METHOD AND APPARATUS FOR ALIGNING INTERFERENCE USING A FEED FORWARD INDEX IN A HIERARCHICAL CELL COMMUNICATION SYSTEM

• US 20120077511A1
• Filed: 05/23/2011
• Published: 03/29/2012
• Est. Priority Date: 09/27/2010
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Lee, Nam Yoon, Shin, Chang Yong, Shin, Won Jae, Noh, Won Jong, Choi, Hyun Ho, Jang, Kyung Hun
• Granted Patent: US 9,331,764 B2
• Time in Patent Office: Days
• US Class Current: 455/452.1
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04B 7/0617 for beam forming
• CPC Class Codes: H04B 7/0634 Antenna weights or vector/matrix coefficients
• CPC Class Codes: H04B 7/0862 receiver computing weights based on information from the transmitter
• CPC Class Codes: H04W 16/32 Hierarchical cell structures

Abstract

Provided is an interference aligning method and apparatus that does not perform full feed-forwarding in a hierarchical cell communication. A macro base station may generate respective transmission beamforming vectors of macro terminals to null interference channels to pico terminals and to remove interference among the macro terminals. The effective interference channels are based on reception beamforming vectors of the pico terminals. The macro base station may transmit, to a macro terminal, a feed-forward indicator (FFI) indicating a method of transmitting information associated with a reception beamforming vector of the macro terminal. The macro terminal may obtain information associated with the reception beamforming vector based on the FFI.

Claims

1. A communication method of a macro base station, the method comprising:

calculating an inter-cell nulling matrix that nulls an effective interference channel between the macro base station and a first pico terminal corresponding to a first pico base station based on a reception beamforming vector of the first pico terminal, and that nulls an effective interference channel between the macro base station and a second pico terminal corresponding to a second pico base station based on a reception beamforming vector of the second pico terminal; and

calculating respective transmission beamforming vectors of macro terminals to remove interference that occurs among the macro terminals, using respective reception beamforming schemes of the macro terminals and the inter-cell nulling matrix.

2. The method of claim 1, wherein the calculating of the respective transmission beamforming vectors of the macro terminals comprises:

obtaining respective transmission beamforming effective vectors of the macro terminals using the inter-cell nulling matrix and serving channels of the macro terminals; and

extracting the respective transmission beamforming vectors of the macro terminals, using the respective transmission beamforming effective vectors of the macro terminals and the inter-cell nulling matrix.

3. The method of claim 1, further comprising:

scheduling macro terminals that do not receive interference from the first pico base station and the second pico base station.

4. The method of claim 1, further comprising:

transmitting demodulation reference signals (DM-RSs) to the macro terminals using the respective transmission beamforming vectors of the macro terminals.

5. The method of claim 1, further comprising:

calculating respective reception beamforming vectors of the macro terminals based on the respective transmission beamforming vectors of the macro terminals; and

feed-forwarding the respective reception beamforming vectors of the macro terminals to the corresponding terminals.

6. The method of claim 5, wherein the calculating comprises:

calculating the respective reception beamforming vectors of the macro terminals using the respective transmission beamforming vectors of the macro terminals and serving channels of the macro terminals, when the respective reception beamforming schemes of the macro terminals are maximal ratio combining (MRC) schemes.

7. The method of claim 1, further comprising:

transmitting a feed-forward indicator (FFI) indicating one of multiple modes associated with a method of transmitting information associated with the respective reception beamforming vectors of the macro terminals to the corresponding terminals.

8. The method of claim 7, wherein the multiple modes include at least two of:

a first mode to perform feed-forwarding of the respective reception beamforming vectors;

a second mode to transmit information associated with a resource to which DM-RSs are to be transmitted, the DM-RSs being used for calculating the respective reception beamforming vectors, and to transmit, using the DM-RSs, information associated with effective serving channels that are based on the transmission beamforming vectors of the macro base station; and

a third mode to transmit information associated with a resource to which DM-RSs that are orthogonal to each other are to be transmitted, the DM-RSs being used for calculating the reception beamforming vectors, and to transmit, using the DM-RSs, information associated with effective serving channels that are based on the transmission beamforming vectors of the macro base station.

9. The method of claim 1, further comprising:

receiving, from the first pico terminal, information associated with the effective interference channel between the macro base station and the first pico terminal, and receiving, from the second pico terminal, information associated with the effective interference channel between the macro base station and the second pico terminal.

10. A communication method of a terminal, the method comprising:

receiving, from a base station, a feed-forward indicator (FFI) that indicates one mode from among multiple modes associated with a method of obtaining a reception beamforming vector of the terminal;

obtaining, from the base station, information for determining the reception beamforming vector, based on a method corresponding to a mode indicated by the FFI; and

determining the reception beamforming vector based on the obtained information.

11. The method of claim 10, wherein the multiple modes include at least two of:

a first mode to receive the reception beamforming vector;

a second mode to obtain, using a demodulation reference signal(DM-RS), information associated with an effective serving channel that is based on a transmission beamforming vector of the base station, and to calculate the reception beamforming vector based on the information associated with the obtained effective serving channel;

a third mode to receive DM-RSs that are orthogonal to each other, and to calculate the reception beamforming vector based on the obtained DM-RSs; and

a fourth mode to determine the reception beamforming vector without using interference with a neighbor cell.

12. The method of claim 11, wherein, if the received FFI indicates the first mode, the obtaining of the information for determining the reception beamforming vector comprises:

obtaining, from the base station, an index of a codebook associated with the reception beamforming vector.

13. The method of claim 11, wherein, if the received FFI indicates the second mode, the obtaining of the information for determining the reception beamforming vector comprises:

receiving, from the base station, information associated with a resource to which the DM-RS is to be transmitted; and

receiving the DM-RS based on the resource to which the DM-RS is to be transmitted.

14. The method of claim 11, wherein, if the received FFI indicates the third mode, the obtaining of the information for determining the reception beamforming vector comprises:

receiving information associated with a resource to which DM-RSs that are orthogonal to each other are to be transmitted; and

receiving the DM-RSs based on the resource to which the DM-RSs that are orthogonal to each other are to be transmitted.

15. A base station for reducing interference on a pico terminal that is served by a pico base station, the base station comprising:

a receiving unit for receiving channel information including a reception beamforming vector of the pico terminal;

a beamforming determining unit for determining a transmission beamforming vector of one or more terminals served by the base station, to reduce interference on the pico terminal, and calculating a reception beamforming vector of the one or more terminals, based on the respective transmission beamforming vector of the one or more terminals; and

a transmitting unit for transmitting, to the one or more terminals, a feed-forward indicator (FFI) indicating one of multiple modes associated with the method of transmitting information associated with the reception beamforming vector.

16. The base station of claim 15, wherein the FFI indicates a first mode, and the transmitting unit further transmits an index of a codebook corresponding to a reception beamforming vector to be used by the one or more terminals.

17. The base station of claim 15, wherein the FFI indicates a second mode, and the transmitting unit further transmits a demodulation reference signal (DM-RS) and information about a serving channel, which are to be used by the one or more terminals to calculate the reception beamforming vector.

18. A terminal served by a base station for reducing interference on a pico terminal that is served by a pico base station, the terminal comprising;

a receiving unit for receiving, from the base station, a feed-forward indicator (FFI) and information for obtaining a reception beamforming vector, wherein the FFI indicates one of a plurality of modes of obtaining the reception beamforming vector; and

a determining unit for determining the reception beamforming vector based on the mode indicated by the FFI and the information for obtaining the reception beamforming vector.

19. The terminal of claim 18, wherein the receiving unit receives a FFI indicating a first mode, the information for obtaining the reception beamforming vector received from the base station comprises an index of a codebook corresponding to the reception beamforming vector, and the determining unit determines the reception beamforming vector based the FFI and the index of the codebook.

20. The terminal of claim 18, wherein the receiving unit receives a FFI indicating a second mode, the information for obtaining the reception beamforming vector received from the base station comprises information associated with a resource to which a demodulation resource signal (DM-RS) is to be transmitted, the receiving unit further receives the DM-RS from the base station based on the information associated with the resource, and the determining unit determines the reception beamforming vector based on the FFI and the received DM-RS.