PRECODER STRUCTURE FOR MIMO PRECODING

• US 20180076863A1
• Filed: 11/27/2017
• Published: 03/15/2018
• Est. Priority Date: 04/07/2010
• Status: Active Grant

• Current Assignee: Telefonaktiebolaget LM Ericsson
• Original Assignee: Telefonaktiebolaget LM Ericsson
• Inventors: Hammarwall, David, Jngren, George
• Granted Patent: US 10,250,308 B2
• Time in Patent Office: Days
• CPC Class Codes: H04B 7/0456 Selection of precoding matrices or codebooks, e.g. using matrices antenna weighting
• CPC Class Codes: H04B 7/0465 taking power constraints at power amplifier or emission constraints, e.g. constant modulus, into account
• CPC Class Codes: H04B 7/0469 taking special antenna structures, e.g. cross polarized antennas into account
• CPC Class Codes: H04B 7/0478 Special codebook structures directed to feedback optimisation
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• 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 7/0647 Variable feedback rate
• CPC Class Codes: H04B 7/065 Variable contents, e.g. long-term or short-short
• CPC Class Codes: H04B 7/10 Polarisation diversity; Directional diversity
• CPC Class Codes: H04L 5/0044 allocation of payload
• CPC Class Codes: H04W 72/21 in the uplink direction of a wireless link, i.e. towards the network

Abstract

The teachings herein present a method and apparatus that implement and use a factorized precoder structure that is advantageous in terms of performance and efficiency. In particular, the teachings presented herein disclose an underlying precoder structure that allows for certain codebook reuse across different transmission scenarios, including for transmission from a single Uniform Linear Array (ULA) of transmit antennas and transmission from cross-polarized subgroups of such antennas. According to this structure, an overall precoder is constructed from a conversion precoder and a tuning precoder. The conversion precoder includes antenna-subgroup precoders of size N_T/2, where N_T represents the number of overall antenna ports considered. Correspondingly, the tuning precoder controls the offset of beam phases between the antenna-subgroup precoders, allowing the conversion precoder to be used with cross-polarized arrays of N_T/2 antenna elements and with co-polarized arrays of N_T antenna elements.

Claims

1. A method in a wireless communication transceiver, wherein another transceiver precodes transmissions to the transceiver based at least in part on the transceiver sending channel state information to the other transceiver that includes precoder information and wherein the method is characterized by:

selecting entries from one or more codebooks as a selected conversion precoder and a selected tuning precoder, or as a selected overall precoder corresponding to a selected conversion precoder and a selected tuning precoder; and

transmitting indications of the selected entries as said precoder information included in the channel state information;

wherein the one or more codebooks include entries comprising N_TQ different conversion precoders, N_T being the number of transmit antenna ports and Q being an integer value, and entries comprising a number of corresponding tuning precoders, or include entries comprising a plurality of overall precoders with each overall precoder comprising the product of a conversion precoder and a tuning precoder; and

wherein each said conversion precoder out of said N_TQ different entries comprises a block diagonal matrix in which each block comprises a DFT-based antenna-subgroup precoder that corresponds to a subgroup of N_T transmit antenna ports at the transceiver and provides N_TQ different DFT based beams for the corresponding subgroup, where the N_TQ different conversion precoders together with one or more of the tuning precoders, correspond to a set of N_TQ different overall precoders, wherein each overall precoder represents a size-N_T DFT-based beam over the N_T transmit antenna ports,

wherein said one or more codebooks includes conversion and tuning precoders or corresponding overall precoders for multiple transmission ranks, and

wherein for transmission rank r>

2

the tuning precoder has 2┌

r/2┐

rows and r columns, where r is the transmission rank;

all non-zero elements of the tuning precoder are constant modulus;

every column of the tuning precoder has exactly two non-zero elements;

every row of the tuning precoder has exactly two non-zero elements; and

two columns of the tuning precoder having non-zero elements in the same two rows are orthogonal to each other.

2. The method of claim 1, further characterized in that the other transceiver is a base station in a wireless communication network and the transceiver is a user equipment, UE, sending said channel state information to said base station.

3. The method of claim 2, further characterized in that transmitting said indications of the selected entries as the precoder information from the UE to the base station comprises transmitting index values indicating the selected entries within the one or more codebooks.

4. The method of any of claim 1, further characterized in that said each antenna-subgroup precoder is a matrix block with N_T/2 rows and belongs to a set of N_TQ different DFT-based beams, where Q is an integer equal to or greater than 2, and where each said tuning precoder includes a phase shift element taken from a 2Q Phase Shift Keying (PSK) alphabet and provides at least 2Q relative phase shifts for offsetting beam phases between the antenna-subgroup precoders in a corresponding one of the conversion precoders.

5. The method of claim 1, wherein the columns of a tuning precoder for rank r is a subset of the columns of a tuning precoder for rank r+1.

6. The method of any of claim 1, further characterized in that each conversion precoder can be written in the form

7. A wireless communication transceiver configured to send channel state information to another wireless communication transceiver that precodes transmissions to the transceiver based at least in part on the channel state information, said transceiver including a receiver for receiving signals from the other transceiver and a transmitter for transmitting signals to the other transceiver, including transmitting signals conveying said channel state information, wherein said transceiver is characterized by:

a memory storing one or more codebooks including entries comprising N_TQ different conversion precoders, N_T being the number of transmit antenna ports, and Q being an integer value, and entries comprising a number of corresponding tuning precoders, or entries comprising a plurality of overall precoders, with each overall precoder comprising the product of a conversion precoder and a tuning precoder, wherein each said conversion precoder out of said N_TQ different entries comprises a block diagonal matrix in which each block comprises a DFT-based antenna-subgroup precoder that corresponds to a subgroup of N_T transmit antenna ports at the transceiver and provides N_TQ different DFT based beams for the corresponding subgroup, where Q is an integer value and where the N_TQ different conversion precoders, together with one or more of the tuning precoders, correspond to a set of N_TQ different overall precoders wherein each overall precoder represents a size-N_T DFT-based beam over the N_T transmit antennas ports; and

a precoding feedback generator configured to select entries from the one or more codebooks as a selected conversion precoder and a selected tuning precoder, or as a selected overall precoder corresponding to a selected conversion precoder and a selected tuning precoder;

said precoding feedback generator further configured to transmit, via said transmitter, indications of the selected entries as precoder information included in said channel state information,

wherein said one or more codebooks includes conversion and tuning precoders or corresponding overall precoders for multiple transmission ranks, and wherein for transmission rank r>

2;

the tuning precoder has 2┌

r/2┐

rows and r columns, where r is the transmission rank;

all of the tuning precoder non-zero elements are constant modulus;

every column of the tuning precoder has exactly two non-zero elements;

every row of the tuning precoder has exactly two non-zero elements; and

two columns of the tuning precoder having non-zero elements in the same two rows are orthogonal to each other.

8. The transceiver of claim 7, further characterized in that the other transceiver is a base station in a wireless communication network and the transceiver is a user equipment, UE, sending said channel state information to said base station.

9. The transceiver of any of claim 7, further characterized in that each conversion precoder can be written in the form

10. A method of precoding multi-antenna transmissions from a wireless communication transceiver to another wireless communication transceiver, based at least in part on receiving channel state information from the other transceiver that includes precoder information, said method characterized by:

identifying the precoder information by selecting entries from one or more codebooks known at the transceiver responsive to selection indications included in the channel state information; and

precoding a transmission to the other transceiver based at least in part on the precoder information;

wherein the one or more codebooks as known by the transceiver include entries comprising N_T Q different conversion precoders, N_T being the number of transmit antenna ports and Q being an integer value, and entries comprising a number of corresponding tuning precoders, or entries comprising a plurality of overall precoders with each overall precoder comprising the product of a conversion precoder and a tuning precoder, and wherein each said conversion precoder out of said N_T Q different entries comprises a block diagonal matrix in which each block comprises a DFT-based antenna-subgroup precoder that corresponds to a subgroup of N_T transmit antenna ports and provides N_T Q different DFT based beams for the corresponding subgroup, wherein the N_T Q different conversion precoders, together with one or more of the tuning precoders, correspond to a set of N_T Q different overall precoders, wherein each overall precoder represents a size- N_T DFT-based beam over the N_T transmit antenna ports,

wherein said one or more codebooks includes conversion and tuning precoders or corresponding overall precoders for multiple transmission ranks, and wherein for transmission rank r>

2;

the tuning precoder has 2┌

r/2┐

rows and r columns, where r is the transmission rank;

all non-zero elements of the tuning precoder are constant modulus;

every column of the tuning precoder has exactly two non-zero elements;

every row of the tuning precoder has exactly two non-zero elements; and

two columns of the tuning precoder having non-zero elements in the same two rows are orthogonal to each other.

11. The method of claim 10, further characterized by performing DFT-based precoding of transmissions from two or more subgroups of the antennas at the transceiver using the antenna-subgroup precoders in one of the conversion precoders, as selected by the transceiver from the one or more codebooks based at least in part on the precoder information.

12. The method of any of claim 10, further characterized in that each conversion precoder can be written in the form

13. A wireless communication transceiver configured to precode multi-antenna transmissions to another wireless communication transceiver based at least in part on receiving channel state information from the other transceiver, said transceiver including a transmitter and a plurality of antennas for transmitting said multi-antenna transmissions and a receiver for receiving the channel state information, and wherein the transceiver is characterized by:

a memory storing one or more codebooks including entries comprising N_TQ different conversion precoders, N_T being the number of transmit antenna ports and Q being an integer value, and entries comprising a number of corresponding tuning precoders, or entries comprising a plurality of overall precoders, with each overall precoder comprising the product of a conversion precoder and a tuning precoder, wherein each said conversion precoder out of said N_TQ different entries comprises a block diagonal matrix in which each block comprises a DFT-based antenna-subgroup precoder that corresponds to a subgroup of N_T transmit antenna ports and provides N_TQ different DFT based beams for the corresponding subgroup, where the N_TQ different conversion precoders together with one or more of the tuning precoders correspond to a set of N_TQ different overall precoders, wherein each overall precoder represents a size-N_T DFT-based beam over the N_T transmit antenna ports;

a feedback processor configured to identify precoder information from the other receiver based on using selection indications included in the channel state information to identify from the one or more codebooks selected conversion and tuning precoders or a selected overall precoder corresponding to selected conversion and tuning precoders; and

a precoding controller and associated precoding circuit configured to precode the transmission to the other transceiver, based at least in part on the precoder information,

wherein said one or more codebooks includes conversion and tuning precoders or corresponding overall precoders for multiple transmission ranks, and

wherein for transmission rank r>

2;

the tuning precoder has 2┌

r/2┐

rows and r columns, where r is the transmission rank;

all non-zero elements of the tuning precoder are constant modulus;

every column of the tuning precoder has exactly two non-zero elements;

every row of the tuning precoder has exactly two non-zero elements, and

two columns of the tuning precoder having non-zero elements in the same two rows are orthogonal to each other.

14. The transceiver of claim 13, further characterized in that the precoding controller and associated precoding circuit are configured to precode the transmission to the other transceiver by performing DFT-based precoding of transmissions from two or more subgroups of the antennas using antenna-subgroup precoders in the conversion or overall precoder selected by the transceiver from the one or more codebooks, where said selection by the transceiver is based at least in part on the precoder information.

15. The transceiver of any of claim 13, further characterized in that each conversion precoder can be written in the form