Bluetooth technology is an open global specification for wireless data and voice communications, based on a low-cost, near-range wireless connection that creates an ad hoc connection for fixed and mobile device communication environments. Its program is written in a 9 x 9 mm microchip.
For example, if Bluetooth technology is introduced into cell phones and laptops, the obnoxious connecting cables between cell phones and laptops can be eliminated and communication can be established wirelessly. Printers, PDAs, desktop computers, fax machines, keyboards, game joysticks and all other digital devices can become part of the Bluetooth system. In addition, Bluetooth wireless technology provides a common interface for existing digital networks and peripherals to form a group of personal, specially connected devices away from a fixed network.
Bluetooth operates in the globally available 2.4GHz ISM (i.e. Industrial, Scientific, Medical) band. The data rate of Bluetooth is 1Mb/s. A time-division duplex transmission scheme is used to achieve full-duplex transmission.
The ISM band is a band open to all radio systems, so using any of these bands can encounter unpredictable sources of interference. For example, certain home appliances, cordless phones, motor home door openers, microwave ovens, etc., can be sources of interference. For this reason, Bluetooth has been specially designed with quick confirmation and frequency hopping schemes to ensure link stability. Frequency hopping technology is divided into a number of frequency hopping channel (hop channel), in a connection, the radio transceiver according to a certain code sequence (i.e., a certain law, technically known as the "pseudo-random code", that is, "false" random code) constantly from one channel "jump" to another channel, only the two sides of the sender and receiver is according to the law of communication, and other interference is impossible to the same law of interference; the frequency hopping technology is divided into a number of frequency hopping channels. The instantaneous bandwidth of frequency hopping is very narrow, but by expanding the spectrum technology to make this narrow bandwidth into a wide bandwidth hundreds of times, so that the possible impact of interference becomes very small.
Bluetooth's faster frequency hopping and shorter data packets than other systems operating in the same frequency band make Bluetooth more stable than any other system.
The use of FEC (Forward Error Correction) suppresses random noise over long distance links. Frequency hopping transceivers applying binary frequency modulation (FM) technology are used to suppress interference and prevent fading.
The Bluetooth baseband protocol is a combination of circuit-switched and packet-switched. Synchronized packets can be transmitted in reserved time slots, each sent at a different frequency. A packet nominally occupies one time slot, but can actually be extended to occupy up to five time slots. Bluetooth can support asynchronous data channels, up to three simultaneous synchronous voice channels, and can transmit both asynchronous data and synchronous voice on a single channel. Each voice channel supports a 64kb/s synchronous voice link. Asynchronous channels can support asymmetric links with a maximum rate of 721kb/s at one end and 57.6kb/s at the other, as well as symmetric links with a rate of 43.2kb/s.
The Bluetooth system consists of the following functional units:
- Wireless Unit
- Link Control Unit
- Link Management
- Software Functions Definitions
Bluetooth technology supports both point-to-point and point-to-multipoint connections. Several piconets can be connected together, and each piconet is identified by its hopping order, and all users of the same piconet are synchronized with this hopping order. The topology can be described as a "multi-piconet" structure. In a "multi-piconet" architecture, full-duplex data rates exceed 6 Mb/s with 10 fully loaded independent piconets.
The voice channel uses a continuously variable slope incremental modulation (CVSD) voice coding scheme and never retransmits voice packets. CVSD encoded speech is still audible even with a bit error rate of 4%.
The Bluetooth air interface is based on an antenna level of 0 dBm. The air interface follows the FCC (Federal Communications Commission) standard for the ISM band with a level of 0dBm. If the global level reaches 100mW or more, the extended spectrum feature can be used to add some supplementary services. The extended spectrum function is realized by 79 frequency hopping points with a start frequency of 2.402 and a termination frequency of 2.480 at an interval of 1MHz. Bandwidth is scaled back in Japan, France and Spain due to certain local regulations. The maximum FH rate is 1660 hops/sec. The ideal connection range is 10 centimeters - 10 meters, but the distance can be extended to 100 meters by increasing the transmit level.
Bluetooth devices need to support some basic interoperability requirements. For some devices, this requirement involves the wireless module, over-the-air protocols, and application layer protocols and object exchange formats. But for others, such as headsets, the requirements are much simpler. Bluetooth devices must be able to recognize each other and load the appropriate software to support higher levels of device performance.
Bluetooth has different requirements for different levels of devices (e.g., PCs, handsets, cell phones, headsets, etc.) For example, you can't expect a Bluetooth headset to provide an address book. But a cell phone, handheld, or laptop would need to have more functional features.
The Bluetooth specification interface can be integrated directly into a laptop or connected via a PC card or USB port.
Use models for laptops include:
- Connecting to a remote network via a Bluetooth cellular phone
- Using a Bluetooth cellular phone as a loudspeaker
- Commercial card transactions between Bluetooth laptops, handhelds, and cellular phones
- Time synchronization between Bluetooth laptops, handhelds, and cellular phones
Bluetooth is a standalone operating system and is not tied to any operating system. Bluetooth specifications for several different commercial operating systems are being refined.
The Bluetooth specification interface can be integrated directly into a cellular phone or connected via an add-on device. Usage models for telephones include (optional):
- Hands-free functionality for telephones via Bluetooth wireless headsets
- Cable-free connectivity with laptops and handhelds
- Commercial card transactions with other Bluetooth phones, laptops, and handhelds
- Automated synchronization of address books with trusted Bluetooth-enabled laptops or handhelds
Other Bluetooth device usage models include:
- Headsets
- Handsets and other portable devices
- Human interface devices
- Data and voice access points