Question

Consider a Bluetooth Piconet with a Master node and six active slaves. Given that the six slaves
follow the same frequency hopping pattern specified by the Master, how do these slaves
communicate with the Master? i.e. send to the Master without interference and also receive,
different information, from the Master.

Answer 1

Answer:

Bluetooth is based on frequency-hopping spread spectrum radio technology, making use of a packet-based structure in a master-slave arrangement. That is, information is transmitted in discrete chunks known as packets, and in each piconet, there exists a master device that dictates which of the other (slave) devices it is communicating with. Devices can also switch roles from master to slave and vice versa, and they belong to multiple piconets, where they are master in one network and slave in another. These two connected piconets are then referred to as a "scatternet".

Information is passed between the master of a piconet and one of its slaves at any given time. All communication is done on radio frequencies in the Industrial, Scientific and Medical (ISM) 2.4 GHz range, and so though it does not require a direct visual line of sight in order to operate, it does require radio line of sight, which can pass through most non-metallic objects. Bluetooth uses a low-powered signal; there are three classes of radios used in Bluetooth devices, with the shortest range being Class 3 radios (whose maximum power output is 1mW, producing a range of up to about one meter) and the longest-range being Class 1 radios (with a maximum output power of 100 mW and a range of 100 meters).

Frequency hopping:

Information is conveyed by modulating the carrier channel frequency, using one of several modulation schemes. Gaussian frequency-shift keying (GFSK) modulation was initially the only type available, but recently other varieties have been enabled. GFSK is simply a type of frequency-shift keying (FSK), which is a modulation scheme where the bits of the transfered information correspond to discrete frequency changes in the carrier signal. The carrier signal is whichever band the device happens to be using at that moment (before it hops to another), and the modified signal is broadcast out.

Because bluetooth uses this frequency-hopping scheme, it is very unlikely that there will be much interference from other devices, be they Bluetooth or not. Given that the hopping patterns are pseudo-random, the chances that another Bluetooth device would use the same pattern and disrupt a large amount of data-flow is very low. Additionally, other devices that simply broadcast at a fixed frequency can only have a minimal impact on the data transferred using bluetooth.

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