Frequency Hopping Spread Spectrum (FHSS) is a spread spectrum technique used in wireless communication systems to transmit data over a range of frequencies. In FHSS, the carrier frequency of the transmitted signal rapidly changes or “hops” according to a predetermined pattern or sequence. This hopping sequence is synchronized between the transmitter and the receiver, allowing them to follow the same frequency-hopping pattern.
Here’s how FHSS works:
Frequency Hopping Sequence: FHSS employs a hopping sequence, which is a predefined list of frequencies that the transmitter uses to send the signal. The transmitter hops from one frequency to another in a sequential manner, based on the hopping sequence.
Synchronization: Both the transmitter and the receiver must be synchronized to the same hopping sequence. This synchronization ensures that the receiver can track the frequency changes and correctly reassemble the transmitted data.
Benefits:
- Interference Resistance: FHSS offers robustness against narrowband interference and jamming. Since the signal frequency is constantly changing, it becomes difficult for an interferer to consistently target the signal.
- Security: FHSS can provide a level of security because unauthorized receivers would need to know the hopping sequence to successfully capture the signal.
- Sharing the Spectrum: FHSS allows multiple FHSS systems to share the same frequency band without interfering with each other, as long as they use different hopping sequences.
Applications: FHSS is commonly used in applications where resistance to interference and jamming is crucial. Some examples include military communication, industrial wireless networks, and certain types of wireless sensor networks.
Bluetooth: One of the well-known applications of FHSS is in Bluetooth technology, where devices in the same network hop between frequencies within the 2.4 GHz ISM (Industrial, Scientific, and Medical) band.
It’s worth noting that while FHSS offers advantages in terms of interference resistance and security, it can also be more complex to implement compared to other modulation schemes. Additionally, the hopping rate and sequence design are important considerations to ensure reliable communication and to meet regulatory requirements for spectrum usage.