On the performance of optimal training-based OFDM with channel estimation error

We analyze the performance of an uncoded orthogonal frequency-division multiplexing (OFDM) system in a quasistatic fading channel where optimal training is being employed for the acquisition of channel state information (CSI). A bit-error probability (BEP) expression is obtained for the linear minimum mean-square error (LMMSE) based channel estimator where the mean-square error (MSE) of the channel estimator is minimized by equispaced, equipowered training with the number of training tones equal to the channel length. Optimal power allocation is obtained by minimizing the BEP expressions. The performances of BPSK, QPSK and 16-QAM schemes are considered. It is shown that while equal power training performs around 3 dB worse than the known channel case, our optimal power channel estimator performance varies between these two, depending on the number of subcarrier to channel length ratio. Numerical examples are presented to further clarify and confirm the analytical findings.