Link adaptation in grant-free multiple access systems

1. A method, comprising:

determining an amount of resource overloading for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determining a modulation and coding scheme (MCS) limit indicating a maximum MCS level for the CTU access region based on the amount of resource overloading; and

sending the MCS limit to a plurality of user equipments (UEs) associated with the CTU access region; and

receiving an uplink transmission from a first UE of the plurality of UEs including an MCS index based on the MCS limit.

2. The method of claim 1 , further comprising:

determining the MCS index from control information included in the uplink transmission; and

attempting to blindly decode data in the uplink transmission using an MCS level corresponding to the MCS index from the control information.

3. The method of claim 2 , wherein:

the control information is within a reserved time-frequency region of the CTU access region; and

said attempting to blindly decode includes blindly decoding the control information using a pre-defined MCS level.

4. The method of claim 1 , further comprising:

determining link adaptation information for a first UE based on monitoring uplink transmissions from the first UE based on the MCS limit, the link adaption information includes an adjusted MCS limit for the first UE; and

transmitting in a control channel the link adaption information to the first UE.

5. The method of claim 4 , wherein:

the link adaption information for the first UE includes a power setting for the first UE.

6. The method of claim 1 , further comprising:

monitoring uplink transmissions from the plurality of UEs in the CTU access region to develop one or more long term statistics associated with uplink performance in the CTU access region;

adjusting the MCS limit based on the one or more long term statistics; and

sending an adjusted MCS limit to the plurality of UEs.

7. The method of claim 1 , further comprising:

adaptively allocating contention transmission units (CTUs) to the CTU access region based on loading in the CTU access region;

wherein determining an amount of resource overloading includes determining an overloading factor based on a number of CTUs that are allocated to the first CTU access region and a number of active UEs.

8. The method of claim 7 , further comprising:

determining the number of CTUs to allocate to the CTU access region based on at least one of a number of active UEs or an amount of uplink traffic.

9. The method of claim 1 , wherein determining an MCS limit comprises:

selecting a first MCS limit in response to a first overloading factor and a second MCS limit in response to a second overloading factor that is higher than the first overloading factor;

wherein the first MCS limit corresponds to a first MCS level that is higher than a second MCS level corresponding to the second MCS limit.

10. A base station, comprising:

a processor; and

a computer readable storage medium having instructions stored thereon for execution by the processor, wherein the instructions configure the processor to:

determine an amount of resource overloading for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determine a modulation and coding scheme (MCS) limit indicating a maximum MCS level for the CTU access region based on the amount of resource overloading;

send the MCS limit to a plurality of user equipments (UEs) associated with the CTU access region; and

receive an uplink transmission from a first UE of the plurality of UEs including an MCS index based on the MCS limit.

11. The base station of claim 10 , wherein the instructions further configure the processor to:

determine the MCS index from control information included in the uplink transmission; and

attempt to blindly decode data in the uplink transmission using an MCS level corresponding to the MCS index from the control information.

12. The base station of claim 10 , wherein the instructions further configure the processor to:

measure a signal to interference plus noise ratio (SINR) for one or more of the plurality of UEs;

determine link adaptation information for a first UE of the plurality of UEs based on the SINR associated with the first UE, the link adaptation information including an adjusted MCS limit for the first UE; and

transmit in a control channel the link adaption information to the first UE.

13. The base station of claim 10 , wherein the instructions further configure the processor to:

monitor uplink transmissions from the plurality of UEs in the CTU access region to develop one or more long term statistics associated with uplink performance in the CTU access region;

adjust the MCS limit based on the one or more long term statistics; and

send an adjusted MCS limit to the plurality of UEs.

14. The base station of claim 10 , wherein:

the multiple access system includes sparse code multiple access (SCMA) system;

the instructions further configure the processor to map a plurality of MCS indices to a plurality of SCMA code book sets and code rates; and

the maximum MCS level corresponds to one of the SCMA code book sets and code rates.

15. The base station of claim 10 , wherein:

the multiple access system includes low density signature orthogonal frequency divisional multiplexing (LDS-OFDM) system;

the instructions further configure the processor to map a plurality of MCS indices to a plurality of modulation schemes and code rates in LDS-OFDM system; and

the maximum MCS level corresponds to one of the plurality of modulation schemes and code rates.

16. The base station of claim 11 , wherein:

the control information is within a reserved time-frequency region of the CTU access region; and

the instructions further configure the processor to attempt to blindly decode the control information included in the uplink transmission using a pre-defined MCS level.

17. A method, comprising:

determining an amount of resource overloading for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determining a modulation and coding scheme (MCS) limit indicating a maximum MCS level for the CTU access region based on the amount of resource overloading;

sending the MCS limit to a plurality of user equipments (UEs) associated with the CTU access region; and

adaptively allocating contention transmission units (CTUs) to the CTU access region based on loading in the CTU access region;

wherein determining an amount of resource overloading includes determining an overloading factor based on a number of CTUs that are allocated to the first CTU access region and a number of active UEs.

18. The method of claim 17 , further comprising:

determining the number of CTUs to allocate to the CTU access region based on at least one of a number of active UEs or an amount of uplink traffic.

19. The method of claim 17 , further comprising:

receiving an uplink transmission from a first UE of the plurality of UEs using a CTU;

determining an MCS index from control information included in the uplink transmission; and

attempting to blindly decode data in the uplink transmission using an MCS level corresponding to the MCS index from the control information.

20. The method of claim 19 , wherein:

the control information is within a reserved time-frequency region of the CTU access region; and

said attempting to blindly decode includes blindly decoding the control information using a pre-defined MCS level.

21. The method of claim 17 , further comprising:

determining link adaptation information for a first UE based on monitoring uplink transmissions from the first UE based on the MCS limit, the link adaption information includes an adjusted MCS limit for the first UE; and

transmitting in a control channel the link adaption information to the first UE.

22. The method of claim 17 , further comprising:

monitoring uplink transmissions from the plurality of UEs in the CTU access region to develop one or more long term statistics associated with uplink performance in the CTU access region;

adjusting the MCS limit based on the one or more long term statistics; and

sending an adjusted MCS limit to the plurality of UEs.

23. A base station, comprising:

a processor; and

a computer readable storage medium having instructions stored thereon for execution by the processor, wherein the instructions configure the processor to:

determine an amount of resource overloading for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determine a modulation and coding scheme (MCS) limit indicating a maximum MCS level for the CTU access region based on the amount of resource overloading; and

send the MCS limit to a plurality of user equipments (UEs) associated with the CTU access region;

wherein the instructions configure to processor to determine an MCS limit by selecting a first MCS limit in response to a first overloading factor and a second MCS limit in response to a second overloading factor that is higher than the first overloading factor;

wherein the first MCS limit corresponds to a first MCS level that is higher than a second MCS level corresponding to the second MCS limit.

24. The base station of claim 23 , wherein the instructions further configure the processor to:

receive an uplink transmission from a first UE of the plurality of UEs using a CTU;

attempt to blindly decode control information included in the uplink transmission using a pre-defined MCS level;

determine an MCS index from the control information included in the uplink transmission; and

attempt to blindly decode data in the uplink transmission using an MCS level corresponding to the MCS index from the control information;

wherein the control information is within a reserved time-frequency region of the CTU access region.

25. The base station of claim 23 , wherein the instructions further configure the processor to:

measure a signal to interference plus noise ratio (SINR) for one or more of the plurality of UEs;

determine link adaptation information for a first UE of the plurality of UEs based on the SINR associated with the first UE, the link adaptation information including an adjusted MCS limit for the first UE; and

transmit in a control channel the link adaption information to the first UE.

26. The base station of claim 23 , wherein the instructions further configure the processor to:

monitor uplink transmissions from the plurality of UEs in the CTU access region to develop one or more long term statistics associated with uplink performance in the CTU access region;

adjust the MCS limit based on the one or more long term statistics; and

send an adjusted MCS limit to the plurality of UEs.

27. The base station of claim 23 , wherein:

the multiple access system includes sparse code multiple access (SCMA) system;

the instructions further configure the processor to map a plurality of MCS indices to a plurality of SCMA code book sets and code rates; and

the maximum MCS level corresponds to one of the SCMA code book sets and code rates.

28. The base station of claim 23 , wherein:

the multiple access system includes low density signature orthogonal frequency divisional multiplexing (LDS-OFDM) system;

the instructions further configure the processor to map a plurality of MCS indices to a plurality of modulation schemes and code rates in LDS-OFDM system; and

the maximum MCS level corresponds to one of the plurality of modulation schemes and code rates.