Assembling forward error correction frames

• US 20060107189A1
• Filed: 10/05/2005
• Published: 05/18/2006
• Est. Priority Date: 10/06/2004
• Status: Active Grant

• Current Assignee: WSOU Investments, LLC (WSOU Holdings, LLC)
• Original Assignee: Nokia Corporation
• Inventors: Hannuksela, Miska, Wenger, Stephan
• Granted Patent: US 7,779,336 B2
• Time in Patent Office: Days
• US Class Current: 714/776
• CPC Class Codes: H03M 13/15 Cyclic codes, i.e. cyclic shifts of codewords produce other codewords, e.g. codes defined by a generator polynomial, Bose-Chaudhuri-Hocquenghem [BCH] codes H03M13/17 takes precedence
• CPC Class Codes: H03M 13/1515 Reed-Solomon codes
• CPC Class Codes: H03M 13/47 Error detection, forward error correction or error protection, not provided for in groups H03M13/01 - H03M13/37
• CPC Class Codes: H03M 13/635 Error control coding in combination with rate matching
• CPC Class Codes: H03M 13/6356 by repetition or insertion of dummy data, i.e. rate reduction
• CPC Class Codes: H04L 1/0041 Arrangements at the transmitter end
• CPC Class Codes: H04L 1/0059 Convolutional codes
• CPC Class Codes: H04L 1/0083 Formatting with frames or packets; Protocol or part of protocol for error control

Abstract

The invention relates to a method for assembling FEC frames for a sequence of groups of coded media packets. In order to reduce a buffer delay at a decoding end (15), it is proposed that the FEC frame is aligned with the groups of media packets. To this end, a number of next subsequent groups are determined, which fit completely into a FEC frame. All coded media packets associated to this determined group or groups, if any, are selected for the FEC frame (step 202,402). Then, the selected coded media packets are encoded to obtain at least one FEC packet for the FEC frame (step 206,406). For fixed FEC frame structures, moreover the introduction of padding packets as additional media packets, if required, is proposed.

Claims

1. A method for assembling forward error correction frames for a sequence of groups of coded media packets, which method comprises for a case where no remaining coded media packets of a group of coded media packets partly included in a preceding forward error correction frame still have to be included in a forward error correction frame:

determining a number of next subsequent groups of coded media packets which fit completely into a forward error correction frame and selecting all coded media packets associated to said determined group or groups of coded media packets, if any, for said forward error correction frame (step 202,402); and

encoding said selected coded media packets to obtain at least one forward error correction packet for said forward error correction frame (step 206,406).

2. The method according to claim 1, further comprising for a case where remaining coded media packets of a group of coded media packets partly included in a preceding forward error correction frame still have to be included in a forward error correction frame, wherein all of said remaining coded media packets fits into a single forward error correction frame:

determining a number of next subsequent groups of coded media packets which fit in addition to said remaining coded media packets completely into a forward error correction frame and selecting said remaining coded media packets and said coded media packets associated to said determined group or groups of coded media packets, if any, for said forward error correction frame (step 202,402); and

encoding said selected coded media packets to obtain at least one forward error correction packet for said forward error correction frame (step 206,406).

3. The method according to claim 1, further comprising for a case where a next group of coded media data does not fit completely into a forward error correction frame or that all remaining coded media packets of a group of coded media data partly included in a preceding forward error correction do not fit into a single forward error correction frame (step 203, 403):

determining a maximum number of next subsequent coded media packets which fit completely into a forward error correction frame and selecting said determined coded media packets for said forward error correction frame (step 208,408); and

encoding said selected coded media packets to obtain at least one forward error correction packet for said forward error correction frame (step 206,406).

4. The method according to claim 1, wherein for said encoding, all selected coded media packets are supplemented to be of a same size as a largest one of said selected coded media packets by adding predetermined data to media data included in said selected coded media packets (steps 204,404), and wherein each of said obtained at least one forward error correction packet has said size of said largest one of said selected coded media packets.

5. The method according to claim 4, wherein for a transmission of said forward error correction frame, all selected coded media packets are transmitted with an original size of included media data, each coded media packets including an indication of a size of included media data (step 207,407).

6. The method according to claim 1, wherein the number of packets belonging to a forward error correction frame is adjustable, and wherein said number is adjusted based on the number of said selected coded media packets (step 205).

7. The method according to claim 6, wherein a number of forward error correction packets to be obtained in said encoding is selected such that a resulting size of said forward error correction frame lies above a predetermined minimum size for a forward error correction frame and below a predetermined maximum size for a forward error correction frame (step 205).

8. The method according to claim 1, wherein the number of coded media packets within a forward error correction frame is fixed to a first predetermined number and wherein the number of forward error correction packets within a forward error correction frame is fixed to a second predetermined number, and wherein in case the number of said selected coded media packets is lower than said first predetermined number, packets comprising padding values as media data in a payload are added to obtain said first predetermined number of coded media packets for said forward error correction frame for said encoding (step 405).

9. The method according to claim 8, wherein for a transmission of said forward error correction frame, said packets comprising padding values are replaced by virtual padding packets having a payload length of zero bytes and indicating a size of said media data including said padding values in a payload header.

10. A forward error correction frame generator (14) for assembling forward error correction frames for a sequence of groups of coded media packets,

wherein for a case where no remaining coded media packets of a group of coded media packets partly included in a preceding forward error correction frame still have to be included in a forward error correction frame, said forward error correction frame generator (14) is adapted to determine a number of next subsequent groups of coded media packets which fit completely into a forward error correction frame and to select all coded media packets associated to said determined group or groups of coded media packets, if any, for said forward error correction frame;

and

wherein said forward error correction frame generator (14) is adapted to encode selected coded media packets to obtain at least one forward error correction packet for said forward error correction frame.

11. An electronic device (10) comprising a forward error correction frame generator (14) according to claim 10.

12. A communication system comprising at least one forward error correction frame generator (14) according to claim 10 and at least one forward error correction decoder (16).

13. A software code for assembling forward error correction frames for a sequence of groups of coded media packets, said software code realizing, for a case where no remaining coded media packets of a group of coded media packets partly included in a preceding forward error correction frame still have to be included in a forward error correction frame, the following step when running in a processing module:

determining a number of next subsequent groups of coded media packets which fit completely into a forward error correction frame and selecting all coded media packets associated to said determined group or groups of coded media packets, if any, for said forward error correction frame (step 202,402); and

encoding said selected coded media packets to obtain at least one forward error correction packet for said forward error correction frame (step 206,406).

14. A software program product storing a software code according to claim 13.

15. A method for assembling forward error correction frames with coded media packets and at least one forward error correction packet, wherein the number of coded media packets within a forward error correction frame is fixed to a first predetermined number and wherein the number of forward error correction packets within a forward error correction frame is fixed to a second predetermined number, said method comprising

in case the number of said coded media packets is lower than said first predetermined number, adding packets comprising padding values as media data in a payload to obtain said first predetermined number of coded media packets for said forward error correction frame (step 405);

and

encoding said coded media packets to obtain said at least one forward error correction packet (step 206,406).

16. The method according to claim 15, wherein for a transmission of said forward error correction frame, said packets comprising padding values are replaced by virtual padding packets having a payload length of zero bytes and indicating a size of said media data including said padding values in a payload header.

17. A forward error correction frame generator (14) for assembling forward error correction frames with coded media packets and at least one forward error correction packet, wherein the number of coded media packets within a forward error correction frame is fixed to a first predetermined number and wherein the number of forward error correction packets within a forward error correction frame is fixed to a second predetermined number,

wherein said forward error correction frame generator (14) is adapted to add packets comprising padding values as media data in a payload, in case the number of said coded media packets is lower than said first predetermined number, to obtain said first predetermined number of coded media packets for said forward error correction frame;

and

wherein said forward error correction frame generator (14) is adapted to encode said coded media packets to obtain at least one forward error correction packet for said forward error correction frame.

18. An electronic device (10) comprising a forward error correction frame generator (14) according to claim 17.

19. A communication system comprising at least one forward error correction frame generator (14) according to claim 17 and at least one forward error correction decoder (16).

20. A software code for assembling forward error correction frames with coded media packets and at least one forward error correction packet, wherein the number of coded media packets within a forward error correction frame is fixed to a first predetermined number and wherein the number of forward error correction packets within a forward error correction frame is fixed to a second predetermined number, said software code realizing the following step when running in a processing module:

in case the number of said coded media packets is lower than said first predetermined number, adding packets comprising padding values as media data in a payload to obtain said first predetermined number of coded media packets for said forward error correction frame (step 405); and

encoding said coded media packets to obtain said at least one forward error correction packet (step 206,406).

21. A software program product storing a software code according to claim 20.