Properties and Power Spectral Densities of CP Based OQAM-OFDM Systems

Offset quadrature amplitude modulation OFDM (OQAM-OFDM) systems have low sidelobes but require complex receivers for broadband channels. To deal with this problem, cyclic prefix (CP)-based OQAM-OFDM systems have been proposed in the literature. In this paper, we study OQAM-OFDM and two existing CP based OQAM-OFDM systems and propose a new CP based system with good spectrum performance. We investigate their properties and analyze their power spectral densities (PSDs). We show that the continuous-time transmitted CP-OQAM-OFDM signal after the CP insertion is equivalent to a truncated signal obtained by inserting CP and cyclic suffix (CS) to the discrete-time input data symbols in the OQAM-OFDM system, which simplifies the calculation of the PSD of the transmitted CP-OQAM-OFDM signal and also implies that the PSD of the CP-OQAM-OFDM may be affected by the truncation. We show that the perfect reconstruction (PR) condition for the CP-OQAM-OFDM system is actually the same as that for the OQAM-OFDM system when the length of the prototype filter is not more than the length of the transmitted CP-OQAM-OFDM signal of each block excluding the CP. We also compare three CP-based OQAM-OFDM systems with windowed CP-OFDM systems. Numerical results show that the theoretical and simulated PSDs of the transmitted signals match well, CP-based OQAM-OFDM systems perform better than windowed CP-OFDM systems considering both the PSD and bit error rate (BER) performances, and the newly proposed CP-based OQAM-OFDM system has the best PSD performance in the three CP based OQAM-OFDM systems with an increase of the data rate overhead.