Distribution matching for probabilistic constellation shaping with an arbitrary input/output alphabet

Patent metadata

Field	Value
Publication number	US-11121903-B2
Application number	US-201816152351-A
Country	US
Kind code	B2
Filing date	Oct 4, 2018
Priority date	Oct 4, 2017
Publication date	Sep 14, 2021
Grant date	Sep 14, 2021

Abstract

Consistent with the present disclosure, an encoder circuit is provided at a transmit side of an optical fiber link that maps an input sequence of bits of fixed length k a sequence of symbols of a codeword of length n, such that the symbols of the codeword define a predetermined transmission probability distribution. Preferably, each symbol of the codeword is generated during a corresponding clock cycle, such that after n clock cycles, a complete codeword corresponding to the input bit sequence is output. On a receive end of the link, a decoder is provided that outputs the k-bit sequence every n clock cycles. Accordingly, buffers need not be provided at the output of the encoder and the input of the decoder, such that processing of the input sequence, codewords, and output sequence may be achieved efficiently without large buffers and complicated circuitry. Moreover, the input sequence, with any binary alphabet may be matched to a desired output distribution with any arbitrary alphabet. Accordingly, probabilistic constellation shaping may be achieved over constellations of arbitrary size. In addition, relatively long codewords, may be encoded and decoded with the apparatus and method disclosed herein. Accordingly, for a fixed SNR a higher SE (more bits per symbol) can be achieved. Alternatively, for a fixed SE, a lower SNR may be sufficient. Moreover, the resulting SE may be finely tailored to a particular optical link SNR to provide data transmission rates that are higher than the low order modulation formats that would otherwise be employed for optical signals carried by such links.

First claim

What is claimed is:

1. An apparatus, comprising:
a local oscillator laser that supplies local oscillator light;
an optical hybrid circuit that receives an incoming optical signal and the local oscillator light, the incoming optical signal being modulated in accordance with an m-quadrature modulated optical signal, where m is greater than or equal to 16;
a photodetector circuit that receives an optical output from the optical hybrid circuit and generates electrical signals;
a decoder circuit that receives a codeword based on the electrical signals, the codeword includes n codeword symbols, where n is an integer, the codeword being indicative of a distribution of modulation symbols carried by the incoming optical signal such that first ones of the modulation symbols having an associated first amplitude are transmitted more frequently than second ones of the modulation symbols having an associated second amplitude that is different than the first amplitude; and
a clock circuit that generates a clock signal,
wherein the decoder circuit processes each of the modulation symbols during a corresponding one of a plurality of clock cycles of the clock signal, such that, during n clock cycles of the plurality of clock cycles of the clock signal, the decoder circuit outputs a data sequence based on the code word and fixed point representations of the codeword, where k is an integer.

2. An apparatus in accordance with claim 1 , wherein third ones of the modulation symbols having an associated third amplitude are transmitted less frequently than the first and second ones of the modulation symbols.

3. An apparatus in accordance with claim 2 , wherein fourth ones of the modulation symbols having an associated fourth amplitude are transmitted less frequently than the first, second, and third ones of the modulation symbols.

4. An apparatus, comprising:
a local oscillator laser that supplies local oscillator light;
an optical hybrid circuit that receives an incoming optical signal and the local oscillator light, the incoming optical signal being modulated in accordance with an m-quadrature modulated optical signal, where m is greater than or equal to 16;
a photodetector circuit that receives an optical output from the optical hybrid circuit and generates electrical signals;
a decoder circuit that receives a codeword based on the electrical signals, the codeword includes n codeword symbols, where n is an integer, the codeword being indicative of a distribution of modulation symbols carried by the incoming optical signal such that first ones of the modulation symbols having an associated first amplitude are transmitted more frequently than second ones of the modulation symbols having an associated second amplitude that is different than the first amplitude; and
a clock circuit that generates a clock signal,
wherein the decoder circuit outputs, during n clock cycles of the clock signal and based on fixed point representations of the codeword, a data sequence based on the codeword, the data sequence having k bits, where k is an integers; and
an inverse labelling circuit converting each of a plurality of binary or non-binary symbols to a corresponding one of the n codeword symbols.

5. An apparatus in accordance with claim 4 , further including a forward error correcting (FEC) decoding circuit that decodes in-phase and quadrature symbols, in accordance with a forward error correction code, to provide the plurality of binary or non-binary symbols.

6. An apparatus in accordance with claim 5 , wherein the binary or non-binary symbols do not include parity bits.

7. An apparatus in accordance with claim 5 , further including a multiplexer that multiplexes the in-phase and quadrature symbols and supplies the multiplexed in-phase and quadrature symbols to the FEC decoding circuit.

8. An apparatus comprising:
a local oscillator laser that supplies local oscillator light;
an optical hybrid circuit that receives an incoming optical signal and the local oscillator light, the incoming optical signal being modulated in accordance with an m-quadrature modulated optical signal, where m is greater than or equal to 16;
a photodetector circuit that receives an optical output from the optical hybrid circuit and generates electrical signals;
a decoder circuit that receives a codeword based on the electrical signals, the codeword includes n codeword symbols, where n is an integer, the codeword being indicative of a distribution of modulation symbols carried by the incoming optical signal such that first ones of the modulation symbols having an associated first amplitude are transmitted more frequently than second ones of the modulation symbols having an associated second amplitude that is different than the first amplitude; and
a clock circuit that generates a clock signal,
wherein the decoder circuit outputs, during n clock cycles of the clock signal and based on fixed point representations of the codeword, a data sequence based on the codeword, the data sequence having k bits, where k is an integers, and,
wherein the decoder circuit calculates a parameter, x, based on one of the n codeword symbols, calculates a parameter, y, such that y is greater than n, and determines that x is within a sub-interval of y corresponding to said one of the n codeword symbols.

9. An apparatus in accordance with claim 8 , wherein the encoder circuit determines y, such that y further satisfies:
2 w ≤y ≤2 w+1

where w is a lowest integer, such that y is greater than n.

10. An apparatus in accordance with claim 8 , wherein the decoder circuit multiplies parameter x by a scaling factor and multiplies y by the scaling factor.

11. An apparatus in accordance with claim 8 , wherein said one of the n codeword symbols is a first one of the n codeword symbols, the encoder circuit redefining the sub-interval based on a number remaining codeword symbols after the first one of the n codeword symbols is output.

12. An apparatus in accordance with claim 11 , wherein first ones of the remaining codeword symbols have a first value and second ones of the remaining codeword symbols have a second value.

13. An apparatus in accordance with claim 11 , wherein each of the remaining codewords symbols has a respective one of a plurality of values, a number of the plurality of values being greater than two.

14. An apparatus in accordance with claim 8 , further including a memory that stores selected ones of the k bits of the data sequence prior to outputting the data sequence.

15. An apparatus in accordance with claim 14 , wherein the memory is a buffer.

16. An apparatus, comprising:
a local oscillator laser that supplies local oscillator light;
an optical hybrid circuit that receives an incoming optical signal and the local oscillator light, the incoming optical signal being modulated in accordance with an m-quadrature modulated optical signal, where m is greater than or equal to 16;
a photodetector circuit that receives an optical output from the optical hybrid circuit and generates electrical signals;
a decoder circuit that receives a codeword based on the electrical signals, the codeword includes n codeword symbols, where n is an integer, the codeword being indicative of a distribution of modulation symbols carried by the incoming optical signal such that first ones of the modulation symbols having an associated first amplitude are transmitted more frequently than second ones of the modulation symbols having an associated second amplitude that is different than the first amplitude; and
a clock circuit that generates a clock signal,
wherein the decode

Assignees

• Infinera Corp

Inventors

• Torbatian Mehdi
• Chan Deyuan
• Sun Han Henry
• Thomson Sandy
• Wu Kuang-Tsan

Classifications

• H04L1/0042

  Encoding specially adapted to other signal generation operation, e.g. in order to reduce transmit distortions, jitter, or to improve signal shape (H04L1/0067 takes precedence) · CPC title

• H04L25/49

  using code conversion at the transmitter; using predistortion; using insertion of idle bits for obtaining a desired frequency spectrum; using three or more amplitude levels {; Baseband coding techniques specific to data transmission systems (spectral shaping H04L25/03828)} · CPC title

• H04B10/541

  Digital intensity or amplitude modulation · CPC title

• H04L27/3433

  using an underlying square constellation · CPC title

• H04J14/0205

  Select and combine arrangements, e.g. with an optical combiner at the output after adding or dropping · CPC title