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:

identifying an MCS for communications between a user agent (UA) and at least one of a base station and a relay node (RN);

selecting the MCS based at least upon a coupling loss of a first link between the UA and the base station and/or a coupling loss of a second link between the UA and the RN;

allocating an uplink (UL) resource for communication from the UA to the RN when a coupling loss of UL communication on the first link is greater than a coupling loss of UL communication on the second link; and

allocating a downlink (DL) resource for communication from the base station to the UA when 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 , further comprising determining an error rate of a communication channel between the UA and at least one of the base station and the RN, wherein the MCS is further selected based upon the error rate and a coupling loss difference between the first link and the second link.

3. The method of claim 1 , further comprising determining an error rate of a communication channel between the UA and at least one of the base station and the RN, wherein the error rate is determined based upon at least one of a number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel or 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 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 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 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 3 , further comprising:

increasing the MCS and/or reducing a transmission power of the UA when the error rate is below a first threshold; and

decreasing the MCS and/or increasing a transmission power of the UA when the error rate is above a second threshold.

8. 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:

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 at least upon a coupling loss of a first link between the UA and the base station and/or a coupling loss of a second link between the UA and the RN;

allocate an uplink (UL) resource for communication from the UA to the RN when a coupling loss of UL communication on the first link is greater than a coupling loss of UL communication on the second link; and

allocate a downlink (DL) resource for communication from the base station to the UA when a power level of DL communication on the second link is less than a power level of DL communication on the first link.

9. The base station of claim 8 , wherein the processor is further 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

select the MCS based upon the error rate and a coupling loss difference between the first link and the second link.

10. The base station of claim 8 , wherein the processor is configured to determine an error rate of a communication channel between the UA and at least one of the base station and the RN, wherein the error rate is determined based at least upon one of a number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel or a Frame Erasure Rate (FER) on the communication channel.

11. The base station of claim 10 , 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.

12. The base station of claim 10 , 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.

13. The base station of claim 10 , wherein the processor is further configured to select a highest MCS level as the MCS if:

an average 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.

14. The base station of claim 10 , wherein the processor is further configured to:

increase the MCS and/or reduce a transmission power of the UA when the error rate is below a first threshold; and

decrease the MCS and/or increase a transmission power of the UA when the error rate is above a second threshold.

15. 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 specifying a Modulation and Coding Scheme (MCS); and

a base station configured to:

allocate an uplink (UL) resource for communication from the UA to the RN when a coupling loss of a first UL channel between the UA and the base station is greater than a coupling loss of a second UL channel between the UA and the RN; and

allocate a downlink (DL) resource for communication from the base station to the UA when a power level of a first DL channel between the UA and the RN is less than a power level of a second DL channel between the base station and the UA.

16. The wireless communication system of claim 15 , wherein the base station is configured to select the MCS using at least one of:

a signal quality value of a communication channel between the UA and the base station;

a coupling loss difference between the first and second UL channels; or

a coupling loss difference between the first and second DL channels.

17. The wireless communication system of claim 15 , wherein the base station is further configured to select the MCS based at least upon an error rate of a communication channel between the UA and the base station, wherein the error rate is based at least upon one of the number of Hybrid Automatic Repeat reQuest (HARQ) transmissions on the communication channel or a Frame Erasure Rate (FER) on the communication channel.

18. The wireless communication system of claim 17 , 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.

19. The wireless communication system of claim 17 , 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.

20. The wireless communication system of claim 17 , wherein the base station is further configured to select a highest MCS level as the MCS if:

an average 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.