RADIO BASE STATION, USER TERMINAL, CELL SELECTION METHOD AND RADIO COMMUNICATION SYSTEM

1 . A radio base station that forms a first cell in a radio communication system in which the first cell that uses a first carrier and a second cell that uses a second carrier of a higher frequency band than the first carrier are arranged to overlap each other, the radio base station comprising:

a determining section that determines an offset value to use in cell selection in a user terminal, based on transmission property information of the second carrier in the second cell; and

a reporting section that reports the offset value to the user terminal.

2 . The radio base station according to claim 1 , wherein the transmission property information includes at least one of the number of transmitting antenna elements provided in a radio base station forming the second cell, a transmission bandwidth used in the radio base station forming the second cells, and beamforming gain of a transmission beam used in the radio base station forming the second cell.

3 . The radio base station according to claim 1 , wherein the determining section determines the offset value based on interference information from a neighboring cell of the second cell.

4 . A user terminal used in a radio communication system in which a first cell that uses a first carrier and a second cell that use a second carrier of a higher frequency band than the first carrier are arranged to overlap each other, the user terminal comprising:

a measurement section that measures received quality of a reference signal from a first radio base station forming the first cell and a second radio base station forming the second cell;

a receiving section that receives an offset value that is reported from the first radio base station; and

a cell selection section that carries out cell selection based on the received quality measured in the measurement section and the offset value received in the receiving section,

wherein the offset value is determined based on transmission property information of the second carrier in the second cell.

5 . The user terminal according to claim 4 , wherein the transmission property information includes at least one of the number of transmitting antenna elements provided in the second radio base station, a transmission bandwidth used in the second radio base station, and beamforming gain of a transmission beam used in the second radio base station.

6 . The user terminal according to claim 4 , wherein the cell selection section applies the offset value to the received quality of a reference signal from the second radio base station.

7 . The user terminal according to claim 6 , wherein, when a best received quality to which the offset value is applied fulfills a predetermined threshold, the cell selection section selects a second cell based on a comparison result of the received quality of a reference signal from the second radio base station.

8 . The user terminal according to claim 6 , wherein, when the best received quality to which the offset value is applied does not fulfill a predetermined threshold, the cell selection section selects a first cell or a second cell based on a comparison result of the received quality of a reference signal from the second radio base stations and the received quality of a reference signal from the first radio base station.

9 . A cell selection method in a radio communication system in which a first cell that uses a first carrier and second cells that use a second carrier of a higher frequency band than the first carrier are arranged to overlap each other, the cell selection method comprising the steps of:

in a first radio base station forming the first cell:

determining an offset value to use in cell selection in a user terminal, based on transmission property information of the second carrier in the second cell; and

reporting the offset value to the user terminal; and

in the user terminal:

measuring received quality of reference signals from the first radio base station and a second radio base station forming the second cell;

receiving an offset value that is reported from the first radio base station; and

carrying out the cell selection based on the received quality that is measured and the offset value that is received.

10 . A radio communication system in which a first cell that uses a first carrier and a second cell that uses a second carrier of a higher frequency band than the first carrier are arranged to overlap each other, wherein:

a first radio base station forming the first cell comprises:

a determining section that determines an offset value to use in cell selection in a user terminal, based on transmission property information of the second carrier in the second cell; and

a reporting section that reports the offset value to the user terminal; and

the user terminal comprises:

a measurement section that measures received quality of reference signals from the first radio base station and a second radio base station forming the second cell;

a receiving section that receives the offset value that is reported from the first radio base station; and

a cell selection section that carries out cell selection based on the received quality that is measured and the offset value that is received.

11 . The user terminal according to claim 5 , wherein the cell selection section applies the offset value to the received quality of a reference signal from the second radio base station.

12 . The radio base station according to claim 2 , wherein the determining section determines the offset value based on interference information from a neighboring cell of the second cell.