System and method for modulation and coding scheme adaptation and power control in a relay network

1. A method for determining a Modulation and Coding Scheme (MCS) for a wireless communication system, the method including:

using an Open Loop Power Control (OLPC) and inner loop link adaptation scheme to select an MCS for communications between a user agent (UA) and at least one of a base station and a relay node (RN), wherein the MCS is selected based upon a path loss between the UA and the at least one of the base station and the RN;

determining an error rate of a communication channel between the UA and the at least one of the base station and the RN;

when the error rate is below a first threshold, at least one of:

increasing the MCS, and

reducing a transmission power of the UA; and

when the error rate is above a second threshold, at least one of:

decreasing the MCS, and

increasing a transmission power of the UA;

allocating an uplink (UL) resource for communication from the UA to the RN and a downlink (DL) resource for communication from the base station to the UA when a coupling loss of UL communication on a first link coupling the UA and the base station is greater than a coupling loss of UL communication on a second link coupling the UA and the RN and a power level of DL communication on the second link is less than a power level of DL communication on the first link.

2. The method of claim 1 , wherein selecting the MCS includes using a signal quality value of a communication channel between the UA and the base station and the coupling loss difference between the first link and the second link to determine the MCS.

3. The method of claim 1 , wherein determining an error rate of a communication channel between the UA and at least one of the base station and the RN includes determining at least one of a number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel and a Frame Erasure Rate (FER) on the communication channel.

4. The method of claim 3 , further comprising selecting a lowest MCS level as the MCS if:

an average number of HARQ transmissions on the communication channel is greater than or equal to a desired number of HARQ transmissions on the communication channel; or

an average Frame Erasure Rate (FER) on the communication channel is greater than or equal to a desired FER.

5. The method of claim 3 , further comprising increasing the MCS by one level if:

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel; or

an average Frame Erasure Rate (FER) on the communication channel is less than a desired FER.

6. The method of claim 3 , further comprising selecting a highest MCS level as the MCS if:

an average Frame Erasure Rate (FER) on the communication channel is less than a desired FER; and

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel.

7. The method of claim 1 , wherein the base station is an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB).

8. The method of claim 1 , including using a margin to modify a value of the error rate of a communication channel between the UA and at least one of the base station and the RN.

9. The method of claim 1 , wherein the MCS is configured to target an approximately 10% Block Error Rate (BLER).

10. A base station for determining a Modulation and Coding Scheme (MCS) for a wireless communication system, the base station comprising:

a processor, the processor being configured to:

use an Open Loop Power Control (OLPC) and inner loop link adaptation scheme to select an MCS for communications between a user agent (UA) and at least one of a base station and a relay node (RN), wherein the MCS is selected based upon a path loss between the UA and the at least one of the base station and the RN;

determine an error rate of a communication channel between the UA and the at least one of the base station and the RN;

when the error rate is below a first threshold, at least one of:

increase the MCS, and

reduce a transmission power of the UA; and

when the error rate is above a second threshold, at least one of:

decrease the MCS, and

increase a transmission power of the UA;

allocate an uplink (UL) resource for communication from the UA to the RN and a downlink (DL) resource for communication from the base station to the UA when a coupling loss of UL communication on a first link coupling the UA and the base station is greater than a coupling loss of UL communication on a second link coupling the UA and the RN and a power level of DL communication on the second link is less than a power level of DL communication on the first link.

11. The base station of claim 10 , wherein the processor is configured to use a signal quality value of a communication channel between the UA and the base station and the coupling loss difference between the first link and the second link to determine the MCS.

12. The base station of claim 10 , wherein the processor is configured to determine at least one of a number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel and a Frame Erasure Rate (FER) on the communication channel.

13. The base station of claim 12 , wherein the processor is further configured to select a lowest MCS level as the MCS if:

an average number of HARQ transmissions on the communication channel is greater than or equal to a desired number of HARQ transmissions on the communication channel; or

an average FER on the communication channel is greater than or equal to a desired FER.

14. The base station of claim 12 , wherein the processor is further configured to increase the MCS by one level if:

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel; or

an average FER on the communication channel is less than a desired FER.

15. The base station of claim 12 , wherein the processor is further configured to select a highest MCS level as the MCS if:

an average Frame Erasure Rate (FER) on the communication channel is less than a desired FER; and

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel.

16. The base station of claim 10 , wherein the base station includes an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB).

17. The base station of claim 10 , wherein the processor is further configured to use a margin to modify a value of the error rate of a communication channel between the UA and at least one of the base station and the RN.

18. The base station of claim 10 , wherein the MCS is configured to target an approximately 10% Block Error Rate (BLER), and wherein the processor is further configured to set a transmission power of the UA based on a path loss of a channel plus an offset, the offset corresponding to a coupling loss difference between the first and second links, wherein the channel is between the UA and the base station.

19. A wireless communication system, comprising:

a user agent (UA) for communicating with a base station and a relay node (RN), the UA being configured to receive an instruction from the base station, the instruction at least one of specifying a Modulation and Coding Scheme (MCS) and instructing the UA to modify a power level of the UA, wherein an Open Loop Power Control (OLPC) and inner loop link adaptation scheme is used to select the MCS and power level specified in the instruction; and

a base station configured to:

determine an error rate of a communication channel between the UA and at least one of the base station and the RN, and

when the error rate is below a first threshold, transmit an instruction to the UA including at least one of an increased MCS and a reduced transmission power specification, and

when the error rate is above a second threshold, transmit an instruction to the UA including at least one of a decreased MCS and an increased transmission power specification,

wherein the base station is configured to allocate an uplink (UL) resource for communication from the UA to the RN and a downlink (DL) resource for communication from the base station to the UA when:

a coupling loss of an UL channel between the UA and the base station is greater than a coupling loss of an UL channel between the UA and the RN, and

a power level of a DL channel between the UA and the RN is less than a power level of a DL channel between the base station and the UA.

20. The system of claim 19 , wherein the base station is configured to use at least one of a signal quality value of a communication channel between the UA and the base station, the coupling loss between the UA and the base station, and the coupling loss between the UA and the RN to determine the MCS for communications between the UA and the at least one of the base station and the RN.

21. The system of claim 19 , wherein the base station is further configured to determine at least one of the number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel and a Frame Erasure Rate (FER) on the communication channel.

22. The system of claim 21 , wherein the base station is further configured to select a lowest MCS level as the MCS if:

an average number of HARQ transmissions on the communication channel is greater than or equal to a desired number of HARQ transmissions on the communication channel; or

an average FER on the communication channel is greater than or equal to a desired FER.

23. The system of claim 21 , wherein the base station is further configured to increase the MCS by one level if:

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel; or

an average FER on the communication channel is less than a desired FER.

24. The system of claim 21 , wherein the base station is further configured to select a highest MCS level as the MCS if:

an average Frame Erasure Rate (FER) on the communication channel is less than a desired FER; and

an average number of HARQ transmissions on the communication channel is less than a desired number of HARQ transmissions on the communication channel.

25. The system of claim 19 , wherein the base station is an evolved universal terrestrial radio access network (E-UTRAN) node B (eNB).

26. The system of claim 19 , wherein the base station is further configured to use a margin to modify a value of the error rate of a communication channel between the UA and at least one of the base station and the RN.

27. The method of claim 1 , wherein the base station uses the OLPC and inner loop link adaptation scheme to select the MCS based upon instantaneous channel quality information and estimations, and wherein the base station uses an outer loop link adaptation and Close Loop Power Control (CLPC) scheme to adjust the MCS and the UA's transmission power based upon long term statistics.

28. The method of claim 1 , further comprising:

receiving sounding reference signals from the UA and the RN;

determining, based on the sounding reference signals, power levels of UL communications between the UA and the base station and between the UA and the RN; and

allocating UL communication channel resources on both the base station and the RN when a receiving power of the UA from the base station is greater than a receiving power of the UA from the RN.