WIRELESS COMMUNICATION SYSTEM AND BASE STATION

• US 20130070625A1
• Filed: 07/10/2012
• Published: 03/21/2013
• Est. Priority Date: 09/16/2011
• Status: Active Grant

• Current Assignee: Hitachi, Ltd.
• Original Assignee: Hitachi, Ltd.
• Inventors: TAMAKI, Tsuyoshi, KATAYAMA, Rintaro, ISHIDA, Hitoshi, FUJISHIMA, Kenzaburo
• Granted Patent: US 8,897,161 B2
• Time in Patent Office: Days
• US Class Current: 370/252
• CPC Class Codes: H04W 36/08 Reselecting an access point
• CPC Class Codes: H04W 36/20 for optimising the interference level

Abstract

To reduce an uplink interference in a network with a first base station of a large output and a second base station of a small output. Detecting the interference, the second base station urges the first base station to hand over a terminal causing it to the second base station. Multiple base stations and one or more terminals exist in this system, each terminal connects with one base station, and a serving base station is changed according to a communication state of each terminal. If the different second base station other than the first base station to which the terminal connects detects a large interference, the second base station will multicast transmit information for urging handover to the base stations except itself. The base station having received the information specifies a terminal giving the interference to the second base station, and makes it to be handed over thereto.

Claims

1. A wireless communication system that comprises a plurality of base stations including a first base station with which a terminal communicates and a second base station to which a radio signal transmitted from the terminal becomes an interference power, and is capable of performing handover of a connection destination of the terminal from the first base station to the second base station,

wherein the second base station, upon detection of the interference power being more than or equal to a previously set threshold, multicast transmits information for urging the handover to multicast reception base stations that are at least a part of the base stations including the first base station, and

wherein the multicast receiver base station having received the information specifies a terminal that is inferred to exert the interference to the second base station that is a multicast source among the terminals connecting to the local base station and performs a handover processing on the terminal.

2. The wireless communication system according to claim 1,

wherein the information that is multicast transmitted includes at least either of time information or frequency information at which an interference power being more than or equal to the previously set threshold is detected, and

wherein specification of the terminal that is inferred to exert the interference to the second base station by the multicast receiver base station is done by specifying the terminal that transmitted the radio signal at a time and/or a frequency at which the interference power was detected based on the time information and/or frequency information included in the information that is multicast transmitted as described above.

3. The wireless communication system according to claim 2,

wherein the multicast receiver base station manages a log of time and frequency at which the base station itself allocated an uplink radio resource to its belonging terminal, and specifies a terminal that transmitted the radio signal at a time and/or a frequency at which the interference power was detected by collating time information and/or frequency information included in the information that was multicast transmitted and a log saying that the uplink radio resource was allocated.

4. The wireless communication system according to claim 3,

wherein the base station and the terminal communicate with each other using a subframe that was divided by a time and/or a frequency,

wherein the second base station stores either or both of time and frequency at which the received power of the radio signal transmitted from the terminal exceeds the threshold within a predetermined time, estimates an interference generation rule that is a generation rule of an uplink signal received power that exceeds the threshold from the record, and multicast transmits the information including the interference generation rule, and

wherein the multicast receiver base station collates the received interference generation rule and a log saying that the base station itself allocated the uplink radio resource to the belonging terminal, and specifies a terminal having a past result of allocation of the uplink radio resource nearest to the interference generation rule.

5. The wireless communication system according to claim 4,

wherein the interference generation rule has:

time information including a time period of a plurality of subframes at which the interference power was detected and an offset of a time at which the interference power was detected for the first time in the measurement period from a previously set reference time in a time direction; and

frequency information including an offset of a frequency at which the interference power was detected for the first time in the measurement period from a previously set reference frequency in a frequency direction and a shift quantity of frequency of a plurality of subframes at which the interference power was detected.

6. The wireless communication system according to claim 1,

wherein the multicast receiver base station specifies a terminal that is inferred to exert the interference to the second base station based on the downlink received power information of the terminal that the base station collects from the belonging terminal.

7. The wireless communication system according to claim 6,

wherein the multicast receiver base station

receives and stores at least a notification of the downlink received power from the second base station at a belonging terminal of the local base station from the terminal,

compares the downlink received powers at respective terminals from the second base station that is a source of the information being multicast transmitted, and

specifies one of the terminals such that the downlink received power exceeds the second threshold as the terminal that is inferred to exert the interference to the second base station.

8. The wireless communication system according to claim 7,

wherein a terminal whose downlink received power is a maximum is specified to be the terminal that is inferred to exert the interference to the second base station.

9. The wireless communication system according to claim 1,

wherein a terminal that was specified is handed over to the second base station of the multicast source.

10. The wireless communication system according to claim 1,

wherein the multicast receiver base station is a single or a plurality of base stations adjacent to the second base station.

11. A base station in a wireless communication system that includes a first base station with which a terminal communicate and a second base station to which a radio signal transmitted from the terminal becomes an interference power and is capable of handing over a serving base station of the terminal, comprising:

an interference power measurement part that inputs therein the radio signal transmitted from the terminal and measures a received power density for each unit time and for each frequency that were previously determined; and

a multicast transmission part that specifies a terminal that is inferred to exert the interference to the local base station and multicast transmits information for urging the handover to multicast receiver base stations that include the first base station and are at least apart of the base stations.

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

an interference generation rule inferring part which infers an interference generation rule that is a generation rule of the received power density being more than or equal to a previously set threshold based on a received power density for each unit time and for each frequency that is measured by the interference power measurement part,

wherein the multicast transmission part multicast transmits the information including the inferred interference generation rule.

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

a mobile-terminal-of-interference-source specifying part that receives information that is multicast transmitted from an other base station having detected an interference power being more than or equal to a previously set threshold, and specifies a terminal that is inferred to exert the interference to the base station of the multicast source among the terminals connecting to the local base station; and

a handover processing part which performs a handover processing about the terminal that the mobile-terminal-of-interference-source specifying part specified.

14. A base station in a wireless communication system that comprises a plurality of base stations including a first base station with which a terminal communicates and a second base station to which a radio signal transmitted from the terminal becomes an interference power, and is capable of performing handover of a connection destination of the terminal, further comprising:

a mobile-terminal-of-interference-source specifying part that receives information that is multicast transmitted from the second base station having detected an interference power being more than or equal to a previously set threshold, and specifies a terminal that is inferred to exert the interference to the second base station of the multicast source among the terminals connecting to the local base station; and

a handover processing part that performs a handover processing about the terminal specified by the mobile-terminal-of-interference-source specifying part.

15. The base station according to claim 14,

wherein the mobile-terminal-of-interference-source specifying part receives an interference generation rule that is based on the interference power detected by the second base station and is multicast transmitted from the second base station, collates a log of an uplink communication resource that the local base station allocated to the terminal and the interference generation rule, and specifies a terminal that is inferred to exert the interference power to the second base station being a source of the multicast.