A Spectral and Energy Efficient Noise Variance and SNR Estimator for DMH OFDM-IM Systems

The classical orthogonal frequency division multiplexing (OFDM) systems gained significant new dimensions with the introduction of index modulation (IM) schemes. However, reduced data rates are the drawback in IM-based systems when implemented using higher-order modulation techniques. Hence, to improve the data rate, we proposed a new OFDM-IM system by varying the inactive subcarriers in in-phase and quadrature-phase in every subblock, namely, a dual-mode homogenous OFDM-IM (DMH OFDM-IM) system. Furthermore, we introduce a novel noise power and signal-to-noise ratio (SNR) estimation algorithm for the proposed system, which operates over a Nakagami-m fading channel. The proposed estimation algorithm makes use of nulled subcarriers available in every subblock of the proposed system to estimate noise power. The introduced estimator is both spectral and energy efficient as it uses inactive subcarriers that carry no energy. Simulation results emphasize that the developed estimator achieves lower noise power and estimates the SNR at an ideal value in contrast to the existing estimators of OFDM system. Moreover, differential noise power (DNP) is determined for the proposed system (DMH OFDM-IM) to track channel variations effectively.