wideband (UWB) for integration with current Bluetooth wireless technology. UWB integration will create a version of the globally popular Bluetooth wireless technology with a high speed/high data rate option. This new version of Bluetooth technology will meet the high-speed demands of synchronizing and transferring large amounts of data as well as enabling high quality video and audio applications for portable devices, multi-media projectors and television sets, wireless VOIP. At the same time, Bluetooth technology will continue catering to the needs of very low power applications such as mice, keyboards and mono headsets, enabling devices to select the most appropriate physical radio for the application requirements, thereby offering the best of both worlds.
Technical information
Communication & connection
A Bluetooth device playing the role of the "master" can communicate with up to 7 devices playing the role of the "slave". This network of "group of up to 8 devices" (1 master + 7 slaves) is called a piconet. A piconet is an ad-hoc computer network of devices using Bluetooth technology protocols to allow one master device to interconnect with up to seven active slave devices (because a three-bit MAC address is used). Up to 255 further slave devices can be inactive, or parked, which the master device can bring into active status at any time.
At any given time, data can be transferred between the master and 1 slave; but the master switches rapidly from slave to slave in a round-robin fashion. (Simultaneous transmission from the master to multiple slaves is possible, but not used much in practice). Either device may switch the master/slave role at any time.
Bluetooth specification allows connecting 2 or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role in one piconet and the slave role in another piconet. These devices have yet to come, though are supposed to appear in 2007.
Setting up connections
Any Bluetooth device will transmit the following sets of information on demand:
- Device Name
- Device Class
- List of services
- Technical information eg: device features, manufacturer, Bluetooth specification, clock offset
Anything may perform an "inquiry" to find other devices to which to connect, and any device can be configured to respond to such inquiries. However if the device trying to connect knows the address of the device it will always respond to direct connection requests and will transmit the information shown in the list above if requested for it. Use of the device's services however may require pairing or its owner to accept but the connection itself can be started by any device and be held until it goes out of range. Some devices can only be connected to one device at a time and connecting to them will prevent them from connecting to other devices and showing up in inquiries until they disconnect the other device.
Every device has a unique 48-bit address. However these addresses are generally not shown in inquiries and instead friendly "Bluetooth names" are used which can be set by the user, and will appear when another user scans for devices and in lists of paired devices.
Most phones have the Bluetooth name set to the manufacturer and model of the phone by default. Most phones and laptops will only show the Bluetooth names and special programs are required to get additional information about remote devices. This can get confusing as, for example, there could be several phones in range named "T610" (see "Bluejacking").
On Nokia phones and the Siemens SX1 the Bluetooth address may be found by entering "*#2820#". On computers running Linux the address and class of a USB Bluetooth dongle may be found by entering "hciconfig hci0 class" as root ("hci0" may need to be replaced by another device name).
Every device also has a 24-bit class identifier. This provides information on what kind of a device it is (Phone, Smartphone, Computer, Headset, etc), which will also be transmitted when other devices perform an inquiry. On some phones this information is translated into a little icon displayed beside the device's name.
Bluetooth devices will also transmit a list of services if requested by another device; this also includes some extra information such as the name of the service and what channel it is on. These channels are virtual and have nothing to do with the frequency of the transmission, much like TCP ports. A device can therefore have multiple identical services.
Pairing
Pairs of devices may establish a trusted relationship by learning (by user input) a shared secret known as a "passkey". A device that wants to communicate only with a trusted device can cryptographically authenticate the identity of the other device. Trusted devices may also encrypt the data that they exchange over the air so that no one can listen in. The encryption can however be turned off and passkeys are stored on the device's file system and not the Bluetooth chip itself. Since the Bluetooth address is permanent a pairing will be preserved even if the Bluetooth name is changed. Pairs can be deleted at any time by either device. Devices will generally require pairing or will prompt the owner before it allows a remote device to use any or most of its services. Some devices such as Sony Ericsson phones will usually accept OBEX business cards and notes without any pairing or prompts. Certain printers and access points will allow any device to use its services by default much like unsecured Wi-Fi networks.
Air Interface
The protocol operates in the license-free ISM band at 2.45 GHz. In order to avoid interfering with other protocols which use the 2.45 GHz band, the Bluetooth protocol divides the band into 79 channels (each 1 MHz wide) and changes channels up to 1600 times per second. Implementations with versions 1.1 and 1.2 reach speeds of 723.1 kbit/s. Version 2.0 implementations feature Bluetooth Enhanced Data Rate (EDR), and thus reach 2.1 Mbit/s. Technically version 2.0 devices have a higher power consumption, but the three times faster rate reduces the transmission times, effectively reducing consumption to half that of 1.x devices (assuming equal traffic load).
Bluetooth differs from Wi-Fi in that the latter provides higher throughput and covers greater distances but requires more expensive hardware and higher power consumption. They use the same frequency range, but employ different multiplexing schemes. While Bluetooth is a cable replacement for a variety of applications, Wi-Fi is a cable replacement only for local area network access. Bluetooth is often thought of as wireless USB whereas Wi-Fi is wireless Ethernet, both operating at much lower bandwidth than the cable systems they are trying to replace. However, this analogy is not accurate since unlike USB, Bluetooth does not require the presence of a host PC. Devices can connect to each other in true peer-to-peer fashion.
Many USB Bluetooth adapters are available, some of which also include an IrDA adapter.
Older (pre-2003) Bluetooth adapters, however, limit the amount of services by offering only the Bluetooth Enumerator and a less-powerful incarnation of Bluetooth Radio. Such devices are able to link computers via Bluetooth, but they unfortunately don't offer much in the way of the twelve or more services that modern adapters are able to utilize.
Bluetooth Profiles
In order to use Bluetooth, a device must be compatible with certain Bluetooth profiles. These define the possible applications. The following profiles are defined and adopted by the Bluetooth SIG:
Advanced Audio Distribution Profile (A2DP)
This is designed to transfer a 2-channel stereo audio stream, like music from an MP3 player, to a headset or car radio. This profile relies on AVDTP and GAVDP. It includes mandatory support for low complexity Sub_Band_Codec (SBC) and supports optionally: MPEG-1,2 Audio, MPEG-2,4 AAC and ATRAC, and is extensible to support manufacturer defined codecs. Bluetake's I-Phono Hi-Fi Sport Headphones are an example of this profile being employed. Most bluetooth stacks implement the SCMS-T copyright protection. In these cases it is not possible to connect the A2DP headphones for high quality audio. E.g. the Motorola HT820 can be used for high quality audio only with certain versions of the Toshiba bluetooth stack.
Audio/Video Remote Control Profile (AVRCP)
This profile is designed to provide a standard interface to control TVs, Hi-fi equipment, etc. to allow a single remote control (or other device) to control all of the A/V equipment to which a user has access. It may be used in concert with A2DP or VDP.
It has the possibility for vendor-dependent extensions. The Generic Media Control Profile (GMCP) is proposed to be an open standard for transfer of media content related information using those extensions.
Basic Imaging Profile (BIP)
This profile is designed for sending images between devices and includes the ability to resize, and convert images to make them suitable for the receiving device. It may be broken down into smaller pieces:
- Image Push -
Allows the sending of images from a device the user controls.
- Image Pull -
Allows the browsing and retrieval of images from a remote device.
- Advanced Image Printing -
print images with advanced options using the DPOF format developed by Canon, Kodak, Fujifilm, and Matsushita
- Automatic Archive -
Allows the automatic backup of all the new images from a target device. For example, a laptop could download all of the new pictures from a camera whenever it is within range.
- Remote Camera -
Allows the initiator to remotely use a digital camera. For example, a user could place a camera on a tripod for a group photo, use their phone handset to check that everyone is in frame, and activate the shutter with the user in the photo.
- Remote Display -
Allows the initiator to push images to be displayed on another device. For example, a user could give a presentation by sending the slides to a video projector.
Basic Printing Profile (BPP)
This allows devices to send text, e-mails, vCards, or other items to printers based on print jobs. It differs from HCRP in that it needs no printer-specific drivers. This makes it more suitable for embedded devices such as mobile phones and digital cameras which cannot easily be updated with drivers dependent upon printer vendors.
Common ISDN Access Profile (CIP)
This provides unrestricted access to the services, data and signalling that ISDN offers.
Cordless Telephony Profile (CTP)
This is designed for cordless phones to work using Bluetooth. It is hoped that mobile phones could use a Bluetooth CTP gateway connected to a landline when within the home, and the mobile phone network when out of range. It is central to the Bluetooth SIG's '3-in-1 phone' use case.
Device ID Profile (DID)
This profile allows a device to be identified above and beyond the Device Class according to the Specification version met, the Manufacturer, product and product version. This could be useful in allowing a PC to identify a connecting device, and download appropriate drivers. It enables similar applications to those the Plug-and-play specification allows.
Dial-up Networking Profile (DUN)
This profile provides a standard to access the Internet and other dial-up services over Bluetooth. The most common scenario is accessing the Internet from a laptop by dialing up on a mobile phone, wirelessly. It is based on SPP, and provides for relatively easy conversion of existing products, through the many features that it has in common with the existing wired serial protocols for the same task. These include the AT command set specified in ETSI 07.07, and PPP.
Fax Profile (FAX)
This profile is intended to provide a well defined interface between a mobile phone or fixed-line phone and a PC with Fax software installed. Support must be provided for ITU T.31 and / or ITU T.32 AT command sets as defined by ITU-T. Data and voice calls are not covered by this profile.
File Transfer Profile (FTP)
Provides access to the file system on another device. This includes support for getting folder listings, changing to different folders, getting files, putting files and deleting files. It uses OBEX as a transport and is based on GOEP.
General Audio/Video Distribution Profile (GAVDP)
Provides the basis for A2DP, and VDP.
Generic Access Profile (GAP)
Provides the basis for all other profiles.
Generic Object Exchange Profile (GOEP)
provides a basis for other data transfer profiles. Based on OBEX.
Hard Copy Cable Replacement Profile (HCRP)
This provides a simple wireless alternative to a cable connection between a device and a printer. Unfortunately it does not set a standard regarding the actual communications to the printer, so drivers are required specific to the printer model or range. This makes this profile less useful for embedded devices such as digital cameras and palmtops, as updating drivers can be problematic.
Hands-Free Profile (HFP)
This is commonly used to allow car hands-free kits to communicate with mobile phones in the car. It uses SCO to carry a mono, PCM audio channel. It is considered to be the killer app for Bluetooth as more Governments are passing legislation to ban the direct use of mobile phones while driving. Currently in version 1.5. In 2002 Audi, with the Audi A8, was the first motor vehicle manufacturer to install Bluetooth technology in a car, enabling the passenger to use a wireless in-car phone. The following year Acura introduced Bluetooth technology integration with the audio system as a standard feature in the third generation Acura TL in a system dubbed HandsFree Link (HFL). Later, BMW added it as an option on its 1 Series, 3 Series, 5 Series, 7 Series and X5 vehicles. Since then, other manufacturers have followed suit, with many vehicles, including the Toyota Prius (Since 2004), 2007 Toyota Camry, and the Lexus LS 430 (Since 2004). 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 a suitcase or in the boot/trunk, for instance. Companies like Parrot or Motorola manufacture Bluetooth hands-free car kits for well-known brand car manufacturers.
Human Interface Device Profile (HID)
Provides support for devices such as mice, joysticks, keyboards, etc. It is designed to provide a low latency link, with low power requirements. Popular devices that feature support for this profile include: Logitech diNovo Media Desktop 2.0, Microsoft Optical Desktop Elite. The unreleased PlayStation 3 controllers will also use BT HID.
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 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.
Intercom Profile (ICP)
This is often referred to as the walkie-talkie profile. It is another TCS based profile, relying on SCO to carry the audio. It is proposed to allow voice calls between two Bluetooth capable handsets, over Bluetooth.
Object Push Profile (OPP)
A basic profile for sending "objects" such as pictures, virtual business cards, or appointment details. It is called push because the transfers are always instigated by the sender (client), not the receiver (server).
Personal Area Networking Profile (PAN)
This profile is intended to allow the use of Bluetooth Network Encapsulation Protocol on Layer 3 protocols for transport over a Bluetooth link.
Phone Book Access Profile (PBAP)
This profile allows exchange of Phone Book Objects between devices. It is likely to be used between a car kit and a mobile phone to allow the car kit to display the name of the incoming caller.
Serial Port Profile (SPP)
This profile is based on the ETSI TS07.10 specification and uses the RFCOMM protocol. It emulates a serial cable to provide a simply implemented wireless replacement for existing RS-232 based serial communications applications, including familiar control signals. It provides the basis for DUN, FAX, HSP and AVRCP profiles.
Service Discovery Application Profile (SDAP)
This mandatory profile is used to find out which profiles are offered by the Server device.
SIM Access Profile (SAP, SIM)
This allows devices such as car phones with built in GSM transceivers to connect to a SIM card in a phone with Bluetooth, so the car phone itself doesn't require a separate SIM card.
Synchronisation Profile (SYNCH)
This profile allows synchronisation of Personal Information Manager (PIM) items. As this profile originated as part of the infrared specifications but has been adopted by the Bluetooth SIG to form part of the main Bluetooth specification, it is also commonly referred to as IrMC Synchronization.
Video Distribution Profile (VDP)
This profile allows the transport of a video stream. It could be used for streaming a recorded video from a PC media center to a portable player, or from a digital video camera to a TV. Support for H.263 baseline is mandatory. Support for MPEG-4 Visual Simple Profile, H.263 profiles 3 and 8 are optionally supported, and covered in the specification.
Wireless Application Protocol Bearer (WAPB)
This is a profile for carrying Wireless Application Protocol, (WAP) over Point-to-Point Protocol over Bluetooth.
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