A LMMSE channel estimator for coherent optical OFDM system

As coherent optical orthogonal frequency-division multiplexing (CO-OFDM) is sensitive to noises, so the channel estimation becomes a key issue for the performance. There are mainly two OFDM channel estimation methods, Least Square (LS) and Linear Minimum Means Square Error (LMMSE) included. LS estimator is used commonly in the CO-OFDM systems due to its simple realization and low complexity. However, the impact of noise is not considered, so the performance will deteriorate when large noise occurs. On the contrary, LMMSE estimator can compensate the losses more accurately than LS. But classic LMMSE estimator is difficult to realize for prior information about the channel needed in advance. In this paper, an improved LMMSE estimator for CO-OFDM systems has been introduced for the first time. Simulation shows that it can bring 2dB SNR gains compared with LS for BER = 10⁻⁴.