# US 10,313,050 B2 · Phase estimation method and apparatus for polarization multiplexing system

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- Number: US 10,313,050 B2
- Document ID: US10313050B2
- Status: Granted
- Kind: B2
- Application number: 15/852,940
- Filed: 2017-12-22
- Published: 2018-05-03
- Granted: 2019-06-04
- Earliest claimed: 2015-06-23
- Assignees: Huawei Technologies Co., Ltd.
- Applicants: Huawei Technologies Co., Ltd.
- Inventors: Yuanda Huang
- Web page: https://patentgrep.com/patent/US10313050B2

## CPC

- H04J 14/06: Polarisation multiplex systems
- H04B 10/2507: for the reduction or elimination of distortion or dispersion
- H04B 10/6165: {Estimation of the phase of the received optical signal, phase error estimation or phase error correction}
- H04B 10/6166: {Polarisation demultiplexing, tracking or alignment of orthogonal polarisation components}
- H04L 7/0075: {with photonic or optical means}
- H04J: MULTIPLEX COMMUNICATION (transmission in general H04B; peculiar to transmission of digital information H04L5/00; systems for the simultaneous or sequential transmission of more than one television signal H04N7/08; in exchanges H04Q11/00; stereophonic systems H04S)
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A phase estimation method and apparatus for a polarization multiplexing system, where the method includes performing, by a receive end, state of polarization (SOP) rotation on a received first SOP signal and second SOP signal according to an angle of previous SOP rotation, extracting a pilot using adaptive filtering, and performing carrier phase estimation according to the extracted pilot. This prevents a noise signal from being extracted and can make a carrier phase estimation result more accurate.

## Claims

### Claim 1

A phase estimation method for a polarization multiplexing system, comprising:
performing, by a receive end, state of polarization (SOP) rotation on a received first SOP signal (Xin) and a second SOP signal (Yin) according to an angle of previous SOP rotation;
extracting, by the receive end, a pilot (Z2) using adaptive filtering, the SOP rotation being performed and the Z2 being extracted by:
performing, by the receive end, the SOP rotation on the received Xin and the Yin using a formula Z2=Xin*hx+Yin*hy;
tracking, by the receive end using the adaptive filtering, an angle of the SOP rotation; and
extracting the Z2 by the receive end using the adaptive filtering, the hx and the hy indicating adaptive filtering coefficients obtained according to the angle of the previous SOP rotation; and
performing, by the receive end, carrier phase estimation according to the Z2, the Xin and the Yin being orthogonal polarization signals.

### Claim 2 (depends on 1)

The method of claim 1, wherein after performing the SOP rotation and extracting the Z2, the method further comprises:
calculating, by the receive end, an error according to the Z2 to obtain an error calculation result (err);
tracking, by the receive end, the angle of the SOP rotation according to the error calculation result; and
updating, by the receive end, the hx and the hy.

### Claim 3 (depends on 2)

The method of claim 2, wherein updating the hx and the hy comprises updating, by the receive end, the hx and the hy using a formula hx′=hx−μ2·conj(Xin)·err and a formula hy′=hy−μ2·conj(Yin)·err, the hx′ and the hy′ indicating updated adaptive filtering coefficients, the conj(Xin) indicating a conjugate number of the Xin, the conj(Yin) indicating a conjugate number of the Yin, and the μ2 indicating a unit update step of the hr and the hy.

### Claim 4 (depends on 1)

The method of claim 1, wherein performing the SOP rotation and extracting the Z2 further comprises:
performing, by the receive end, the SOP rotation on the received Xin and the Yin according to the angle of the previous SOP rotation to obtain an SOP signal (Z1) after the SOP rotation; and
extracting, by the receive end using the adaptive filtering, the Z2 from the Z1.

### Claim 5 (depends on 1)

The method of claim 1, wherein before performing the SOP rotation, the method further comprises performing, by the receive end, pre-filtering on the received Xin and the Yin.

### Claim 6 (depends on 1)

The method of claim 1, wherein after extracting the Z2, the method further comprises:
determining, by the receive end according to the Z2, a clock phase error between the receive end and a transmit end of the Xin and the Yin; and
performing, by the receive end, clock phase adjustment according to the clock phase error such that clock phases of the transmit end and the receive end are synchronous.

### Claim 7 (depends on 6)

The method of claim 6, wherein performing the clock phase adjustment comprises:
adjusting, by the receive end, a clock source of the receive end according to the clock phase error such that the clock phases of the transmit end and the receive end are synchronous;
delaying, by the receive end, the Xin and the Yin according to the clock phase error such that the clock phases of the transmit end and the receive end are synchronous; or
adjusting, by the receive end, the clock source of the receive end according to the clock phase error, and delaying the Xin and the Yin according to the clock phase error such that the clock phases of the transmit end and the receive end are synchronous.

### Claim 8

A phase estimation method for a polarization multiplexing system, comprising:
performing, by a receive end, state of polarization (SOP) rotation on a received first SOP signal (Xin) and a second SOP signal (Yin) according to an angle of previous SOP rotation;
extracting, by the receive end, a pilot (Z2) using adaptive filtering, the SOP rotation being performed and the Z2 being extracted by:
performing, by the receive end, the SOP rotation on the received Xin and the Yin according to the angle of the previous SOP rotation to obtain an SOP signal (Z1) after the SOP rotation;
extracting, by the receive end using the adaptive filtering, the Z2 from the Z1; and
performing, by the receive end, the SOP rotation on the received Xin and the Yin using a formula Z1=a·Xin+b·Yin, the a and the b being weighting coefficients obtained according to the angle of the previous SOP rotation, the Z2 being extracted from the Z1 comprising extracting, by the receive end using a formula Z2=Z1*h, the Z2 from the Z1, the h indicating an adaptive filtering coefficient, and the * indicating convolution; and
performing, by the receive end, carrier phase estimation according to the Z2, the Xin and the Yin being orthogonal polarization signals.

### Claim 9 (depends on 8)

The method of claim 8, wherein after extracting the Z2 from the Z1, the method further comprises:
calculating, by the receive end, an error according to the Z2 to obtain an error calculation result;
tracking, by the receive end, an angle of the SOP rotation according to the error calculation result; and
updating, by the receive end, the weighting coefficients and the adaptive filtering coefficient.

### Claim 10

A phase estimation apparatus for a polarization multiplexing system, comprising:
a non-transitory computer-readable storage medium storing instructions; and
a processor coupled to the non-transitory computer-readable storage medium, the instructions causing the processor to be configured to:
perform state of polarization (SOP) rotation on a received first SOP signal (Xin) and a second SOP signal (Yin) according to an angle of previous SOP rotation;
extract a pilot (Z2) using adaptive filtering, the SOP rotation being performed and the Z2 being extracted by:
performing the SOP rotation on the received Xin and the Yin using a formula Z2=Xin*hx+Yin*hy;
tracking, using the adaptive filtering, an angle of the SOP rotation; and
extracting, using the adaptive filtering, the Z2, the hx and the hy indicating adaptive filtering coefficients obtained according to the angle of the previous SOP rotation; and
perform carrier phase estimation according to the extracted Z2, the Xin and the Yin being orthogonal polarization signals.

### Claim 11 (depends on 10)

The apparatus of claim 10, wherein the instructions further cause the processor to be configured to:
calculate an error according to the pilot to obtain an error calculation result (err);
track the angle of the SOP rotation according to the err; and
update the hx and the hy.

### Claim 12 (depends on 11)

The apparatus of claim 11, wherein the instructions further cause the processor to be configured to update the hx and the hy using a formula hx′=hx−μ2·conj(Xin)·err and a formula hy′=hy−μ2·conj(Yin)·err, the hx′ and the hy′ indicating updated adaptive filtering coefficients, the conj(Xin) indicating a conjugate number of the Xin, the conj(Yin) indicating a conjugate number of the Yin, and the μ2 indicating a unit update step of the hx and the hy.

### Claim 13 (depends on 10)

The apparatus of claim 10, wherein when performing the SOP rotation and extracting the Z2, the instructions further cause the processor to be configured to:
perform the SOP rotation on the received Xin and the Yin according to the angle of the previous SOP rotation to obtain an SOP signal (Z1) after the SOP rotation; and
extract, using the adaptive filtering, the Z2 from the Z1.

### Claim 14 (depends on 13)

The apparatus of claim 13, wherein the instructions further cause the processor to be configured to:
perform SOP rotation on the received Xin and the Yin using a formula Z1=a·Xin+b·Yin to obtain the Z1, the a and the b being weighting coefficients obtained according to the angle of the previous SOP rotation; and
extract, using a formula Z2=Z1*h, the Z2 from the Z1, the h indicating an adaptive filtering coefficient, and the * indicating convolution.

### Claim 15 (depends on 14)

The apparatus of claim 14, wherein the instructions further cause the processor to be configured to:
calculate an error according to the Z2 to obtain an error calculation result;
track an angle of the SOP rotation according to the error calculation result; and
update the weighting coefficients and the adaptive filtering coefficient.

### Claim 16 (depends on 10)

The apparatus of claim 10, wherein before performing the SOP rotation on the received Xin and the Yin, the instructions further cause the processor to be configured to perform pre-filtering on the received Xin and the Yin.

### Claim 17 (depends on 10)

The apparatus of claim 10, wherein after extracting the Z2, the instructions further cause the processor to be configured to:
determine, according to the Z2, a clock phase error between the receive end and a transmit end of the Xin and the Yin; and
perform clock phase adjustment according to the clock phase error such that clock phases of the transmit end and the receive end are synchronous.

### Claim 18 (depends on 17)

The apparatus of claim 17, wherein the instructions further cause the processor to be configured to:
adjusting a clock source of the receive end according to the clock phase error such that the clock phases of the transmit end and the receive end are synchronous;
delaying the Xin and the Yin according to the clock phase error such that the clock phases of the transmit end and the receive end are synchronous; or
adjusting the clock source of the receive end according to the clock phase error, and delay the Xin and the Yin such that the clock phases of the transmit end and the receive end are synchronous.