New channel estimation schemes exploiting reliable decision feedback symbols for OFDM systems

Abstract

The conventional pilot-aided orthogonal frequency division multiplexing (OFDM) systems use the fixed number of pilots to estimate the channel. In this thesis, we propose new channel estimation schemes that exploit reliable decision feedback symbols in the OFDM systems. The reliability of the decision feedback symbols depends on its error rate. In other words, the reliable symbol has a low symbol error rate. The process of the proposed scheme is follows. In the first place, the channel estimation process is performed by the conventional pilot-aided estimation scheme. Next, the estimated channel equalizes the channel distortion, and then the symbol detection process is operated. From the decision symbols, quasi-pilots are extracted based on their reliability. The quasi-pilot means the decision symbols that will be employed as pilots to estimate the channel. The reliable quasi-pilots are the symbols whose subcarrier’s channel gain is greater than the threshold value. These reliable quasi-pilots and pilots are used to estimate the channel again. This method gives more accurate estimated channel and lower bit error rate (BER) than conventional method. In order to prove these results, we calculate the Cramér Rao Lower Bound (CRLB) of estimated channel, and computer simulations are performed. Simulation results show that the mean square error of estimated channel is closed to CRLB, and BER of the proposed scheme is lower than conventional method.