What is frequency hopping spread spectrum?

Frequency Hopping Spread Spectrum (FHSS) is a transmission method where the carrier frequency rapidly changes, or "hops," across a wide band of frequencies. These hops occur in a specific order determined by a pseudo-random sequence known to both the transmitter and receiver. Because the sequence appears random to unauthorized listeners, the signal is difficult to intercept or jam. The receiver must follow the exact same list of channels in perfect sync to piece the original message back together. Options mentioning phase-shifting describe a different type of spread spectrum (direct-sequence), while amplitude modulation and companding are unrelated techniques.