A receiver with iterative soft decision and forward error correction

As a receiving method suitable for channels with intersymbol interference s uch as frequency selective fading, a method is proposed in which the soft d ecision using the hard decision sequence generated from the data after forw ard error correction (FEC) is alternated with FEC. In the conventional rece iver with a serial configuration of the equalizer, deinverter, and decoder, the performance of the equalizer significantly affects the overall receive r characteristics. Hence, the performance of the equalizer is emphasized. O n the other hand, in the proposed method the error generated in the initial equalization can be corrected by repetitive soft decision and FEC. Therefo re, the method does not strongly depend on the performance of the equalizer used in the initial equalization. Hence, even if an equalizer requiring a smaller amount of process with a somewhat degraded performance is used in t he initial equalization in place of a high-performance equalizer, the amoun t of process for the entire receiver can be decreased without degrading the characteristics of the proposed method very much. In this paper, the chara cteristics of the proposed method are evaluated by computer simulation. The following are the confirmed conclusions. (1) The proposed method using the maximum-likelihood sequence estimation (MLSE) as the equalization has supe rior BER characteristics over the conventional method using a maximum a pos teriori (MAP) equalizer and MLSE. (2) In a transmission channel with a larg e delay spread, the degradation of the BER characteristics of the proposed method using the delayed decision-feedback sequence estimation (DDFSE) in p lace of MLSE is very slight while the amount of processing can be reduced s ubstantially from that in the conventional method using MLSE, (C) 2000 Scri pta Technica.