Frequency Hopping Spread Spectrum (FHSS)

Frequency Hopping Spread Spectrum (FHSS) rapidly changes a signal’s carrier frequency among multiple channels according to a sequence known to the transmitter and receiver. It is used in licence-exempt systems to improve coexistence and resistance to narrowband interference.

Scope and Application

FHSS equipment operates under market-specific rules. Relevant examples include the 902–928 MHz and 2400–2483.5 MHz bands in the United States and Canada, while European equipment must be assessed under the applicable ETSI standard and frequency allocation.

United States: 47 CFR §15.247

• 902–928 MHz, 20 dB bandwidth below 250 kHz: At least 50 hopping channels; up to 1 W conducted output power.

• 902–928 MHz, 20 dB bandwidth from 250 kHz to the 500 kHz maximum: At least 25 hopping channels; with 25–49 channels, conducted output power is limited to 0.25 W.

• 2400–2483.5 MHz: At least 15 hopping channels. At least 75 non-overlapping channels permit up to 1 W; with 15–74 channels, the limit is 0.125 W.

• Channel spacing: At least 25 kHz or the full 20 dB bandwidth. In the 2.4 GHz band, systems operating at no more than 125 mW may alternatively use 25 kHz or two-thirds of the 20 dB bandwidth.

Canada: ISED RSS-247

ISED RSS-247 is an independent Canadian rule set and must not be described as identical to FCC §15.247. Channel count, bandwidth and power requirements must be determined from the applicable RSS-247 provisions for the specific system.

Certification and Testing

Testing is market-specific and may include hopping-channel count, channel spacing, dwell time, output power and unwanted emissions. Authorization may involve FCC equipment certification, ISED certification or EU RED conformity assessment under the applicable harmonized standard.