Diversity-Achieving Quadrature Space-Frequency Index Modulation

Quadrature space-frequency index modulation (QSF-IM) is a recently developed space-frequency transmission scheme which generalizes the idea of quadrature spatial modulation into both spatial and frequency domains. However, QSF-IM lacks of transmit diversity. In this letter, by combining QSF-IM and space-frequency code designing, a novel diversity-achieving QSF-IM (DA-QSFIM) scheme which can achieve the second-order transmit diversity is proposed. In the proposed scheme, the real and imaginary parts of a symbol vector are respectively multiplied by two different precoding matrices and then they are placed into space-frequency resource block in diagonal or anti-diagonal form for transmission. Theoretical performance analysis and simulation results are presented to validate the superiority of DA-QSFIM over other existing schemes in terms of bit error rate (BER) performance under both Rayleigh and Rician channels.