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Bluetooth is a wireless technology standard, which is used to exchange data from fixed and mobile devices in a short distance (using short wave UHF radio waves from 2.4 to 2.485 GHz [3] in ISM frequency band) and establish a personal local area network (Pan). Jaap haartsen, a Dutch electrical engineer, worked in Ericsson, a telecom supplier, in 1994 and was initially considered a wireless alternative to RS-232 data cables.
Bluetooth is managed by the Bluetooth special interest group (SIG), which has more than 30000 member companies in the fields of telecommunications, computing, network and consumer electronics. IEEE standardizes Bluetooth as IEEE 802.15.1, but no longer maintains it. Bluetooth SIG supervises the establishment of specifications, manages certification procedures and protects trademarks. Manufacturers must meet Bluetooth SIG standards to sell as Bluetooth devices. The patent network is applicable to the technology and has been authorized to each qualified device.
The working frequency of Bluetooth is between 2402 and 2480 MHz, or between 2400 and 2483.5 MHz, including 2 MHz wide protection band at the bottom and 3.5 MHz wide protection band at the top. This is in the world's unlicensed (but unregulated) industrial, scientific and medical (ISM) 2.4 GHz short range radio band. Bluetooth uses a radio technology called frequency hopping spread spectrum. Bluetooth divides the transmitted data into packets, and transmits each packet on one of the 79 designated Bluetooth channels. The bandwidth of each channel is 1 MHz. When adaptive frequency hopping (AFH) is enabled, it usually performs 800 hops per second. Low power Bluetooth uses a 2 MHz interval and can accommodate 40 channels.
At first, Gaussian frequency shift keying (GFSK) modulation is the only available modulation scheme. Due to the introduction of Bluetooth 2.0 + EDR, it can also be used between compatible devices? /4-dqpsk (differential quadrature phase shift keying) and 8DPSK modulation. It is said that devices using GFSK operate in basic rate (BR) mode, in which the instantaneous bit rate may be 1 Mbit / s. The term enhanced data rate (EDR) is used to describe α / 4-dpsk and 8DPSK schemes, each providing 2 and 3 Mbit / s, respectively. The combination of these (BR and EDR) modes in Bluetooth radio technology is classified as "br / EDR radio".
Bluetooth is a packet based protocol with master / slave architecture. A host in a piconet can communicate with up to seven slaves. All devices share the master clock. Packet exchange is based on the basic clock defined by the host, with an interval of 312.5 μ s. Two clock ticks form a 625 μ s slot, and two slots form a 1250 μ s slot pair. In the simple case of single slot data packet, the host sends in even slot and receives in odd slot. Instead, the slave receives in an even slot and transmits in an odd slot. The length of the packet can be 1, 3 or 5 timeslots, but in all cases, the transmission of the master starts from the even timeslot, while the transmission of the slave starts from the odd timeslot.
The above applies to "classic" Bluetooth. The low power Bluetooth technology introduced in the 4.0 specification uses the same spectrum, but different. See Bluetooth low power radio interface.
