Improved orthogonal frequency division multiplexing with generalised index modulation

Recently, the generalisation of orthogonal frequency division multiplexing with index modulation (OFDM-IM) was proposed in the authors' previous works. Two generalisation schemes of OFDM-IM, named as OFDM with type-1 generalised index modulation (OFDM-GIM1) and OFDM-GIM2, have been proposed and investigated. In OFDM-GIM1, the number of active subcarriers in an OFDM subblock is no longer fixed. In OFDM-GIM2, independent index modulation is performed on the in-phase and quadrature component of quadrature phase shift keying symbol of each subcarrier. Through such ways, a higher spectral efficiency than that of OFDM-IM may be achieved. In this study, the authors focus on further improving OFDM-GIM2's spectral efficiency by introducing joint I/Q index modulation where the two index modulations on the in-phase and quadrature components are no longer entirely independent. In other words, in the proposed scheme, the input bit string jointly decides the indices of active subcarriers for in-phase and quadrature components. As a result, more bits can be transmitted per OFDM frame. Computer simulation results clearly show the proposed scheme's superiority in both spectral efficiency and bit error rate performance compared with the existing OFDM-GIM2.