COORDINATED TRANSMISSION METHOD, COORDINATED TRANSMISSION SYSTEM, CENTRAL STATION AND RADIO BASE STATION

• US 20110080884A1
• Filed: 10/01/2010
• Published: 04/07/2011
• Est. Priority Date: 10/01/2009
• Status: Active Grant

• Current Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Original Assignee: NTT Docomo Incorporated (Nippon Telegraph and Telephone Corporation)
• Inventors: Hagiwara, Junichiro, Benjebbour, Anass, Ohwatari, Yusuke, Okumura, Yukihiko
• Granted Patent: US 8,730,883 B2
• Time in Patent Office: Days
• US Class Current: 370/329
• CPC Class Codes: H04B 7/022 Site diversity; Macro-diversity using two or more spaced independent antennas H04B7/04
• CPC Class Codes: H04W 16/28 using beam steering

Abstract

A coordinated transmission method of the invention has the steps of selecting a directional pattern corresponding to an area in which a radio terminal locates, from among a plurality of directional patterns determined respectively corresponding to a plurality of resources in frequency domains where the plurality of directional patterns is configured so that a plurality of radio base stations surrounding the area transmits, to the area, directional beams of same frequency domain resources to face one another, while not transmitting the directional beams of the same frequency domain resources using the same frequency domain resources to areas adjacent to the area, and of distributing a signal to transmit to the radio terminal according to the selected directional pattern, determining a frequency domain and directions of directional beams regarding the distributed signal, and delivering the signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.

Claims

1. A coordinated transmission method in which a plurality of radio base stations simultaneously transmit signals to a radio terminal locating in an area formed by adjacent sectors of the plurality of radio base stations, comprising:

selecting a directional pattern corresponding to the area in which the radio terminal locates, from among a plurality of directional patterns determined respectively corresponding to a plurality of resources in frequency domains, the plurality of directional patterns being configured so that the plurality of radio base stations surrounding the area transmits, to the area, directional beams of same frequency domain resources to face one another, while not transmitting directional beams using the same frequency domain resources to areas adjacent to the area; and

distributing a signal to transmit to the radio terminal according to the selected directional pattern, determining a frequency domain and directions of directional beams regarding the distributed signal, and delivering the signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.

2. The coordinated transmission method according to claim 1, wherein the plurality of directional patterns is determined respectively corresponding to a plurality of resources in time domains, in addition to the plurality of resources in frequency domains.

3. The coordinated transmission method according to claim 2, wherein the plurality of directional patterns is determined respectively corresponding to the plurality of resources in time domains, in accordance with traffic conditions in the area.

4. The coordinated transmission method according to claim 1, wherein the plurality of resources in frequency domains is a plurality of frequency blocks of an OFDMA system, and the plurality of directional patterns is determined respectively corresponding to the plurality of frequency blocks.

5. The coordinated transmission method according to claim 1, wherein the signal distributed according to the directional pattern is delivered to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal, by using multiuser MIMO transmission for performing precoding by a Block Diagonalization Zero-Forcing method.

6. A coordinated transmission system in which a plurality of radio base stations simultaneously transmit signals to a radio terminal locating in an area formed by adjacent sectors of the plurality of radio base stations, comprising:

a selection section for selecting a directional pattern corresponding to the area in which the radio terminal locates, from among a plurality of directional patterns determined respectively corresponding to a plurality of resources in frequency domains, the plurality of directional patterns being configured so that the plurality of radio base stations surrounding the area transmits, to the area, directional beams of the same frequency domain resources to face one another, while not transmitting directional beams of the same frequency domain resources using the same frequency domain resources to areas adjacent to the area; and

a delivery section for distributing a signal to transmit to the radio terminal according to the selected directional pattern, determining a frequency domain and directions of directional beams regarding the distributed signal, and delivering the signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.

7. A central station connected to a plurality of radio base stations in a coordinated transmission system in which the plurality of radio base stations simultaneously transmit signals to a radio terminal locating in an area formed by adjacent sectors of the plurality of radio base stations, comprising:

a selection section for selecting a directional pattern corresponding to the area in which the radio terminal locates, from among a plurality of directional patterns determined respectively corresponding to a plurality of resources in frequency domains, the plurality of directional patterns being configured so that the plurality of radio base stations surrounding the area transmits, to the area, directional beams of same frequency domain resources to face one another, while not transmitting directional beams of the same frequency domain resources using the same frequency domain resources to areas adjacent to the area; and

a delivery section for distributing a signal to transmit to the radio terminal according to the selected directional pattern, determining a frequency domain of and directions of directional beams regarding the distributed signal, and delivering the signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.

8. The central station according to claim 7, wherein the plurality of directional patterns is determined respectively corresponding to a plurality of resources in time domains, in addition to the plurality of resources in frequency domains.

9. The central station according to claim 8, wherein the plurality of directional patterns is determined respectively corresponding to a plurality of resources in time domains, in accordance with traffic conditions.

10. The central station according to claim 7, wherein the plurality of resources in frequency domains is a plurality of frequency blocks of an OFDMA system, and the plurality of directional patterns is determined respectively corresponding to the plurality of frequency blocks.

11. The central station according to claim 7, wherein the delivery section delivers the signal distributed according to the directional pattern to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal, by using multiuser MIMO transmission for performing precoding by a Block Diagonalization Zero-Forcing method.

12. The central station according to claim 7, wherein the delivery section includes:

a signal distribution section for distributing the signal to transmit to the radio terminal according to the selected directional pattern;

a plurality of modulation sections corresponding to the number of radio terminals that the plurality of radio base stations is capable of holding; and

a plurality of transmission sections corresponding to the number of radio base stations connected to the central station;

each of the plurality of modulation sections modulates the signal distributed by the signal distribution section; and

each of the plurality of transmission sections transmits the modulated signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.

13. A radio base station in a coordinated transmission system in which a plurality of radio base stations simultaneously transmit signals to a radio terminal locating in an area formed by adjacent sectors of the plurality of radio base stations, comprising:

a selection section for selecting a directional pattern corresponding to the area in which the radio terminal locates, from among a plurality of directional patterns determined respectively corresponding to a plurality of resources in frequency domains, the plurality of directional patterns being configured so that the plurality of radio base stations surrounding the area transmits, to the area, directional beams of same frequency domain resources to face one another, while not transmitting directional beams of the same frequency domain resources using the same frequency domain resources to areas adjacent to the area; and

a delivery section for distributing a signal to transmit to the radio terminal according to the selected directional pattern, determining a frequency domain and directions of directional beams regarding the distributed signal, and delivering the signal to each of the plurality of radio base stations that simultaneously transmits the signal to the radio terminal.