Method and terminal for feeding back channel state information

Abstract

A method and terminal for feeding back channel state information are applied to a 4-antenna system. The method includes: a terminal acquiring channel state information, the terminal performing joint encoding on PMI1 information and RI information into a 4-bit or 5-bit feedback report, or, performing joint encoding on PMI1 information and PMI2 information into a 4-bit feedback report, or, the PMI2 information using 2-bit feedback; and the terminal feeding back the feedback report in a physical uplink control channel.

Claims

1. A method for feeding back channel state information, applied to a 4-antenna system, comprising: a terminal acquiring channel state information, the channel state information comprising Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information and channel quality information; and the terminal feeding back the channel state information in a physical uplink control channel, wherein when RI=3 or 4, the PMI2 information comprises 2 bits, and the PMI2 indicates one codeword in a first set of codewords, and the first set of codewords comprises 4 codewords selected from a codebook corresponding to Ranks 3 and 4 in a Rel-8 codebook, wherein the Rel-8 codebook refers to the codebook defined in 3GPP TS 36.211 V8.9.0; wherein the first set of codewords comprises: using 0.sup.th, 1.sup.st, 2.sup.nd, and 3.sup.rd codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a first group, using 8.sup.th, 9.sup.th, 10.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a second group, selecting 2 codewords from the first group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the second group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 2.sup.nd, 8.sup.th, and 10.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a third group, using 1.sup.st, 3.sup.rd, 9.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a fourth group, selecting 2 codewords from the third group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the fourth group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 2.sup.nd, 3.sup.rd, and 10.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a fifth group, using 2.sup.nd, 8.sup.th, 9.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a sixth group, selecting 2 codewords from the fifth group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the sixth group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 1.sup.st, 2.sup.nd, and 9.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a seventh group, using 3.sup.rd, 10.sup.th, 8.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as an eighth group, selecting 2 codewords from the seventh group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the eighth group and putting the 2 codewords in the first set of codewords.

2. A method for feeding back channel state information, comprising: a terminal acquiring channel state information, the channel state information comprising Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information and channel quality information; the terminal feeding back the channel state information in a physical uplink control channel, wherein when RI=1 or 2, the PMI2 information is 2 bits, and indicates one codeword in a second set of codewords, and the second set of codewords consists of: 0.sup.th, 1.sup.st, 4.sup.th, and 5.sup.th codewords in a codebook corresponding to rank 1 in an LTE-A Rel12 version or 0.sup.th, 1.sup.st, 4.sup.th, and 5.sup.th codewords in a first or second codebook corresponding to rank 2 in the LTE-A Rel12 version, wherein the LTE-A Rel12 version refers to 3GPP TS 36.213 V12.0.0; wherein the method is applied to a system having only 4 downlink antenna ports.

3. A method for feeding back channel state information, applied to a 4-antenna system, comprising: a terminal acquiring channel state information, the channel state information comprising Rank Indicator (RI) information, a first class of Precoding Matrix Indicator (PMI1) information and a second class of Precoding Matrix Indicator (PMI2) information; the terminal performing joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report; the terminal feeding back the feedback report in a physical uplink control channel; wherein the feedback report is used for indicating one of a set of combination information formed by the PMI1 and the PMI2, and codewords indicated by the set of combination information comprise codewords in a codebook corresponding to Rank 1 or a first or second codebook corresponding to Rank 2 in a Long Term Evolution-Advanced (LTE-A) Rel12 version, wherein the LTE-A Rel12 version refers to 3GPP TS 36.213 V12.0.0; wherein when RI=1, the codewords indicated by the set of combination information comprise codewords in the codebook corresponding to Rank 1 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet: a model $\left[\begin{array}{c}u\\ e^{j\frac{m\pi }{4}}.Math.e^{j\frac{n\pi }{2}}.Math.u\end{array}\right]m=0,1n=0,1,2,3,$ wherein u is a 2-dimensional column vector; or when RI=2, the codewords indicated by the set of combination information comprise codewords of a first codebook corresponding to Rank 2 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet a model $\left[\begin{array}{cc}{u}_{i_1}& u_{i_2}\\ e^{j{\theta }_m}{u}_{i_1}& -e^{j{\theta }_m}{u}_{i_2}\end{array}\right]i_1,i_2,m=0~15,$ wherein θ.sub.m is any real number, and u.sub.i is a 2-dimensional column vector.

4. The method according to claim 3, wherein all of the codewords indicated by the set of combination information meet m=0; or one half of the codewords indicated by the set of combination information meet the model when m=0, and the other half of the codewords indicated by the set of combination information meet the model when m=1; or all of the codewords indicated by the set of combination information meet m=1.

5. The method according to claim 3, wherein a set of codewords indicated by the set of combination information is: $\left[\begin{array}{c}{u}_i\\ e^{j{\theta }_i}{u}_i\end{array}\right]i=0~15,$ wherein θ.sub.i is any real number, and u.sub.i is a 2-dimensional column vector.

6. A terminal, comprising: a channel state information acquisition unit, configured to acquire channel state information, the channel state information comprising Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information and channel quality information; and a feedback unit, configured to feed back the channel state information in a physical uplink control channel, wherein when RI=3 or 4, the PMI2 information comprises 2 bits, the PMI2 indicates one codeword in a first set of codewords, and the first set of codewords comprises 4 codewords selected from a codebook corresponding to Ranks 3 and 4 in a Rel-8 codebook, wherein the Rel-8 codebook refers to the codebook defined in 3GPP TS 36.211 V8.9.0; wherein the first set of codewords comprises: using 0.sup.th, 1.sup.st, 2.sup.nd, and 3.sup.rd codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a first group, using 8.sup.th, 9.sup.th, 10.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a second group, selecting 2 codewords from the first group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the second group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 2.sup.nd, 8.sup.th, and 10.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a third group, using 1.sup.st, 3.sup.rd, 9.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a fourth group, selecting 2 codewords from the third group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the fourth group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 2.sup.nd, 3.sup.rd, and 10.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a fifth group, using 2.sup.nd, 8.sup.th, 9.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a sixth group, selecting 2 codewords from the fifth group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the sixth group and putting the 2 codewords in the first set of codewords; or using 0.sup.th, 1.sup.st, 2.sup.nd, and 9.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as a seventh group, using 3.sup.rd, 10.sup.th, 8.sup.th, and 11.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook as an eighth group, selecting 2 codewords from the seventh group and putting the 2 codewords in the first set of codewords, and selecting 2 codewords from the eighth group and putting the 2 codewords in the first set of codewords.

7. A terminal, comprising: a channel state information acquisition unit, configured to acquire channel state information, the channel state information comprising Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information and channel quality information; and a feedback unit, configured to feed back the channel state information in a physical uplink control channel, wherein, when RI=1 or 2, the PMI2 information is 2 bits, and indicates one codeword in a second set of codewords, and the second set of codewords consists of: 0.sup.th, 1.sup.st, 4.sup.th, and 5.sup.th codewords in a codebook corresponding to rank 1 in an LTE-A Rel12 version or 0.sup.th, 1.sup.st, 4.sup.th, and 5.sup.th codewords in a first or second codebook corresponding to rank 2 in the LTE-A Rel12 version, wherein the LTE-A Rel12 version refers to 3GPP TS 36.213 V12.0.0; wherein the terminal feeds back the channel state information to a system having only 4 downlink antenna ports.

8. A terminal, comprising: a channel state information acquisition unit, configured to acquire channel state information, the channel state information comprising Rank Indicator (RI) information, a first class of Precoding Matrix Indicator (PMI1) information and a second class of Precoding Matrix Indicator (PMI2) information; an encoding unit, configured to perform joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report, wherein the feedback report is used for indicating one of a set of combination information formed by the PMI1 and the PMI2, and codewords indicated by the set of combination information comprise codewords in a codebook corresponding to Rank 1 or a first or second codebook corresponding to Rank 2 in a Long Term Evolution-Advanced (LTE-A) Rel12 version, wherein the LTE-A Rel12 version refers to 3GPP TS 36.213 V12.0.0; and a feedback unit, configured to feed back the feedback report in a physical uplink control channel; wherein when the RI=1, the codewords indicated by the set of combination information comprise codewords in the codebook corresponding to Rank 1 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet: a model $\left[\begin{array}{c}u\\ e^{j\frac{m\pi }{4}}.Math.e^{j\frac{n\pi }{2}}.Math.u\end{array}\right]m=0,1n=0,1,2,3,$ wherein u is a 2-dimensional column vector; or wherein when RI=2, codewords indicated by the set of combination information comprise codewords of a first codebook corresponding to Rank 2 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet a model $\left[\begin{array}{cc}{u}_{i_1}& u_{i_2}\\ e^{j{\theta }_m}{u}_{i_1}& -e^{j{\theta }_m}{u}_{i_2}\end{array}\right]i_1,i_2,m=0~15,$ wherein θ.sub.m is any real number, and u.sub.i is a 2-dimensional column vector.

9. The terminal according to claim 8, wherein all of the codewords indicated by the set of combination information meet m=0; or one half of the codewords indicated by the set of combination information meet the model when m=0, and the other half of the codewords indicated by the set of combination information meet the model when m=1; or all of the codewords indicated by the set of combination information meet m=1.

10. The terminal according to claim 8, wherein a set of codewords indicated by the set of combination information is: $\left[\begin{array}{c}{u}_i\\ e^{j{\theta }_i}{u}_i\end{array}\right]i=0~15,$ wherein θ.sub.i is any real number, and u.sub.i is a 2-dimensional column vector.

11. The method according to claim 5, wherein the $u_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$ wherein in {u.sub.i, i=0˜15}, 2 values are $\left[\begin{array}{c}1\\ 1\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ j\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ -1\end{array}\right],$ 2 values are $\hspace{1em}\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ -j\end{array}\right],$ and 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right].$

12. The method according to claim 3, wherein for all the i.sub.1 and i.sub.2, i.sub.1=i.sub.2; or in the codewords, one half of the codewords meet i.sub.2=i.sub.1, and the other half of the codewords meet i.sub.2≠i.sub.1; or $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$ wherein in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\hspace{1em}\left[\begin{array}{c}1\\ 1\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ j\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ -1\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ -j\end{array}\right],$ and 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\hspace{1em}\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]$ respectively; or when RI=2, codewords indicated by the set of combination information comprise codewords of a second codebook corresponding to Rank 2 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet a model $\left[\begin{array}{cc}{u}_{i_1}& u_{i_3}\\ e^{j{\theta }_m}{u}_{i_2}& e^{j{\theta }_n}{u}_{i_4}\end{array}\right]i_1,i_2,i_3,i_4,m,n=0~15,$ wherein θ.sub.m,θ.sub.n are any real numbers, and u.sub.i is a 2-dimensional column vector, wherein the u.sub.i.sub.1,u.sub.i.sub.2,u.sub.i.sub.3,u.sub.i.sub.4 meet i.sub.2=i.sub.1=i.sub.4=i.sub.3.

13. The terminal according to claim 10, wherein $u_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$ wherein in {u.sub.i, i=0˜15}, 2 values are $\left[\begin{array}{c}1\\ 1\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ j\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ -1\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$ 2 values are $\left[\begin{array}{c}1\\ -j\end{array}\right],$ and 2 values are $\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right].$

14. The terminal according to claim 8, wherein for all the i.sub.1 and i.sub.2, i.sub.1=i.sub.2 or in the codewords, one half of the codewords meet i.sub.2=i.sub.1, and the other half of the codewords meet i.sub.2≠i.sub.1; or the $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$ wherein in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ 1\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ j\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ -1\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$ 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are $\left[\begin{array}{c}1\\ -j\end{array}\right],$ and 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are ${\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]}_{}$ respectively; or when the RI=2, codewords indicated by the set of combination information comprise codewords of a second codebook corresponding to Rank 2 in the LTE-A Rel12 version, and the codewords indicated by the set of combination information meet a model $\left[\begin{array}{cc}{u}_{i_1}& u_{i_3}\\ e^{j{\theta }_m}{u}_{i_2}& e^{{\mathrm{j\theta }}_n}{u}_{i_4}\end{array}\right]$ $i_1,i_2,i_3,i_4,m,n=0~15,$ wherein θ.sub.m,θ.sub.n are any real numbers, and u.sub.i is a 2-dimensional column vector, wherein the u.sub.i.sub.1,u.sub.i.sub.2,u.sub.i.sub.3,u.sub.i.sub.4 meet i.sub.2=i.sub.1=i.sub.4=i.sub.3.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a diagram of a method for feeding back channel state information according to an embodiment of the present invention;

(2) FIG. 2 is a diagram of a method for feeding back channel state information according to an embodiment of the present invention;

(3) FIG. 3 is a diagram of a method for feeding back channel state information according to an embodiment of the present invention;

(4) FIG. 4 is a diagram of a method for feeding back channel state information according to an embodiment of the present invention;

(5) FIG. 5 is a block diagram of a terminal according to an embodiment of the present invention;

(6) FIG. 6 is a block diagram of a terminal according to an embodiment of the present invention;

(7) FIG. 7 is a block diagram of a terminal according to an embodiment of the present invention; and

(8) FIG. 8 is a block diagram of a terminal according to an embodiment of the present invention.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTION

(9) The embodiments of the present invention will be described in detail below in conjunction with accompanying drawings. It should be illustrated that without a conflict, the embodiments in the present application and the features in the embodiments can be combined with each other randomly.

(10) In addition, although a logical order is illustrated in the flowchart, in some cases, the steps illustrated or described can be performed in an order different from here.

(11) The embodiments of the present invention provide a method for feeding back channel state information, applied to a 4-antenna system, comprising:

(12) a terminal acquiring channel information, the channel information comprising a first class of Precoding Matrix Indicator (PMI1) information and Rank Indicator (RI) information; the terminal performing joint encoding on the PMI1 information and the RI information into a 4-bit or 5-bit feedback report, wherein the feedback report is used for indicating one of a set of combination information formed by the RI information and the PMI1 information, and the set of combination information comprises:

(13) combination information of information of RI=1 with M1 PMI1 respectively;

(14) combination information of information of RI=2 with M2 PMI1 respectively;

(15) combination information of information of RI=3 with one PMI1;

(16) combination information of information of RI=4 with one PMI1;

(17) wherein M1=M2=4, or M1=16 and M2=8, or M1=8 and M2=16, or M1=16 and M2=4, or M1=4 and M2=16; and

(18) the terminal feeding back the feedback report in a physical uplink control channel.

(19) Alternatively, when RI=1 or RI=2, the 8 PMI1 indexes are 0.sup.th, 2.sup.nd, 4.sup.th, 6.sup.th, 8.sup.th, 10.sup.th, 12.sup.th and 14.sup.th codewords;

(20) alternatively, when RI=1 or RI=2, the 4 PMI1 indexes are 0.sup.th, 4.sup.th, 8.sup.th and 12.sup.th codewords;

(21) alternatively, when RI=1 or RI=2, the 4 PMI1 indexes are 0.sup.th, 2.sup.nd, 4.sup.th and 6.sup.th codewords;

(22) alternatively, the 4 PMI1 indexes respectively corresponding to the extracted codewords when RI=1 and when RI=2 are the same, such as 0, 2, 4, 6, or 0, 4, 8, 12, or 0, 2, 4, 6, 8, 10, 12, 14;

(23) alternatively, the 4 PMI1 indexes respectively corresponding to the extracted codewords when RI=1 and when RI=2 are not the same.

(24) The embodiments of the present invention provide a method for feeding back channel state information, applied to a 4-antenna system, comprising: feeding back Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information, and channel quality information in a physical uplink control channel. When RI=3 or 4, the PMI2 information comprises 2 bits, and indicates one codeword in the set X of codewords. The set X of codewords comprises:

(25) using 0.sup.th, 1.sup.st, 2.sup.nd, and 3.sup.rd codewords in the Rel-8 codebook indicated by the PMI2 indexes as a first group, using 8.sup.th, 9.sup.th, 10.sup.th, and 11.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a second group, and forming the 4 codewords by selecting 2 codewords from the first group and selecting 2 codewords from the second group; wherein the Rel-8 codebook in the present disclosure refers to the codebook defined in 3GPP TS 36.211 V8.9.0. Specifically, the 4 codewords indicated by the 4 PMI2 indexes are:

(26) 8.sup.th, 9.sup.th, 10.sup.th, and 11.sup.th codewords in the Rel-8 Rank3,4 codebook; or

(27) 12.sup.th, 13.sup.th, 14.sup.th, and 15.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(28) 0.sup.th, 2.sup.nd, 12.sup.th, and 14.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(29) 4.sup.th, 5.sup.nd, 6.sup.th, and 7.sup.th codewords of the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(30) 0.sup.th, 1.sup.st, 2.sup.nd, and 3.sup.rd codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(31) 0.sup.th, 1.sup.st, 3.sup.rd, and 10.sup.th codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(32) 0.sup.th, 1.sup.st, 8.sup.th, and 11.sup.th codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(33) 0.sup.th, 1.sup.st, 2.sup.nd and 9.sup.th codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(34) 1.sup.st, 3.sup.rd, 9.sup.th and 11.sup.th codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook; or

(35) 0.sup.th, 2.sup.nd, 8.sup.th and 10.sup.th codewords in the codebook corresponding to Ranks 3 and 4 in the Rel-8 codebook.

(36) Alternatively, using 0.sup.th, 2.sup.nd, 8.sup.th and 10.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a third group, using 1.sup.st, 3.sup.rd, 9.sup.th, and 11.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a fourth group, and forming the 4 codewords by selecting 2 codewords from the third group and selecting 2 codewords from the fourth group.

(37) Alternatively, the 4 PMI2 indexes indicate 0.sup.th, 1.sup.st, 3.sup.rd, and 10.sup.th codewords in the Rel-8 codebook.

(38) Alternatively, the 4 PMI2 indexes indicate 3.sup.rd, 8.sup.th, 10.sup.th, and 11.sup.th codewords in the Rel-8 codebook.

(39) Alternatively, the 4 PMI2 indexes indicate 2.sup.nd, 9.sup.th, 8.sup.th, and 11.sup.th codewords in the Rel-8 codebook.

(40) Alternatively, using 0.sup.th, 2.sup.nd, 3.sup.rd and 10.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a fifth group, using 2.sup.nd, 8.sup.th, 9.sup.th, and 11.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a sixth group, and forming the 4 codewords by selecting 2 codewords from the fifth group and selecting 2 codewords from the sixth group.

(41) Alternatively, the 4 PMI2 indexes indicate 2.sup.nd, 3.sup.rd, 9.sup.th, and 10.sup.th codewords in the Rel-8 codebook.

(42) Alternatively, using 0.sup.th, 1.sup.st, 2.sup.nd and 9.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as a seventh group, using 3.sup.rd, 10.sup.th, 8.sup.th, and 11.sup.th codewords in the Rel-8 codebook indicated by the PMI2 indexes as an eighth group, and forming the 4 codewords by selecting 2 codewords from the seventh group and selecting 2 codewords from the eighth group.

(43) The 4 codewords and the 8 codewords are actually selected by selecting some elements from one large set to form one small set, which needs to have a better quantization efficiency, so as to obtain better performance with minimum information and acquire the tradeoff between the CSI quantization accuracy and the transmission link performance.

(44) The embodiments of the present invention provide a method for feeding back channel state information, applied to a 4-antenna system, comprising: feeding back Rank Indicator (RI) information, a second class of Precoding Matrix Indicator (PMI2) information, subband indication information, and channel quality information in a physical uplink control channel. When RI=1 or 2, the PMI2 comprises 2 bits, and indicates one codeword in a set X of codewords. The set X of codewords comprises:

(45) 0.sup.th, 1.sup.st, 2.sup.nd, and 3.sup.rd codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes; or

(46) 0.sup.th, 1.sup.st, 8.sup.th, and 9.sup.th codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes; or

(47) 0.sup.th, 4.sup.th, 8.sup.th, and 12.sup.th codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes; or

(48) 0.sup.th, 4.sup.th, 5.sup.th, and 12.sup.th codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes; or

(49) 0.sup.th, 1.sup.st, 4.sup.th, and 5.sup.th codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes; or

(50) 12.sup.th, 13.sup.th, 14.sup.th, and 15.sup.th codewords in the codebook of the table 4 or table 5-a or table 5-b indicated by the PMI2 indexes.

(51) The embodiments of the present invention provide a method for feeding back channel state information, applied to a 4-antenna system, comprising: feeding back Rank Indicator (RI) information, a first class of Precoding Matrix Indicator (PMI1) information, and a second class of Precoding Matrix Indicator (PMI2) information in the physical uplink control channel. When RI=1, the terminal performs joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report, and the feedback report is used for indicating one of a set of combination information formed by the PMI1 and the PMI2, and the PMI1 and the second PMI2 indicate codewords in the Rank1 codebook in the LTE-A Rel12 version; wherein the LTE-A Rel12 version in the present disclosure refers to 3GPP TS 36.213 V12.0.0. The codewords indicated by combination information are:

(52) the codewords complying with a model

(53) 0$\left[\begin{array}{c}u\\ e^{j\frac{m\pi }{4}}.Math.e^{j\frac{n\pi }{2}}.Math.u\end{array}\right]m=0,1n=0,1,2,3,$
wherein u is a 2-dimensional column vector.

(54) All codewords meet the model when m=0; or

(55) one half of the codewords meet the model when m=0, and the other half of the codewords meet the model when m=1; or

(56) all codewords fed back in the physical uplink control channel meet the model when m=1.

(57) A set of codewords corresponding to the set of combination information of the PMI1 and the PMI2 is:

(58) $\left[\begin{array}{c}{u}_i\\ e^{j{\theta }_i}{u}_i\end{array}\right]i=0\sim 15,$
wherein θ.sub.i is any real number, and u.sub.i is a 2-dimensional column vector.

(59) $u_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, 8 values are

(60) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
and 8 values are

(61) $\left[\begin{array}{c}1\\ -1\end{array}\right];\mathrm{or}{u}_i\in \left\{\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, 8 values are

(62) $\left[\begin{array}{c}1\\ j\end{array}\right],$
and 8 values are

(63) $\left[\begin{array}{c}1\\ -j\end{array}\right];\mathrm{or}{u}_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, 8 values are

(64) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
and 8 values are

(65) $\left[\begin{array}{c}1\\ j\end{array}\right];\mathrm{or}{u}_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, 4 values are

(66) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
4 values are

(67) 0$\left[\begin{array}{c}1\\ -1\end{array}\right],$
4 values are

(68) $\left[\begin{array}{c}1\\ j\end{array}\right],$
and 4 values are

(69) $\left[\begin{array}{c}1\\ -j\end{array}\right];\mathrm{or}{u}_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, 2 values are

(70) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
2 values are

(71) $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$
2 values are

(72) $\left[\begin{array}{c}1\\ j\end{array}\right],$
2 values are

(73) $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$
2 values are

(74) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
2 values are

(75) $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$
2 values are

(76) $\left[\begin{array}{c}1\\ -j\end{array}\right],$
and 2 values are

(77) 0$\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right].$

(78) Alternatively,

(79) $u_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\right\},$
in {u.sub.i, i=0˜15}, when 4 values of u.sub.i are

(80) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
m=0, when 4 values of u.sub.i are

(81) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
m=1, when 4 values of u.sub.i are

(82) $\left[\begin{array}{c}1\\ j\end{array}\right],$
m=0, and when 4 values of u.sub.i are

(83) $\left[\begin{array}{c}1\\ -j\end{array}\right],$
m=1.

(84) Alternatively,

(85) $u_i\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$
wherein, in {u.sub.i, i=0˜15}, when 2 values of u.sub.i are

(86) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
m=0, when 2 values of u.sub.i are

(87) $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$
m=0, when 2 values of u.sub.i are

(88) $\left[\begin{array}{c}1\\ j\end{array}\right],$
m=0, when 2 values of u.sub.i are

(89) 0$\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$
m=0, when 2 values of u.sub.i are

(90) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
m=1, when 2 values of u.sub.i are

(91) $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$
m=1, when 2 values of u.sub.i are

(92) $\left[\begin{array}{c}1\\ -j\end{array}\right],$
m=1, and when 2 values of u.sub.i are

(93) $\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right],$
m=1.

(94) When RI=2, the terminal performs joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report; the feedback report is used for indicating one of a set of combination information formed by the PMI1 and the PMI2, and the PMI1 and the PMI2 indicate codewords in the codebook of table 5-a of the Rank2 in the LTE-A Rel12 version. The codewords indicated by combination information are characterized in that:

(95) the codewords comply with a model

(96) $\left[\begin{array}{cc}{u}_{i_1}& u_{i_2}\\ e^{j{\theta }_m}{u}_{i_1}& -e^{j{\theta }_m}{u}_{i_2}\end{array}\right]i_1,i_2,m=0\sim 15,$
wherein θ.sub.m may be any real number, and u.sub.i is a 2-dimensional column vector.

(97) in the model, for all i.sub.1 and i.sub.2, i.sub.1=i.sub.2; or

(98) in the codewords, one half of the codewords meet i.sub.2=i.sub.1, and the other half of the codewords meet i.sub.2≠i.sub.1.

(99) $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\right\},$
wherein, in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(100) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
and 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(101) ${\left[\begin{array}{c}1\\ -1\end{array}\right]}_{}$
respectively; or

(102) $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\right\},$
wherein, in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(103) 0$\left[\begin{array}{c}1\\ j\end{array}\right],$
and 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(104) ${\left[\begin{array}{c}1\\ -j\end{array}\right]}_{}$
respectively; or

(105) $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ 1\end{array}\right]\right\},$
wherein, in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(106) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
and 8 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(107) ${\left[\begin{array}{c}1\\ j\end{array}\right]}_{}$
respectively; or

(108) $u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\right\},$
wherein, in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 6 values of u.sub.i.sub.1 are

(109) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
2 values of u.sub.i.sub.1 are

(110) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
6 values of u.sub.i.sub.1 are

(111) $\left[\begin{array}{c}1\\ j\end{array}\right],$
and 2 values of u.sub.i.sub.1 are

(112) $\left[\begin{array}{c}1\\ -j\end{array}\right];$
and 2 values of u.sub.i.sub.2 are

(113) 0$\left[\begin{array}{c}1\\ 1\end{array}\right],$
4 values of u.sub.i.sub.2 are

(114) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
4 values of u.sub.i.sub.2 are

(115) $\left[\begin{array}{c}1\\ j\end{array}\right],$
and 6 values of u.sub.i.sub.2 are

(116) $\left[\begin{array}{c}1\\ -j\end{array}\right];\mathrm{or}$$u_{i_1},u_{i_2}\in \left\{\left[\begin{array}{c}1\\ 1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -1\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right]\left[\begin{array}{c}1\\ -j\end{array}\right]\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\right\},$
wherein, in {u.sub.i.sub.1,u.sub.i.sub.2, i=0˜15}, 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(117) $\left[\begin{array}{c}1\\ 1\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(118) $\left[\begin{array}{c}1\\ e^{j\frac{\pi }{4}}\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(119) $\left[\begin{array}{c}1\\ j\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(120) $\left[\begin{array}{c}1\\ e^{j\frac{3\pi }{4}}\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(121) $\left[\begin{array}{c}1\\ -1\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(122) $\left[\begin{array}{c}1\\ e^{j\frac{5\pi }{4}}\end{array}\right],$
2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(123) 00$\left[\begin{array}{c}1\\ -j\end{array}\right],$
and 2 values of u.sub.i.sub.1,u.sub.i.sub.2 are

(124) 01$\left[\begin{array}{c}1\\ e^{j\frac{7\pi }{4}}\end{array}\right]\hspace{1em}$
respectively.

(125) When RI=2, the terminal performs joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report; the feedback report is used for indicating one of a set of combination information formed by the PMI1 and the PMI2, and the PMI1 and the PMI2 indicate codewords in the Rank2-b codebook in the LTE-A Rel12 version. The codewords indicated by combination information are characterized in that:

(126) the codewords comply with a model

(127) 02$\left[\begin{array}{cc}{u}_{i_1}& u_{i_3}\\ e^{j{\theta }_m}{u}_{i_2}& e^{j{\theta }_n}{u}_{i_4}\end{array}\right]i_1,i_2,i_3,i_4,m,n=0\sim 15,$
wherein θ.sub.m,θ.sub.n may be any real numbers, and u.sub.i is a 2-dimensional column vector.

(128) For all the u.sub.i.sub.1,u.sub.i.sub.2,u.sub.i.sub.3,u.sub.i.sub.4 in the codeword model, i.sub.2=i.sub.1=i.sub.4=i.sub.3; or

(129) all codewords meet i.sub.2=i.sub.1 and i.sub.4=i.sub.3, and one half of the codewords meet i.sub.2=.sub.1=i.sub.4=i.sub.3, and the other half of the codewords meet i.sub.1≠i.sub.3; or

(130) all codewords meet i.sub.2=i.sub.1 and i.sub.4=i.sub.3, and the number of codewords which meet i.sub.2=i.sub.1=i.sub.4=i.sub.3 is more than the number of codewords which meet i.sub.1≠i.sub.3; or

(131) one half of the codewords meet i.sub.2=i.sub.1=i.sub.4=i.sub.3, a quarter of the codewords meet i.sub.2=i.sub.1, i.sub.4=i.sub.3 and i.sub.1≠i.sub.3, and a quarter of the codewords meet i.sub.1=i.sub.4, i.sub.2=i.sub.3, and i.sub.1≠i.sub.2.

(132) The embodiment provides a method for feeding back channel state information. FIG. 1 is a first flowchart of the channel feedback method according to the embodiment of the present invention. As shown in FIG. 1, the method comprises the following steps.

(133) In step S102, a terminal acquires channel state information, wherein the channel state information comprises a first class of Precoding Matrix Indicator (PMI1) information and Rank Indicator (RI) information.

(134) In step S104, the terminal performs joint encoding on the PMI1 information and the RI information into a 5-bit feedback report.

(135) In step S106, the terminal feeds back the feedback report in a physical uplink control channel.

(136) With the above steps, joint encoding is performed on the PMI1 and the RI in the channel state information, and the 5-bit feedback report is obtained and is fed back, which overcomes the problem in the related art that the transmission performance of the system is poor due to a large overhead of the feedback channel information, reduces the overhead of the channel information feedback, and improves performance of a terminal feeding back the channel information, thereby improving the transmission performance of the system. The above 5-bit feedback report is used for indicating one of a set of combination information formed by the RI information and the PMI1 information. The set comprises N elements, wherein N is more than 16 and less than or equal to 32.

Embodiment 1-1-1

(137) Alternatively, the RI/PMI1 joint encoded set is shown in the following table 6:

(138) TABLE-US-00007 TABLE 6 5 bits in total, information of RI and a part of i.sub.1 0-7  RI = 1: 8 indexes of i.sub.1 8-15 RI = 2: 8 indexes of i.sub.1 16 RI = 3: 1 index of i.sub.1 17 RI = 4: 1 index of i.sub.1

Embodiment 1-1-2

(139) Alternatively, the RI/PMI1 joint encoded set is shown in the following table 7:

(140) TABLE-US-00008 TABLE 7 5 bits in total, information of RI and a part of i.sub.1  0-15 RI = 1: 16 indexes of i.sub.1 16-23 RI = 2: 8 indexes of i.sub.1 24 RI = 3: 1 index of i.sub.1 25 RI = 4: 1 index of i.sub.1 26-31 Reserved

Embodiment 1-1-3

(141) Alternatively, the RI/PMI1 joint encoded set is shown in the following table 8:

(142) TABLE-US-00009 TABLE 8 5 bits in total, information of RI and a part of i.sub.1 0-7 RI = 1: 8 indexes of i.sub.1  8-23 RI = 2: 16 indexes of i.sub.1 24 RI = 3: 1 index of i.sub.1 25 RI = 4: 1 index of i.sub.1 26-31 Reserved

(143) Alternatively, joint encoding may also be performed on the PMI1 and the RI in the channel information, and a 4-bit feedback report is obtained and is fed back, which comprises the following steps, as shown in FIG. 2.

(144) In step S202, a terminal acquires channel state information, the channel state information comprising PMI1 information and RI information.

(145) In step S204, the terminal performs joint encoding on the PMI1 information and the RI information into a 4-bit feedback report.

(146) In step S206, the terminal feeds back the feedback report in a physical uplink control channel.

(147) The above 4-bit feedback report is used for indicating one of a set of combination information formed by the RI information and the PMI1. The set comprises N elements, wherein N is more than 8 and less than or equal to 16.

(148) The above steps overcome the problem in the related art that the transmission performance of the system is poor due to a large overhead of the feedback channel information, reduces the overhead of the channel information feedback, and improves performance of a terminal feeding back the channel information, thereby improving the transmission performance of the system. The N elements are actually selected by selecting some elements from one large set to form one small set, which needs to have a better quantization efficiency, so as to obtain better performance with minimum information and acquire the tradeoff between the CSI quantization accuracy and the transmission link performance.

(149) The following is specific embodiments when codewords are extracted specifically.

Embodiment 1-1

(150) The joint encoding table is as follows:

(151) TABLE-US-00010 TABLE 9 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 4, 8, 12 4-7 2 0, 4, 8, 12 8 3 0 9 4 0 10-15 Reserved NA

(152) Values of a joint encoding table are as follows: by taking a first row as an example, when the value of the feedback report is 0, RI=1 and i.sub.1=0; when the value of the feedback report is 1, RI=1 and i.sub.1=4; when the value of the feedback report is 2, RI=1 and i.sub.1=8; and when the value of the feedback report is 3, RI=1 and i.sub.1=12.

Embodiment 1-2

(153) The joint encoding table is as follows:

(154) TABLE-US-00011 TABLE 10 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 2, 4, 6 4-7 2 0, 2, 4, 6 8 3 0 9 4 0 10-15 Reserved NA

Embodiment 1-3

(155) The joint encoding table is as follows:

(156) TABLE-US-00012 TABLE 11 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-7 1 0, 2, 4, 6, 8, 10, 12, 14  8-15 2 0, 2, 4, 6, 8, 10, 12, 14 16 3 0 17 4 0 18-31 Reserved NA

Embodiment 1-4

(157) The joint encoding table is as follows:

(158) TABLE-US-00013 TABLE 12 I.sub.RI/PMI1 RI Codebook index i.sub.1  0-15 1 0-15 16-23 2 0, 2, 4, 6, 8, 10, 12, 14 24 3 0 25 4 0 26-31 Reserved NA

Embodiment 1-5

(159) The joint encoding table is as follows:

(160) TABLE-US-00014 TABLE 13 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-7 1 0, 2, 4, 6, 8, 10, 12, 14  8-23 2 0-15 24 3 0 25 4 0 26-31 Reserved NA

Embodiment 1-6

(161) The joint encoding table is as follows:

(162) TABLE-US-00015 TABLE 14 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 4 , 8, 12 4-7 2 0, 2, 4, 6 8 3 0 9 4 0 10-15 Reserved NA

Embodiment 1-7

(163) The joint encoding table is as follows:

(164) TABLE-US-00016 TABLE 15 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 2, 4, 6 4-7 2 0, 4, 8, 12 8 3 0 9 4 0 10-15 Reserved NA

Embodiment 1-8

(165) The joint encoding table is as follows:

(166) TABLE-US-00017 TABLE 16 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-7 1 0, 2, 4, 6, 8, 10, 12, 14  8-11 2 0, 4, 8, 12 12 3 0 13 4 0 14-15 Reserved NA

Embodiment 1-9

(167) The joint encoding table is as follows:

(168) TABLE-US-00018 TABLE 17 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 2, 4, 6  4-11 2 0, 2, 4, 6, 8, 10, 12, 14 12 3 0 13 4 0 14-15 Reserved NA

Embodiment 1-10

(169) The joint encoding table is as follows:

(170) TABLE-US-00019 TABLE 18 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-7 1 0, 2, 4, 6, 8, 10, 12, 14  8-11 2 0, 2, 4, 6 12 3 0 13 4 0 14-15 Reserved NA

Embodiment 1-11

(171) The joint encoding table is as follows:

(172) TABLE-US-00020 TABLE 19 I.sub.RI/PMI1 RI Codebook index i.sub.1 0-3 1 0, 4, 8, 12  4-11 2 0, 2, 4, 6, 8, 10, 12, 14 12 3 0 13 4 0 14-15 Reserved NA

(173) The embodiment provides a method for feeding back channel state information, which comprises the following steps, as shown in FIG. 3.

(174) In step S302, a terminal acquires channel information, the channel information comprising a first class of Precoding Matrix Indicator (PMI1) information and a second class of Precoding Matrix Indicator (PMI2) information.

(175) In step S304, the terminal performs joint encoding on the PMI1 information and the PMI2 information into a 4-bit feedback report.

(176) In step S306, the terminal feeds back the feedback report in a physical uplink control channel.

(177) With the method, the overhead of the PMI1 and the PMI2 can be effectively reduced, and it can be ensured that the performance will not be reduced significantly.

(178) The 4-bit feedback report corresponds to 16 combinations of the PMI1 and the PMI2. The combination of the PMI1 and the PMI2 corresponds to codewords in the LTE-A Rel 12.

(179) When RI=1, the embodiment is described as follows.

Embodiment 2-1-1

(180) TABLE-US-00021 TABLE 20 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 1 0-3 0, 4, 8, 12 0-3 0, 2, 9, 11/0, 2, 8, 10

Embodiment 2-1-2

(181) TABLE-US-00022 TABLE 21 Relationship between PMI1 and Relationship between PMI2 and the the codebook index i.sub.1 codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 1 0-1 0, 4 0-7 0, 2, 4, 6, 9, 11, 13, 15/ 0, 2, 4, 6, 8, 10, 12, 14/0, 1, 2, 3, 8, 9, 10, 11

Embodiment 2-1-3

(182) TABLE-US-00023 TABLE 22 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 1 0-1 0, 8 0-7 0, 1, 2, 3, 8, 9, 10, 11

Embodiment 2-1-4

(183) TABLE-US-00024 TABLE 23 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI1 Codebook index i.sub.2 1 0-1 0, 8 0-7 0, 1, 2, 3, 8, 9, 10, 11

Embodiment 2-1-5

(184) TABLE-US-00025 TABLE 24 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 1 0 0 0-15 0-15

(185) For the condition of Rank2, the embodiment is described as follows.

Embodiment 2-2-1

(186) TABLE-US-00026 TABLE 25 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 2 0 0 0-15 0-15

Embodiment 2-2-2

(187) TABLE-US-00027 TABLE 26 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 2 0 8 0-15 0-15

Embodiment 2-2-3

(188) TABLE-US-00028 TABLE 27 Relationship between PMI1 and Relationship between PMI2 the codebook index i.sub.1 and the codebook index i.sub.2 RI I.sub.PMI1 Codebook index i.sub.1 I.sub.PMI2 Codebook index i.sub.2 2 0-1 0, 4 0-7 0, 1, 2, 3, 4, 5, 6, 7

(189) The embodiments of the present invention further provide a method for feeding back channel state information, which comprises the following steps, as shown in FIG. 4.

(190) In step S401, a terminal acquires channel information, wherein the channel information at least comprises a second class of Precoding Matrix Indicator (PMI2) information and Channel Quality Information (CQI) corresponding to a subband and subband position indication information; and the terminal generates a feedback report and the PMI2 occupies 2 bits;

(191) In step S403, the terminal feeds back the feedback report in the physical uplink control channel.

(192) With the above steps, when a subband PMI2 is fed back, some codewords only are extracted from the original codebook to form a new codebook for quantizing the feedback; and during Ranks 3 and 4, the overhead corresponding to the feedback of the subband PMI2 is merely 2 bits, and the corresponding 4 codewords are described in the following embodiments.

Embodiment 3-1

(193) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(194) TABLE-US-00029 TABLE 28 Rank3 Rank4 codewords codewords 0 PMI2 is 0 03$\hspace{1em}\left[\begin{array}{ccc}1& 1& 1\\ 1& 1& -1\\ 1& -1& -1\\ 1& -1& 1\end{array}\right]$ 04$\hspace{1em}\left[\begin{array}{cccc}1& 1& 1& 1\\ 1& 1& -1& -1\\ 1& -1& 1& -1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 1 05$\hspace{1em}\left[\begin{array}{ccc}1& -j& -1\\ j& 1& j\\ -1& -j& 1\\ -j& 1& -j\end{array}\right]$ 06$\hspace{1em}\left[\begin{array}{cccc}1& -j& -1& j\\ j& 1& j& 1\\ -1& -j& 1& j\\ -j& 1& -j& 1\end{array}\right]$ 2 PMI2 is 2 07$\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ -1& -1& 1\end{array}\right]$ 08$\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& -1\\ 1& 1& -1& -1\\ 1& 1& 1& 1\\ 1& -1& -1& 1\end{array}\right]$ 3 PMI2 is 9 09$\hspace{1em}\left[\begin{array}{ccc}1& 1& -j\\ j& -j& -1\\ 1& 1& j\\ j& -j& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& -j& 1& -j\\ j& 1& -j& -1\\ 1& j& 1& j\\ j& -1& -j& 1\end{array}\right]$

Embodiment 3-2

(195) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(196) TABLE-US-00030 TABLE 29 Rank3 Rank4 codewords codewords 0 PMI2 is 1 $\hspace{1em}\left[\begin{array}{ccc}1& -j& -1\\ j& 1& j\\ -1& -j& 1\\ -j& 1& -j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -j& -1& j\\ j& 1& j& 1\\ -1& -j& 1& j\\ -j& 1& -j& 1\end{array}\right]$ 1 PMI2 is 3 $\hspace{1em}\left[\begin{array}{ccc}1& j& -1\\ -j& 1& -j\\ -1& j& 1\\ j& 1& j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& j& -1& -j\\ -j& 1& -j& 1\\ -1& j& 1& -j\\ j& 1& j& 1\end{array}\right]$ 2 PMI2 is 9 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -j\\ j& -j& -1\\ 1& 1& j\\ j& -j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -j& 1& -j\\ j& 1& -j& -1\\ 1& j& 1& j\\ j& -1& -j& 1\end{array}\right]$ 3 PMI2 is 11 $\hspace{1em}\left[\begin{array}{ccc}1& 1& j\\ -j& j& -1\\ 1& 1& -j\\ -j& j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& j& 1& j\\ -j& 1& j& -1\\ 1& -j& 1& -j\\ -j& -1& j& 1\end{array}\right]$

Embodiment 3-3

(197) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(198) TABLE-US-00031 TABLE 30 Rank3 Rank4 codewords codewords 0 PMI2 is 0 $\hspace{1em}\left[\begin{array}{ccc}1& 1& 1\\ 1& 1& -1\\ 1& -1& -1\\ 1& -1& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& 1& 1& 1\\ 1& 1& -1& -1\\ 1& -1& 1& -1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 2 $\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ -1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& -1\\ 1& 1& -1& -1\\ 1& 1& 1& 1\\ 1& -1& -1& 1\end{array}\right]$ 2 PMI2 is 8 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -1\\ 1& 1& 1\\ -1& 1& -1\\ -1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& -1& -1\\ 1& 1& 1& 1\\ -1& 1& 1& -1\\ -1& 1& -1& 1\end{array}\right]$ 3 PMI2 is 10 $\hspace{1em}\left[\begin{array}{ccc}1& -1& -1\\ -1& 1& -1\\ -1& -1& 1\\ 1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& -1& 1\\ -1& -1& 1& 1\\ -1& 1& -1& 1\\ 1& 1& 1& 1\end{array}\right]$

Embodiment 3-4

(199) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(200) TABLE-US-00032 TABLE 31 Rank3 Rank4 codewords codewords 0 PMI2 is 0 $\hspace{1em}\left[\begin{array}{ccc}1& 1& 1\\ 1& 1& -1\\ 1& -1& -1\\ 1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& 1& 1\\ 1& 1& -1& -1\\ 1& -1& 1& -1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 1 $\hspace{1em}\left[\begin{array}{ccc}1& -j& -1\\ j& 1& j\\ -1& -j& 1\\ -j& 1& -j\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& -j& -1& j\\ j& 1& j& 1\\ -1& -j& 1& j\\ -j& 1& -j& 1\end{array}\right]$ 2 PMI2 is 3 $\hspace{1em}\left[\begin{array}{ccc}1& j& -1\\ -j& 1& -j\\ -1& j& 1\\ j& 1& j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& j& -1& -j\\ -j& 1& -j& 1\\ -1& j& 1& -j\\ j& 1& j& 1\end{array}\right]$ 3 PMI2 is 10 $\hspace{1em}\left[\begin{array}{ccc}1& -1& -1\\ -1& 1& -1\\ -1& -1& 1\\ 1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& -1& 1\\ -1& -1& 1& 1\\ -1& 1& -1& 1\\ 1& 1& 1& 1\end{array}\right]$

Embodiment 3-5

(201) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(202) TABLE-US-00033 TABLE 32 Rank3 Rank4 codewords codewords 0 PMI2 is 2 $\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ -1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& -1\\ 1& 1& -1& -1\\ 1& 1& 1& 1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 8 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -1\\ 1& 1& 1\\ -1& 1& -1\\ -1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& -1& -1\\ 1& 1& 1& 1\\ -1& 1& 1& -1\\ -1& 1& -1& 1\end{array}\right]$ 2 PMI2 is 9 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -j\\ j& -j& -1\\ 1& 1& j\\ j& -j& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& -j& 1& -j\\ j& 1& -j& -1\\ 1& j& 1& j\\ j& -1& -j& 1\end{array}\right]$ 3 PMI2 is 11 $\hspace{1em}\left[\begin{array}{ccc}1& 1& j\\ -j& j& -1\\ 1& 1& -j\\ -j& j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& j& j\\ -j& j& 1& -1\\ 1& 1& -j& -j\\ -j& j& -1& 1\end{array}\right]$

Embodiment 3-6

(203) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(204) TABLE-US-00034 TABLE 33 Rank3 Rank4 codewords codewords 0 PMI2 is 2 $\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ -1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& -1\\ 1& 1& -1& -1\\ 1& 1& 1& 1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 3 $\hspace{1em}\left[\begin{array}{ccc}1& j& -1\\ -j& 1& -j\\ -1& j& 1\\ j& 1& j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& j& -1& -j\\ -j& 1& -j& 1\\ -1& j& 1& -j\\ j& 1& j& 1\end{array}\right]$ 2 PMI2 is 9 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -j\\ j& -j& -1\\ 1& 1& j\\ j& -j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -j& 1& -j\\ j& 1& -j& -1\\ 1& j& 1& j\\ j& -1& -j& 1\end{array}\right]$ 3 PMI2 is 10 $\hspace{1em}\left[\begin{array}{ccc}1& -1& -1\\ -1& 1& -1\\ -1& -1& 1\\ 1& 1& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& -1& -1& 1\\ -1& -1& 1& 1\\ -1& 1& -1& 1\\ 1& 1& 1& 1\end{array}\right]$

Embodiment 3-7

(205) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(206) TABLE-US-00035 TABLE 34 Rank3 Rank4 codewords codewords 0 PMI2 is 0 $\hspace{1em}\left[\begin{array}{ccc}1& 1& 1\\ 1& 1& -1\\ 1& -1& -1\\ 1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& 1& 1\\ 1& 1& -1& -1\\ 1& -1& 1& -1\\ 1& -1& -1& 1\end{array}\right]$ 1 PMI2 is 1 $\hspace{1em}\hspace{1em}\left[\begin{array}{ccc}1& -j& -1\\ j& 1& j\\ -1& -j& 1\\ j& 1& -j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -j& -1& j\\ j& 1& j& 1\\ -1& -j& 1& j\\ -j& 1& -j& 1\end{array}\right]$ 2 PMI2 is 2 $\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ -1& -1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& -1\\ 1& 1& -1& -1\\ 1& 1& 1& 1\\ 1& -1& -1& 1\end{array}\right]$ 3 PMI2 is 3 $\hspace{1em}\left[\begin{array}{ccc}1& j& -1\\ -j& 1& -j\\ -1& j& 1\\ j& 1& j\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& j& -1& -j\\ -j& 1& -j& 1\\ -1& j& 1& -j\\ j& 1& j& 1\end{array}\right]$

Embodiment 3-8

(207) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(208) TABLE-US-00036 TABLE 35 Rank3 Rank4 codewords codewords 0 PMI2 is 8 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -1\\ 1& 1& 1\\ -1& 1& -1\\ -1& 1& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& 1& -1& -1\\ 1& 1& 1& 1\\ -1& 1& 1& -1\\ -1& 1& -1& 1\end{array}\right]$ 1 PMI2 is 9 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -j\\ j& -j& -1\\ 1& 1& j\\ j& -j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -j& 1& -j\\ j& 1& -j& -1\\ 1& j& 1& j\\ j& -1& -j& 1\end{array}\right]$ 2 PMI2 is 10 $\hspace{1em}\left[\begin{array}{ccc}1& -1& -1\\ -1& 1& -1\\ -1& -1& 1\\ 1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& -1& 1\\ -1& -1& 1& 1\\ -1& 1& -1& 1\\ 1& 1& 1& 1\end{array}\right]$ 3 PMI2 is 11 $\hspace{1em}\left[\begin{array}{ccc}1& 1& j\\ -j& j& -1\\ 1& 1& -j\\ -j& j& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& j& j\\ -j& j& 1& -1\\ 1& 1& -j& -j\\ -j& j& -1& 1\end{array}\right]$

Embodiment 3-9

(209) When the codewords included in the Rank3,4 codebook are codewords in the Rel-8 Rank3,4 codebook illustrated in table 2, preferably, the 4 codewords extracted therefrom may be as follows.

(210) TABLE-US-00037 TABLE 36 Rank3 Rank4 codewords codewords 0 PMI2 is 12 $\hspace{1em}\left[\begin{array}{ccc}1& 1& 1\\ 1& 1& -1\\ 1& -1& 1\\ -1& 1& 1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& 1& 1& -1\\ 1& 1& -1& 1\\ 1& -1& 1& 1\\ -1& 1& 1& 1\end{array}\right]$ 1 PMI2 is 13 $\hspace{1em}\left[\begin{array}{ccc}1& 1& -1\\ 1& 1& 1\\ -1& 1& 1\\ 1& -1& 1\end{array}\right]$ 0$\hspace{1em}\left[\begin{array}{cccc}1& 1& -1& 1\\ 1& 1& 1& -1\\ -1& 1& 1& 1\\ 1& -1& 1& 1\end{array}\right]$ 2 PMI2 is 14 $\hspace{1em}\left[\begin{array}{ccc}1& -1& 1\\ -1& 1& 1\\ 1& 1& 1\\ 1& 1& -1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& 1& 1\\ 1& 1& -1& 1\\ 1& 1& 1& -1\\ -1& 1& 1& 1\end{array}\right]$ 3 PMI2 is 15 $\hspace{1em}\left[\begin{array}{ccc}1& -1& -1\\ -1& 1& -1\\ -1& -1& 1\\ -1& -1& -1\end{array}\right]$ $\hspace{1em}\left[\begin{array}{cccc}1& -1& -1& -1\\ -1& 1& -1& -1\\ -1& -1& 1& -1\\ -1& -1& -1& 1\end{array}\right]$