Mobile Communication System Using Adaptive Multi-Antenna

• US 20100222051A1
• Filed: 03/02/2010
• Published: 09/02/2010
• Est. Priority Date: 09/06/2007
• Status: Active Grant

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: YOSHIDA, Makoto, WATANABE, Masahiro, FUJITA, Hiroshi
• Granted Patent: US 8,532,646 B2
• Time in Patent Office: Days
• US Class Current: 455/422.100
• CPC Class Codes: H04B 7/0413 MIMO systems
• CPC Class Codes: H04B 7/0613 using simultaneous transmission H04B7/0686 takes precedence
• CPC Class Codes: H04B 7/0689 using different transmission schemes, at least one of them being a diversity transmission scheme

Abstract

A mobile communication system using an adaptive multiantenna realizes improvement of reception characteristics, effective use of the band, and optimization of the throughput in comparison with a system in which application of the same multiantenna communication method is continued irrespective of a variation of the number of radio relay stations. The mobile communication system comprises a radio base station, a radio relay station, and mobile terminal stations for communicating with the radio base station through a radio relay station. The radio base station has a multiantenna and is characterized in that the radio base station judges if there is any variation of the number of radio relay stations when the radio base station carries out transmission through a radio relay station, and the radio base station communicates with the mobile terminal station by switching the multiantenna communication method using the multiantenna depending on the delay time of the feedback signal from the mobile terminal station if there is a variation of the number of radio relay stations.

Claims

1. A mobile communication system using an adaptive multi-antenna, comprising:

a wireless base station;

a wireless relay station; and

a mobile terminal station which performs communication with the wireless base station via the wireless relay station,

wherein the wireless base station has a multi-antenna, and

a multi-antenna communication method is switched according to estimation of the delay time of feedback signals from the mobile terminal station.

3. The mobile communication system using an adaptive multi-antenna according to claim 1, wherein the multi-antenna communication method comprises a closed-loop method which uses feedback signals from the mobile terminal station, and an open-loop method which does not use the feedback signals.

4. The mobile communication system using an adaptive multi-antenna according to claim 1, wherein the multi-antenna communication method to be switched comprises a channel-tracking method which controls each antenna of the multi-antenna to track variations in a wireless propagation channel, and a direction-tracking method which forms directionality in an optimum transmission direction.

5. The mobile communication system using an adaptive multi-antenna according to claim 1, wherein a threshold value of the delay time of feedback signals for switching the multi-antenna communication method is changed by the mobility of the mobile terminal station.

6. The mobile communication system using an adaptive multi-antenna according to claim 1, wherein the delay time of feedback signals from the mobile terminal station corresponds to a delay time between a timing of measurement at the mobile terminal station used for the multi-antenna communication method, and a timing of multi-antenna transmission based on information on the results of the measurement which is fed back to the wireless base station.

2. A mobile communication system using an adaptive multi-antenna, comprising:

a wireless base station;

a wireless relay station; and

a mobile terminal station to perform communication with the wireless base station via the wireless relay station,

wherein the wireless base station has a multi-antenna; and

a multi-antenna communication method is switched according to a traffic quantity.

7. The mobile communication system using an adaptive multi-antenna according to claim 2, wherein switching of the multi-antenna communication method between a closed-loop method and an open-loop method is performed according to a traffic quantity in a feedback signal band used in the closed-loop method.

8. The mobile communication system using an adaptive multi-antenna according to claim 2, wherein switching of the multi-antenna communication method between a closed-loop method and an open-loop method is performed according to changes in a feedback signal band used in the closed-loop method.

9. A wireless base station which performs communication with a mobile terminal station via a wireless relay station in a mobile communication system, and which has a multi-antenna, the wireless base station comprising:

a judgment unit, when transmission is performed through the wireless relay station in the communication with the mobile terminal station, to judge whether there is a change in the number of the wireless relay stations;

a delay time judgment unit to judge the delay time of feedback signals from the mobile terminal station; and

a multi-antenna method selection unit, when the judgment unit judges that there is a change in the number of the wireless relay stations, to switch a multi-antenna communication method that uses the multi-antenna, according to the delay time of feedback signals from the mobile terminal station.

10. The wireless base station in a mobile communication system according to claim 9, wherein the multi-antenna method selection unit selects, as the multi-antenna communication method, a closed-loop method which uses feedback signals from the mobile terminal station, and an open-loop method which does not use the feedback signals.

11. The wireless base station in a mobile communication system according to claim 9, wherein the multi-antenna method selection unit selects, as the multi-antenna communication method to be switched, a channel-tracking method which controls each antenna of the multi-antenna to track variations in a wireless propagation channel, and a direction-tracking method which forms directionality in an optimum transmission direction.

12. The wireless base station in a mobile communication system according to claim 9, further comprising:

a threshold value table in which is set a feedback signal delay time threshold value for switching the multi-antenna communication method; and

a terminal mobility judgment unit to judge the mobility of the mobile terminal station,

wherein the delay time threshold value set in the threshold value table is updated when the mobility of the mobile terminal station, judged by the terminal mobility judgment unit, changes.

13. The wireless base station in a mobile communication system according to claim 10, wherein the multi-antenna method selection unit switches between a closed-loop method and an open-loop method according to a traffic quantity in a feedback signal band used in the closed-loop method.

14. The wireless base station in a mobile communication system according to claim 10, wherein the multi-antenna method selection unit switches the multi-antenna communication method between a closed-loop method and an open-loop method according to changes in a feedback signal band used in the closed-loop method.

15. The wireless base station according to claim 11, further comprising:

a first antenna for direction tracking, configured by a set of a plurality of antennas placed at a placement interval which heightens the correlation between antennas;

a second antenna for channel tracking, configured by a set of a plurality of antennas placed at a placement interval which lowers the correlation between antennas;

an antenna switcher to perform switching between the first antenna and second antenna; and

a communication control unit to control the antenna switcher so as to perform switching between the first antenna and second antenna corresponding to selection of channel tracking or direction tracking by the multi-antenna method selection unit.