Prior to this, the leader in the wireless communication industry was infrared transmission, which is familiar to everyone. But infrared has a fatal disadvantage that the transmission technology of the infrared interface must work within the visible range. The existence of this drawback provides a new opportunity for the development of Bluetooth.
In addition, in terms of range of use, the difference between infrared and Bluetooth is still very obvious. Infrared technology is generally suitable for low-cost, cross-platform, point-to-point high-speed data connections, especially embedded systems, such as: device interconnection, information gateways, etc. Bluetooth is different. Bluetooth technology was proposed as a "cable replacement" technology, which has evolved into a personal information network platform today. It mainly has the following three main uses: voice / data access, peripheral equipment interconnection, and personal local area network.
Infrared, which was invented in 1974, brought us a new way of connection. More importantly, it brought us a new concept and made us feel a wireless refresh. In 1998, Bluetooth technology stood out and attracted me with its strong advantages, and it has the potential to cover infrared rays. What is the difference between Bluetooth protocol and infrared transmission protocol?
Bluetooth
1. concept
Bluetooth (BLUETOOTH) is a new wireless transmission method introduced in 1998. In fact, it is a short-distance wireless communication technology that replaces data cables. It realizes point-to-point or point-to-multipoint connection information exchange through low-bandwidth radio waves. This network model is also known as a private space network (PAN, Personal Area Network), and is based on a mini network constructed by multiple micro networks or elaborate Bluetooth masters / accessories. Each micro network is composed of 8 active devices. It is composed of 255 auxiliary devices, and multiple micro-networks are connected to form an expanded network, which facilitates and quickly communicates between various devices. It is an open specification for wireless transmission of voice and data, and is a low-cost, short-distance wireless connection technology.
2. Technical characteristics:
The characteristics of Bluetooth technology include: frequency hopping technology to resist signal fading; fast frequency hopping and short packet technology to reduce co-frequency interference and ensure the reliability of transmission; forward error correction coding technology to reduce randomness during long-distance transmission Noise impact; use 2.4GHz ISM band, no need to apply for a license; use FM modulation to reduce the complexity of the device. The transmission rate of this technology is designed to be 1MHz, and full-duplex communication is performed in a time-division manner. The baseband protocol is a combination of circuit switching and packet switching. A frequency hopping frequency sends a synchronous packet, and each packet occupies a time slot, which can also be expanded to 5 time slots. Bluetooth technology supports one asynchronous data channel or three concurrent synchronous voice channels, or one channel that simultaneously transmits asynchronous data and synchronous voice. 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 a connection
Before the piconet is established, all devices are in a ready state. In this state, the unconnected device monitors the message every 1.28s. Once the device is woken up, it monitors the information on the pre-set 32 ​​frequency hopping frequencies. The number of frequency hopping varies from region to region, but 32 frequency hopping frequencies are adopted by most countries. The connection process is initiated by the master device. If the address of a device is known, a page message is used to establish a connection; if the address is unknown, an inquiry message following the page information is used to establish a connection. In the piconet, devices without data transmission are transferred to the 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 from the hold mode, data transmission can be resumed immediately. When connecting several piconets or managing low-power devices, the hold mode is often used. The 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 uses three error detection and correction methods: 1/3 forward error correction coding (FEC); 2/3 forward error correction coding; automatic request retransmission (ARQ).
(3) Authentication and encryption Authentication and encryption services are provided by the physical layer. Authentication uses a password-response method. During the connection process, one or two authentications may be required, or no authentication is 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 users have a higher level of confidentiality requirements, they can use effective transport layer and application layer security mechanisms.
(4) Software structure Bluetooth devices should be interoperable. For some devices, from radio compatible modules and air interfaces to application layer protocols and object exchange formats, interoperability is required; for other devices (such as headsets) Equipment, etc.) are much looser. The goal of the Bluetooth project is to ensure that any device with a Bluetooth mark can be interchanged. 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 identify the high-level 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, and users cannot expect that the headset contains an address book. Bluetooth compatibility means that it has radio compatibility, has the ability to send and receive voice and the ability to discover other Bluetooth devices, and more functions are to be completed by mobile phones, handheld devices and notebook computers.
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