Bluetooth

Bluetooth

Bluetooth architecture

Bluetooth architecture mainly defines two types of networks: Piconet and Scatternets.

Piconet is a Bluetooth network that consists of one primary node and seven secondary nodes. So it can have up to 8 nodes, however it can consist of 255 parked nodes which need to be activated to be into an active state. The main distance range of a piconet can go to about 10 meters. There can only be one primary master in each piconet. The connections between transfer of data from primary to slave can be one-one or one-many. Slave to Slave communications are not possible. 

Scatternets are formed by combining various piconets. A slave in one piconet can act as a master in another piconet. It can receive messages from the first piconet is the master. Such nodes are called as bridge slaves. So a node can be a member in two piconets but not a master in both.

The Radio layer in the protocol stack

The Bluetooth radio layer corresponds to the physical layer of OSI Models. It functions with radio transmissions and modulation. For modulation it uses GFSK, an FSK with a Gaussian bandwidth layering. Bluetooth uses Frequency hopping spread spectrum to avoid interference with other networks and devices. It is also divided into 79 channels with MHz each. It uses a GHz ISM band in a range of 10 meters.

Baseband layer

It uses a form of TDMA called TDD-TDMA ( a half duplex system which the receiver can send and receive data but not in  the time. They communicate together in time slots. It communicates at time slot of 625 mono-seconds. If the Primary has no slaves then it communicates at an even numbered slot and vice-versa. Multiplexing happens at the sender side and de-multiplexing at the receivers side.