Currently I am studying about a modulation technique FBMC (Filter Bank Multicarrier) which is a predecessor of OFDM. The difference with OFDM is that, FBMC does not have a CP (Cyclic Prefix) which is a better use of spectrum. On the other hand, it is susceptible to ISI (Inter Symbol Interference) due to the absence of GI (Guard Interval) when transmitted over wireless channel.1. FBMC uses prototype filters to shape the out of band emission to lower the interference.

There is a concept of FBMC-OQAM (sometimes referred as staggered multitone or SMT), where the input signal is first converted to QAM symbols and further processed into OQAM symbols[2].

Can anyone explain to me in very simple words / general context:

#. What is the purpose of OQAM (ref.2 has a figure) and how it is making the signal orthogonal?

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  • $\begingroup$ Can you post the figures since not everyone will be able to download the documents since many will have to pay to download? $\endgroup$ Sep 29, 2020 at 20:59
  • 1
    $\begingroup$ updated with figure $\endgroup$
    – SAM
    Sep 29, 2020 at 21:05

1 Answer 1


Actually, in theory and error performance there is no difference. But in practice, OQPSK decrases the maximum phase alteriation from 180 to 90 degrees which is better for RF power amplifiers.


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