1. Bluetooth working frequency:

Bluetooth operates in the 2.4GHz worldwide ISM (industrial, scientific, medical) band, in order to ensure the use of the Bluetooth worldwide. Transmission power Bluetooth antenna system meets the FCC requirements for ISM band 0dBm. Maximum system hopping rate of 1600 hops / sec, between 2.402GHz to 2.480GHz, using 79 1MHz bandwidth frequency. System design communication interval of 10 meters (0db), if the transmit power is increased (20db), this interval may be up to 100 meters in a time division manner full-duplex communication (TDD), the transmission rate is designed to 1MHz. Using forward error correction (FEC) coding techniques to reduce random noise long-distance transmission. With anti-fading voice strong ability to continuously variable slope modulation (CVSD) in order to improve voice quality encoding using frequency modulation, reducing the complexity of the device.

2. Bluetooth hardware module consists of:

Bluetooth comprises two main modules: radio frequency unit (the RF), baseband (BB) and the control link (LM) cells is due to a common world Bluetooth uses frequency band, the interference signals from outside are unavoidable, the use of Bluetooth rapid confirmation and frequency hopping scheme, the band into FM channel number of the (Hop channel), Bluetooth transceiver sends pseudo forthwith code according to certain rules in the first connection, constantly switching from one channel to another channel, only transceiver letter machines are in accordance with the law of communication, the exclusion of other interference sources.

BB responsible for frequency hopping and Bluetooth data transmission and information frame. LM is responsible for establishing and dismantling of the connection. They realize functions include: Synchronous Connection Oriented (SCO) and asynchronous connectionless (ACL) support connection mode; error control, you can use a variety of detection and correction ways, including forward error correction (FEC); physical layer authentication and encryption; link management.

There are three error correction scheme in the BB:
a. 1/3 ratio before forward error correction (FEC)
b. 2/3 BB ratio of Bluetooth protocol is a combination of circuit switching and packet switching, the SCO connection in the time slot in the channel can transmit synchronous data packets, each data packet transmitted at different frequencies, each voice channel support 64kbps synchronous voice. Bluetooth simultaneously supports asynchronous data channels, and three simultaneous synchronous voice channels, one channel is capable of delivering asynchronous data and synchronous voice. ACL connection in asynchronous data channels to support one end of 723.2 kb / s and repercussions 57.6kb / s asymmetric connection, and symmetric bidirectional 433.9Kb / s connection.

3. Error Correction:
 
Forward Error Correction
c. automatic data retransmission request (ARQ)

Forward error correction is to reduce the number of retransmission of data, reducing the amount of data transmission in automatic retransmission request mechanism for data transmitted in the next time slot time slot it must be confirmed at the receiving end of the header data by mistake after detecting and CRC check before confirmation message back to the originator, otherwise it returns an error message.

4. encryption and authentication

Bluetooth baseband physical layer provides encryption for user authentication based on the "request - response" algorithm, individual Bluetooth devices can establish trust domains, only the establishment of a Bluetooth device to communicate with each other in the same trust domain.

1895 Italy Makeni use spark generate electromagnetic waves, it has in 9M, 975M and 3000M place where receive electromagnetic signals from wireless communications has opened up a new era, by radiation and propagation of electromagnetic waves through space to convey information from the wireless communication the early development of telegraph transmission now spread to telephone, fax, data, image, and so on. Lower frequency wireless communications in the early stages of use, narrow frequency range, the main use of long wave and medium wave, as technology advances, the use of the frequency range gradually expanded, and now the wireless communications from the long wave frequency submillimeter wave band, until light .

Frequency wavelength band name
Extremely Low Frequency (ELF) 3-30Hz extremely long wave 100-10Mm
Ultra-low frequency (SLF) 30-300Hz long wave 10-1Mm
Ultra low frequency (ULF) 300-3000Hz Specialty wave 1000-100km
Very Low Frequency (VLF) 3-30kHz VLF 100-10km