Bluetooth technology is an open global wireless data and voice communication standard. Based on low-cost short-distance wireless connection, it establishes a special connection for the communication environment of fixed and mobile devices. This program is written in a 9×9 mm microchip.
For example, if Bluetooth technology is introduced into mobile phones and laptops, the annoying connection line between mobile phones and laptops can be removed and communication can be established wirelessly. Printers, PDA's, desktop computers, fax machines, keyboards, joysticks and all other digital devices can be part of the Bluetooth system. In addition, Bluetooth wireless technology also provides a universal interface for existing digital networks and peripheral devices, so as to form a group of personal dedicated connection devices far away from fixed networks.
Bluetooth works in the global 2.4GHz ISM (industrial, scientific and medical) frequency band. The data rate of Bluetooth is 1 MB/s ... Time division duplex transmission scheme is used to realize full duplex transmission.
ISM band is open to all radio systems, so using one of the bands will encounter unpredictable interference sources. For example, some household appliances, cordless phones, garage door openers, microwave ovens, etc. , may be interference. For this reason, Bluetooth has specially designed a fast acknowledgement and frequency hopping scheme to ensure the stability of the link. Frequency hopping technology divides the frequency band into several frequency hopping channels. In a connection, the radio transceiver constantly "hops" from one channel to another according to a certain code sequence (that is, a certain law, technically called "pseudo-random code", that is, "false" random code). Only the transmitter and receiver communicate according to this law, and other interferences cannot interfere according to the same law. The instantaneous bandwidth of frequency hopping is very narrow, but this narrow bandwidth is expanded to a hundred times of broadband by spread spectrum technology, which makes the possible impact of interference very small.
Compared with other systems operating in the same frequency band, Bluetooth has faster frequency hopping and shorter data packets, which makes Bluetooth more stable than other systems. The use of FEC (Forward Error Correction) suppresses the random noise of long-distance links. Frequency hopping transceiver using binary frequency modulation (FM) technology is used to suppress interference and prevent fading.
Bluetooth baseband protocol is a combination of circuit switching and packet switching. Synchronous data packets can be transmitted in reserved time slots, and each data packet is sent at a different frequency. A data packet nominally occupies one time slot, but in fact it can be extended to occupy five time slots. Bluetooth can support asynchronous data channels, up to three simultaneous voice channels, and can also use one channel to transmit asynchronous data and synchronous voice simultaneously. Each voice channel supports 64kb/s synchronous voice link. Asynchronous channels can support asymmetric connections with a maximum rate of 72 1kb/s at one end and 57.6kb/s at the other end, or symmetric connections with a rate of 43.2 kb/s. ..
Bluetooth system consists of the following functional units:
Wireless unit
Link control unit
Link management
Software function definition
Bluetooth technology supports point-to-point and point-to-multipoint connections. Several piconets can be connected together, and each piconet can be identified by frequency hopping sequence. All users of the same piconet are synchronized with this frequency hopping sequence. Its topological structure can be described as a "multi-piconet" structure. In the "multi-piconet" structure, in the case of 10 full-load independent piconet, the full-duplex data rate exceeds 6 MB/s.
The voice channel adopts continuous variable slope incremental modulation (CVSD) voice coding scheme, and never retransmits voice packets. CVSD coding is good at dealing with lost and damaged speech samples. Even if the bit error rate reaches 4%, the voice encoded by CVSD can still be heard.
The Bluetooth air interface is based on an antenna level of 0dBm. The air interface follows the ISM band standard of FCC (Federal Communications Commission), and the level is 0dBm. If the global level is above 100mW, you can use the spread spectrum function to add some supplementary services. The spectrum spreading function is realized by 79 frequency hopping points, starting frequency is 2.402, ending frequency is 2.480, and the interval is 1MHz. Due to some local regulations, Japan, France and Spain all reduced their bandwidth. The maximum frequency hopping rate is 1660 hops/second. The ideal connection range is 10 cm- 10 m, but the distance can be extended to 100 m by improving the transmission level.
Bluetooth devices need to support some basic interoperability requirements. For some devices, this requirement involves wireless module, air protocol, application layer protocol and object exchange format. But for other devices, such as headphones, this requirement is much simpler. Bluetooth devices must be able to recognize each other and load corresponding software to support a higher level of device performance.
Bluetooth has different requirements for different levels of equipment (such as PC, handset, mobile phone, earphone, etc.). For example, you can't expect a Bluetooth headset to provide an address book. However, mobile phones, mobile phones and laptops need more functional features.
Bluetooth profile interface can be directly integrated into notebook computer, or connected through PC card or USB interface.
The usage modes of notebook computers include:
Connect to a remote network through a Bluetooth phone.
Use Bluetooth mobile phone as speaker
Business card transactions among Bluetooth laptops, mobile phones and mobile phones
Time Synchronization among Bluetooth Laptop, Mobile Phone and Mobile Phone
Bluetooth is an independent operating system and does not depend on any operating system. Bluetooth profiles of several different commercial operating systems are being improved.
Bluetooth mode interface can be directly integrated into the cellular phone or connected through other devices. The usage modes of the mobile phone include (optional):
Realize the hands-free function of mobile phone through Bluetooth wireless headset.
Wireless connection with laptop and mobile phone
Trade with business cards of other Bluetooth phones, laptops and mobile phones.
Automatically synchronize the address book with a trusted Bluetooth laptop or mobile phone.
Usage patterns of other Bluetooth devices include:
earphone
Mobile phones and other portable devices
Man-machine interface equipment
Data and voice access points