Frequency hopping spread spectrum is when two devices move around different channels randomly to avoid interference. Some implementations can be adaptive and don’t use too noisy channels. FHSS can help improve security by ensuring that only the connected devices know the order in which the frequencies will be changed to. Direct estimation is one of the most effective and widely used algorithms to track a frequency. A pseudorandom sequence known by both the transmitter and receiver is used to switch the frequency channels.[^3] The receiver can be made to listen on two or more channels at the same time.[^3]
Direct Sequence Spread Spectrum - relative to FHSS
Direction Finding - useful in spread-spectrum technologies
LFSR - used in spread-spectrum radios
FHSS Initialization
2.4 GHz ISM Band
Link-16 - uses frequency-hopping
Boeing PTS-P - uses frequency hopping
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