Probabilistic signal shaping using a self-referencing sequence

Abstract

A shaping encoder configured to generate a stream of output bit-words, wherein different bit-word values have different respective rates of occurrence to cause the optical transmitter connected to the shaping encoder to transmit constellation symbols of relatively high energy less frequently than constellation symbols of relatively low energy. The stream of output bit-words is self-referencing in that it encodes one of the input bitstreams applied to the shaping encoder in one or more designated bits of the output bit-words and is generated using a dither stream that can be recovered by the shaping decoder solely based on those one or more designated bits. As a result, some of the circuitry used in the shaping encoder at the transmitter and in the shaping decoder at the receiver can be identical, which can advantageously be used, e.g., to reduce the production costs.

1 - 14 . (canceled) 
     
     
         15 . An apparatus comprising:
 an optical data receiver that comprises an optical demodulator and an electronic decoder connected to receive a stream of values measured by the optical demodulator, the electronic decoder being configured to extract a bitstream of sign or parity values from the measured stream of values, the electronic decoder further being configured to redundancy-decode the stream of measured values based on a pseudorandom process in which the bitstream of sign or parity values is a seed bitstream; and   wherein the stream of values measured by the optical demodulator represents a stream of constellation symbols in which an occurrence rate of specific constellation symbols decreases with symbol energies.   
     
     
         16 . The apparatus of  claim 15 , wherein the bitstream of sign or parity values extracted by the electronic decoder is a bitstream of sign values. 
     
     
         17 . The apparatus of  claim 15 , wherein the bitstream of sign or parity values extracted by the electronic decoder is a bitstream of parity values. 
     
     
         18 . The apparatus of  claim 15 ,
 wherein the electronic decoder comprises a dither-stream generator configured to generate a dither stream in response to the seed bitstream, the dither stream comprising a sequence of bit-words, each of said bit-words being generated to encode a corresponding bit of the seed bitstream in a designated bit thereof; and   wherein the electronic decoder is configured to redundancy-decode the stream of measured values using the dither stream.   
     
     
         19 . The apparatus of  claim 18 , wherein the dither-stream generator is configured to generate the dither stream such that a distribution of values of the bit-words is approximated by a Gaussian function. 
     
     
         20 . (canceled) 
     
     
         21 . The apparatus of  claim 15 , wherein the electronic decoder is configured to maintain a constant ratio between a number of constellation symbols received via the stream of constellation symbols and a number of bits in a corresponding outputted decoded data stream. 
     
     
         22 . The apparatus of  claim 15 , wherein the electronic decoder comprises an FEC decoder configured to correct measurement errors in the measured stream of values based on data redundancy thereof.