Short-distance representation-wireless bluetooth

Bluetooth is certainly familiar to everyone. It is also a popular wireless community. It is also a representative of short-range wireless. This article will detail the principles, features, and advantages and disadvantages of wireless bluetooth. Through this article, I hope you will have some knowledge about the infinite Bluetooth.

Bluetooth is a short-distance radio connection system that connects different electronic devices. It works like a radio. An electronic device equipped with wireless bluetooth can receive external messages for specific instructions. However, wireless bluetooth can not only receive, but also "transmit". Therefore, electronic devices equipped with wireless bluetooth can communicate with each other.

Currently, most computer accessories, such as printers and screens, must be connected to wires to transmit messages to each other. However, Bluetooth is transmitted through its short-distance receiving system, so that these accessories can still transmit commands without being refuted offline, so that they can truly "wireless" the world. For example, if a mobile phone is not connected to a telephone line, you cannot "access the Internet" to receive emails. However, with the help of Bluetooth, you only need to receive emails through the mobile phone, then it is sent to the laptop to enable "wireless" Internet access. However, the use of Bluetooth is still not comprehensive enough. Due to its short range, it can only be used indoors for the time being. Therefore, you need to enjoy the convenience of wireless connection and can only be used indoors.

1. Working Frequency of Bluetooth:
Bluetooth works at the GHz global ISM (industrial, scientific, and medical) frequency band to ensure the worldwide use of wireless bluetooth. the antenna transmit power of the Bluetooth system conforms to the FCC's requirement for the ISM Band 0 dBm. The maximum frequency hopping rate of the system is 1600 hops/second. Between GHz and GHz, 79 1 MHz bandwidth frequency points are used. The communication distance designed by the system is 10 M 0 dB). If the transmit power is increased by 20 dB), the distance can reach 100 m. full-duplex communication TDD in Time Division mode), with a transmission rate of 1 MHz. The forward correction (FEC) encoding technology is used to reduce the impact of random noise during long-distance transmission. The voice adopts a Continuous Variable Slope modulation (CVSD) encoding method with strong anti-fading capability to improve the voice quality. The frequency modulation method is used to reduce the complexity of the equipment.

2. Components of the Bluetooth hardware module:
Bluetooth mainly includes two modules: Radio Frequency Unit (RF), baseband BB) and Link Management LM ).
It is precisely because Bluetooth uses a universal frequency band around the world that interference signals from outside are inevitable. wireless bluetooth uses a fast validation and frequency hopping solution, divide the frequency band into several Hop channels). In a single connection, the bluetooth receiver and sender send pseudo-instant codes according to certain rules, and constantly convert from one Channel to another, only the receiving and sending machines communicate according to this rule, and other interference signal sources are excluded.
BB is responsible for the transmission of frequency hopping and Bluetooth data and information frames. LM is responsible for establishing and removing connections. Their functions include: support for Synchronous and targeted connections to SCO) and asynchronous connections without an ACL. Error Control supports multiple methods of checking and correcting errors, this includes forward Correction Code (FEC), physical layer authentication and encryption, and link management.
The BB protocol of Bluetooth is a combination of circuit switching and group switching. in SCO connections, synchronous data packets can be transmitted in the channel's time slot, and each data packet is transmitted at different frequencies, each voice channel supports synchronous voice at 64 Kbps. At the same time, Bluetooth supports asynchronous data channels and three synchronous voice channels. One channel can also transmit asynchronous data and synchronous voice simultaneously. The ACL connection supports the asymmetric connection of 723.2 kb/s at one end of the asynchronous data channel and the response 57.6kb/s, and the symmetric connection of two-way 433.9Kb/s.

3. Error Correction Technology:
There are three error correction schemes in BB:
A. 1/3 ratio forward correction (FEC)
B. Forward correction with a ratio of 2/3
C. Automatic Data re-sending (ARQ)
Forward correction is used to reduce the number of data resends and reduce the amount of data transmitted. the data transmitted in the time slot in the automatic request resend mechanism must be confirmed in the next time slot, the message returned to the sender after the data receiver passes the header error detection and CRC verification. Otherwise, an error message is returned.

4. encryption and authentication
The Bluetooth Baseband module provides encryption on the physical layer. authentication is based on the "request-response" algorithm, and personal wireless bluetooth devices can establish trust domains, only wireless bluetooth devices established in the unified trust domain can communicate with each other.
In, markeni of Italy used electric spark to generate electromagnetic waves, which received electromagnetic signals at 9 M, M, and M. From then on, it opened up a new era of wireless communication, through the radiation and transmission of electromagnetic waves, through spatial communication, wireless communication has evolved from early telegraph transmission to current transmission of telephone, fax, Data, images, and so on. In the early stage, wireless communication is used less frequently and the frequency range is narrow. It mainly uses long waves and medium waves. as technology advances, the frequency range is gradually expanded, the current frequency of wireless communication ranges from the ultra-long wave to the sub-millimeter band to the light wave.
Frequency band name Wavelength
Extremely low frequency ELF) 3-30Hz extremely long wave 100-10 Mm
Ultra-low frequency SLF) 30-300Hz ultra-long wave 10-1 Mm
Ultra Low Frequency ULF) 300-3000Hz special wave 1000-100 km
Very Low Frequency VLF) 3-30 kHz very low frequency 100-10 km