CLOSED-LOOP TRANSMISSION FEEDBACK IN WIRELESS COMMUNICATION SYSTEMS
A method and apparatus for providing channel feedback is provided herein. During operation a covariance matrix at time t (R) is calculated by the mobile as a function of a received downlink signal. In order to reduce overhead, R is normalized and quantized by the mobile using multiple codebook entries plus at least one constant for quantization. The mobile then transmits the normalized and quantized covariance matrix back to the base station as bit values indicating the selected entries from the codebook plus bit values corresponding to the at least one constant. The base unit then uses the covariance matrix estimate to determine appropriate channel beamforming weights, and instructs transmit beamforming circuitry to use the appropriate weights.
1 . A method for closed-loop transmission feedback in wireless communication system, the method comprising the steps of:
receiving by a wireless node, a request for a codebook-based covariance matrix (CBCM) feedback;
calculating by the wireless node, a covariance matrix (R) as a function of a received downlink signal;
quantizing, by the wireless node, the covariance matrix (R) into indices using at least a rank two approximation of the covariance matrix; and
transmitting the indices for the quantized covariance matrix.
2 . The method of claim 1 wherein the step of quantizing the covariance matrix into indices using at least a rank two approximation of the covariance matrix includes the step of quantizing the covariance matrix as a function of at least two vectors selected from a codebook of vectors and where the indices are codebook indices.
3 . The method of claim 2 wherein the step of quantizing the covariance matrix includes the step of at least one b bit scalar quantization.
4 . The method of claim 1 wherein the step of quantizing the covariance matrix includes the step of normalizing the covariance matrix (R).
5 . The method of claim 4 wherein the step of normalizing R is accomplished by setting R=R/trace(R).
6 . The method of claim 1 wherein the received downlink signal comprises pilot symbols.
7 . The method of claim 1 wherein the step of quantizing R comprises the steps of:
finding the dominant eigenvector (u 1 ) of R, and its eigenvalue q 1 ;
determining e 1 as the quantization of q 1 to b bits;
choosing v 1 as the vector from V that is closest to u 1 ;
computing {tilde over (R)}=R−e 1 v 1 v 1 H ;
finding a dominant eigenvector (u 2 ) of {tilde over (R)} and its eigenvalue q 2 ;
determining e 2 as the quantization of q 2 to b bits;
choosing v 2 as the vector from V that is closest to u 2 ; and
transmitting codebook indices of v 1 and v 2 along with e 1 and e 2 .
8 . The method of claim 1 wherein the step of transmitting the indices causes a base station to use appropriate channel beamforming weights.
9 . An apparatus comprising:
a receiver receiving a request for a codebook-based covariance matrix (CBCM) feedback;
circuitry calculating a covariance matrix (R) as a function of a received downlink signal, and quantizing the covariance matrix (R) into indices using at least a rank two approximation of the covariance matrix; and
a transmitter transmitting the indices for the quantized covariance matrix.
10 . The apparatus of claim 9 wherein quantizing the covariance matrix includes the step of normalizing the covariance matrix (R).
11 . The apparatus of claim 9 wherein quantizing the covariance matrix into indices using at least a rank two approximation of the covariance matrix includes the step of quantizing the covariance matrix as a function of at least two vectors selected from a codebook of vectors and where the indices are codebook indices.
12 . The apparatus of claim 9 wherein quantizing the covariance matrix includes the step of at least one b bit scalar quantization.
13 . The apparatus of claim 9 wherein the received downlink signal comprises pilot symbols.
14 . The apparatus of claim 10 wherein normalizing R is accomplished by setting R=R/trace(R).
15 . The apparatus of claim 9 wherein quantizing R comprises:
finding the dominant eigenvector (u 1 ) of R, and its eigenvalue q 1 ;
determining e 1 as the quantization of q 1 to b bits;
choosing v 1 as the vector from V that is closest to u 1 ;
computing {tilde over (R)}=R−e 1 v 1 v 1 H ;
finding a dominant eigenvector (u 2 ) of {tilde over (R)} and its eigenvalue q 2 ;
determining e 2 as the quantization of q 2 to b bits;
choosing v 2 as the vector from V that is closest to u 2 ; and
transmitting codebook indices of v 1 and v 2 along with e 1 and e 2 .
16 . The apparatus of claim 9 wherein transmitting the indices for the quantized covariance matrix causes a base station to use appropriate channel beamforming weights.