Variable Spectral Efficiency Optical Modulation Schemes

Abstract

A transmitter of a communications system includes a first encoder configured to apply a shaping operation to a data signal to generate a shaped data signal, a second encoder configured to encode the shaped data signal according to a forward error correction (FEC) scheme to generate an encoded signal, and a constellation mapper configured to modulate the encoded signal to symbol values according to a modulation scheme to generate a corresponding symbol stream for transmission through the communications system. The shaping operation reduces average constellation energy for constellations of the modulation scheme.

What is claimed is: 
     
         1 . A method of handling a received signal, the method comprising:
 recovering received symbols from the received signal;   demodulating the received symbols according to a modulation scheme to derive forward error correction (FEC) encoded bits;   decoding the FEC encoded bits with error correction according to a FEC scheme to derive first recovered signals; and   performing a mapping operation on the first recovered signals to generate recovered data signals, the mapping operation effecting an inverse of a shaping operation.   
     
     
         2 . A receiver in a communications system, the receiver comprising:
 a detector configured to recover a stream of received symbols from a signal received over a channel; and   a digital signal processor configured to demodulate the received symbols according to a modulation scheme to derive forward error correction (FEC) encoded bits, to decode the FEC encoded bits with error correction according to a FEC scheme to derive first recovered signals, and to perform a mapping operation on the first recovered signals to generate recovered data signals, the mapping operation effecting an inverse of a shaping operation.