Link Adaptation In Grant-Free Multiple Access Systems

• US 20170034845A1
• Filed: 07/27/2015
• Published: 02/02/2017
• Est. Priority Date: 07/27/2015
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Liu, Bin, Stirling-Gallacher, Richard, Wang, Jian
• Granted Patent: US 9,743,423 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/0009 by adapting the channel coding H04L1/1812 takes precedence
• CPC Class Codes: H04L 1/0023 characterised by the signalling
• CPC Class Codes: H04W 24/08 Testing, supervising or monitoring using real traffic
• CPC Class Codes: H04W 28/0289 Congestion control load shedding arrangements in network planning H04W16/08; performing reselection for handling the traffic H04W36/22; wireless traffic scheduling H04W72/12
• CPC Class Codes: H04W 72/1268 of uplink data flows
• CPC Class Codes: H04W 72/23 in the downlink direction of a wireless link, i.e. towards a terminal
• CPC Class Codes: H04W 74/04 Scheduled access hybrid access H04W74/02
• CPC Class Codes: H04W 74/0833 Random access procedures, e.g. with 4-step access

Abstract

A BS determines 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. The BS determines a modulation and coding scheme (MCS) limit indicating a maximum MCS level for the CTU access region. The BS sends the MCS limit to a plurality of user equipments (UEs) associated with the first CTU access region. A UE receives from the base station the MCS limit and determines a first MCS index within the MCS limit for a first uplink transmission. The UE sends the first uplink transmission to the base station using a CTU in the CTU access region. The first uplink transmission includes user data and the first MCS index determined at the first UE.

Claims

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.

2. The method of claim 1, 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.

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; 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 at least one of an MCS index or 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; and

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

11. The base station of claim 10, 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.

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; and

transmit in a control channel the link adaption information to the plurality of UEs.

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.

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.

16. A method, comprising:

receiving from a base station a modulation and coding scheme (MCS) limit for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determining at a user equipment (UE) a first MCS index within the MCS limit; and

sending a first uplink transmission to the base station using a CTU in the CTU access region, the first uplink transmission including user data and the first MCS index determined at the UE.

17. The method of claim 16, wherein sending the uplink transmission includes:

sending the user data using a first MCS level corresponding to the first MCS index; and

sending the first MCS index using a pre-defined MCS level within a reserved time-frequency region of the CTU access region.

18. The method of claim 16, further comprising:

determining at the UE at least one of channel state information or estimated path loss;

wherein determining the first MCS index includes selecting the first MCS index based on at least one of the channel state information or the estimated path loss.

19. The method of claim 18, further comprising:

determining at the first UE an uplink traffic characteristic;

wherein determining the first MCS index includes selecting the first MCS index based on the uplink traffic characteristic and the at least one of the channel state information or the estimated path loss.

20. The method of claim 19, further comprising:

determining a maximum MCS level based on the uplink traffic characteristic and the at least one of the channel state information or the estimated path loss;

wherein determining the first MCS index includes selecting the first MCS index by applying a back-off value to the maximum MCS level to determine a reduced MCS level corresponding to the first MCS index.

21. The method of claim 16, further comprising:

determining an uplink transmission success rate at the UE;

selecting a second MCS level within the MCS limit based on the uplink transmission success rate; and

sending a second uplink transmission at the second MCS level, the second uplink transmission including a second MCS index corresponding to the second MCS level.

22. The method of claim 16, wherein the first uplink transmission is sent using a first transmission power, the method further comprising:

determining an uplink transmission success rate at the UE;

selecting a second transmission power within a maximum power based on the uplink transmission success rate; and

sending a second uplink transmission at the second transmission power.

23. A user equipment (UE), 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;

receive from a base station a modulation and coding scheme (MCS) limit for a contention transmission unit (CTU) access region associated with a grant-free uplink transmission scheme in a multiple access system;

determine at the UE a first MCS index within the MCS limit; and

send a first uplink transmission to the base station using a CTU in the CTU access region, the first uplink transmission including user data and the first MCS index determined at the first UE.

24. The user equipment of claim 23, wherein the instructions configure the processor to transmit the uplink transmission by:

transmitting the user data using a first MCS level corresponding to the first MCS index; and

transmitting the first MCS index using a pre-defined MCS level within a reserved time-frequency region of the CTU access region.

25. The user equipment of claim 23, wherein the instructions further configure the processor to:

determine at the UE at least one of channel state information or estimated path loss;

determine at the UE an uplink traffic characteristic;

wherein the instructions configure the processor to determine the first MCS index by selecting the first MCS index based on the uplink traffic characteristic and the at least one of the channel state information or the estimated path loss.

26. The user equipment of claim 25, wherein the instructions further configure the processor to:

select a transmission power for the first uplink transmission based on the estimated path loss.

27. The user equipment of claim 23, wherein the first uplink transmission is transmitted using a first transmission power, the instructions further configure the processor to:

determine an uplink transmission success rate at the UE;

compare the uplink transmission success rate with a threshold;

in response to the uplink transmission success rate being greater than the threshold and the MCS index being less than the MCS limit, send a second uplink transmission at a second MCS level that is greater than the first MCS level, the second uplink transmission including a second MCS index corresponding to the second MCS level; and

in response to the uplink transmission success rate being greater than the threshold and the MCS index reaching the MCS limit, send the second uplink transmission at a third transmission power to the base station, the third transmission power is less than the first transmission power.

28. The user equipment of claim 27, wherein the instructions further configure the processor to:

in response to the uplink transmission rate being less than the threshold and the first transmission power reaching the maximum transmission power, select a third MCS index that is less than the first MCS index and send the second uplink transmission using a third MCS level corresponding to the third MCS index; and

in response to the uplink transmission rate being less than the threshold and the first transmission power being less than the maximum transmission power, send the second uplink transmission at a second transmission power to the base station, the second transmission power is greater than the first transmission power.