The principle of anti-noise is its connection composition principle. A reasonable connection method can reduce noise to the greatest extent! The following is about the origin and application of Bluetooth and its development, as well as the answers you are looking for! Bluetooth "(Bluetooth) technology was jointly announced in May 1998 by five world-famous companies - Ericsson, Nokia, Toshiba, International Business Machines Corporation (IBM) and Intel. Bluetooth is a new wireless communication technology, named after Harald Bruce, a Danish emperor more than a thousand years ago. It is mainly used for links between portable devices that are currently very close to each other. Although the use of infrared transceiver links can eliminate the need for wires or cables, it has many inconveniences. Not only is the distance limited to 1 to 2 meters, but it must also be directly in line of sight. Alignment, there can be no obstruction in the middle, and it is limited to linking between two devices at the same time, and cannot link more devices at the same time. On the other hand, people are familiar with radio communication technology, which can achieve long-distance communication. It can realize satellite communication and even space communication. The purpose of "Bluetooth" technology is to use short-distance, low-cost wireless multimedia communication technology to connect various mobile communication equipment, fixed communication equipment, computers and their terminal equipment, and various devices in a small area. A variety of digital systems (including digital cameras, digital video cameras, etc.) and even household appliances are connected to achieve seamless resource sharing. In July 1999, Bluetooth officially announced Bluetooth Version 1.0. Bluetooth has become the communication field. A new hot spot at present is very likely to become an international standard for small-range wireless multimedia communications in the near future.
2 Technical characteristics of Bluetooth
Bluetooth technology utilizes short-range, low-frequency capabilities. The low-cost wireless connection replaces cable connections and provides a unified connection to existing data networks and small peripheral device interfaces. It has many superior technical features, some of the main technical features are introduced below.
2.1 Radio Frequency Characteristics
The working frequency band of Bluetooth devices is selected from the 2.4GHz ISM (Industrial, Scientific, Medical) frequency band that can be used freely worldwide, so that users can operate in the 2400-2500MHz band without applying. Select the appropriate Bluetooth radio transceiver frequency band. The channels are 23 or 79, the channel spacing is 1MHz, the modulation method is GFSK with BT=0.5, and the modulation index is 0.28~0.35. The transmitter uses FM modulation, which can reduce the complexity of the equipment. The maximum transmit power is divided into three levels, 100mW (20dBm), 2.5mW (4dBm), 1mW (0dBm), and power control is required in the range of 4 to 20dBm. , therefore, the effective communication distance between Bluetooth devices is approximately 10 to 100m.
2.2 TDMA structure
The data transmission rate of Bluetooth is 1Mb/s, which is transmitted in the form of data packets in time slots of 0.625μs per time slot. The Bluetooth system supports real-time synchronous directional connections and non-real-time asynchronous non-directional connections. Bluetooth technology supports one asynchronous data channel, three concurrent synchronous voice channels or one simultaneous transmission of asynchronous data and synchronous voice channels. Each voice channel supports 64KB/S synchronous voice, and the asynchronous channel supports an asymmetric connection with a maximum rate of 721KB/S and a reverse response speed of 57.6KB/s, or a symmetric connection with a rate of 432.6KB/S.
2.3 Use frequency hopping technology
Frequency hopping is one of the key technologies used by Bluetooth.
Corresponding to single-slot packets, the frequency hopping rate of Bluetooth is 1600 hops/second; for multi-slot packets, the frequency hopping rate is reduced; but when building a link, it is increased to 3200 hops/second. Using such a high frequency modulation rate, the Bluetooth system has sufficiently high anti-interference capabilities, simple hardware equipment, and superior performance.
2.4 Networking of Bluetooth devices
Bluetooth provides point-to-point and point-to-multipoint wireless connections based on the concept of network. Within any effective communication range, all devices are equal , and follows the same working pattern. Based on the TDMA principle and the equality of Bluetooth devices, any Bluetooth device can be used as both a master device (Master) and a slave device (Slaver) in a master-slave network (Piconet) and a scattered network (Scatternet), or at the same time. It is both a master device (Master) and a slave device (Slaver). Therefore, there is no concept of slave stations in the Bluetooth system. In addition, all devices are removable, making networking very convenient.
2.5 Hierarchical structure of software
Like many communication systems, the Bluetooth communication protocol adopts a hierarchical structure, and its program is written in a 9mm×9mm microchip. The bottom layer is common to all types of applications, while the high layer varies depending on the specific application. It is generally divided into two methods: computer background and non-computer background. The former realizes the connection between high and low layers through the host control interface HCI (Host Control Interface). The latter does not require HCI. The hierarchical structure allows maximum versatility and flexibility of its equipment. According to the communication protocol, various Bluetooth devices can discover other Bluetooth devices through manual or automatic query no matter where they are, thus forming a master-slave network and a decentralized network to realize various functions provided by the system and are very convenient to use.
3 Functional modules of the Bluetooth system
The basic functional modules of the Bluetooth system are shown in Figure 1. Its functional modules include antenna units, link controllers, link management, and software functions.
3.1 Wireless Technical Specifications
The Bluetooth antenna is a microstrip antenna. The Bluetooth wireless interface is designed based on conventional wireless transmission power 0dbm and complies with the ISM frequency band of the Federal Communications Commission (FCC). Regulation. The application of spread spectrum technology allows the power to be increased to 100dbm, which can meet the needs of different countries. In Japan, Spain, and France, because the local frequency bands are relatively narrow, internal software can be used to convert them.
3.2 Baseband technical specifications
The baseband describes the digital signal processing part of the device, that is, the Bluetooth link controller, which completes the baseband protocol and other underlying link procedures. It mainly includes the following aspects:
(1) Establishment of network connection.
(2) Link type and grouping type.
The link type determines which grouping mode can be used on a specific link. Bluetooth baseband technology supports two link types: synchronous connection-oriented type SCO (mainly used for voice) and asynchronous non- Connection type ACL (mainly used for packet data).
(3) Error correction
The baseband controller uses 3 error correction methods: 1/3 rate forward error correction coding (FEC), 2/3 rate forward error correction Encoding (FEC), automatic request for retransmission of data (ACL).
(4) Authentication and encryption
The Bluetooth baseband part provides users with protection and information confidentiality mechanisms at the physical layer. Authentication is based on the "request-response" algorithm. Authentication is a key part of the Bluetooth system, which allows users to establish a trust domain for personal Bluetooth devices, such as only allowing the owner's own laptop to communicate through the owner's own mobile phone. Encryption is used to protect personal information on the connection. Keys are managed by higher levels of the program. Network transport protocols and applications can provide users with a strong security mechanism.
3.3 Link Management Protocol
The link management (LM) software module carries the link data settings, authentication, link hardware configuration and other protocols. LM can discover other remote LMs and communicate with them through LMP (Line Management Protocol). The LM module provides the following services:
(1) Sending and receiving data.
(2) Request name.
(3) Link address query.
(4) Establish connection.
(5) Authentication.
(6) Link mode negotiation and establishment.
(7) Determine the type of frame.
(8) Set the device to sniff mode. The master can only send data regularly in specific time slots.
(9) Set the device to hold mode. Devices working in hold mode stop receiving data for a long period of time in order to save energy, on average every time the link is activated, which is defined by LM and specifically operated by LC (Link Controller).
(10) Set the device to pause mode when the device does not need to transmit or receive data but still needs to maintain synchronization. A device in pause mode periodically activates and tracks synchronization while checking for page messages.
(11) Establish a network connection.