Closed-loop transmission feedback in wireless communication systems
View Patent ↗An orthogonal frequency division multiplexing wireless communication terminal, that communicates with a base unit, obtains a set of analog coefficients by transforming a transmit spatial covariance matrix, modulates the set of analog coefficients onto multiple channels to form a feedback waveform, and transmits the feedback waveform to the base unit.
1. A method in an orthogonal frequency division multiplexing (OFDM) wireless communication terminal, the method comprising:
computing a transmit spatial covariance matrix corresponding to a channel estimated on a first set of two or more OFDM subcarriers corresponding to a received waveform;
obtaining a set of analog coefficients by transforming the transmit spatial covariance matrix;
modulating the set of analog coefficients onto a first portion of a second set of two or more OFDM subcarriers corresponding to a transmitted waveform, where each analog coefficient is mapped to a single OFDM subcarrier; and
modulating a pilot symbol onto a second portion of the second set of OFDM subcarriers, where the pilot symbol is from a finite constellation of complex symbols.
2. The method of claim 1 , wherein transforming the transmit spatial covariance matrix comprises:
extracting a set of entries of the transmit spatial covariance matrix; and
obtaining the set of analog coefficients based on the extracted set of entries.
3. The method of claim 2 further comprising transforming the set of entries by a spreading code to obtain the set of analog coefficients.
4. The method of claim 1 , wherein transforming the transmit spatial covariance matrix comprises
computing an eigenvector of the spatial covariance matrix,
scaling the eigenvector,
obtaining entries of the scaled eigenvector as the set of analog coefficients.
5. The method of claim 4 , wherein scaling includes multiplying the eigenvector by an associated factor based on a corresponding eigenvalue.
6. The method of claim 4 , wherein scaling includes multiplying the eigenvector by an associated factor based on a corresponding eigenvalue of a signal to noise ratio.
7. The method of claim 4 , wherein scaling includes multiplying the eigenvector by a factor chosen by the wireless communication terminal.
8. The method of claim 1 further comprising:
computing multiple transmit spatial covariance matrices, each of the multiple spatial covariance matrices corresponding to a channel estimated on a corresponding set of two or more OFDM subcarriers corresponding to the received waveform
obtaining a set of analog coefficients by transforming each of the transmit spatial covariance matrices.
9. The method of claim 1 further comprising receiving a message indicating the first set of two or more OFDM subcarriers corresponding to the received waveform.
10. The method of claim 1 , obtaining the set of analog coefficients without quantization.
11. The method of claim 1 further comprising receiving a message indicating the second set of two or more OFDM subcarriers corresponding to the transmitted waveform.
12. The method of claim 1 , wherein the transmit spatial covariance matrix is transformed to a second matrix wherein all diagonal elements of the second matrix are equal, and wherein the analog coefficients are obtained by extracting two or more entries of the second matrix.
13. The method of claim 12 ,
wherein the transmit spatial covariance matrix is transformed to the second matrix using the following transformation
μ
=
1
N
T
∑
i
=
1
N
T
R
ii
Φ
=
diag
(
μ
R
11
,
μ
R
22
,
…
μ
R
N
T
N
T
)
R
~
=
Φ
R
Φ
where N T is the number of transmit antennas, R is the transmit spatial covariance matrix, R ii is the (i)th diagonal entry of the transmit spatial covariance matrix, i is an integer, R T the second matrix, and all diagonal elements of the second matrix are equal;
the analog coefficients are based on an extracted set of entries L, where L=N T (N T +1)/2−(N T −1) unique entries of the second matrix obtained by exploiting Hermitian symmetry of the second matrix (R T,ii =conj(R T,ji ) R T,ij being the (i,j)th entry of the second matrix) and selecting one diagonal element.
14. A orthogonal frequency division multiplexing (OFDM) wireless communication base unit comprising:
a processor
the processor is configured to obtain analog coefficients from a first portion of a second set of two or more OFDM subcarriers based on pilot symbols modulated on a second portion of the second set of two or more OFDM subcarriers, wherein the second set of two or more OFDM subcarriers correspond to a waveform received by the base unit,
the analog coefficients obtained by transforming a transmit spatial covariance matrix, the transmit spatial covariance matrix based on a first set of two or more OFDM subcarriers corresponding to a waveform transmitted from the base unit, and
the processor is configured to determine transmission parameters corresponding to the first set of two or more OFDM subcarrier based on the obtained analog coefficients.
15. The base unit of claim 14 , wherein the processor is configured to select one or more OFDM sub-carriers for transmission to the terminal based on the analog coefficients.
16. The base unit of claim 14 , wherein the processor is configured to request a wireless communication terminal to measure the transmit spatial covariance matrix on the first set of two or more OFDM subcarriers corresponding to the waveform transmitted from the base unit.
17. The base unit of claim 14 , wherein the analog coefficients are obtained by transforming transmit spatial covariance matrices, each of the transmit spatial covariance matrices based on a corresponding set of two or more OFDM subcarriers corresponding to the waveform transmitted from the base unit.
18. The base unit of claim 14 , wherein the processor is configured to determine one or more of a number of data streams to be transmitted, to transmit weight vectors and a modulation and coding scheme corresponding to a wireless communication terminal applicable for transmission on one or more of the first set of OFDM subcarriers.
19. The base unit of claim 14 ,
wherein the processor is configured to obtain two or more sets of analog coefficients corresponding to two or more wireless communication terminals from corresponding sets of OFDM subcarriers on the waveform received by the base unit,
wherein, based on the multiple sets of analog coefficients, the controller is configured to determine one or more of a number of data streams to be transmitted, transmit weight vectors and a modulation and coding scheme corresponding to each wireless communication terminal based on the multiple sets of analog coefficients applicable for transmission on the one or more of the first set of OFDM subcarriers.
20. An orthogonal frequency division multiplexing wireless communication terminal comprising:
the terminal configured to compute a transmit spatial covariance matrix corresponding to a channel estimated on a first set of two or more orthogonal frequency division multiplexing (OFDM) subcarriers corresponding to a received waveform,
the terminal configured to obtain a set of analog coefficients by transforming the transmit spatial covariance matrix,
the terminal configured to modulate the set of analog coefficients onto a first portion of a second set of two or more OFDM subcarriers corresponding to a transmitted waveform, where each analog coefficient is mapped to a single OFDM subcarrier, and
the terminal configured to modulate a pilot symbol onto a second portion of the second set of OFDM subcarriers.
21. The terminal of claim 20 , wherein the set of analog coefficients are obtained without quantization.
22. The terminal of claim 20 , wherein the pilot symbol is from a finite constellation of complex symbols.