Bluetooth Modulation Processes

Bluetooth uses FHSS (Frequency Hopping Spread Spectrum) technique which is
used in spread spectrum signal transmission.  To understand Frequency
hoping spread spectrum, its is necessary to understand how spread spectrum
technology works.

In spread spectrum, all you do is-spread your signal onto a very high
frequency carrier wave form at the transmitter and retrieve the same at the
receiver. The trick is - not only you, all other users will use the same
bandwidth. The only way in which the receiver can know who you are - is by using
some kind of pin to detect your signal. Your carrier wave is generated using
this code and transmitted.

At the receiver, we multiple the same carrier wave to generate the original
signal.

Now coming to FHSS,

The name itself says it involves something like frequency and hopping. Here,
our data signal will use single frequency of the complete carrier band and keep
hopping to a different frequency. The way in which your signal hops over the
carrier frequency is determined by a code. The code is such that no two users
use same frequency to transmit at any given time. So in a sense you are
achieving orthogonality here.

the modulation is FSK