METHOD AND SYSTEM FOR MIMO COMMUNICATION

Abstract

A MIMO system (100) and a method of generating a precoder for use in a MIMO system (100), when communicating with a UE (115), are provided. The method comprises receiving, from the UE (115), channel information relating to a channel on which data is transmitted; decomposing the channel information into components representing a transmission component and a signal strength component; and generating the precoder according to the transmission component and the signal strength component.

Claims

1. A method of generating a precoder for use in a MIMO (Multiple-Input Multiple-Output) system when communicating with a UE (User Equipment), the method comprising: receiving, from the UE, channel information relating to a channel on which data is transmitted; decomposing the channel information into components representing a transmission component and a signal strength component; and generating the precoder according to the transmission component and the signal strength component.

2. The method of claim 1, wherein the channel information is decomposed using singular value decomposition (SVD).

3. The method of claim 2, wherein the transmission component comprises a unitary matrix of the singular value decomposition and the signal strength component comprises diagonal matrix of the singular value decomposition.

4. The method of claim 2, wherein the singular value decomposition is computed according to the following equation $U.Math..Math.\Lambda .Math..Math.V^H=\frac{1}{{\sigma }^2}.Math.H^H.Math.H$ where U and V comprise left and right unitary matrices of the singular value decomposition, Λ comprises singular values of the singular value decomposition, H is the channel information, σ.sup.2 is a noise variance of the UE, and the superscript H is the Hermitian transpose.

5. The method of claim 4, wherein the noise variance of the UE is estimated according to channel information.

6. The method of claim 5, wherein the noise variance σ.sup.2 is estimated according to the following equation ${\sigma }^2=\frac{P}{\underset{l=1}{\overset{L}{.Math.}}.Math.{\mathrm{SINR}}_l.Math.\text{/}.Math.L}$ where L is the number of codewords used for the UE, P is the transmit power, and SINR.sub.l is the signal-to-interference-plus-noise ratio for the UE.

7. The method of claim 1, further comprising determining a power allocation matrix according to the signal strength component, wherein the precoder is further generated according to the power allocation matrix.

8. The method of claim 7, wherein the power allocation matrix is determined according to the signal strength component and a Lagrange multiplier.

9. The method of claim 8, wherein the power allocation matrix D is determined according to the following equation $D_{n,n}=\sqrt{{\left(\frac{1}{\sqrt{\upsilon .Math..Math.{\Lambda }_{n,n}}}-\frac{1}{{\Lambda }_{n,n}}\right)}^{+}}$ $D_{n,m}=0,m\ne n$ where Λ comprises singular values of the singular value decomposition, υ is the Lagrange multiplier and the sign ( ).sup.+ means that if ( )<0 then assign ( )=0.

10. The method of claim 9, wherein the precoder F is generated according to the following equation $F=\mathrm{WD}$ $W=\left[\begin{array}{ccc}{V}_{1,1}& \mathrm{.Math.}& V_{1,\mathrm{RI}}\\ \mathrm{.Math.}& \ddots & \mathrm{.Math.}\\ V_{N_{\mathrm{TX}},1}& \mathrm{.Math.}& V_{N_{\mathrm{TX}},\mathrm{RI}}\end{array}\right]$ where N.sub.TX is the number of transmit antennas of the MIMO system and RI is the Rank of the MIMO system.

11. The method of claim 8, wherein the Lagrange multiplier υ is determined by: a) Setting υ=(υ.sub.max+υ.sub.min)/2; b) Computing the following quantity $\hat{P}=\underset{n=1}{\overset{\mathrm{RI}}{.Math.}}.Math.\frac{1}{{\Lambda }_{n,n}}.Math.{\left(\sqrt{\frac{{\Lambda }_{n,n}}{\upsilon }}-1\right)}^{+};$ c) If {circumflex over (P)}>P setting υ.sub.min=υ otherwise setting υ.sub.max=υ; d) repeating steps a)-c) until |{circumflex over (P)}−P|<ε, where ε is a threshold for convergence, υ.sub.max and υ.sub.min are initially set to maximum and minimum values of the Lagrange multiplier, RI is the Rank of the MIMO system, P is the transmit power and the sign ( ).sup.+ means that if ( )<0 then assign ( )=0.

12. The method of claim 1, wherein the MIMO system is a TDD (Time-Division Duplexing) system, and a channel matrix is estimated from the reciprocal channel.

13. The method of claim 1, wherein the MIMO system is an FDD (Frequency-Division Duplexing) system, and a representative channel is derived from a precoder matrix indicator (PMI) of the channel information.

14. A MIMO system including: a plurality of antennas for providing data to a UE; a processor coupled to the antennas; and a memory coupled to the processor, the memory including instruction code executable by the processor for: receiving, from the UE, channel information relating to a channel on which the data is transmitted; decomposing the channel information into components representing a transmission component and a signal strength component; generating a precoder according to the transmission component and the signal strength component; and providing data to the UE on the plurality of antennas, wherein the data is encoded using the precoder.

15. The system of claim 14, wherein the MIMO system is an FDD system.

16. The system of claim 14, wherein the MIMO system is a TDD system.

17. The system of claim 14, wherein the channel information is decomposed using singular value decomposition (SVD) according to the following equation $U.Math..Math.\Lambda .Math..Math.V^H=\frac{1}{{\sigma }^2}.Math.H^H.Math.H$ where U and V comprise left and right unitary matrices of the singular value decomposition, λ comprises singular values of the singular value decomposition, H is the channel information, σ.sup.2 is a noise variance of the UE, and the superscript H is the Hermitian transpose.

18. The system of claim 17, wherein the noise variance σ.sup.2 is estimated according to the following equation ${\sigma }^2=\frac{P}{\underset{l=1}{\overset{L}{.Math.}}.Math.{\mathrm{SINR}}_l.Math.\text{/}.Math.L}$ where L is the number of codewords used for the UE, P is the transmit power, and SINR.sub.l is the signal-to-interference-plus-noise ratio for the UE.

19. The system of claim 17, wherein the precoder is further generated according to the power allocation matrix, and wherein the power allocation matrix D is determined according to the following equation $D_{n,n}=\sqrt{{\left(\frac{1}{\sqrt{\upsilon .Math..Math.{\Lambda }_{n,n}}}-\frac{1}{{\Lambda }_{n,n}}\right)}^{+}}$ $D_{n,m}=0,m\ne n$ where λ comprises singular values of the singular value decomposition and υ is a Lagrange multiplier and the sign ( ).sup.+ means that if ( )<0 then assign ( )=0.

20. The system of claim 19 wherein the Lagrange multiplier υ is determined by: a) Setting υ=(υ.sub.max+υ.sub.min)/2; b) Computing the following quantity $\hat{P}=\underset{n=1}{\overset{\mathrm{RI}}{.Math.}}.Math.\frac{1}{{\Lambda }_{n,n}}.Math.{\left(\sqrt{\frac{{\Lambda }_{n,n}}{\upsilon }}-1\right)}^{+};$ c) If {circumflex over (P)}>P setting υ.sub.min=υ otherwise setting υ.sub.max=υ; d) repeating steps a)-c) until |{circumflex over (P)}−P|<ε, where ε is a threshold for convergence, υ.sub.max and υ.sub.min are initially set to maximum and minimum values of the Lagrange multiplier, RI is the Rank of the MIMO system, P is the transmit power and the sign ( ).sup.+ means that if ( )<0 then assign ( )=0.

21. (canceled)

Description

BRIEF DESCRIPTION OF DRAWINGS

[0067] Various embodiments of the invention will be described with reference to the following drawings.

[0068] FIG. 1 illustrates a MIMO system according to an embodiment of the present invention.

[0069] FIG. 2 illustrates a method of downlink data transmission and CSI feedback of the MIMO system of FIG. 1.

[0070] FIG. 3 illustrates a method of generating a precoder for use in a MIMO system when communication with a UE, according to an embodiment of the present invention.

[0071] FIG. 4 illustrates a method of computing a Lagrange multiplier, according to an embodiment of the present invention.

[0072] Preferred features, embodiments and variations of the invention may be discerned from the following Description of Embodiments which provides sufficient information for those skilled in the art to perform the invention. The Description of Embodiments is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way.

DESCRIPTION OF EMBODIMENTS

[0073] FIG. 1 illustrates a MIMO system 100 according to an embodiment of the present invention. The MIMO system 100 includes an eNodeB 105 including a plurality of antennas 110, and a UE 115 including a plurality of antennas 120. The eNodeB 105 transmits data to the UE 115 on the same time-frequency from the plurality of antennas 120.

[0074] The use of multiple transmit antennas 110 and receive antennas 120 in the MIMO communication system 100 enables the eNodeB 105 to encode and transmit data on a number of spatial channels independently, possibly with different rates. Each antenna pair 110, 120 creates a different radio-antenna chain through which data may be transmitted.

[0075] The UE 115 computes noise power estimates, signal power estimates and channel estimates between the eNodeB 105 and that UE 115. The computed estimates are used to minimise interference between transmission layers by precoding. Precoding is used to support multi-layer transmission in multi-antenna wireless communications. Mathematically, a single user (SU)-MIMO system is described as follows.

y=HVx+n   (Equation 1)

[0076] In Equation 1:

[0077] y is a received signal of size N.sub.RX×1,

[0078] x is a data signal of size RI×1,

[0079] H of size N.sub.RX×N.sub.TX is an estimated channel matrix in TDD or representative channel derived from PMI in FDD,

[0080] F is a precoder matrix N.sub.TX×r.sub.F (in most cases r.sub.F=RI), and

[0081] n is an additive white Gaussian noise of size N.sub.RX×1.

[0082] FIG. 2 illustrates a method 200 of downlink data transmission and CSI feedback of the MIMO system 100 of FIG. 1. The eNodeB 105 transmits downlink (DL) data to the UE 115 on its antennas 110 and the UE receives the DL data on multiple receive-antennas 120 at step 205. For minimizing inter-layer interferences, the UE 115 provides channel status information (CSI), which includes a precoder matrix indicator (PMI), to the eNodeB 105 at step 210.

[0083] The feedback of the CSI from the UE 115 to the eNodeB 105 enables the eNodeB 105 to modify subsequent DL signals to account for changing conditions and to maximise data throughput, as discussed in further detail below. In particular, the channel information may be decomposed into components representing a transmission component and a signal strength component from which the precoder is generated.

[0084] FIG. 3 illustrates a method 300 of generating a precoder for use in a MIMO system when communication with a UE, according to an embodiment of the present invention. The method 300 can be used to generate a minimum-mean-squared-error optimised precoding in TDD transmission and to improve performance as compared to method which directly uses reported PMI in FDD transmission.

[0085] At block 305, singular values of the following decomposition are determined according to the following equation 2.

[00011]$\begin{array}{cc}U.Math..Math.\Lambda .Math..Math.V^H=\frac{1}{{\sigma }^2}.Math.H^H.Math.H& \left(\mathrm{Equation}.Math..Math.2\right)\end{array}$

[0086] In the above equation 2, U and V comprise left and right unitary matrices of the singular value decomposition, Λ comprises singular values of the singular value decomposition, H is a channel matrix of the user, σ.sup.2 is a noise variance of the UE, and the superscript H is the Hermitian transpose.

[0087] At block 310, a Lagrange multiplier υ is determined, for example as discussed in further detail below with reference to FIG. 4.

[0088] At block 315, a power allocation matrix D is determined according to the following equation 3.

[00012]$\begin{array}{cc}{D}_{n,n}=\sqrt{{\left(\frac{1}{\sqrt{\upsilon .Math..Math.{\Lambda }_{n,n}}}-\frac{1}{{\Lambda }_{n,n}}\right)}^{+}}.Math..Math.D_{n,m}=0,m\ne n& \left(\mathrm{Equation}.Math..Math.3\right)\end{array}$

[0089] At block 320, the precoder matrix F is generated according to the following equation 4.

[00013]$\begin{array}{cc}F=\mathrm{WD}.Math..Math.W=\left[\begin{array}{ccc}{V}_{1,1}& \mathrm{.Math.}& V_{1,\mathrm{RI}}\\ \mathrm{.Math.}& \ddots & \mathrm{.Math.}\\ V_{N_{\mathrm{TX}},1}& \mathrm{.Math.}& V_{N_{\mathrm{TX}},\mathrm{RI}}\end{array}\right]& \left(\mathrm{Equation}.Math..Math.4\right)\end{array}$

[0090] In the above equation, N.sub.TX is the number of transmit antennas of the MIMO system and RI is the Rank of the MIMO system.

[0091] FIG. 4 illustrates a method of computing a Lagrange multiplier, according to an embodiment of the present invention.

[0092] At block 405, minimum and maximum values of the Lagrange multiplier υ.sub.min and υ.sub.max are set.

[0093] At block 410, the Lagrange multiplier υ is set as υ=(υ.sub.max+υ.sub.min)/2.

[0094] At block 415, the following quantity is computed according to equation 5:

[00014]$\begin{array}{cc}\hat{P}=\underset{n=1}{\overset{\mathrm{RI}}{.Math.}}.Math.\frac{1}{{\Lambda }_{n,n}}.Math.{\left(\sqrt{\frac{{\Lambda }_{n,n}}{\upsilon }}-1\right)}^{+}& \left(\mathrm{Equation}.Math..Math.5\right)\end{array}$

[0095] where the sign ( ).sup.+ means that if ( )<0 then assign ( )=0.

[0096] If {circumflex over (P)}>P then the minimum value of the Lagrange multiplier is set in 420 as υ.sub.min=υ, otherwise the maximum value of the Lagrange multiplier is set in 425 as υ.sub.max=υ.

[0097] Blocks 410-415 are repeated until |P−P|<ε, upon which the Lagrange multiplier υ is output in block 430, where ε is a threshold for convergence.

[0098] According to certain embodiments, the noise variance σ.sup.2 is estimated from the reported CQI (Channel Quality Indicator) as follows:

[0099] a) Find SINR.sub.l based on the SINR thresholds in the CQI table.

[0100] Calculate σ.sup.2 using SINR.sub.l, number of codewords L and transmit power P as the following equation.

[00015]${\sigma }^2=\frac{P}{\underset{l=1}{\overset{L}{.Math.}}.Math.{\mathrm{SINR}}_l.Math.\text{/}.Math.L}$

[0101] In the above equation, L is the number of codewords used for the UE, P is the transmit power, and SINR.sub.l is the signal-to-interference-plus-noise ratio for the UE.

[0102] While only two antennas are depicted above, the skilled addressee will readily appreciate that any number of suitable antennas can be used on the eNodeB and/or UE.

[0103] According to certain embodiments, the MIMO system is a TDD system, and a channel matrix is estimated from the reciprocal channel. Alternatively, the MIMO system is an FDD system, and a representative channel is derived from a precoder matrix indicator (PMI) of the channel information.

[0104] In the present specification and claims (if any), the word “comprising” and its derivatives including “comprises” and “comprise” include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0105] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0106] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.

[0107] This application is based upon and claims the benefit of priority from Australian provisional patent application No. 2014905071, filed on Dec. 15, 2014, the disclosure of which is incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

[0108] 100 MIMO SYSTEM [0109] 105 eNB [0110] 110, 120 ANTENNA [0111] 115 UE