Investigation of near optimum iterative equalizers and decoders for optical coherent Gbit/s transmission

Inhalt:
We investigate a receiver for coherent optical communication with QPSK modulated signals. The receiver consists of a BCJR equalizer and LDPC decoding which are arranged as a turbo equalizer. Target is to find dedicated LDPC codes with overhead of about 7% to 14%. It turns out, that an LDPC code with overhead Oc = 12.5% and codeword length N = 9198 is most suitable with respect to performance, complexity and overhead. Furthermore the performance of the receiver is compared to a simpler receiver which compensates chromatic dispersion by the use of FIR filters. The comparison shows a gain of the turbo equalizer of up to 2.5 dB.