What is the difference between FDD and FDM? (Same for TDD and TDM)


Hello All.

Does anybody have a good explanation why we use FDD instead of FDM?

Hi @CarlosFuente

I have found a very nice (and easy) explanation of your question. :wink:

As explained there:

  • Multiplexing - Isolate signals to different users in the downlink from base station to user.

    • FDM is a way to share the Downlink spectrum resource
  • Duplexing - Isolate up and down links.

    • FDD is a way to split between Uplink and Downlink signals

So, we can use FDM and FDD together (in fact, GSM does this when it has more than one carrier)
And we can also use FDM in a TDD system (in TD-LTE we call the FDM aspect “PRBs”)

I believe this image help to understand (anyone agree/disagree)?