Optical receiving device

Patent metadata

Field	Value
Publication number	US-9374170-B2
Application number	US-201414560495-A
Country	US
Kind code	B2
Filing date	Dec 4, 2014
Priority date	Dec 24, 2013
Publication date	Jun 21, 2016
Grant date	Jun 21, 2016

Abstract

An optical receiving device includes: an adaptive equalizer that includes a position estimation unit configured to estimate, based on a first signal component and a second signal component of a reception signal generated by reception of a training sequence pattern transmitted from an optical transmitter, a symbol position of the reception signal, and generates an estimated symbol position, a delay unit configured to provide a delay difference between the first signal component and the second signal component, a control unit configured to set a plurality of symbol displacement amount candidates of displacement amounts for the estimated symbol position, causes the delay unit to generate a plurality of delay differences, and generates a channel estimation symbol position used for channel estimation, and an error rate calculation unit configured to calculate an error rate of the signal restored by an adaptive equalization unit.

First claim

What is claimed is:

1. An optical receiving device, comprising:
an adaptive equalizer that comprises:
a position estimation unit configured to estimate, based on a first signal component and a second signal component of a reception signal generated by reception of a training sequence pattern transmitted from an optical transmitter, a symbol position of the reception signal, and generates an estimated symbol position,
a delay unit configured to provide a delay difference between the first signal component and the second signal component,
a control unit configured to set a plurality of symbol displacement amount candidates of displacement amounts for the estimated symbol position, causes the delay unit to generate a plurality of delay differences, and generates a channel estimation symbol position used for channel estimation,
a channel estimation unit configured to perform, based on the channel estimation symbol position, channel estimation on a transmission path with the optical transmitter, using the first signal component and the second signal component between which the delay difference is provided by the delay unit, and generates parameters for realizing a characteristic opposite to a transmission path characteristic obtained by the channel estimation,
an adaptive equalization unit in which the parameters generated by the channel estimation unit are set and that performs adaptive equalization on the first signal component and the second signal component between which the delay difference is provided by the delay unit, and restores a signal, and
an error rate calculation unit configured to calculate an error rate of the signal restored by the adaptive equalization unit, wherein
the control unit acquires, from the error rate calculation unit, an error rate for each of the plural delay differences with respect to each of the plural symbol displacement amount candidates, and obtains a final channel estimation symbol position so that the acquired error rate is less than or equal to a reference value and the delay difference provided between the first signal component and the second signal component by the delay unit becomes a maximum available value, and
the channel estimation unit generates, based on the final channel estimation symbol position, parameters to be set in the adaptive equalization unit in a case where the delay difference provided by the delay unit is zero.

2. The optical receiving device according to claim 1 , wherein
the delay unit includes a first buffer that delays the first signal component, and a second buffer that delays the second signal component, and the control unit sets the number of buffer stages of one of the first buffer and the second buffer to zero stages, sets the number of buffer stages of the other to zero or more stages, in accordance with a current delay difference, and obtains the channel estimation symbol position by adding, to the estimated symbol position, a value of a current symbol displacement amount candidate and a value obtained by rounding up or rounding down, to a closest whole number, an absolute value of a value obtained by dividing the current delay difference by two.

3. The optical receiving device according to claim 1 , wherein
the delay unit includes a first FIR filter that compensates a characteristic of the first signal component, and a second FIR filter that compensates a characteristic of the second signal component, and the optical receiving device further includes a tap coefficient control unit that provides a delay difference between the first signal component that passes through the first FIR filter and the second signal component that passes through the second FIR filter, by shifting tap coefficients of the first FIR filter or tap coefficients of the second FIR filter in accordance with a current delay difference.

4. An optical receiving device comprising:
an adaptive equalizer that comprises:
a position estimation unit configured to estimate, based on a first signal component and a second signal component of a reception signal generated by reception of a training sequence pattern transmitted from an optical transmitter, a symbol position of the reception signal, and generates an estimated symbol position,
a control unit configured to set a plurality of symbol displacement amount candidates of displacement amounts for the estimated symbol position, and generates a channel estimation symbol position used for channel estimation,
a channel estimation unit configured to perform, based on the channel estimation symbol position, channel estimation on a transmission path with the optical transmitter, using the first signal component and the second signal component, and generates parameters for realizing a characteristic opposite to a transmission path characteristic obtained by the channel estimation,
an adaptive equalization unit in which the parameters generated by the channel estimation unit are set and that performs adaptive equalization on the first signal component and the second signal component, and restores a signal, and
an error rate calculation unit configured to calculate an error rate of the signal restored by the adaptive equalization unit, wherein
the control unit provides a plurality of delay differences between the first signal component and the second signal component with respect to each of the plural symbol displacement amount candidates, by controlling availability or unavailability of taps in which the parameters of the adaptive equalization unit are set, acquires, from the error rate calculation unit, an error rate for each of the plural delay differences, and obtains a final channel estimation symbol position so that the acquired error rate is less than or equal to a reference value and the delay difference becomes a maximum available value, and
the channel estimation unit generates, based on the final channel estimation symbol position, parameters to be set in the adaptive equalization unit in a case where all the taps are available.

5. The optical receiving device according to claim 4 , wherein
in accordance with a current delay difference, the control unit sets, to zero, tap coefficients on a leading side for one of a first FIR filter used for the first signal component and a second FIR filter used for the second signal component, included in the adaptive equalization unit, the number of the tap coefficients on the leading side corresponding to a value obtained by rounding up, to a closest whole number, an absolute value of a value obtained by dividing the current delay difference by two, and sets, to zero, tap coefficients on a trailing side for the other, the number of the tap coefficients on the trailing side corresponding to a value obtained by rounding down, to a closest whole number, an absolute value of a value obtained by dividing the current delay difference by two, or alternatively, the control unit sets, to zero, tap coefficients on a leading side for one of the first FIR filter used for the first signal component and the second FIR filter used for the second signal component, the number of the tap coefficients on the leading side corresponding to a value obtained by rounding down, to a closest whole number, an absolute value of a value obtained by dividing the current delay difference by two, and sets, to zero, tap coefficients on a trailing side for the other, the number of the tap coefficients on the trailing side corresponding to a value obtained by rounding up, to a closest whole number, an absolute value of a value obtained by dividing the current delay difference by two.

6. The optical receiving device according to claim 1 , wherein
under the condition that the error rate is less than or equal to the reference value with respect to each of the plural symbol displacement amount candidates, t

Assignees

• Fujitsu Ltd

Inventors

• Oota Masato
• Katou Tomoki
• Hatae Kazuhiko
• Nakashima Hisao
• Yamazaki Manabu

Classifications

• H04L25/03292

  with channel estimation circuitry · CPC title

• H04B10/6162

  Compensation of polarization related effects, e.g., PMD, PDL · CPC title

• H04B10/07953

  Monitoring or measuring OSNR, BER or Q · CPC title

• H04B10/616 Primary

  Details of the electronic signal processing in coherent optical receivers · CPC title

• H04L25/03133

  with a non-recursive structure (H04L25/03127 takes precedence) · CPC title