Editing Frequency-hopping spread spectrum (section)

{{Short description|Radio signal transmission method}}
{{Redirect|FHSS}}
{{Use American English|date = December 2019}}
{{Modulation techniques}}
{{Multiplex techniques}}
'''Frequency-hopping spread spectrum''' ('''FHSS''') is a method of transmitting radio signals by rapidly changing the carrier frequency among many frequencies occupying a large spectral band. The changes are controlled by a code known to both [[transmitter]] and [[receiver (radio)|receiver]]. FHSS is used to avoid interference, to prevent eavesdropping, and to enable [[code-division multiple access]] (CDMA) communications.

The frequency band is divided into smaller sub-bands. Signals rapidly change ("hop") their carrier frequencies among the center frequencies of these sub-bands in a determined order. Interference at a specific frequency will affect the signal only during a short interval.<ref name="ref 1">{{cite book| title=Principles of Spread-Spectrum Communication Systems, 4th ed.| year=2018|last1=Torrieri|first1=Don}}</ref>

FHSS offers four main advantages over a fixed-frequency transmission:

# FHSS signals are highly resistant to [[narrowband]] [[Interference (communication)|interference]] because the signal hops to a different frequency band.
# Signals are difficult to intercept if the frequency-hopping pattern is not known.
# Jamming is also difficult if the pattern is unknown; the signal can be jammed only for a single hopping period if the spreading sequence is unknown.
# FHSS transmissions can share a frequency band with many types of conventional transmissions with minimal mutual interference. FHSS signals add minimal interference to narrowband communications, and vice versa.