Noise reduction principle of bluetooth headset

Anti-noise principle is its connection principle. Reasonable connection can minimize noise! The following is about the origin and application of Bluetooth, as well as its development, and the answer you are looking for! Bluetooth technology is a new wireless communication technology jointly announced by five world-famous companies-Ericsson, Nokia, Toshiba, International Business Machines Corporation (IBM) and Intel (Intel) in May 1998, borrowing the words of a Danish emperor, Hara Bruce, more than a thousand years ago. It is put forward in view of the fact that the links between very close portable devices are mainly realized by infrared links (IrDA). Although the application of infrared transceiver link can avoid the connection of wires or cables, it is inconvenient to use, not only the distance is limited to 1 ~ 2m, but also it must be directly aligned in the line of sight without any obstruction, and it is only limited to the link between two devices, and more devices cannot be linked at the same time. On the other hand, people are familiar with radio communication technology and can realize long-distance communication, satellite communication and even space communication. "The purpose of Bluetooth technology is to connect all kinds of mobile communication equipment, fixed communication equipment, computers and their terminal equipment, and all kinds of digital systems (including digital cameras and digital video cameras, etc.). ) even household appliances in a small area to achieve seamless resource sharing. 1July, 1999, Bluetooth officially released the Bluetooth technical specification Bluetooth version 1.0. Bluetooth has become a new hotspot in the field of communication, and it is very likely to become an international standard for small-scale wireless multimedia communication in the near future.

2 technical characteristics of Bluetooth

Bluetooth technology replaces wired connection with short-distance and low-cost wireless connection, thus providing a unified connection for existing data networks and small peripheral interfaces. It has many superior technical properties. The following are some main technical features.

2. 1 RF characteristics

The working frequency band of Bluetooth equipment is 2.4GHz ISM (industrial, scientific and medical) band which can be freely used all over the world. Users can choose the appropriate frequency band of Bluetooth transceiver in the range of 2400 ~ 2500 MHz without application. There are 23 or 79 channels, the channel interval is 1MHz, and time division duplex is adopted. The modulation method is GFSK, BT= 0.5, and the modulation index is 0.28 ~ 0.35. Bluetooth wireless transmitter adopts FM modulation mode, which can reduce the complexity of the equipment. The maximum transmission power is divided into three grades, 100mW(20dBm), 2.5mW(4dBm) and 1mW(0dBm). The power control requirement is in the range of 4 ~ 20 DBM. Therefore, the effective communication distance between Bluetooth devices is about10 ~100 m..

2.2 TDMA structure

The data transmission rate of Bluetooth is 1Mb/s, and it is transmitted in the form of 0.625μs data packets per time slot. Bluetooth system supports real-time synchronous directional connection and non-real-time asynchronous non-directional connection, and Bluetooth technology supports one asynchronous data channel, three simultaneous synchronous voice channels or one channel that simultaneously transmits asynchronous data and synchronous voice. Each voice channel supports 64KB/S synchronous voice, and the asynchronous channel supports asymmetric connection with the maximum rate of 72 1KB/S, reverse response speed of 57.6KB/s, or symmetric connection with the rate of 432.6 KB/s. ..

2.3 using frequency hopping technology

Frequency hopping is one of the key technologies of Bluetooth. Corresponding to a single slot packet, the frequency hopping rate of Bluetooth is 1600 hops/second; For multi-slot packets, the frequency hopping rate decreases; However, during the chain construction, it increased to 3200 hops/second. With such a high frequency modulation rate, the Bluetooth system has strong anti-interference ability, simple hardware equipment and superior performance.

2.4 Networking of Bluetooth devices

Bluetooth provides point-to-point and point-to-multipoint wireless connection according to the concept of network. In any effective communication range, all devices are equal and follow the same working mode. Based on the principle of TDMA and the equality of Bluetooth devices, any Bluetooth device can be both a master device and a slave device in piconets and decentralized networks. Therefore, Bluetooth system has no concept of slave station, all devices are mobile, and networking is very convenient.

2.5 Hierarchical structure of software

Like many communication systems, the communication protocol of Bluetooth adopts hierarchical structure, and its program is written on a 9mm× 9mm microchip. The bottom layer is common to all kinds of applications, while the top layer is different depending on the specific application, which can be roughly divided into two ways: computer background and non-computer background. The former realizes the connection between high-level and low-level through HCI (host control interface). The latter does not require HCI. The layered structure makes its equipment have the greatest versatility and flexibility. According to the communication protocol, various Bluetooth devices can find other Bluetooth devices manually or automatically, thus forming a master-slave network and a decentralized network, realizing various functions provided by the system, which is very convenient to use.

Three functional modules of Bluetooth system

The basic functional modules of Bluetooth system are shown in figure 1. Its functional modules include antenna unit, link controller, link management and software functions.

3. 1 wireless technical specification

Bluetooth antenna is a microstrip antenna, and the Bluetooth wireless interface is designed based on conventional wireless transmission power of 0dbm, which meets the requirements of FCC ISM frequency band. The application of spread spectrum technology can increase the power to 100dbm, which can meet the needs of different countries. In Japan, Spain and France, because the local frequency band is relatively narrow, it can be converted by internal software.

3.2 Baseband Technical Specification

The digital signal processing part of the baseband description device, namely the Bluetooth link controller, completes the baseband protocol and other underlying link programs. Mainly includes the following aspects:

(1) Establish a network connection.

(2) Link type and packet type.

The link type determines which packet mode can be used on a specific link. Bluetooth baseband technology supports two link types: synchronous connection-oriented SCO (mainly used for voice) and asynchronous connectionless ACL (mainly used for packet data).

(3) Error correction

The baseband controller adopts three error correction methods: 1/3 rate forward error correction coding (FEC), 2/3 rate forward error correction coding (FEC) and automatic repeat request (ACL).

(4) Authentication and encryption

Bluetooth baseband part provides users with protection and information confidentiality mechanism at the physical layer. Authentication is based on "request-response" algorithm. Authentication is a key part of Bluetooth system, which allows users to establish a trust domain for personal Bluetooth devices, such as allowing only the owner's own laptop to communicate through the owner's own mobile phone. Encrypt personal information used to protect the connection. The key is managed by the upper layer of the program. Network transmission protocols and applications can provide users with powerful security mechanisms.

3.3 Link Management Protocol

Link Management (LM) software module carries data setting, authentication, link hardware configuration and other protocols of the link. LM can find other remote LM and communicate with them through LMP (Key Path Management Protocol). The LM module provides the following services:

(1) Send and receive data.

(2) The name of the request.

(3) Link address query.

(4) establish a connection.

(5) certification.

(6) Link mode negotiation and establishment.

(7) Determine the type of framework.

(8) Set the device to sniffing mode. The host can only send data regularly in specific time slots.

(9) Set the device to hold mode. In order to save energy, the equipment working in the hold mode stops receiving data for a long time and activates the link once on average, which is defined by LM and operated by LC (Link Controller).

(10) When the device does not need to send or receive data but still needs to keep synchronization, set the device to pause mode. Devices in pause mode periodically activate and track synchronization while checking paging messages.

(1 1) Establish a network connection.