SNR Estimation for Low Bit Rate OFDM Systems in AWGN Channel

Orthogonal Frequency Division Multiplexing (OFDM) is a promising approach to achieve higher data rates with sufficient performance. However a measure of channel state is desired in order to decide upon transition to these rates. Signal-to-Noise Ratio (S1NR) is such a measure and an estimator operating in low transmission rates, such as BPSK or using the preamble data would be proper. In this work two online SNR estimators are developed for OFDM systems, operating on BPSK modulation or on the preamble data. It is shown that the convergence of the algorithms to the actual SNR value is achieved from about 0 dBs or even lower. The impact of the channel estimation used on the SNR estimation accuracy is given and improvements, regarding the computational cost, on one of them are given. Finally a transmission procedure for an OFDM modem using these SNR estimators is given.