Conjugate root offset-QAM for orthogonal multicarrier transmission

Abstract

Current implementations of orthogonal frequency-division multiplexing (OFDM)/offset quadrature amplitude modulation (OQAM) are restricted to band-limited symmetric filters. To circumvent this, non-symmetric conjugate root (CR) filters are proposed for OQAM modulation. The idea is applied to Generalized Frequency Division Multiplexing (GFDM) and a method for achieving transmit diversity with OQAM modulation is presented. The proposal reduces implementation complexity compared to standard OQAM by modifying the transmit phase space which is exploited by a real-valued fast Fourier transform (FFT) operation. Generalized frequency division multiplexing (GFDM)/CR-OQAM outperforms conventional GFDM using QAM modulation in terms of symbol error rate in fading multipath channels and provides a more localized spectrum compared to GFDM/OQAM.