． Concept: BLUETOOTH is a new wireless transmission method launched in 1998. It is actually a short-distance wireless communication technology that replaces data cables. It realizes point-to-point or point-to-multipoint connection information through low-bandwidth radio waves. comminicate. This network mode is also called Personal Area Network (PAN). It is based on a mini-network constructed by multiple micro-networks or exquisite Bluetooth master controllers/accessories. Each micro-network consists of 8 active devices. It is composed of 255 auxiliary devices, and multiple micro-networks are connected to form an enlarged network, thereby realizing communication between various devices conveniently and quickly. It is an open specification for wireless transmission of voice and data. It is a low-cost, short-distance wireless connection technology.
2． Technical features: The features of Bluetooth technology include: using frequency hopping technology to resist signal fading; using fast frequency hopping and short packet technology to reduce co-channel interference and ensuring transmission reliability; using forward error correction coding technology to reduce long-distance transmission The influence of random noise at the time; using the 2.4GHz ISM frequency band, no need to apply for a license; using FM modulation method to reduce the complexity of the equipment. The transmission rate of this technology is designed to be 1MHz, and full-duplex communication is performed in a time division manner. Its baseband protocol is a combination of circuit switching and packet switching. One frequency hopping frequency sends a synchronization packet, and each packet occupies one time slot, which can also be extended to 5 time slots. Bluetooth technology supports 1 asynchronous data channel or 3 concurrent synchronous voice channels, or 1 channel that transmits asynchronous data and synchronous voice simultaneously. Each voice channel supports 64kb/s synchronous voice; the asynchronous channel supports an asymmetric connection with a maximum rate of 721kb/s and a reverse response rate of 57.6kb/s, or a symmetric connection of 432.6kb/s.
3. Protocol:
(1) Establish connection
Before the piconet is established, all devices are in a ready state. In this state, the unconnected device listens for messages every 1.28s. Once the device wakes up, it listens for information on the 32 preset hopping frequencies. The number of frequency hopping varies from region to region, but 32 hopping frequencies are used by the vast majority of countries. The connection process is initiated by the master device. If the address of a device is known, the page message (Page message) is used to establish the connection; if the address is unknown, the inquiry message (Inquiry message) following the page information is used to establish the connection. In the piconet, equipment without data transmission enters an energy-saving working state. The master device can set the slave device to hold mode. At this time, only the internal timer works; the slave device can also request to switch to hold mode. After the device is transferred out of the hold mode, data transmission can be resumed immediately. Holdover is often used when connecting several piconets or managing low-power devices. Monitoring mode and sleep mode are two other low-power working modes. Bluetooth baseband technology supports two connection methods: connection-oriented (SCO) method, mainly used for voice transmission; connectionless (ACL) method, mainly used for packet data transmission.
(2) Error control
The baseband controller adopts 3 error detection and correction methods: 1/3 forward error correction coding (FEC); 2/3 forward error correction Encoding; Automatic Request for Retransmission (ARQ).
(3) Authentication and encryption
Authentication and encryption services are provided by the physical layer. Authentication adopts password-response method. During the connection process, authentication may be required once or twice, or no authentication may be required. Authentication is an important part of any Bluetooth system. It allows users to add trusted Bluetooth devices themselves. For example, only the user's own laptop can communicate through the user's own mobile phone. The purpose of the Bluetooth security mechanism is to provide an appropriate level of protection. If the user has higher-level confidentiality requirements, effective transport layer and application layer security mechanisms can be used.
(4) Software structure
Bluetooth devices should be interoperable. For some devices, everything from radio compatibility modules and air interfaces to application layer protocols and object exchange formats To achieve interoperability; the requirements for other devices (such as headsets, etc.) are much looser. The goal of the Bluetooth program is to ensure that any device bearing the Bluetooth mark can operate interchangeably. Software interoperability begins with link-level protocol multiplexing, device and service discovery, and packet segmentation and reassembly. Bluetooth devices must be able to recognize each other and the high-level functions that each other supports by installing the appropriate software. Interoperability requires the use of the same application layer protocol stack. Different types of Bluetooth devices have different requirements for compatibility, and users cannot expect the headset to contain an address book. The compatibility of Bluetooth means that it has radio compatibility, voice transceiver capabilities and the ability to discover other Bluetooth devices. More functions must be completed by mobile phones, handheld devices and laptops. To achieve these functions, the Bluetooth software architecture will utilize existing specifications, such as OBEX, vCard/vCalendar, HID (Human Interface Device), and TCP/IP, rather than developing new specifications. Device compatibility requires being able to adapt to Bluetooth specifications and existing protocols.
4. Advantages: Bluetooth transmission is carried out through RF (2.4GHZ) carrier, so it has the basic characteristics of electromagnetic waves, has larger power, can increase the transmission distance, and has no angle and directionality restrictions, has wall penetration, and can be used on objects Reflection, mirroring, and diffraction. Bluetooth is mainly used for short-distance transmission (up to 10 meters) of data and voice (1Mbps). It consumes very low energy and can connect many components at the same time with fast transmission speed.
5. Disadvantages: The cost of Bluetooth is very high; RF technology is susceptible to frequency interference; the wall-penetrating feature has problems with data security protection; Bluetooth started relatively late, and there is currently no clear and unified standard, and compatibility issues have not yet been resolved. .
The name of Bluetooth comes from the 10th century Danish King Harald Blatand - translated as Harold Bluetooth in English (because he liked to eat blue plums very much, so his teeth were blue every day). In the preparatory stage of the industry association, a highly expressive name was needed to name this high-tech technology. Industry organizers, after a night of discussions about European history and future endless technological developments, some thought it would be more appropriate to name it after King Blatand. King Blatand united what is now Norway, Sweden and Denmark; he was as articulate and sociable as the upcoming technology, which would be defined as allowing coordinated work between different industrial sectors, maintaining individual systems Good communication between fields, such as work between computing, mobile phones and the automotive industry. So the name was decided.
In the Danish city of Jelling, there is a monument erected in the church. This monument was erected to commemorate the achievements of King Blatand and his father, the first king of Denmark, "Gorm the Old". Interestingly, this particular stone was lost after a war between Harald and his son Sven Forkbeard, and no one had seen the stone for nearly 600 years. Sven won (and had his father exiled), and since the stone with the ancient Norse writings on it was Harald's glory, Sven buried it. It was only in recent years that a farmer became curious about the large mound on his farm and finally discovered the stone.
This logo was originally designed by the Scandinavian company when the business association was announced. The logo retains the traditional character of its name, which includes the Old Norse letter "H", which looks very similar to an asterisk and a "B", both of which can be seen if you look closely at the logo.
Therefore, as the name implies, the concept of Bluetooth is: Specifically, Bluetooth is a short-distance, single-point-to-multipoint voice and data information transmission and exchange standard that uses RF radio frequency (Radio Frequency) technology. Its data transmission rate is 1Mbps, and the communication distance of this technology is 10cm ~ 10m. If a signal amplification device is added, the communication distance can be extended to 100m, and it can bypass non-metallic obstacles. Bluetooth works in the 2.4GHz industrial/scientific/medical radio band. This band is not restricted by the radio management departments of various countries. Therefore, it has global promotion value. Compared with the current infrared wireless transmission IrDA technology used in laptops and other devices, Bluetooth has the characteristics of long transmission distance, no transmission angle, and no interference from obstacles.
Introduction to the history of Bluetooth
Bluetooth is a radio technology that supports short-distance communication between devices (generally within 10m). It can conduct wireless information exchange between many devices including mobile phones, PDAs, wireless headsets, laptops, related peripherals, etc. The standard of Bluetooth is IEEE802.15, which operates in the 2.4GHz frequency band and has a bandwidth of 1Mb/s.
"Bluetooth" was originally a king who unified Denmark in the 10th century. He unified Sweden, Finland and Denmark at that time. Naming this new technical standard after him means unifying the fragmented situation. Bluetooth technology uses advanced technologies such as high-speed frequency hopping (FH, Frequency Hopping) and time division multiple access (TDMA, Time DivesionMulti-access) to connect several digital devices (various mobile devices, fixed communication equipment, Computers and their terminal equipment, various digital data systems, such as digital cameras, digital video cameras, etc., and even various household appliances and automation equipment) are linked in a network. Bluetooth technology will be a unified bridge for various peripheral device interfaces in the network. It eliminates the connections between devices and replaces them with wireless connections.
Bluetooth is a short-range wireless communication technology. Electronic devices can be connected to each other through Bluetooth, eliminating the need for traditional wires. Through the wireless receiver on the chip, electronic products equipped with Bluetooth technology can communicate with each other within a distance of ten meters, and the transmission speed can reach 1 megabyte per second. In the past, the transmission technology of infrared interface required the electronic device to be within the line of sight, but now with Bluetooth technology, such trouble can be eliminated.
Bluetooth is a technical standard for short-range wireless digital communications jointly proposed by Toshiba, Ericsson, IBM, Intel and Nokia in May 1998. The goal is to achieve a maximum data transmission speed of 1Mb/s (effective transmission speed of 721kb/s) and a maximum transmission distance of 10 meters. Users can use the 2.4GHz ISM (Industrial, Scientific, and Medical) frequency band without applying. 79 channels with a bandwidth of 1MHz are set up on the Internet, and the frequency is switched 1,600 times per second and the spectrum diffusion technology of the hobbing method is used to realize the transmission and reception of radio waves.
Advantages of Bluetooth technology: supports voice and data transmission; uses radio technology, has a large transmission range, can penetrate different substances and diffuse between substances; uses frequency hopping spread spectrum technology, which has strong anti-interference and is not easy to Eavesdropping; using spectrum that is unrestricted in all countries, theoretically, there is no interference problem; low power consumption; low cost. Disadvantages of Bluetooth: slow transmission speed. Technical performance parameters of Bluetooth: The effective transmission distance is 10cm~10m, and the transmission power can be increased to 100 meters or even further. The transceiver operates at 2.45GHz and covers 79 channels (from 2.402GHz to 2.480GHz) 1MHz apart. Data transmission technology uses short packets, frequency hopping spread spectrum technology, 1600 times/second to prevent eavesdropping and avoid interference; each time a packet is transmitted, the size of the packet ranges from 126 to 287 bits; the content of the packet can include data or voice, etc. Service information.
The data transmission bandwidth for a synchronous connection can reach 32.6Kbps in each direction, which is close to 10 times the typical analog connection rate of 56kb/s Modem. The asynchronous connection allows a data transmission rate of up to 721kb/s in one direction for uploading or downloading. This The rate in the opposite direction is 57.6kb/s; the data transmission channel is reserved for 3 concurrent synchronous voice channels, each with a bandwidth of 64kb/s; voice and data can also be mixed in one channel to provide a 64kb/s synchronous voice connection and an asynchronous data connection. The network connection uses encryption technology and uses password verification to connect the device. It can form a Bluetooth micronet (Piconet) with up to 7 other devices at the same time. One Bluetooth device can join 8 different piconets at the same time. Each micronet has its own With a transmission bandwidth of 1Mb/s, when more than two devices share a Channel, a Bluetooth micronet can be formed, and one of the devices will dominate the transmission volume. When the device has not yet joined the Bluetooth micronet, it Enter the standby state first.