Method and apparatus for downstream transmission

An apparatus, for use by an Optical Network Unit (ONU) communicatively connected to an Optical Line Terminal (OLT), comprising:

• at least one memory storing computer program code;
• and
• at least one processor configured to execute the computer program code and cause the apparatus to perform,
• receiving a sequence of 4-level pulse amplitude modulation (PAM4) symbols from the OLT;
• deriving, for a codeword to be processed, from the received sequence of PAM4 symbols, a sequence of pairs of bit indicators, respective one of the pairs corresponding to respective one of the symbols and comprising a least significant bit (LSB) indicator and a most significant bit (MSB) indicator, the sequence of pairs comprising a first subset of pairs and a second subset of pairs, the first and the second subset being determined based on a de-mapping scheme and a de-interleaving scheme, and respectively comprising pairs corresponding to PAM4 symbols located N symbols apart in the sequence of PAM4 symbols;
• determining said codeword based on LSB indicators of the first subset of pairs, and MSB indicators of the second subset of pairs;
• wherein, the de-mapping scheme indicates a relationship between bit indicators of a respective pair and the corresponding PAM4 symbol, and the de-interleaving scheme indicates a de-interleaving step of k bit indicators and a first number N of codewords that are interleaved at the OLT, with N being an even number.

A method, for use by an Optical Line Terminal (OLT) communicatively connected to optical network units (ONUs) comprising:

• interleaving a first number N of codewords according to an interleaving scheme, obtaining an interleaved bit stream, wherein, N is an even number;
• mapping the interleaved bit stream into a sequence of 4-level pulse amplitude modulation (PAM4) labels according to a mapping scheme, with a respective PAM4 label comprising a least significant bit (LSB) and a most significant bit (MSB) respectively corresponding to a bit in the interleaved bit stream;
• transmitting a sequence of PAM4 symbols generated based on the sequence of PAM4 labels to the ONUs;
• wherein, bits from respective one of the N codewords are assigned to LSBs of a first subset of labels, and to MSBs of a second subset of labels, with the first and the second subset of labels being determined based on the interleaving scheme and the mapping scheme and respectively comprising labels located N labels apart in the sequence of PAM4 labels.

A method, for use by an Optical Network Unit (ONUs) communicatively connected to an Optical Line Terminal (OLT) comprising:

• receiving a sequence of 4-level pulse amplitude modulation (PAM4) symbols from the OLT;
• deriving, for a codeword to be processed, from the received sequence of PAM4 symbols, a sequence of pairs of bit indicators, respective one of the pairs corresponding to respective one of the symbols and comprising a least significant bit (LSB) indicator and a most significant bit (MSB) indicator, the sequence of pairs comprising a first subset of pairs and a second subset of pairs, the first and the second subset being determined based on a de-mapping scheme and a de-interleaving scheme, and respectively comprising pairs corresponding to PAM4 symbols located N symbols apart in the sequence of PAM4 symbols;
• determining said codeword based on LSB indicators of the first subset of pairs, and MSB indicators of the second subset of pairs;
• wherein, the de-mapping scheme indicates a relationship between bit indicators of a respective pair and the corresponding PAM4 symbol, and the de-interleaving scheme indicates a de-interleaving step of k bit indicators and a first number N of codewords that are interleaved at the OLT, with N being an even number.