# US 2014/0195878 A1 · Method of decoding a differentially encoded phase modulated optical data signal

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- Number: US 2014/0195878 A1
- Document ID: US20140195878A1
- Status: Published application
- Kind: A1
- Application number: 14/122,290
- Filed: 2012-06-15
- Published: 2014-07-10
- Earliest claimed: 2011-06-21
- Assignees: Alcatel Lucent
- Applicants: Alcatel Lucent
- Inventors: Luca Razzetti; Carlo Costantini; Marianna Pepe; Andreas Leven; Stephan Ten Brink; Laurent Schmalen
- Web page: https://patentgrep.com/patent/US20140195878A1

## CPC

- H04L 1/0045: {Arrangements at the receiver end}
- H04B 10/6165: {Estimation of the phase of the received optical signal, phase error estimation or phase error correction}
- H04L 1/0047: {Decoding adapted to other signal detection operation (in conjunction with sequence estimation or equalization H04L25/03286)}
- H04L 1/005: {Iterative decoding, including iteration between signal detection and decoding operation}
- H04L 1/0054: {Maximum-likelihood or sequential decoding, e.g. Viterbi, Fano, ZJ algorithms}
- H04L 1/0057: {Block codes (H04L1/0061, H04L1/0064 take precedence)}
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)
- H04B: TRANSMISSION

## Abstract

Proposed is a method of decoding a differentially encoded PSK modulated optical data signal carrying FEC encoded data values. The optical signal is corrected by an estimated phase offset. From the corrected signal, respective likelihood values for the FEC encoded data values are derived, using an estimation algorithm which accounts for a differential encoding rule used for differentially encoding the optical signal. The derived likelihood values are limited to a predetermined range of values. From the limited likelihood values, FEC decoded data values are derived, using an algorithm which accounts for a FEC encoding rule used for FEC encoding the FEC encoded data values.

## Claims

### Claim 1

A method of decoding a differentially encoded phase-shift keying modulated optical data signal carrying forward error correction (FEC) encoded data values, comprising:
correcting said differentially encoded phase-shift keying modulated optical signal by an estimated phase offset,
deriving from the corrected differentially encoded phase-shift keying modulated optical signal respective likelihood values for said FEC encoded data values using an estimation algorithm which accounts for a differential encoding rule used for differentially encoding said differentially encoded phase-shift keying modulated optical signal,
limiting the derived likelihood values to a predetermined range of likelihood values, and
deriving from the limited likelihood values FEC decoded data values using an algorithm which accounts for a FEC encoding rule used for FEC encoding of said FEC encoded data values.

### Claim 2 (depends on 1)

The method according to claim 1,
wherein said predetermined range of likelihood values has an upper limit and a lower limit, and wherein said upper limit and said lower limit depend on a predetermined phase slip probability.

### Claim 3 (depends on 1)

The method according to claim 1,
wherein said step of limiting said derived likelihood values includes transforming said derived likelihood values into said limited likelihood values using a function for which a limited likelihood value is defined by a derived likelihood value and said predetermined phase slip probability.

### Claim 4 (depends on 1)

The method according to claim 1, wherein said method comprises instead of said step of
deriving from said limited likelihood values FEC decoded data values, the steps of
deriving from said limited likelihood values updated likelihood values using an algorithm which accounts for a FEC encoding rule used for FEC encoding of said FEC encoded data values,
limiting said updated likelihood values to a predetermined range of values,
deriving from said corrected signal respective new likelihood values for said FEC encoded data values using the limited updated likelihood values and an estimation algorithm which accounts for a differential encoding rule used for differentially encoding the differentially encoded phase-shift keying modulated optical signal,
limiting said new likelihood values to a predetermined range of values, and
deriving from the new limited likelihood values FEC decoded data values using an algorithm which accounts for a FEC encoding rule used for FEC encoding of said FEC encoded data values.

### Claim 5 (depends on 1)

The method according to claim 1, further comprising coherent reception of said optical signal by mixing said differentially encoded phase-shift keying modulated optical signal with a local optical signal provided by a local oscillator.

### Claim 6 (depends on 1)

The method according to claim 1, wherein a sign of a likelihood value indicates a value to which said FEC encoded data value is assumed to be equal to, and wherein an amplitude of a likelihood value indicates a likelihood of said FEC encoded data value being equal to the assumed value.

### Claim 7 (depends on 1)

The method according to claim 1, wherein said estimation algorithm used for deriving said likelihood values for said FEC encoded data values uses a predetermined noise variance value.

### Claim 8

A device for decoding a differentially encoded phase-shift keying modulated optical data signal carrying forward error correction (FEC) encoded data values, said device being adapted to
correct said differentially encoded phase-shift keying modulated optical signal by an estimated phase offset,
derive from the corrected differentially encoded phase-shift keying modulated optical signal respective likelihood values for said FEC encoded data values using an estimation algorithm which accounts for a differential encoding rule used for differentially encoding said differentially encoded phase-shift keying modulated optical signal,
limit the derived likelihood values to a predetermined range of values, and
derive from the limited likelihood values FEC decoded data values using an algorithm which accounts for a FEC encoding rule used for FEC encoding of said FEC encoded data values.