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How Bluetooth Technology Work?


The technology of Bluetooth centers around a 9mm x 9mm microchip, which functions as a low cost and short range radio link. Bluetooth Technology provide a 10 meter personal bubble that support simultaneous transmission of both voice 
and data for multiple devices. Up to 8 devices can be connected in a piconet, and uo to 10 piconets can exist within the 10 meter bubble. Each piconet support
up to 3 simultaneous full duplex voice devices.
The gross data rate is 1 Mb/s, but the actual data rate are 432 kbps for full
duplex transmission,721/56kbps for asymmetric transmission, and 384 kbps for
tms2000 transmission.
Bluetooth wireless technology is designed to be as secure as a wire with up to 128-bit public/private key authentication, and streaming cipher up to 64 bit based on a5 security.

Transmission types and rates :
The baseband (single channel per line) protocol combines circuit and packet switching. To assure that packets do not arrive out of order, slots (up to five) can be reserved for synchronous packets. As noted earlier, a different hop signal is used for each packet. Circuit switching can be either asynchronous or synchronous. Up to three synchronous (voice) data channels, or one synchronous and one asynchronous data channel, can be supported on one channel. Each synchronous channel can support a 64 Kb/s transfer rate, which is fully adequate for voice transmissions. An asynchronous channel can transmit as much as 721 Kb/s in one direction and 57.6 Kb/s in the opposite direction. It is also possible for an asynchronous connection to support 432.6 Kb/s in both directions if the link is symmetric.

Radio frequency and spectrum hopping :
What if there’s a lot of radio noise? Won’t that interfere with Bluetooth connections? As a rule, the answer is no. It is designed to use fast acknowledgement and frequency hopping, which will make connections robust. It is packet-based, and will jump to a new frequency after each packet is received, which not only helps limit interference problems, but also adds to security. Data rates are one megabyte/second, including headers. Full duplex transmissions (both directions at once) are accomplished via time division multiplexing.
The Bluetooth radio chip functions at 2.4 gigahertz, which is in the unlicensed ISM (Industrial Scientific Medical) band. It separates the 2.4 gigahertz frequency band into 79 hops one megahertz apart, starting with 2.402 and ending with 2.480 (though this bandwidth is narrower in Japan, France, and Spain). This spread spectrum is used to hop from one channel to another, pseudo-randomly, which adds a strong layer of security. Up to 1600 hops per second can be made. The standard frequency range is 10 centimeters to 10 meters, and can be extended to at least 100 meters by increasing transmission power.

Data transmission:
Data can be transmitted both synchronously and asynchronously. The Synchronous Connection Oriented (SCO) method is used primarily for voice, and Asynchronous Connectionless (ACL) is primarily for data. Within a piconet, each master-slave pair can use a different transmission mode, and modes can be changed at any time. Time Division Duplex (TDD) is used by both SCO and ACL, and both support 16 types of packets, four of which are control packets that are the same in each type. Because of the need for smoothness in data transmission, SCO packets are generally delivered via reserved intervals, that is, the packets are sent in groups without allowing other transmissions to interrupt. SCO packets can be transmitted without polling by the sending unit. ACL links support both symmetric and assymetric transmissions.
Bandwidth is controlled by the master unit, which determines how much of the total each slave unit can use. Slaves cannot transmit data until they have been polled by the master, and the master can broadcast messages to the slave units via ACL link.

Network arrangement:
Bluetooth network arrangements (topology) can be either point-to-point or point-to-multipoint. Any unit in a piconet can establish a connection to another piconet to form a scatternet. See the figure, which diagrams a scatternet in which piconet A, which consists of four units, is connected to piconet B, consisting of two units. Note that the master unit of A is not the link Bluetooth network arrangements (topology) can between the two piconets.

Error correction and security:
on code (FEC), 2/3 rate forward error correction code FEC, and automatic repeat request (ARQ). The FEC methods are designed to reduce the number of retransmissions. However, the over hea Three error correction techniques have been defined: 1/3 rate forward error corrected significantly slows transmissions, so is generally not used in relatively error-free environments, with the exception of packet headers. The ARQ scheme requires that the header error and cyclic redundancy checks are okay. When they are, an acknowledge is sent. When they aren’t, the data is resent.
Security is provided in three ways: through pseudo-random frequency band hops, authentication, and encryption. Frequency band hops make it difficult for anyone to eavesdrop. Authentication allows a user to control connectivity to only devices specified. Encryption uses secret key lengths of 1, 40, and 64 bits. The quality of security is excellent for most applications. However, it is not the highest level available, and for those users who require it, the suggestion is to investigate separate network transfer protocols and security software.




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