Frequency-Hopping Spread Spectrum (FHSS)

• FHSS is a method of transmitting radio signals by rapidly switching a carrier among many frequency channels, using a pseudorandom or pseudonoise sequence known to both transmitter and receiver.
• The advantage of this system is that the signal sees a different channel and a different set of interfering signals during each hop.
• This system helps to avoid the problem of failing communication at a particular frequency, because of a fade or a particular or unintentional interference.
• It is utilized as a multiple access method in the frequency-hopping Code Division Multiple Access (FH-CDMA) schemes.
• FHSS is also useful to counter eavesdropping, as well as to obstruct the frequency jamming of telecommunications

Block Diagram for FHSS Transmitter:

Block Diagram for FHSS Receiver:

• The above figure shows the Block diagram of the FHSS system for both transmitter and receiver.
• For transmission, binary data are fed into a modulator using some digital-to-analog encoding scheme, such as Frequency Shift Keying (FSK) or Binary Phase Shift Keying (BPSK).
• A PN source serves as an index into a table of frequencies each K bit on the PN source specifies one of the 2k carrier frequencies.
• At each successive interval, a new carrier frequency is selected.
• This frequency is then modulated by the signal produced from the initial modulator to produce a new signal with the same shape.
• On reception, the spread spectrum signal is demodulated using the same sequence of PN-derived frequencies and then demodulated to produce the output data.

Difference between Fast Hopping and Slow Hopping