Soft packet combining for superposition coding
A method is proposed to enable a UE performing codeword level interference cancellation (CW-IC) to know whether an interfering transport block (TB) is a new transmission or retransmission. With this knowledge, the UE knows whether the soft channel bits stored in a soft buffer are to be discarded or combined with the soft channel bits newly obtained.
1. A method, comprising:
encoding a first transport block (TB 1 ) to be transmitted to a first user equipment (UE) over a time-frequency resource by a base station;
encoding a second transport block (TB 2 ) to be transmitted to a second UE, wherein the second TB 2 is superposed with the first TB 1 ;
determining a first new data indicator (NDI 1 ) and a second new data indicator (NDI 2 ) indicating whether TB 1 and TB 2 are new transport blocks or retransmission transport blocks respectively; and
transmitting encoded information bits of the transport blocks to the UEs, wherein the base station also transmits NDI 1 and NDI 2 to the first UE for interference cancellation.
2. The method of claim 1 , wherein the base station schedules the first UE and the second UE for non-orthogonal multiple access (NOMA) operation, and wherein the first UE is a high-geometry UE and the second UE is a low-geometry UE respectively.
3. The method of claim 1 , wherein TB 1 and TB 2 are superposed and transmitted over the same time-frequency resource but with different transmission power levels.
4. The method of claim 1 , wherein the base station schedules the first UE to decode and cancel the superposed second transport block TB 2 via codeword level interference cancellation (CW-IC).
5. The method of claim 1 , wherein TB 1 transmission is associated with a first hybrid automatic request (HARQ) process number of the first UE, and wherein TB 2 transmission is associated with a second HARQ process number of the second UE.
6. The method of claim 5 , wherein NDI 2 is toggled if TB 2 is a new TB with respect to a previous TB transmitted in a previous subframe associated with the second HARQ process number of the second UE.
7. A method, comprising:
storing soft channel bits of a first plurality of encoded information bits associated with a first transport block (TB 1 ) from a base station intended for a first user equipment (UE), wherein TB 1 is associated with a first HARQ process number of the first UE, and wherein the soft channel bits of the first plurality of encoded information bits are stored by the first UE in a first soft buffer of the first UE;
storing soft channel bits of a second plurality of encoded information bits associated with a second transport block (TB 2 ) from the base station intended for a second UE, wherein TB 2 is superposed with TB 1 and is associated with a second HARQ process number of the second UE, and wherein the soft channel bits of the second plurality of encoded information bits are stored by the first UE in a second soft buffer of the first UE;
receiving a first new data indicator (NDI 1 ) and a second new data indicator (NDI 2 ) indicating whether TB 1 and TB 2 are new transport blocks or retransmission transport blocks respectively; and
determining whether to perform soft packet combining for TB 1 and TB 2 based on NDI 1 and NDI 2 respectively.
8. The method of claim 7 , wherein the first UE and the second UE are scheduled for non-orthogonal multiple access (NOMA) operation, and wherein the first UE is a high-geometry UE and the second UE is a low-geometry UE respectively.
9. The method of claim 7 , wherein TB 1 and TB 2 are superposed and transmitted over the same time-frequency resource but with different transmission power levels.
10. The method of claim 7 , wherein the first UE is scheduled by the base station to decode and cancel the superposed second transport block TB 2 via codeword level interference cancellation (CW-IC).
11. The method of claim 7 , wherein NDI 2 is toggled if TB 2 is a new TB with respect to a previous TB transmitted in a previous subframe associated with the second HARQ process number of the second UE.
12. The method of claim 11 , wherein NDI 2 indicates that TB 2 is a new TB, and wherein the first UE clears the second soft buffer associated with the second HARQ process number of the second UE.
13. The method of claim 11 , wherein NDI 2 indicates that TB 2 is a retransmission TB, and the first UE performs soft packet combining via the second soft buffer associated with the second HARQ process number of the second UE.
14. A first user equipment (UE), comprising:
a soft buffer that stores soft channel bits of a first plurality of encoded information bits associated with a first transport block (TB 1 ) from a base station intended for the first UE, wherein TB 1 is associated with a first HARQ process number of the first UE;
a second soft buffer that stores soft channel bits of a second plurality of encoded information bits associated with a second transport block (TB 2 ) from the base station intended for a second UE, wherein TB 2 is superposed with TB 1 and is associated with a second HARQ process number of the second UE;
a receiver that receives a first new data indicator (NDI 1 ) and a second new data indicator (NDI 2 ) indicating whether TB 1 and TB 2 are new transport blocks or retransmission transport blocks respectively; and
a processor that determines whether to perform soft packet combining for TB 1 and TB 2 based on NDI 1 and NDI 2 respectively.
15. The UE of claim 14 , wherein the first UE and the second UE are scheduled for non-orthogonal multiple access (NOMA) operation, and wherein the first UE is a high-geometry UE and the second UE is a low-geometry UE respectively.
16. The UE of claim 14 , wherein TB 1 and TB 2 are superposed and transmitted over the same time-frequency resource but with different transmission power levels.
17. The UE of claim 14 , wherein the first UE is scheduled by the base station to decode and cancel the superposed second transport block TB 2 via codeword level interference cancellation (CW-IC).
18. The UE of claim 14 , wherein NDI 2 is toggled if TB 2 is a new TB with respect to a previous TB transmitted in a previous subframe associated with the second HARQ process number of the second UE.
19. The UE of claim 18 , wherein NDI 2 indicates that TB 2 is a new TB, and wherein the first UE clears the second soft buffer associated with the second HARQ process number of the second UE.
20. The UE of claim 18 , wherein NDI 2 indicates that TB 2 is a retransmission TB, and the first UE performs soft packet combining via the second soft buffer associated with the second HARQ process number of the second UE.