This is a brief overview of RF modulation techniques. If you're interested in the detail, links to tutorials are provided at the end.
Frequency-Hopping Spread Spectrum (FHSS)
The FHSS modulation technique uses the available channels to transmit and receive data, but rather than staying on any one channel, it rapidly switches between channels using a pseudorandom pattern that is based on an initial key, which is shared between the participants of the communication session.
If interference affects only a few of the channels, this interference is minimized because each channel is used only briefly. If the interference is broad, it can still affect all the channels that are in use. This modulation technique requires that the initial seed or key be shared, but after that has happened, it is very difficult to eavesdrop on.
IEEE 802.11 wireless networks use this technique for modulation, while Bluetooth uses an adaptive version of this technique that stops using channels where interference or weak signals exist.
