Precoding with partially stale feedback

Patent metadata

Field	Value
Publication number	US-9363002-B2
Application number	US-201213414932-A
Country	US
Kind code	B2
Filing date	Mar 8, 2012
Priority date	Mar 8, 2012
Publication date	Jun 7, 2016
Grant date	Jun 7, 2016

Abstract

A system and method in which a base station treats the Channel State Information (CSI) from wireless terminals as only partially-stale, and exploits this partially-stale CSI to predict the current channel from old estimates of the channel. The predicted channel is then used to design a precoder. The base station shapes the transmitted signal with the precoder so as to match it as closely as possible to the current channel. Particular embodiments thus combine the benefits of the stale feedback scheme with precoding to match the channel. Consequently, the signal received at a terminal is better conditioned, thereby providing a greater overall boost in performance of the communication arrangement between the base station and the terminal. The usage of partially-stale CSI can be important for dense networks with a large number of simple terminals.

First claim

What is claimed is:

1. A method of providing wireless transmissions between a processor-controlled base station and a plurality of terminals via a communication channel established in a wireless network, wherein the base station includes a plurality of transmit antennas, the method comprising steps of:
using the processor, receiving respective terminal-specific Channel State Information (CSI) feedback from each of a first terminal and a second terminal in the plurality of terminals, wherein each terminal-specific CSI feedback corresponds to all antenna element-specific transmissions from the base station to either of the first and the second terminals, wherein the antenna element-specific transmissions temporally precede the terminal-specific CSI feedback;
using the processor, determining a predicted communication channel based on a pre-determined number of time-wise consecutive channel estimates, wherein the predicted communication channel represents a prediction of the communication channel based on partially stale CSI feedback, wherein the pre-determined number of time-wise consecutive channel estimates are generated by repeating the reception of the CSI feedback from the first and the second terminals and determination of channel estimate for a pre-determined number of temporally consecutive base station transmissions, wherein the pre-determined number of time-wise consecutive channel estimates represents a pre-determined number of time-wise correlated CSI feedbacks;
using the processor, shaping at least one terminal-specific transmission intended for the corresponding one or both of the first and the second terminals based on the predicted communication channel; and
using the processor, providing a common transmission intended for both of the first and the second terminals, wherein the providing step includes:
using the predicted communication channel to determine a precoder matrix;
determining effective antenna element-specific channel parameters based on past precoder matrices and CSI feedback from each of the first and the second terminals; and
formulating a combined symbol based on the effective antenna element-specific channel parameters and information symbols included in an earlier terminal-specific transmission to at least one of the first and the second terminals.

2. The method of claim 1 , wherein the communication channel is a Radio Frequency (RF) channel.

3. The method of claim 1 , wherein the step of determining the predicted communication channel includes:
using the processor, determining a channel estimate of the communication channel based on the respective terminal-specific CSI feedback received from each of the first and the second terminals; and
using the processor, determining the predicted communication channel based on the pre-determined number of time-wise consecutive channel estimates.

4. The method of claim 3 , wherein the plurality of transmit antennas includes a first antenna and a second antenna, and wherein receiving the respective terminal-specific CSI feedback includes:
using the first transmit antenna, at a first time, transmitting over the communication channel a first symbol intended for the first terminal;
using the second transmit antenna, at the first time, transmitting over the communication channel a second symbol intended for the first terminal;
receiving the CSI feedback from the first terminal including estimates of a first pair of antenna element-specific parameters related to a status of the communication channel at the first time; and
receiving the CSI feedback from the second terminal including estimates of a second pair of antenna element-specific parameters related to the status of the communication channel at the first time.

5. The method of claim 4 , wherein the step of determining the channel estimate includes:
determining the channel estimate associated with the first time using the estimates of the first and the second pairs of antenna element-specific parameters.

6. The method of claim 5 , wherein the step of repeating the reception of the terminal-specific CSI feedback and determination of the channel estimate includes:
using the first antenna, at a second time, transmitting over the communication channel a third symbol intended for the second terminal;
using the second antenna, at the second time, transmitting over the communication channel a fourth symbol intended for the second terminal;
receiving the CSI feedback from the second terminal including estimates of the second pair of antenna element-specific parameters related to a status of the communication channel at the second time;
receiving the CSI feedback from the first terminal including estimates of the first pair of antenna element-specific parameters related to the status of the communication channel at the second time; and
determining the channel estimate associated with the second time using the estimates of the first and the second pairs of antenna element-specific parameters received in response to the transmissions of the third and the fourth symbols at the second time.

7. The method of claim 3 , wherein the step of determining the predicted communication channel includes:
determining the predicted communication channel by using a moving average of the pre-determined number of time-wise consecutive channel estimates.

8. The method of claim 3 , wherein the pre-determined number of temporally consecutive base station transmissions includes more than one transmissions, and wherein the pre-determined number of time-wise consecutive channel estimates includes more than one estimates.

9. The method of claim 1 , wherein the step of shaping at least one transmission includes at least one of the following:
applying the precoder to at least one terminal-specific transmission intended for the first terminal prior to sending the transmission to the first terminal, and
applying the precoder to at least one terminal-specific transmission intended for the second terminal prior to sending the transmission to the second terminal.

10. The method of claim 9 , wherein the precoder is one of the following: a zero-forcing precoder based on an inverse of the predicted communication channel; and an eigen-beamformer based on a unitary matrix.

11. The method of claim 9 , wherein determining the precoder includes one of the following:
separately determining each of the following:
a first precoder for a first terminal-specific transmission intended for the first terminal,
a second precoder for a second terminal-specific transmission intended for the second terminal, and
a third precoder for a combined symbol to be transmitted by the processor as the common transmission to both of the first and the second terminals, wherein the combined symbol includes a channel-status related information associated with the first and the second terminal-specific transmissions along with information related to the contents of the first and the second terminal-specific transmissions; and
jointly selecting the first, the second, and the third precoders prior to applying any of the first, the second, and the third precoders to a corresponding one or more terminal- specific transmissions.

12. The method of claim 11 , wherein jointly selecting the first, the second, and the third precoders includes:
evaluating a channel capacity using a plurality of sets of pre-determined precoders, wherein the channel capacity is based on individual channel capacities modeled for the first and the second terminals; and
selecting that one of the plurality of sets of pre-determined precoders which results in a highest value for the channel capacity under evaluation, wherein the selected

Assignees

• Khayrallah Ali S
• Wang Yi-Pin Eric
• Ericsson Telefon Ab L M

Inventors

• Khayrallah Ali S
• Wang Yi-Pin Eric

Classifications

• H04L25/03949

  equalizer selection or adaptation based on feedback (multiple signaling inclusive of a precoding command for adapting the transmitter H04L1/0031; feedback for transmit diversity systems H04B7/0619; selection of codebook or precoding matrix for MIMO diversity systems H04B7/0456) · CPC title

• H04B7/0626 Primary

  Channel coefficients, e.g. channel state information [CSI] · CPC title

• H04B7/0434

  using multiple eigenmodes · CPC title

• H04B7/022

  Site diversity; Macro-diversity (using two or more spaced independent antennas H04B7/04) · CPC title

• H04L25/03898

  codebook-based design (selection of codebook or precoding matrix for MIMO diversity systems H04B7/0456) · CPC title