Bluetooth is an open standard for wireless data and voice transmission that connects a variety of communication devices, computers and their terminals, digital data systems, and even home appliances wirelessly. Its transmission distance is 10cm to 10m, and if the power is increased or some peripherals are added, the transmission distance can reach 100m. It adopts 2.4GHz ISM band and FM, frequency hopping technology, using right-to-error correction coding, ARQ, TDD and baseband protocols.TDMA is 0.625μs per time slot, and the baseband complies with the rate of 1Mb/s. Bluetooth supports real-time voice and data transmission at 64kb/s, with voice coding as CVSD, and the transmit power is 1mW, 2.5mW, and 100mW, respectively, and uses a globally standardized 48-bit device identification code. Because Bluetooth uses a wireless interface to replace the wired cable connection, it has strong portability and is suitable for a wide range of occasions, coupled with the technology's low power consumption, low harm to the human body, and the application is simple and easy to implement, so it is easy to promote.
Bluetooth technology
SIG organization in July 26, 1999 launched the Bluetooth technical specifications 1.0 version. The system structure of Bluetooth technology is divided into three major parts: the underlying hardware module, the intermediate protocol layer and the high-level application. The underlying hardware part includes radio frequency hopping (RF), baseband (BB) and link management (LM). The RF layer filters and transmits data bit streams through microwaves in the 2.4GHz unauthorized ISM band. The protocol of this layer mainly defines the conditions that Bluetooth transceivers need to satisfy for normal operation in this band. Baseband is responsible for frequency hopping and the transmission of Bluetooth data and information frames. Link management is responsible for connecting, establishing and dismantling links and performing security controls.
Bluetooth technology combines circuit-switched and packet-switched features to enable asynchronous data communications, support for up to three simultaneous synchronous voice channels, and the ability to use a single channel to transmit both asynchronous data and synchronous voice. Each voice channel supports a synchronous voice link of 64 kb/sec. Asynchronous channels can support asymmetric links with a maximum rate of 721kb/sec at one end and 57.6kb/sec at the other, as well as symmetric links with a rate of 43.2kb/sec.
The intermediate protocol layer includes the logical link control and adaptation protocol, the service discovery protocol, the serial emulation protocol, and the telephony communication protocol. The logical link control and adaptation protocol has the function of completing data disassembly, controlling the quality of service and multiplexing protocols, and this layer of protocols is the basis for the realization of the other layers of protocols. The Service Discovery Protocol layer provides a mechanism for upper layer applications to discover the services available in the network and their characteristics. The serial port emulation protocol layer has the capability to emulate a 9-pin RS232 serial port. The telephony communication protocol layer provides call control commands for voice and data between Bluetooth devices.
The Host Control Interface (HCI) layer is the interface between hardware and software in the Bluetooth protocol, and 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 entities above the HCI run on the host computer, while the functions below the HCI are performed by the Bluetooth device, and the two interact through a transport layer that is transparent to both ends.
At the top of the Bluetooth stack are various high-level application frameworks. The more typical ones are dial-up networking, headset, LAN access, file transfer, etc., which correspond to an application mode. Various applications can realize 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 cell phones and earbuds through the Audio layer in the protocol stack; multiple PCs or laptops can quickly and flexibly transfer files and *** enjoy information without any wires, and synchronized operation can also be realized between multiple devices. This means that you can also synchronize the operation of your PCs with other devices.
In short, the entire Bluetooth protocol is simple and uses a retransmission mechanism to ensure link reliability, and a variety of security mechanisms can be implemented in the baseband, link management, and application layers for hierarchical security, and frequency hopping technology to eliminate interference from other wireless devices in the network environment.
Application Prospects
Bluetooth technology has a wide range of applications, and can be widely used in local area networks for all types of data and voice devices, such as PCs, dial-up networks, laptops, printers, fax machines, digital cameras, cell phones, and high-quality headsets, etc. Bluetooth's wireless communication method connects the above devices to a Piconet, and multiple Piconets can be connected to each other. Multiple micro-micro-network can also be connected to each other, thus realizing the communication between various types of equipment at any time and anywhere. Typical environments where Bluetooth technology is applied include wireless office environment, automotive industry, information appliances, medical equipment, school education and factory automation. At present, the initial products of bluetooth has come out, some chip manufacturers have begun to improve the chip with bluetooth function. At the same time, some powerful software companies or the introduction of their own protocol stack software, or with chip makers to launch a Bluetooth technology to achieve the specific program. Nevertheless, Bluetooth technology to really popularize the following problems need to be solved: first of all, to reduce costs; secondly, to achieve convenient, practical, and really bring benefits to people; thirdly, to be safe, stable and reliable work; fourthly, to introduce an authoritative international standard as soon as possible. Once the above problems are solved, Bluetooth will rapidly change the way people live and work, and greatly improve people's quality of life.