Communication through Bluetooth

Piconet: When two or more Bluetooth devices are connected together (wirelessly), it forms a type of personal area network called Piconet. Each piconet can contain up to eight different Bluetooth devices.
Scatternet: Multiple piconets can be connected in larger scatternets. Linking from piconet to piconet enables Bluetooth devices to connect to larger local area networks, and to the global Internet.

Communication with and within piconets:

Within each piconet, one device serves as the master, while the other seven devices function as slaves. When all these seven devices communicate with a same frequency range of 2.4GHz at a time, the band will get so crowded that the various devices could start interfering with one another. To minimize interference issues, Bluetooth radios utilize a technique called spread spectrum frequency hopping.

Spread spectrum: Spread spectrum refers to a number of different techniques that divide the available radio band by frequency, time, or some other method.

Frequency Hopping: Frequency hopping is a common spread spectrum technique, where a signal hops from one frequency to another during the course of a single transmission. This technique also helps for secured communications.
In the Bluetooth module, the Bluetooth radio is constantly and randomly changing frequencies among a broad spectrum of frequencies, hopping to a new frequency after transmitting or receiving each packet of data. The Bluetooth transmission doesn’t stay on a single frequency for a long time to get impacted by interference with that frequency.

When two Bluetooth devices are connected together, they should hop at a same frequency, and in a correct sequence. The sequence is assigned by the internal clock setting in the Master unit. The slave units synchronize to the master unit’s clock, and so the datas get transferred without any interference.

Bluetooth radios can execute up to 1600 hops per second. The signal hops among 79 frequencies between 2.402GHz and 2.480GHz, at 1MHz intervals.

The Bluetooth signals are mainly data signals and voice signals.

For data transmission, Data signals utilize a technology called packet switching. With packet switching, data is divided into small groups, or packets, before it is transmitted. For voice transmission, Voice signals utilize a technology called circuit switching. With circuit switching, messages are not sliced into packets; instead, a dedicated channel (or circuit) is established for the duration of the transmission.

Speed of communication:

The communication in Bluetooth devices happens with a speed of 1Mbps (megabyte per second).