System and Method for Reduced Feedback in Multiuser Multiple Input, Multiple Output Wireless Communications

• US 20110205963A1
• Filed: 02/24/2010
• Published: 08/25/2011
• Est. Priority Date: 02/24/2010
• Status: Active Grant

• Current Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Original Assignee: Futurewei Technologies Incorporated (Huawei Investment & Holding Co., Ltd.)
• Inventors: Xia, Pengfei, Rong, Zhigang, Tang, Yang
• Granted Patent: US 8,705,443 B2
• Time in Patent Office: Days
• US Class Current: 370/328
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0663 using vector or matrix manipulations
• CPC Class Codes: H04L 25/0204 of multiple channels
• CPC Class Codes: H04L 25/0248 Eigen-space methods

Abstract

A system and method for reduced feedback in MU-MIMO communications is provided. A method for transmitter operations includes transmitting a pilot signal, receiving channel information feedback from a set of K communications devices served by a transmitter, where K is a non-negative integer value and K≧2, selecting M communications devices out of the set of K communications devices, where M is a non-negative integer value and M≦K, computing a precoder for each of the M selected communications devices based on the channel information feedback, and simultaneously transmitting information to the M selected communications devices. The channel information feedback includes partial information for a communications channel between the transmitter and a communications device, the selecting being based on the channel information feedback, and the information transmitted to each communications device in the M selected communications devices being precoded using a computed precoder associated with the communications device.

Claims

1. A method for transmitter operations, the method comprising:

transmitting a pilot signal;

receiving channel information feedback from a set of K communications devices served by a transmitter, where K is a non-negative integer value and K≧

2, wherein the channel information feedback from a communications device comprises partial information for a communications channel between the transmitter and the communications device;

selecting M communications devices out of the set of K communications devices, where M is a non-negative integer value and M≦

K, wherein the selecting is based on the channel information feedback;

computing a precoder for each of the M selected communications devices based on the channel information feedback; and

simultaneously transmitting information to the M selected communications devices, wherein the information transmitted to each communications device in the M selected communications devices is precoded using a computed precoder associated with the communications device.

2. The method of claim 1, further comprising reconstructing the channel information feedback using a codebook.

3. The method of claim 1, wherein the channel information feedback from the communications device comprises a signaling space for the communications device.

4. The method of claim 3, wherein the channel information feedback further comprises a null space for the communications device.

5. The method of claim 1, wherein computing a precoder comprises:

selecting one of the M selected communications devices;

computing a joint null space for a remaining M−

1 selected communications devices of the M selected communications devices with respect to the selected communications device;

computing a precoder for the selected communications device; and

repeating the selecting one of the M selected communications devices, the computing a joint null space, and the computing a precoder for the selected communications devices for each of the M−

1 selected communications devices.

6. The method of claim 5, wherein computing a joint null space comprises computing

[V₂₁, . . . , V_M1]^H=Û

_i1{circumflex over (D)}_i1{circumflex over (V)}_i1^H,

where Û

_i1 is a matrix of eigenvectors for aggregation of feedback signaling spaces, {circumflex over (D)}_i1 is a matrix of non-zero eigenvalues for the aggregation of feedback signaling spaces, V_i=[V₁₁, . . . , V_M1], iε

{1, . . . , C_K^M} is an aggregation of signaling spaces of the M selected communications devices fedback by the M selected communications devices, V₁₁ is a feedback signaling space for the selected communications device, {circumflex over (V)}_i1=[{circumflex over (V)}_i11,{circumflex over (V)}_i10], and {circumflex over (V)}_i10 is a null space of [V₂₁, . . . , V_M1].

7. The method of claim 6, wherein [V₂₁, . . . , V_M1]^H=Û

_i1{circumflex over (D)}_i1{circumflex over (V)}_i1^H is computed using singular value decomposition.

8. The method of claim 5, wherein computing a precoder for the selected communications device comprises maximizing

{circumflex over (V)}_i10P_i1,

where {circumflex over (V)}_i10 is a joint null space of [V₂₁, . . . , V_M1], P_i1 is a power allocation matrix and expressible as

P_i1=arg{max(log₂det(I+SNR₁(D₁V₁₁^H{circumflex over (V)}_i10P_i1)²))}.

9. The method of claim 8, wherein the channel information feedback further comprises a matrix of non-zero eigenvalues (D₁) for the downlink channel between the transmitter and the selected communications device, wherein matrix D₁V₁₁^H{circumflex over (V)}_i10 is expressible as

D₁V₁₁^H{circumflex over (V)}_i10=U_i1IID_i1IIV_i1II^H

using singular value decomposition, and wherein P_i1 is expressible as

P_i1=V_i1II(:

,1;

N)×

Q,

with notation V_i1II(;

,1;

N) representing selecting a first N columns of V_i1II, where V_i1II is the joint null space of D₁V₁₁^H{circumflex over (V)}_i10, Q is a power allocation diagonal matrix and N≦

N_R, and N_R is a number of receive antennas at the selected communications device.

10. The method of claim 8, wherein matrix V₁₁^H{circumflex over (V)}_i10 is expressible as

V₁₁^H{circumflex over (V)}_i10=U_i1IID_i1IIV_i1II^H

using singular value decomposition, and wherein P_i1 is expressible as

P_i1=V_i1II(:

,1;

N)×

Q,

with notation V_i1II(;

,1;

N) representing selecting a first N of V_i1II, where V_i1II is the joint null space of V₁₁^H{circumflex over (V)}_i10, Q is a power allocation diagonal matrix and N≦

N_R, and N_R is a number of receive antennas at the selected communications device.

11. A method for receiver operations, the method comprising:

receiving a pilot signal;

estimating a channel between a receiver and a transmitter serving the receiver;

computing components of the channel estimate;

transmitting the components of the channel estimate to the transmitter; and

receiving a transmission from the transmitter, wherein the transmission is precoded using a precoding vector determined based on the components of the channel estimate, and wherein the transmission is part of a multi-user multiple input, multiple output transmission.

12. The method of claim 11, further comprising quantizing the components of the channel estimate with a codebook.

13. The method of claim 11, wherein computing components of the channel estimate comprises applying singular value decomposition on the channel estimate.

14. The method of claim 13, wherein applying singular value decomposition results in the channel estimate being expressed as

H_k=U_kD_kV_k^H,

where H_k is the channel estimate, U_k is a matrix of eigenvectors for the channel, D_k is a matrix of non-zero eigenvalues for the channel, and V_k is a N_T×

N_T unitary matrix given as

V_k=[v_k1, . . . , v_kNT]=[V_k1,V_k0],

in which V_k1 and V_k0 represent a signaling space and a null space of the k-th MS, respectively.

15. The method of claim 14, wherein transmitting the components of the channel estimate comprises transmitting the signaling space (V_k1).

16. The method of claim 14, further comprising quantizing the signaling space with a codebook.

17. The method of claim 14, wherein transmitting the components of the channel estimate comprises transmitting the null space (V_k0).

18. A communications controller comprising:

a scheduler configured to select M users for transmission in a transmission opportunity, where M is a non-negative integer value greater than or equal to one, wherein the selection is based on channel feedback information provided by the users, wherein the channel feedback information comprises partial channel information;

a beamforming unit coupled to the scheduler, the beamforming unit configured to map information for the selected users onto beamforming vectors for transmission; and

a beamforming vector unit coupled to the beamforming unit, the beamforming vector unit configured to compute a null space for each of the users selected by the scheduler and to compute beamforming vectors for each of the users based on the channel feedback information.

19. The communications controller of claim 18, wherein the beamforming vector unit comprises:

a null space unit configured, for each of the M users, to select a user and to compute a joint null space for each of remaining M−

1 users with respect to the selected user; and

a precode compute unit coupled to the null space unit, the precode compute unit configured, for each of the M users, to compute a precoder for the selected user that maximizes a throughput for the selected user.

20. The communications controller of claim 18, wherein the scheduler comprises a user select unit configured to select the M users based on maximizing throughput, service history, user priority, information priority, and combinations thereof.