FBMC/OQAM Modulators with Half Complexity

The Filter Bank MultiCarrier (FMBC) concept can be seen as an extension of the Orthogonal Frequency Division Multiplex (OFDM) principle. Indeed, in the case where each sub-carrier uses an Offset Quadrature Amplitude Modulation (OQAM), we get with the FBMC/OQAM system a multicarrier modulation scheme with relaxed orthogonality constraints so that, differently from OFDM, a cyclic prefix (CP) is no longer required. However, the OQAM principle, that permits to separately handle the real and imaginary parts of the complex QAM symbols, presents an implementation drawback. Indeed, compared to OFDM at the same bit rate, the Inverse Fast Fourier Transform (IFFT) has to run twice faster. In this paper, we show that for FBMC/OQAM, the IFFT outputs present properties that can be exploited by a pruned IFFT implementation. Moreover, in some specific cases, a reduction of the computational complexity can also be operated at the filtering stage.