Coherent Versus Non-Coherent Subcarrier Index Modulation Systems

In this paper, three non-coherent index modulation (IM) schemes are proposed and analyzed. All schemes are based on subcarrier index modulation (SIM) in which an OFDM symbol is divided to groups of subcarriers and part of the subcarriers within each group are only active. The first scheme is called differential subcarrier index shift keying (DSISK). In DSISK, the index of the active subcarrier within a group is the only source of information and no modulated data symbol is transmitted. The second scheme is named differential subcarrier index modulation (DSIM), which transmits a modulated symbols on the active subcarriers and data bits are conveyed in both the index of the active subcarriers and the transmitted data symbols. The last scheme named as differential subcarrier index quadrature modulation (DSIQM) enhances the data rate of DSIM by activating two subcarrier indexes. One subcarrier will transmit the real part of the modulated symbol, whereas the second active subcarrier modulates the quadrature component of the active subcarrier. A unified upper bound formula for computing the average bit error probability is derived for all presented schemes. Analytical results are corroborated through Monte Carlo simulation results, where a close match is reported at pragmatic signal-to noise ratio (SNR) values.