Simple DSP-IDFT techniques for generating spectrally efficient FDM signals

Spectrally Efficient Frequency Division Multiplexing (SEFDM) system promises bandwidth savings by multiplexing overlapped non-orthogonal sub-carriers. Work in the literature has confirmed that despite the non-orthogonal structure of the sub-carriers, efficient detection of the SEFDM signal is achievable. However, loosing orthogonality brings along many design and implementation challenges. In particular, the generation of the signal requires a bank of independent modulators which becomes particularly complex with the increase in the number of carriers. In this work, we propose simple framework for the generation of the SEFDM signal based on the Inverse Discrete Fourier Transform (IDFT). The proposed designs employ similar building blocks as Orthogonal Frequency Division Multiplexing (OFDM) based systems, hence, would facilitate an easy migration and/or coexistence with OFDM on the transmitter side. Furthermore, the proposed framework may facilitate the IDFT design for any Frequency Division Multiplexed (FDM) signal with arbitrary sub-carriers spacing. The equivalence of the IDFT generated signal and the modulators based signal is proved mathematically, nonetheless, numerical simulations were performed to verify that equivalence and to test for the performance of the digitally generated signal in AWGN channel. Numerical results confirmed the required spectrum compression and bite error rate (BER) performance at a much reduced complexity.