Method for packet-level FEC encoding a stream of source packets using shifted interleaving

1. A method for transmitting interleaved shares of packet-level forward-error-correction encoded packets, each share including source packets and wildcard packets, wherein a given time shift occurs between consecutive shares, the method comprising the steps of:

determining a current state;

associating a packet with a share based on the current state;

determining a position of the packet within the share based on the given time shift; and,

if the position of the packet corresponds to a source packet position, computing a contribution from the packet to wildcard packets of the share and transmitting the packet as a source packet, or, if the position of the packet corresponds to a wildcard packet position, transmitting the packet as a wildcard packet,

wherein positions of two consecutive packets within two shares are not the same, and

wherein the above steps are performed by a processor.

2. A method according to claim 1 , wherein the given time shift is a difference in time between points of consecutive shares.

3. A method according to claim 1 , wherein multiple shares of packets are transmitted as a lot, and wherein the method further comprises the steps of:

determining the given time shift, S, based on:

a number of source packets per share, K,

a number of wildcard packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers; and

shifting a share by the given time shift, S, relative to a previous share, wherein S=(K+E)/L.

4. A method according to claim 3 , wherein:

the multiple shares of packets form an interleaved arrangement, and

the step of determining a position of the packet within the share includes determining P=C−R*5 modulo (K+E), wherein:

P represents the position of the packet within the share,

C represents a column number in the arrangement,

R represents a share number in the lot.

5. A method according to claim 4 , wherein:

0≦P≦(K+E−1);

0≦R≦(L−1); and

C=is any one of 0, 1, 2, 3, . . . .

6. A method of shifting interleaved shares of packet-level forward-error-correction encoded packets to be transmitted, in which multiple shares of packets are transmitted as a lot, the method comprising the steps of:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers; and

shifting each interleaved share of packet-level forward-error correction encoded packets by the time shift, S, relative to a corresponding previous share, wherein S=(K+E)/L, wherein positions of two consecutive packets within two shares are not the same, and wherein the above steps are performed by a processor.

7. A method according to claim 6 , wherein the step of shifting includes shifting a start point of the interleaved share by the time shift, S, relative to a start point of the corresponding previous share.

8. A method according to claim 6 , further comprising the step of:

determining a position, P, of a packet in the interleaved share based on an interleaved arrangement of packets according to:

P=C−R*S modulo( K+E ),

wherein:

C represents a column number in the arrangement,

R represents a share number in the lot.

9. A method according to claim 8 , wherein:

0≦P≦(K+E−1);

0≦R≦(L−1); and

C=is any one of 0, 1, 2, 3, . . . .

10. A method according to claim 8 , wherein the time shift, S, represents a number of columns the interleaved share is shifted relative to the corresponding previous share.

11. A method according to claim 8 , further comprising the step of:

if P<K, determining an error-correction contribution to the interleaved share from a source packet at the position, P.

12. A method for transmitting interleaved shares of packet-level forward-error-correction encoded packets to be transmitted, in which multiple shares of packets are transmitted as a lot, the method comprising the steps of:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers, and

wherein S=(K+E)/L;

shifting a share by the time shift, S, relative to a previous share;

arranging the lot packets to be transmitted according to columns and rows, with C representing a column number and R representing a row number, wherein 0≦R≦(L−1) and R corresponds to a share in the lot;

transmitting a packet at a first position identified by R and C;

determining a next position such that:

if R+1=L, set R=0 and increase C by 1, or,

if R+1<L, then set R=R+1; and

transmitting a packet at the next position,

wherein positions of two consecutive packets within two shares are not the same.

13. A method according to claim 12 , further comprising the step of:

determining a position, P, of a packet in a share of the lot based on an interleaved arrangement of packets according to P=C−R*S modulo (K+E).

14. A method according to claim 13 , wherein:

C=is any one of 0, 1, 2, 3, . . . , and

0≦P≦(K+E−1).

15. A method according to claim 13 , wherein the time shift, S, represents a number of columns a share of the lot is shifted relative to a previous share of the lot.

16. A method according to claim 13 , further comprising the step of:

if P<K, determining an error-correction contribution to the share from a source packet at the position, P.

17. A computer programmed to perform transmitting of interleaved shares of packet-level forward-error-correction encoded packets, each share including source packets and wildcard packets, wherein a given time shift occurs between consecutive shares, by using a processor to perform the steps of:

determining a current state;

associating a packet with a share based on the current state;

determining a position of the packet within the share based on the given time shift; and,

if the position of the packet corresponds to a source packet position, computing a contribution from the packet to wildcard packets of the share and transmitting the packet as a source packet, or, if the position of the packet corresponds to a wildcard packet position, transmitting the packet as a wildcard packet,

wherein positions of two consecutive packets within two shares are not the same.

18. A computer programmed to perform shifting of interleaved shares of packet-level forward-error-correction encoded packets to be transmitted, in which multiple shares of packets are transmitted as a lot, by using a processor to perform the steps of:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers; and

shifting each interleaved share of packet-level forward-error correction encoded packets by the time shift, S, relative to a corresponding previous share, wherein S=(K+E)/L, wherein positions of two consecutive packets within two shares are not the same.

19. A computer programmed to perform transmitting of interleaved shares of packet-level forward-error-correction encoded packets to be transmitted, in which multiple shares of packets are transmitted as a lot, by using a processor to perform the steps of:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers, and

wherein S=(K+E)/L; shifting a share by the time shift, S, relative to a previous share;

arranging the lot packets to be transmitted according to columns and rows, with C representing a column number and R representing a row number, wherein 0≦R≦(L−1) and R corresponds to a share in the lot;

transmitting a packet at a first position identified by R and C;

determining a next position such that:

if R+1=L, set R=0 and increase C by 1, or,

if R+1<L, then set R=R+1; and transmitting a packet at the next position, wherein positions of two consecutive packets within two shares are not the same.

20. A communications system for transmitting interleaved shares of packet-level forward-error-correction encoded packets, each share including source packets and wildcard packets, wherein a given time shift occurs between consecutive shares, comprising:

a transmitter configured to perform:

determining a current state;

associating a packet with a share based on the current state;

determining a position of the packet within the share based on the given time shift; and,

if the position of the packet corresponds to a source packet position,

computing a contribution from the packet to wildcard packets of the share and transmitting the packet as a source packet, or, if the position of the packet corresponds to a wildcard packet position, transmitting the packet as a wildcard packet,

wherein positions of two consecutive packets within two shares are not the same.

21. A communications system for transmitting shifted interleaved shares of packet-level forward-error-correction encoded packets, in which multiple shares of packets are transmitted as a lot, comprising:

a transmitter configured to perform:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers; and

shifting each interleaved share of packet-level forward-error correction encoded packets by the time shift, S, relative to a corresponding previous share, wherein S=(K+E)/L,

wherein positions of two consecutive packets within two shares are not the same.

22. A communications system for transmitting interleaved shares of packet-level forward-error-correction encoded packets to be transmitted, in which multiple shares of packets are transmitted as a lot, comprising:

a transmitter configured to perform:

determining a time shift, S, based on:

a number of source packets per share, K,

a number of error-correcting packets per share, E, and

a number of shares per lot, L,

wherein K, E and L are integers, and

wherein S=(K+E)/L;

shifting a share by the time shift, S, relative to a previous share;

arranging the lot packets to be transmitted according to columns and rows, with C representing a column number and R representing a row number, wherein 0≦R≦(L−1) and R corresponds to a share in the lot;

transmitting a packet at a first position identified by R and C;

determining a next position such that:

if R+1=L, set R=0 and increase C by 1, or,

if R+1<L, then set R=R+1; and

transmitting a packet at the next position,

wherein positions of two consecutive packets within two shares are not the same.