2. Technical characteristics: Bluetooth technology features include: frequency hopping technology, anti-signal degradation; fast frequency hopping and short packet technology to reduce the co-frequency interference, to ensure the reliability of the transmission; the use of forward error correction coding technology, to reduce the impact of the random noise of the long-distance transmission; the use of the 2.4GHz ISM band, without the need to apply for a license; the use of FM modulation to reduce the complexity of the device. FM modulation reduces the complexity of the equipment. The technology is designed for a transmission rate of 1 MHz, full-duplex communication in a time-division mode, and its baseband protocol is a combination of circuit-switched and packet-switched. One synchronous packet is sent at a hopping rate, with each packet occupying one time slot, which can be extended to five time slots. Bluetooth technology supports one asynchronous data channel or three concurrent synchronous voice channels, or one channel that transmits both asynchronous data and synchronous voice. Each voice channel supports 64kb/s synchronous voice; the asynchronous channel supports asymmetric connections with a maximum rate of 721kb/s and a reverse answer rate of 57.6kb/s or symmetric connections with 432.6kb/s.
3. Protocol:
(1) Establishment of Connection
Before the establishment of a micro-micro network, all devices are in a ready state. In this state, unconnected devices listen for messages every 1.28s, and once a device is woken up, it listens for messages on a pre-set frequency of 32 hopping frequencies. The number of hopping frequencies varies from region to region, but the 32 hopping frequencies are used by the vast majority of countries. The connection process is initialized by the master device. If the address of a device is known, a Page message is used to establish the connection; if the address is unknown, an Inquiry message immediately following the Page message is used to establish the connection. In a micro-micro network, devices with no data transmission move to an energy-saving operating state. The master device can set the slave device to the hold mode, at this time, only the internal timer works; the slave device can also request to transfer to the hold mode. Data transmission can be resumed immediately after the device is transferred out of the hold mode. The hold mode is often used when connecting several pico networks or managing low-power devices. Listening mode and sleep mode are two other low-power operating modes. Bluetooth baseband technology supports two connection methods: the connection-oriented (SCO) method, mainly used for voice transmission, and the connectionless (ACL) method, mainly used for packet data transmission.
(2) Error Control
The baseband controller uses three types of error detection and correction methods: 1/3 forward error correction coding (FEC); 2/3 forward error correction coding (FEC); and automatic request retransmission (ARQ).
(3) Authentication and Encryption
Authentication and encryption services are provided by the physical layer. Authentication is done using a password-response method, and may be required once or twice during the connection process, or no authentication is required. Authentication is an important part of any Bluetooth system and allows the user to add trusted Bluetooth devices on their own, e.g., only the user's own laptop can communicate through the user's own cell phone. The purpose of Bluetooth security mechanisms is to provide an appropriate level of protection, and if the user has higher levels of confidentiality requirements, effective transport and application layer security mechanisms can be used.
(4) Software Architecture
Bluetooth devices should be interoperable, from radio-compatible modules and air interfaces up to application layer protocols and object exchange formats for some devices; for others (e.g., headset devices, etc.) the requirements are much less stringent. The goal of the Bluetooth Initiative is to ensure that any device with a Bluetooth tag can operate interchangeably. Software interoperability begins with link-level protocols for multiplexing, device and service discovery, and packet segmentation and reorganization. Bluetooth devices must be able to recognize each other and identify the high-level functionality supported by each other 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 do not have the luxury of an address book contained within the headset. Bluetooth compatibility means that it has radio compatibility, the ability to send and receive voice and the ability to discover other Bluetooth devices, and more functionality to be accomplished by cell phones, handhelds and laptops. In order to realize these functions, Bluetooth software architecture will make use of existing specifications, such as OBEX, vCard/vCalendar, HID (Human Interface Device) and TCP/IP, rather than developing new specifications. Device compatibility requires the ability to adapt to Bluetooth specifications and existing protocols.
4. Advantages: Bluetooth transmission is carried out through the RF (2.4GHZ) carrier, so it has the basic characteristics of electromagnetic waves, there is a greater power, can increase the transmission distance, and there is no angle and directional limitations, with through the wall, can be reflected between the object, the mirror set up, bypassing shot. Bluetooth is mainly used for short distance transmission (up to 10 meters) data and voice (1Mbps), power consumption is very low energy, while being able to connect many components, fast transmission speed.
5. Disadvantages: Bluetooth cost is very high; RF technology is susceptible to frequency interference; through-the-wall characteristics of the data security protection set the problem; Bluetooth started relatively late, there is no clear, unified standards, compatibility issues have not yet been able to solve.
Bluetooth's name comes from the 10th century Danish King Harald Blatand - English translation for Harold Bluetooth (because he was very fond of eating blue plums, so the teeth every day with blue). During the preparatory phase of the industry association, a very expressive name was needed for the new technology. The organizers, after a night's discussion on the history of Europe and the future of infinite technology, some thought that the name of King Blatand, who united the present Norway, Sweden and Denmark, and whose eloquent and sociable personality was akin to that of this upcoming technology, which was to be defined as one that allowed for the coordination of the different industrial sectors, keeping the various system areas working in harmony with each other. The technology will be defined as allowing coordination between different industrial sectors, maintaining good communication between various system areas, such as computing, cell phones and the automotive industry. And so the name was decided.
In the Danish city of Jelling, there is a monument in the church that honors the achievements of King Blatand and his father, Denmark's first king, Gorm the Old. Interestingly, this particular stone was lost after a battle between Harald and his son Sven Forkbeard, and no one has seen it for almost 600 years; Sven won (and exiled his father), and because the stone with the ancient Norse inscription was an honor to Harald, Sven buried it. It wasn't until the last few years that a farmer became curious about this large mound of dirt on his farm and finally discovered the stone.
The logo was originally designed by Scandinavian when the business association was announced. The logo retains the traditional character of its name, containing the Old Norse letter "H", which looks very similar to an asterisk and a "B", both of which can be seen when looking closely at the logo.
Therefore, as the name suggests, the concept of Bluetooth is: specifically, Bluetooth is a short-range, single-point-to-multipoint voice and data information transmission and exchange standard using RF radio frequency (RadioFrequency) technology. Its data transfer rate of 1Mbps, the technology's communication distance of 10cm ~ 10m, if you increase the signal amplification device, its communication distance can be extended to 100m, and can bypass non-metallic obstacle objects. Bluetooth operates in the 2.4GHz industrial/scientific/medical radio band, which is not subject to the restrictions of national radio administrations, so it has global promotion value. Compared with the current infrared wireless transmission IrDA technology in laptop computers and other devices, Bluetooth has a long transmission distance, no transmission angle, and is not affected by obstacle interference and other characteristics.
Bluetooth history
Bluetooth is a radio technology that supports short-range communication (generally within 10 meters). Including cell phones, PDAs, wireless headsets, laptops, related peripherals and many other devices for wireless information exchange. The standard of Bluetooth is IEEE802.15, working in 2.4GHz frequency band, bandwidth of 1Mb/s.
"Bluetooth" (Bluetooth) was originally a king in the 10th century to unify Denmark, who united Sweden, Finland and Denmark at that time. Naming this new technology standard after him means unifying a fragmented situation. Bluetooth technology uses advanced technologies such as high-speed frequency hopping (FH, Frequency Hopping) and time division multiple access (TDMA, Time DivesionMuli-access) to most cheaply connect several digitalized devices in close proximity (various mobile devices, fixed communication devices, computers and their terminal equipment, various digital Data systems, such as digital cameras, digital video cameras, and even a variety of household appliances, automation equipment) in a network link. Bluetooth technology will be the network of a variety of peripheral devices interface to the unified bridge, which eliminates the connection between the device, replaced by a wireless connection.
Bluetooth is a short-range wireless communication technology that allows electronic devices to be connected to each other via 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, infrared interfaces required electronic devices to be within line-of-sight distance, and now with Bluetooth technology, this trouble can be eliminated.
Bluetooth (Bluetooth) is a technology standard for short-range wireless digital communications proposed by Toshiba, Ericsson, IBM, Intel, and Nokia in May 1998***. Its goal is to achieve the highest data transmission speed of 1Mb / s (effective transmission speed of 721kb / s), the maximum transmission distance of 10 meters, the user does not have to apply for the use of 2.4GHz ISM (industrial, scientific, medical) band, in which the establishment of 79 bandwidth for the 1MHz channel, with the switching of the frequency 1600 times per second, the hobble way of spectrum diffusion technology to achieve the The technology is used to send and receive radio waves.
Advantages of Bluetooth technology: support for voice and data transmission; the use of radio technology, transmission range is large, can penetrate different substances as well as diffusion between substances; the use of frequency hopping spread spectrum technology, anti-interference is strong, it is not easy to eavesdrop; the use of the spectrum in all countries are not subject to limitations, theoretically, there is no problem of interference; low power consumption; low cost. Disadvantages of Bluetooth: slow transmission speed. Bluetooth's technical performance parameters: effective transmission distance of 10cm ~ 10m, increase the transmit power can reach 100 meters, or even farther. The transceiver operates at 2.45GHz and covers 79 channels separated by 1MHz (from 2.402GHz to 2.480GHz). The data transmission technology uses short packets, frequency hopping spread spectrum technology, 1600 times/second, to prevent eavesdropping and avoid interference; one packet is transmitted at a time, the size of the packet ranges from 126 to 287 bits; the contents of the packet can contain information about different services such as data or voice. Data transmission bandwidth is 32.6Kbps in each direction for synchronous connections, which is close to 10 times the analog connection rate of a typical 56kb/s Modem, and asynchronous connections allow for data transmission rates of up to 721kb/s in one direction for uploads or downloads, when the rate in the opposite direction is 57.6kb/s; the data transmission channels are set aside for three concurrent, synchronous voice channels, each with 64kb/s bandwidth. Each has a bandwidth of 64kb/s; voice and data can also be mixed in one channel, providing a 64kb/s synchronous voice connection and an asynchronous data connection. Network connection using encryption technology, while using password authentication to connect the device, can be simultaneously with other devices up to 7 constitute a Bluetooth micro-network (Piconet), a Bluetooth device can simultaneously join 8 different micro-networks, each micro-network respectively 1Mb/s transmission bandwidth, when more than 2 devices **** to enjoy a Channel, can constitute a Bluetooth micro-network, and one device dominates the transmission volume, and when one device dominates the transmission volume, the Bluetooth micro-network can be formed. one of the devices dominates the transmission volume, when the device has not yet joined the Bluetooth micro-network, it first enters standby mode.