Method and apparatus for predicting precoding matrix in MIMO system

1. A method for predicting precoding matrix (PM) in a MIMO System, comprising:

obtaining a present PM based on a present transmission;

fitting the present PM and previous PMs with a predefined model; and

determining a forthcoming PM which is expected to be used in the next transmission based on the fitting,

wherein determining the forthcoming PM which is expected to be used in the next transmission based on the fitting comprises:

determining a step size based on the fitting;

extrapolating on the fitting result with the step size, based on the predefined model; and

obtaining the forthcoming PM based on the extrapolation, and

wherein determining the step size based on the fitting comprises:

defining a plurality of PMs by using different step sizes based on the fitting;

calculating an error metric between each of the plurality of PMs and a set of the previous PMs; and

determining a step size corresponding to the maximum error metric.

2. The method of claim 1 , wherein fitting the present PM and previous PMs with the predefined model comprises:

evaluating goodness-of-fit of a plurality of predefined models based on the present PM and the previous PMs; and

selecting the model with the best goodness-of-fit as the predefined model.

3. The method of claim 2 , wherein evaluating goodness-of-fit of the plurality of models based on the present PM and the previous PMs comprises:

calculating an error metric between each of the plurality of models and a set of present PM and the previous PMs; and

determining the model corresponding to the minimum error metric as a model with the best goodness-of-fit.

4. The method of claim 1 , wherein fitting the present PM and previous PMs with a predefined model comprises:

fitting the present PM and previous PMs with a curve on a Grassmannian manifold.

5. The method of claim 1 , wherein obtaining the forthcoming PM based on the extrapolation comprises:

calculating a focusing factor according to the previous PMs and previously predicted PMs;

focalizing a PM set on the forthcoming PM by using the focusing factor based on a root codebook;

selecting, from the PM set, the most similar PM to the forthcoming PM as a target PM; and

determining the index of the target PM in the PM set.

6. The method of claim 5 , wherein calculating the focusing factor according to the previous PMs and previously predicted PMs comprises:

calculating, with one of a plurality of candidate focusing factors, the sum of error metrics between the previous PMs and previously predicted PMs, wherein one sum corresponds to one of the plurality of candidate focusing factors;

determining the candidate focusing factor corresponding to the minimum sum as the focusing factor; and

quantizing the focusing factor so as to be fed back to a transmitter.

7. The method of claim 5 , wherein focalizing the PM set on the present PM by using the focusing factor based on a root codebook comprises:

calculating a rotation matrix based on the present PM and the reference point of the root codebook;

focalizing a set of reference PMs on the reference point by applying the focusing factor to the root codebook; and

calculating the PM set based on the rotation matrix and the set of reference PMs.

8. The method of claim 5 , wherein determining the index of the target PM in the PM set further comprises:

quantizing the index so as to be fed back to a transmitter.

9. A method for communication with a predicted precoding matrix (PM) in a FDD MIMO system, comprising:

predicting a forthcoming PM which is expected to be used in the next transmission by using the method of claim 1 ;

obtaining a quantized focusing factor and a quantized index of a target PM; and

feeding back the quantized focusing factor and the quantized index of the target PM to a transmitter.

10. The method of claim 9 , wherein feeding back the quantized focusing factor and the quantized index of the target PM to the transmitter comprises:

signaling the quantized focusing factor at a transmission interval multiple times of the transmission interval at which the quantized index of the target PM is signaled.

11. The method of claim 9 , wherein feeding back the quantized focusing factor and the quantized index of the target PM to the transmitter comprises:

appending each bit of the quantized focusing factor to the quantized index of the target PM in a most-significant-bit order; and

signaling the appended quantized index to the transmitter.

12. A receiver in a FDD MIMO system, comprising:

a predicting device, configured to predict a forthcoming precoding matrix (PM) which is expected to be used in the next transmission by using the method of claim 1 ;

an obtaining device, configured to obtain a quantized focusing factor and a quantized index of a target PM; and

a feedback device, configured to feed back the quantized focusing factor and the quantized index of the target PM to a transmitter.

13. The receiver of claim 12 , wherein the feedback device comprises:

means for signaling the quantized focusing factor at a transmission interval multiple times of the transmission interval at which the quantized index of the target PM is signaled.

14. The receiver of claim 12 , wherein the feedback device comprises:

means for appending each bit of the quantized focusing factor to the quantized index of the target PM in a most-significant-bit order; and

means for signaling the appended quantized index to the transmitter.

15. An apparatus for predicting precoding matrix (PM) in a MIMO System, comprising:

an obtaining device, configured to obtain a present PM based on a present transmission;

a fitting device, configured to fit the present PM and previous PMs with a predefined model; and

a determining device, configured to determine a forthcoming PM which is expected to be used in a next transmission based on fitting of the fitting device,

wherein the determining device comprises:

means for determining a step size based on the fitting;

means for extrapolating on the fitting result with the step size, based on the predefined model; and

means for obtaining the forthcoming PM based on the extrapolation, and

wherein the means for determining the step size based on the fitting comprises:

means for defining a plurality of PMs by using different step sizes based on the fitting;

means for calculating an error metric between each of the plurality of PMs and a set of the previous PMs; and

means for determining a step size corresponding to the maximum error metric.

16. The apparatus of claim 15 , wherein the fitting device comprises:

means for evaluating goodness-of-fit of a plurality of predefined models based on the present PM and the previous PMs; and

means for selecting the model with the best goodness-of-fit as the predefined model.

17. The apparatus of claim 16 , wherein the means for evaluating goodness-of-fit of the plurality of models based on the present PM and the previous PMs comprises:

means for calculating an error metric between each of the plurality of models and a set of the present PM and the previous PMs; and

means for determining the model corresponding to the minimum error metric as a model with the best goodness-of-fit.

18. The apparatus of claim 15 , wherein the fitting device comprises:

means for fitting the present PM and previous PMs with a curve on a Grassmannian manifold.

19. The apparatus of claim 15 , wherein the means for obtaining the forthcoming PM based on the extrapolation comprises:

means for calculating a focusing factor according to the previous PMs and previously predicted PMs;

means for focalizing a PM set on the forthcoming PM by using the focusing factor based on a root codebook;

means for selecting, from the PM set, the most similar PM to the forthcoming PM as a target PM; and

means for determining the index of the target PM in the PM set.

20. The apparatus of claim 19 , wherein the means for calculating a focusing factor according to the previous PMs and previously predicted PMs comprises:

means for calculating, with one of a plurality of candidate focusing factors, the sum of error metrics between the previous PMs and previously predicted PMs, wherein one sum corresponds to one of the plurality of candidate focusing factors;

means for determining the candidate focusing factor corresponding to the minimum sum as the focusing factor; and

means for quantizing the focusing factor so as to be fed back to a transmitter.

21. The apparatus of claim 19 , wherein the means for focalizing a PM set on the present PM by using the focusing factor based on a root codebook comprises:

means for calculating a rotation matrix based on the present PM and the reference point of the root codebook;

means for focalizing a set of reference PMs on the reference point by applying the focusing factor to the root codebook; and

means for calculating the PM set based on the rotation matrix and the set of reference PMs.

22. The apparatus of claim 19 , wherein the means for determining the index of the target PM in the PM set further comprises:

means for quantizing the index so as to be fed back to a transmitter.

23. A method for predicting precoding matrix (PM) in a MIMO System, comprising:

obtaining a present PM based on a present transmission;

fitting the present PM and previous PMs with a predefined model; and

determining a forthcoming PM which is expected to be used in the next transmission based on the fitting,

wherein determining the forthcoming PM which is expected to be used in the next transmission based on the fitting comprises:

determining a step size based on the fitting;

extrapolating on the fitting result with the step size, based on the predefined model; and

obtaining the forthcoming PM based on the extrapolation, and

wherein obtaining the forthcoming PM based on the extrapolation comprises:

calculating a focusing factor according to the previous PMs and previously predicted PMs;

focalizing a PM set on the forthcoming PM by using the focusing factor based on a root codebook;

selecting, from the PM set, the most similar PM to the forthcoming PM as a target PM; and

determining the index of the target PM in the PM set.