Compressing user data transmitted between a lower layer split central unit and a radio unit using bitmap representations

1. A method of transmitting data from a lower-layer split central unit (LLS-CU) to a radio unit (RU) in a network node of a wireless communication system for transmission by the RU over a wireless interface, the method comprising:

mapping, at the LLS-CU, user data and a plurality of reference symbols to be transmitted with the user data by the RU to resource elements to provide mapped data;

compressing the mapped data including the plurality of reference symbols using a bitmap representation of the mapped data to obtain compressed data;

transmitting the bitmap representation from the LLS-CU to the RU; and

transmitting the compressed data from the LLS-CU to the RU.

2. The method of claim 1 , further comprising:

transmitting an indication to the RU that the mapped data comprises the bitmap representation.

3. The method of claim 2 , wherein the indication comprises a field in a header of a message carrying the bitmap representation of the mapped data.

4. The method of claim 3 , wherein the field comprises a udCompHdr field or a udCompParam field of a user plane-downlink (UP-DL) message.

5. The method of claim 2 , wherein the indication comprises a field in a data-associated control information (DACI) message transmitted from the LLS-CU to the RU.

6. The method of claim 2 , wherein the indication and the bitmap representation are carried in a same message from the LLS-CU to the RU.

7. The method of claim 2 , wherein the indication, the bitmap representation, and the compressed data are carried in a same message from the LLS-CU to the RU.

8. The method of claim 1 , wherein the bitmap representation of the mapped data includes bit positions that correspond to ones of a plurality of resource elements of a physical resource block (PRB) to which the mapped data is mapped.

9. The method of claim 1 , wherein the bitmap representation is transmitted to the RU in a data-associated control information (DACI) message.

10. The method of claim 9 , wherein the bitmap representation is carried in a reMask field of the DACI message.

11. The method of claim 1 , wherein the bitmap representation is transmitted to the RU in a user plane-downlink (UP-DL) message in which the compressed data is transmitted.

12. The method of claim 11 , wherein the bitmap representation comprises a signal regarding the mapping of the resource elements.

13. The method of claim 12 , wherein the signal comprises a list of samples that are not sent to the RU and a list of samples that are sent to the RU.

14. The method of claim 2 , wherein the indication is transmitted in a user plane-downlink (UP-DL) message in which the compressed data is transmitted.

15. The method of claim 1 , further comprising:

receiving the bitmap representation at the RU;

receiving the compressed data at the RU;

uncompressing the compressed data using the bitmap representation at the RU to recover the mapped data; and

transmitting the mapped data over the wireless interface.

16. The method of claim 1 , wherein said mapping comprises mapping user data with the plurality of reference symbols to be transmitted by the RU to the resource elements to provide the mapped data.

17. The method of claim 16 , wherein the user data comprises pre-compressed user data.

18. The method of claim 1 , wherein the mapped data corresponds to a physical resource block that only contains reference symbols, and wherein the compressed data only comprises reference symbols.

19. The method of claim 1 , wherein transmitting the compressed data comprises transmitting only non-zero symbols corresponding to non-zero entries in the bitmap representation.

20. A network node, comprising:

a processor circuit;

a transceiver coupled to the processor circuit; and

a memory coupled to the processor circuit, wherein the memory comprises machine-readable computer program instructions that, when executed by the processor circuit, cause the processor circuit to perform operations comprising:

mapping, at a lower-layer split central unit (LLS-CU), user data and a plurality of reference symbols to be transmitted with the user data by a radio unit (RU) to resource elements to provide mapped data;

compressing the mapped data including the plurality of reference symbols using a bitmap representation of the mapped data to obtain compressed data;

transmitting the bitmap representation from the LLS-CU to the RU; and

transmitting the compressed data from the LLS-CU to the RU.