Method and apparatus for estimating a channel quality indicator (CQI) for multiple input multiple output (MIMO) systems

1. A method for determining a channel quality indicator (CQI) in a transmission system associated with an effective channel and a diversity transmission scheme, the method comprising:

identifying a plurality of independent diversity branches in the diversity transmission scheme, wherein each one of the independent diversity branches corresponds to a different portion of the effective channel;

computing, using receiver circuitry, a plurality of effective Signal-to-Noise Ratio (SNR) values, wherein each effective value corresponds to a respective one of the identified independent diversity branches; and

combining, using the receiver circuitry, the computed effective SNR values for the identified independent diversity branches to generate a CQI value.

2. The method for determining the CQI of claim 1 , further comprising:

computing a plurality of Signal-to-Interference and Noise Ratio (SINR) values for each one of the independent diversity branches, wherein each SINR value is associated with a respective transmission instance received at the receiver circuitry; and

computing the effective SNR value for each one of the independent diversity branches based on the computed SINR values.

3. The method for determining the CQI of claim 2 , further comprising:

averaging the effective SNR values over the independent diversity branches to compute a global effective SNR; and

mapping the global effective SNR to the CQI value.

4. The method for determining the CQI of claim 1 , wherein each one of the independent diversity branches comprises one of a codeword and a stream transmitted in the transmission system.

5. The method for determining the CQI of claim 1 , wherein each one of the independent diversity branches comprises a combination of (i) a precoding matrix W and (ii) a per-stream phase matrix U, wherein the precoding matrix W is associated with a respective tone received at the receiver circuitry.

6. The method for determining the CQI of claim 5 , wherein each one of the independent diversity branches further comprises a cyclic delay matrix D, wherein the precoding cyclic delay matrix D is associated with the respective tone received at the receiver circuitry.

7. The method for determining the CQI of claim 6 , further comprising:

identifying a plurality of combinations of (i) a precoding matrix W l selected from a plurality of L precoding matrices, (ii) a cyclic delay phase k selected from a plurality of K delay phases, and (iii) a transmitted stream s selected from a plurality of S transmitted streams;

for each tone i received at the receiver circuitry, computing a plurality of SINR is (l,k) values, wherein each one of the SINR is (l,k) values corresponds to one of the identified combinations;

computing an effective SNR eff,s (l,k) value for each one of the identified combinations; and

averaging the computed SNR eff,s (l,k) values over the identified combinations to generate a global effective SNR.

8. The method for determining the CQI of claim 1 , wherein each one of the independent diversity branches comprises a pair of transmit antennas and wherein the pair of transmit antennas are configured to transmit orthogonal vectors.

9. The method for determining the CQI of claim 8 , further comprising:

for each transmission instance i received at the receiver circuitry, computing a plurality of SINR i (l) values associated with each one of the pairs of transmit antennas;

computing an effective SNR eff (l) value for each one of the pairs of transmit antennas; and

averaging the computed SNR eff (l) values over the pairs of transmit antennas to generate a global effective SNR.

10. The method for determining the CQI of claim 1 , wherein the diversity transmission scheme is one of cyclic delay diversity (CDD), space-frequency block coding (SFBC), space-time block coding (STBC), and SFBC/STBC with antenna selection.

11. The method for determining the CQI of claim 1 , wherein each diversity branch comprises at least one component of the effective channel, wherein the plurality of diversity branches includes less than all components of the effective channel.

12. A receiver for determining a channel quality indicator (CQI) in a transmission system associated with an effective channel and a diversity transmission scheme, the receiver comprising processing circuitry configured to:

identify a plurality of independent diversity branches in the diversity transmission scheme, wherein each one of the independent diversity branches corresponds to a different portion of the effective channel;

compute, using processing circuitry, a plurality of effective Signal-to-Noise Ratio (SNR) values, wherein each effective value corresponds to a respective one of the identified independent diversity branches; and

combine, using the processing circuitry, the computed effective SNR values for the identified independent diversity branches to generate a CQI value.

13. The receiver of claim 12 , wherein the processing circuitry is further configured to:

compute a plurality of Signal-to-Interference and Noise Ratio (SINR) values for each one of the independent diversity branches, wherein each SINR value is associated with a respective transmission instance received at the receiver; and

compute the effective SNR value for each one of the independent diversity branches based on the computed SINR values.

14. The receiver of claim 13 , wherein the processing circuitry is further configured to:

average the effective SNR values over the independent diversity branches to compute a global effective SNR; and

map the global effective SNR to the CQI value.

15. The receiver of claim 12 , wherein

each one of the independent diversity branches comprises one of a codeword and a stream transmitted in the transmission system.

16. The receiver of claim 12 , wherein

each one of the independent diversity branches comprises a combination of (i) a precoding matrix W and (ii) a per-stream phase matrix U, wherein the precoding matrix W is associated with a respective tone received at the receiver.

17. The receiver of claim 16 , wherein

each one of the independent diversity branches further comprises a cyclic delay matrix D, wherein the precoding cyclic delay matrix D is associated with the respective tone received at the receiver.

18. The receiver of claim 17 , wherein the processing circuitry is further configured to:

identify a plurality of combinations of (i) a precoding matrix W l selected from a plurality of L precoding matrices, (ii) a cyclic delay phase k selected from a plurality of K delay phases, and (iii) a transmitted stream s selected from a plurality of S transmitted streams;

for each tone i received at the receiver circuitry, compute a plurality of SINR is (l,k) values, wherein each one of the SINR is (l,k) values corresponds to one of the identified combinations;

compute an effective SNR eff,s (l,k) value for each one of the identified combinations; and

average the computed SNR eff,s (l,k) values over the identified combinations to generate a global effective SNR.

19. The receiver of claim 12 , wherein

each one of the independent diversity branches comprises a pair of transmit antennas and wherein the pair of transmit antennas are configured to transmit orthogonal vectors.

20. The receiver of claim 19 , wherein the processing circuitry is further configured to:

for each transmission instance i received at a receiver of the transmission system, compute a plurality of SNR eff,s (l,k) values associated with each one of the pairs of transmit antennas;

compute an effective SNR eff,s (l) value for each one of the pairs of transmit antennas; and

average the computed SNR eff (l) values over the pairs of transmit antennas to generate a global effective SNR.

21. The receiver of claim 12 , wherein the diversity transmission scheme is one of cyclic delay diversity (CDD), space-time block coding (STBC), and SFBC/STBC with antenna selection.