Saturday, 7 May 2011

How does Bluetooth work?

How does Bluetooth work?

The technical details of Bluetooth´s function are very complex, and are best studied in detail in the PDF-format documents that can be found on the Bluetooth website.

But, superficially speaking, Bluetooth uses frequency hopping in time-slots. Bluetooth has been designed to operate in noisy radio frequency environments, and uses a fast acknowledgment and a frequency-hopping scheme to make the communications link robust, communication-wise. Bluetooth radio modules avoid interference from other signals by hopping to a new frequency after transmitting or receiving a packet.

Compared with other systems operating in the same frequency band, the Bluetooth radio typically hops faster and uses shorter packets. This is because short packages and fast hopping limit the impact of microwave ovens and other sources of disturbances. Use of Forward Error Correction (FEC) limits the impact of random noise on long-distance links.

Transmission power levels

The Bluetooth radio is built into a small microchip and operates in a globally available frequency band ensuring communication compatibility worldwide. The Bluetooth specification has two power levels defined;

• a lower power level that covers the shorter personal area within a room, and
• a higher power level that can cover a medium range, such as within a home.

Software controls and identity coding built into each microchip ensure that only those units preset by their owners can communicate.

Communication routes

One thing that can be noted from the figure above is that, although Bluetooth works in an ad-hoc fashion (and not server-based) all communication is done visavi the Master unit. There is no direct communication between slave units. Nor is it intended for the Master to route messages between slave units. Rather, if slave units find that they want to talk directly to each other, they would form a new piconet, with one of them acting as Master. This does not mean that they have to leave the previous piconet. More likely, they will be parked in the "old" net unless they decide to quit the "old" net altogether. This is not a big decision for the slave units; reconfiguration in Bluetooth is dynamic and very fast.

Technical prestanda

The Bluetooth base-band protocol is a combination of circuit and packet switching. Time slots can be reserved for synchronous packets. A frequency hop is done for each packet that is transmitted. A packet nominally covers a single time slot, but can be extended to cover up to five slots.

Bluetooth can support;

• an asynchronous data channel, or
• up to 3 simultaneous synchronous voice channels, or
• a channel which simultaneously supports asynchronous data and synchronous voice.

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