Method and apparatus of enhancing performance of downlink multi-user multiple-input-multiple-output transmissions in wireless communication system

1. A method of enhancing performance of downlink multi-user multiple-input-multiple-output transmissions in a wireless communication system comprising a communication device and a network, the method comprising:

generating a feedback report comprising a correlation-based validity threshold (CVT), wherein the CVT is configured to maintain deviation of channel quality indication (CQI) within a pre-defined deviation value of CQI; and

transmitting the feedback report from the communication device to the network.

2. The method of claim 1 , wherein the feedback report further comprises a precoding matrix index (PMI), a best companion PMI (BCI) and a multi-user channel quality indication (MU-CQI).

3. The method of claim 2 , wherein the MU-CQI is derived from a CQI function of the PMI and the BCI.

4. The method of claim 2 , wherein the CVT is derived from a CQI function of the PMI, the BCI and any other precoder in a codebook other than the BCI.

5. The method of claim 4 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

ξ 2 =q ( W PMI ,W N — BCI );

c =arg min| W BCI *W N — BCI |, subject to (ξ 1 −ξ 2 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — BCI denotes the any other precoder in the codebook other than the BCI, Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

6. The method of claim 4 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

ξ 2 =q ( W N — PMI ,W BCI );

c =arg min| W PMI *W N — PMI |, subject to (ξ 1 −ξ 2 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — PMI denotes the any other precoder in the codebook other than the PMI, Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

7. The method of claim 4 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

c =arg min| W BCI *W N — BCI |, subject to (ξ 0 −ξ 1 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — BCI denotes the any other precoder in the codebook other than the BCI, ξ 0 denotes the CQI under single-user MIMO assumption (SU-CQI), Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

8. The method of claim 4 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

c =arg min| W PMI *W N — PMI |, subject to (ξ 0 −ξ 1 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — PMI denotes the any other precoder in the codebook other than the PMI, ξ 0 denotes the CQI under single-user MIMO assumption (SU-CQI), Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

9. A method of enhancing performance of downlink multi-user multiple-input-multiple-output transmissions in a wireless communication system comprising a communication device and a network, the method comprising:

generating a feedback report comprising a compromised multi-user channel quality indication (MU-CQI), a precoding matrix index (PMI), a best companion PMI (BCI) and an optimal MU-CQI; and

transmitting the feedback report from the communication device to the network;

wherein the compromised MU-CQI is derived from a cross-correlation threshold and a CQI function of the PMI, the BCI and any other precoder in a codebook other than the BCI, and the cross-correlation threshold is configured by the network or pre-defined in a specification.

10. The method of claim 9 , wherein the optimal MU-CQI is derived from a CQI function of the PMI and the BCI.

11. The method of claim 9 , wherein the compromised MU-CQI is derived according to the following equations:

j *=arg min W |W PMI *W j |, subject to | W BCI *W j |≧r,W j ≠W BCI

ξ com =q ( W PMI ,W j *);

wherein ξ com denotes the compromised MU-CQI, W PMI denotes the PMI, W BCI denotes the BCI, j denotes the precoder entry index in the codebook, r denotes the cross-correlation threshold for the PMI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

12. The method of claim 9 , wherein the compromised MU-CQI is derived according to the following equations:

j *=arg min W |W j *W BMI |, subject to | W PMI *W j |≧r,W j ≠W PMI

ξ com =q ( W j *,W BCI );

wherein ξ com denotes the compromised MU-CQI, W PMI denotes the PMI, W BCI denotes the BCI, j denotes the precoder entry index in the codebook, r denotes the cross-correlation threshold for the PMI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

13. A communication apparatus for a wireless communication system, comprising:

a processing means;

a storage unit, for storing a program code, wherein the program code instructs the processing means to execute the following steps:

generating a feedback report comprising a correlation-based validity threshold (CVT), wherein the CVT is configured to maintain deviation of channel quality indication (CQI) within a pre-defined deviation value of CQI; and

transmitting the feedback report from a communication device to a network.

14. The communication apparatus of claim 13 , wherein the feedback report further comprises a precoding matrix index (PMI), a best companion PMI (BCI) and a multi-user channel quality indication (MU-CQI).

15. The communication apparatus of claim 14 , wherein the MU-CQI is derived from a CQI function of the PMI and the BCI.

16. The communication apparatus of claim 14 , wherein the CVT is derived from a CQI function of the PMI, the BCI and any other precoder in a codebook other than the BCI.

17. The communication apparatus of claim 16 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

ξ 2 =q ( W PMI ,W N — BCI );

c =arg min| W BCI *W N — BCI |, subject to (ξ 1 −ξ 2 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — BCI denotes the any other precoder in the codebook other than the BCI, Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

18. The communication apparatus of claim 16 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

ξ 2 =q ( W N — PMI ,W BCI );

c =arg min| W PMI *W N — PMI |, subject to (ξ 1 −ξ 2 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — PMI denotes the any other precoder in the codebook other than the PMI, Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

19. The communication apparatus of claim 16 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

c =arg min| W BCI *W N — BCI |, subject to (ξ 0 −ξ 1 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — BCI denotes the any other precoder in the codebook other than the BCI, ξ 0 denotes the CQI under single-user MIMO assumption (SU-CQI), Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

20. The communication apparatus of claim 16 , wherein the CVT is derived according to the following equations:

ξ 1 =q ( W PMI ,W BCI );

c =arg min| W PMI *W N — PMI |, subject to (ξ 0 −ξ 1 )≦Δξ, where Δξ≧0

wherein c denotes the CVT, W PMI denotes the PMI, W BCI denotes the BCI, W N — PMI denotes the any other precoder in the codebook other than the PMI, ξ 0 denotes the CQI under single-user MIMO assumption (SU-CQI), Δξ denotes the pre-defined deviation value of CQI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

21. A communication apparatus for a wireless communication system, comprising:

a processing means;

a storage unit, for storing a program code, wherein the program code instructs the processing means to execute the following steps:

generating a feedback report comprising a compromised multi-user channel quality indication (MU-CQI), a precoding matrix index (PMI), a best companion PMI (BCI) and an optimal MU-CQI; and

transmitting the feedback report from a communication device to a network;

wherein the compromised MU-CQI is derived from a cross-correlation threshold and a CQI function of the PMI, the BCI and any other precoder in a codebook other than the BCI, and the cross-correlation threshold is configured by the network or pre-defined in a specification.

22. The communication apparatus of claim 21 , wherein the optimal MU-CQI is derived from a CQI function of the PMI and the BCI.

23. The communication apparatus of claim 21 , wherein the compromised MU-CQI is derived according to the following equations:

j *=arg min W |W PMI *W j |, subject to | W BCI *W j |≧r,W j ≠W BCI

ξ com =q ( W PMI ,W j *);

wherein ξ com , denotes the compromised MU-CQI, W PMI denotes the PMI, W BCI denotes the BCI, j denotes the precoder entry index in the codebook, r denotes the cross-correlation threshold for the PMI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.

24. The communication apparatus of claim 21 , wherein the compromised MU-CQI is derived according to the following equations:

j *=arg min W |W j *W BMI |, subject to | W PMI *W j |≧r,W j ≠W PMI

ξ com =q ( W j *,W BCI );

wherein ξ com denotes the compromised MU-CQI, W PMI denotes the PMI, W BCI denotes the BCI, j denotes the precoder entry index in the codebook, r denotes the cross-correlation threshold for the PMI, * denotes the complex-conjugate operation, and the function q denotes a CQI function.