In-phase and quadrature filter shape index modulation

Abstract

This paper proposes a novel modulation scheme called “In Phase and Quadrature-Filter Shape Index Modulation” (IQ-FSIM). It aims to enhance the spectral/energy efficiencies (SE/EE) while generalizing several existing modulations and index modulation (IM) domains. In this system, the bitstream is divided into three sub-streams. The first is mapped using amplitude–phase modulation, and the other two are mapped separately to an index of a filter shape at the in-phase and quadrature components. IQ-FSIM in SISO mode enhances the SE by 2log _2 N (double FSIM gain), thanks to the independent indexation of N different filter shapes on each component changing at the symbol rate. A low-complexity matched filter-based detector that reaches the optimal joint ML performance is proposed. The theoretical lower bounds for the probability of filter index error and the symbol/bit error rate (SER/BER) are derived and validated. The computational complexity of the proposed IQ-FSIM transceiver is estimated and compared to its predecessor FSIM, where it is shown that IQ-FSIM provides up to 93.7% complexity reduction compared to FSIM along with different advantages. In addition, the results reveal that both IQ-FSIM and its special case FSIM, even with non-optimal filter shapes, outperform the equivalent schemes with/without IM of the same SE in AWGN, flat, and frequency-selective fading channels.