What exactly is the Bluetooth function on a mobile phone?

"Bluetooth" is an open standard for wireless data and voice transmission. It connects various communication equipment, computers and their terminal equipment, various digital data systems, and even household appliances wirelessly. Its transmission distance is 10cm ~ 10m. If the power is increased or certain peripherals are added, the transmission distance can reach 100m. It uses the 2.4GHz ISM frequency band and frequency modulation and frequency hopping technology, and uses weighted error correction coding, ARQ, TDD and baseband protocols. Each time slot of TDMA is 0.625μs, and the baseband compliance rate is 1Mb/s. Bluetooth supports 64kb/s real-time voice transmission and data transmission. The voice encoding is CVSD, the transmission power is 1mW, 2.5mW and 100mW respectively, and uses a globally unified 48-bit device identification code. Because Bluetooth uses a wireless interface to replace wired cable connections, it has strong portability and is suitable for a variety of occasions. In addition, the technology has low power consumption, is less harmful to the human body, is simple to apply, and is easy to implement, so it is easy to promote. Bluetooth technology The SIG organization launched version 1.0 of the Bluetooth technology specification on July 26, 1999. The system structure of Bluetooth technology is divided into three parts: the underlying hardware module, the intermediate protocol layer and the high-level application. The underlying hardware part includes wireless frequency hopping (RF), baseband (BB) and link management (LM). The wireless frequency hopping layer implements the filtering and transmission of data bit streams through the microwave of the 2.4GHz unlicensed ISM band. This layer of protocol mainly defines the conditions that the Bluetooth transceiver needs to meet to operate normally in this frequency band. The baseband is responsible for frequency hopping and the transmission of Bluetooth data and information frames. Link management is responsible for connecting, establishing and tearing down links and performing security control. Bluetooth technology combines the characteristics of circuit switching and packet switching, can carry out asynchronous data communication, can support up to 3 simultaneous synchronous voice channels, and can also use one channel to transmit asynchronous data and synchronous voice at the same time. Each voice channel supports a 64kb/sec synchronous voice link. The asynchronous channel can support an asymmetric connection with a maximum rate of 721kb/sec on one end and a rate of 57.6kb/sec on the other end, or a symmetric connection of 43.2kb/sec. The intermediate protocol layer includes logical link control and adaptation protocols, service discovery protocols, serial port emulation protocols and telephone communication protocols. Logical link control and adaptation protocols have the functions of completing data disassembly and assembly, controlling service quality and reusing protocols. This layer of protocols is the basis for the implementation of other layer protocols. The service discovery protocol layer provides a mechanism for upper-layer applications to discover the services and their characteristics available in the network. The serial port simulation protocol layer has the function of simulating a 9-pin RS232 serial port. The telephone communication protocol layer provides call control instructions for voice and data between Bluetooth devices. The host control interface layer (HCI) is the interface between software and hardware in the Bluetooth protocol. It provides a unified command interface for calling hardware such as baseband, link management, status and control registers. When communicating between Bluetooth devices, the protocol software entity above HCI runs on the host, while the functions below HCI are completed by the Bluetooth device. The two interact through a transport layer that is transparent to both ends. At the top of the Bluetooth protocol stack are various high-level application frameworks. The more typical ones include dial-up network, headset, LAN access, file transfer, etc., each of which corresponds to an application mode. Various applications can implement wireless communication through their corresponding application modes. Dial-up network applications can access the Piconet through the emulated serial port, and data devices can also access the traditional LAN; users can realize wireless transmission of audio streams in mobile phones and earbuds through the Audio layer in the protocol stack; and more Without any connection between PCs or laptops, files can be transferred and information shared quickly and flexibly, and multiple devices can also be operated simultaneously.