OUT-OF-GROUP INTERFERENCE REDUCTION IN WIRELESS COMMUNICATION SYSTEMS

• US 20120057540A1
• Filed: 09/06/2011
• Published: 03/08/2012
• Est. Priority Date: 09/06/2010
• Status: Active Grant

• Current Assignee: Fujitsu Limited, University of Edinburgh
• Original Assignee: Fujitsu Limited, University of Edinburgh
• Inventors: FANG, Yiwei, THOMPSON, John
• Granted Patent: US 8,565,175 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• CPC Class Codes: H04B 7/024 Co-operative use of antennas of several sites, e.g. in co-ordinated multipoint or co-operative multiple-input multiple-output [MIMO] systems
• 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: H04W 24/08 Testing, supervising or monitoring using real traffic
• CPC Class Codes: H04W 72/121 for groups of terminals or users
• CPC Class Codes: H04W 72/541 using the level of interference

Abstract

In a MIMO wireless communication system, a plurality of base stations (BSs) are provided each of which can transmit signals to, and receive signals transmitted from, one or more user equipments (UEs). The BSs are also organised into a plurality of groups. In a given group of BSs serving one or more UEs, those serving BSs coordinate with each other to simultaneously transmit signals to the one or more served UEs, and one or more of the served UEs feed back information to one or more of those serving BSs. The fed back information incorporates inter-group noise information related to interference between different BS groups. The method involves processing signals for simultaneous transmission by BSs of a group to one or more UEs served by that group and using the information fed back to the BSs of that group to improve system performance.

Claims

1. A method for use in a multiple-input multiple-output wireless communication system in which:

a plurality of base stations are provided each of which can transmit signals to, and receive signals transmitted from, one or more user equipments;

the base stations are organised into a plurality of groups;

in a given group of base stations serving one or more user equipments, those serving base stations coordinate with each other to simultaneously transmit signals to the one or more served user equipments, and one or more of the served user equipments feed back information to one or more of those serving base stations, wherein said information incorporates inter-group noise information related to interference between different base station groups, and

wherein the method involves processing signals for simultaneous transmission from base stations of a group to one or more user equipments served by that group, said processing using the inter-group noise information fed back to the base station(s) of that group to improve transmission capacity.

4. A method according to claim 1, wherein:

the information fed back by one or more of the user equipments served by a given group of base stations also includes intra-group noise information related to interference in said given group which is associated with transmissions between said served user equipments and different individual serving base stations of said group, and

the processing of signals for simultaneous transmission from base stations of the group to one or more user equipments served by that group also uses the intra-group noise information.

5. A method according to claim 1, wherein:

a noise-related parameter is defined which incorporates the inter-group noise information, and

the processing involves using the parameter to precode signals for simultaneous transmission from base stations of a group to one or more user equipments served by that group.

6. A method as claimed in claim 5, wherein:

the inter-group noise information includes noise power Ĩ

₀ which represents the component of the total power of the noise in the system that is associated with inter-group interference,

information fed back by the user equipments(s) further includes noise power Ñ

₀ which represents the component of the total power of the noise in the system that is associated with background noise, and

the noise-related parameter, μ

, is calculated using an equation equivalent to the following;

7. A method as claimed in claim 6, wherein:

N_B represents the number of base stations in a group, N_U represents the number of user equipments served by the base stations of that group in a given time slot, N_R represents the number of antennas on each user equipment, N_T represents the number of transmitter antennas on each base station in the group, and a channel between the base stations of the group and the user equipments served by the group is represented by a channel matrix H∈

C<sup>NRNU×

NTNB</sup>, and

the precoding of signals for simultaneous transmission from the base stations of the group to one or more user equipments served by the group involves calculating a precoding matrix F using an equation equivalent to the following;

F=H^H(HH^H+μ

I)<sup>−

1</sup>.

8. A method as claimed in claim 6, wherein:

N_B represents the number of base stations in a group, N_U represents the number of user equipments served by the base stations of that group in a given time slot, N_R represents the number of antennas on each user equipment, N_T represents the number of transmitter antennas on each base station in the group, and a channel between the base stations of the group and the user equipments served by the group is represented by a channel matrix H∈

C<sup>NRNU×

NTNR</sup> where H=[H₁^T, . . . , H_NU^T]^T and H_k(k∈

[1, . . . , N_U]) represents the channel from the N_T N_B transmitter antennas to the N_R antennas of a user equipment k, and

the precoding of signals for simultaneous transmission from the base stations of the group to user equipment k served by the group involves calculating a precoding matrix F_k using an equation equivalent to the following;

F_k=(_k+μ

I)<sup>−

1</sup>H_k^H

where

_k=[H₁^T, . . . H<sub>k−

1</sub>^T, H_k+1^T, . . . H_NU^T]^T.

9. A method as claimed in claim 8, wherein scheduling of user equipments is performed by:

(i) finding a first user equipment having the strongest channel from amongst the user equipments served by the group by, for each user equipment, examining the norm of its channel H_x and past average transmission capacity R_x using an equation equivalent to;

10. A method as claimed in claim 6, wherein:

N_B represents the number of base stations in a group, N_U represents the number of user equipments served by the base stations of that group in a given time slot, N_R represents the number of antennas on each user equipment, N_T represents the number of transmitter antennas on each base station in the group, a channel between the base stations of the group and the user equipments served by the group is represented by a channel matrix H∈

C<sup>NRNU×

NTNB</sup> where H=[H₁^T, . . . , H_NU^T]^T and H_k(k∈

[1, . . . , N_U]) represents the channel from the N_T N_B transmitter antennas to the N_R antennas of a user equipment k served by the group, a singular value decomposition of H_k is H_k=U_kΣ

_kV_k^H where U_k=[u_k1, . . . u_{kNU] and Vk}=[v_k1, . . . , v_kNU], a receiver filter of user equipment k is u_k1, the largest eigenvalue in Σ

_k represented by σ

_k1, and an equivalent channel Γ

_k for user equipment k after the receiver filter u_k1 is applied represented by Γ

_k=u_k1H_k=σ

_k1v_k1, and

the precoding of signals for simultaneous transmission from the base stations of the group to the user equipment k involves calculating a precoding matrix F_k using an equation equivalent to the following;

F_k=(_k+μ

I)<sup>−

1</sup>Γ

_k^H

where

_k=[64₁^T, . . . Γ

<sub>k−

1</sub>^T, Γ

_k+1^T, . . . , Γ

_NU^T]^T.

11. A method as claimed in claim 10, wherein scheduling of user equipments is performed by:

(i) finding a first user equipment having the strongest channel from amongst the user equipments served by the group by, for each user equipment, examining the norm of its channel Γ

_x and past average transmission capacity R_x using an equation equivalent to;

12. A method claimed in claim 6, wherein:

N_B represents the number of base stations in a group, N_U represents the number of user equipments served by the base stations of that group in a given time slot, N_R represents the number of antennas on each user equipment, N_T represents the number of transmitter antennas on each base station in the group, a channel between the base stations of the group and the user equipments served by the group is represented by a channel matrix H∈

C<sup>NRNUN×

NTNB</sup> where H=[H₁^T, . . . , H_NU^T]^T and H_k(k∈

[1, . . . , N_U]) represents the channel from the N_T N_B transmitter antennas to the N_R antennas of a user equipment k served by the group, T∈

C<sup>NTNB×

NTNB</sup> represents an equivalent precoding matrix, W_k is the covariance of the total noise affecting a user equipment k, {umlaut over (H)}_k=(H_kT_K)^HW_k<sup>−

1</sup>H_kT_k represents an equivalent channel matrix, a singular value decomposition of {umlaut over (H)}_k is {umlaut over (H)}_k=Ü

_k{umlaut over (Σ

)}_k{umlaut over (V)}_k^H where

13. A method as claimed in claim 10, wherein scheduling of user equipments is performed by:

(i) finding a first user equipment having the strongest channel from amongst the user equipments served by the group by, for each user equipment, examining the norm of its channel Γ

_x and past average transmission capacity R_x using an equation equivalent to;

14. A method according to claim 6 wherein, in order to find the value of the noise-related μ

;

(i) a number of candidate values of β

are selected;

(ii) for each selected candidate β

value, a trial value for μ and

a corresponding trial precoding matrix F are calculated;

(iii) for each trial μ

value and trial precoding matrix F thus calculated, a system transmission capacity is calculated; and

(iv) the trial μ

value that delivered the greatest calculated system transmission capacity is selected as the value for μ

.

15. A method as claimed in claim 1, wherein precoding of signals for simultaneous transmission from base stations of the group to one or more user equipments served by that group is performed by, or at, one or more of those base stations.

16. A non-transitory computer-readable medium storing a computer program which, when executed on a computer operating in a multiple-input multiple-output wireless communication system, causes the computer to perform the method as claimed in claim 1.

2. A multiple-input multiple-output wireless communication system comprising:

a plurality of base stations, each of which can transmit signals to, and receive signals transmitted from, one or more user equipments, wherein the base stations are organised into a plurality of groups; and

in a given group of base stations serving one or more user equipments, those serving base stations coordinate with each other to simultaneously transmit signals to the one or more served user equipments, and one or more of the served user equipments feed back information to one or more of those serving base stations, said information incorporating inter-group noise information related to interference between different base station groups;

wherein signals are processed for simultaneous transmission from base stations of a group to one or more user equipments served by that group and said processing uses the inter-group noise information fed back to the base station(s) of that group to improve transmission capacity.

3. An apparatus for use in a multiple-input multiple-output wireless communication system, the system comprising:

a plurality of base stations, each of which can transmit signals to, and receive signals transmitted from, one or more user equipments, wherein the base stations are organised into a plurality of groups; and

in a given group of base stations serving one or more user equipments, those serving base stations coordinate with each other to simultaneously transmit signals to the one or more served user equipments, and one or more of the served user equipments feed back information to one or more of those serving base stations, said information incorporating inter-group noise information related to interference between different base station groups;

wherein the apparatus processes signals for simultaneous transmission from base stations of a group to one or more user equipments served by that group and, said processing uses the inter-group noise information fed back to the base station(s) of that group to improve transmission capacity.