Effect of Subcarrier Activation Ratio on the Performance of OFDM-IM over Rayleigh Fading Channel

Abstract

Orthogonal frequency division multiplexing with index modulation (OFDM-IM) is acquiring increasing attention due to its advantages over classical OFDM. These advantages include superior BER performance and transmit power saving since only a subset of the subcarriers is activated to transmit $M$ -QAM symbols and the remaining subcarriers are turned OFF. The vast majority of the literature studies the OFDM-IM by assuming certain subcarrier activation ratios, $r$ , together with other system parameters without figuring out the possible variation in system performance at other $r$ values. In this letter, the effect of $r$ and $M$ on the spectral efficiency (SE) and BER of OFDM-IM is investigated. An inequality is developed to maximize SE while power saving is maintained. Moreover, the BER performance of an OFDM-IM system exploiting a maximum subcarrier energy detector over multipath Rayleigh channel is analyzed. An approximate average BER expression is derived and the effect of $r$ and $M$ is discussed. Computer simulation has showed the validity of the derived expressions.