I am having difficulty finding information about how is CDMA used in a FHSS system. In wikipedia, it mentions:

FHSS is used to avoid interference, to prevent eavesdropping, and to enable code-division multiple access (CDMA) communications.

Can somebody explain how it works, what exactly would be done at the transmitter and the receiver, and how it is different from CDMA applied to a DSSS system?


1 Answer 1


Exactly the same way:

  • In DSSS, the spreading sequences for different users are chosen to be orthogonal, and
  • In FHSS, the hopping sequences for different users are chosen to be orthogonal.
  • \$\begingroup\$ I can see in the wiki link about CDMA (en.wikipedia.org/wiki/Code-division_multiple_access ) that the spectrum is spread by XORing with a faster pseudo-code, thus increasing necessary bandwitdh. My guess is that this is about DSSS. Is this right? If so, what exactly is the equivalent procedure to FHSS? \$\endgroup\$
    – NickG
    Jan 15, 2021 at 20:20
  • 2
    \$\begingroup\$ "pseudo-code": you mean pseudo-random sequence, I guess? The equivalent procedure is using a pseudo-random sequence of frequencies to hop to. It's really 100% the same, just that you replace "chip" with "hop", and "code element" with "hopping sequence element". \$\endgroup\$ Jan 15, 2021 at 20:33
  • \$\begingroup\$ So, in FHSS, how exactly is the "multiple access" property achieved? Can I have multiple transmitters using the same sub-channel at a given time, or is it that many subchannels can be used simultaneously? Also, in DSSS, increase of bit rate of transmitted signal, means more bandwitdth requirements. How are bandwitdh requirements affected with FHSS? \$\endgroup\$
    – NickG
    Jan 16, 2021 at 14:50
  • \$\begingroup\$ as said, the hopping sequences are orthogonal. The bandwidth question really is something that you can answer yourself through minimal thought! \$\endgroup\$ Jan 16, 2021 at 14:52

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