A Novel Noise Variance and SNR Estimator for OFDM-IM Systems over Nakagami-m Fading Channel

Noise power (Variance) and signal-to-noise ratio (SNR) are the key performance evaluation parameters of wireless communication systems. In this article, a novel algorithm is proposed that effectively estimates the noise power and SNR for orthogonal frequency division multiplexing with index modulation (OFDM-IM) systems operating over a time-varying Nakagami-m fading channel. The inactive subcarriers in each group of the OFDM-IM system simplify the analysis and lead to noise power estimation under ideal as well as realistic conditions of the wireless channel. At the receiver side, by using the proposed algorithm the position of inactive subcarriers can be identified effectively, as these positions are dynamic in the OFDM-IM system. Another simplified algorithm is proposed at the transmitter side for effectively transmitting the inactive subcarriers. The noise power on the sub-channel, average noise power, and average SNR are calculated. Differential noise power can also be estimated to track the channel variations effectively. None of the noise power and SNR estimators are available in the literature for the OFDM-IM systems. Hence, the performance of the proposed estimator is compared with the noise power and SNR estimators available for the classical OFDM systems. Moreover, the performance is also tested in terms of normalized mean square error (NMSE) using extensive computer simulations. The proposed estimator achieves significant improvements in spectral efficiency, energy efficiency, and also achieves much lower computational complexity in contrast to the estimators for the classical OFDM systems.