TRANSMISSION AND RECEPTION OF DUOBINARY MULTILEVEL PULSE-AMPLITUDE-MODULATED OPTICAL SIGNALS USING SUBSEQUENCE-BASED ENCODER

摘要

Methods and apparatus to transmit and receive information bits encoded in duobinary, multilevel pulse-amplitude-modulated (PAM) optical signals are described. The transmitted optical signal (34) has a narrow optical spectrum and a low symbol rate. Information bits (21) are encoded in a M-ary PAM symbol sequence (24), where M greater than or equal to 3. The subsequence-based encoder decomposes the PAM symbol sequence into (M-1) subsequences, precodes each subsequence, performs duobinary filtering on each precoded subsequence, and forms a weighted sum of the duobinary precoded subsequences. The weighted sum of duobinary precoded subsequences is lowpass filtered and modulated onto an optical electric field (28). The receiver processes a received optical electric field (36) to obtain an electrical signal proportional to the received optical intensity, and performs M-ary symbol-by-symbol decisions to recover the transmitted information bits, without potential error propagation.