What is Bluetooth? Everyone laughed, but I really didn't know that my mobile phone had Bluetooth, but I didn't know anything, let alone use it.

1. Concept: Bluetooth, a new wireless transmission mode introduced by 1998, is actually a short-distance wireless communication technology that replaces data cables, and realizes point-to-point or point-to-multipoint information exchange through low-bandwidth radio waves. This network mode, also known as Personal Network (PAN), is based on multiple mini-networks or mini-networks constructed by exquisite Bluetooth master devices/accessories. Each microgrid consists of 8 active devices and 255 accessory devices, and a plurality of microgrids are connected to form an extended network, so that communication between various devices can be realized conveniently and quickly. It is an open standard to realize wireless transmission of voice and data, and it is a low-cost and short-distance wireless connection technology.

2. Technical features: The features of Bluetooth technology include: using frequency hopping technology to resist signal fading; Adopt fast frequency hopping and short packet technology to reduce co-frequency interference and ensure transmission reliability; Adopt forward error correction coding technology to reduce the influence of random noise in long-distance transmission; Use ISM band 2.4GHz, without applying for a license; Frequency modulation is adopted to reduce the complexity of the equipment. The transmission rate of this technology is designed as 1MHz, and full-duplex communication is carried out in time division mode. Its baseband protocol is a combination of circuit switching and packet switching. A frequency hopping sends a synchronization packet, and each packet occupies one time slot, which can also be extended to five time slots. Bluetooth technology supports 1 asynchronous data channel or 3 simultaneous synchronous voice channels, or 1 channel for transmitting asynchronous data and synchronous voice at the same time. Each voice channel supports 64kb/s synchronous voice; Asynchronous channels support asymmetric connections with a maximum rate of 72 1kb/s and a reverse response rate of 57.6kb/s, or symmetric connections with a rate of 432.6 kb/s. ..

3. Agreement:

(1) establish a connection

Before the piconet is established, all devices are in a ready state. In this state, the unconnected device listens for messages every1.28s. Once the device is awakened, it listens for messages with a preset frequency of 32 hops. The frequency of frequency hopping varies in different regions, but most countries use the frequency of 32 frequency hopping. The connection process is initiated by the master device. If the address of the device is known, the connection is established by using a paging message; If the address is unknown, the connection is established by using a query message immediately following the paging information. In a piconet, devices without data transmission enter an energy-saving working state. The master device can set the slave device to hold mode, at which time only the internal timer works; The slave can also request to switch to the hold mode. After the device is turned off by holding mode, data transmission can be resumed immediately. Hold mode is usually used when connecting multiple piconets or managing low-power devices. Monitoring mode and sleep mode are two other low-power working modes. Bluetooth baseband technology supports two connection modes: connection-oriented (SCO) mode, which is mainly used for voice transmission; Connectionless (ACL) mode, mainly used for packet data transmission.

(2) Error control

The baseband controller adopts three error detection and correction methods: 1/3 forward error correction coding (FEC); 2/3 forward error correction coding; Automatic repeat request (ARQ).

(3) Authentication and encryption

The physical layer provides authentication and encryption services. Authentication adopts password response method. During the connection process, authentication may or may not be required once or twice. Authentication is an important part of any Bluetooth system, which allows users to add trusted Bluetooth devices themselves. For example, only users' own laptops can communicate through their own mobile phones. The purpose of Bluetooth security mechanism is to provide an appropriate level of protection. If users have higher confidentiality requirements, effective transport layer and application layer security mechanisms can be used.

(4) Software structure

Bluetooth devices should be interoperable. For some devices, it is necessary to realize the interoperability from radio compatibility module, air interface to application layer protocol and object exchange format. Requirements for other equipment (such as head mounted equipment, etc.). ) it is much looser. The goal of the Bluetooth project is to ensure that any devices with Bluetooth tags can interoperate. Software interoperability begins with the multiplexing of link layer protocols, the discovery of devices and services, and the segmentation and reassembly of data packets. Bluetooth devices must be able to recognize each other and identify the advanced functions supported by each other by installing appropriate software. Interoperability requires the same application layer protocol stack. Different types of Bluetooth devices have different requirements for compatibility, so users can't expect headphones to contain address books. Bluetooth compatibility refers to radio compatibility, voice transceiving ability and the ability to find other Bluetooth devices. More functions should be completed by mobile phones, handheld devices and notebook computers. In order to realize these functions, Bluetooth software architecture will make use of existing specifications, such as OBEX, vCard/vCalendar, HID and TCP/IP, instead of developing new specifications. The compatibility of the device requires that it can adapt to bluetooth profile and existing protocols.

4. Advantages: Bluetooth transmission is carried out by radio frequency (2.4GHZ) carrier, so it has the basic characteristics of electromagnetic waves, high power, can increase the transmission distance, and has the ability to penetrate walls, and can reflect, mirror and diffract between objects. Bluetooth is mainly used for short-distance transmission of data and voice (1Mbps) (farthest 10 meter), with extremely low power consumption, and can connect multiple components at the same time, with high transmission speed.

5. Disadvantages: Bluetooth is expensive; Radio frequency technology is susceptible to frequency interference; Data security protection settings based on wall penetration characteristics; Bluetooth started late, there is no clear and unified standard at present, and the compatibility problem has not been solved.

The name of Bluetooth comes from Danish King Harald Blatand in the 10 century. In the preparatory stage of the trade association, an expressive name is needed to name this high-tech. Industry organizers, after a night of discussion about the history of Europe and the infinite development of science and technology in the future, some people think that it is most appropriate to name it after King Blatter. King Blatter unified Norway, Sweden and Denmark. Just like this upcoming technology, technology will be defined as allowing coordination between different industrial fields, such as computing, mobile phones and automobile industries. So the name is decided.

In Jelling, Denmark, there is a monument in the church. This monument was erected to commemorate the achievements of King Blatin and his father, the first Danish king "Old Golm". Interestingly, this special stone was lost after a war between harald and his son Sven Fokbeard. No one has seen this stone for nearly 600 years. Sven won (and exiled his father), because this stone engraved with ancient Nordic characters is the glory of harald, so Sven buried it. Until recent years, a farmer became curious about this big mound on his farm and finally found this stone.

This logo was originally designed by Scandinavian companies when the business association announced it. The logo retains the traditional features of its name, including the ancient Nordic letter "H", which looks very similar to the asterisk and "B". You can see both carefully on the trademark.