FHSS is a spread spectrum technique that uses frequency agility to spread data over more than 83 MHz of spectrum. Frequency agility is the ability of a radio to change transmission frequency quickly, within the useable RF frequency band. In the US, based on standards set by the FCC, FHSS WLANs use the 83 MHz around the 2.4 GHz ISM band. Figure shows a FHSS block diagram.

In FHSS systems, the carrier changes frequency, or it can be said to hop, according to a pseudo-random sequence and this is sometimes referred to as a hopping code. This sequence defines the FHSS channel. It is a list of frequencies, to which the carrier will hop at specified time intervals. The transmitter uses this hop sequence to select its transmission frequency. The carrier will remain at a given frequency for a specified period of time, which is referred to as the dwell time. The transmitter will then use a small amount of time, referred to as the hop time, to move to the next frequency. When the list of frequencies has been completely traversed, the transmitter will start over and repeat the sequence.

The receiver radio is synchronized to the hopping sequence of the transmitting radio to enable the receiver to be on the right frequency at the right time.

Interactive Activity Interactive Activity: Frequency Hopping Spread Spectrum This activity demonstrates two different types of frequency hopping spread spectrum (FHSS).