# US 2013/0156420 A1 · Adaptive forward error correction in passive optical networks

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- Number: US 2013/0156420 A1
- Document ID: US20130156420A1
- Status: Published application
- Kind: A1
- Application number: 13/331,255
- Filed: 2011-12-20
- Published: 2013-06-20
- Earliest claimed: 2011-12-20
- Assignees: Broadlight Ltd.
- Inventors: Assaf Amitai; David Avishai; Eli Elmoalem
- Web page: https://patentgrep.com/patent/US20130156420A1

## CPC

- H04B 10/07953: {Monitoring or measuring OSNR, BER or Q}
- H04B 10/272: Star-type networks {or tree-type networks}
- H04B 10/5055: {using a pre-coder}
- H04L 1/0009: {by adapting the channel coding (H04L1/1812 takes precedence)}
- H04L 1/0025: {Transmission of mode-switching indication}
- H04L 1/20: using signal quality detector
- H04L 2001/0093: {Point-to-multipoint}
- H04B: TRANSMISSION
- H04L: TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION (arrangements common to telegraphic and telephonic communication H04M)

## Abstract

A method for an adaptive forward error correction (FEC) in a passive optical network. The method comprises selecting an initial downstream FEC code to be applied on downstream data transmitted from an optical line terminal (OLT) to a plurality of optical network units (ONUs) of the PON; communicating the selected downstream FEC code to the plurality of ONUs; receiving at least one downstream bit error ratio (BER) value from at least one ONU of the plurality of ONUs, wherein the downstream BER value is measured respective to downstream data received at the at least one ONU; changing the selected downstream FEC code to a new downstream FEC code based on a plurality of downstream BER values measured by the at least one ONU; and communicating the new downstream FEC code to the plurality of ONUs.

## Claims

### Claim 1

A method for an adaptive forward error correction (FEC) in a passive optical network, comprising:
selecting an initial downstream FEC code to be applied on downstream data transmitted from an optical line terminal (OLT) to a plurality of optical network units (ONUs) of the PON;
communicating the selected downstream FEC code to the plurality of ONUs;
receiving at least one downstream bit error ratio (BER) value from at least one ONU of the plurality of ONUs, wherein the downstream BER value is measured respective to downstream data received at the at least one ONU;
changing the selected downstream FEC code to a new downstream FEC code based on a plurality of downstream BER values measured by the at least one ONU; and
communicating the new downstream FEC code to the plurality of ONUs.

### Claim 2 (depends on 1)

The method of claim 1, wherein the new downstream FEC code is set to a different FEC code when one or more the downstream BER values measured for the downstream FEC code have been changed.

### Claim 3 (depends on 2)

The method of claim 2, wherein a stronger FEC code is set for the new downstream FEC code when the downstream BER value is higher than at least one of: a maximum allowable downstream BER and a previously measured downstream BER value; and wherein a weaker FEC code is set for the new downstream FEC code when the downstream BER value is lower than a previously measured downstream BER value, wherein the stronger FEC code corrects more errors than the weaker FEC code.

### Claim 4 (depends on 1)

The method of claim 1, wherein the initial downstream FEC code is selected based on at least a topology of the PON.

### Claim 5 (depends on 1)

The method of claim 1, wherein downstream FEC codes are communicated using any one of in-band handshake messages and out of band handshake messages periodically sent to the plurality of ONUs.

### Claim 6 (depends on 1)

The method of claim 1, further comprising:
for each of the plurality of ONUs in the PON,
determining an upstream FEC mode, the upstream FEC mode is any one of: FEC-enabled and FEC-disabled;
selecting an upstream FEC code for an ONU determined to be in the upstream FEC-enabled mode;
communicating to the ONU the selected upstream FEC code and the upstream FEC mode;
measuring an upstream BER of upstream burst data transmitted by the ONU;
changing the selected upstream FEC code to a new upstream FEC code based on the upstream BER value; and
communicating the new upstream FEC code to the ONU.

### Claim 7 (depends on 6)

The method of claim 6, wherein the new upstream FEC code is set to a different FEC code when the BER value measured for the upstream FEC code is changed.

### Claim 8 (depends on 7)

The method of claim 7, wherein a stronger FEC code is set for the new upstream FEC code when the upstream BER value is higher than at least one of: a maximum allowable upstream BER and a previously measured upstream BER value; and wherein a weaker FEC code is set for the new upstream FEC code when the BER value is lower than a previously measured upstream BER value, wherein the stronger FEC code corrects more errors than the weaker FEC code.

### Claim 9 (depends on 6)

The method of claim 6, wherein the upstream FEC codes are communicated to the ONU by the OLT using any one of: a vendor specific downstream ONU management and control interface (OMCI) message, out of band handshake messages and a downstream unicast physical layer operations and maintenance (PLOAM) message.

### Claim 10 (depends on 6)

The method of claim 6, wherein the PON is at least a ten-Gigabit PON (XG-PON).

### Claim 11 (depends on 10)

The method of claim 10, wherein any one of the downstream FEC code and the upstream FEC code includes a FEC code not defined in a communication standard of the XG-PON.

### Claim 12 (depends on 11)

The method of claim 11, wherein the downstream FEC code also includes a RS(248,216) code.

### Claim 13 (depends on 11)

The method of claim 11, wherein the upstream FEC code also includes a RS(248,232) code.

### Claim 14 (depends on 10)

The method of claim 10, wherein the downstream data is encapsulated in a XG-PON1 downstream physical (PHY) frame having a fixed length of 125 microsecond.

### Claim 15

An apparatus implemented in an optical line terminal (OLT) configured to perform an adaptive forward error correction (FEC) in a passive optical network, comprising:
a processor for at least setting a downstream FEC code based on a plurality of measured downstream BER values and setting for an optical network unit (ONU) in the PON an upstream FEC mode and an upstream FEC code based on a measured upstream BER value;
a FEC encoder/decoder for FEC encoding data using the downstream FEC code and for FEC decoding upstream burst data received from an ONU based on its respective upstream FEC code;
a BER measurement unit for measuring an upstream BER value for the ONU; and
a memory for storing a list of FEC codes that can be set for the upstream FEC code and the downstream FEC code, wherein the memory also stores an upstream FEC code and an upstream FEC mode set for the ONU.

### Claim 16 (depends on 15)

The apparatus of claim 15, further comprises:
a physical layer adapter for assembling downstream physical frames sent to the ONU and de-assembling upstream physical frames received from the ONU, wherein the downstream physical frames and the upstream physical frames are compliant with a communication standard of the PON.

### Claim 17 (depends on 16)

The apparatus of claim 16, wherein the processor is further configured to:
select an initial downstream FEC code to be applied on downstream data;
communicate the selected downstream FEC code to the ONU;
receive at least one downstream BER value from at least one ONU, wherein the downstream BER value is measured with respective to downstream data received at the at least one ONU; and
change the selected downstream FEC code to a new downstream FEC code based on a plurality of downstream BER values, the new downstream FEC code is set to a different FEC code when one or more of the plurality the downstream BER values measured for the downstream FEC code have been changed; and
communicating the new downstream FEC code to the ONU.

### Claim 18 (depends on 17)

The apparatus of claim 17, wherein a stronger FEC code is set for the downstream FEC code when the downstream BER value is at least one of: above a maximum allowable downstream BER and is higher than a previously measured downstream BER value; and wherein a weaker FEC code is set for the downstream FEC code when the BER value is lower than a previously measured downstream BER value, wherein the stronger FEC code corrects more errors than the weaker FEC code.

### Claim 19 (depends on 18)

The apparatus of claim 18, wherein the processor is further configured to:
determine the upstream FEC mode for the ONU, the upstream FEC mode is any one of: FEC-enabled and FEC-disabled;
select the upstream FEC code for to the ONU determined to be in the upstream FEC-enabled mode;
communicate to the ONU the upstream FEC code and the upstream FEC mode;
receive an upstream BER value of upstream burst data transmitted by the ONU as measured by the BER measurement unit;
change the selected upstream FEC code to a new upstream FEC code based on the upstream BER value, the new upstream FEC code is set to a different FEC code when the upstream BER value measured for the upstream FEC code is changed; and
communicate the new upstream FEC code to the ONU.

### Claim 20 (depends on 19)

The apparatus of claim 19, wherein a stronger FEC code is set for the upstream FEC code when the upstream BER value is at least one of above a maximum allowable upstream BER and is higher than a previously measured upstream BER value; and wherein a weaker FEC code is set for the upstream FEC code when the BER value is lower than a previously measured upstream BER value, wherein the stronger FEC code corrects more errors than the weaker FEC code.

### Claim 21 (depends on 19)

The apparatus of claim 19, wherein the PON is at least a ten-Gigabit PON (XG-PON), wherein any one of the downstream FEC code and the upstream FEC code includes a FEC code not defined in a communication standard of the XG-PON.

### Claim 22

A non-transitory computer readable medium having stored thereon instructions for causing a processor to perform an adaptive forward error correction (FEC) in a passive optical network (PON), comprising:
selecting an initial downstream FEC code to be applied on downstream data transmitted from an optical line terminal (OLT) to a plurality of optical network units (ONUs) of the PON;
communicating the selected downstream FEC code to the plurality of ONUs;
receiving at least one downstream BER value from at least one ONU of the plurality of ONUs, wherein the downstream BER value is measured respective to downstream data received at the at least one ONU; and
changing the selected downstream FEC code to a new downstream FEC code based on a plurality of downstream BER values measured by the at least one ONU; and
communicating the new downstream FEC code to the plurality of ONUs.