VARIABLE SPECTRAL EFFICIENCY OPTICAL MODULATION SCHEMES
A received signal is received over a noise channel. A stream of received symbols is recovered from the received signal. Each symbol is decoded into one or more bits, where a decoded bit of the symbol has a high probability of being in error, and a probability of being a ‘1’ substantially different from 0.5. An inverse mapping is performed on the decoded bits, where the output of the inverse mapping is a stream of bits with a very low probability of being in error and a probability of being a ‘1’ substantially equal to 0.5.
1 . A method of handling a received signal, the method comprising:
receiving a received signal over a noisy channel;
recovering a stream of received symbols from the received signal;
decoding each symbol into one or more bits, where a decoded bit of the symbol has a high probability of being in error, and a probability of being a ‘1’ substantially different from 0.5; and
performing an inverse mapping on the decoded bits, where the output of the inverse mapping is a stream of bits with a very low probability of being in error and a probability of being a ‘1’ substantially equal to 0.5.
2 . The method as recited in claim 1 , wherein the inverse mapping comprises error correction followed by inverse shaping.
3 . The method as recited in claim 2 , wherein the error correction achieves a frame error rate that is much less than 10 −12 .
4 . The method as recited in claim 1 , wherein the inverse mapping performed on the stream of bits operates on a block basis.
5 . The method as recited in claim 1 , wherein the received signal is an optical received signal.
6 . 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 noisy channel;
a digital signal processor configured to decode each symbol into one or more bits, where a decoded bit of the symbol has a high probability of being in error, and a probability of being a ‘1’ substantially different from 0.5, and to perform an inverse mapping on the decoded bits, where the output of the inverse mapping is a stream of bits with a very low probability of being in error and a probability of being a ‘1’ substantially equal to 0.5.
7 . The receiver as recited in claim 6 , wherein the inverse mapping comprises error correction followed by inverse shaping.
8 . The method as recited in claim 7 , wherein the error correction achieves a frame error rate that is much less than 10 −12 .
9 . The receiver as recited in claim 6 , wherein the inverse mapping performed on the stream of bits operates on a block basis.
10 . A method of transmitting a data signal using a transmitter of a communications system, the method comprising:
applying a shaping operation to the data signal to generate a shaped data signal, the shaping operation creating bits with a probability of being a ‘1’ substantially different from 0.5;
encoding the shaped data signal according to a systematic forward error correction (FEC) scheme to generate an encoded signal, the systematic FEC scheme creating overhead bits with a probability of being a ‘1’ substantially equal to 0.5; and
modulating the encoded signal to symbol values according to a modulation scheme to generate a corresponding symbol stream, bits of the symbol values being categorized as belonging to a first category or a second category, where modulating the encoded symbol to the symbol values involves mapping substantially all of the bits with a probability of being a ‘1’ substantially equal to 0.5 to symbol value bits of the first category and mapping substantially all of the bits with a probability of being a ‘1’ substantially different from 0.5 to symbol value bits of the second category.
11 . The method as recited in claim 10 , wherein the communications system is an optical communications system and modulating the encoded signal comprises modulating a carrier light according to the symbol stream to generate an optical signal for transmission through the optical communications system.