Enhancement of download multi-user multiple-input multiple-output wireless communications

• US 8,798,011 B2
• Filed: 04/26/2012
• Issued: 08/05/2014
• Est. Priority Date: 04/29/2011
• Status: Active Grant

• Current Assignee: NEC Corporation
• Original Assignee: NEC Laboratories America Inc (NEC Corporation)
• Inventors: Prasad, Narayan, Yue, Guosen, Jiang, Meilong, Khojastepour, Mohammad A., Rangarajan, Sampath
• Primary Examiner(s): Duong, Frank
• Application Number:
  US13/456,881
• Publication Number:
  US 20120275314A1
• Time in Patent Office: 831 Days
• Field of Search: 370328-339
• US Class Current: 370/335
• CPC Class Codes: H04B 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0452 Multi-user MIMO systems
• CPC Class Codes: H04B 7/0469 taking special antenna structures, e.g. cross polarized antennas into account
• CPC Class Codes: H04B 7/0486 taking channel rank into account
• CPC Class Codes: H04B 7/0626 Channel coefficients, e.g. channel state information [CSI]
• CPC Class Codes: H04B 7/063 Parameters other than those covered in groups H04B7/0623 - H04B7/0634, e.g. channel matrix rank or transmit mode selection
• CPC Class Codes: H04B 7/065 Variable contents, e.g. long-term or short-short
• CPC Class Codes: H04W 24/10 Scheduling measurement reports ; Arrangements for measurement reports

Abstract

A method implemented in a user equipment configured to be used in a multi-user (MU) multiple-input multiple-output (MIMO) wireless communications system is disclosed. In an aspect, the user equipment transmits to a base station a first channel state information (CSI) report determined according to a single-user (SU) MIMO rule and a second CSI report determined according to an MU-MIMO rule.

Claims

1. A method implemented in a user equipment configured to be used in a multi-user (MU) multiple-input multiple-output (MIMO) wireless communications system, the method comprising:

transmitting to a base station a first channel state information (CSI) report determined according to a single-user (SU) MIMO rule;

transmitting to the base station a second CSI report determined according to an MU-MIMO rule;

assuming a particular number of columns in U₁; and

assuming either a substantially equal power per scheduled stream or a non-uniform power allocation in which a first fraction of energy per resource element (EPRE) is shared substantially equally among one or more columns of U₁ with a second fraction of the EPRE being shared substantially equally among one or more columns in U₁, where U₁ and U₁ represent precoding matrices used by the base station to transmit data to the user equipment and a co-scheduled user equipment, respectively.

2. The method of claim 1, wherein the first CSI report is transmitted in a first interval configured for SU CSI reporting and the second CSI report is transmitted in a second interval configured for the second CSI report.

3. The method of claim 1, wherein the first CSI report and the second CSI report are transmitted in a common interval configured for CSI reporting.

4. The method of claim 1, wherein the first CSI report is transmitted in a first interval configured for SU CSI reporting and the first CSI report and the second CSI report are transmitted in a second interval configured for combined CSI reporting.

5. The method of claim 1, further comprising:

receiving at least one of sequence configuration information and sub-sequence configuration information from the base station,

wherein the sequence configuration information comprises at least one of first periodicity and first offset for the first CSI report, and

wherein the sub-sequence configuration information comprises at least one of second periodicity and second offset for the second CSI report.

6. The method of claim 1, wherein the first CSI report includes at least one of a preferred rank, a precoder of the preferred rank, and a corresponding quantized SINR (signal to interference plus noise ratio).

7. The method of claim 1, wherein the second CSI report comprises at least one of channel quality indicator (CQI) and a precoding matrix indicator (PMI).

8. The method of claim 1, further comprising:

assuming a post scheduling model.

9. The method of claim 8, wherein the post scheduling model can be expressed as

y₁={circumflex over (D)}₁^1/2{circumflex over (V)}₁^†

U₁s₁+{circumflex over (D)}₁^1/2({circumflex over (V)}₁^†

+R₁^†

Q₁^†

)U₁s₁+η

₁,

where y₁ represents an N×

1 received signal vector on a representative resource element in a resource block (RB), N being the number of receive antennas at the user equipment, {circumflex over (D)}₁^1/2 is a diagonal matrix of effective channel gains, {circumflex over (V)}₁ denotes a semi-unitary matrix whose columns represent preferred channel directions and {circumflex over (V)}₁^†

represents Hermitian of {circumflex over (V)}₁, U₁ and U₁ represent precoding matrices used by the base station to transmit data to the user equipment and a co-scheduled user equipment, respectively, s₁ and s₁represent transmit symbol vectors intended for the user equipment and the co-scheduled user equipment, respectively, Q₁ is a semi-unitary matrix whose columns lie in the orthogonal complement of {circumflex over (V)}₁, and R₁ is a matrix which satisfies the Frobenius-norm constraint ∥

R₁∥

_F²≦

ε

₁², ε

₁ being the residual error norm, and η

₁ represents an additive noise vector.

10. The method of claim 9, wherein Q₁^†

{circumflex over (V)}₁=0.

11. The method of claim 9, wherein {circumflex over (D)}₁^1/2 and {circumflex over (V)}₁ are equal to diagonal matrices of dominant unquantized singular values and dominant unquantized right singular vectors, respectively, of a downlink channel matrix.

12. The method of claim 9, further comprising:

setting U₁=Ĝ

₁ where Ĝ

₁ is a precoder; and

assuming the columns of U₁ are isotropically distributed in the subspace defined by I−

Ĝ

₁Ĝ

₁^†

(orthogonal complement of Ĝ

₁).

13. The method of claim 9, further comprising:

assuming Q₁=0.

14. The method of claim 1, further comprising:

receiving from the base station an indication of at least one of the first fraction of the EPRE and the second fraction of EPRE.

15. A method implemented in a base station configured to be used in a multi-user (MU) multiple-input multiple-output (MIMO) wireless communications system, the method comprising:

receiving from a user equipment a first channel state information (CSI) report determined according to a single-user (SU) MIMO rule; and

receiving from the user equipment a second CSI report determined according to an MU-MIMO rule,

wherein the user equipment assumes a particular number of columns in U₁, and assumes either a substantially equal power per scheduled stream or a non-uniform power allocation in which a first fraction of energy per resource element (EPRE) is shared substantially equally among one or more columns of U₁with a second fraction of the EPRE being shared substantially equally among one or more columns in U₁, where U₁ and U₁ represent precoding matrices used by the base station to transmit data to the user equipment and a co-scheduled user equipment, respectively.

16. A multi-user (MU) multiple-input multiple-output (MIMO) wireless communications system, comprising:

a base station; and

a user equipment,

wherein the user equipment transmits to the base station a first channel state information (CSI) report determined according to a single-user (SU) MIMO rule, and a second CSI report determined according to an MU-MIMO rule, and

wherein the user equipment assumes a particular number of columns in U₁, and assumes either a substantially equal power per scheduled stream or a non-uniform power allocation in which a first fraction of energy per resource element (EPRE) is shared substantially equally among one or more columns of U₁ with a second fraction of the EPRE being shared substantially equally among one or more columns in U₁, where U₁ and U₁ represent precoding matrices used by the base station to transmit data to the user equipment and a co-scheduled user equipment, respectively.