Method for Transmitting of Reference Signals and Determination of Precoding Matrices for Multi-Antenna Transmission

• US 20110205930A1
• Filed: 05/14/2009
• Published: 08/25/2011
• Est. Priority Date: 11/03/2008
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Astely, David, Jöngren, George, Rahman, Muhammad Imadur
• Granted Patent: US 8,737,507 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0469 taking special antenna structures, e.g. cross polarized antennas into account
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0639 Using selective indices, e.g. of a codebook, e.g. pre-distortion matrix index [PMI] or for beam selection
• CPC Class Codes: H04B 7/0691 using subgroups of transmit antennas
• CPC Class Codes: H04L 2025/03426 transmission using multiple-input and multiple-output channels
• CPC Class Codes: H04L 2025/03802 Signalling on the reverse channel
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 5/0023 Time-frequency-space
• CPC Class Codes: H04L 5/005 of common pilots, i.e. pilots destined for multiple users or terminals

Abstract

Techniques are disclosed for determining transmitter antenna weights at a base station (12) having more available transmit antennas (150) than the available number of reference signals. An exemplary method includes transmitting (530) a plurality of reference signals and receiving (540) channel feedback data derived by a mobile terminal (14) from the reference signals. The reference signals are each assigned to a corresponding one of two or more antenna groupings, wherein at least a first one of the antenna groupings comprises two or more transmit antennas (150), and transmitted using at least one transmit antenna (150) from the corresponding antenna grouping. The method further includes determining (550) a first beam-forming vector for the first one of the antenna grouping and mapping (570) the one or more data streams to the transmit antennas (150) according to a final precoding matrix that depends on the channel feedback data and the first beam-forming vector, to obtain a weighted transmit signal for each of the antennas (150).

Claims

1-18. -18. (canceled)

19. A method of transmitting one or more data streams to a mobile terminal from a plurality of transmit antennas, the method comprising:

assigning each of a plurality reference signals to a corresponding one of two or more antenna groupings, wherein at least a first one of the antenna groupings comprises two or more transmit antennas;

transmitting each of the reference signals using at least one transmit antenna from the corresponding antenna grouping;

receiving channel feedback data derived by the mobile terminal from the reference signals;

determining a first beam-forming vector for the first one of the antenna groupings; and

mapping the one or more data streams to the transmit antennas according to a final precoding matrix that depends on the channel feedback data and the first beam-forming vector, to obtain a weighted transmit signal for each of the transmit antennas.

20. The method of claim 19, wherein the transmit antennas are grouped so that propagation channel coefficients corresponding to each transmit antenna are more highly correlated within an antenna grouping than between any two transmit antennas from different antenna groupings.

21. The method of claim 19, wherein the received channel feedback data includes an indicator corresponding to a recommended precoder matrix selected by the mobile terminal and wherein mapping the one or more data streams to the transmit antennas comprises computing the final precoding matrix by calculating the Kronecker product of the recommended precoder matrix and the beam-forming vector.

22. The method of claim 19, wherein determining a beam-forming vector for the first one of the antenna groupings comprises estimating a direction of arrival for uplink signals received from the mobile terminal.

23. The method of claim 19, wherein determining a beam-forming vector for the first one of the antenna groupings comprises estimating a dominant eigenvector based on an average of uplink channel statistics.

24. The method of claim 19, further comprising determining a second beam-forming vector for a second one of the antenna groupings and wherein said calculating comprises calculating the final precoding matrix based on the channel feedback data and the first and second beam-forming vectors.

25. The method of claim 24, wherein determining the second beam-forming vector comprises re-using the first beam-forming vector for the second one of the antenna groupings.

26. The method of claim 24, wherein said calculating comprises calculating the final precoding matrix based on the channel feedback data and the average of the first and second beam-forming vectors.

27. The method of claim 19, wherein the transmit antennas comprise a dual-polarized four-column array and wherein first and second antenna groupings each comprise four co-polarized antenna elements.

28. A base station configured to transmit data to a mobile terminal from a plurality of transmit antennas, comprising:

a transmitter configured to assign each of a plurality of reference signals to a corresponding one of two or more antenna groupings, wherein at least a first one of the antenna groupings comprises two or more transmit antennas, and to transmit each of the reference signals using at least one transmit antenna from the corresponding antenna grouping;

a receiver configured to receive channel feedback data derived by the mobile terminal from the reference signals,

a precoding processor configured to determine a first beam-forming vector for the first one of the antenna groupings and to map the one or more data streams to the transmit antennas according to a final precoding matrix that depends on the channel feedback data and the first beam-forming vector, to obtain a weighted transmit signal for each of the transmit antennas.

29. The base station of claim 28, wherein the transmit antennas are grouped so that propagation channel coefficients corresponding to each transmit antenna are more highly correlated within an antenna grouping than between any two transmit antennas from different antenna groupings.

30. The base station of claim 28, wherein the received channel feedback data includes an indicator corresponding to a recommended precoder matrix selected by the mobile terminal and wherein the precoding processor is configured to compute the final precoding matrix by calculating the Kronecker product of the recommended precoder matrix and the beam-forming vector.

31. The base station of claim 28, wherein the precoding processor is configured to determine a beam-forming vector for the first one of the antenna groupings by estimating a direction of arrival for uplink signals from the mobile terminal.

32. The base station of claim 28, wherein the precoding processor is configured to determine a beam-forming vector for the first one of the antenna groupings by estimating a dominant eigenvector based on an average of uplink channel statistics.

33. The base station of claim 28, wherein the precoding processor is configured to determine a second beam-forming vector for a second one of the antenna groupings and to calculate the final precoding matrix based on the channel feedback data and the first and second beam-forming vectors.

34. The base station of claim 33, wherein the precoding processor is configured to determine the second beam-forming vector by re-using the first beam-forming vector for the second one of the antenna groupings.

35. The base station of claim 33, wherein the precoding processor is configured to calculate the final precoding matrix based on the channel feedback data and the average of the first and second beam-forming vectors.

36. The base station of claim 28, wherein the transmit antennas comprise a dual-polarized four-column array and wherein first and second antenna groupings each comprise four co-polarized antenna elements.