FEEDBACK INTERVAL CONTROL

• US 20120230274A1
• Filed: 05/14/2012
• Published: 09/13/2012
• Est. Priority Date: 12/21/2009
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: XIAO, Hui, SARPERI, Luciano Pietro Giacomo
• Granted Patent: US 8,902,834 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 7/0417 Feedback systems
• CPC Class Codes: H04B 7/0421 utilizing implicit feedback, e.g. steered pilot signals
• CPC Class Codes: H04B 7/0478 Special codebook structures directed to feedback optimisation
• 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 7/0632 Channel quality parameters, e.g. channel quality indicator [CQI]
• 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

Abstract

A multiple-input multiple-output (MIMO) wireless communication systems that includes a plurality of adjacent cells, each containing one or more base stations operable to transmit signals to, and receive signals transmitted from, one or more users. The users are operable to feed back to the relevant base station(s) channel state information relating to channel(s) between the relevant base station(s) and the users, and the base stations are operable to adapt signals for transmission to users, based on the fed back channel state information, to account for channel variations. The proposed method involves obtaining information related to time-variation in channel spatial structure, and adjusting the timing with which a user feeds back channel state information, based on the time variation in channel spatial structure. The invention helps to achieve a suitable balance between the feedback overhead and system performance, and may be operable in systems operating according to various CoMP transmission modes.

Claims

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

a plurality of adjacent cells are provided each containing one or more base stations operable to transmit signals to, and receive signals transmitted from, one or more users,

a user is operable to feed back to the relevant base station(s) channel state information relating to channel(s) between the relevant base station(s) and that user; and

base stations are operable to adapt signals for transmission to users, based on the fed back channel state information, to account for channel variations;

the method comprising;

obtaining information related to time-variation in channel spatial structure; and

adjusting the timing with which a user feeds back channel state information, based on the time variation in channel spatial structure.

2. The method according to claim 1 further comprising:

defining a threshold of a parameter related to time variation in channel spatial structure;

calculating the parameter at successive times, and

causing or allowing user feedback of channel state information to one or more base stations at times when the parameter equals or exceeds the threshold.

3. The method according to claim 2, wherein the channel spatial structure of each channel can be represented by a channel matrix, the method further comprising using the channel matrix for one or more channels in calculating the said parameter.

4. The method according to claim 3, wherein coordination is performed between cells, or between portions of cells, for reducing inter-cell interference.

5. The method according to claim 4, wherein the transmission scheme used for transmitting signals from one or more base stations to a user involves one of coordinated scheduling (CS), coordinated beamforming (CB), joint processing (JP) with local precoding, or joint processing (JP) with weighted local precoding, and the method further comprises:

using the channel matrix for each of the coordinated cells, or coordinated portions of cells, to calculate the said parameter for each said cell or cell portion, and

causing or allowing user feedback of channel state information to the base station of a cell or cell portion when the parameter for that cell or cell portion equals or exceeds the threshold.

6. The method according to claim 5, further comprising calculating the parameter, d_wd—

_corr, using the equation;

7. The method according to claim 4, wherein the transmission scheme used for transmitting signals from one or more base stations to a user involves joint processing (JP) with global precoding, and the method further comprises

calculating a concatenated channel matrix from the channel matrices of each of the coordinated cells or coordinated portions of cells,

using the concatenated channel matrix to calculate the said parameter, and

causing or allowing user feedback of channel state information to the base stations of the coordinated cells or portions of cells at times when the parameter equals or exceeds the threshold.

8. The method according to claim 7, further comprising calculating the parameter, d_wd—

_corr, using the equation;

9. The method according to claim 4, wherein the transmission scheme used for transmitting signals from one or more base stations to a user involves joint processing (JP) with MBSFN precoding, and the method further comprises

calculating an added up channel matrix from the channel matrices of each of the coordinated cells or coordinated portions of cells,

using the added up channel matrix to calculate the said parameter, and

causing or allowing user feedback of channel state information to the base stations of the coordinated cells or portions of cells at times when the parameter equals or exceeds the threshold.

10. The method according to claim 9, further comprising calculating the parameter, d_wd—

_corr, using the equation;

11. A user equipment for use in a multiple-input multiple-output (MIMO) wireless communication system in which a plurality of adjacent cells, or sectors of cells, are provided each containing one or more base stations operable to transmit signals to, and receive signals transmitted from, the user equipment,

wherein the user equipment is operable to:

feed back to the relevant base station(s) channel state information relating to channel(s) between the relevant base station(s) and the user equipment, thereby enabling the base station(s) to adapt signals for transmission to the user equipment, based on the fed back channel state information;

obtain information related to time-variation in channel spatial structure; and

adjust the timing with which channel state information is fed back based on the time variation in channel spatial structure.

12. The user equipment according to claim 11, wherein the user equipment is further operable to:

receive from a base station a threshold of a parameter related to time variation in channel spatial structure;

calculate the parameter at successive times, and

feedback channel state information to one or more base stations at times when the parameter equals or exceeds the threshold.

13. The user equipment according to claim 12, wherein the channel spatial structure of each channel can be represented by a channel matrix, and the user equipment is further operable to use the channel matrix for one or more channels in calculating the said parameter.

14. The user equipment according to claim 12, wherein coordination is performed between cells, or between portions of cells, for reducing inter-cell interference, and the user equipment calculates the said.

15. A multiple-input multiple-output (MIMO) wireless communication system in which:

a plurality of adjacent cells or sectors of cells are provided, each containing one or more base stations operable to transmit signals to, and receive signals transmitted from, one or more users,

one or more users are operable to feed back to the relevant base station(s) channel state information relating to channel(s) between the relevant base station(s) and each said user;

base stations are operable to adapt signals for transmission to users, based on fed back channel state information, to account for channel variations, wherein

information related to time-variation in channel spatial structure is obtained and

the timing with which a user feeds back channel state information is adjusted based on time variation in channel spatial structure.

16. A base station for use in a multiple-input multiple-output (MIMO) wireless communication system as claimed in claim 15, wherein the base station is operable to:

transmit to one or more users a threshold of a parameter related to time variation in channel spatial structure, whereby one or more of the users calculate the parameter at successive times and feedback channel state information to the base station, and/or to one or more other base stations, at times when the parameter equals or exceeds the threshold.