FrequencyHopping

Frequency hopping, or frequency hopping spread spectrum (FHSS), is a method of transmitting radio signals by rapidly switching a carrier among many discrete frequencies within a given band according to a predefined hopping sequence. The signal is spread over a wider portion of the spectrum than an equivalent fixed-frequency transmission, which helps resist narrowband interference and can complicate interception if the sequence is not known.

Operation relies on synchronization between transmitter and receiver. Both ends use the same hopping sequence and timing, so they hop together from channel to channel with a defined dwell time on each frequency. The sequence can be based on a pseudo-random pattern or a shared key, and the hopping rate and channel spacing are design choices that affect performance and regulatory compliance.

Applications and examples vary. FHSS has been used in military communications and early consumer radio systems, and elements of FHSS appear in modern technologies such as Bluetooth, where a form of frequency hopping among multiple channels mitigates interference. The 2.4 GHz band has historically hosted FHSS devices under regulatory rules that govern dwell times and hopping patterns.

Advantages of FHSS include resilience to narrowband interference, reduced probability of persistent conflicts when multiple users share the band, and the ability to operate without requiring a large contiguous spectrum. Drawbacks include the need for precise synchronization between transmitter and receiver, potential regulatory constraints on hopping behavior, and generally lower spectral efficiency and data rates compared with some newer spread-spectrum or multicarrier techniques in certain environments.

Overall, FHSS remains a foundational technique in spread-spectrum communications, valued for interference tolerance and spectrum sharing capabilities in appropriate regulatory contexts.