Method and system for mitigating Raman crosstalk in an Ethernet passive optical network

• US 20060257148A1
• Filed: 05/09/2006
• Published: 11/16/2006
• Est. Priority Date: 05/13/2005
• Status: Active Grant

• Current Assignee: Avago Technologies General IP PTE Limited (Broadcom, Inc.)
• Original Assignee: Teknovus Inc. (Broadcom, Inc.)
• Inventors: Brown, Benjamin J., Hirth, Ryan E., Kramer, Glen, Lamb, Lowell D.
• Granted Patent: US 7,660,528 B2
• Time in Patent Office: Days
• US Class Current: 398/71
• CPC Class Codes: H04B 10/2537 due to scattering processes, e.g. Raman or Brillouin scattering
• CPC Class Codes: H04B 10/27 Arrangements for networking
• CPC Class Codes: H04B 10/272 Star-type networks or tree-type networks
• CPC Class Codes: H04J 14/02 Wavelength-division multiplex systems
• CPC Class Codes: H04J 14/0226 Fixed carrier allocation, e.g. according to service
• CPC Class Codes: H04J 14/0227 Operation, administration, maintenance or provisioning [OAMP] of WDM networks, e.g. media access, routing or wavelength allocation
• CPC Class Codes: H04J 14/0232 for downstream transmission
• CPC Class Codes: H04J 14/0247 Sharing one wavelength for at least a group of ONUs
• CPC Class Codes: H04J 14/0252 Sharing one wavelength for at least a group of ONUs, e.g. for transmissions from-ONU-to-OLT or from-ONU-to-ONU
• CPC Class Codes: H04J 14/028 WDM bus architectures
• CPC Class Codes: H04J 14/0282 WDM tree architectures
• CPC Class Codes: H04J 14/0283 WDM ring architectures

Abstract

One embodiment of the present invention provides a system for mitigating Raman crosstalk between downstream data and video transmission in an Ethernet passive optical network (EPON), wherein the EPON includes an optical line terminal (OLT) and one or more optical network units (ONU'"'"'s). During operation, the system transmits a data stream from the OLT to the ONU'"'"'s on a first wavelength that is substantially at 1490 nm. The system also transmits a video signal stream from the OLT to the ONU'"'"'s on a second wavelength that is substantially at 1550 nm. The system modifies the bit sequence for the data stream to change the power spectral distribution (PSD) for the data stream, thereby reducing power spectral content in the frequency range where significant Raman crosstalk can occur between data and video signal streams.

Claims

1. A method for mitigating Raman crosstalk between downstream data and video transmission in an Ethernet passive optical network (EPON), wherein the EPON includes an optical line terminal (OLT) and one or more optical network units (ONU'"'"'s), the method comprising:

transmitting a data stream from the OLT to the ONU'"'"'s on a first wavelength;

transmitting a video signal stream from the OLT to the ONU'"'"'s on a second wavelength; and

changing the bit sequence for the data stream to change the power spectral distribution (PSD) for the data stream, thereby reducing power spectral content in the frequency range where significant Raman crosstalk can occur between data and video signal streams.

2. The method of claim 1, wherein the first wavelength is substantially 1490 nm, and the second wavelength is substantially 1550 nm.

3. The method of claim 1, wherein changing the bit sequence for the data stream involves changing a standard idle pattern.

4. The method of claim 3, wherein changing the standard idle pattern involves lengthening the IDLE ordered_sets based on the IEEE 802.3-2005 standard, thereby spreading the transmission power across a wide range of frequencies and reducing power at frequencies where significant Raman crosstalk can occur.

5. The method of claim 3, wherein changing the standard idle pattern involves replacing a repeating 20-bit idle pattern with a repeating 80-bit idle pattern.

6. The method of claim 5, wherein the 80-bit idle pattern includes the following ordered_sets based on the IEEE 802.3-2005 standard:

/I1+/I2−

/I1−

/I2+/.

7. The method of claim 3, wherein changing the standard idle pattern involves scrambling the idle pattern.

8. The method of claim 3, wherein changing the standard idle pattern involves replacing idle periods with null packets addressed to an unused or null Logical Link Identifier (LLID), thereby reducing occurrences of repeating idle patterns.

9. The method of claim 8, wherein the null packets include data with random or predetermined values, or values obtained with a predetermined method.

10. The method of claim 8, further comprising transmitting specially chosen data in the null packets, thereby reducing power spectral content in the frequency range where significant Raman crosstalk can occur.

11. The method of claim 10, wherein each null packet includes a repeating hexadecimal value of B5, which after 8B/10B encoding results in a constantly repeating pattern of “

. . . 1010101010 . . . ”

12. A method for mitigating Raman crosstalk between downstream data and video transmission in an EPON, wherein the EPON includes an OLT and one or more ONU'"'"'s, the method comprising:

transmitting a data stream from the OLT to the ONU'"'"'s on a first wavelength;

transmitting a video signal stream from the OLT to the ONU'"'"'s on a second wavelength;

reducing transmission power for the data stream; and

applying forward error correction (FEC) to the data stream, thereby mitigating the effect of Raman crosstalk on the video transmission without significantly reducing the signal-to-noise ratio (SNR) for the data transmission.

13. A method for mitigating Raman crosstalk between downstream data and video transmission in an EPON, wherein the EPON includes an OLT and one or more ONU'"'"'s, the method comprising:

transmitting a data stream from the OLT to the ONU'"'"'s on a first wavelength through a first fiber;

transmitting a video signal stream from the OLT to the ONU'"'"'s on a second wavelength through a second fiber; and

combining the two streams propagating through the two fibers immediately prior to splitting the combined streams for distribution to the ONU'"'"'S, thereby minimizing the distance over which the two streams co-propagate and mitigating the effect of Raman crosstalk.

14. A system for mitigating Raman crosstalk between downstream data and video transmission in an EPON, wherein the EPON includes an OLT and one or more ONU'"'"'s, the system comprising:

a first transmission mechanism configured to transmit a data stream from the OLT to the ONU'"'"'s on a first wavelength;

a second transmission mechanism configured to transmit a video signal stream from the OLT to the ONU'"'"'s on a second wavelength; and

a modification mechanism configured to change the bit sequence for the data stream to change the power spectral distribution (PSD) for the data stream, thereby reducing power spectral content in the frequency range where significant Raman crosstalk can occur between data and video signal streams.

15. The system of claim 14, wherein the first wavelength is substantially 1490 nm, and the second wavelength is substantially 1550 nm.

16. The system of claim 14, wherein while changing the bit sequence for the data stream, the modification mechanism is configured to change a standard idle pattern.

17. The system of claim 16, wherein while changing the standard idle pattern, the modification mechanism is configured to lengthen the IDLE ordered_sets based on the IEEE 802.3-2005 standard, thereby spreading the transmission power across a wide range of frequencies and reducing power at frequencies where significant Raman crosstalk can occur.

18. The system of claim 16, wherein while changing the standard idle pattern, the modification mechanism is configured to replace a repeating 20-bit idle pattern with a repeating 80-bit idle pattern.

19. The system of claim 18, wherein the 80-bit idle pattern includes the following ordered_sets based on the IEEE 802.3-2005 standard:

/I1+/I2−

/I1−

/I2+/.

20. The system of claim 16, wherein while changing the standard idle pattern, the modification mechanism is configured to scramble the idle pattern.

21. The system of claim 16, wherein while changing the standard idle pattern, the modification mechanism is configured to replace idle periods with null packets addressed to an unused or null Logical Link Identifier (LLID), thereby reducing occurrences of repeating idle patterns.

22. The system of claim 21, wherein the null packets include data with random or predetermined values, or values obtained with a predetermined method.

23. The system of claim 21, wherein the modification mechanism is configured to fill the null packets with specially chosen data, thereby reducing power spectral content in the frequency range where significant Raman crosstalk can occur.

24. The system of claim 23, wherein the modification is configured to fill the null packets with a repeating hexadecimal value of B5, which after 8B/10B encoding results in a constantly repeating pattern of “

. . . 1010101010 . . . ”

25. A system for mitigating Raman crosstalk between downstream data and video transmission in an EPON, wherein the EPON includes an OLT and one or more ONU'"'"'s, the system comprising:

a first transmission mechanism configured to transmit a data stream from the OLT to the ONU'"'"'s on a first wavelength;

a second transmission mechanism configured to transmit a video signal stream from the OLT to the ONU'"'"'s on a second wavelength;

a power control mechanism configured to reduce transmission power for the data stream; and

an FEC mechanism configured to apply FEC to the data stream, thereby mitigating the effect of Raman crosstalk on the video transmission without significantly reducing the SNR for the data transmission.

26. A system for mitigating Raman crosstalk between downstream data and video transmission in an EPON, wherein the EPON includes an OLT and one or more ONU'"'"'s, the system comprising:

a first transmission mechanism configured to transmit a data stream from the OLT to the ONU'"'"'s on a first wavelength through a first fiber;

a second transmission mechanism configured to transmit a video signal stream from the OLT to the ONU'"'"'s on a second wavelength through a second fiber; and

an optical combiner configured to combine the two streams propagating through the two fibers immediately prior to splitting the combined streams for distribution to the ONU'"'"'s, thereby minimizing the distance over which the two streams co-propagate and mitigating the effect of Raman crosstalk.