A Modified EVM SNR Estimation Method for QAM OFDM Systems in AWGN Channel

Signal-to-Noise Ratio (SNR) is an important parameter in many receivers to improve their performance. In this paper, we develop a modified Error Vector Magnitude (mEVM) SNR estimation algorithm for Orthogonal Frequency Division Multiplexed (OFDM) systems in Additive White Gaussian Noise (AWGN) channels. At first mEVM is introduced for QPSK modulation. We also generalize the idea to 16- and 64-QAM modulation using two groups of selected data: data representing a specific single constellation point and data belonging to a group (up to 4) of neighboring constellation points. Criteria used to measure its performance are the SNR estimation accuracy compared to the actual SNR, the variance of the estimation and the mean square error (MSE). Computer simulations show that the proposed estimator for both types of data selection at SNR values of practical interest for each modulation type is highly accurate and reliable for OFDM systems, outperforming previously published generic QPSK SNR estimators. Finally the impact of the channel estimation method used to improve signal's reception, on the SNR estimation accuracy is examined.